Behavioral and neurochemical effects of dietary methyl donor deficiency combined with unpredictable chronic mild stress in rats

Methyl donor deficiencies and chronic stress cause depression independently, but their interaction has never been thoroughly evaluated. In our study, methyl donor deficient diet and chronic stress condition consisted respectively of a B2, B9, B12, and choline-free diet and a chronic mild stress procedure. Rats were randomly assigned to six groups with three "diet" conditions (free-feeding, pair-fed and methyl donor deficient diet) and two "stress" conditions (no-stress and stress) and were evaluated in the open-field, the elevated plus-maze and the forced swimming test. After the behavioral evaluation, corticosterone and homocysteine plasma levels were measured and dopamine, DOPAC, serotonin, 5HIAA concentrations were evaluated in several brain areas. Rats given a methyl donor deficient diet for 11 weeks causing elevated plasma homocysteine levels were compared to pair-fed and free-feeding rats with or without unpredictable chronic mild stress. Regardless of stress environmental conditions, the methyl donor deficient diet decreased plasma corticosterone levels and caused disinhibition in the elevated plus-maze condition relative to both control groups. However, stress potentiated the effects of the deficient regimen on rearing in the open-field and climbing in the forced swim test. The dietary changes involved in behavior and plasma corticosterone could be caused by homocysteine-induced decreases in dopamine and 5-hydroxytryptamine metabolites in selective brain regions and it can be noted that regardless of stress-conditions, methyl donor deficient diet decreases DOPAC/dopamine and 5HIAA/serotonin ratios in striatum and hypothalamus and selectively 5HIAA/serotonin ratio in the sensorimotor cortex. Our experimental data is particularly relevant in the context of neuropsychiatric disorders frequently associated with folate deficiency and hyperhomocysteinemia.

Intact neurobehavioral development and dramatic impairments of procedural-like memory following neonatal ventral hippocampal lesion in rats

Neonatal ventral hippocampal lesions (NVHL) in rats are considered a potent developmental model of schizophrenia. After NVHL, rats appear normal during their preadolescent time, whereas in early adulthood, they develop behavioral deficits paralleling symptomatic aspects of schizophrenia, including hyperactivity, hypersensitivity to amphetamine (AMPH), prepulse and latent inhibition deficits, reduced social interactions, and spatial working and reference memory alterations. Surprisingly, the question of the consequences of NVHL on postnatal neurobehavioral development has not been addressed. This is of particular importance, as a defective neurobehavioral development could contribute to impairments seen in adult rats. Therefore, at several time points of the early postsurgical life of NVHL rats, we assessed behaviors accounting for neurobehavioral development, including negative geotaxis and grip strength (PD11), locomotor coordination (PD21), and open-field (PD25). At adulthood, the rats were tested for anxiety levels, locomotor activity, as well as spatial reference memory performance. Using a novel task, we also investigated the consequences of the lesions on procedural-like memory, which had never been tested following NVHL. Our results point to preserved neurobehavioral development. They also confirm the already documented locomotor hyperactivity, spatial reference memory impairment, and hyperresponsiveness to AMPH. Finally, our rseults show for the first time that NVHL disabled the development of behavioral routines, suggesting dramatic procedural memory deficits. The presence of procedural memory deficits in adult rats subjected to NHVL suggests that the lesions lead to a wider range of cognitive deficits than previously shown. Interestingly, procedural or implicit memory impairments have also been reported in schizophrenic patients.

Impaired striatum-dependent behavior in GASP-1-knock-out mice

G protein-coupled receptor (GPCR) associated sorting protein-1 (GASP-1) is suspected to play a key role in recycling and degradation of several GPCRs. In a previous study, we have shown that GASP-1-knock-out (GASP-1-KO) mice displayed deficits in acquiring a cocaine self-administration task, associated with an exacerbated down-regulation of striatal dopaminergic and cholinergic receptors. Among several possibilities, GASP-1 deficiency could have impaired memory processes underlying the acquisition of the operant conditioning task. Therefore, the present study investigated cognitive performances of GASP-1-KO mice and their wild-type littermates (WT) in a broad variety of memory tasks. Consistent with a deficit in procedural memory, GASP-1-KO mice showed delayed acquisition of a food-reinforced bar-press task. During water-maze training in hidden- or visible-platform paradigms, mutant and WT mice acquired the tasks at the same rate. However, GASP-1 mice exhibited persistent thigmotaxic swimming, longer distance to the platform, and reduced swim speed. There was no deficit in several tasks requiring simple behavioral responses (Barnes maze, object recognition and passive avoidance tasks). Thus, the ability to acquire and/or express complex responses seems affected in GASP-1-deficient mice. Hippocampal functions were preserved, as the retention of an acquired memory in spatial tasks remained unaffected. The pattern of behavioral deficits observed in GASP-1-KO mice is coherent with current knowledge on the role of striatal GPCRs in acquisition/expression of skilled behavior and in motivation. Together with the previous findings, the so far established phenotype of GASP-1-KO mice makes them a potentially exciting tool to study striatal functions.

Effects of ethanol and ecstasy on conditioned place preference in the rat

The club drug ecstasy (3,4-methylenedioxymethylamphetamine or MDMA) is often taken recreationally with ethanol (EtOH). We have shown previously that EtOH potentiates the psychomotor effects of MDMA in rats. More recently, we demonstrated in striatal slices that MDMA produced preferential release of serotonin, but when combined with EtOH, the preferential release shifted to dopamine, raising the possibility that administration of EtOH may increase the reward effect of MDMA. To address this possibility, adult male Long-Evans rats were tested for conditioned place preference following treatment with saline, EtOH (0.75 g/kg), MDMA (6.6 mg/kg) or the combination. The only condition that produced a preference for the compartment associated with the drug was that of the drug combination. The current data are in line with anecdotal reports and one study in humans, indicating that EtOH alters the pharmacological effects of MDMA including self reports of enhanced or prolonged euphoria. Thus, administration of EtOH might increase the risk for compulsive use of MDMA, an issue that warrants further study.

Complete recovery of olfactory associative learning by activation of 5-HT4 receptors after dentate granule cell damage in rats

Bilateral intradentate injections of 3.0microg of colchicine induced a substantial loss of granule cells and damage to the overlying pyramidal cell layer in region CA1 in adult male Long-Evans rats. All rats with such lesions showed a significant associative learning deficit in an olfactory discrimination task, while being unimpaired in the procedural component of this task. Injection of a partial selective 5-HT(4) agonist (SL65.0155; 0.01mg/kg, i.p., vs. saline) before the third of six training sessions enabled complete recovery of associative learning performance in the lesioned rats. Activation of 5-HT(4) receptors by a selective agonist such as SL65.0155 might therefore provide an opportunity to reduce learning and memory deficits associated with temporal lobe damage, and could be useful for the symptomatic treatment of memory dysfunctions related to pathological aging such as Alzheimer's disease.

Reversible inactivation of the dorsal hippocampus by tetrodotoxin or lidocaine: A comparative study on cerebral functional activity and motor coordination in the rat

Reversible inactivation of the hippocampus by lidocaine or tetrodotoxin is used to investigate implications of this structure in memory processes. Crucial points related to such inactivation are the temporal and spatial extents of the blockade. We compared effects of intrahippocampal infusions of commonly-used doses of lidocaine (5 or 10 mug) or tetrodotoxin (5 or 10 ng) in rats at two post-infusion delays (5 or 30 min), using 2-deoxyglucose autoradiography to visualize local cerebral glucose metabolism, and beam-walking performance to assess motor coordination. In addition, memory retrieval was evaluated in a water maze after bilateral infusions of 10 mug lidocaine. A unilateral tetrodotoxin infusion induced dose- and time-dependent reductions of 2-deoxyglucose uptake in the vicinity of the infusion site (dorsal hippocampus: -29% to -67%) and in other ipsi- and contralateral brain regions (ventral hippocampus, lateral thalamus, cortical regions). The maximal effect was at 10 ng, at the delay of 30 min between the tetrodotoxin infusion and the 2-deoxyglucose injection. Uni- and bilateral infusions of tetrodotoxin induced dramatic motor coordination deficits. Conversely, lidocaine reduced 2-deoxyglucose uptake (-19%) in the dorsal hippocampus only at 10 mug, with weak extrahippocampal effects. Whether infused uni- or bilaterally and regardless of the dose, lidocaine did not alter motor coordination. When infused bilaterally, however, 10 microg of lidocaine impaired short-term retrieval of spatial information in a water maze. Because lidocaine i) induced a weak though significant functional blockade mainly restricted to the infusion site, ii) had no consequences on motor coordination and, nevertheless iii) altered short-term spatial memory retrieval, we conclude that acute intrahippocampal infusions of lidocaine may offer some advantages over tetrodotoxin at the doses used herein.

Electrolytic lesions of the ventral subiculum weakly alter spatial memory but potentiate amphetamine-induced locomotion

Adult Long-Evans male rats were subjected to electrolytic lesions of the ventral subiculum, and tested for locomotor activity in the home cage, reference and working memory in the water maze, working memory in the radial maze, and D-amphetamine-induced locomotion (1mg/kg, i.p.). When compared to their sham-operated counterparts, lesioned rats showed nocturnal hyperactivity, no reference memory deficit, but working memory was impaired in the water maze and during the initial stage of radial-maze testing. Their locomotor responsiveness to D-amphetamine was exaggerated. Histological verifications confirmed lesions in the ventral subiculum. Material stained for acetylcholinesterase activity indicated septohippocampal and commissural/associational sprouting, accounting for partial damage to the perforant paths. These results showed that ventral subiculum lesions (i) do not alter the capability of rats to learn repeatedly presented spatial information, and (ii) impair, but do not prevent, spatial working memory, suggesting that the ventral subiculum is preferentially involved in short-term memory for spatial locations. Given the electrolytic nature of the lesion, the lesion-induced potentiation of the locomotor response to amphetamine is probably easier explained by partial disruption of the perforant paths than by damage to neurons of the ventral subiculum.

A double dissociation between serial reaction time and radial maze performance in rats subjected to 192 IgG-saporin lesions of the nucleus basalis and/or the septal region

The cholinergic basal forebrain has been implicated in aspects of cognitive function including memory and attention, but the precise contribution of its major components, the basalocortical and the septohippocampal systems, remains unclear. Rats were subjected to lesions of either the nucleus basalis magnocellularis (Basalis), the medial septum/vertical limb of the diagonal band of Broca (Septum), or both nuclei (Basalis + Septum), using the selective cholinotoxin 192 IgG-saporin. Cognitive performance was evaluated in tasks taxing attention (the five-choice serial reaction time task, 5-CSRTT) and spatial working memory (radial arm maze, RAM). Nucleus basalis lesions disrupted performance of the 5-CSRTT, as demonstrated by decreased choice accuracy, increased incidence of missed trials, increased latencies to respond correctly, and a disrupted pattern of response control. Combined lesions of the Basalis and Septum resulted in qualitatively similar deficits to Basalis lesions alone, although interestingly, these rats were unimpaired on measures of response speed, and showed weaker deficits on accuracy and omissions. Decreasing the attentional load by lengthening stimulus duration reversed some of the deficits in Basalis and Basalis + Septum rats, suggesting an attentional deficit rather than motivation or motor perturbations. Performance in rats with septal lesions was only affected when task difficulty was increased. In the RAM an opposing pattern of effects was observed, with Septum and Basalis + Septum rats showing dramatic impairments, and Basalis rats performing normally. Taken together, these data provide clear evidence for a functional dissociation between septohippocampal and basalocortical cholinergic systems in aspects of cognitive function.

Presynaptic modulation of acetylcholine, noradrenaline, and serotonin release in the hippocampus of aged rats with various levels of memory impairments

Aged (25-27 months) Long-Evans female rats were distinguished according to whether they showed no significant impairment (AU), moderate impairment (AMI), or severe impairment (ASI) in a spatial reference-memory task. Young (3-5 months) rats served as controls. Electrically evoked overflow of tritium was assessed in hippocampal slices preloaded with [3H]choline or [3H]serotonin (5-HT). Nicotine-evoked overflow of tritium was measured after preloading with [3H]noradrenaline (NA). Choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activity, and concentration of monoamines were assessed in homogenates. Aged rats exhibited reduced accumulation of [3H]choline and [3H]5-HT, increased accumulation of [3H]NA, and weaker electrically evoked overflow of [3H]acetylcholine ([3H]ACh) and [3H]5-HT. The overflow of [3H]NA was not altered consistently by aging. Roughly, drugs acting presynaptically had comparable effects in aged rats: oxotremorine and CP 93,129 inhibited the overflow of [3H]ACh, CP 93,129 and UK 14,304 reduced that of [3H]5-HT. ChAT or AChE activity, and 5-HT concentration were not changed by age; NA concentration was reduced. When significant, changes were comparable in AU, AMI, and ASI rats. Data show that aging alters cholinergic and serotonergic hippocampal innervations, release of ACh and 5-HT, but not presynaptic release-modulating mechanisms. These alterations do not account for variability in water-maze performance of aged rats.

Polymeric hydrogels placed into a fimbria-fornix lesion cavity promote fiber (re)growth: a morphological study in the rat

To examine the regeneration capacity of dorsal septohippocampal neurons in the presence of an artificial growth-promoting substrate, biocompatible polymeric hydrogels were implanted between the septum and the hippocampus in a fimbria-fornix lesion cavity. Unmodified (control) or aminosugar-containing (glucosamines or N-acetyl-glucosamines) hydrogels were implanted immediately or ten days after the lesions. Six months later, brain sections were processed for cresyl-violet, acetylcholinesterase, and immunocytochemical (glial fibrillary acidic protein, protein S100, neurofilaments, laminin, fibronectin) staining. All hydrogels were well integrated in the brain, constituting a stable bridge between the septum and the hippocampus. Weak gliosis occasionally surrounded the hydrogel in rats from the immediate-implantation group, whereas a more pronounced gliosis was observed in those from the delayed-implantation group. The hydrogels contained blood vessels and were invaded by host cells including astrocytes. Astrocytes formed a loose tissue network filling the porous structure of the hydrogels. Within the hydrogels, laminin-, fibronectin- or neurofilaments-immunopositive networks were also observed. Moreover, numerous acetylcholinesterase-positive fibers penetrated into the hydrogels from the septal, cortical and striatal areas. Fibre penetration was most important in the N-acetylglucosamines-containing hydrogels. Despite these features, the hippocampus failed to show any increase of acetylcholinesterase-staining as compared to that seen in lesion-only rats. These results confirm the regeneration capacity of severed septohippocampal neurons into polymeric substrates used as a bridge inserted in a fimbria-fornix lesion cavity. As such, biomaterials might be of clinical interest not only in the case of spinal cord sections, but also in cases of brain trauma.

Presynaptic regulation of neurotransmitter release in the cortex of aged rats with differential memory impairments

Cluster analysis of water-maze reference-memory performances of 25-27-month-old (compared to 3-5-month-old) rats distinguished subpopulations of young adult rats (YOUNG), aged rats with no significant impairment (AU), aged rats with moderate impairment (AMI), and aged rats with severe impairment (ASI). In the frontoparietal cortex, we subsequently assessed the electrically evoked release of tritium in slices preloaded with [3H]choline, [3H]noradrenaline (NA), or [3H]serotonin (5-HT) and the effects of an agonist (oxotremorine, UK 14,304, and CP 93,129) of the respective autoreceptors. Cholinergic and monoaminergic markers were measured in homogenates. Overall, aged rats exhibited reduced accumulation of [3H]choline (-25%) and weaker evoked transmitter release (in % of accumulated tritium: -44%, -20%, and -34%, for [3H]acetylcholine, [3H]NA, and [3H]5-HT, respectively). In all rats, the inhibitory effects of the autoreceptor agonists on the evoked release of [3H] were comparable. Acetylcholinesterase (AChE), not choline acetyltransferase (ChAT), activity was reduced. The results suggest age-related modifications in the cholinergic, noradrenergic, and serotonergic innervation of the frontoparietal cortex, alterations of evoked transmitter release, but no interference with presynaptic autoinhibition of the release. Neither of these alterations seemed to account for the cognitive impairment assessed.

Intrastriatal infusions of methoctramine improve memory in cognitively impaired aged rats

Alterations of striatal cholinergic markers may correlate with cognitive impairments in aged rats. M2 muscarinic receptors were found to be presynaptic inhibitory autoreceptors on striatal cholinergic interneurons. The effect of bilateral intrastriatal infusions of the M2 muscarinic receptor antagonist methoctramine was assessed, in cognitively impaired aged (24-26 months) Long-Evans female rats, on memory performances in a water maze. Compared with vehicle infusions, methoctramine injected bilaterally (1 microg/side) in the dorsolateral striatum, significantly improved procedural memory performance while having no effect on spatial working memory. Our results suggest that, in cognitively impaired aged rats, the blockade of M2 muscarinic receptors in the dorsolateral striatum improves procedural memory probably by enhancing the release of acetylcholine.

Neurotransmitter release and its presynaptic modulation in the rat hippocampus after selective damage to cholinergic or/and serotonergic afferents

Male Long-Evans rats sustained injections of 5,7-dihydroxytryptamine (5,7-DHT) into the fimbria-fornix and the cingular bundle or/and intraseptal injections of 192 IgG-saporin to induce serotonergic or/and cholinergic hippocampal denervations; Sham-operated rats served as controls. Four to ten weeks after lesioning, we measured (i). the electrically evoked release of acetylcholine ([3H]ACh), noradrenaline ([3H]NA) and serotonin ([3H]5-HT) in hippocampal slices in the presence of drugs acting on auto- or heteroreceptors, (ii). the nicotine-evoked release of NA and (iii). the choline acetyltransferase (ChAT) activity and the concentration of monoamines in homogenates. Saporin lesions reduced the accumulation of [3H]choline, the release of [3H]ACh and the ChAT activity, but increased the concentration of NA and facilitated the release of [3H]NA evoked by nicotine. 5,7-DHT lesions reduced the accumulation and the release of [3H]5-HT, the concentration of 5-HT, and also facilitated the release of [3H]NA evoked by nicotine. Accumulation and electrically evoked release of [3H]NA were not altered by either lesion. The combination of both toxins resulted in an addition of their particular effects. The 5-HT(1B) receptor agonist, CP 93129, and the muscarinic agonist, oxotremorine, reduced the release of [3H]ACh in control and 5,7-DHT-lesioned rats; in rats injected with saporin, their effects could not be measured reliably. CP 93129 and the alpha(2)-adrenoceptor agonist, UK 14304, reduced the release of [3H]5-HT in all groups by about 65%.

IN CONCLUSION

(i). selective neurotoxins can be combined to enable controlled and selective damage of hippocampal transmitter systems; (ii). 5-HT exerts an inhibitory influence on the nicotine-evoked release of NA, but partial serotonergic lesions do not influence the release of ACh at a presynaptic level and (iii). presynaptic modulatory mechanisms involving auto- and heteroreceptors may be conserved on fibres spared by the lesions.

Does the release of acetylcholine in septal slices originate from intrinsic cholinergic neurons bearing p75ntr receptors? a study using 192 IgG-saporin lesions in rats

In previous studies electrically-evoked release of acetylcholine in septal slices was demonstrated. The present experiment aimed at verifying if this release involved intrinsic neurons bearing p75(NTR) receptors. Long-Evans rats sustained injections of 192 IgG-saporin into the medial septum/diagonal band of Broca (0.8 microg). Sham-operated rats served as controls. Two to 3.5 weeks later, the electrically-evoked release of acetylcholine ([(3)H]ACh) was measured in slices from the lateral septum (LS), medial septum (MS) and diagonal band of Broca (DBB). Choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activity, and monoamine concentrations were measured in the septum, cortex and hippocampus. The lesion extent was also assessed by ChAT immunostaining in a separate series of rats. In the septum, the number of ChAT-positive neurons was depleted dramatically (>90% at the level of the injection site). In the hippocampus, the lesions reduced ChAT and AChE activity by 91% and 84%, respectively. In the cortex, this reduction was weaker (-55% and -47%). In the septal region, the reduction was either weak or not significant. The evoked release of acetylcholine in septal slices was not reduced, except in the slices from the LS (-64%). The effects of physostigmine and atropine confirmed the presence of autoreceptors. Our data exclude that a major part of the acetylcholine released by MS and DBB slices derived from intrinsic neurons bearing p75(NTR) receptors. In the LS, part of the released acetylcholine might be from projections of such neurons located in the LS, MS and/or DBB. These data also suggest that the MS and the DBB may be the target of extrinsic cholinergic innervation that does not bear p75(NTR) receptors.

Grafts of fetal septal cells after cholinergic immunotoxic denervation of the hippocampus: a functional dissociation between dorsal and ventral implantation sites

Three-month-old Long-Evans rats were subjected to intraseptal infusions of 0.8 microg of 192 IgG-saporin followed, 2 weeks later, by intrahippocampal suspension grafts containing fetal cells from the medial septum and the diagonal band of Broca. The suspensions were implanted in the dorsal or the ventral hippocampus. Sham-operated and lesion-only rats were used as controls. Between 18 and 32 weeks after grafting, all rats were tested in a water maze (using protocols placing emphasis on reference memory or on working memory) and an eight-arm radial maze. The lesion produced extensive cholinergic denervation of the hippocampus, as evidenced by reduced acetylcholinesterase-positivity and acetylcholine content. Depending upon their implantation site, the grafts restored an acetylcholinesterase-positive reinnervation pattern in either the dorsal or the ventral hippocampus. Nevertheless, the grafts failed to normalize the concentration of acetylcholine in either region. The cholinergic lesion impaired working memory performance in both the water maze and the radial maze. To a limited degree, reference memory was also altered. Grafts placed in the ventral hippocampus had no significant behavioral effect, whereas those placed in the dorsal hippocampus normalized working memory performance in the water maze. Our data show that infusion of 192 IgG-saporin into the septal region deprived the hippocampus of its cholinergic innervation and altered spatial working memory more consistently than spatial reference memory. Although the cholinergic nature of the graft-induced reinnervation remains to be established more clearly, these results further support the idea of a functional dissociation between the dorsal and the ventral hippocampus, the former being preferentially involved in spatial memory.

Homotopic grafts of septal neurons combined to polymeric hydrogels placed into a fimbria-fornix lesion cavity attenuate locomotor hyperactivity but not mnemonic dysfunctions in rats

PURPOSE

We studied the behavioral effects of an intracavitary implantation of poly[N-(2-hydroxypropyl)-methacrylamidel (PHPMA) hydrogels combined to intraseptal grafts of fetal septal cell suspensions in adult female rats subjected to aspirative fimbria-fornix lesions. The hydrogels were used as substrates for bridging the lesion cavity between the septum and the hippocampus.

METHODS

Control groups included sham-operated or lesion-only rats, as well as lesioned rats with only the hydrogel bridge in the lesion cavity, only the graft in the septum, or an intrahippocampal graft of a septal cell suspension as a control for the standardly used ectopic transplantation strategy. Up to 10 months after grafting surgery, all rats were tested for locomotor activity in their home cage, sensorimotor performances using a beam-walking test, and cognitive performances in a radial maze, a water maze and a T-maze (rewarded alternation).

RESULTS

The lesions induced hyperlocomotion, sensorimotor disturbances and severe alterations of cognitive functions. We found that neither the grafts or the hydrogels, nor the combination of both, induced any significant enhancement of sensorimotor or cognitive performances. Nevertheless, in rats with both intraseptal (homotopic) grafts and a hydrogel implant, the locomotor activity did no longer differ from that found in sham-operated controls. Histological analysis showed that the hydrogels contained acetylcholinesterase(AChE)-positive fibers and that the hippocampal region in contact with the hydrogel exhibited AChE-positive reaction products over several hundreds of micrometers.

CONCLUSIONS

These results are complementary to our previous report on electrophysiological evidence of septo-hippocampal reconnections (Duconseille et al., Rest. Neurol. Neurosci. 15, 1999, 305-317). They further suggest that septal neurons grafted homotopically and/or neurons from the host brain are able to elongate axonal processes through a PHPMA substrate up to the hippocampus. Although they did not affect the cognitive consequences of the lesion, the changes enabled by the homotopic grafts combined to the hydrogel have attenuated the lesion-induced hyperactivity.

Effects of room and cage familiarity on locomotor activity measures in rats

Locomotor activity measures are often used in behavioral neuroscience. There is, however, a large variability in the protocols assessing locomotor activity which may, more or less, strongly be influenced by exploration and reactivity to novelty in unfamiliar situations. Using Long-Evans male rats, we investigated how far changes, such as placing rats in a cage physically identical to the home cage supplied with fresh sawdust but kept in a familiar room, or placing the familiar home cage with the rat inside in another (unfamiliar) room, may influence the level of locomotor activity. We showed that both changes resulted in significantly increased locomotion in the first 2 h after placing the rats in the respective test situation, but there is no significant additive effect. These changes performed right before the start of the test do not alter diurnal or nocturnal locomotor activity once the first 2 h have elapsed. The results illustrate that rats kept in an environment with stable proximal features (cage, sawdust) can react by increased activity in response to more distal novelty (experimental room), and conversely, that rats in a familiar environment react to proximal changes in the home cage.

Cognitive performances and locomotor activity following dentate granule cell damage in rats: role of lesion extent and type of memory tested

Intradentate injection of colchicine is one of the techniques used to destroy granule cells. This study compared the behavioral effects of various amounts of colchicine (1.0, 3.0, and 6.0 microg; Col 1, Col 3, and Col 6, respectively) injected into the dentate gyrus of adult Long-Evans male rats. Starting 10 days after lesion surgery, behavioral testing assessed home-cage and open-field locomotion, alternation in a T-maze, water-maze, and radial-maze learning according to protocols placing emphasis on reference, and working memory. All of these tasks are sensitive to hippocampal disruption. Histological verifications showed that the extent of the lesions depends on the dose of colchicine (index of dentate gyrus shrinkage: -33% in Col 1, -54% in Col 3, and -67% in Col 6 rats). Colchicine dose-dependently increased nocturnal home cage activity (an effect found 10 days but not 5 months after surgery), but had no significant effect on open-field locomotion or T-maze alternation. A dose-dependent reference memory impairment was found during the acquisition of spatial navigation in the water maze; Col 3 and Col 6 rats were more impaired than Col 1 rats. During the probe trial (platform removed), control rats spent a longer distance swimming over the platform area than all rats with colchicine lesions. In the working memory version of the test, all rats with colchicine lesions showed significant deficits. The deficits were larger in Col 3 and Col 6 rats compared to Col 1 rats. The lesions had no effect on swimming speed. In the radial-maze test, there was also a dose-dependent working memory impairment. However, reference memory was disrupted in a manner that did not differ among the three groups of lesioned rats. Our data are in line with the view that the dentate gyrus plays an important role in the acquisition of new information and is an integral neural substrate for spatial reference and spatial working memory. They also suggest that damage to granule cells might have more pronounced effects on reference than on working memory in the radial maze. Finally, they demonstrate that part of the variability in the conclusions from previous experiments concerning the role of granule cells in cognitive processes, particularly in spatial learning and memory, may be due to the type of tests used and/or the extent of the damage produced.

Electrically evoked release of glutamate in rat hippocampal slices: effects of various drugs and fimbria-fornix lesions

A model of electrically evoked release of glutamate from rat hippocampus was developed and used to detect possible changes induced by lesions of hippocampal afferences. Neuronal glutamate in hippocampal slices was labelled by preincubation with [3H]glutamine. The slices were then superfused with physiological medium in the presence of the glutamate uptake inhibitor L-transpyrrolidine-2,4-dicarboxylic acid (100 microM or 3 microM) and stimulated twice electrically (S1, S2: 240 pulses, 3 Hz, 2 ms, 26-30 mA); various drugs were added before S2. In order to determine the basal and evoked outflow of [3H]glutamate only, the mixture of 3H-labelled compounds (glutamine, glutamate and GABA) was separated by ion exchange chromatography in superfusate fractions and slices. The electrically evoked overflow of [3H]glutamate was largely Ca2+-dependent and tetrodotoxin-sensitive and hence represented action potential-induced exocytotic release of [3H]glutamate. Evoked [3H]glutamate release was significantly increased by the adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 0.1 microM), suggesting the presence of endogenous inhibitory adenosine, and reduced by the A1 receptor agonist N6-cyclopentyladenosine (1 microM, antagonized by DPCPX, 0.1 microM). There was no evidence for a cholinergic, serotonergic, or adrenergic modulation of the evoked release of [3H]glutamate: the corresponding selective agonists (or antagonists) were ineffective. After aspirative lesions of the septohippocampal pathways the hippocampal noradrenaline content was markedly increased, whereas cholinergic and serotonergic markers were reduced. The evoked release of [3H]glutamate in hippocampal slices of lesioned rats was significantly increased by a mechanism which still has to be determined, but which is not related to alterations in A1 receptor function. It is concluded that the present model was able to detect lesion-induced differences in electrically evoked release of [3H]glutamate, but the relationship of these differences to changes of noradrenergic, cholinergic or serotonergic hippocampal innervations remains to be established.

Effects of MDL 73005 on water-maze performances and locomotor activity in scopolamine-treated rats

The stimulation of 5-HT1A receptors in the raphe or their blockade in the hippocampus can reduce cognitive deficits induced by blockade of muscarinic receptors in the hippocampus. We investigated the effects of MDL 73005 (8-[2-(2,3-dihydro-1,4-benzodioxin-2-ylmethylamino) ethyl]-8-azaspiro[4,5] decane-7,9-dione methyl sulphonate), an agonist at 5-HT1A somatodendritic autoreceptors and an antagonist at postsynaptic 5-HT1A receptors in rats treated systemically with scopolamine. Spatial memory was assessed in a water maze using protocols testing reference and working memory. Home cage locomotor activity was also determined. Working memory and locomotor activity were evaluated before and after para-chlorophenylalanine (pCPA) treatment. Scopolamine produced a weak impairment of reference memory at 0.5 mg/kg, and a more pronounced impairment of working memory at 0.25 and 0.5 mg/kg. MDL 73005 alone (2 mg/kg, i.p.) had no effect, but prevented the memory impairments induced by 0.25 mg/kg of scopolamine. Scopolamine induced hyperlocomotion. MDL 73005 alone did not affect locomotor activity, but exacerbated the hyperlocomotion induced by 0.5 mg/kg of scopolamine. pCPA did not abolish the effects of MDL 73005, suggesting that these effects were not due to an action at presynaptic receptors, or even that they involved receptors other than serotonergic ones (e.g., D2). In conclusion, MDL 73005 is able to antagonise moderate spatial memory dysfunctions induced by systemic muscarinic blockade.

Central cholinergic depletion induced by 192 IgG-saporin alleviates the sedative effects of propofol in rats

We examined the effect of central cholinergic depletion on the sedative potency of propofol in rats. Depletion was produced by intracerebroventricular administration of an immunotoxin specific to cholinergic neurones (192 IgG-Saporin; 2 microg). As a result of this lesion, acetylcholine concentration was reduced by about 40% in the frontoparietal cortex and in the hippocampus but was essentially normal in the striatum and cerebellum. Sedation in rats was assessed as the decrease in locomotor activity. Sedative potency of propofol (30 mg kg(-1) i.p.) was reduced by about 50% in rats who received the injection of 192 IgG-Saporin as compared to controls. These results show that a central cholinergic depletion alleviates the sedative effect of propofol, and indicates that basal forebrain cholinergic neurones might mediate part of the sedative/hypnotic effects of propofol.

Serotonergic modulation of hippocampal acetylcholine release after long-term neuronal grafting

Adult female rats sustained aspirative fimbria-fornix lesions and, 2 weeks later, received intrahippocampal grafts of fetal septal or mixed septal-raphe cell suspensions. Twenty-four months later, the extracellular concentration of hippocampal acetylcholine (ACh) was determined by microdialysis. Basal ACh levels (5-65 fmol/5 microl sham-operated rats) were strongly reduced after lesioning (3-7 fmol/5 microl). In septally transplanted and septal-raphe co-transplanted rats, hippocampal ACh concentrations were restored to near-normal levels (15-25 fmol/5 microl), indicating long-term functional survival of hippocampal transplants. After administration of citalopram (100 microM by infusion) and fenfluramine (20 mg/kg i.p.), the hippocampal ACh efflux was increased by 2- to 3-fold in all groups of rats. The relative increase of ACh was highest in co-transplanted rats, an effect which was possibly due to functional interactions between grafted raphe and septal neurons.

Immunohistochemical and neurochemical correlates of learning deficits in aged rats

This study examined whether cholinergic and monoaminergic dysfunctions in the brain could be related to spatial learning capabilities in 26-month-old, as compared to three-month-old, Long-Evans female rats. Performances were evaluated in the water maze task and used to constitute subgroups with a cluster analysis statistical procedure. In the first experiment (histological approach), the first cluster contained young rats and aged unimpaired rats, the second one aged rats with moderate impairment and the third one aged rats with severe impairment. Aged rats showed a reduced number of choline acetyltransferase- and p75(NTR)-positive neurons in the nucleus basalis magnocellularis, and choline acetyltransferase-positive neurons in the striatum. In the second experiment (neurochemical approach), the three clusters comprised young rats, aged rats with moderate impairment and aged rats with severe impairment. Alterations related to aging consisted of reduced concentration of acetylcholine, norepinephrine and serotonin in the striatum, serotonin in the occipital cortex, dopamine and norepinephrine in the dorsal hippocampus, and norepinephrine in the ventral hippocampus. In the first experiment, there were significant correlations between water maze performance and the number of; (i) choline acetyltransferase- and p75(NTR)-positive neurons in the nucleus basalis magnocellularis; (ii) choline acetyltransferase-positive neurons in the striatum and; (iii) p75(NTR)-positive neurons in the medial septum. In the second experiment, water maze performance was correlated with the concentration of; (i) acetylcholine and serotonin in the striatum; (ii) serotonin and norepinephrine in the dorsal hippocampus; (iii) norepinephrine in the frontoparietal cortex and; (iv) with other functional markers such as the 5-hydroxyindoleacetic acid/serotonin ratio in the striatum, 3,4-dihydroxyphenylacetic acid/dopamine ratio in the dorsal hippocampus, 5-hydroxyindoleacetic acid/serotonin and homovanillic acid/dopamine ratios in the frontoparietal cortex, and 3,4-dihydroxyphenylacetic acid/dopamine ratio in the occipital cortex. The results indicate that cognitive deficits related to aging might involve concomitant alterations of various neurochemical systems in several brain regions such as the striatum, the hippocampus or the cortex. It also seems that these alterations occur in a complex way which, in addition to the loss of cholinergic neurons in the basal forebrain, affects dopaminergic, noradrenergic and serotonergic processes.

Selective lesions of the entorhinal cortex, the hippocampus, or the fimbria-fornix in rats: a comparison of effects on spontaneous and amphetamine-induced locomotion

Using adult Long-Evans male rats, this experiment compared spontaneous (assessed 15 days and 4.5 months after surgery) and amphetamine-induced (assessed from 4.5 months after surgery onwards; 1 mg/kg, i.p., ten injections, 48 h apart) locomotor activity following N-methyl-D-aspartate lesions of the entorhinal cortex, electrolytic lesions of the fimbria-fornix, or ibotenate lesions of the hippocampus. Sham-operated rats were used as controls. Hippocampal and fimbria-fornix lesions, but not entorhinal-cortex lesions induced diurnal and nocturnal hyperactivity, which was attenuated over time, but only in rats with fimbria-fornix lesions. Amphetamine-induced hyperlocomotion was assessed in a familiar environment. Lesions of the entorhinal cortex potentiated the locomotor effects of amphetamine, but not lesions of the hippocampus or interruption of the axons in the fimbria-fornix pathway. Sensitization appeared to be decreased by fimbria-fornix lesions and to be prevented by hippocampal lesions. Rats with entorhinal-cortex lesions behaved as if they had already been sensitized by the lesion. These results clearly show that lesions of the fimbria-fornix, the hippocampus, and of the entorhinal cortex have different effects on spontaneous and amphetamine-induced hyperactivity, as they also have on learning and memory tasks.

Preserved olfactory short-term memory after combined cholinergic and serotonergic lesions using 192 IgG-saporin and 5,7-dihydroxytryptamine in rats

Young adult Long-Evans female rats were subjected to intracerebroventricular injections of 150 microg 5,7-dihydroxytryptamine (5,7-DHT), 2 microg 192 IgG-saporin, or a combination of both neurotoxins. All rats were tested for olfactory recognition (short-term memory) using a task based on spontaneous exploration of odor sources. Compared with animals undergoing sham operations, 5,7-DHT reduced the concentration of serotonin by 60-80% in the frontoparietal cortex, hippocampus, striatum and the olfactory bulbs. After 192 IgG-saporin treatment, acetylcholine concentrations were reduced by approximately 40% in all these structures, except the striatum. Neither lesion induced a significant deficit in olfactory recognition. These data suggest that combined lesions of cholinergic and serotonergic neurons in the rat brain do not alter olfactory perception or olfactory short-term memory.

Intraseptal infusions of 8-OH-DPAT in the rat impairs water-maze performances: effects on memory or anxiety?

In the rat, 5-HT1A receptors are found on medial septal cholinergic neurons. The effects of intraseptal infusions of the 5-HT1A receptor agonist 8-OH-DPAT (8-hydroxy-2-(di-n-propyl-amino)-tertralin) were assessed on reference memory performances in a water maze. Compared with vehicle infusions, 0.5 and 4 microg of 8-OH-DPAT significantly impaired (but did not prevent) acquisition of the task and probe-trial performances. The results suggest that activation of 5-TH1A receptors in the (medial) septal area impairs spatial learning, perhaps directly by reducing the hippocampal cholinergic tonus, or indirectly by an effect on anxiety.

Intracerebral transplants and memory dysfunction: circuitry repair or functional level setting?

Intracerebral grafting techniques of fetal neural cells have been used essentially with two main types of lesion paradigms, namely damage to long projection systems, in which the source and the target are clearly separate, and damage to neurons that are involved in local circuits within a small (sub)region of the brain. With the first lesion paradigm, grafts placed homotopically (in the source) are not appropriate because their fibers grow poorly through the host parenchyma and fail to reach their normal target. To be successful, the grafts must be placed ectopically in the target region of the damaged projection systems, where generally they work as level-setting systems. Conversely, with the second paradigm, the grafts are supposed to compensate for a local loss of neurons and must be placed homotopically to induce functional effects that are based on the reconstruction of a point-to-point circuitry. By inserting a biological or artificial bridging-substrate between the source and the target of long projection systems, it might be possible to combine the positive effects of both homotopic and ectopic grafting by achieving both target reinnervation and normal control of the grafted neurons within the source area. These issues are illustrated and discussed in this review.

Combined lesions of cholinergic and serotonergic neurons in the rat brain using 192 IgG-saporin and 5,7-dihydroxytryptamine: neurochemical and behavioural characterization

This study assessed behavioural and neurochemical effects of i.c.v. injections of both the cholinergic toxin 192 IgG-saporin (2 microgram) and the serotonergic toxin 5,7-dihydroxytryptamine (5,7-DHT; 150 microgram) in Long-Evans female rats. Dependent behavioural variables were locomotor activity, forced T-maze alternation, beam walking, Morris water-maze (working and reference memory) and radial-maze performances. After killing by microwave irradiation, the concentrations of acetylcholine, monoamines and 5-hydroxyindoleacetic acid (5-HIAA) were measured in the hippocampus, frontoparietal cortex and striatum. 192 IgG-saporin reduced the concentration of acetylcholine by approximately 40% in the frontoparietal cortex and hippocampus, but had no effect in the striatum. 5,7-DHT lesions reduced the concentration of serotonin by 60% in the frontoparietal cortex and 80% in the hippocampus and striatum. Noradrenaline was unchanged in all structures except the ventral hippocampus where it was slightly increased in rats given 192 IgG-saporin. Cholinergic lesions induced severe motor deficits but had no other effect. Serotonergic lesions produced diurnal and nocturnal hyperactivity but had no other effect. Rats with combined lesions were more active than those with only serotonergic lesions, showed motor dysfunctions similar to those found in rats with cholinergic lesions alone, and exhibited impaired performances in the T-maze alternation test, the water-maze working memory test and the radial-maze. Taken together and although cholinergic lesions were not maximal, these data show that 192 IgG-saporin and 5,7-DHT lesions can be combined to selectively damage cholinergic and serotonergic neurons, and confirm that cholinergic-serotonergic interactions play an important role in some aspects of memory, particularly in spatial working memory.

Modulation of acetylcholine and 5-hydroxytryptamine release in hippocampal slices of rats with fimbria-fornix lesions and intrahippocampal grafts containing cholinergic and/or serotonergic neurons

Three-month-old Long-Evans female rats sustained aspirative lesions of the dorsal septohippocampal pathways and, 2 weeks later, received intrahippocampal suspension grafts containing fetal cells from the mesencephalic raphe (rich in serotonergic neurons; RAPHE), the medial septum and the diagonal band of Broca (rich in cholinergic neurons; SEPT), or a mixture of both (COTR). Lesion-only (LES) and sham-operated rats (SHAM) were used as controls. Hippocampal slices of these rats (5-9 month after surgery) were preincubated with [3H]choline or [3H]5-HT, superfused continuously (in the presence of hemicholinium-3 or fluvoxamine) and stimulated electrically (360 pulses, 2 ms, 3 Hz, 26-28 mA) in order to study the presynaptic modulation of acetylcholine (ACh) and serotonin (5-HT) release. The accumulation of [3H]choline and the evoked overflow of [3H]ACh were significantly reduced in slices from LES and RAPHE rats, but reached a close-to-normal level in SEPT and COTR rats. As to accumulation and overflow of [3H]5-HT, the lesion-induced reduction was compensated for only in RAPHE and COTR rats. The relative amount of evoked [3H]5-HT release (in % of tissue-3H) was significantly increased in LES and SEPT rats. Only slight differences (group LES) were found in the sensitivity of muscarinic and serotonergic autoreceptors towards oxotremorine and CP 93,129, respectively. Moreover, CP 93,129 induced a significantly weaker inhibition of ACh release in slices of COTR rats than in all other groups. Using the 5-HT1A receptor agonist 8-OH-DPAT and antagonist Way 100,635, no evidence for a modulatory influence of 5-HT1A receptors was found in RAPHE and COTR rats. It is concluded that despite substantial lesion- and graft-induced changes in the amount of ACh and 5-HT released by hippocampal slices of lesion-only or grafted rats, the presynaptic modulation of these transmitters is only slightly affected by changes in the neuronal environment.

Intrahippocampal grafts containing cholinergic and serotonergic fetal neurons ameliorate spatial reference but not working memory in rats with fimbria-fornix/cingular bundle lesions

Three-month-old Long-Evans female rats sustained aspirative lesions of the dorsal septohippocampal pathways and, 2 weeks later, received intrahippocampal suspension grafts containing cells from the mesencephalic raphe, cells from the medial septum and the diagonal band of Broca, or a mixture of both. Lesion-only and sham-operated rats were used as controls. All rats were tested for locomotor activity 1 week, 3 and 5 months after lesion surgery, for spatial working memory in a radial maze from 5 to 9 months, and for reference and working memory in a water tank during the 9th month after lesioning. Determination of hippocampal concentration of acetylcholine, noradrenaline, and serotonin was made after completion of behavioral testing. Compared to sham-operated rats, all rats with lesions, whether grafted or not, exhibited increased levels of locomotor activity and made more errors in the radial maze. The lesioned rats were also impaired in the probe trial (30 first seconds) of the water-tank test made according to a protocol requiring intact reference memory capabilities. While rats with septal or raphe grafts were also impaired, the rats with co-grafts showed performances not significantly different from those of sham-operated rats. With a protocol requiring intact working memory capabilities, all lesioned rats, whether grafted or not, were impaired in the water-tank test. In the dorsal hippocampus of lesion-only rats, the concentration of acetylcholine and serotonin was significantly reduced. In rats with septal grafts or co-grafts, the concentration of acetylcholine was close to normal, as was that of serotonin in rats with raphe grafts or co-grafts. These results confirm previous findings showing that co-grafts enabled the neurochemical properties of single grafts to be combined. Data from the water-tank test suggest that cholinergic and serotonergic hippocampal reinnervations by fetal cell grafts may induce partial recovery of spatial reference, but not working memory capabilities in rats.

The potentiation of amphetamine-induced hyperlocomotion by fimbria-fornix lesions in rats is abolished by intrahippocampal grafts rich in serotonergic neurons

Three-month old Long-Evans female rats were submitted to aspirative lesions of the fimbria-fornix and intrahippocampal grafts of a cell suspension prepared from a region of the fetal brain including the septum and the diagonal band of Broca (rich in cholinergic neurons) or the raphe (rich in serotonergic neurons). A group of lesioned rats was grafted with both suspensions mixed. Lesion-only and sham-operated rats served as controls. Four months after the lesions, all rats were tested daily for locomotor activity in their home cage, 1 day without being injected, 2 days with an injection of NaCl and 5 days with an injection of 1 mg/kg (i.p.) d-amphetamine. The effects of the lesions and grafts were assessed by measuring the accumulation of [3H]-choline or [3H]-5-hydroxytryptamine (5-HT) by hippocampal slices, and the electrically-evoked release of tritium. Amphetamine injections produced hyperlocomotion which was potentiated by the lesion. This lesion-induced potentiation was also found in rats with septal grafts, but not in those with raphe or co-grafts. The uptake and electrically-evoked release of [3H]-acetylcholine or [3H]-5-HT were reduced in hippocampal slices from lesion-only rats. In rats which received grafts of septal cells or co-grafts, but not in those with raphe grafts, uptake and release of [3H]-acetylcholine were close to normal. Uptake and release of [3H]-5-HT were close to normal in rats with raphe grafts or with co-grafts, but not in those with septal grafts. Altogether, these data suggest that damage to the serotonergic afferents of the hippocampus might play some role in the potentiation of amphetamine-induced hyperlocomotion associated with fimbria-fornix lesions.

Modulation of 5-hydroxytryptamine release in hippocampal slices of rats: effects of fimbria-fornix lesions on 5-HT1B-autoreceptor and alpha2-heteroreceptor function

Fimbria-fornix lesions disrupt important parts of serotonergic and noradrenergic hippocampal afferents and elicit sprouting of sympathetic fibers from the superior cervical ganglion. Since 5-hydroxytryptamine (5-HT) release in the hippocampus is modulated by 5-HT1B auto- and alpha2-heteroreceptors, we investigated whether such lesions may alter these presynaptic mechanisms. Hippocampal slices of sham-operated (SHAM) and fimbria-fornix-lesioned (LES) rats (14 months after surgery) were preincubated with [3H]5-HT, superfused continuously, and stimulated electrically using two stimulation conditions: either (a) 360 pulses 3 Hz, or (b) 20 pulses 100 Hz (2 ms, 28 mA, 4 V/chamber). The amount of [3H]5-HT taken up by slices from LES rats was significantly reduced, whereas the evoked 5-HT release (in percent of tissue-3H) was unchanged compared to that of SHAM rats. The 5-HT1B agonist CP 93,129 or the alpha2-agonist UK 14,304 reduced the evoked 5-HT release more potently in slices from LES rats, but only using stimulation condition (a), which permits inhibition by endogenously released transmitters. In LES rats, the facilitatory effect of the 5-HT antagonist metitepine was weaker, whereas that of the alpha2-antagonist idazoxane was more pronounced than in SHAM rats. In LES rats, hippocampal 5-HT content was reduced to about 45% of SHAM levels, whereas that of noradrenaline was increased by about 30% (high-performance liquid chromatography). We conclude: (1) despite LES-induced changes in tissue levels of endogenous ligands, there is no down- or upregulation of 5-HT1B-autoreceptors or alpha2-heteroreceptors on serotonergic neurons in the denervated rat hippocampus. (2) The reduced endogenous autoinhibition (by 5-HT) seems to be compensated for by an increased heteroinhibition (by noradrenaline).

Sensitivity to cholinergic drug treatments of aged rats with variable degrees of spatial memory impairment

As a first step, the present experiment aimed at characterizing learning and memory capabilities, as well as some motor and sensorimotor faculties, in aged (24-26.5 months) Long-Evans female rats. As a second step, a psychopharmacological approach was undertaken in order to examine the sensitivity of aged rats to muscarinic blockade and to cholinomimetic treatments. Young adult (3-5.5 months) and aged rats were tested for beam-walking performance, locomotor activity in the home cage and an open field, and spatial learning/memory performance in a water maze and a radial maze. Spontaneous alternation rates were assessed in a T-maze. Statistical analysis discriminated between aged rats showing moderate impairment (AMI) and those showing severe impairment (ASI) in the water maze test. Beside their different degrees of impairment in the water maze, AMI and ASI rats were similarly (no significant difference) impaired in beam-walking capabilities, home cage activity and radial maze performance. In the spontaneous alternation task aged rats were not impaired and, in the open-field test, AMI rats were hypoactive, but not as much as ASI rats. Neither of the cognitive deficits was correlated with a locomotor or a sensorimotor variable, or with the body weight. When tested in the radial maze, a low dose of scopolamine (0.1 mg/kg i.p.) produced memory impairments which were significant in AMI and ASI rats, but not in young rats. Combined injections of scopolamine and physostigmine (0.05 and 0.1 mg/kg) or tacrine (THA, 3 mg/kg) showed physostigmine (0.1 mg/kg) to compensate for the scopolamine-induced impairments only in AMI rats. whereas THA was efficient in both AMI and ASI rats. The results indicate: (i) that rats with different degrees of spatial memory impairment in the water maze are similarly hypersensitive to muscarinic blockade when tested in a radial maze test; and (ii) that under the influence of a dose of scopolamine which is subamnesic in young rats, aged rats respond to anticholinesterase treatments according to the level of performance achieved in the water maze: moderately impaired rats are sensitive to both physostigmine and THA, whereas more severely impaired rats are sensitive only to THA.

Sympathetic sprouting: no evidence for muscarinic modulation of noradrenaline release in hippocampal slices of rats with fimbria-fornix lesions

Lesions of the septohippocampal pathways elicit sprouting of sympathetic fibers from the superior cervical ganglion, a phenomenon which, within a few months, raises the hippocampal noradrenaline (NA) content above normal. In peripheral sympathetic fibers, the release of NA is modulated via presynaptic muscarinic receptors. Such receptors have not been detected so far on terminals of noradrenergic neurons originating in the locus coeruleus. Whether the release of NA could become sensitive to muscarinic modulation in the hippocampus following sympathetic fiber ingrowth was the major question in this experiment. The contribution of presynaptic nicotinic receptors was also studied. Slices from the ventral hippocampus (only dentate gyrus+CA3 region) of sham-operated (SHAM) and fimbria-fornix lesioned (LES) Long-Evans rats (8-10 months after surgery) were preincubated with [3H]NA and stimulated either once (S1) with 100 microM nicotine or (in parallel experiments) twice electrically (S1, S2), using conditions (six pulses 100 Hz, 2 ms, 28 mA, 4 V/chamber) that precluded autoinhibition. In experiments using electrical stimulation, the superfusion medium contained desipramine (1 microM). In LES rats, the tissue NA content had almost doubled (171% of SHAM levels), but the amount of [3H]NA taken up by the slices was unchanged, and the overflow evoked at S1 by both nicotinic and electrical stimulation was significantly reduced in comparison with SHAM rats. In both groups, the addition of oxotremorine or oxotremorine+atropine (1 microM, each) before S2 failed to affect the electrically evoked overflow of 3H. Nicotine-induced NA release was inhibited by hexamethonium (100 microM) in both groups, although significantly less potently in LES rats. Tissue activity of choline acetyltransferase was reduced in LES rats to 15% of SHAM levels and the 5-hydroxytryptamine content was also strongly diminished (38% of SHAM values). It is concluded that lesion-induced sprouting of sympathetic fibers into the hippocampus is not accompanied by the emergence of a muscarinic modulation of NA release in this tissue, and that the sensitivity of the presynaptic stimulatory effect of nicotine was modified by the lesion.

Spatial memory, habituation, and reactions to spatial and nonspatial changes in rats with selective lesions of the hippocampus, the entorhinal cortex or the subiculum

Various spatial memory deficits have been described in rats with damage to the hippocampal formation (including the subiculum and the entorhinal cortex) and particularly in rats with selective lesions of the hippocampus proper. So far, the involvement of the entorhinal cortex in spatial memory is still controversial and the role of the subiculum is poorly documented. The aim of the present study was to compare the behavioural effects of selective lesions of the hippocampus, the entorhinal cortex or the subiculum in (a) a water-maze task using testing procedures sensitive to the disruption of reference or working memory and (b) in an object exploration task designed to evaluate habituation and subsequently reactions to changes of the spatial layout of objects (spatial change) or to the substitution of a familiar object by a new one (nonspatial change). Our results showed several similarities between the behavioural consequences of damage to each of the three structures. A few differences were also noted. Hippocampal rats were impaired in all spatial tasks, but they reacted like controls to a nonspatial change. The rats sustaining lesions of the entorhinal cortex or the subiculum were not impaired in the reference-memory procedure of the water-maze task and showed a deficit in reacting to a nonspatial change. Overall, our results confirm the central role of the hippocampus in spatial memory and also suggest a role for the entorhinal cortex and the subiculum in processing spatial informations. In addition, they indicate that the entorhinal cortex and the subiculum may have a hippocampal-independent role in memory.

Fimbria-fornix vs selective hippocampal lesions in rats: effects on locomotor activity and spatial learning and memory

The behavioral effects of interrupting the axons that pass in the fimbria and dorsal fornix were compared with the effects of selective removal of the cells that comprise the hippocampus with ibotenic acid. Starting 4.5 months after surgery, lesioned and control rats were (i) trained in both the Morris water maze and the eight-arm radial maze using protocols that placed an emphasis on either working memory (WM) or reference memory (RM) and (ii) tested for locomotor activity in the home cage. In comparison to sham-operated rats, the rats from both lesion groups were impaired in most learning/memory tasks, but there were some interesting differences between the two lesioned groups. When compared to rats with fimbria-fornix lesions (FIFX rats), hippocampal rats (HIPP rats) were slower in learning to swim to a visible platform and showed a greater impairment than FIFX rats in the radial-maze task when the testing procedure required the utilization of RM and WM in a more demanding WM task. In the test of locomotor activity, FIFX and control rats did not differ, but HIPP rats were more active than the rats in both other groups. The pattern of results obtained after a 4.5-month recovery period support the following general conclusions. (1) While there are some similarities in the effects on behavior of interrupting the axons in the fimbria-fornix compared to removing the hippocampus, there are some important differences. (2) From the findings that are available, a possible explanation to account for the difference between FIFX and HIPP rats is that the 4.5-month survival time permitted some recovery in the group of rats with FIFX lesions. (3) While it is well known that the Morris water maze and the radial-arm maze tasks provide useful measures of spatial learning and memory processes, our results suggest that the information provided by the two spatial learning tasks may differ in important respects.

Modulation of hippocampal acetylcholine release after fimbria-fornix lesions and septal transplantation in rats

Female Long-Evans rats sustained electrolytic lesions of the fimbria and the dorsal fornix causing a partial lesion of the septohippocampal pathway. Two weeks later, the rats received intra-hippocampal grafts of fetal septal cell suspensions. Nine to twelve months later, the release of acetylcholine (ACh) in the hippocampus of sham-operated, lesion-only and grafted rats was measured by microdialysis. The extent of cholinergic (re)innervation was determined by acetylcholinesterase (AChE) staining and densitometry. In both lesion-only and grafted rats, the ratio of ACh release to AChE staining intensity was increased as compared to sham-operated rats, indicating a loss of endogenous inhibitory mechanisms. Scopolamine (0.5 mg/kg i.p.), a muscarinic antagonist, increased ACh release in all treatment groups. 8-OH-DPAT (0.5 mg/kg s.c.), an agonist at serotonergic 5HT1A-receptors, induced an increase of hippocampal ACh release in sham-operated rats. This effect was lost in lesion-only rats, but was fully restored by neuronal grafting. As 8-OH-DPAT influences hippocampal ACh release by a postsynaptic action, this finding indicates that the host brain exerts a serotonergic influence on the grafted cholinergic neurons.

Behavioral effects of GM1 ganglioside treatment and intrahippocampal septal grafts in rats with fimbria-fornix lesions

The monosialoganglioside GM1 is a compound with neurotrophic properties found to foster functional recovery in various paradigms of brain damage. The present experiment examined whether systemic treatment with GM1 may facilitate behavioral recovery in rats with fimbria-fornix lesions and intrahippocampal grafts rich in cholinergic neurons. Among 68 Long-Evans female rats, 46 sustained a bilateral electrolytic lesion of the fimbria and the dorsal fornix and 22 were sham-operated. Fourteen days later, half the lesioned rats were subjected to intrahippocampal grafts of a fetal septal cell suspension. Starting a few hours after lesion surgery and over a 2-month period, half the rats of each surgical treatment group received a daily injection of GM1 (30 mg/kg i.p.), the other half being injected with saline as a control. All rats were subsequently tested for locomotor activity and radial maze learning. The lesions induced locomotor hyperactivity and impaired learning performances in both an uninterrupted and an interrupted radial maze testing procedure. In all rats with surviving grafts, the grafts had provided the hippocampus with a new and dense organotypic acetylcholinesterase-positive innervation pattern which did not differ between saline- and GM1-treated subjects. The scores/performances of the rats that had received only the grafts or only the GM1 treatment did not differ significantly from those of their respective lesion-only counterparts. However, in the radial-arm maze task, the grafted rats given GM1 showed improved learning performances as compared with their saline-treated counterparts: they used more efficient visit patterns under the uninterrupted testing conditions and made fewer errors under the interrupted ones. The results suggest that GM1 treatment or intrahippocampal grafts used separately do not attenuate the lesion-induced behavioral deficits measured in this experiment. However, when GM1 treatment and grafts are used conjointly, both may interact in a manner allowing part of these deficits to be attenuated.

Comparison of the behavioral and morphological effects of colchicine- or neutral fluid-induced destruction of granule cells in the dentate gyrus of the rat

Virtually complete destruction of dentate gyrus granule cells by colchicine injections produced a persistent incapacity to solve spatial problems in rats. A topographically more selective but only locally complete destruction of granule cells using injections of neutral fluid (NFL) impaired acquisition during the initial stages of Morris water maze testing, thus indicating that limited degeneration of granule cells may weakly but significantly alter spatial learning capabilities. A subamnestic dose (0.08 mg/kg ip) of the NMDA antagonist MK-801 worsened radial maze performance only in NFL-treated rats, suggesting that there may be a synergistic interaction between NMDA blockade and limited granule cell degeneration.

The fimbria-fornix/cingular bundle pathways: a review of neurochemical and behavioural approaches using lesions and transplantation techniques

Extensive lesions of the fimbria-fornix pathways and the cingular bundle deprive the hippocampus of a substantial part of its cholinergic, noradrenergic and serotonergic afferents and, among several other behavioural alterations, induce lasting impairment of spatial learning and memory capabilities. After a brief presentation of the neuroanatomical organization of the hippocampus and the connections relevant to the topic of this article, studies which have contributed to characterize the neurochemical and behavioural aspects of the fimbria-fornix lesion "syndrome" with lesion techniques differing by the extent, the location or the specificity of the damage produced, are reviewed. Furthermore, several compensatory changes that may occur as a reaction to hippocampal denervation (sprouting changes in receptor sensitivity and modifications of neurotransmitter turnover in spared fibres) are described and discussed in relation with their capacity (or incapacity) to foster recovery from the lesion-induced deficits. According to this background, experiments using intrahippocampal or "parahippocampal" grafts to substitute for missing cholinergic, noradrenergic or serotonergic afferents are considered according to whether the reported findings concern neurochemical and/or behavioural effects. Taken together, these experiments suggest that appropriately chosen fetal neurons (or other cells such as for instance, genetically-modified fibroblasts) implanted into or close to the denervated hippocampus may substitute, at least partially, for missing hippocampal afferents with a neurochemical specificity that closely depends on the neurochemical identity of the grafted neurons. Thereby, such grafts are able not only to restore some functions as they can be detected locally, namely within the hippocampus, but also to attenuate some of the behavioural (and other types of) disturbances resulting from the lesions. In some respects, also these graft-induced behavioural effects might be considered as occurring with a neurochemically-defined specificity. Nevertheless, if a graft-induced recovery of neurochemical markers in the hippocampus seems to be a prerequisite for also behavioural recovery to be observed, this neurochemical recovery is neither the one and only condition for behavioural effects to be expressed, nor is it the one and only mechanism to account for the latter effects.

A comparison of behavioural effects and morphological features of grafts rich in cholinergic neurons placed in two sites of the denervated rat hippocampus

This study compared the morphological characteristics and the behavioural effects of intrahippocampal septal cell suspension grafts injected either just above the pyramidal cell layer of the hippocampal region CA1 or within the dorsal leaf of the dentate gyrus (DG) in rats subjected to electrolytic fimbria-fornix lesions. The behavioural tests determined home-cage and open-field activity, as well as radial-maze performance. Cresyl-violet staining, acetylcholinesterase (AChE) histochemistry, and parvalbumin, glial fibrillary acidic protein and glutamic acid decarboxylase immunocytochemistry were used for morphological assessments. The cross-sectional area of the grafts was measured between 0.8 mm and 5.3 mm posterior to Bregma and used as an index of their development. Whether injected into CA1 or DG, the grafts provided the partially denervated hippocampus with a dense AChE-positive reinnervation. Both types of grafts were devoid of reactive astrocytes (although reactive astrocytes were found close to the graft-host interface), contained almost no parvalbumin-positive neurons and showed a high density of GAD-positive terminals. One of the main differences between the two groups of grafted rats was that the suspension injected into the DG yielded grafts that, in the vicinity of the injection sites (between 2.3 mm and 4.3 mm posterior to Bregma), had a cross-sectional area exceeding that of the grafts placed into CA1 by about 63-110% (average 79%), the latter being more dispersed than the former in the coronal plane. In addition, rats with grafts in the DG exhibited granule cell degeneration in the vicinity of the injection sites, whereas rats with grafts in region CA1 showed no damage near the injection sites. Concerning the behavioural data, we found that fimbria-fornix lesions induced hyperactivity in both the home cage and the open field and impaired radial-maze performance. Compared with the lesion-only rats, the grafted rats in both groups had further increased open-field and home-cage activity. While the grafts placed into region CA1 slightly, but significantly, accentuated the lesion-induced deficit in radial-maze performance, those placed into the DG had no effect. These results suggest that intrahippocampal grafts may, in some (still unspecified) conditions, produce adverse behavioural effects or no behavioural effects, despite an acceptable graft-induced cholinergic reinnervation of the hippocampus. They do not allow a clear answer to the question of whether intra-DG and intra-CA1 septal suspension grafts exhibiting almost comparable morphological features (except in their size and their dispersion in the vicinity of the injection sites) induce behavioural effects that would depend on intrahippocampal location of the grafts. They suggest, however, that the granule cell degeneration caused by the implantation procedure, in conjunction with the intragyral development of the graft, probably does not account for some of the reported adverse behavioural effects of intrahippocampal basal forebrain grafts. Finally, the finding that septal cell suspensions placed into the DG yielded larger grafts than when an equivalent number of cells was injected into CA1 might be explained by a larger lesion-induced neurotrophic activity in DG than in region CA1, although both regions had undergone a similar degree of cholinergic denervation.

A comparison of the effects of two fimbria-fornix lesion techniques on beam-walking performance in the rat: aspiration versus electrolysis

This experiment was aimed at comparing the sensorimotor correlates of fimbria-fornix lesions made with either a classical aspiration technique that also removes part of the overlying cortical structures, or an electrolytic one that does not encroach upon these cortical structures. About 4 months after lesion surgery, Long-Evans female rats which had sustained an aspiration or an electrolytic fimbria-fornix lesion at the age of 90 days were tested to measure their beam-walking performance as an index for their sensorimotor capabilities. We found that after an aspiration lesion, the rats presented sensorimotor deficits which did not occur after an electrolytic lesion. After having found that electrolytic lesions of the fimbria and the fornix produced neurochemical deficits (in the dorsal hippocampus) and cognitive alterations close to those resulting from aspiration lesions, it is concluded from the present experiment that the electrolytic lesion technique is an interesting alternative to an aspiration technique, essentially because the former does not induce the sensorimotor deficits due to the partial damage that an aspiration technique produces in the medial parietal cortex. As the electrolytic lesion technique may minimize the risk of introducing a sensorimotor bias in the accuracy of cognitive evaluations, the present result might be of interest to neuroscientist using a fimbria-fornix lesion paradigm in order to investigate the efficacy of drugs, grafts or other treatments on the recovery from cognitive deficits.

Downregulation of muscarinic- and 5-HT1B-mediated modulation of [3H]acetylcholine release in hippocampal slices of rats with fimbria-fornix lesions and intrahippocampal grafts of septal origin

Adult Long-Evans female rats sustained electrolytic fimbria-fornix lesions and, two weeks later, received intrahippocampal suspension grafts of fetal septal tissue. Sham-operated and lesion-only rats served as controls. Between 6.5 and 8 months after grafting, both the [3H]choline accumulation and the electrically evoked [3H]acetylcholine ([3H]ACh) release were assessed in hippocampal slices. The release of [3H]ACh was measured in presence of atropine (muscarinic antagonist, 1 microM), physostigmine (acetylcholinesterase inhibitor, 0.1 microM), oxotremorine (muscarinic agonist, 0.01 microM-10 microM), mecamylamine (nicotinic antagonist, 10 microM), methiothepin (mixed 5-HT1/5-HT2 antagonist, 10 microM), 8-OH-DPAT (5-HT1A agonist, 1 microM), 2-methyl-serotonin (5-HT3 agonist, 1 microM) and CP 93129 (5-HT1B agonist, 0.1 microM-100 microM), or without any drug application as a control. In lesion-only rats, the specific accumulation of [3H]choline was reduced to 46% of normal and the release of [3H]ACh to 32% (nCi) and 43% (% of tissue tritium content). In the grafted rats, these parameters were significantly increased to 63%, 98% and 116% of control, respectively. Physostigmine reduced the evoked [3H]ACh release and was significantly more effective in grafted (-70%) than in sham-operated (-56%) or lesion-only (-54%) rats. When physostigmine was superfused throughout, mecamylamine had no effect. Conversely, atropine induced a significant increase of [3H]ACh release in all groups, but this increase was significantly larger in sham-operated rats (+209%) than in the other groups (lesioned: +80%; grafted: +117%). Oxotremorine dose-dependently decreased the [3H]ACh release, but in lesion-only rats, this effect was significantly lower than in sham-operated rats. Whatever group was considered, 8-OH-DPAT, methiothepin and 2-methyl-serotonin failed to induce any significant effect on [3H]ACh release. In contrast, CP 93129 dose-dependently decreased [3H]ACh release. This effect was significantly weaker in grafted rats than in the rats of the two other groups. Our data confirm that cholinergic terminals in the intact hippocampus possess inhibitory muscarinic autoreceptors and serotonin heteroreceptors of the 5-HT1B subtype. They also show that both types of receptors are still operative in the cholinergic terminals which survived the lesions and in the grafted cholinergic neurons. However, the muscarinic receptors in both lesioned and grafted rats, as well as the 5-HT1B receptors in grafted rats show a sensitivity which seems to be downregulated in comparison to that found in sham-operated rats. In the grafted rats, both types of downregulations might contribute to (or reflect) an increased cholinergic function that results from a reduction of the inhibitory tonus which ACh and serotonin exert at the level of the cholinergic terminal.

Serotonergic modulation of cholinergic function in the central nervous system: cognitive implications

Accumulating evidence suggests that serotonin may modulate cholinergic function in several regions of the mammalian brain and that these serotonergic/cholinergic interactions influence cognition. The first part of this review is an overview of histological, electrophysiological and pharmacological (in vitro, in vivo) data indicating that, in several brain regions (e.g., hippocampus, cortex and striatum), there are neuroanatomical substrates for a serotonergic/cholinergic interaction, and that alterations in serotonergic activity may induce functional changes in cholinergic neurons. In the second part, the review focuses on experimental approaches showing or suggesting that central cholinergic and serotonergic mechanisms are cooperating in the regulation of cognitive functions. These arguments are based on lesion, intracerebral grafting and pharmacological techniques. It is concluded that not all mnesic perturbations induced by concurrent manipulations of the serotonergic and cholinergic systems can be attributed to a serotonergic modification of the cholinergic system. The cognitive faculties of an organism arise from interactions among several neurotransmitter systems within brain structures such as, for instance, the hippocampus or the cortex, but also from influences on memory of other general functions that may involve cerebral substrates different from those classically related to mnesic functions (e.g., attention, arousal, sensory accuracy, etc.).

Rats with fimbria-fornix lesions display a place response in a swimming pool: a dissociation between getting there and knowing where

Some theories of hippocampal formation function postulate that it is involved in using the relationships between distal cues for spatial navigation. That rats with damage to the hippocampal formation are impaired in learning place responses of escaping to a platform hidden just below the surface of the water of a swimming pool, supports this view. Using rats with fimbria-fornix (FF) lesions, we examined whether their impairment is related to an inability to learn how to reach the platform as opposed to learning its location. In a first experiment, the FF rats were impaired in learning to swim to a hidden platform but could swim to a visible platform. In a second experiment, after being pretrained to swim to a visible platform, the FF rats swam to, paused, and searched the vicinity of the platform's previous location when it was removed. This finding showed that the FF rats expected to find the platform at that location. Additional tests confirmed that they had learned a place response. Despite having acquired a place response, they still could not acquire new place responses when only the hidden platform training procedure was used. Thus, these results in dissociating the processes of "getting there" and "knowing where" suggest that the FF rats' impairment may be in some process of motoric control, such as path integration, rather than in learning the location of the platform in relation to ambient cues. The results are discussed in relation to relevant theories of hippocampal function.

Sympathetic sprouting: time course of changes of noradrenergic, cholinergic, and serotonergic markers in the denervated rat hippocampus

As a first step for experiments investigating the presynaptic characteristics of sympathetic fibers grown into the denervated hippocampus, we studied the time course of changes of neurochemical markers in the rat hippocampus, subsequent to aspiration lesions of the fimbria-fornix and the overlying callosal and cortical structures. At various postsurgical delays (1, 2, 8, 24, and 40 weeks), the activity of choline acetyltransferase, the high-affinity synaptosomal uptake of choline and noradrenaline, and the concentrations of noradrenaline, serotonin, and 5-hydroxyindoleacetic acid were measured in a dorsal, an intermediate, and a ventral part of the hippocampus. Levels of all markers were significantly reduced shortly (1-2 weeks) after the lesions. However, whereas the cholinergic (choline uptake and choline acetyltransferase activity) and the serotonergic (concentrations of serotonin and 5-hydroxyindoleacetic acid) markers remained significantly reduced for up to 40 weeks, both noradrenergic markers recovered to near-normal (noradrenaline uptake) or even supranormal (noradrenaline concentration) levels, although with clear-cut differences in the time course and the regional characteristics. The noradrenaline content reached control levels already 8 weeks after lesion surgery and was about two to three times higher 40 weeks later, with the most dramatic effects in the ventral hippocampus. In contrast, high-affinity noradrenaline uptake reached control values only 24 weeks after lesion and exceeded them only in the ventral hippocampus 40 weeks after surgery.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of intrahippocampal grafts, training, and postoperative housing on behavioral recovery after septohippocampal damage in the rat

This study examined whether the expression of behavioral effects of grafts rich in cholinergic neurons placed into the hippocampus of rats with septohippocampal damage may be modulated by postoperative housing or training conditions. Among 91 Long-Evans female rats, 61 sustained a bilateral aspirative lesion of the fimbria-fornix fibers and all overlying tissue, while 30 were given sham operations. Ten days after surgery, fetal septal suspension grafts were performed in the hippocampus of half the lesioned rats. Two days later, all rats were randomly assigned to one of three housing or training conditions: standard, standard with daily training, and enriched. Two and 5 months later, the rats were tested for learning using a Hebb-Williams maze. At both these delays, performance was clearly impaired in lesioned rats and was found to be ameliorated by grafts only in rats which had received daily training. Cresyl violet staining and acetylcholinesterase histochemistry showed that, irrespective of the housing or training conditions, all grafts had survived and provided the denervated hippocampus with a substantial cholinergic reinnervation. Our results suggest that the beneficial behavioral effects of intrahippocampal suspension grafts of septal cells may depend on the postsurgical training or handling conditions of the graft recipients. This result might be of importance for interpreting some behavioral effects of grafts, since in most studies in which grafts were found to induce beneficial behavioral effects (especially on learning capacity), these effects were generally observed at the end of a rather long testing period. Moreover, the present findings show that this delay, before graft function is expressed, might be linked not only to the time needed by grafts to establish a functional reinnervation in the host brain, but also to the training and/or handling conditions of the graft recipient.

Behavioural and neurochemical effects of superior cervical ganglionectomy in rats with septo-hippocampal lesions

This longitudinal study, extending over 12 months, assessed the behavioural and biochemical effects of hippocampal sympathetic ingrowth (HSI) into the partially denervated hippocampus. Male Long-Evans rats received fimbria-fornix lesions (FIFO) or sham operations at 90 days of age. At the same time half of the rats from each group sustained bilateral ablation of the superior cervical ganglia (SCGX). A battery of behavioural tests, measuring spontaneous alternation, activity in the open field and home cage, and radial-maze performance, were employed, starting after one very short (16 days) and one extended (216 days) post-operative delay. Neurochemical analyses measuring choline acetyltransferase (ChAT) activity, high-affinity choline (HACU) and noradrenaline uptake by hippocampal synaptosomes (HANU), hippocampal noradrenaline ([NA]), serotonin ([5-HT]) and 5-hydroxyindoleacetic acid ([5-HIAA]) concentrations were carried out in a dorsal, a "middle" and a ventral region of the hippocampus. Lesion of the FIFO induced a significant and enduring deficit in radial-maze performance, in addition to a persistent locomotor hyperactivity. ChAT and HACU were significantly depleted in all three regions of the hippocampus at 12 months, and these deficits were negatively correlated with maze performance. SCGX in the presence of the FIFO lesion significantly reduced [NA] in the middle region of the hippocampus, as compared to SCGX rats, and contributed to a restoration of lesion-induced depletions in [5-HT] and [5-HIAA] in the middle and ventral hippocampal regions, whilst failing to elicit any behavioural changes at either time point. It is concluded that if lesion-induced HSI indeed occurred, as is suggested by neurochemical evidence, it had no effect upon the observed behavioural deficits elicited by transection of the FIFO in the rat.

Hippocampal amino acid concentrations after raphe and/or septal cell suspension grafts in rats with fimbria-fornix lesions

Two weeks after infracallosal electrolytic fimbria-fornix lesions, Long-Evans female rats received intrahippocampal suspension grafts of either fetal septal or mesencephalic raphe tissue, or a mixture of both. Ten months after lesion surgery, the concentrations of alanine, aspartate, GABA, glutamate, glutamine, glycine, serine and taurine were determined in a dorsal, a "middle" and a ventral region of the hippocampus. We found neither the lesions nor the grafts to have significantly modified the concentration of these amino acids which, in all groups, presented a regional heterogeneity in their hippocampal distribution. GABA, glutamate and glutamine were highest in the ventral hippocampus, whereas the other amino acids were highest in the dorsal region. Our results (i) show that fimbria-fornix lesions do not result in lasting effects on hippocampal concentrations of the assessed amino acids, (ii) confirm the regional heterogeneity in the distribution of these amino acids in the hippocampus and (iii) demonstrate that cell suspension grafts of fetal septal or mesencephalic raphe tissue, as well as grafts of a mixture of both of these tissues, do not exert a non-specific effect on either of the amino acid concentrations measured. These data complete those of the preceeding paper [Kiss et al. (1990) Neuroscience 36, 61-72] concerning the effects of the same grafts on hippocampal cholinergic, serotonergic and noradrenergic markers, as well as on several behavioural variables.

The effects of intrahippocampal raphe and/or septal grafts in rats with fimbria-fornix lesions depend on the origin of the grafted tissue and the behavioural task used

Long-Evans female rats sustained electrolytic lesions of the fimbria and the dorsal fornix and, two weeks later, received intrahippocampal suspension grafts of fetal tissue. The grafts were prepared from regions including either the medial septum and the diagonal band of Broca (septal grafts), or the mesencephalic raphe (raphe grafts), or from both these regions together (co-grafts). All rats were submitted to a series of behavioural tests (home cage and open-field locomotion, spontaneous alternation, radial-arm maze and Morris water maze performance) run over two periods after grafting (one to nine weeks and 20-35 weeks). Two weeks after completion of behavioural testing, histological (acetylcholinesterase and Cresyl Violet staining) and/or neurochemical (choline acetyltransferase activity, high-affinity synaptosomal uptake of choline and serotonin, noradrenaline, serotonin and 5-hydroxyindolacetic acid concentrations) verifications were performed on the hippocampus. Compared to sham-operated rats, lesion-only rats exhibited hyperactivity which was transient in a familiar environment (home cage) and lasting in an unfamiliar one (open field), decreased rates of spontaneous T-maze alternation, and impaired memory performance in both the radial-arm maze and the Morris water maze. These rats also showed decreased cholinergic and serotonergic markers with a maximal depletion in the septal two-thirds of the hippocampus. Noradrenaline concentration tended to be increased in the dorsal third of the hippocampus, but was not modified in the other two-thirds. While septal grafts specifically increased the cholinergic markers and raphe grafts the serotonergic ones, neither of these grafts produced a lasting effect on any behavioural variable. Conversely, the co-grafts, which increased both the cholinergic and serotonergic markers in the septal two-thirds of the hippocampus, completely normalized the Morris water maze probe trial performance, but failed to affect any of the other behavioural variables. Our present results confirm that grafts of fetal neurons injected into the denervated hippocampus may induce a neurochemical recovery that depends on the anatomical origin of the grafted cells, and that co-grafting two fetal brain regions allows the combination of their individual neurochemical properties. Furthermore, our results show that these neurochemical effects of the co-grafts may be involved in the recovery of behavioural function observed in the water maze. However, somewhat paradoxically, those effects appear inefficient for inducing any recovery in other behavioural tasks, even in the radial-arm maze; which is assumed to measure similar spatial functions.(ABSTRACT TRUNCATED AT 400 WORDS)