Adrenoreceptor antagonist treatment influences recovery of learning following medial septal lesions and hippocampal sympathetic ingrowth

Acetylcholine and noradrenaline differentially regulate hippocampus-dependent spatial learning and memory

Severe loss of cholinergic neurons in the basal forebrain nuclei and of noradrenergic neurons in the locus coeruleus are almost invariant histopathological hallmarks of Alzheimer's disease. However, the role of these transmitter systems in the spectrum of cognitive dysfunctions typical of the disease is still unclear, nor is it yet fully known whether do these systems interact and how. Selective ablation of either neuronal population, or both of them combined, were produced in developing animals to investigate their respective and/or concurrent contribution to spatial learning and memory, known to be severely affected in Alzheimer's disease. Single or double lesions were created in 4-8 days old rats by bilateral intraventricular infusion of two selective immunotoxins. At about 16 weeks of age, the animals underwent behavioural tests specifically designed to evaluate reference and working memory abilities, and their brains were later processed for quantitative morphological analyses. Animals with lesion to either system alone showed no significant reference memory deficits which, by contrast, were evident in the double-lesioned subjects. These animals could not adopt an efficient search strategy on a given testing day and were unable to transfer all relevant information to the next day, suggesting deficits in acquisition, storage and/or recall. Only animals with single noradrenergic or double lesions exhibited impaired working memory. Interestingly, ablation of cholinergic afferents to the hippocampus stimulated a robust ingrowth of thick fibres from the superior cervical ganglion which, however, did not appear to have contributed to the observed cognitive performance. Ascending cholinergic and noradrenergic afferents to the hippocampus and neocortex appear to be primarily involved in the regulation of different cognitive domains, but they may functionally interact, mainly at hippocampal level, for sustaining normal learning and memory. Moreover, these transmitter systems are likely to compensate for each other, but apparently not via ingrowing sympathetic fibres.

Hippocampal body changes in pure partial onset sleep and pure partial onset waking epileptic patients

The aim of the current study was to evaluate for the first time the hippocampal changes in patients with pure sleep and pure waking epilepsy. A total of 35 patients with pure partial onset sleep epilepsy and 35 patients with pure partial onset waking epilepsy matched for age and sex ratio were enrolled. MR images were analyzed to determine hippocampal body changes. Rounding ratio of hippocampal body was defined as short axis divided by long axis and hippocampal bodies with ratios ≥ 0.70 were considered rounded. Hippocampal sclerosis and atrophy were found in nine (25.7 %) and seven (20.0 %) patients with pure sleep epilepsy, and in 12 (34.3 %) and 11 (31.4 %) patients with pure waking epilepsy, respectively (P > 0.05 for the comparison between sleep and waking epilepsy). However, proportion of subjects with rounded hippocampal bodies (15, 42.9 % vs. 3, 8.6 % for patients with sleep and waking epilepsy, respectively) and rounding ratios of both left and right hippocampal bodies (0.66 ± 0.13 and 0.61 ± 0.12, respectively for left and right hippocampal bodies in sleep epileptic patients vs. 0.57 ± 0.11 and 0.55 ± 0.11, respectively for left and right hippocampal bodies in waking epileptic patients) were increased in patients with sleep epilepsy (P < 0.05). Further, in sleep epileptic patients with left sided hippocampal body rounding, epileptiform discharges were more readily lateralized to the left temporal lobe (P < 0.05). In conclusion, hippocampal sclerosis and atrophy are not different between pure partial onset sleep and waking epileptic patients. However, rounding ratio and frequency of hippocampal body rounding are increased in sleep epileptic patients.

The role of the septo-hippocampal cholinergic projection in T-maze rewarded alternation

Administration of 192IgG-saporin, a cholinergic neurotoxin, to the medial septum destroys the cell bodies from which the septo-hippocampal cholinergic projection originates, leading to reductions in both hippocampal acetylcholinesterase (AChE) and choline acetyltransferase (ChAT). Despite reports that 192IgG-saporin-induced cholinergic loss leads to post-operative impairments in acquisition and performance of spatial memory tasks, a number of other reports have described intact spatial memory performance following these lesions. Factors that might account for these different outcomes include variations in toxin injection sites or volumes, and post-operative testing at times that might permit regeneration of damaged neuronal processes. We, therefore, assessed the effects of intraseptal microinjection of 192IgG-saporin, in rats, on the post-operative retention of pre-operatively acquired discrete-trial rewarded alternation in the T-maze. This design allowed us to assess the effects of the lesion 7 days post-surgery, at which point, at best, incomplete neuronal regeneration would have been expected to have occurred. The lesion led to a profound loss of hippocampal AChE staining, and a clear inflammatory response, as assessed by proliferation of OX42-stained macrophages in the medial septum and diagonal band nuclei, but there was no impairment in spatial working memory.

Hippocampal sympathetic ingrowth occurs following 192-IgG-Saporin administration

Electrolytic lesions of the medial septal region leads to an unusual neuronal reorganization in which peripheral sympathetic fibers, originating from the superior cervical ganglia, grow into the cholinergically denervated areas of the hippocampus. Since these lesions disrupt cells and fibers of passage which are non-cholinergic, there has been a debate whether Hippocampal Sympathetic Ingrowth is due only to cholinergic denervation of the hippocampus. Using the intraseptal administration of 192-IgG-Saporin, a specific cholinergic neurotoxin, we have found that hippocampal sympathetic ingrowth occurs in the cholinergically denervated hippocampus at 4, 8 and 12 weeks post Saporin injection. These results clearly suggest that hippocampal sympathetic ingrowth is due to the specific loss of the cholinergic projection from the medial septum.

Apoptotic protein expression and activation of caspases is changed following cholinergic denervation and hippocampal sympathetic ingrowth in rat hippocampus

Following cholinergic denervation of the hippocampus by medial septal lesions, an unusual neuronal reorganization occurs in which peripheral adrenergic fibers arising from superior cervical ganglia grow into the hippocampus (hippocampal sympathetic ingrowth). Recent studies suggest that a similar process, in which sympathetic noradrenergic axons invade the hippocampus, can occur in Alzheimer's disease patients. In the last few years, the occurrence of apoptotic cell death has been studied in Alzheimer's disease patients and in animal models of this disorder. Several studies suggest that the hippocampus is an important area to be considered for apoptotic cell death. In our studies in the rat hippocampus, we have measured the expression of inducers and blockers of apoptosis in membrane, cytosolic and mitochondrial fractions, and the activity of caspases. The level of cytosolic Fas was increased in cholinergic denervation compared to control and hippocampal sympathetic ingrowth groups. The membrane Fas ligand expression was significantly increased in hippocampal sympathetic ingrowth and in cholinergic denervation compared to the control group. The level of caspase-3 (CPP32) was increased in the cholinergic denervation group compared to control and hippocampal sympathetic ingrowth groups. The cytosolic expression of bcl-x was increased in hippocampal sympathetic ingrowth compared to control and cholinergic denervation. The cytosolic activity of caspase-3 appeared to be significantly decreased in hippocampal sympathetic ingrowth and increased in cholinergic denervation groups compared to control and cholinergic denervation/hippocampal sympathetic ingrowth, respectively. From the present results, we suggest that cholinergic denervation may be responsible for pro-apoptotic responses, while hippocampal sympathetic ingrowth may protect neurons from apoptosis in rat dorsal hippocampus.

Effect of phospholipase C and protein kinase C following cholinergic denervation and hippocampal sympathetic ingrowth in rat hippocampus

Following cholinergic denervation of the hippocampus by medial septal lesions, an unusual neuronal reorganization occurs in which peripheral adrenergic fibers arising from the superior cervical ganglia grow into the hippocampus (hippocampal sympathetic ingrowth). We have reported previously that cholinergic denervation and hippocampal sympathetic ingrowth differentially affected cholinergically stimulated phosphoinositide hydrolysis, concentration and affinity of muscarinic receptors, Go-protein level and protein kinase C activity. To complete these studies, we determined whether cholinergic denervation and hippocampal sympathetic ingrowth influenced phospholipase C and protein kinase C expression in dorsal hippocampal membranes and cytosol. Using immunoblotting methods, the results showed that the 100,000 mol. wt subunit of phospholipase Cbeta was increased in the membrane fraction in the hippocampal sympathetic ingrowth group by 45% compared to controls and the 150,000 mol.wt subunit was increased by 75% and 59% compared to controls and cholinergic denervation, respectively. For protein kinase C detection, immunoblots were prepared using antibodies selective for "classical" protein kinase C members (alpha, beta, gamma) and for the "novel" protein kinase C subfamily members (delta, &theta;). Membrane protein kinase Cbeta was decreased in hippocampal sympathetic ingrowth by 35% compared to controls and by 41% compared to cytosolic hippocampal sympathetic ingrowth. Membrane protein kinase Cbeta was decreased in cholinergic denervation by 28% compared to controls. When compared to membranes from controls and the cholinergic denervation group, and to cytosolic fractions from the hippocampal sympathetic ingrowth groups, respectively, the following membrane protein kinase isoforms were found to be decreased by hippocampal sympathetic ingrowth: gamma by 55%, 40% and 57%; delta by 91.5%, 70% and 120%; theta; by 95%, 100% and 86%.In conclusion, our results may indicate the connection between the previously reported differential influence of hippocampal sympathetic ingrowth and cholinergic denervation on cholinergically stimulated phosphoinositol hydrolysis. The "normalization" of phosphoinositol hydrolysis found in hippocampal sympathetic ingrowth may be due to the increase in phospholipase Cbeta expression in hippocampal sympathetic ingrowth membrane fractions. Since the activation of protein kinase C is known to block phosphoinositol hydrolysis, hippocampal sympathetic ingrowth "normalization" of phosphoinositol hydrolysis may result from a reduction in protein kinase expression in hippocampal sympathetic ingrowth membranes.

Coactivation of beta-adrenergic and cholinergic receptors enhances the induction of long-term potentiation and synergistically activates mitogen-activated protein kinase in the hippocampal CA1 region

Interactions between noradrenergic and cholinergic receptor signaling may be important in some forms of learning. To investigate whether noradrenergic and cholinergic receptor interactions regulate forms of synaptic plasticity thought to be involved in memory formation, we examined the effects of concurrent beta-adrenergic and cholinergic receptor activation on the induction of long-term potentiation (LTP) in the hippocampal CA1 region. Low concentrations of the beta-adrenergic receptor agonist isoproterenol (ISO) and the cholinergic receptor agonist carbachol had no effect on the induction of LTP by a brief train of 5 Hz stimulation when applied individually but dramatically facilitated LTP induction when coapplied. Although carbachol did not enhance ISO-induced increases in cAMP, coapplication of ISO and carbachol synergistically activated p42 mitogen-activated protein kinase (p42 MAPK). This suggests that concurrent beta-adrenergic and cholinergic receptor activation enhances LTP induction by activating MAPK and not by additive or synergistic effects on adenylyl cyclase. Consistent with this, blocking MAPK activation with MEK inhibitors suppressed the facilitation of LTP induction produced by concurrent beta-adrenergic and cholinergic receptor activation. Although MEK inhibitors also suppressed the induction of LTP by a stronger 5 Hz stimulation protocol that induced LTP in the absence of ISO and carbachol, they had no effect on LTP induced by high-frequency synaptic stimulation or low-frequency synaptic stimulation paired with postsynaptic depolarization. Our results indicate that MAPK activation has an important, modulatory role in the induction of LTP and suggest that coactivation of noradrenergic and cholinergic receptors regulates LTP induction via convergent effects on MAPK.

Effects of pertussis toxin and galpha-protein-specific antibodies on phosphoinositide hydrolysis in rat brain membranes after cholinergic denervation and hippocampal sympathetic ingrowth

Cholinergic denervation of the hippocampal formation, via medial septal lesions, induces peripheral noradrenergic fibers, originating from the superior cervical ganglion, to grow into the hippocampus. We have previously reported that cholinergic denervation and hippocampal sympathetic ingrowth differentially affect guanosine-5'-O-(3-thiotriphosphate)- as well as guanosine-5'-O-(3-thiotriphosphate) + carbachol-stimulated polyphosphoinositide hydrolysis, suggesting an alteration in G proteins and/or the entire receptor complex. To examine the type of G protein which may be involved in these effects, rat dorsal hippocampal membranes were preincubated with pertussis toxin in the presence of guanosine-5'-O-(3-thiotriphosphate) and guanosine-5'-O-(3-thiotriphosphate) + carbachol. Pertussis toxin reduced guanosine-5'-O-(3-thiotriphosphate) in all groups, while guanosine-5'-O-(3-thiotriphosphate) + carbachol-stimulated phosphoinositide hydrolysis was reduced in controls and animals without sympathetic ingrowth but not in animals with hippocampal sympathetic ingrowth. This suggests that pertussis toxin-sensitive G proteins may be involved in the mediation of phosphoinositide hydrolysis. To confirm this hypothesis, membranes were preincubated with antibodies to Galphao and Gq/11. The Go antibody significantly decreased guanosine-5'-O-(3-thiotriphosphate) in all groups, while guanosine-5'-O-(3-thiotriphosphate) +carbachol-stimulated phosphoinositide hydrolysis was reduced only in hippocampal sympathetic ingrowth. Impairment of guanosine-5'-O-(3-thiotriphosphate) and carbachol-stimulated phosphoinositide hydrolysis was also decreased in all groups when preincubated with Gq/11 antibody. To determine whether hippocampal sympathetic ingrowth or cholinergic denervation altered the concentration of various G proteins, immunoblotting methodology was utilized. Gq/11 concentrations were found to be equivalent among groups. The density of Go1, Go2, and Go3 isoforms was significantly increased in the cholinergic denervation, while in the hippocampal sympathetic ingrowth only group Go3 was significantly increased. When assessed as total Go protein, density was increased significantly only in the cholinergic denervation group. Overall, these results suggest that hippocampal sympathetic ingrowth and cholinergic denervation induce alterations in phosphoinositide hydrolysis through both the Gq/11 and the Go proteins and that the coupling between muscarinic receptor and G protein is the possible site which affects changes in phosphoinositide turnover. Our results also suggest that cholinergic denervation and hippocampal sympathetic ingrowth may mediate phosphoinositide hydrolysis through an effect on different isoforms of the same G protein.

Stimulation of alpha-1 adrenergic receptors facilitates spatial learning in rats

The present experiments were designed to examine the effects of alpha-1 adrenergic stimulation and inhibition on memory encoding and to investigate whether the alpha-1 adrenergic and muscarinic cholinergic systems interact in the regulation of spatial navigation behavior in the Morris water maze test and we also studied the effects of D-cycloserine, a partial agonist at the glycine binding site on the N-methyl-D-aspartate (NMDA) receptor complex, on the performance of scopolamine-treated rats in this task. Pre-training subcutaneous administration of St-587 (a putative alpha-1 agonist) at 1000 micrograms kg-1 or 1500 micrograms kg-1 improved water maze navigation to a hidden platform. Prazosin (an alpha-1 antagonist), 300-2000 micrograms kg-1, did not significantly impair the spatial navigation performance. Pre-training administration of prazosin 1000 micrograms kg-1, but not 300 micrograms kg-1, slightly potentiated the deficit in water maze navigation seen after scopolamine (200 micrograms kg-1, pre-training intraperitoneal injection). Pre-training administration of St-587 at a dose 1500 micrograms kg-1, but not 500 micrograms kg-1, slightly ameliorated the scopolamine-induced (200 micrograms kg-1) impairment in performance of rats. Pre-training administration of prazosin at doses 300 or 1000 micrograms kg-1 or St-587 at doses 500 micrograms kg-1 or 1500 micrograms kg-1 did not have any significant influence on the scopolamine-induced (200 micrograms kg-1) increase of swimming speed. Furthermore, D-cycloserine at the dose of 300 micrograms kg-1 but not 1000 or 3000 micrograms kg-1 reversed the scopolamine (200 micrograms kg-1)-induced deficit in acquisition of the water maze task but not the increase in motor output (increased swimming speed). These results indicate that the stimulation of alpha-1 adrenoceptors may facilitate the encoding of new information. These findings suggest that alpha-1 adrenergic mechanisms do not participate or at least are not the most critical part of the noradrenergic system in the interaction between noradrenaline and muscarinic receptors in the modulation of learning and memory. In addition, these results suggest that D-cycloserine may be effective in alleviating states of central cholinergic hypofunction.

Cholinergic denervation and sympathetic ingrowth result in persistent changes in hippocampal muscarinic receptors

Our laboratory has been utilizing the model of hippocampal sympathetic ingrowth, which has been suggested to occur in Alzheimer's disease, to investigate the effects of cholinergic denervation and hippocampal rearrangements. After cholinergic denervation by medial septal lesions, peripheral sympathetic fibres originating from the superior cervical ganglia grow into the rat hippocampus. This hippocampal sympathetic ingrowth can be prevented by superior cervical ganglionectomy. We examined the long-term effects of these treatments on muscarinic receptors by comparing [3H]quinuclidinyl benzilate binding in rat dorsal hippocampus four and 12 weeks post lesion. Four groups of animals were employed, including controls (sham lesion+sham ganglionectomy), animals with ingrowth (medial septal lesion+ sham ganglionectomy), animals with cholinergic denervation alone (medial septal lesion+ ganglionectomy), and ganglionectomy alone (sham lesion+ganglionectomy) animals. In dorsal hippocampus four weeks post lesion, binding affinity was similar among all groups, while muscarinic receptor number was increased in ingrowth animals as compared to both the control (P<0.0002) and ganglionectomy animals (P<0.01). By 12 weeks, receptor affinity was significantly decreased in ingrowth (P<0.0001) and cholinergic denervation (P<0.0003) groups, and receptor number remained significantly elevated in ingrowth animals as compared to control (P<0.01), ganglionectomy (P<0.02) and cholinergic denervation (P<0.01) groups. The decrease in muscarinic receptor affinity may provide some insight into the ineffectiveness of cholinomimetic therapies in Alzheimer's disease, in that agonist efficacy would be reduced at the receptor.

Working memory failure by combined blockade of muscarinic and beta-adrenergic transmission in the rat hippocampus

INTRAHIPPOCAMPAL administration of the muscarinic acetylcholine receptor antagonist scopolamine at a dose of 3.2 micrograms/side significantly increased the number of errors (attempts to pass through two incorrect panels of the three panel-gates at four choice points) in the working memory task with a three-panel runway setup, whereas 0.32 microgram/side scopolamine did not affect working memory errors. The beta-adrenoceptor antagonist propranolol (10 mg/kg, i.p.) had no effect on working memory error, but it produced a significant increase in working memory errors when administered in combination with intrahippocampal scopolamine at the behaviourally ineffective dose (0.32 microgram/side). The increase in working memory errors induced by intrahippocampal administration of 0.32 microgram/side scopolamine to rats treated with 10 mg/kg propranolol was decreased by concurrent injection of the cholinesterase inhibitor physostigmine (3.2 micrograms/side). D-Cycloserine (the partial agonist at the glycine bindings site on the NMDA receptor/channel complex) at a dose of 10 micrograms/side reduced the increase in working memory errors induced by intrahippocampal 0.32 microgram/side scopolamine combined with 10 mg/kg propranolol. These results suggest that neural mechanisms regulated cooperatively by hippocampal muscarinic and beta-adrenergic transmission underlie working memory performance, and that modification of NMDA function contributes to such interactive regulation of working memory processes in the hippocampus.

Noradrenergic DSP-4 lesions aggravate impairment of working memory produced by hippocampal muscarinic blockade in rats

To clarify the interactions between hippocampal cholinergic and adrenergic systems in working memory function of rats, the effects of hippocampal muscarinic receptor blockade combined with noradrenaline depletion on this behavior were examined with a three-panel runway task. Intrahippocampal administration of the muscarinic receptor antagonist scopolamine at a dose of 3.2 micrograms/side significantly increased the number of errors (attempts to pass through two incorrect panels of the three panel-gates at four choice points) in the working memory task, whereas the 0.32 microgram/side dose of scopolamine did not affect working memory errors. Administration of the noradrenergic neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) at 50 mg/kg IP caused a marked reduction in hippocampal noradrenaline concentration, but it had no effect on working memory errors. Intrahippocampal administration of 0.32 microgram/side scopolamine, the behaviorally ineffective dose in intact rats, significantly increased the number of working memory errors in the noradrenaline-depleted animals. These results suggest that hippocampal muscarinic/noradrenergic interactions are involved in neural processes mediating working memory function of rats.

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.

Effect of hippocampal sympathetic ingrowth and cholinergic denervation on hippocampal phospholipase C activity and G-protein function

Following cholinergic denervation of the hippocampal formation, via medial septal lesions, peripheral noradrenergic fibers, originating from the superior cervical ganglion, grow into the hippocampus. In previous studies, we have found that hippocampal sympathetic ingrowth and cholinergic denervation alone (animals with concurrent medial septal lesions and superior cervical ganglionectomy) alter phosphoinositide turnover and muscarinic cholinergic receptors in such a way as to suggest an alteration in coupling between the muscarinic cholinergic receptors and phosphoinositol turnover. To test this hypothesis we examined the effect of hippocampal sympathetic ingrowth and cholinergic denervation on phospholipase C activity, G-protein function and the whole receptor complex by measuring the amount of phosphoinositide hydrolysed in hippocampal membranes of the rat. Neither hippocampal sympathetic ingrowth nor cholinergic denervation was found to alter phospholipase C activity when activated by increasing concentrations of Ca2+. In dorsal hippocampus, cholinergic denervation, when compared to hippocampal sympathetic ingrowth and controls, was found to decrease the amount of phosphoinositol hydrolysed when stimulated with the GTP analog, guanosine-5'-O-(3-thiotriphosphate). When guanosine-5'-O-(3-thiotriphosphate) plus carbachol (1 mM) was utilized to stimulate the entire receptor complex, phosphoinositol hydrolysis was found to be decreased in the cholinergic denervation group as compared to both hippocampal sympathetic ingrowth and control groups. This effect was maximum at 3 microM guanosine-5'-O-(3-thiotriphosphate). These results suggest that both hippocampal sympathetic ingrowth and cholinergic denervation affect the efficiency of coupling between the muscarinic cholinergic receptors and phosphoinositol turnover, with cholinergic denervation decreasing and hippocampal sympathetic ingrowth "normalizing" efficiency. Further, they suggest that the G-protein is the site at which hippocampal sympathetic ingrowth and cholinergic denervation mediate their effects. The results of these experiments are also discussed within the context of recent findings demonstrating G-protein abnormalities in Alzheimer's disease.

Effects of St-587 and prazosin on water maze and passive avoidance performance of scopolamine-treated rats

The present experiments were designed to investigate whether the alpha-1 adrenergic and muscarinic cholinergic systems interact in the regulation of spatial navigation behavior in the Morris water maze test and passive avoidance performance. Pretraining administration of scopolamine, a muscarinic antagonist, markedly impaired the acquisition of water maze task (a hidden platform version) as well as retention of this task. The drug also impaired slightly navigation to a visible platform. Pretraining subcutaneous administration of St-587 (alpha-1 agonist) at 2000 micrograms/kg slightly improved the water maze navigation to a hidden platform in control rats, but its effect was not augmented in scopolamine-treated rats. Pretraining administration of prazosin (alpha-1 antagonist) 1000 micrograms/kg or 2000 micrograms/kg did not significantly potentiate the scopolamine (muscarinic cholinergic antagonist)-induced (doses 200 micrograms/kg and 100 micrograms/kg, pretraining intraperitoneal injection) deficit in water maze navigation. Pretraining administration of prazosin at doses 1000 micrograms/kg and 2000 micrograms/kg or St-587 at doses 1000 micrograms/kg and 2000 micrograms/kg did not have any significant influence on scopolamine-induced (200 micrograms/kg or 400 micrograms/kg) disruption in passive avoidance performance. These findings suggest that alpha-1 adrenergic mechanisms do not participate or are not the most important component of the noradrenergic system in the interaction between noradrenaline and muscarinic receptors in the modulation of learning and memory. The analysis of results indicates that activation of alpha-1 adrenoceptors might facilitate the acquisition of water maze task in its initial phase, for instance, switching from wall hugging strategy to an active exploration strategy. Furthermore, the present data suggest that muscarinic cholinergic blockade may affect both mnemonic and nonmnemonic processes in rats.

Sympathetic sprouting reverses decreases in membrane-associated activity of protein kinase C following septohippocampal denervation of the rat hippocampus

Hippocampal sympathetic ingrowth (HSI), a form of neuronal plasticity, is induced by medial septal lesions and consists of the sprouting of peripheral sympathetic fibers, arising from the superior cervical ganglion, into the dentate gyrus and CA3 region of the hippocampus. HSI has been previously shown to alter learned and spontaneous behaviors, phosphatidyl inositide hydrolysis, and the antagonist binding kinetics of both muscarinic cholinergic receptors and phorbol ester receptors. We now report that sympathetic sprouting reverses decreases in membrane-associated activity of protein kinase C (PKC) following septohippocampal denervation of the rat hippocampus. Further, no changes were found in alpha, beta or gamma PKC isoenzymes among experimental groups, suggesting that the group A PKC isoforms do not mediate the observed changes in activity and phorbol ester binding.

Cholinergic denervation-like changes in rat hippocampus following developmental lead exposure

We investigated the effects of developmental lead exposure from embryonic day 16 (E16) through postnatal day 28 (PN28), on cholinergic and catecholaminergic markers in the septohippocampal pathway in rats through fourth month of age. Lead exposure resulted in a persistent 30-40% reduction of [3H]hemicholinium-3 ([3H]HC-3) binding in the hippocampus through PN120, and 20-30% reduction of septal and hippocampal choline acetyltransferase (ChAT) activity which persisted through PN84 but returned to control levels in both septum and hippocampus at PN112. The muscarinic ligand [3H]quinuclidinyl benzylate ([3H]QNB) binding was reduced in the septum at PN28 but did not differ significantly from controls at PN56-PN112. Neither short- nor long-term effects of Pb exposure on [3H]QNB binding were seen in the hippocampus. Similar to the effects of fimbria-fornix transection, Pb exposure resulted in a long-term 50-90% increase of tyrosine hydroxylase(TH) activity in the hippocampus, although neither treatment affected TH activity in the septum. The lead-induced increase in hippocampal TH was significantly attenuated by superior cervical ganglionectomy. It is concluded that the effects of perinatal lead exposure resemble in several respects those seen following surgical disruption of the septohippocampal pathway in adult animals. The denervation-like effects in the hippocampus may be an important factor in long-term learning and cognitive impairments following developmental exposure to low-levels of lead.

The effect of hippocampal sympathetic ingrowth and cholinergic denervation on hippocampal M2 cholinergic receptors

After cholinergic denervation of the hippocampus, via medial septal (MS) lesions, peripheral sympathetic fibers, originating from the superior cervical ganglia, grow into the hippocampus. In this study, we sought to determine the effect of hippocampal sympathetic ingrowth (HSI) on the M2 subtype of muscarinic cholinergic receptors, by examining the membrane binding of [3H]AF-DX 384 in hippocampal tissue from control rats, rats with HSI and rats with MS lesions + concurrent ganglionectomy (CD group). In dorsal hippocampus, Kd was found to be increased while Bmax was decreased in the CD group as compared with both the HSI and control group which did not differ from one another. In ventral hippocampus, Kd was found to be increased while Bmax was decreased in the CD group when compared only with the control group. These results suggest that sympathetic ingrowth, which has its greatest concentration in dorsal hippocampus, can 'normalize' the M2 receptor in hippocampus.

The effect of cholinergic denervation and hippocampal sympathetic ingrowth on the internalization of muscarinic receptors in rat hippocampus

Following cholinergic denervation of the hippocampus by medial septal (MS) lesions, an unusual neuronal reorganization occurs in which peripheral sympathetic fibers, originating from the superior cervical ganglia, grow into the hippocampus (hippocampal sympathetic ingrowth; HSI). Previously, we have found that with MS lesions, animals with (the HSI(+) group) and without (HSI(-) group) ingrowth differed in carbachol stimulated PI hydrolysis, in PKC activity, and in muscarinic cholinergic receptors (mAChR). In this study, performed in hippocampal slices obtained four weeks after MS lesions, we utilized the hydrophilic muscarinic antagonist [3H]N-methylscopolamine ([3H]NMS) and hydrophobic muscarinic antagonist [3H]quinuclidinyl benzilate ([3H]QNB) in the presence of either 4-alpha-phorbol or phorbol 12,13-dibutyrate (PDBu) to determine the effect of MS lesions with and without ingrowth on PKC-mediated mAChR internalization. In the presence of PDBu, a group effect was observed in [3H]NMS binding, with control groups > HSI(+) group > HSI(-) group. However, [3H]QNB binding was similar across groups. These results suggest that the cholinergic denervation of the hippocampus enhances the internalization of mAChRs, which is modified in the presence of HSI.

Hippocampal sympathetic ingrowth and cholinergic denervation uniquely alter muscarinic receptor subtypes in the hippocampus

Following cholinergic denervation of the hippocampus by medial septal lesions, and unusual neuronal reorganization occurs, in which peripheral sympathetic fibers, originating from the superior cervical ganglia, grow into the hippocampus. Previously, we have found that both hippocampal sympathetic ingrowth (HSI) and cholinergic denervation (CD), alone, altered the total number and affinity of muscarinic cholinergic receptors (mAChR). In this study, we utilized the muscarinic antagonist [3H]Pirenzepine, in combination with membrane radioligand binding techniques, to determine the effects of HSI and CD on hippocampal M1 and M1 + M3 mAChR subtypes, 4 weeks after MS lesions. In both the dorsal and ventral hippocampus, HSI was found to markedly diminish the number of M1 AChRs, while CD was found to increase the number of M1 AChRs. Neither treatment affected the affinity of the M1 AChR. However, when M1 + M3 binding was assessed, CD was found to decrease the affinity in both hippocampal regions, without altering the number of receptors. Neither affinity nor number of M1 + M3 receptors was altered by HSI. The results of this study suggest that both cholinergic denervation and hippocampal sympathetic ingrowth uniquely affect hippocampal muscarinic receptors.

Action on noradrenergic transmission of an anticholinesterase: 9-amino-1,2,3,4-tetrahydroacridine

The mechanism by which 9-amino-1,2,3,4-tetrahydroacridine (THA) inhibits beta-adrenoceptor linked cyclic AMP formation and its possible relationship with the cholinergic system were studied. In addition, the effect of THA on alpha 1-adrenoceptor coupled transduction systems was also investigated. THA was not able to influence the concentration-response curve for forskolin indicating that it is not acting on the catalytic subunit of the adenylate cyclase complex. On the other hand a cholinergic component seems to participate in the action of THA on beta-adrenoceptor stimulated adenylate cyclase activity since the blockade of muscarinic receptors with atropine (10 microM) partially prevented the reduction in cyclic AMP formation attained by THA in the hippocampus, in isoprenaline-stimulated conditions. This effect is not reproducible by another potent anticholinesterase physostigmine. Moreover, THA at concentrations up to micromolar did not affect alpha 1-adrenoceptor stimulated cyclic AMP formation or phosphoinositide hydrolysis. In conclusion, the neuropharmacological profile of THA is not to be restricted to the cholinergic system and its effectiveness in improving age-associated cognitive deterioration may involve an action on the beta-adrenoceptor coupled signal transduction system. Moreover, the action of THA on the beta-adrenergic and cholinergic systems in the brain could be relevant to the amelioration of cognitive deterioration and could lead to the development of new therapeutic strategies.

Effects of intraseptally injected noradrenergic drugs on hippocampal sodium-dependent-high-affinity-choline-uptake in 'resting' and 'trained' mice

It has been shown in numerous studies that memory testing can alter presynaptic cholinergic activity within the hippocampus. In the present experiments, the role of the noradrenergic input to the septal cholinergic neurons in the immediate increase in cholinergic activity induced by the first training session of a spatial reference memory task in an 8-arm radial maze was investigated. The effects of bilateral intraseptal injections of noradrenergic drugs on hippocampal sodium-dependent-high-affinity-choline-uptake (SDHACU) were studied in 'resting' animals (basal level) or in 'trained' animals injected 20 min before training and sacrificed immediately after the test. The results showed that: (1) the injection of maprotiline, a noradrenaline reuptake inhibitor (0.06 ng/site), induced an increase in hippocampal SDHACU in 'resting' animals, whereas the alpha 2-adrenoceptor agonist UK 14304 (1.5 ng) significantly reduced the basal level of SDHACU; (2) none of the alpha-adrenoceptor antagonists used (phenoxybenzamine, 10 and 100 ng; BE 2254, 100 and 500 ng; yohimbine, 0.5 and 50 ng) significantly affected the basal level of hippocampal SDHACU, and only the alpha 1-adrenoceptor antagonist BE 2254 (500 ng) significantly reduced the testing-induced activation of SDHACU. Taken together, these findings suggest that noradrenaline may exert a bimodal regulatory influence on the activity of septo-hippocampal cholinergic neurons. The behavior-induced activation of hippocampal SDHACU could be partly mediated by the stimulation of alpha 1-adrenoceptors, whereas postsynaptic alpha 2-adrenoceptors may be important for the maintenance of a tonic inhibition of the steady-state cholinergic activity in the hippocampus.(ABSTRACT TRUNCATED AT 250 WORDS)

Hippocampal sympathetic ingrowth and cholinergic denervation alter hippocampal muscarinic cholinergic receptors

Cholinergic denervation of the hippocampus by medial septal (MS) lesions results in the ingrowth of peripheral sympathetic fibers, originating from the superior cervical ganglia, into the hippocampus. To determine the effect of hippocampal sympathetic ingrowth (HSI) [3H]-QNB (L-quinuclidinyl [benzilic-4,4(n)] binding was assessed in the dorsal and ventral hippocampus four weeks after MS lesions. In dorsal hippocampus, HSI was found to significantly increase the number (Bmax) of [3H]-QNB binding sites and to normalize the decrease in affinity found in animals with MS lesions plus ganglionectomy (i.e., no ingrowth). In ventral hippocampus, HSI was found to normalize the increased number of binding sites and decreased affinity found in animals with MS lesions without ingrowth. No effect on either Kd or Bmax was found in animals that had undergone ganglionectomy with sham MS lesions. These results suggest that HSI can induce changes in hippocampal muscarinic cholinergic receptors.

Female circulating sex hormones and hippocampal sympathetic ingrowth

Following cholinergic denervation of the hippocampal formation, via medial septal (MS) lesions, sympathetic fibers, originating from the superior cervical ganglia, growth into the hippocampus. Previous studies have demonstrated a sexually dimorphic effect of this neuronal rearrangement on recovery of a spatial-learning task, with this rearrangement being detrimental in male but protective in female rats. Circulating male sex hormones were found to interact with this effect in male animals. In this study we assessed the role of circulating female sex hormones on the behavioral and biochemical effects of hippocampal sympathetic ingrowth (HSI). For the behavioral studies female rats underwent either sham ovariectomy (sham OVARX) or OVARX and were taught a standard radial-8-arm maze task. Following attainment of criterion, animals underwent one of three surgical procedures: sham surgery; MS lesions+sham ganglionectomy (MS); HSI group; MS lesions+ganglionectomy (MSGx). As in our previous study, animals with HSI (i.e. MS group) were found to recover learning faster (in fact, these animals did not differ from controls) than animals with MS lesions without HSI. Gonadal status did not affect this behavioral recovery. For the biochemical studies hippocampal norepinephrine (NE) and choline acetyltransferase (ChAT) were measured in animals sham OVARX and OVARX, 8-12 weeks after the neurosurgical procedure. MS lesions (i.e. MSGx; MS) were found to reduce ChAT activity, regardless of circulating sex hormones. In controls NE levels were similar between OVARX and sham OVARX. NE levels were markedly elevated in the OVARX MS group compared to all other groups including sham OVARX. In the MSGx groups, NE levels were reduced compared to controls, while comparisons between these groups revealed a significant reduction in NE levels in the OVARX MSGx group compared to sham OVARX MSGx group. These studies suggest that female circulating sex hormones interact with brain injury in a very complex manner. However, this interaction does not appear to mediate the changes in behavior observed after HSI.

The role of interactions between the cholinergic system and other neuromodulatory systems in learning and memory

Extensive evidence indicates that disruption of cholinergic function is characteristic of aging and Alzheimer's disease (AD), and experimental manipulation of the cholinergic system in laboratory animals suggests age-related cholinergic dysfunction may play an important role in cognitive deterioration associated with aging and AD. Recent research, however, suggests that cholinergic dysfunction does not provide a complete account of age-related cognitive deficits and that age-related changes in cholinergic function typically occur within the context of changes in several other neuromodulatory systems. Evidence reviewed in this paper suggests that interactions between the cholinergic system and several of these neurotransmitters and neuromodulators--including norepinephrine, dopamine, serotonin, GABA, opioid peptides, galanin, substance P, and angiotensin II--may be important in learning and memory. Thus, it is important to consider not only the independent contributions of age-related changes in neuromodulatory systems to cognitive decline, but also the contribution of interactions between these systems to the learning and memory deficits associated with aging and AD.

The effect of gonadal steroids on the behavioral and biochemical effects of hippocampal sympathetic ingrowth

Following cholinergic denervation of the hippocampal formation, via medial septal lesions, sympathetic fibers, originating from the superior cervical ganglia, grow into the hippocampus. Previous studies have demonstrated a detrimental effect of these fibers on recovery of a spatial-learning task in male but not female animals. In this study we assessed the role of circulating male sex hormones on the behavioral and biochemical effects of hippocampal sympathetic ingrowth (HSI). For the behavioral studies male Sprague-Dawley rats underwent either sham gonadectomy or gonadectomy and were taught a standard radial 8-arm maze task. Following attainment of criterion animals underwent one of three surgical procedures: sham surgery, MS lesions, MS lesions + ganglionectomy. MS lesions, regardless of the presence of HSI, were found to severely impair reacquisition of the task in both sham-gonadectomized and gonadectomized animals. As expected, in the sham-gonadectomized group, MSGx animals reacquired the task faster than the MS group. However, gonadectomy was found to block the detrimental effect of HSI on behavior. For the biochemical studies hippocampal norepinephrine (NE) and choline acetyltransferase (ChAT) were measured eight weeks after surgery in sham-gonadectomized and gonadectomized animals. MS lesions were found to significantly reduce the ChAT activity, regardless of circulating sex hormones. Gonadectomy was found to significantly reduce the level of NE associated with HSI, while having no effect on central NE in CON or MSGx animals. These studies suggest that circulating male sex hormones can influence both the behavioral and biochemical processes associated with HSI.