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

Molecular signals into the insular cortex and amygdala during aversive gustatory memory formation

In this paper, we will provide evidence of the putative molecular signals and biochemical events that mediate the formation of long-lasting gustatory memory trace. When an animal drinks a novel taste (the conditioned stimulus; CS) and it is later associated with malaise (unconditioned stimulus; US), the animal will reject it in the next presentation, developing a long-lasting taste aversion, i.e., the taste cue becomes an aversive signal, and this is referred to as conditioning taste aversion. Different evidence indicates that the novel stimulus (taste) induces a rapid and strong cortical acetylcholine activity that decreases when the stimulus becomes familiar after several presentations. Cholinergic activation via muscarinic receptors initiates a series of intracellular events leading to plastic changes that could be related to short- and/or long-term memory gustatory trace. Such plastic changes facilitate the incoming US signals carried out by, in part, the glutamate release induced by the US. Altogether, these events could produce the cellular changes related to the switch from safe to aversive taste memory trace. A proposed working model to explain the biochemical sequence of signals during taste memory formation will be discussed.

Effects of beta-amyloid protein on serotoninergic, noradrenergic, and cholinergic markers in neurons of the pontomesencephalic tegmentum in the rat

The effects on serotoninergic, noradrenergic and cholinergic markers on neurons of the pontomesencephalic tegmentum nuclei were studied in rats following local administration of fibrillar beta-amyloid peptide (Abeta1-40) into the left retrosplenial cortex. Focal deposition of Abeta in the retrosplenial cortex resulted in a loss of serotoninergic neurons in the dorsal and median raphe nuclei. The dorsal raphe nucleus showed a statistically significant reduction of 31.7% in the number of serotoninergic neurons and a decrease (up to 17.38%) in neuronal density in comparison with the same parameters in uninjected controls. A statistically significant reduction of 50.3%, together with a significant decrease of 53.94% in the density of serotoninergic neurons, was also observed in the median raphe nucleus as compared with control animals. Furthermore, a significant reduction of 35.07% in the number of noradrenergic neurons as well as a statistically significant decrease of 56.55% in the density of dopamine-beta-hydroxylase-immunoreactive neurons were also found in the locus coeruleus as compared with the corresponding hemisphere in uninjected controls. By contrast, a reduction of 24.37% in the number of choline acetyltransferase-positive neurons and a slight decrease (up to 22.28%) in the density of cholinergic neurons, which were not statistically significant, was observed in the laterodorsal tegmental nucleus in comparison with the same parameters in control animals. These results show that three different neurochemically defined populations of neurons in the pontomesencephalic tegmentum are affected by the neurotoxicity of Abeta in vivo and that Abeta might indirectly affect serotoninergic, noradrenergic and cholinergic innervation in the retrosplenial cortex.

Noradrenergic innervation of the developing and mature septal area of the rat

The noradrenergic innervation of the developing and mature septal area of the rat was examined with light and electron microscopic immunocytochemistry using an antibody against dopamine-beta-hydroxylase. At birth, a small number of relatively thick noradrenergic fibers were found to innervate the lateral septum (mainly its intermediate part) and the nuclei of the vertical and horizontal limbs of the diagonal band of Broca. By postnatal day 7, a substantial increase in their density was observed. At this age some labeled fibers left the medial forebrain bundle and invaded the nucleus of the horizontal limb of the diagonal band. These fibers then ran in a ventrodorsal direction and innervated the nucleus of the vertical limb before entering the medial septum. Immunoreactive fibers were finer and more varicose than at birth. In the subsequent 2 weeks, the density of labeled fibers in the septal area was further increased. By postnatal day 21, the distribution pattern and density of the noradrenergic innervation appeared similar to the adult. In the adult, noradrenergic fibers exhibited more varicosities than in younger rats. Electron microscopic analysis revealed a low proportion (peaked at P7) of noradrenergic varicosities engaged in synaptic contacts throughout development. The overwhelming majority of these synapses were symmetrical, predominantly with small or medium-sized dendrites. The present findings provide the morphological basis for the functional interactions between noradrenergic afferents and neuronal elements in the septal area. The low proportion of synaptic contacts found in this study suggests that noradrenaline may exert its action in the septal area mainly through transmission by diffusion (volume transmission), as has been suggested for other areas of the developing and adult brain.

p-Chloroamphetamine blocks physostigmine-induced memory enhancement in rats with unilateral nucleus basalis lesions

The present experiment examined whether p-chloroamphetamine (PCA), a serotonergic releasing/depleting agent, would block the memory-enhancing effect of physostigmine in rats with N-methyl-D-aspartic acid (NMDA)-induced unilateral lesions of the nucleus basalis of Meynert (uni-nbM). Six groups of subjects with uni-nbM lesions in addition to an isolated sham-operated control group were included. Subjects were trained and tested 72 h later on a one-trial passive avoidance task. Thirty minutes before training, rats with uni-nbM lesions were injected with either 1.0 or 5.0 mg/kg PCA or saline. Immediately after training, approximately half the subjects in each group were injected with either saline or 0.06 mg/kg physostigmine. Animals in the sham group received saline injections. Saline-injected animals with uni-nbM lesions performed poorly at test, a deficit that was reversed with physostigmine. Pretraining injections of PCA blocked physostigmine's memory-enhancing effect, although motor impairment during training may have contributed to decrements in test performance in animals injected with 5.0 mg/kg. Subjects were killed about 10 days later and their frontal cortices examined for choline acetyltransferase (ChAT). Results from the neurochemical analysis revealed that the lesion decreased ChAT levels and that the injection of 1.0 mg/kg PCA exaggerated this lesion-induced depletion. Implications for the interaction between acetylcholine and serotonin are discussed.

Neonatal ethanol exposure produces a hyperalgesia that extends into adolescence, and is associated with increased analgesic and rewarding properties of nicotine in rats

RATIONALE

Drug exposure during CNS development may alter subsequent dependence liability. We postulated that early alcohol exposure might produce persistent alterations in responses to noxious stimuli. Because relief of physical discomfort may be negatively reinforcing, changes in responses to noxious stimuli produced by early alcohol exposure may increase the rewarding properties of nicotine, a potent analgesic. Such factors may contribute to the high level of alcohol and nicotine co-abuse in humans.

OBJECTIVES

The purpose of this study was to determine whether neonatal ethanol exposure in rats altered responses to noxious stimuli, and whether nicotine would then be more rewarding to the alcohol-exposed offspring, perhaps via its analgesic actions.

METHODS

Neonatal rats received ethanol by gavage (5.0 or 6.5 g/kg) on postnatal days (PND) 9-13. An iso-caloric control group was also included. Rats were then tested to assess responsiveness to a mild noxious heat stimulus, as measured in the tail-flick assay (PND 14 and PND 28), for their response to acute analgesic injections of either nicotine or ethanol (PND 28), and for nicotine induced conditioned place preference (CPP) (PND 36).

RESULTS

Neonatal ethanol exposure produced hyperalgesia during the first 24 h after alcohol withdrawal (PND 14) that continued through PND 28. The analgesic effects of 12.5 microg/kg nicotine were enhanced approximately 2-fold in adolescent rats with previous ethanol histories, relative to controls. These ethanol-exposed rats also showed a significant CPP to nicotine, whereas controls showed no CPP.

CONCLUSIONS

Persistent decreases in tail-flick response latencies suggestive of hyperalgesia were observed following neonatal ethanol exposure in the rat. These changes were accompanied by increases in the analgesic and place-conditioning effects of nicotine in adolescence. If similar effects occur in humans, prenatal alcohol exposure may play a role in an increased risk for the rewarding effects and dependence liability of nicotine later in life.

Cholinergic activity enhances hippocampal long-term potentiation in CA1 during walking in rats

Long-term potentiation (LTP) at the basal-dendritic synapses of CA1 pyramidal cells was induced by a single 200 Hz stimulation train (0.5-1 sec duration) in freely behaving rats during one of four behavioral states: awake-immobility (IMM), walking, slow-wave sleep (SWS), and rapid eye movement sleep (REM). Field EPSPs generated by basal-dendritic excitation of CA1 were recorded before and up to 1 d after the tetanus. After a tetanus during any behavioral state, basal-dendritic LTP was >170% of the baseline for the first hour after the tetanus and decayed to approximately 120% 1 d after. LTP induced during walking was significantly larger than that induced during IMM, SWS, or REM, which had similar LTP magnitudes. To test the hypothesis that septohippocampal cholinergic activity enhanced LTP during walking as compared with IMM, rats were either pretreated with muscarinic cholinergic antagonist scopolamine or injected with IgG192-saporin in the medial septum to selectively lesion cholinergic septohippocampal neurons. Pretreatment with scopolamine decreased the LTP induced during walking but did not affect that induced during IMM, such that the difference between the LTP induced during walking and IMM was abolished after scopolamine. Rats injected with IgG192-saporin showed no difference in the LTP induced during walking and IMM, and scopolamine did not reduce the LTP during walking. In contrast, sham-lesion rats showed larger LTP induced during walking than IMM, and the LTP induced during walking was attenuated by scopolamine. This is the first demonstration of an enhancement of hippocampal LTP by physiologically activated cholinergic inputs.

Analysis of the role of the 5-HT1B receptor in spatial and aversive learning in the rat

The present study examined the role of the 5-HT1B receptor in learning and memory. The ability of the 5-HT1B receptor agonist anpirtoline and the selective 5-HT1B receptor antagonist NAS-181 to affect spatial learning in the water maze (WM) and aversive learning in the passive avoidance (PA) task were examined in the rat. Anpirtoline (0.1-1.0 mg/kg, s.c.) caused a dose-dependent impairment of learning and memory in both the WM and PA tasks. NAS-181 (1.0-10 mg/kg, s.c.) failed to alter performance of the WM task, but produced a dose-dependent (0.1-20 mg/kg) facilitation of PA retention. Furthermore, treatment with NAS-181 (10 mg/kg) fully blocked the impairment of the WM and PA performance caused by anpirtoline (1.0 mg/kg). In contrast, NAS-181 (3.0-10 mg/kg) did not attenuate the spatial learning deficit and the impairment of PA retention caused by scopolamine (0.1 mg/kg in WM task, 0.3 mg/kg in PA task, s.c.), a nonselective muscarinic antagonist. Moreover, a subthreshold dose of scopolamine (0.1 mg/kg) blocked the facilitation of PA retention induced by NAS-181 (1.0-10 mg/kg). In addition, the behavioral disturbances (eg thigmotaxic swimming and platform deflections) induced by anpirtoline and scopolamine were analyzed in the WM task and correlated with WM performance. These results indicate that: (1) 5-HT1B receptor stimulation and blockade result in opposite effects in two types of cognitive tasks in the rat, and that (2) the 5-HT1B antagonist NAS-181 can facilitate some aspects of cognitive function, most likely via an increase of cholinergic transmission. These results suggest that 5-HT1B receptor antagonists may have a potential in the treatment of cognitive deficits resulting from loss of cholinergic transmission.

The cholinergic hypothesis of age and Alzheimer's disease-related cognitive deficits: recent challenges and their implications for novel drug development

The cholinergic hypothesis was initially presented over 20 years ago and suggests that a dysfunction of acetylcholine containing neurons in the brain contributes substantially to the cognitive decline observed in those with advanced age and Alzheimer's disease (AD). This premise has since served as the basis for the majority of treatment strategies and drug development approaches for AD to date. Recent studies of the brains of patients who had mild cognitive impairment or early stage AD in which choline acetyltransferase and/or acetylcholinesterase activity was unaffected (or even up-regulated) have, however, led some to challenge the validity of the hypothesis as well as the rationale for using cholinomimetics to treat the disorder, particularly in the earlier stages. These challenges, primarily based on assays of post mortem enzyme activity, should be taken in perspective and evaluated within the wide range of cholinergic abnormalities known to exist in both aging and AD. The results of both post mortem and antemortem studies in aged humans and AD patients, as well as animal experiments suggest that a host of cholinergic abnormalities including alterations in choline transport, acetylcholine release, nicotinic and muscarinic receptor expression, neurotrophin support, and perhaps axonal transport may all contribute to cognitive abnormalities in aging and AD. Cholinergic abnormalities may also contribute to noncognitive behavioral abnormalities as well as the deposition of toxic neuritic plaques in AD. Therefore, cholinergic-based strategies will likely remain valid as one approach to rational drug development for the treatment of AD other forms of dementia.

Atropine, an anticholinergic drug, impairs memory retrieval of a high consolidated avoidance response in mice

Immediate post-training intraperitoneal administration of the centrally acting anticholinesterase physostigmine (70.0, or 150.0 microg/kg) enhanced retention of male CF-1 mice tested 48 h after training in a one-trial step-through inhibitory avoidance task (0.8 mA, 50 Hz, 1 s footshock). The effect was observed in mice that received saline 30 min before the retention test; on the contrary, the pre-test administration of the centrally active muscarinic cholinergic antagonist, atropine (1.0 mg/kg, i.p.), but not methylatropine (1.0 mg/kg, i.p.), instead of saline, prevents the enhancement of retention induced by both doses of the anticholinesterase when given immediately after training. The high retention performance caused by post-training physostigmine was recovered following a second administration of the same doses of the drug, 10 min after the pre-test injections of atropine. Since, physostigmine do not influence memory retrieval when given prior to the retention test, and its post-training effects are not due to the induction of state-dependency, the recover of the high retention performance was probably due to a classical interaction between a muscarinic competitive antagonist and an indirect cholinergic agonist. Further, atropine probably does not modify the memory trace by erasing it, but by producing a poor retrieval.

The psychopharmacology of huperzine A: an alkaloid with cognitive enhancing and neuroprotective properties of interest in the treatment of Alzheimer's disease

Huperzine A (HupA), extracted from a club moss (Huperzia serrata), is a sesquiterpene alkaloid and a powerful and reversible inhibitor of acetylcholinesterase (AChE). It has been used in China for centuries for the treatment of swelling, fever and blood disorders. It has demonstrated both memory enhancement in animal and clinical trials and neuroprotective effects. Recently it has undergone double-blind, placebo-controlled clinical trials in patients with Alzheimer's disease (AD), with significant improvements both to cognitive function and the quality of life. Most of the clinical trials are from China, but HupA and derivatives are attracting considerable interest in the West, where AD is a major and growing concern. Furthermore, both animal and human safety evaluations have demonstrated that HupA is devoid of unexpected toxicity. Other interesting aspects of HupA pharmacological profile relate to its neuroprotective properties: it has been shown in animal studies that HupA can be used as a protective agent against organophosphate (OP) intoxication and that it reduces glutamate-induced cell death.

Peripheral 8-OH-DPAT and scopolamine infused into the frontal cortex produce passive avoidance retention impairments in rats

The present study determined whether peripheral injections of the 5HT(1A) agonist (8-OH-DPAT), scopolamine infusions into the frontal cortex, or a combination of both drug treatments would produce impairments in rats trained on passive avoidance. Using a 2x2 design, rats were infused with either bacteriostatic water or 30 microg/1 microl of scopolamine HCl into the frontal cortex 30 min before being trained on passive avoidance. This was followed by injections (ip) of either 0.1% ascorbic acid/bacteriostatic water or 30 microg/kg of 8-OH-DPAT 15 min later. All subjects were tested for retention 72h later. At test, the initial latency to enter into the black shocked compartment and the total time spent in the white safe compartment (TTW) were recorded. Analysis of the latency data indicated that scopolamine and 8-OH-DPAT, when administered singly or in combination, produced amnesia for the task. Assessment of TTW scores, however, revealed that of the three drug-treated groups, only animals treated with 8-OH-DPAT alone tended to avoid the previously shocked black compartment and spend more time in the white safe compartment. These data indicate that either stimulating 5-HT(1A) or blocking frontal cortical muscarinic receptors at training impairs passive avoidance performance and that the deficit following the latter treatment is somewhat more extensive. Implications for the role frontal cortical muscarinic and 5HT(1A) receptors play in learning and memory are discussed.

Involvement of central muscarinic receptors in social and nonsocial learning in sheep

Within 12 h following parturition, ewes develop visual and auditory recognition of their lamb. To investigate whether central cholinergic muscarinic transmission plays a specific role in this social learning, we studied the effects of a muscarinic antagonist on neonate recognition via visual/auditory cues and acquisition of a nonsocial visual discrimination. Injections of scopolamine (100 microg/kg; a muscarinic antagonist crossing the blood-brain barrier) after birth did not affect maternal behavior but impaired visual/auditory recognition of the offspring. Recognition impairment did not occur in mothers treated with methylscopolamine (100 microg/kg; a peripheral muscarinic antagonist), indicating that central muscarinic transmission is specifically involved in this social learning. Similar doses of scopolamine strongly delayed learning of a nonsocial, visual discrimination task in comparison to either control or methylscopolamine-treated ewes. Performance on this task was not affected when scopolamine treatment was applied after learning, demonstrating that central muscarinic receptors are necessary for acquisition but not for retrieval. These results suggest that the central muscarinic transmission participates in the establishment of visual/auditory recognition of conspecifics. Moreover, activation of central muscarinic receptors is critical for learning regardless of the social properties of the stimulus.

Regional infusions of serotonin into the striatum and memory consolidation

Lesions, temporal inactivation, electrical stimulation and administration of drugs that antagonize synaptic activity of the striatum lead to significant deficits of memory. Also, it has been shown that interruption of dopaminergic, GABAergic, or cholinergic activity in discrete areas of this structure is sufficient to disrupt cognitive functions. In spite of the known interactions among dopamine, GABA, acetylcholine, and serotonin, there is a notable scarcity of data germane to the participation of striatal serotonin in learning and memory. It was important, therefore, to investigate the possible involvement of serotonin in cognition. In light of the differential distribution of serotonergic elements within the striatum, a prediction was made that focal injections of serotonin into distinctive regions would produce dissimilar effects on memory. Rats were trained in a one-trial step-through inhibitory avoidance task and a retention test was carried out 24 h later. Posttraining injections of serotonin into the dorsal and ventral aspects of the posterior region produced strong amnesia compared to similar injections into the dorsal and ventral aspects of the anterior region. The present findings support the hypothesis that striatal serotonergic activity is involved in memory functions and also provide further evidence of neurochemical heterogeneity within the striatum regarding memory consolidation.

The ameliorating effects of acute and chronic administration of LiuWei Dihuang Wang on learning performance in rodents

The ameliorating effects of LiuWei Dihuang Wang (LDW) after single, one-week or two-week treatment of scopolamine (SCOP)-induced and p-chloroamphetamine (PCA)-induced amnesia by using the passive avoidance task and the facilitatory effects on two-way active avoidance performance in rats were studied. LDW (2 g/kg) after single treatment significantly prolonged the shortened step-through latency induced by SCOP and PCA. Then, SCOP- and PCA-induced amnesia was reversed by 1 and 0.1-1 g/kg LDW with one-week consecutive treatment respectively. For two-week consecutive treatment with LDW, the reversal from SCOP- and PCA-induced amnesia required only 0.01 g/kg. However, the rats treated with LDW only at 0.5, but not 0.01-0.1 g/kg, before or after each training session showed an increasing number of avoidances and a decreasing number of escapes on days 2-5 of learning. LDW at any dose alone did not influence the step-through latency in the training trial produced by non-shock rats, the motor activity and pentobarbital-induced hypnosis in rodents. These results suggest that LDW possesses the anti-amnestic and cognitive-enhancing activities related to the memory processes, and these activities were parallel to treatment duration and dependent on the learning models.

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.

Effects of intrahippocampal injection of GABAergic drugs on memory retention of passive avoidance learning in rats

The effect of post-training intrahippocampal injection of gamma-aminobutyric acid (GABA) receptor agonists and antagonists, immediately after a training session on memory retention of passive avoidance learning in rats, was measured in the presence and absence of physostigmine. Post-training treatments were carried out in all the experiments. The different doses of the GABAA receptor agonist muscimol (2, 4 and 6 microg/rat) decreased memory retention in rats dose-dependently. The higher response was obtained with 6 microg/rat of the drug. When the GABAA receptor antagonist bicuculline (0.5, 1, 2 and 4 microg/rat) was administered, only one dose of the drug (1 microg/rat) increased memory retention; however, the antagonist reduced the effect of muscimol. The GABAB receptor agonist, baclofen (0.25, 0.5, 1 and 2 microg/rat) also reduced memory retention in the animals. Intrahippocampal injection of lower doses of the GABAB receptor antagonist CGP35348 (P-[3-aminopropyl]-p-diethoxymethyl-phosphinic acid) (2.5, 5, 10 microg/rat) did not effect memory retention, although the higher doses of the drug (25 and 50 microg/rat) decreased memory retention. The doses of antagonist (2.5, 5 and 10 microg/rat), which did not elicit any response alone, reduced the effect of baclofen. The inhibitory response of CGP35348 was also decreased by bicuculline. In another series of experiments, physostigmine improved memory retention. The GABA receptor agonists, muscimol and baclofen, as well as the GABA receptor antagonists bicuculline and CGP35348, decreased the effect of physostigmine. Atropine decreased memory retention by itself and potentiated the response of muscimol and baclofen. It is concluded that GABAA and GABAB receptor activation may be involved in the impairment of memory retention.

Neuroactive steroid mechanisms and GABA type A receptor subunit assembly in hypothalamic and extrahypothalamic regions

Gonadal- and neuronal-derived steroids are capable of altering brain functions through two basic mechanisms: slow (genomic) and rapid (novel nongenomic membrane) types of activities. The genomic activities that are circumscribed to the numerous neuronal and glial expressed receptor actions involve transcriptional processes regulated largely by classical steroids. On the other hand, rapid nongenomic activities are linked to the stereoselective interactions of potent neuroactive steroids. It appears that both of these steroid mechanisms can be successfully evoked at the ligand-gated heteroligomeric GABA type A receptor. However, the precise structural prerequisites and type of molecular steroid interactions implicated in this neuronal target have not been fully investigated. This article reviews the most common subunits (alpha, beta, and gamma) of the native GABA type A receptor involved in signaling pathways of slow and rapid steroidal mechanisms. Different beta-containing compositions (alpha1beta1-3gamma2) are necessary for the slow type of mechanism, whereas different alpha-containing constructs (alpha2-6beta 1/2 gamma2/2L) are linked to the rapid type. Because of the major role played by neuroactive steroids in GABA-dependent neuroendocrine and sociosexual events, distinction of the specific subunit combination is essential not only for elucidating neuronal communicative expressions during such events but also for elucidating their potential neuroprotective role in neurodegenerative disorders.

The effects of galanin on long-term synaptic plasticity in the CA1 area of rodent hippocampus

Learning and memory involve complex changes in neuronal excitability including long-lasting synaptic plasticity of glutamatergic synapses. The observation that the neuropeptide galanin affects performance in a number of behavioural models predicts that galanin should affect synaptic processes underlying learning. The present study in rat and mouse hippocampal slices now demonstrates that galanin inhibits long-term potentiation induced by both tetanic and theta-burst stimulation in both apical and basal dendrites of CA1 pyramidal neurones but does not affect long-term depression. This selective effect on long-term potentiation does not appear to be mediated through inhibition of N-methyl-D-aspartate or metabotropic glutamate receptor function, but likely resides downstream of receptor activation, possibly at the level of the kinase cascade that converts short-term into long-term potentiation. Our results indicate possible mechanisms by which the neuropeptide galanin may act at the molecular level to influence learning and memory in vertebrates.

Preprotachykinin A gene expression after administration of 3,4-methylene dioxymethamphetamine (Ecstasy)

This study tested the effects of 8 days of subchronic administration of 3,4-methylene dioxymethamphetamine (MDMA) (5 mg/kg b.w.) on preprotachykinin A mRNA levels in discrete rat brain regions. In situ hybridization examined preprotachykinin A mRNA levels in the core and shell of the nucleus accumbens, the islands of Calleja, the olfactory tubercle, the dorsal and ventral caudate-putamen, the bed nucleus of the stria terminalis, the medial preoptic area, the medial habenular nucleus and in the postero-dorsal part of the medial amygdala. Higher levels of preprotachykinin A mRNA were found in the core and shell of the nucleus accumbens, in the islands of calleja, in the olfactory tubercle, in the bed nucleus of the stria terminalis, in the medial habenular nucleus and the postero-dorsal part of the medial amygdala, compared to control animals. Conversely, increased preprotachykinin A mRNA levels were observed in the dorsal and ventral caudate-putamen in MDMA treated when compared to control rats. In the social memory test, MDMA significantly impaired rats' short-term working memory. These results show that chronic exposure to MDMA strongly affects preprotachykinin A mRNA levels in discrete rat brain regions. These changes occur in experimental conditions in which working memory is markedly reduced, suggesting that changes in gene expression of tachykinin mechanisms may contribute to the effects of MDMA on memory function.

Effects of pretraining intrastriatal administration of p-chloroamphetamine on inhibitory avoidance

Pretraining systemic administration of p-chloroamphetamine (PCA) consistently produces retention deficits of inhibitory avoidance. This drug causes a widespread acute release of serotonin from cerebral neuronal terminals, but it is not known where in the brain PCA exerts its disruptive cognitive effects. The present experiment was aimed at determining whether the striatum is a site of action of this drug. PCA (5 microg) was infused, bilaterally, into the striatum of rats at 30, 15, or 5 min before training of inhibitory avoidance, and retention of the task was measured 24 h later. An inversely related time-dependent deficit was found. Together with the results from appropriate control groups, this result strongly suggest that systemic PCA produces its reported cognitive effects, at least in part, through its pharmacological action within the striatum.

Combined 192 IgG-saporin and 5,7-dihydroxytryptamine lesions in the male rat brain: a neurochemical and behavioral study

In a previous experiment [Eur J Neurosci 12 (2000) 79], combined intracerebroventricular injections of 5,7-dihydroxytryptamine (5,7-DHT; 150 microg) and 192 IgG-saporin (2 microg) in female rats produced working memory impairments, which neither single lesion induced. In the present experiment, we report on an identical approach in male rats. Behavioral variables were locomotor activity, T-maze alternation, beam-walking, Morris water-maze (working and reference memory) and radial-maze performances. 192 IgG-saporin reduced cholinergic markers in the frontoparietal cortex and the hippocampus. 5,7-DHT lesions reduced serotonergic markers in the cortex, hippocampus and striatum. Cholinergic lesions induced motor deficits, hyperactivity and reduced T-maze alternation, but had no other effect. Serotonergic lesions only produced hyperactivity and reduced T-maze alternation. Beside the deficits due to cholinergic lesions, rats with combined lesions also showed impaired radial-maze performances. We confirm that 192 IgG-saporin and 5,7-DHT injections can be combined to produce concomitant damage to cholinergic and serotonergic neurons in the brain. In female rats, this technique enabled to show that interactions between serotonergic and basal forebrain cholinergic mechanisms play an important role in cognitive functions. The results of the present experiment in male rats are not as clear-cut, although they are not in obvious contradiction with our previous results in females.

Enhanced inhibitory avoidance training protects against the amnesic effect of p-chloroamphetamine

The contribution of acetylcholine (ACh) to memory processing is well documented, but it has been proposed that it is not necessary for memory consolidation after an enhanced learning experience. It has been suggested that serotonin (5-HT) interacts with ACh during memory consolidation, although the nature of this interaction is unknown in the case of strong learning. As an initial approach to the study of these interactions, we determined whether training of inhibitory avoidance using relatively high aversive stimulation protects against the typical retention deficits produced by pre-training administration of the 5-HT releaser p-chloroamphetamine (PCA). Rats were trained after intraperitoneal administration of PCA or isotonic saline, using 2.0, 2.5, 3.0 or 3.5 mA and retention of the task was measured 24 h later. A significant amnesic state was observed only in the PCA groups that had been trained with the two lower intensities. These results indicate that 5-HT systems behave similarly to ACh systems, in the sense that the amnesic effect produced by interference with their physiological activity may be cancelled when animals are submitted to an intense learning situation.

Endogenous histamine in the medial septum-diagonal band complex increases the release of acetylcholine from the hippocampus: a dual-probe microdialysis study in the freely moving rat

The effects of histaminergic ligands on both ACh spontaneous release from the hippocampus and the expression of c-fos in the medial septum-diagonal band (MSA-DB) of freely moving rats were investigated. Because the majority of cholinergic innervation to the hippocampus is provided by MSA-DB neurons, we used the dual-probe microdialysis technique to apply drugs to the MSA-DB and record the induced effects in the projection area. Perfusion of MSA-DB with high-KCl medium strongly stimulated hippocampal ACh release which, conversely, was significantly reduced by intra-MSA-DB administration of tetrodotoxin. Histamine or the H2 receptor agonist dimaprit, applied directly to the hippocampus, failed to alter ACh release. Conversely, perfusion of MSA-DB with these two compounds increased ACh release from the hippocampus. Also, thioperamide and ciproxifan, two H3 receptor antagonists, administered into MSA-DB, increased the release of hippocampal ACh, whereas R-alpha-methylhistamine, an H3 receptor agonist, produced the opposite effect. The blockade of MSA-DB H2 receptors, caused by local perfusion with the H2 receptor antagonist cimetidine, moderated the spontaneous release of hippocampal ACh and antagonized the facilitation produced by H3 receptor antagonists. Triprolidine, an H1 receptor antagonist, was without effect. Moreover, cells expressing c-fos immunoreactivity were significantly more numerous in ciproxifan- or thioperamide-treated rats than in controls, although no colocalization of anti-c-fos and anti-ChAT immunoreactivity was observed. These results indicate a role for endogenous histamine in modulating the cholinergic tone in the hippocampus.

Nicotinic--serotonergic interactions in brain and behaviour

This review focuses on nicotinic--serotonergic interactions in the central nervous system (CNS). Nicotine increases 5-hydroxytryptamine (5-HT) release in the cortex, striatum, hippocampus, dorsal raphé nucleus (DRN), hypothalamus, and spinal cord. As yet, there is little firm evidence for nicotinic receptors on serotonergic terminals and thus nicotine's effects on 5-HT may not necessarily be directly mediated, but there is strong evidence that the 5-HT tone plays a permissive role in nicotine's effects. The effects in the cortex, hippocampus, and DRN involve stimulation of 5-HT(1A) receptors, and in the striatum, 5-HT(3) receptors. The 5-HT(1A) receptors in the DRN play a role in mediating the anxiolytic effects of nicotine and the 5-HT(1A) receptors in the dorsal hippocampus and lateral septum mediate its anxiogenic effects. The increased startle and anxiety during nicotine withdrawal is mediated by 5-HT(1A) and 5-HT(3) receptors. The locomotor stimulant effect of acute nicotine is mediated by 5-HT(1A) receptors and 5-HT(2) receptors may play a role in the expression of a sensitised response after chronic nicotine treatment. Unfortunately, the role of 5-HT(1A) receptors in mediating nicotine seeking has not yet been investigated and would seem an important area for future research. There is also evidence for nicotinic--serotonergic interactions in the acquisition of the water maze, passive avoidance, and impulsivity in the five-choice serial reaction task.

CHF2819: pharmacological profile of a novel acetylcholinesterase inhibitor

CHF2819 is a novel orally active acetylcholinesterase inhibitor (AChEI) developed for the treatment of Alzheimer's disease (AD). CHF2819 is a selective inhibitor of AChE, it is 115 times more potent against this enzyme than against butyrylcholinesterase (BuChE). Moreover, CHF2819 is more selective for inhibition of central (brain) AChE than peripheral (heart) AChE. In vivo CHF2819, 0.5, 1.5, and 4.5 mg/kg p.o., significantly and in dose-dependent manner increased acetylcholine (ACh) levels in hippocampus of young adult rats. Moreover, aging animals, with lower basal ACh levels than young adult rats, also exhibit a marked increase in hippocampal levels of this neurotransmitter after administration of CHF2819. At 1.5 mg/kg p.o. CHF2819 attenuated scopolamine-induced amnesia in a passive avoidance task. Furthermore, it decreased dopamine (DA) levels and increased extracellular levels of 5-hydroxytryptamine (5-HT) in the hippocampus, without modifying norepinephrine (NE) levels. By oral administration to young adult rats CHF2819 did not affect extracellular hippocampal levels of glutamate (Glu), aspartate (Asp), gamma-aminobutyric acid (GABA), taurine (Tau), arginine (Arg) or citrulline (Cit). Functional observational battery (FOB) screening demonstrated that CHF2819 (1.5 and 4.5 mg/kg p.o.) does not affect activity, excitability, autonomic, neuromuscular, and sensorimotor domains, as well as physiological endpoints (body weight and temperature). CHF2819 induced, however, involuntary motor movements (ranging from mild tremors to myoclonic jerks) in a dose-dependent manner. The neurochemical and behavioral profiles of CHF2819 suggest that this orally active novel AChEI could be of clinical interest for the treatment of Alzheimer-type dementia associated with multiple neurotransmitter abnormalities in the brain. In particular, CHF2819 might be a useful therapeutic drug for AD patients with cognitive impairment accompanied by depression.

Cholinergic and serotonergic activities are required in triggering conditioned NK cell response

The purpose of the study was to examine the importance of the cholinergic system in triggering the conditioned NK cell response. The fact that serotonergic system can modulate cholinergic functions suggested that it might be involved in conditioned NK cell response. To evaluate the potential pathways, cholinergic and serotonergic antagonists were applied centrally at either the conditioned association or recall stage, to interfere with the conditioned NK cell response. The results showed that both the cholinergic and serotonergic systems were necessary for eliciting the conditioned enhancement of NK cell activity. Involvements of the two systems were found to be critical for establishing the conditioned association and recall of the conditioned response. The blocks are believed to be receptor mediated. The receptors identified to be involved in the regulation of the conditioned NK cell response were: M(1), M(2) and M(3) muscarinic; nicotinic; 5 HT(1) and 5 HT(2) receptors.

The amygdala mediates memory consolidation for an amphetamine conditioned place preference

Drug-induced conditioned place preference (CPP) behavior requires memory for an association between environmental cues and the affective state produced by the drug treatment. The present study investigated whether memory consolidation underlying an amphetamine CPP could be modulated by post-training intra-amygdala infusion of the local anesthetic drug bupivacaine. On 4 alternating days adult male Long-Evans rats received peripheral injections of amphetamine (2.0 mg/kg) or saline vehicle prior to confinement for 30 min to one of two compartments of a place preference apparatus, followed by post-training intra-amygdala infusions of bupivacaine (0.75% solution/1.0 microl) or saline. On day 5 the rats were given a drug-free 20-min test session, and the amount of time spent in each of the pairing compartments of the apparatus was recorded. On the test day, rats receiving post-training intra-amygdala saline injections displayed an amphetamine conditioned place preference. Post-training intra-amygdala infusions of bupivacaine blocked amphetamine CPP. Intra-amygdala infusions of bupivacaine that were delayed 1 h post-training did not block amphetamine CPP, indicating a time-dependent effect of the treatment on memory storage processes. Pre-training or pre-retention test intra-amygdala infusions of bupivacaine also blocked acquisition and expression of an amphetamine CPP, respectively. The findings indicate that the mechanism(s) by which amphetamine elicits conditioned approach responses to environmental cues can be manipulated post-training, and suggest a role for the amygdala in acquisition, consolidation, and expression of amphetamine CPP behavior.

Effects of novelty and habituation on acetylcholine, GABA, and glutamate release from the frontal cortex and hippocampus of freely moving rats

The involvement of the forebrain cholinergic system in arousal, learning and memory has been well established. Other neurotransmitters such as GABA and glutamate may be involved in the mechanisms of memory by modulating the forebrain cholinergic pathways. We studied the activity of cortical and hippocampal cholinergic, GABAergic and glutamatergic systems during novelty and habituation in the rat using microdialysis. After establishing basal release of the neurotransmitters, the animals were transferred to a novel environment and allowed to explore it twice consecutively for 30 min (60 min apart; exploration I and II). The motor activity was monitored. Samples were collected throughout the experiment and the release of acetylcholine (ACh), GABA and glutamate was measured. During the two consecutive explorations of the arena, cortical and hippocampal, ACh release showed a significant tetrodotoxin-dependent increase which was higher during exploration I than II. The effect was more pronounced and longer-lasting in the hippocampus than in the cortex. Cortical GABA release increased significantly only during exploration II, while hippocampal GABA release did not increase during either exploration. Motor activity was higher during the first 10 min of exploration I and II and then gradually decreased during the further 20 min. Both cortical and hippocampal ACh release were positively correlated with motor activity during exploration II, but not during I. During exploration II, cortical GABA release was inversely correlated, while hippocampal GABA release was positively correlated to motor activity. No change in cortical and hippocampal glutamate release was observed. In summary, ACh released by the animal placed in a novel environment seems to have two components, one related to motor activity and one related to attention, anxiety and fear. This second component disappears in the familiar environment, where ACh release is directly related to motor activity. The negative relationship between cortical GABA levels and motor activity may indicate that cortical GABAergic activity is involved in habituation.

Effects of the antidepressant/antipanic drug phenelzine and its putative metabolite phenylethylidenehydrazine on extracellular gamma-aminobutyric acid levels in the striatum

Phenelzine (PLZ) is a non-selective monoamine oxidase inhibitor (MAOI) commonly used to treat depression and panic disorder. As expected, PLZ increases brain levels of dopamine, norepinephrine, and serotonin. Interestingly, PLZ also elevates brain levels of gamma-aminobutyric acid (GABA), and previous studies have suggested that these increases may also contribute to the anxiolytic effects of PLZ. Using in vivo microdialysis in conscious, freely moving rats, combined with high performance liquid chromatography, the present experiments determined that PLZ (15 or 30 mg/kg, free base weight) increases extracellular levels of GABA in the caudate-putamen and nucleus accumbens. The results also indicated that phenylethylidenehydrazine (PEH; 29.6 mg/kg, free base weight), a putative intermediate metabolite of PLZ that is not an MAOI, also significantly increases extracellular GABA levels in the caudate-putamen. These findings provide further evidence that GABA may play an important role in the actions of PLZ and suggest that PEH should be pursued further as a GABAergic drug in its own right.

Effect of huperzine A on working memory in reserpine- or yohimbine-treated monkeys

The effect of huperzine A, a reversible and selective acetylcholinesterase inhibitor, on reserpine- or yohimbine-induced spatial working memory deficits in monkeys has been examined using the delayed response task that depends on the integrity of prefrontal cortex. Reserpine (0.1 mg/kg, i.m.) or yohimbine (0.01 mg/kg, i.m.) led to significant impairments in the monkeys' ability to perform the delayed response task. Huperzine A (0.01 mg/kg, i.m. in reserpine-treated monkeys; 0.01-0.1 mg/kg, i.m. in yohimbine-treated monkeys) significantly improved the reserpine- or yohimbine-induced memory impairments. The effect of huperzine A on memory impairments exhibited an inverted U-shaped dose-response pattern. Our data suggest that huperzine A may improve working memory via an adrenergic mechanism.

Opioid receptor regulation of muscarinic acetylcholine receptor-mediated synaptic responses in the hippocampus

A common feature of many synapses is their regulation by neurotransmitters other than those released from the presynaptic terminal. This aspect of synaptic transmission is often mediated by activation of G protein coupled receptors (GPCRs) and has been most extensively studied at amino acid-mediated synapses where ligand gated receptors mediate the postsynaptic signal. Here we have investigated how opioid receptors modulate synaptic transmission mediated by muscarinic acetylcholine receptors (mAChRs) in hippocampal CA1 pyramidal neurones. Using a cocktail of glutamate and gamma-amino-butyric acid (GABA) receptor antagonists a slow pirenzepine-sensitive excitatory postsynaptic potential (EPSP(M)) that was associated with a small increase in cell input resistance could be evoked in isolation. This response was enhanced by the acetylcholine (ACh) esterase inhibitor physostigmine (1 microM) and depressed by the vesicular ACh transport inhibitor vesamicol (50 microM). The mu-opioid receptor agonists DAMGO (1-5 microM) and etonitazene (100 nM), but not the delta- and kappa-opioid receptor selective agonists DTLET (1 microM) and U-50488 (1 microM), potentiated this EPSP(M) (up to 327%) without affecting cell membrane potential or input resistance; an effect that was totally reversed by naloxone (5 microM). In contrast, postsynaptic depolarizations and increases in cell input resistance evoked by carbachol (3 microM) were unaffected by DAMGO (1-5 microM) but were abolished by atropine (1 microM). Taken together these data provide good evidence for a mu-opioid receptor-mediated presynaptic enhancement of mAChR-mediated EPSPs in hippocampal CA1 pyramidal neurones.

Regulation of muscarinic acetylcholine receptor-mediated synaptic responses by GABA(B) receptors in the rat hippocampus

1. Both GABA(B) and muscarinic acetylcholine receptors (mAChRs) influence hippocampal-dependent mnemonic processing. Here the possibility of a direct interaction between GABA(B) receptors and mAChR-mediated synaptic responses has been studied using intracellular recording in rat hippocampal slices. 2. The GABA(B) receptor agonist (-)-baclofen (5-10 microM) depressed an atropine-sensitive slow EPSP (EPSP(M)) and occluded the GABA(B)-receptor-mediated IPSP (IPSP(B)) which preceded it. These inhibitory effects were accompanied by postsynaptic hyperpolarization (9 +/- 2 mV) and a reduction in cell input resistance (12 +/- 3 %). 3. The selective GABA(B) receptor antagonist CGP 55845A (1 microM) fully reversed the depressant effects of (-)-baclofen (5-10 microM) such that in the combined presence of (-)-baclofen and CGP 55845A the EPSP(M) was 134 +/- 21 % of control. 4. (-)-Baclofen (5-10 microM) caused a small (28 +/- 11 %) inhibition of carbachol-induced (3.0 microM) postsynaptic depolarizations and increases in input resistance. 5. CGP 55845A (1 microM) alone caused an increase in the amplitude of the EPSP(M) (253 +/- 74 % of control) and blocked the IPSP(B) that preceded it. 6. In contrast, the selective GABA uptake inhibitor NNC 05-0711 (10 microM) increased the amplitude of the IPSP(B) by 141 +/- 38 % and depressed the amplitude of the EPSP(M) by 58 +/- 10 %. This inhibition was abolished by CGP 55845A (1 microM). 7. Taken together these data provide good evidence that synaptically released GABA activates GABA(B) receptors that inhibit mAChR-mediated EPSPs in hippocampal CA1 pyramidal neurones. The mechanism of inhibition may involve both pre- and postsynaptic elements.

Ameliorative effects of a cognitive enhancer, T-588, on place learning deficits induced by transient forebrain ischemia in rats

In the present study, we investigated the effect of (1R)-1-benzo[b]thiophen-5-yl-2-[2-(diethylamino)ethoxy]ethan-1-ol hydrochloride (T-588), a newly synthesized cognitive enhancer, on place learning deficits in rats with damage selective to the hippocampal CA1 subfield induced by transient forebrain ischemia. Three weeks after the ischemic insult, T-588 was daily administered (0.3 or 3.0 mg/kg/day po). Place learning was tested in a task in which the rat was required to alternatively visit two places located diametrically opposite each other in an open field. The ischemic rats without the treatment of T-588 displayed severe learning impairment in this task; their performance level was significantly inferior to that of the sham-operated rats. The treatment of T-588 improved dose-dependently the task performance in ischemic rats, although no apparent protective effects on ischemic damage were found histologically. These results suggested that T-588 has ameliorative effects on learning deficits induced by brain ischemia, which could be produced through enhancement of residual cognitive functions.

Cortical alterations of angiotensin converting enzyme, angiotensin II and AT1 receptor in Alzheimer's dementia

We investigated the immunohistochemical alterations of angiotensin converting enzyme (ACE), angiotensin II and AT1 receptor in the parietal cortex in Alzheimer's dementia (AD) to reveal the contributive role of the brain renin-angiotensin system in the disease process. In controls, ACE, angiotensin II and AT1 immunoreactivities were localized to pyramidal neurons of the cortex. The staining intensity was distinctly increased in AD for all three antigens, involving predominantly cortical layer V, which may reflect the enhanced brain renin-angiotensin system activity in the disease process. In addition, a prominent perivascular ACE and angiotensin II immunoreactivity surrounding some cortical vessels in aged controls and AD patients points to an underlying microvascular pathology in the process of neurodegeneration.

Sleep and memory deficits in the rat produced by experimental infection with Trypanosoma cruzi

We investigated whether the infection with Trypanosoma cruzi in rats could produce functional alterations of the central nervous system. The experimental group received an injection of 150,000 trypomastigotes / rat, whereas the control group received a saline injection. Spontaneous alternation behavior (SAB) tests and sleep-wake cycle recordings were obtained at the end of the parasitaemia. Results showed that the infected animals had significant sleep impairments, as denoted by an increase in the number of wake periods and a reduction of rapid eye movement sleep amount. SAB performance was also found to be impaired in these animals, as compared to the control group. Our results suggest that the rat is a suitable model for brain dysfunction studies in Chagas' disease.

Cholinesterase inhibitors for behavioral disturbance in dementia

The authors review the literature from the last year examining the benefits of cholinesterase inhibitors in the treatment of behavioral disturbance in Alzheimer's disease (AD) and other dementias. Previous review has indicated that cholinesterase inhibitors have psychotropic properties. We found more evidence to support both the benefits of cholinesterase inhibitors in behavioral disturbance, and that specific behaviors may be selectively responsive to treatment.

5-HT1A receptor agonist (8-OH-DPAT) and 5-HT2 receptor agonist (DOI) disrupt the non-cognitive performance of rats in a working memory task

The present study investigated the role of 5 -HT1A and 5 -HT2 receptors in the execution of a working memory task (delayed non-matching to position, DNMTP) by assessing the influence of 8-OH-DPAT (5-HT1A receptor agonist) and DOI (5-HT2 receptor agonist) on the performance of rats lesioned with 5,7-dihydroxytryptamine (5,7-DHT) and their controls. Post-mortem neurochemical analysis revealed that serotonin and 5-hydroxyindoleacetic acid levels were reduced in examined brain areas (especially in the hippocampus where there was a 90 percent reduction). Noradrenaline concentrations were also decreased (mostly on the same side of the injection) by about 20 percent. 5,7-DHT lesioned rats did not significantly differ from their controls in performance in the DNMTP task. At the 30 microg/kg dose, 8-OH-DPAT did not affect the DNMTP-performance of rats, but at the higher dose (100 microg/kg) it reduced the probability of responding to the sample lever. DOI (100 and 300 microg/kg) also interfered with the non-cognitive performance of rats. Since neither of these agonists affected significantly the choice accuracy, they do not appear to influence the working memory per se. The 5,7-DHT lesioned rats did not differ from their controls in response to these agonists. These results suggest that the combination of 5-HT1A receptor stimulation by 8-OH-DPAT and 5-HT2 receptor stimulation by DOI can interfere with the non-cognitive performance of rats in the DNMTP task. The results further indicate that the effect of 8-OH-DPAT may be mediated through post-synaptic rather than pre-synaptic 5-HT1A receptors.

Reversal of morphine-induced memory impairment in mice by withdrawal in Morris water maze: possible involvement of cholinergic system

The effects of morphine and morphine withdrawal on memory performance were examined in mice by using Morris water maze task. Morphine-induced memory impairment at the doses of 5 and 10 mg/kg recovered after repeated administration. Oxotremorine, a muscarinic receptor agonist, at the dose of 0.1 mg/kg ip, and physostigmine, a cholinesterase inhibitor, at the dose of 0.1 mg/kg ip, significantly antagonized morphine (10 mg/kg sc)-induced memory impairment in mice. Furthermore, repeated naloxone (0.5 mg/kg ip) attenuated scopolamine (0.2 mg/kg ip)-induced memory impairment. By using escalating doses of morphine for 13 days, morphine-induced memory impairment was continuously maintained. When withdrawal was precipitated by naloxone (5 mg/kg ip), or administration of oxotremorine (0.1 and 0.2 mg/kg ip) or physostigmine (0.05 and 0.1 mg/kg ip), the impairment was completely reversed. These results suggest that morphine-induced memory impairment could be partially due to the inhibition of the central cholinergic activity.

Radix Angelica Sinensis extracts ameliorate scopolamine- and cycloheximide-induced amnesia, but not p-chloroamphetamine-induced amnesia in rats

The effects of the methanolic extract of Radix Angelica Sinensis (Umbellifera) (abbreviated as RAS extract) and n-hexane fraction of RAS extract (RAS(H) fraction) on the various drugs-induced amnesia in rats were studied by using passive avoidance task. RAS extract (1 g/kg) significantly prolonged the shortened step-through latency induced by SCOP and CXM, but not PCA. Furthermore, RAS(H) fraction (1 g/kg) also significantly prolonged the shortened step-through latency induced by SCOP and CXM but not PCA. RAS extract at any dose alone did not influence the step-through latency in the training trial produced by non-shocked rats, but it plus PCA prolonged the latency compared with PCA alone. However, RAS(H) fraction (1 g/kg) prolonged the latency in the training trial produced by non-shocked rats, but it plus any induced drugs did not differ from any induced drugs alone. These results suggest that the attenuating effects of RAS extract on the various drugs-induced amnesia were related to the memory processes. n-Hexane fraction of RAS extract might be one of the active fractions of RAS extract in the treatment of amnesia.

The ameliorating effect of the water layer of Fructus Schisandrae on cycloheximide-induced amnesia in rats: interaction with drugs acting at neurotransmitter receptors

Our previous study indicated that the water layer present in Fructus Schisandra(FS(w)) at 10 and 25 mg kg(-1)significantly counteracted cycloheximide (CXM)-induced amnesia. Therefore, the mechanism of action of the ameliorating effect of FS(w)on CXM-induced amnesia in the passive avoidance task was investigated in rats. The ameliorating effect of FS(w)on CXM-induced amnesia was depressed by scopolamine. The serotonin releaser, p -chloroamphetamine significantly antagonized the ameliorating effect of FS(w)on CXM-induced amnesia. Furthermore, the ameliorating effect was also inhibited by the 5-HT(1A)receptor agonist 8-OH-DPAT, but potentiated by the 5-HT(2)receptor antagonist ritanserin. Finally, the GABA(A)receptor antagonist bicuculline blocked the ameliorating effect of FS(w). These results suggest that the beneficial effect of FS(w)on CXM-induced amnesia is amplified by treatment with serotonergic 5-HT(2)receptor antagonists, but reduced by serotonergic 5-HT(1A)receptor agonists as well as GABA(A)and cholinergic receptor antagonists.

Alzheimer's disease: more than a 'cholinergic disorder' - evidence that cholinergic-monoaminergic interactions contribute to EEG slowing and dementia

The loss of cognitive (particularly mnemonic) abilities constitutes a prominent symptom of Alzheimer's disease (AD). These cognitive symptoms occur in close relation to the slowing of the electroencephalogram (EEG), and it is likely that the inability of cortical circuits to maintain an activated state contributes to the behavioral disorganization in AD. The 'cholinergic hypothesis' of AD suggests that many of the cognitive and EEG symptoms are related to the atrophy of basal forebrain cholinergic neurons, which innervate the neocortex and hippocampus, among others. However, data from behavioral and electrophysiological studies in rats suggest that selective reductions in cholinergic transmission result in relatively small mnemonic impairments, and only a partial reduction in EEG activation. Thus, cholinergic atrophy alone may not be sufficient to cause the marked changes in cognition and cortical activity typical of AD. Cholinergic deficits do, however, make neural circuits susceptible to additional neurodegenerative processes. In rats, lowered serotonergic or noradrenergic activity alone often produces only minor impairments in learning/memory tasks and does not block EEG activation. The same monoaminergic deficits, however, result in severe behavioral impairments, and reduce or abolish EEG activation when they occur in a brain already affected by lowered cholinergic activity. There is an abundance of evidence that monoamines are reduced in AD. These degenerative processes, when occurring in a neural environment compromised by cholinergic atrophy, may then contribute to the disturbances in cortical processing and cognition/behavior in AD. A prediction derived from this theory is that an enhancement of monoaminergic functions may have beneficial effects on behavior and cortical activity. Preliminary experiments support this idea: combined cholinergic-monoaminergic stimulation can be more effective in reversing behavioral (Morris water maze) impairments and EEG slowing in rats with multiple neurotransmitter deficiencies than cholinergic enhancement alone. Thus, a stimulation of monoaminergic activity, in conjunction with cholinergic therapies, may provide an effective treatment option for AD.

Involvement of central cholinergic mechanisms in the effects of oxytocin and an oxytocin receptor antagonist on retention performance in mice

Oxytocin (OT, 0.10 microg/kg, sc) impaired retention of a one-trial step-through inhibitory avoidance task when injected into male Swiss mice 10 min after training, as indicated by retention performance 48 h later. In contrast, the immediate post-training administration of the putative oxytocin receptor antagonist d(CH(2))(5)[Tyr(Me)(2), Thr(4), Thy-NH(9)(2)] OVT (AOT, 0.30 microg/kg, sc) significantly enhanced retention performance. Neither OT nor AOT affected response latencies in mice not given footshock on the training trial, and neither the impairing effects of OT nor the enhancing effects of AOT were seen when the training-treatment interval was 180 min, suggesting that both treatments influenced memory storage. The effects of OT (0.10 microg/kg, sc) on retention were prevented by AOT (0.03 microg/kg, sc) given immediately after training, but 10 min prior to OT treatment. The central acting anticholinesterase physostigmine (35, 70, or 150 microg/kg, i.p.), but not its quaternary analogue neostigmine (150 microg/kg, i.p.), reversed the impairment of retention performance induced by OT, whereas low subeffective doses of the centrally active muscarinic cholinergic antagonist atropine (0.5 mg/kg, i.p.) or the central acting nicotinic cholinergic antagonist mecamylamine (5 mg/kg, i.p.), but not methylatropine (0.5 mg/kg, i.p.) or hexamethonium (5 mg/kg, i.p.) prevented the enhancement of retention performance caused by AOT. We suggest that oxytocin negatively modulates the activity of central cholinergic mechanisms during the posttraining period that follows an aversively motivated learning experience, leading to an impairment of retention performance of the inhibitory avoidance response.

Cholinergic modulation of neocortical long-term potentiation in the awake, freely moving rat

The neocortex has proven resistant to LTP induction using standard in vitro and acute, in vivo preparations. Because the neocortex is widely thought to be involved in long-term information storage, this resistance raises questions about the validity of LTP as a memory model. Recently, we have shown that the neocortex of freely moving rats reliably supports LTP, provided that the stimulation is spaced and repeated over days. The following experiments were designed to evaluate the neuromodulatory role played by cholinergic systems in the induction of LTP in this preparation. Chronically implanted rats received either low- or high-intensity LTP-inducing tetani in combination with the administration of either a cholinergic agonist or antagonist injected systemically. Potentiation was evidenced as amplitude changes in both early and late components of the evoked field potential, the former including population spikes. The cholinergic agonist facilitated LTP induction in the late component of both high- and low-intensity groups. The cholinergic antagonist blocked LTP induction in the early component of the high-intensity group. The possibility that there are component-specific modulatory effects of cholinergic agents on the induction of neocortical LTP is discussed.

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.

Protection from phenytoin-induced cognitive deficit by Bacopa monniera, a reputed Indian nootropic plant

Many epileptic patients suffer from cognitive impairments; both the underlying pathology and antiepileptic drug therapy can cause such deficits. Phenytoin, one of the widely used anticonvulsants, is known to adversely affect cognitive function. A reputed Indian nootropic plant Bacopa monniera (BM) was evaluated alone and in combination with phenytoin for its effect on (a) passive-avoidance (PA) task; (b) maximal electroshock seizures; and (c) locomotor activity in mice. Phenytoin (PHT, 25 mg/kg po x 14 days) adversely affected cognitive function in the PA task. BM extract (40 mg/kg x 7 days), given along with phenytoin in the second week of the two-week regimen, significantly reversed PHT-induced impairment. Both acquisition and retention of memory showed improvement without affecting its anticonvulsant activity. The observed cognitive effects of PHT and BM were found to be independent of motor stimulation. The results provide evidence for potential corrective effect of BM in cognitive deficit associated with PHT therapy.

Potentiation of brain acetylcholine neurons by Kami-Untan-To (KUT) in aged mice: implications for a possible antidementia drug

The effects of a traditional Japanese herbal medicine, Kami-Untan-To (KUT), on brain choline (Ch) and Acetylcholine (ACh) levels in aged mice were examined. Further, the expression of choline acetyltransferase (ChAT) in the medial septum (MS), the vertical limbs of the diagonal band of Broca (VDB), and the nucleus basalis Meynert (NBM) was examined by immunohistochemistry. Following an oral administration of KUT to the aged mice for 3 months, ACh levels in the cortex, striatum and hippocampus were increased significantly. The density of ChAT-immunoreactive cells located in MS, VDB, and NBM in the KUT-treated group was increased significantly as compared to the non-treatment group. The survival rate of aged mice was significantly higher in the KUT-treated group as compared to that in the nontreated group. Our results suggest that KUT potentiates the brain acetylcholinergic system, and may become a possible anti-dementia drug.