Blockade of cholinergic receptors by an irreversible antagonist, propylbenzilylcholine mustard (PrBCM), in the rat cerebral cortex causes deficits in passive avoidance learning

Studies were made on the effects of blockade of muscarinic acetylcholine (mACh) receptors in the rat cerebral cortex on learning and memory assessed by performance of a step-through passive avoidance task. Bilateral injection of propylbenzilylcholine mustard (PrBCM) into both the frontal and parietal cortex at doses of 2.25 X 4 to 22.5 X 4 micrograms decreased mACh receptors dose-dependently, as assessed by [3H]quinuclidinyl benzilate binding studies. When the training trial of a step-through passive avoidance task was performed 24 h after injection of 7.5 X 4 to 22.5 X 4 micrograms PrBCM into the frontal and parietal cortex, and then a retention test was made 24 h after the training trial, the treated rats showed shorter latencies than controls. In contrast, injection of PrBCM into the occipital cortex had no significant effect on performance in the test. These results confirm the notion that cholinergic neurotransmission in the cerebral cortex, especially the frontoparietal cortex, is important in learning and memory. The effects of injection of PrBCM (22.5 X 4 micrograms) into the frontoparietal cortex on 3 postulated phases of the learning and memory process (i.e. registration, retention and recall) were also examined. When PrBCM was injected 24 h before the training trial, no retention of the task was observed 14 days after the training trial. However, when PrBCM was injected 24 h after the training trial, retention of the task 14 days after the training trial was not affected. When PrBCM was injected 3-24 h after the initial training trial, the latencies in the retention test examined 24 h later were shorter than those of control rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Behavioral impairment in the rat after colchicine lesions of the hippocampus and nucleus basalis

Rats were given bilateral injections of colchicine into the nucleus basalis (NBM; 1.0 or 2.0 micrograms/site), hippocampus (HPC; 1.25 or 2.5 micrograms/site), or both areas (COM; 1.0 NBM, 1.25 HPC) and examined for changes in locomotor activity, passive avoidance behavior, and spatial navigation in a water maze task. Colchicine injected into the HPC caused a dose-related increase in locomotor activity 7 days after treatment which declined with repeated testing. Motor activity in NBM-lesioned rats was not significantly different from control. Rats with the COM lesion were more active than controls 7 days after treatment and remained hyperactive over the 3 week testing period. Retention of a step-through passive avoidance task was examined 18 days after surgery. HPC lesions had no apparent effect on passive avoidance behavior. NBM lesions causes a dose-dependent decrease in step-through latencies, while latencies in the combined group were comparable to the low dose NBM group. In the spatial navigation task, HPC and COM lesions impaired acquisition, with little indication of learning in the combined group. NBM lesions had no effect in the water maze. These data suggest that combined lesions of the NBM and HPC cause lasting behavioral impairments and may be useful as a model for neurodegenerative disorders such as Alzheimer's disease.     

Nociceptin system plays a role in the memory retention: involvement of naloxone benzoylhydrazone binding sites.

We investigated the role of nociceptin system in learning and memory in mice. The deficiency of nociceptin receptors and nociceptin itself did not affect the alternation behavior in the Y-maze test. In the passive avoidance test, the step-through latencies of nociceptin receptor knockout mice were longer than those of wild-type mice. Nociceptin shortened the step-through latency in wild-type mice. This impairment on passive avoidance task was reversed by naloxone benzoylhydrazone (NalBzoH), indicating that the amnesic effects of nociceptin may be mediated through the NalBzoH recognition sites. These suggest that nociceptin system plays an important role in the memory retention of passive avoidance task, and NalBzoH-recognized sites are involved in nociceptin-induced impairment of the memory retention.     

Pharmacological consequences of nicotinergic plus serotonergic manipulations

The present study investigates the effects of concurrent manipulations of nicotinic cholinergic receptors (nicotinic cholinergic agonist: nicotine 0.03, 0.1, 0.3 mg/kg, nicotinic cholinergic antagonist: mecamylamine 7.5 mg/kg) and serotonin neurons (p-chlorophenylalanine (PCPA), 400/kg mg on each of 3 days) on spatial navigation (water maze, WM) and passive avoidance (PA) performance. Nicotine did not affect PA performance but at the highest dose slightly impaired WM performance. PCPA did not affect WM navigation or PA performance in saline or nicotine-treated rats. Nicotine restored WM and PA performance defect in mecamylamine pretreated rats. PCPA aggravated the WM defect and decreased the WM performance-improving effect of nicotine in mecamylamine pretreated rats. PCPA did not aggravate the PA performance defect of mecamylamine but completely blocked the PA performance-improving effect of nicotine in mecamylamine pretreated rats. These results suggest that serotonergic and nicotinergic cholinergic systems jointly modulate performance in WM and PA tests.     

AF64A, a cholinergic neurotoxin, selectively depletes acetylcholine in hippocampus and cortex, and produces long-term passive avoidance and radial-arm maze deficits in the rat

The behavioral and biochemical effects of AF64A, a presynaptic cholinergic neurotoxin, were investigated. Bilateral administration of this compound into the lateral cerebral ventricles produced transient and dose-related effects on sensorimotor function and long-term impairments of cognitive behavior. Male Fischer-F344 rats dosed with either 15 or 30 nmol of AF64A reacted 29–62% faster than CSF-injected controls in a hot-plate test 14 (but not 1, 7, 21 or 28) days following dosing. The group administered 15 nmol of AF64A was also significantly more active (41%) than controls 28 days following dosing. The activity level of this group was comparable to that of controls at other times and hyperactivity was never observed in the 30 nmol group. Retention of a step-through passive avoidance task, assessed 35 days after dosing, was impaired in both 15 and the 30 nmol groups. Their step-through latencies were significatlly shorter than the control latencies, and they exhibited more partial entries during the 24-h retention test. Radial-arm maze performance, measured 60–80 days following treatment, was markedly impaired in the treated groups. Animals treated with AF64A made fewer correct responses in their first 8 choices, required more total selections to complete the task, and had an altered pattern of spatial responding in the maze. The neurochemical changes produced by AF64A, determined 120 days after dosing, were specific to the cholinergic system and consisted of decreases of ACh in both the hippocampus (15 and 30 nmol groups) and the frontal cortex (30 nmol group). The concentrations of catecholamines, indoleamines, their metabolites and choline in various brain regions were not affected by AF64A. Furthermore, histological analysis revealed that the doses of AF64A used in the present study did not damage the hippocampus, the fimbria-fornix, the septum or the caudate nucleus. These data support the contention that cholinergic processes in the hippocampus, nd/or frontal cortex play an important role in learning and memory processes. Furthermore, based upon the behavioral and biochemical data presented, it is suggested that AF64A could be a useful pharmacological tool for examining the neurobiological substrates of putative cholinergic disorder such as senile dementia of the Alzheimer's type.     

Synergistic improvement effect of nicotine-ghrelin co-injection into the anterior ventral tegmental area on morphine-induced amnesia

In the present study the effect of ghrelin or ghrelin/nicotine injection into the anterior ventral tegmental area (aVTA) on morphine-induced amnesia in passive avoidance learning have been evaluated. Also, the role of the aVTA nicotinic receptors in possible ghrelin-induced effects has been investigated. All animals were bilaterally implanted with chronic cannulas in the aVTA. A step-through type passive avoidance task was used for measurement of memory. We found that post-training subcutaneous (s.c.) injection of morphine (0.5–7.5 mg/kg) dose-dependently reduced the step-through latency, indicating morphine-induced amnesia. Post-training bilateral infusion of ghrelin (0.3, 1.5 and 3 nmol/μl) in a dose-dependent manner reversed amnesia induced by morphine (7.5 mg/kg, s.c.). Furthermore, reversal effect of ghrelin (3 nmol/μl) was blocked by pre-treatment of intra-aVTA administration of mecamylamine (1–3 μg/rat), a nicotinic acetylcholine receptor antagonist. Intra-aVTA administration of the higher dose of mecamylamine (3 μg/rat) into the aVTA by itself decreased the step-through latency and induced amnesia. In addition, post-training intra-aVTA administration of nicotine (0.25, 0.5, 1 μg/rat) which alone cannot affect memory consolidation, decreased significantly the amnesia induced by morphine (7.5 mg/kg, s.c.). Co-treatment of an ineffective dose of ghrelin (0.3 nmol/μl) with an ineffective dose of nicotine (0.25 μg/rat) significantly increased step-through latency of morphine (7.5 mg/kg, s.c.) treated animals, indicating the synergistic effect of the drugs. Taken together, our results suggest that intra-aVTA administration of ghrelin reversed morphine-induced amnesia and that ghrelin interacts synergistically with nicotine to mitigate morphine-induced amnesia.     

Characteristics of changes in cholinergic function and impairment of learning and memory-related behavior induced by olfactory bulbectomy

Memory function after olfactory bulbectomy (OBX) was examined in two tasks, namely, step-through passive avoidance task and elevated plus-maze task. OBX mice showed a significant impairment of learning and memory-related behavior on the 7th and 14th day, as measured by passive avoidance task but not elevated plus maze task. The impairment of learning and memory-related behavior on the 14th day was improved by administration of the cholinesterase inhibitor physostigmine (0.1 mg/kg, i.p.), the non-selective muscarinic agonist oxotremorine (0.1 mg/kg, i.p.) or the selective muscarinic M(1) agonist McN-A-343 (10 microg/mouse, i.c.v.). In contrast, administration of the nicotinic agonist lobeline (5-9.8 mg/kg, i.p.) or the selective muscarinic M(2) antagonist methoctramine (2.25-18 microg/mouse, i.c.v.) has no effect on the impairment of learning and memory-related behavior induced by OBX. In addition, we have demonstrated that the intensity of choline acetyltransferase (ChAT) fluorescence is significantly decreased in the cortex, hippocampus and amygdala on the 14th day after OBX. These results suggest that the impairment of learning and memory-related behavior induced by OBX may be caused by degeneration of cholinergic neurons and muscarinic M(1) receptors play an important role in the improvement process.     

Pyroglutamic acid improves learning and memory capacities in old rats

The effects of the arginine salt of pyroglutamic acid (2-oxo-pyrrolidone carboxylic acid, PCA) on learning and memory capacities of old rats were studied in a subchronic treatment schedule (i.p. injection of 0.1 and 1 g/kg/day for 15 days). The acquisition and extinction of active avoidance behaviour were studied in a pole-jumping test situation. The retention of passive avoidance response was examined in a step-through passive avoidance task. PCA facilitated the rate of acquisition of pole-jumping response, and inhibited the extinction of the response. The dose of 1 g/kg was more potent than 0.1 g/kg in this respect. Also in the passive avoidance task, the treatment with PCA was followed by an improvement of avoidance retention. These results indicate that PCA is a behaviourally active compound in that it improves learning and memory capacities in old rat.     

Absence of alpha7-containing neuronal nicotinic acetylcholine receptors does not prevent nicotine-induced seizures

Nicotine is the primary addictive component in tobacco, and at relatively low doses it affects cardiovascular responses, locomotor activity, thermoregulation, learning, memory, and attention. At higher doses nicotine produces seizures. The mechanisms underlying the convulsive effects of nicotine are not known, but studies conducted on a number of inbred strains of mice have indicated a positive correlation between the number of alpha-bungarotoxin (alpha-BTX) binding sites in the hippocampus and the sensitivity to nicotine-induced seizures. Because alpha7-containing neuronal nicotinic acetylcholine receptors (nAChRs) represent the major binding site for alpha-BTX, mice lacking the alpha7 nAChR subunit were predicted to be less sensitive to the convulsive effects of nicotine. To test this hypothesis, we injected nicotine intraperitoneally in alpha7 mutant mice and found that the dose-response curve for nicotine-induced seizures was similar in the alpha7 +/+, alpha7 +/- and alpha7 -/- mice. The retained sensitivity to the convulsant effects of nicotine could not be explained by the presence of cholinergic compensatory mechanisms such as increases in mRNA levels for other nAChR subunits, or changes in binding levels or affinity for nicotinic ligands such as epibatidine and nicotine. These findings indicate that alpha7 may not be necessary for the mechanisms underlying nicotine-induced seizures.     

Antiamnesic effects of azaindolizinone derivative ZSET845 on impaired learning and decreased ChAT activity induced by amyloid-β 25–35 in the rat

Antiamnesic effects of a newly synthesized azaindolizinone derivative ZSET845 were assessed in rats made learning ability deficient by amyloid-beta (Abeta)25-35 treatment. Intracerebroventricular injection of Abeta25-35 induced a marked decrease in step-through latency in passive avoidance task and reduction in choline acetyltransferase (ChAT) activity in the medial septum and hippocampus, but not in the basal forebrain and cortex. The number of ChAT-immunoreactive cells was decreased in the medial septum. Oral administration of ZSET845 at a dose of 1 or 10 mg/kg ameliorated learning impairment in passive avoidance task and enhanced ChAT activity in the basal forebrain, medial septum and hippocampus, and increased in the number of ChAT-immunoreactive cells in the medial septum in Abeta-treated rats to the levels of vehicle-injected control rats. These results suggest that ZSET845 is worth testing for further preclinical study aimed for the treatment of senile dementia such as Alzheimer's disease.     

Antiamnesic effects of azaindolizinone derivative ZSET845 on impaired learning and decreased ChAT activity induced by amyloid-beta 25-35 in the rat

Antiamnesic effects of a newly synthesized azaindolizinone derivative ZSET845 were assessed in rats made learning ability deficient by amyloid-beta (Abeta)25-35 treatment. Intracerebroventricular injection of Abeta25-35 induced a marked decrease in step-through latency in passive avoidance task and reduction in choline acetyltransferase (ChAT) activity in the medial septum and hippocampus, but not in the basal forebrain and cortex. The number of ChAT-immunoreactive cells was decreased in the medial septum. Oral administration of ZSET845 at a dose of 1 or 10 mg/kg ameliorated learning impairment in passive avoidance task and enhanced ChAT activity in the basal forebrain, medial septum and hippocampus, and increased in the number of ChAT-immunoreactive cells in the medial septum in Abeta-treated rats to the levels of vehicle-injected control rats. These results suggest that ZSET845 is worth testing for further preclinical study aimed for the treatment of senile dementia such as Alzheimer's disease.     

Intra hippocampal injection of testosterone impaired acquisition, consolidation and retrieval of inhibitory avoidance learning and memory in adult male rats

The hippocampus is essentially involved in learning and memory, and is known to be a target for androgen actions. Androgen receptors are densely expressed in CA1 of rat hippocampus, and mediate the effects of testosterone (T) on learning and memory. T depletion or administration can modulate neural function and cognitive performance. We conducted series of experiments to further investigate the effect of castration or intra hippocampal injection of T on acquisition, consolidation and retrieval of inhibitory avoidance learning and memory. Male adult rats were bilaterally cannulated into CA1 of hippocampus, and then received T (1, 10, 20, 40 and 80mug/0.5mul/side) or vehicle (DMSO), 30min before training, immediately after training and 30min before retrieval in inhibitory avoidance task. Castration was made by gonadectomy of male rats and behavioral tests performed 4 weeks later. Our results showed that gonadectomy of male rats did not influence performance on inhibitory avoidance task, as compared to sham-operated rats. We have also found that pre-training, post-training and pre-retrieval intra CA1 injections of T significantly decreased step-through latencies in inhibitory avoidance learning at doses 1 and 80, 20, and 20 and 40mug/0.5mul/side, respectively. The data suggest that intra CA1 administration of T could impair learning and memory acquisition, consolidation and retrieval, while systemic androgen's depletion have no effect on memory, in inhibitory avoidance task.     

Genetically dystrophic mdx/mdx mice exhibit decreased response to nicotine in passive avoidance

mdx mice are considered as a genetic homologous of human Duchenne muscular dystrophy. Recent evidence demonstrates that in mouse sympathetic ganglion dystrophin is involved in the stabilization of nicotinic acetylcholine receptor clusters. The purpose of this study was to verify possible effects of dystrophin alterations at the central level. This was assessed by evaluating the response to nicotine administration in mdx and wild-type mice. Thus the effects of post-training nicotine administrations (0.1, 0.25 and 0.5 mg/kg) were tested in mice subjected to a passive avoidance memory task, that measures the ability of mice to remember on test day a shock received 24 h before. Nicotine enhanced memory in wild-type as well as in mdx mice. However, the doses needed to increase memory in mdx were higher than in wild-type. These results are discussed in terms of possible functional changes in central nicotinic acetylcholine receptor in mdx mice.     

Rat strain differences in response to galanin on the Morris water task

Galanin acts as an inhibitory modulator of cholinergic transmission in the septohippocampal pathway of the rat. Centrally administered galanin induces performance deficits on rodent learning and memory tasks, including delayed non-matching to position, T-maze delayed alternation, passive avoidance, starbust radial maze acquisition, and the Morris water task. The present study investigates differences in responsiveness to intraventricularly administered galanin across three strains of laboratory rat on acquisition of spatial learning in the Morris water task. Sprague-Dawley rats showed normal performance during training, but lack of selective quadrant search on the probe trial in response to galanin treatment. Long-Evans rats showed no effects of galanin on performance during training or probe trial. Wistar rats showed longer latencies to reach the hidden platform during training, and lack of selective quadrant search on the probe trial in response to galanin. Performance on the visible platform task and on locomotor activity in the open field was normal in rats treated with galanin. These results are consistent with an interpretation of strain differences in sensitivity to the inhibitory actions of galanin on learning and memory.     

Effects of excitotoxic median raphe lesion on working memory deficits produced by the dorsal hippocampal muscarinic receptor blockade in the inhibitory avoidance in rats

The experiments investigated the interactions between median raphe nucleus (MRN) serotonergic and septo-hippocampal muscarinic cholinergic systems in the modulation of forming and storing performances of working memory. Rats with ibotenic acid-induced MRN-lesion bilaterally received scopolamine (2-4 microg/each side) infusion into the dentate gyrus of the dorsal hippocampus and were tested in a single trial step-through inhibitory avoidance. Initial preference to the dark compartment (escape latency) was taken as the measure of non-mnemonic behaviours and response latency to enter the dark compartment immediately after the foot-shock was used to measure working memory. The high-dose scopolamine infusion 10 min before the training decreased escape latencies in the sham-lesioned rats, whereas had no effect in the MRN-lesioned rats. Although MRN lesion per se did not alter response latency, it alleviated pre-training scopolamine-induced decrease, but aggravated post-training scopolamine-induced reduction in this parameter. These results suggest that the antagonistic interactive processes between MRN-serotonergic and hippocampal cholinergic systems modulate non-mnemonic component of working memory formation, whereas the storing performance of working memory is modulated by the synergistic interactions between these systems in the hippocampus, mainly in the dentate gyrus.     

Crocus sativus L. extracts antagonize memory impairments in different behavioural tasks in the rat

The effects of extracts of Crocus sativus L. (CSE), on memory were investigated in the rat by using the object recognition and the step-through passive avoidance task. In the first study, post-training administration of CSE (30 and 60 g/kg) successfully counteracted extinction of recognition memory in the normal rat, suggesting that CSE modulates storage and/or retrieval of information. In a subsequent study, pre-training treatment with CSE (30 and 60 mg/kg) significantly antagonized the scopolamine (0.75 mg/kg)-induced performance deficits in the step-through passive avoidance test. These results support and extend prior findings about the implication of CSE in learning and memory mechanisms.     

Endogenous GLP-1 modulates hippocampal activity in beta-amyloid protein-treated rats.

We examined the relationship between the histochemical distribution of endogenous GLP-1 (7-36) amide in the hippocampus and memory impairment assessed by a step-through type passive avoidance task in rats continuously infused with beta-amyloid protein (1-40) into the lateral cerebroventricle using a mini-osmotic pump. Our results demonstrated that endogenous GLP-1 (7-36) amide appears in the hippocampus accompanied by progression of memory impairment. Electrophysiological studies also indicated that endogenous GLP-1 inhibits hippocampal neuronal activity in beta-amyloid protein-treated rats.     

Postnatal administration of two peptide solutions affects passive avoidance behaviour of young rats.

The effects of two subcutaneously injected peptide solutions CERE (100 mg/kg b. wt.) and E021 (1 mg/kg b. wt.) and of 0.9% saline on passive avoidance reaction (PAR) of young rats were examined. Animals were trained and tested in a step-through avoidance task using a footshock of 0.5 mA or 1 mA. Step-through latencies were observed up to 200 s and from these data the percentage of good learners (latency = 200 s) and bad learners (latency < 200 s) was calculated. Two experimental schedules were performed (n > 6). In Expt. 1 rat pups were chronically treated with the substances within the first 7 days after birth. In Expt. 2 the 7 days of treatment started in the 4th postnatal week. In both experiments PAR acquisition was trained on the 28th day after birth (learning trial), PAR extinction testing started on the 29th day (retention trials). After applying a 0.5-mA footshock, rat pups treated with E021 within the first 7 days of life (Expt. 1) displayed significantly slower PAR extinction when compared to saline- and CERE-treated rats. In the 1 mA groups, significant differences in step-through latencies were measured between 0.9% saline- and E021-pretreated animals on retention day 11 and between saline and CERE on retention days 9 and 13. E021-treated rats of Expt. 2, receiving a footshock intensity of 0.5 mA, showed significant lower step-through latencies when compared to E021-treated rats of Expt. 1. In Expt. 2 no significant differences between treatment groups were observed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of acute and sub-chronic nicotine pretreatment on morphine state-dependent learning

In the present study, the effects of acute and sub-chronic pretreatment of nicotine on impairment of memory formation and the state-dependent learning by morphine have been investigated in mice. Pre-training administration of morphine (5mg/kg) decreased the learning of a one-trial passive avoidance task, which was reversed by pre-test administration of the same dose of morphine. Amnesia induced by pre-training morphine was also significantly reversed in nicotine (0.001, 0.01 and 0.1 mg/kg)-treated animals on the test day. Morphine induced amnesia was also reversed in animals which had previously received sub-chronic injections of nicotine, once daily for 3 days followed by 14 days of no drug treatment. The restoration of memory by pre-test morphine was also reduced in animals which had previously received once daily injections of atropine (0.25, 0.5 and 1 mg/kg, i.p.) for 3 days after 14 of being days drug free. In the animals, restoration of memory by sub-chronic nicotine administration, was also decreased by once daily administration of atropine (0.25, 0.5 and 1 mg/kg) 10 min prior to injection of nicotine (0.1 microg/kg/day, for 3 days) but not with SCH 23390; R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine HCl (0.01, 0.05 and 0.1 mg/kg) or sulpiride (25, 50 and 100 mg/kg) during 3-days of treatment with nicotine. The results suggest that nicotine may induce sensitization which affects the impairment of memory formation via cholinergic but not dopaminergic systems.     

Nicotinic receptors in the dorsal and ventral hippocampus differentially modulate contextual fear conditioning

Nicotine administration alters various forms of hippocampus‐dependent learning and memory. Increasing work has found that the dorsal and ventral hippocampus differentially contribute to multiple behaviors. Thus, the present study examined whether the effects of nicotine in the dorsal and ventral hippocampus have distinct influences on contextual fear learning in male C57BL/6J mice. Direct infusion of nicotine into the dorsal hippocampus resulted in an enhancement of contextual fear learning, whereas nicotine infused into the ventral hippocampus resulted in deficits. Nicotine infusions into the ventral hippocampus did not alter hippocampus‐independent cued fear conditioning or time spent in the open arm of the elevated plus maze, a measure of anxiety, suggesting that the effects are due to alterations in contextual learning and not other general processes. Finally, results from using direct infusions of MLA, a low‐affinity α7 nicotinic acetylcholine receptor (nAChR) antagonist, in conjunction with systemic nicotine, provide evidence that α7‐nAChRs in the ventral hippocampus mediate the detrimental effect of ventral hippocampal nicotine on contextual fear learning. These results suggest that with systemic nicotine administration, competition exists between the dorsal and ventral hippocampus for behavioral control over contextual learning. © 2012 Wiley Periodicals, Inc.