Panax ginseng extract improves the scopolamine-induced disruption of 8-arm radial maze performance in rats

The effects of Panax ginseng ethanol extract and its water (WSF)- and lipid-soluble (LSF) fractions on the scopolamine-induced disruption of radial maze performance in rats were examined. Ginseng root was refluxed with ethanol, and WSF and LSF were prepared from this ethanol extract. Scopolamine (0.075-0.3 mg/kg, i.p.) dose-dependently impaired the maze performance. However, the oral administration of Panax ginseng ethanol extract and WSF (2-8 g dried root/kg) 90 min before testing improved the maze performance disrupted by scopolamine (0.3 mg/kg) in a dose-dependent manner, but LSF failed to attenuate the disruption. These data suggest that ginseng extract possesses a beneficial effect regarding spatial cognitive impairment and that the water-soluble fraction of ginseng extract mainly contributes to the effect of the ethanol extract.

Involvement of sigma 1 receptor in (+)-N-allylnormetazocine-stimulated hippocampal cholinergic functions in rats

The effects of the stereoisomers of N-allylnormetazocine (SKF-10,047) on the hippocampal cholinergic functions were compared in rats. A putative sigma 1 receptor agonist, (+)-SKF-10,047, elicited an increase of hippocampal extracellular acetylcholine level and anti-amnesic effect against scopolamine-induced memory dysfunctions in rats. These phenomena were not produced by (-)-SKF-10,047, and were reversed by haloperidol, a putative sigma 1 receptor antagonist. Such stereoselectivity and antagonism imply an involvement of sigma 1 receptors in these (+)-SKF-10,047-stimulated hippocampal cholinergic functions.

Synthesis and structure-activity studies of a series of 1-oxa-2,8-diazaspiro[4.5]decan-3-ones and related compounds as M1 muscarinic agonists

A series of novel 2,8-dialkyl-1-oxa-2,8-diazaspiro[4.5]decan-3-ones and 2,8-dimethyl-1,2,8-triazaspiro[4.5]-decan-3-one (13), related to M1 muscarinic agonists YM796 and RS86, were synthesized by using Michael addition reaction of hydroxyurea or methylhydrazine to alpha, beta-unsaturated esters followed by cyclization reaction. These compounds were assessed for binding affinities for M1 and M2 receptors and in vivo muscarinic activity: namely, amelioration of scopolamine-induced impairment in rat passive avoidance tasks and induction of hypothermia, tremor, and salivation. 2,8-Dimethyl-1-oxa-2,8-diazaspiro[4.5]decan-3-one (6a) exhibited high affinities for both M1 and M2 receptors, showed antiamnesic activity (0.1 mg/kg, s.c.) and induced hypothermia (3 mg/kg, s.c.). In addition, 6a stimulated phosphoinositide hydrolysis in rat hippocampal slices, indicating partial agonistic activity for M1 muscarinic receptors. The alteration of the methyl group at N2 of 6a increased the selectivity in binding affinities for M1 over M2 receptors, but resulted in loss of M1 agonistic activity or antiamnesic activity. Compound 13 exhibited only low affinity for M1 receptors, suggesting that a basic nitrogen atom is not tolerated in M1 receptor binding as a substitute for an oxygen atom or a carbonyl group at the 1-position of 6a or RS86. None of these derivatives exhibited high selectivity for antiamnesic effect over induction of hypothermia compared to YM796.

NS-3(CG3703), a TRH analog, ameliorates scopolamine-induced memory disruption in rats

The effects of a metabolically stable TRH analog, N-[[(3R, 6R)-6-methyl-5-oxo-3-thiomorpholinyl]carbonyl]-L-histidyl-L- prolinamide tetrahydrate (NS-3, CG3703) on the scopolamine-induced memory disruption in maze performance tests were investigated in rats. a) In the delayed nonmatching-to-sample (DNMS) task using a T-maze, NS-3 (0.3 mg/kg) produced a significant reversal of the marginal disruption of choice accuracy induced by scopolamine (0.3 mg/kg) at the short (5 s) and long (120, 480 s) interval delays. Physostigmine (0.5 mg/kg) produced a significant reversal only at a 5-s interval delay. b) In the eight-arm radial maze task, NS-3 (0.3 mg/kg) significantly reversed the deficit of choice accuracy induced by scopolamine (0.3 mg/kg), whereas neither TRH (3-30 mg/kg) nor physostigmine (0.1-1 mg/kg) had any effect. The consistent reversal of these maze-learning performances by NS-3, but not by TRH or physostigmine, may be due to its potent enhancement of cholinergic and noradrenergic neuronal activities.

Effect of huperzine A, a novel acetylcholinesterase inhibitor, on radial maze performance in rats

Rats were trained to run in a spatial, radial arm maze using a procedure to determine two memory functions, working and reference memory. The muscarinic antagonist, not the nicotinic antagonist, impaired both working and reference memory of rats. Scopolamine (0.125, 0.15, and 0.2 mg/kg, IP, 30 min before a session) significantly impaired choice accuracy in the eight-arm maze. In contrast, mecamylamine (5, 10, and 15 mg/kg) did not affect the performance. Huperzine A (0.1, 0.2, and 0.3 mg/kg, IP, 30 min before testing) and physostigmine (0.3 mg/kg, IP, 20 min before testing) could reverse scopolamine-induced deficits in the task. Chronic treatment with huperzine A (0.25 mg/kg, PO, once a day) for 8 consecutive days was as potent as acute treatment on attenuating the scopolamine-induced amnesia.

Bidirectional modulation of scopolamine-induced working memory impairments by muscarinic activation of the medial septal area

The hypotheses that the medial septal area (MSA) is critical for working memory and that MSA neural activity is positively regulated by cholinergic inputs leads to two testable predictions: (1) working memory can be bidirectionally modulated by muscarinic manipulations of the MSA and (2) muscarinic activation of the MSA can enhance memory under conditions of mnemonic impairment. Memory was assessed by T-maze spatial alternation following intraseptal infusion of muscarinic drugs in rats pretreated with intraperitoneal (IP-) injections of scopolamine. Scopolamine dose-dependently impaired working memory and shifted the hippocampal theta activity to a higher peak frequency. Intraseptal scopolamine mimicked the behavioral effects of IP-scopolamine, and intraseptal carbachol appeared to reverse both the behavioral and physiological effects of IP-scopolamine. The results indicate that the amnestic effect of antimuscarinic drugs may be due to an interaction in the MSA and that conditions of memory impairment may be alleviated by selective muscarinic activation of the MSA.

Antagonism of scopolamine-induced memory impairments in rats by the muscarinic agonist RU 35,926 (CI-979)

The promnesic effects of RU 35,926 (CI-979), a muscarinic receptor agonist, were evaluated on memory impairments induced by the muscarinic antagonist scopolamine, using a radial arm maze task, in comparison with tetrahydroaminoacridine (THA), a cholinesterase inhibitor. Groups of rats were trained in a standard version of the radial maze until they had attained an asymptotic level of performance. The animals were then retested with one trial a day. Twenty minutes before each retest, the rats were given subcutaneous administration of 0.1 mg/kg scopolamine. Oral administration of RU 35,926 (0.02, 0.05, 0.1, 0.2, and 0.5 mg/kg) 30 min before memory retest markedly reduced or suppressed the scopolamine-induced deficit. This reduction was evidenced by a significant decrease in the different types of errors and an increase in the number of correct responses. THA (3 mg/kg, intraperitoneally or orally) given 20 min to testing also significantly reduced or suppressed the scopolamine-induced deficits. These results show that RU 35,926 possesses the capacity to reduce memory impairments induced by a deficit of cholinergic transmission in the rat.

NS-3 (CG3703), an analog of thyrotropin-releasing hormone, ameliorates cognitive impairment in rats

The effects of thyrotropin-releasing hormone (TRH) and its analog, N-[[(3R,6R)-6-methyl-5-oxo-thiomorpholinyl] carbonyl]-L-histidyl-L- prolinamide tetrahydrate (NS-3, CG3703) on disturbance of memory of a passive avoidance response (PAR) and an escape response in rats were investigated. NS-3 improved amnesia caused by scopolamine, electroconvulsive shock (ECS), and cycloheximide (CXM), but TRH improved only the ECS-induced amnesia. NS-3 reversed learning deficits caused by hypercapnia, but TRH had no effect. These differences in the effect between NS-3 and TRH may be due to their biological half-life in rat plasma. These results suggest that NS-3 possesses more potent antiamnestic effects than TRH in rats.

The effects of anxiolytics and anxiogenics on evaluation of learning and memory in an elevated plus-maze test in mice

We examined the effects of anxiolytics and anxiogenics on evaluation of learning and memory in the elevated plus-maze test in mice. Transfer latency (TL), the time mice took to move from the open arm to the enclosed arm, was used as an index of learning and memory. The TL on day 2 was shorter than that on day 1 with the maze at a height of 40 cm, and was not affected by anxiolytics and anxiogenics such as 8-OH-DPAT (0.4 mg/kg), picrotoxin (2 mg/kg), and FG-7142 (20 mg/kg), but was affected by diazepam (8 mg/kg). On the other hand, the TL on day 2 was prolonged by changing the experimental room between day 1 and day 2. TL on day 1 and day 2. TL on day 2 was prolonged by treatment with scopolamine before the trial on day 1 compared with vehicle-treated groups. This scopolamine-induced prolongation of TL was reversed by pretreatment with physostigmine and piracetam. The TL on day 2 was also prolonged by treatment with cycloheximide or normobaric hypoxia initiated immediately after the trial on day 1. The cycloheximide- and hypoxia-induced prolongation of TL were reversed by pretreatment with piracetam. These results indicate that disruption of learning and memory and its amelioration, induced by the treatments described above, can be detected using the plus-maze test, suggesting that the elevated plus-maze test could be used for evaluation of learning and memory without influence of anxiolytics and anxiogenics.

Effects of the cholinomimetic SDZ ENS-163 on scopolamine-induced cognitive impairment in humans

Scopolamine-induced cognitive impairment was used in healthy men to evaluate the central nervous system activity of the new cholinomimetic SDZ ENS-163. Eighteen subjects were treated in a crossover design with oral placebo/intravenous saline, 50 mg of oral SDZ ENS-163/intravenous saline, oral placebo/0.4 mg of intravenous scopolamine, and 50 mg of oral SDZ ENS-163/0.4 mg of intravenous scopolamine. The administration of placebo with scopolamine caused significant cognitive impairment, as assessed by the Computerized Neuropsychological Test Battery (CNTB), and also decreased salivation and heart rate. In contrast, SDZ ENS-163 with saline had no effect on CNTB scores, increased salivation, and increased heart rate. Despite the observed cholinomimetic effects of SDZ ENS-163 when administered with saline, the changes in CNTB scores, heart rate, and salivation were indistinguishable between placebo/scopolamine and SDZ ENS-163/scopolamine. Thus, 50 mg of oral SDZ ENS-163 has cholinomimetic activity in normal men, but this dose is insufficient to reverse the muscarinic effects of 0.4 mg of intravenous scopolamine.

Facilitation of acetylcholine release and cognitive performance by an M(2)-muscarinic receptor antagonist in aged memory-impaired

Aged memory-impaired (AI) and unimpaired (AU) 24-25-month-old Long-Evans rats were used to investigate the integrity of various cholinergic markers during normal aging and to establish if alterations can possibly relate to cognitive disabilities. AI and AU rats were classified on the basis of their performance in the Morris swim maze task. Choline acetyltransferase activity (ChAT) was not differentially altered in various cortical and hippocampal areas between these two groups. Similarly, quantitative receptor autoradiography did not reveal significant differences in 3H-pirenzepine/muscarinic M1 and 3H-hemicholinium-3/high-affinity choline uptake binding sites in AI versus AU rats. In contrast, 3H-AF-DX 384/putative muscarinic M2 binding was significantly increased in certain cortical and hippocampal areas of the age-impaired animals. These increments were correlated with decreased in vivo acetylcholine (ACh) release capacity in the AI rats. Most interestingly, the muscarinic M2 antagonist BIBN-99 reversed, in a dose-dependent manner, the impaired ACh release as well as the cognitive deficits observed in the AI group. Similarly, BIBN-99 reversed scopolamine-induced amnesia in young animals. The efficacy of BIBN-99 likely relates to its antagonistic properties on negative muscarinic M2 autoreceptors that are apparently increased in the AI animals, leading to altered ACh release. Taken together, these findings strengthen the role of ACh in learning and memory and may have implications for the treatment of degenerative disorders associated with impaired cholinergic functions, such as Alzheimer's disease.

Linopirdine (DuP 996) improves performance in several tests of learning and memory by modulation of cholinergic neurotransmission

The actions of linopirdine (DuP 996; 3,3-bis[4-pyrindinylmethyl]-1-phenylindolin-2-one) were evaluated in rats and mice in several cognitive behavioral tests, and for its effects on hippocampal acetylcholine (ACh) overflow in rats. Using mice treated with the muscarinic receptor antagonist, scopolamine, we studied the effects of linopirdine on retention of a passive avoidance task. Linopirdine (0.1 and 1 mg/kg) ameliorated the scopolamine-induced deficit, but at doses ranging from 0.01-1 mg/kg, it did not affect passive avoidance retention in normal (untreated) mice. In a scopolamine-induced hyperactivity test, linopirdine (1 mg/kg) decreased the motoric stimulation associated with the cholinergic hypofunction, without affecting locomotor activity on its own. Using rats, we studied the effects of linopirdine on performance in the Morris water maze spatial memory task. Young rats treated with atropine (30 mg/kg), a muscarinic receptor antagonist, took significantly longer to locate the submerged platform across 12 trials. Linopirdine (0.01 and 0.1, but not 1 mg/kg) ameliorated the atropine deficit. In addition, linopirdine (0.1 mg/kg) ameliorated the deficit in cognition-impaired aged rats (23-24 mo), but did not affect unimpaired aged rats. In terms of neurochemical action, linopirdine (1, 10, and 100 microM) produced a concentration-dependent increase in K(+)-evoked ACh overflow from superfused rat hippocampal slices. Also, linopirdine (10 microM) similarly increased ACh release in young control rats and cognition-impaired and nonimpaired aged rats. Our results confirm and extend findings from other studies that demonstrate the cognition-enhancing action of linopirdine in rodent models.(ABSTRACT TRUNCATED AT 250 WORDS)

Nicotine reverses scopolamine-induced impairment of performance in passive avoidance task in rats through its action on the dopaminergic neuronal system

Interest has recently focused on tobacco and/or nicotine in relation to senile dementia of the Alzheimer type because the population of patients with this disease among tobacco smokers is significantly smaller than in nonsmokers. We investigated whether, in relation to the dopaminergic neuronal system, nicotine was effective in ameliorating the impairment of performance in passive avoidance tasks in rats induced by scopolamine, an inhibitor of muscarinic acetylcholine receptors. Scopolamine and nicotine were coadministered to rats 30 min before the acquisition trial. Some rats received scopolamine alone; they showed much shorter step-through latency (STL) than the control group in the retention test. Nicotine significantly prolonged the decreased STL induced by scopolamine. The effects of nicotine were inhibited by the preadministration of mecamylamine, SCH 23390, and (-)sulpiride, which are nicotinic acetylcholine, D1, and D2 receptor antagonists, respectively. These results suggest that nicotine, by activating the nicotinic acetylcholinergic and dopaminergic neuronal systems, ameliorates the impairment of performance in the passive avoidance task induced by a muscarinic acetylcholine receptor blocker.

Ondansetron fails to attenuate a scopolamine-induced deficit in a Stone maze task

The 5-HT3 receptor antagonist ondansetron has previously been reported to improve cognition in the mouse, rat and marmoset in a variety of behavioural paradigms. The present study used the Stone maze to test the effect of ondansetron on the deficit caused by scopolamine in the performance of a highly complex spatial memory task in the rat. Ondansetron administered over a large dose range (1.0 ng kg-1-1.0 micrograms kg-1, i.p., b.d.) for a period of 10-15 days failed to attenuate the scopolamine deficit. Indeed at one dose level ondansetron (100 ng kg-1, i.p., b.d.) administered in combination with scopolamine (0.5 mg kg-1, i.p.) significantly potentiated the deficit, compared with the performance of rats receiving scopolamine alone.

Estrogen and estrogen-progesterone treatments counteract the effect of scopolamine on reinforced T-maze alternation in female rats

The purpose of the experiments was to determine if steroid hormone treatments would attenuate the effect of the muscarinic receptor blocker scopolamine on a memory task. Ovariectomized rats were trained first to alternate for food reward between the arms of a T maze. Following training, females treated with scopolamine hydrobromide (0.2 mg/kg ip) did not alternate correctly between the arms of the T maze and responded at chance levels. However, when estradiol benzoate (25 micrograms) was administered 72, 48, and 24 hr before testing alone or in combination with progesterone (500 micrograms) administered 4-6 hr before testing, females alternated successfully between the arms of the T maze following scopolamine administration. Results indicate that gonadal steroids can completely counteract the impairment of T maze performance induced by scopolamine in female rats.

5-HT1A receptor agonists improve the performance of normal and scopolamine-impaired rats in an operant delayed matching to position task

A series of experiments examined the effects of 5-HT1A ligands alone and in combination with the muscarinic antagonist scopolamine on short term working memory in the rat. The behavioural paradigm was a discrete trial, operant delayed matching to position task, with delays of 0, 5, 15 and 30 s. The 5-HT1A ligands tested were the full agonist, 8-OH DPAT (0, 0.1, 0.3 and 1 mg/kg), the partial agonist, ipsapirone (0, 1, 3 and 10 mg/kg), and the purported antagonist, NAN 190 (0, 1, 2, and 4 mg/kg). 1-PP (0, 0.1, 0.3, 1 mg/kg), the major metabolite of ipsapirone, was also tested. The lowest dose of 8-OH DPAT significantly improved matching accuracy at the longest delay, whereas the highest dose impaired matching accuracy and increased the latency to respond. Ipsapirone also significantly improved the accuracy of performance at a dose of 3 mg/kg, but the doses of 1 and 10 mg/kg did not significantly affect performance. NAN-190, at the highest dose tested (4 mg/kg), impaired matching accuracy, whereas the two lower doses did not significantly affect performance. The highest dose also increased the latency to respond. 1-PP had no effect on performance. Scopolamine HBr (0.14 mg/kg) caused a delay dependent impairment in matching accuracy, and had no effect on missed trials or the latency to respond. Low doses of 8-OH DPAT (0.1 and 0.3 mg/kg) significantly attenuated the scopolamine induced accuracy impairment, whereas 1 mg/kg 8-OH DPAT potentiated the impairment. Ipsapirone (3 mg/kg) also significantly improved the performance of scopolamine impaired rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of (R)-alpha-methylhistamine and scopolamine on spatial learning in the rat assessed using a water maze

The effects of (R)-alpha-methylhistamine ((R)-alpha-MeHA, a selective H3-receptor agonist) and scopolamine (SCOP, a muscarinic antagonist) were investigated on spatial learning and memory in the rat (Hooded Lister) using a water maze (WM). (R)-alpha-MeHA treatment (6.3 and 10 mg/kg IP) had no apparent effect on spatial learning but did result in enhanced spatial recall at the higher dose, assessed by a transfer (probe) test after training. In contrast, SCOP (0.5 mg/kg IP) induced a learning and memory deficit measured both during and after training. In animals treated with (R)-alpha-MeHA and SCOP, (R)-alpha-MeHA partially (6.3 mg/kg) and completely (10 mg/kg) reversed the SCOP-induced deficit during the training phase, while in the post-training transfer test, (R)-alpha-MeHA (10 mg/kg) significantly reduced the SCOP-induced memory deficit. None of the treatments described resulted in impaired visual acuity as demonstrated by a raised platform test. These results are consistent with a role for histamine in cognitive processes and suggest a possible interaction between central histamine and cholinergic mechanisms associated with rodent spatial learning and memory.

Effects of vasoactive intestinal peptide (VIP) on scopolamine-induced amnesia in the rat

The effects of vasoactive intestinal peptide (VIP) on spatial cognitive deficits induced in the rat by injections of scopolamine were examined in a radial arm maze. A single intraperitoneal (i.p.), subcutaneous (s.c.) or intracerebroventricular (i.c.v.) injection of VIP inhibited the reduction in the number of initial correct responses in rats with scopolamine-induced amnesia. The inhibition was associated with a bell-shaped dose-response curve. Thus, VIP appears to have an ameliorating effect on spatial cognitive deficits induced by scopolamine in the rat.

Nefiracetam enhances acetylcholine outflow from the frontal cortex: in vivo microdialysis study in the rat

The effects of nefiracetam [DM-9384; N-(2, 6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl)acetamide], a cognitive enhancer, on extracellular acetylcholine and glutamic acid in the frontal cortex were studied using brain microdialysis in freely moving rats. Nefiracetam administration (1 mg/kg, p.o.) doubled the amount of acetylcholine in the dialysate. When tetrodotoxin was added to the perfusion solution, the basal level of acetylcholine decreased and nefiracetam caused no increase in acetylcholine outflow. The amount of glutamic acid in the dialysates was not affected by nefiracetam. These results suggest that nefiracetam increases the amount of acetylcholine within the cholinergic synaptic clefts.

Mecamylamine reverses physostigmine-induced attenuation of scopolamine-induced hyperactivity

It has previously been demonstrated that the muscarinic antagonist scopolamine induces hyperactivity in rodents, which is reversed by physostigmine but not by directly acting agonists such as pilocarpine. This may suggest that non-muscarinic actions of physostigmine may be responsible for its reversal of scopolamine-induced hyperactivity. We have found, in male Wistar rats, whose activity was measured on electromagnetic detector plates, that the central nicotinic receptor antagonist mecamylamine (3 mg/kg) reverses the blockade of scopolamine-induced behavioural activation induced by physostigmine. This suggests that activation of nicotinic receptors can counteract the effects of muscarinic blockade. Interestingly, however, treatment with nicotine does not block scopolamine-induced hyperactivity, suggesting that the exogenous and endogenous ligands may have different receptor or neuronal substrates.

Effect of DAU 6215, a novel 5-HT3 receptor antagonist, on scopolamine-induced amnesia in the rat in a spatial learning task

The effects of different doses (1, 10, 30, and 100 micrograms/kg, IP) of a new 5-hydroxytryptamine3 (5-HT3) receptor antagonist, 3-alpha-tropanyl)1H-benzimidazolone-3-carboxamide chloride (DAU 6215), on memory and performance deficits induced by SC 0.2 mg/kg scopolamine were assessed in the Morris water maze task. No effect was observed on the performance of rats treated with DAU 6215 alone. The doses of 10 and 30 micrograms/kg DAU 6215 attenuated these scopolamine-induced behavioral deficits.

Peripherally administered IL-1 alpha interferes with scopolamine-induced amnesia in mice

We studied the effects of human recombinant interleukin-1 alpha on scopolamine-induced amnesia for a passive avoidance response in the mouse. Post-training intraperitoneal administration of the cytokine (0.25 or 0.50 microgram/mouse) significantly reduced the amnesic effect of scopolamine (1.0 mg/kg i.p.). Our results indicate that peripheral interleukin-1 alpha can influence behavior and suggest the involvement of the cholinergic system in the neuromodulatory actions of this cytokine.

Evidence for a central cholinergic effect of high-dose thiamine

In vitro animal studies have suggested that thiamine is involved in the presynaptic release of acetylcholine. Total thiamine content in cholinergic nerve terminals is comparable with that of acetylcholine, and the phosphorylation state of thiamine changes with release of acetylcholine. Thiamine binds to nicotinic receptors and may exhibit anticholinesterase activity. Based on these observations, we investigated the effects of pharmacological doses of thiamine on the cognitive deficits induced by the anticholinergic scopolamine in healthy young adults using a randomized, double-blind, placebo-controlled, double-crossover design. Drug effects were assessed by P3 event-related potential, quantitated electroencephalography, and free recall memory. Conditions included (1) baseline, (2) thiamine 5 gm p.o. and scopolamine 0.007 mg/kg IM, and (3) lactose PO and scopolamine 0.007 mg/kg IM. Thiamine significantly reduced adverse effects of scopolamine on P3 latency, spectral components of electroencephalography, and memory recall. The results are consistent with a cholinomimetic effect of thiamine in the central nervous system. Additional studies are needed to delineate the basic mechanisms and possible therapeutic efficacy of thiamine at pharmacological dosages.

The interaction of L-deprenyl and scopolamine on spatial learning/memory in rats

L-Deprenyl, a specific MAO-B inhibitor, has been reported to improve learning/memory in some cognitive tests in aged rats. The present study investigated whether L-deprenyl could alleviate the spatial learning deficit induced by muscarinic blockade and aging in OFA rats. Scopolamine (0.25 mg/kg) impaired the acquisition of a water maze task in adult rats and increased their swimming speeds. L-Deprenyl (0.25 mg/kg, 14 days) had no effect on water maze performance in saline treated adult rats, but markedly alleviated the learning deficit induced by scopolamine and increased the time and distance of swimming in the training quadrant when the platform was removed (spatial probe trial). L-Deprenyl partly reduced the effect of scopolamine on speed of swimming. Nevertheless, administration of l-deprenyl (0.25 mg/kg, 14 days) had no effect on spatial learning/memory in aged rats. We suggest that the l-deprenyl-scopolamine interaction in the water maze test may be considered as a premise for further investigations of l-deprenyl as cognition enhancer.

Dopaminergic involvement in the improving effects of dynorphin A-(1-13) on scopolamine-induced impairment of alternation performance

The present study was designed to clarify whether dopamine systems are involved in the effect of dynorphin A-(1-13), an endogenous kappa-opioid receptor agonist, on the scopolamine-induced impairment of spontaneous alternation performance related to working memory in mice. Sulpiride (10 and/or 30 mg/kg), a dopamine D2-selective antagonist, markedly improved the impairment of alternation performance and significantly reduced the increase in total arm entries (i.e. locomotor activity) induced by scopolamine (1 mg/kg). In contrast, SCH 23390 (0.01, 0.03 and 0.1 mg/kg), a dopamine D1-selective antagonist, did not influence the impairment of alternation performance, whereas it dose dependently reduced total arm entries in scopolamine-treated mice RU 24213 (1 mg/kg), a dopamine D2-selective agonist, almost completely reversed the improving effect of dynorphin A-(1-13) (3 micrograms) on the scopolamine-induced impairment of alternation performance and reduced total arm entries, although it was without effects on behavioral responses in normal mice. However, SKF 38393 (3 and 10 mg/kg), a dopamine D1-selective agonist, failed to change alternation performance or total arm entries in normal or scopolamine-treated mice. These findings suggest that the impairment of spontaneous alternation performance induced by scopolamine is improved by the blockade of dopamine D2 receptors. Furthermore, the improving effect of dynorphin A-(1-13) on the scopolamine-induced impairment of spontaneous alternation performance may be based upon the inhibition of dopaminergic activity through the mediation of kappa-opioid receptors.