Utility of an elevated plus-maze for dissociation of amnesic and behavioral effects of drugs in mice

Dissociation of memory and anxiety in a repeated elevated plus maze paradigm: forebrain cholinergic mechanisms

The effect of intraseptal injection of the cholinergic immunotoxin 192-IgG-saporin on behavior in the elevated plus maze was investigated. A 5-min test-retest paradigm, with minute-by-minute analysis of the first session, was used to evaluate both anxiety and memory in this task. Biochemical analyses revealed a decrease in acetylcholinesterase (AChE) activity in the hippocampus (HPC), septum, and frontal cortex of animals injected with IgG-192 saporin (237.5 ng) when compared with controls. No statistical differences were found between groups in terms of behaviors associated with locomotor activity, conventional measures of anxiety, or ethological behaviors during either session 1 or 2. During test session 2 the controls exhibited decreased exploratory activity and increased indices of anxiety. In contrast, the saporin-treated rats did not exhibit these experience-dependent behavioral changes from session 1 to 2. The minute-by-minute analysis showed a significant decrease in exploratory as well in anxiety associated behaviors during the first session for the control group, but not for the saporin-treated group. These results suggest that the cholinergic innervation of the HPC, the frontal cortex, or both forebrain structures, modulate the initiation of exploratory activity which, results in the acquisition and retention of spatial information, but does not affect the expression of anxiety in the elevated plus-maze.

Oxiracetam prevents the MK-801 induced amnesia for the elevated plus-maze in mice

We investigated the effect of the nootropic substance oxiracetam on the impairment of memory induced in mice by the non-competitive NMDA antagonist MK-801. Memory capacities of animals having different experience were evaluated using the elevated plus-maze test. Oxiracetam was injected immediately after the acquisition session(s), MK-801 was given 30 min before the retention session which followed 24 h after the acquisition session(s). In slightly experienced animals (Section 3.1), oxiracetam (3 and 30 mg/kg, s.c.) prevented MK-801 (0.15 mg/kg, i.p.) induced memory deficits characterized by a prolongation of the transfer latency. In well-trained animals (Section 3.2), oxiracetam (30 mg/kg, s.c.) attenuated MK-801 (0.15,0. 25 and 0.4 mg/kg, i.p.) induced amnesia for a spatial orientation in the elevated plus-maze. These results show that oxiracetam interacted with the glutamatergic NMDA receptor system and forestalled the impairment of retrieval of long-term memory. The results also justify the usage of the elevated plus-maze method in the evaluation of potential anti-amnesic or nootropic drugs.

Nonconvulsive Kainic Acid-Induced Seizures Elicit Age-Dependent Impairment of Memory for the Elevated Plus-Maze

The goal of this study was to evaluate changes in spatial learning in adult and immature rats during and after nonconvulsive seizures. An elevated plus-maze was used in 18- and 25-day-old and adult rats. Kainic acid (KA 6 mg/kg) was administered 60 minutes before the first exposure (Experiment 1) or after a 3-day pretraining (Experiment 2, only adult rats). Animals were retested three times with 24-hour intervals. EEG activity was monitored in 18-day-old rats. KA prolonged the transfer latency (TL) in all age groups. In the youngest group the TL was prolonged 24 hours after KA when epileptic EEG graphoelements were still registered. In both older groups, prolonged TL was measured only 60 minutes after KA. In the pretrained adults, significantly prolonged TLs persisted for 24 hours after KA. KA changed the performance of adult and immature rats in the elevated plus maze not only during nonconvulsive seizures but also 24 hours later.

Does dihydrohonokiol, a potent anxiolytic compound, result in the development of benzodiazepine-like side effects?

The aims of this study were to assess whether dihydrohonokiol, 3'-(2-propenyl)-5-propyl-(1,1'-biphenyl)-2,4'-diol (DHH-B), a potent anxiolytic compound, developed benzodiazepine-like side effects. A 1 mg kg(-1) dose of diazepam, almost equivalent to the minimum dose for the anxiolytic effect, disrupted the traction performance, potentiated hexobarbital-induced sleeping and impaired learning and memory performance. DHH-B, even at a dose of 1 mg kg(-1) (i.e. five times higher than the minimum dose for significant anxiolytic effect) neither developed diazepam-like side effects nor enhanced the side effects of diazepam. Rather, the potentiation by diazepam of hexobarbital-induced sleeping was reduced by 1 mg kg(-1) DHH-B. Furthermore, mice treated with 10 daily administrations of 1 and 5 mg kg(-1) diazepam, but not 0.2-5 mg kg(-1) DHH-B, showed precipitated withdrawal symptoms characterized by hyper-reactivity, tremor and tail-flick reaction when they were challenged with flumazenil (10 mg kg(-1) i.p.). These results suggest that, unlike the benzodiazepine anxiolytic diazepam, DHH-B is less likely to induce motor dysfunction, central depression, amnesia or physical dependence at the effective dose required for the anxiolytic effect.

Concurrent modulation of anxiety and memory

We have previously shown that the ventromedial prefrontal cortex (vmPFC) is involved in spontaneous working memory and anxiety-related behaviour in CD-1 mice. Specifically, pretrial microinjection of the kappa(1) agonist, U-69,593, in the infralimbic (IL) area of the vmPFC produced a robust anxiolytic behavioural profile in the elevated plus-maze and enhanced spontaneous working memory in the Y-maze. In the present study we sought to determine whether these effects were specific to IL kappa receptors. We hypothesized that microinjection of the kappa antagonist, norBNI, in the IL cortex would influence anxiety and spontaneous memory in an opposite direction to the effects produced by the kappa(1) agonist. In week 1, transfer-latency reference memory and anxiety were tested in the elevated plus-maze in two separate trials with an intertrial interval of 24 h. In week 2, spontaneous working memory was tested in the Y-maze followed immediately by defensive/withdrawal anxiety in the open field for one half of the animals in each group, and the other half was tested in reverse order. Pretreatment with one injection of vehicle, 1, 5 or 10 nmol/0.5 microl norBNI in the IL cortex dose-dependently reduced transfer-latencies and produced an anxiogenic behavioural profile in the first elevated plus-maze trial. Following a 24 h delay, transfer-latency reference memory was not influenced, but a robust anxiogenic behavioural profile was observed in the second no-injection anxiety trial in the elevated plus-maze relative to control animals. In week 2, the same groups of mice were again pretreated with one injection of the same doses of norBNI in the IL cortex and tested in the open field and Y-maze. NorBNI pretreatment was anxiogenic in the defensive/withdrawal anxiety test and disrupted spontaneous working memory regardless of testing order. The present results show the influence of kappa receptor modulation on anxiety induction and spontaneous working memory. These results also support the hypothesis that immediate memory processing may modulate the induction of anxiety-related behaviours.

U-69,593 microinjection in the infralimbic cortex reduces anxiety and enhances spontaneous alternation memory in mice

The present report investigated the contributions of the ventromedial prefrontal cortex to the control of spontaneous alternation/working memory and anxiety-related behaviour. In Experiment 1, we examined the effects of microinjections of the selective kappa(1) receptor agonist, U-69,593, in the infralimbic cortex (IL) of CD-1 mice on several ethologically-derived anxiety indices in the elevated plus-maze (EPM) and defensive/withdrawal (D/W) anxiety in the open field, as well as on memory in the EPM transfer-latency (T-L) test and implicit spontaneous alternation memory (SAP) in the Y-maze. In week 1, pretreatment with one injection of vehicle, 1, 10 or 25 nmol/1.0 microliter U-69,593 in the IL dose-dependently prolonged T-L and produced a dose-dependent anxiolytic behavioural profile in the first EPM trial. Following a 24-h delay, the same mice were given a drug-free second trial in the EPM tests of T-L memory and anxiety. Whereas T-L memory was not disturbed, small but detectable carry-over effects were observed in trial-2 EPM behaviour relative to vehicle-treated animals. In week 2, the same groups of mice were again pretreated with one injection of the same doses of U-69,593 in the IL and given a D/W test in an open field, followed immediately by an 8-min SAP trial in the Y-maze. The smallest U-69,593 dose was anxiolytic in the D/W test, and SAP/working memory was dose-dependently enhanced in the Y-maze. In Experiment 2, we evaluated whether 0.5 microliter volume microinjections would produce comparable behavioural and carry-over effects in the IL of three new groups of CD-1 mice, in the event that the 1.0 microl volume injections used in Experiment 1 diffused beyond the IL and therefore may have confounded some effects. Experiment 2 procedures were carried out in the same manner as in Experiment 1, except the animals were tested in reverse order. Thus in week 1, SAP memory was tested in the Y-maze followed by D/W anxiety in the open field for half of the animals in each group, and the other half was tested in reverse order. In week 2, T/L memory and anxiety were tested in the EPM in 2 trials as described in Experiment 1. Pretreatment with one injection of vehicle, 10 or 25 nmol/0.5 microliter U-69,593 in the IL reduced D/W anxiety and enhanced SAP memory regardless of testing order in week 1. In week 2, the same groups of mice were again pretreated with one injection of the same doses of U-69,593 in 0.5 microliter volumes in the IL and tested in the EPM. In a similar fashion to Experiment 1, U-69,593 dose-dependently prolonged T/L and produced an anxiolytic behavioural profile in the first EPM trial. Following a 24-h delay, T/L recall memory was again not significantly influenced, but a robust anxiolytic behavioural profile was observed in the second drug-free anxiety trial in the EPM relative to vehicle-treated animals. Results are discussed relative to a) injection volumes and testing order, b) the possible influence kappa receptors may exert on neurochemical responsivity to anxiety-provoking environments in the IL area of the mPFC, c) the possibility that kappa-mediated anxiolysis from the IL in CD-1 mice results from interactions with neurochemical systems involved in the blunting of incoming anxiety-provoking information, d) evidence that SAP memory may be an implicit subtype of working memory, and e) the possibility that IL implicit working memory processes may modulate the induction and expression of anxiety-related behaviour.

Brain renin angiotensin system (RAS) in stress-induced analgesia and impaired retention

Physiological stress is known to produce analgesia and memory disruption. Brain renin angiotensin system (RAS) has been reported to participate in stress response and plays a role in the processing of sensory information. Angiotensin receptors (AT), particularly AT1 subtypes have been reported to be distributed in brain areas that are intimately associated with stress response. The purpose of present study was to examine the modulation of AT1 receptor in the immobilization stress and angiotensin II (AngII)-induced analgesia and impaired retention, and to determine whether resultant behavioral changes involve common sensory signals. Result of present experiments showed that immobilization stress in mice and rats, and intracerebroventricular (ICV) administration of AngII (10 and 20 ng) in rats produced an increase in tail-flick latency. Similarly, post training administration of AngII or immobilization stress produced impairment of retention tested on plus-maze learning and on passive avoidance step-down task. Both these responses were sensitive to reversal by prior treatment with losartan (10 and 20 mg/kg), an AT1 AngII receptor antagonist. On the other hand, naloxone, an opiate antagonist preferentially attenuated the stress and AngII-induced analgesia and retention deficit induced by immobilization stress, but failed to reverse the AngII induced retention deficit. These results suggest immobilization stress-induced analgesia and impaired retention involves the participation of brain RAS. Further, failure of naloxone to reverse AngII-induced retention impairment shows. AngII-induced behavioral changes are under control of different sensory inputs.

Involvement of cholinergic system in losartan-induced facilitation of spatial and short-term working memory

In the present study we have shown the potential memory enhancing property of losartan, a selective Ang II AT1 receptor antagonist. Nootropic activity of losartan in mice was assessed by using passive avoidance step-down task and elevated plus-maze as a measure of short-term working and spatial memory respectively. Losartan at higher dose (10 mg/kg i.p) improved the basal performance in retention testing in both the test paradigms. Prior administration of losartan also attenuated retention deficit induced by scopolamine (0.3 mg/kg i.p). Moreover, physostigmine (0.05 mg/kg i.p) potentiated memory enhancing properties of losartan administered at lower dose (5 mg/kg i.p). On the basis of above observations it is concluded that the memory enhancing properties of losartan can be attributed to increased cholinergic activity.

Concurrent administration of subeffective doses of scopolamine and MK-801 produces a short-term amnesia for the elevated plus-maze in mice

Amnesic properties of scopolamine, a muscarinic receptor antagonist, and MK-801, a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, were evaluated in mice by means of the elevated plus-maze test. In this test, transfer latency, the time mice took to move from the open arm to the enclosed arm, was used as an index of learning and memory. The 3-day pretreatment training dramatically decreased transfer latencies. On the 4th day, the retention trial was performed 30 min after the intraperitoneal injection of scopolamine (Experiment 1) or MK-801 (Experiment 2). The doses of 0.25 and 0.5 mg/kg of scopolamine as well as the doses of 0.1, 0.15, 0.2 and 0.4 mg/kg of MK-801 significantly prolonged the transfer latency as compared with both that in the saline-treated group and that measured on the 3rd day. In Experiment 3, subthreshold doses of these two drugs given in combination (which were ineffective when given alone: scopolamine 0.25 mg/kg, MK-801 0.075 mg/kg) significantly prolonged the transfer latency on the fourth day. However, an amnesic effect of scopolamine plus MK-801 was transient. On the 5th day, no differences in the transfer latency were found. This finding clearly indicates that there is a close relationship between cholinergic and glutamatergic systems and that both systems play an important role in a spatial orientation of mice on the elevated plus-maze.

Scopolamine-induced convulsions in food given fasted mice: effects of physostigmine and MK-801

We recently reported that scopolamine pretreated mice fasted for 48 h developed clonic convulsions soon after they were allowed to eat a small amount of food for 30 s. The present experiments were performed to determine whether animals also develop convulsions when they were allowed to eat ad libitum and to find some evidence for the contribution of the cholinergic and/or glutamatergic systems in the underlying mechanism(s) of convulsions. Animals fasted for 48 h were treated with 3 mg/kg scopolamine or saline. Twenty minutes later, they were allowed to eat either ad libitum or a small portion of food for 30 s. Scopolamine pretreated animals after starting to eat ad libitum or a small amount in a restricted time developed convulsions in a few minutes, the incidence being 76 and 54%, respectively. Pretreatment of 0.17 mg/kg MK-801, the noncompetitive NMDA antagonist, decreased the incidence of scopolamine-induced convulsions (22%) without affecting latency to the onset of seizures. Pretreatment of 0.1 mg/kg physostigmine, the cholinesterase inhibitor, changed neither the incidence (90%) nor latency to the onset of scopolamine-induced convulsions.

Effect of alaptide, its analogues and oxiracetam on memory for an elevated plus-maze in mice

In the present study, the elevated plus-maze was used to evaluate memory in female mice. In Experiment 1, the mice retested on day 1, 4 or 7 after the initial session escaped from the open arm into the enclosed arm in a significantly shorter time than those retested on day 10 or 14. Thus, a 10-day inter-session interval was chosen for testing drugs which were expected to enhance memory. In Experiment 2, in the retest performed on day 10, both alaptide (cyclo(L-alanyl-1-amino-1- cyclopentanecarbonyl)) and oxiracetam, given immediately after the 1st session, reduced the transfer latency from the open arm into the enclosed arm as compared with that of the controls. In Experiment 3, a similar effect, i.e., the retention of spatial information, was facilitated by post-session injections of 5 out of 21 alaptide analogues. The new compounds represent the 2,5-piperazinedione derivatives which contain 1-amino-1-cyclo-alkanecarboxylic acid (C3 to C7 ring). The cyclopentane- and cyclohexane-ring was substituted by an alkyl group. In the series with the cycloalkane ring, the importance of the structure of alaptide was confirmed again, which underlines the importance of the cyclopentane ring; the active structures had L-alanine instead of glycine as the second amino acid. Isomers of the cyclohexane series which contained methyl or tert-butyl were most active when the substitution was at position 3. Our results demonstrate that the model of long-term memory can be used to discriminate between closely related chemical structures.

Plus-maze retest profile in mice: importance of initial stages of trail 1 and response to post-trail cholinergic receptor blockade

Recent research has shown that a single undrugged prior experience of the elevated plus-maze produces significant behavioural changes upon 24-h retest in rats and mice. Typically, when reexposed to the maze, animals display an increased avoidance of the open arms and a corresponding preference for the enclosed sections of the apparatus. Using ethological analyses, the present series of experiments sought to further characterize this phenomenon in mice and to determine whether or not it involves cholinergic receptor mechanisms. Results confirmed that behaviour during Trial 2 is markedly different to that seen on initial exposure, and that such changes are independent of the duration of Trial 1 (2 vs. 5 min). Retest behavioural changes included reduced entry latencies, reduced open arm entries, less time on the open arms and centre platform, lower levels of exploratory head-dipping, and increased entries into and time spent in the closed arms. The importance to the retest phenomenon of the first few minutes of initial exposure was further suggested by min-by-min analyses of the behaviour of animals naive to the maze. Results showed that behaviour during the first min is characterized by high levels of risk assessment from the centre platform and relatively low, but equal, levels of open- and closed-arm exploration. From min 2 onwards, however, behaviour showed a marked change with increasing open arm/centre platform avoidance, increasing closed-arm preference, and decreasing levels of risk assessment and exploratory head-dipping. Thus, it would appear that this within-session aversive learning transfers between sessions to account for behavioural profiles on retest. Irrespective of the duration of Trial 1 (2 or 5 min), posttrial administration of the muscarinic antagonist, scopolamine (0.1-1.0 mg/kg), failed to significantly alter the behavioural changes seen between trials. Data are discussed in relation to the apparent sensitization of fear produced by plus-maze exposure, its possible relation to phobia acquisition, and the need for further research on underlying mechanisms.

Only controls: effect of handling, sham injection, and intraperitoneal injection of saline on behavior of mice in an elevated plus-maze

In male NIH-Swiss mice intraperitoneal injection of physiological saline significantly diminished (vs. naive mice) the ratio of the number of entries into open arms over the sum of entries into open and closed arms, and significantly prolonged time spent in closed arms. These two effects are considered to be typical for anxiety-inducing drugs (anxiogens). The time spent in open arms and at the intersection was unaffected. An equal number of entries into closed and also open arms was observed among fast- and slow-moving individuals. This is an argument against using the number of entries into arms as a measure of locomotor activity of mice. Additional measurement of locomotor activity in actometers is needed to check whether drugs used in experiments with elevated plus-maze alter locomotor activity. Injection of saline significantly shortened the latency of reaching one of the closed arms from the free end of an open arm. Handling, sham injection, and injection significantly diminished the shortening of latency in a second experiment (vs the latency in the first one), a parameter used as a criterion of memory and learning. Thus, saline-treated groups taken as controls in pharmacological experiments possess the behavioral profile of stressed and anxious animals in an elevated plus-maze, a device used as a model of anxiety and a model for studying memory and learning in mice and rats.

Ameliorating effects of histidine on scopolamine-induced learning deficits using an elevated plus-maze test in mice

We investigated the effects of histidine on scopolamine-induced learning deficits in the elevated plus-maze test in mice. In this test, 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. Intraperitoneal administration of scopolamine (0.5 mg/kg) prolonged the TL on day 2 compared with that in the saline-treated group. Histidine loading (500, 800 and 1600 mg/kg) reversed the prolongation of the TL induced by scopolamine. This ameliorating effect of histidine was abolished by alpha-fluoromethylhistidine, an inhibitor of histidine decarboxylase, suggesting that histidine itself has no such ameliorating effect. Moreover, the ameliorating effect of histidine was antagonized by a histamine H1 receptor antagonist, pyrilamine. However, zolantidine, a histamine H2 receptor antagonist, showed no antagonism of the effect of histidine. Thus, histamine, a decarboxylated product of histidine, elicited an ameliorating effect on scopolamine-induced learning deficit via histamine H1 receptors in mice. These findings clearly indicated that there is a close relationship between histaminergic and cholinergic systems in the brain, and that histamine may play certain important roles in learning and memory.

PRE-084, a sigma selective PCP derivative, attenuates MK-801-induced impairment of learning in mice

We investigated the effect of the sigma selective PCP derivative PRE-084 on the impairment of learning induced in mice by the noncompetitive NMDA antagonist MK-801. Learning capacities were evaluated using the spontaneous alternation in a Y-maze test for spatial working memory, the step-down passive avoidance and the elevated plus-maze test for long-term memory. At doses about 1 mg/kg IP, PRE-084 significantly attenuated MK-801 (0.2 mg/kg IP) induced impairment of learning. The dose-response curve was bell-shaped which is typical for cognition enhancers. The effect of PRE-084 was antagonized by BMY-14802 (10 mg/kg IP) and suppressed by a chronic treatment with haloperidol (4 mg/kg/day SC for 7 days). Furthermore, PRE-084 did not affect scopolamine (1 mg/kg SC) induced amnesia but significantly attenuated mecamylamine (10 mg/kg IP) induced amnesia. These results show that sigma sites mediate a modulation of the NMDA receptor complex-dependent learning processes and may similarly affect the cholinergic nicotinic memory processes. Moreover, the PCP derivative PRE-084, acting selectively at sigma sites, reverses the amnesia induced by a drug acting at the PCP site.

Behavioral evidence for a modulating role of sigma ligands in memory processes. I. Attenuation of dizocilpine (MK-801)-induced amnesia

The potentiating effect of low doses of sigma ligands on the N-methyl-D-aspartate (NMDA)-induced excitation of pyramidal CA3 dorsal hippocampal neurons has recently been reported. In the present study, we investigated behavioral effects relevant to these findings in the experimental amnesia induced by the non-competitive NMDA antagonist, dizocilpine (MK-801), in mice. At doses below 1 mg/kg s.c., the sigma ligands, 1,3-di-(2-tolyl)guanidine (DTG), (+)-SKF 10,047, and (+)-pentazocine, but not their (-)-isomers, significantly decreased MK-801 (100 microgram/kg s.c.)-induced impairment of spontaneous alternation performances in 8-min sessions of a Y-maze exploration, an index of spatial working memory, without affecting the concomitant hyperlocomotion. The effect of DTG (100 micrograms/kg s.c.) was completely antagonized by the simultaneous administration of BMY 14802 (10 mg/kg i.p.) and NE-100 (1 mg/kg i.p.), two putative sigma antagonists, which had no effect by themselves. In long-term memory tests (step-down and step-through types of passive avoidance, elevated plus-maze), DTG exhibited a significant attenuation of MK-801-induced amnesia, at doses of 10 and 100 micrograms/kg s.c. In all tests of short- and long-term memory, the effects exhibited by the sigma ligands tested had a bell-shaped curve; no effect was seen at 1 mg/kg. DTG did not affect the impairment of alternation induced by CPP (5 mg/kg i.p.): the modulation may selectively target the blockade of NMDA receptor-associated ion channels. Moreover, DTG (1-1000 micrograms/kg) did not affect the impairment induced by scopolamine (1 mg/kg i.p.) or diazepam (4 mg/kg i.p.), but significantly prevented the impairment induced by mecamylamine (10 mg/kg i.p.). These results suggest that the potentiating effect of sigma ligands on NMDA receptor-mediated glutamatergic neurotransmission, already demonstrated electrophysiologically, may have some relevance to learning and memory processes in the hippocampus. A similar modulation may also affect cholinergic nicotinic systems.

Characterization of the effects of scopolamine on the habituation of exploratory activity: differential effects of oxotremorine and physostigmine

1. Habituation was regarded as a difference between exploratory activity measured first (session 1) and that measured second (session 2) in a novel environment. 2. Scopolamine (1.0 mg/kg) significantly increased the horizontal activity in sessions 1 and 2 when administered prior to session 1, resulting in the impairment of habituation. 3. Haloperidol (0.2 mg/kg) inhibited scopolamine-induced hypermotility in session 1, but it did not inhibit the scopolamine-induced impairment of habituation in session 2. 4. The direct cholinergic agonist oxotremorine (0.03 mg/kg), unlike the cholinesterase inhibitor physostigmine, significantly inhibited the scopolamine-induced impairment of habituation in the horizontal and vertical activities. 5. These results suggest that the direct stimulation of cholinergic receptors is more effective for scopolamine-induced amnesia than the indirect stimulation of cholinergic receptors by cholinesterase inhibitors in the habituation task.

Effects of several amnesic drugs on the habituation of exploratory activity in mice as indexed by horizontal and vertical activities

1. The effects of several drugs on the habituation of exploratory activity in mice were investigated by using animal movement analyzing systems which could detect horizontal and vertical activities. 2. Habituation was regarded as the difference between exploratory activity measured first (session 1) and that measured second (session 2). 3. Scopolamine (1, 3 and/or 6 mg/kg), pirenzepine (20 and 40 micrograms) injected immediately after session 1, cycloheximide (30 mg/kg), diazepam (1, 2 and/or 4 mg/kg) and dizocilpine (0.05, 0.1 and/or 0.2 mg/kg), unlike butylscopolamine (1, 3 and 6 mg/kg) or haloperidol (0.2 and 0.4 mg/kg), significantly increased horizontal activity but not always vertical activity in session 2. 4. From the results obtained, it appears that the increase in horizontal activity in session 2 is more appropriate as an indicator of the impairments of memory processes than that in vertical activity.

Titrating matching-to-sample performance in pigeons: effects of diazepam, morphine, and cholinergic agents

Five adult, male White Carneau pigeons were trained to respond under a titrating matching-to-sample schedule of reinforcement. Under this titration schedule, each trial began with the presentation of a sample stimulus (red or green light) on the center key of a three-key pigeon chamber. Completion of 15 responses on the center key resulted in the termination of the stimulus presentation and the initiation of a delay period. The length of the delay changed as a function of the pigeon's performance. During the first five trials of each session, the delay was fixed at 3 s in length. On the sixth and all subsequent trials, the length of the delay was either increased, did not change, or decreased such that accuracy was maintained at approximately 80%. Following the delay, two of the three pigeon keys were transilluminated with different colored lights (red or green). A single response upon the key transilluminated with the same stimulus color as the sample stimulus resulted in the presentation of food. A response on the key transilluminated with the stimulus color that did not match the sample stimulus resulted in a time-out period. Using this procedure, the effects of two drugs of abuse, diazepam (0.03-3 mg/kg) and morphine (0.03-10 mg/kg), a muscarinic antagonist, scopolamine (0.003-0.3 mg/kg), the quaternary derivative of scopolamine, methylscopolamine (0.003-0.3 mg/kg), a cholinesterase inhibitor, physostigmine (0.003-0.1 mg/kg), and the quaternary derivative of physostigmine, neostigmine (0.003-0.1 mg/kg), were determined. Diazepam decreased matching accuracy such that a decrease in the mean delay value for the session was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

U-50,488H, a kappa-opioid receptor agonist, markedly prevents memory dysfunctions induced by transient cerebral ischemia in mice

Transient ischemia produced marked memory dysfunctions in mice on three different tasks, spontaneous alternation, elevated plus-maze and passive avoidance, as tested 1, 1-2, and 2-3 days after ischemic insult, respectively. U-50,488H, a kappa-opioid receptor agonist, administered 20 min before ischemic insult markedly prevented the impairment of spontaneous alternation, the prolongation of transfer latency in elevated-plus maze and the shortening of step-through latency in passive avoidance induced by transient ischemia. The protective effect of U-50,488H (30 mg/kg) on ischemia-induced memory dysfunctions observed in the three tasks was almost completely reversed by pretreatment with nor-binaltorphimine (4 micrograms, i.c.v.), a kappa-selective opioid antagonist. Although U-50,488H (30 mg/kg) did not affect body temperature in sham mice, it blocked hypothermia induced by ischemic insult. These results suggest that the protective effect of U-50,488H on memory dysfunctions in ischemic mice is associated with the activation of kappa-opioid receptors and is not based upon hypothermia.

Dynorphin A-(1-13) markedly improves scopolamine-induced impairment of spontaneous alternation performance in mice

The effect of intracerebroventricular (i.c.v.) injection of dynorphin A-(1-13) on the memory process was examined in mice, using spontaneous alternation performance related to working memory in a Y-maze. Dynorphin A-(1-13) (1, 3 and 10 micrograms) influenced neither spontaneous alternation performance nor total arm entries, which are considered to reflect locomotor activity. In contrast, dynorphin A-(1-13) (3 and 10 micrograms) significantly improved the impairment of spontaneously alternation performance induced by scopolamine (1 mg/kg s.c.). Simultaneously, the scopolamine-induced increase in total arm entries was markedly attenuated by dynorphin A-(1-13) (10 micrograms). The effect of dynorphin A-(1-13) (3 micrograms) on the scopolamine-induced impairment of spontaneous alternation was almost completely reversed by pretreatment with nor-binaltorphimine (4 micrograms i.c.v.), a kappa-selective opioid antagonist. These findings suggest that dynorphin A-(1-13) improves through the mediation of kappa-opioid receptors the scopolamine-induced impairment of spontaneous alternation performance associated with working memory.

Dynorphin A-(1-13) potently prevents memory dysfunctions induced by transient cerebral ischemia in mice

The effect of dynorphin A-(1-13), an endogenous kappa-opioid receptor agonist, on memory dysfunctions induced by transient cerebral ischemia in mice was investigated by using three different tasks, namely, spontaneous alternation, elevated plus-maze performance, and passive avoidance behavior. Transient ischemia produced a marked memory dysfunction in mice, as assessed in the three tasks, which were carried out consecutively 1 to 3 days after the ischemic insult. The i.c.v. injection of dynorphin A-(1-13) before the ischemic insult potently prevented the impairment of spontaneous alternations, the prolongation of transfer latency in the elevated plus-maze and the shortening of step-through latency in the passive avoidance task induced by transient ischemia. Dynorphin A-(1-13) (10 micrograms), however, did not affect the body temperature of the sham-operated or the ischemic mice. The protective effect of dynorphin A-(1-13) (10 micrograms) on ischemia-induced memory dysfunctions observed in the three tasks was almost completely reversed by pretreatment with nor-binaltorphimine (4 micrograms, i.c.v.), a kappa-selective opioid receptor antagonist. These results suggest that dynorphin A-(1-13) prevents memory dysfunctions in ischemic mice through the activation of kappa-opioid receptors.

Evaluation of learning and memory mechanisms employing elevated plus-maze in rats and mice

1. The effect of drugs affecting learning and memory was investigated using transfer latency (TL) as parameter for acquisition and retention of memory process on elevated plus-maze both in rats and mice. Further the validity of the procedure was envisaged. 2. The results provide an evidence for utility of shortened TL on 2nd day trial in old rats and mice as a parameter for retention or consolidation of memory, while treatment of drugs 30 min prior to 1st day may also be utilised for acquisition related action of drugs. 3. The drugs producing acquisition deficits namely scopolamine (0.1-0.5 mg/kg) and MK 801 (0.05-0.1 mg/kg) did not affect the shortened TL on elevated plus-maze in rats while nootropics, like piracetam (150 mg/kg) and captopril (30 mg/kg) reduced the shortened TL. The memory enhancing effect of these agent was reversed by scopolamine (0.3 mg/kg) and MK 801 (0.1 mg/kg) both in rats and mice. The results suggested the acquisition affecting drugs, however, did not show any effect on retention parameter (shortened TL) but can reverse the retention facilitatory action of nootropics. The results also provide indirect evidence for participation of cholinergic and NMDA-receptor blockade in the mechanism of these drugs. 4. Scopolamine and MK 801 produced acquisition deficits in mice, as they increased the TL on 1st and 2nd day trial while physostigmine (0.05 mg/kg) decreased the 2nd day TL. Physostigmine (0.1 mg/kg) reversed scopolamine and MK 801 induced acquisition deficits suggested participation of cholinergic and NMDA- receptor in learning process. 5. The results validate the utility of the elevated plus-maze for evaluation of possible nootropic action of drugs.