Modulary effects of oxytocin and carbetocin on stress-induced changes in rat behavior in the open-field.

Oxytocin (OXY) has been shown to attenuate some of the physiological and behavioral alterations appearing in stressed rats. Carbetocin (CBT), an oxytocin analog [deamino-1-monocarba-(2-O-methyltyrosine)-oxytocin], was designed to exert prolonged action. In the present study we investigated the impact of these peptides on the behavioral changes in rats exposed repeatedly to restraint stressors. Wistar male rats were exposed to restraint for 1 hour; saline or drugs were administered intraperitoneally immediately after stress termination. Recording of the exploratory activity in the open-field started 60 min later. To explore the possibility of persisting effects of stress and/or drugs, the procedure was repeated for three consecutive days. Restraint moderately suppressed locomotion and rearing, and increased grooming. OXY in 0.3 mg/kg dose showed a tendency to restore the suppressed exploratory activity. In contrast, 1 mg/kg dose potentiated the stress-induced behavioral deficit. Both OXY doses slightly increased grooming. CBT in the same two doses restored the stress-induced deficits in locomotion and rearing but did not influence grooming. The locomotor depression after 1 mg dose of OXY was found also in non-stressed rats in contrast to the increased activity after CBT. The data support the view that post-stress administered CBT exerts a significant effect on the stress-altered spontaneous behavior.

Effects of two types of restraint stress on spontaneous behavior of Sprague-Dawley and Lewis rats.

The purpose of this study was to evaluate the action of two types of stressors in Sprague-Dawley (S-D) and Lewis (LEW) rats differing in their hypothalamic-pituitary-adrenal axis activity on locomotion and rearing in an open space. Exposure to restraint immobilization alone (IMO) or this immobilization combined with cold water (22 degrees C) immersion (IMO+C) lasted for 1 h and started 2 or 5 h before the test. To evaluate the acute and persisting effects of both stressors, four trials were performed in one-week intervals; rats were exposed to the stressors in trial 1 and 3. While in LEW rats both acute stressors produced reduction of locomotion and rearing in all stressed groups, S-D rats responded with a decrease of both parameters only after IMO+C presented 2 h before testing. Neither strain displayed a changed performance one week after the first stress exposure. One week after the second stress exposure rats of both strains exhibited a tendency to an increase of both parameters reaching the significance in several experimental groups. The findings indicate: a) the IMO+C produced stronger behavioral alteration than IMO alone; b) the behavioral responses to stressors were more pronounced in LEW compared to S-D strain; c) change from the reduction of activity to its increase may be interpreted as bi-directional manifestation of long-term effects of immobilization stress.

Effects of stress and of amphetamine on passive avoidance conditioning in rats.

This study examined the effects of immobilization stress combined with water immersion (ICS) and/or amphetamine (AM) on different memory phases in the passive avoidance task in rats. The performance of rats was evaluated in the retention tests 24 and 48 h after a single acquisition trial. ICS exposure lasting 1 h impaired retention of the learned avoidance response if applied 2 to 4 h before or immediately after training. The stressor did not affect retrieval if presented 5 or 2 h before the retention test. AM was used i.p. at the dose of 8 or 1 mg/kg. Neither 8 mg AM administered 4 h before nor 8 or 1 mg doses given after training did not impair the retention performance in unstressed rats. The 1 mg AM prevented the impairment of retention in animals exposed to the stressor 3 or 4 h before training but had no effect when the stronger impairment was induced by ICS 2 h before training. However, when given 1 h before retention testing, 1 mg AM attenuated even the severe impairment induced by the pre-training stressor exposure. Our results suggest that ICS impairs primarily the early phase of memory consolidation and a low dose of AM can prevent this effect.

Kynurenic acid prevented social recognition deficits induced by MK-801 in rats.

MK-801 impaired social recognition potency of adult male rats when given immediately after the initial interaction with a juvenile rat. Administration of kynurenic acid prior to the initial interaction protected the adults against recognition deficits induced by MK-801. When re-exposed at a delay of 30 min to the familiar juvenile, social investigation in the adults was significantly reduced. Thus, the adults are able to remember olfactory stimuli emitted by juvenile con-specifics.

N-methyl-D-aspartate prevented memory deficits induced by MK-801 in mice.

An interaction between N-methyl-D-aspartate (NMDA) and MK-801 was examined in mice using a modified elevated plus-maze paradigm that allows assessment of the adaptive form of spatial memory. NMDA administered (s.c.) immediately after the acquisition session protected the animals against the amnesia induced by MK-801 given shortly before the retention session. Behavioral performance, expressed as the transfer latency, and therefore spatial memory potency of NMDA plus MK-801 treated animals was comparable with that of both NMDA-treated animals and the controls.

Impaired passive avoidance acquisition in Wistar rats after restraint/cold stress and/or stresscopin administration.

Stresscopin (SCP) and related peptides are new members of the corticotropin-releasing factor (CRF) peptide family that are selective ligands for CRF type 2 receptor; these ligands are essential for maintaining homeostasis after stress. SCP (i.p. injections) was tested on the passive avoidance learning task in stressed Wistar rats; it impaired the formation of memory trace. The retention performance deficit induced by SCP was comparable with the deficit induced by the stressor of restraint/cold. More profound impairment of avoidance response occurred following combined application of SCP and stressor. More specific actions of SCP can be expected from its studies with targeted intracerebral applications.

An animal model of nonconvulsive status epilepticus: a contribution to clinical controversies.

PURPOSE: To characterize electroencephalographic and behavioral effects as well as electrophysiologic and morphologic consequences of a subconvulsive dose of pilocarpine in lithium chloride-pretreated rats. METHODS: Pilocarpine (15 mg/kg) was administered intraperitoneally to adult rats pretreated with lithium chloride (3 mEq/kg, i.p.). Behavior was observed for 2 h and videotaped in three consecutive sessions. At the same time, EEG was recorded from the sensorimotor cortex and the dorsal hippocampus. Threshold intensities of currents necessary to elicit hippocampal afterdischarges were determined 24 h and 1 week after the pilocarpine administration. The brains were histologically examined 1 week after pilocarpine administration using Nissl stain. RESULTS: Pilocarpine induced time-limited nonconvulsive status epilepticus (NCSE). Epileptic EEG activity concurrent with prominent behavioral features was observed both in the neocortex and, predominantly, in the hippocampus. No changes in afterdischarge thresholds were observed in the dorsal hippocampus 24 h and 1 week after NCSE. One week after NCSE, seizure-related brain damage was found mainly in the motor neocortical fields. CONCLUSIONS: Pilocarpine-induced NCSE in rats strongly resembles a short-term human complex partial status epilepticus. Our animal model is suitable for studying the possible adverse effects of prolonged nonconvulsive seizures.

Nonconvulsive status epilepticus in rats: impaired responsiveness to exteroceptive stimuli.

An animal model of human complex partial status epilepticus induced by lithium chloride and pilocarpine administration was developed in our laboratory. The objective of the study was to provide a detailed analysis of both ictal and postictal behavior and to quantify seizure-related morphological damage. In order to determine the animal's responsiveness to either visual or olfactory stimuli, adult male rats were submitted to the following behavioral paradigms: the object response test, the social interaction test, and the elevated plus-maze test. The rotorod test was used to evaluate motor performance. Two weeks after status epilepticus, brains were morphologically examined and quantification of the brain damage was performed. Profound impairment of behavior as well as responsiveness to exteroceptive stimuli correlated with the occurrence of epileptic EEG activity. When the epileptic EEG activity ceased, responsiveness of the pilocarpine-treated animals was renewed. However, remarkable morphological damage persisted in the cortical regions two weeks later. This experimental study provides support for the clinical evidence that even nonconvulsive epileptic activity may cause brain damage. We suggest that the model can be used for the study of both functional and morphological consequences of prolonged nonconvulsive seizures.

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.

Behavioural effects of a subconvulsive dose of kainic acid in rats.

Kainic acid can induce a continuum of non-convulsive seizures characterised by epileptic automatisms and convulsive motor seizures depending on the dose. There are scarce data on the behavioural effects of low doses of kainate inducing only non-convulsive seizures. Therefore, we studied spontaneous behaviour of adult male rats using a method of positive habituation based on a detailed analysis of patterns and attention of animals to a stimulus object. Twenty-three animals were individually tested in the experimental arena on two consecutive days. Comparing the data from the first two exposures, a conspicuous habituation in all animals was observed. On experimental day 3, 12 rats received kainate (6 mg/kg intraperitoneally) and the remaining 11 animals received a physiological saline. After 1 h, animals were put into the arena with an object localised in the centre. It was found that both kainate and saline treated animals exhibited a significant increase in the total number of central area visits, and both the total and mean time spent in the vicinity of the object. However, the mean time spent was significantly shorter in kainate treated rats. Furthermore. kainate rats exhibited a significant decrease in rearing as compared with the controls. In addition, an epileptic automatism (wet dog shakes) was observed in seven out of 12 animals given kainate. The comparison of transition matrices between consecutive behavioural categories showed significant differences between the kainate and control groups. Our results demonstrate that a non-convulsive dose of kainate induced changes in the structure of spontaneous behaviour and impaired the processes related to maintenance of attention.

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.

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.

Kynurenic acid and 5,7-dichlorokynurenic acids improve social and object recognition in male rats.

The present study describes the effect of kynurenic (KYNA) and 5,7-dichlorokynurenic (DCKA) acids, acting as selective antagonists at the glycine site on the NMDA receptor complex, upon short-term memory of male rats. Oxiracetam (OXIR) or pramiracetam (PRAM) were used as reference compounds. In the social recognition test, adult animals were injected SC with a drug or vehicle immediately after the first exposure to a juvenile male, 21-24 days old, and reexposed to the same or a novel juvenile 120 min later. Time spent by adults in social investigation of juveniles was measured. Animals treated with KYNA or DCKA (0.3, 3 and 30 mg/kg in both cases) and OXIR (30 and 60 mg/kg) had significantly reduced investigation time when reexposed to the same juvenile as compared to controls. No reduction of investigation time was found in those drugged animals reexposed to a novel juvenile. The findings suggest that KYNA and DCKA improved retention of memory for olfactory stimuli in adult male rats. In the object recognition test, the duration of exploration of two identical objects during the sample trial and the familiar and a new object during the choice trial, performed 60 min later, was evaluated. Drugs or vehicles were administered SC 30 min prior to the sample trial. On choice one, animals treated with KYNA or DCKA (0.6 and 30 mg/kg in both cases) and PRAM (30 mg/kg) spent more time in exploring a new object than the familiar one as compared to controls. This suggests that the drugged animals were able to remember the familiar object.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of excitatory amino acid antagonists on social recognition of male rats.

The effects of NMDA and non-NMDA glutamate receptor antagonists were evaluated on social recognition of adult male rats. Adult animals were injected (s.c.) with drug or saline immediately after the initial exposure to a juvenile male, 21-24 days old, and re-exposed to the same or to a novel juvenile 30min later. If the time spent by animals in social investigation during re-exposure to the same juvenile was comparable with the time measured during the initial exposure and with the time of animals re-exposed to a novel juvenile, the effect of a drug was designated as amnesia. Such an effect was found in adult animals administered 1 and 1.5mg/kg phencyclidine, 0.1mg/kg dizoclipine, 2.5mg/kg CPP, and 4mg/kg CGS 19755. Amnesic effects were observed at doses not affecting motor performance. No amnesic effect was produced by CNQX and NBQX (2.5, 5 and 10mg/kg). These results show that while recognition capacity in adult male rats is disrupted by several NMDA antagonists, non-NMDA antagonists do not interfere with short-term retention of individual odours. This suggests that NMDA glutamate receptors may be involved in the processing of socially relevant olfactory information.

Social recognition in ovariectomized and estradiol-treated female rats.

The behavioral phenomenon of social recognition has been extensively investigated in male rats. The present paper provides an insight into the recognition capacity of female rats studied throughout a sequence of hormonal states: after ovariectomy, after estradiol treatment, and several weeks after the termination of estradiol therapy. Investigatory behavior of the female oriented toward a juvenile male, 22-24 days old, was recorded during the 5-min exposure period. Reexposure was performed 30 or 120 min after the initial exposure. Reduction of the investigation time during reexposure to the same juvenile was used as a recognition criterion. It was found that: (a) Three weeks after ovariectomy, the investigation time of females was decreased upon reexposure to the same juvenile at 30 min. At this time point the investigation time of females reexposed to a novel juvenile was similar to that observed during the initial exposure. Both the same as well as a novel juvenile were thoroughly reinvestigated by females when 120 min elapsed between exposures. (b) Three weeks later, administration of estradiol dipropionate to ovariectomized animals (always 100 micrograms per animal at Days 10 and 3 before the testing) resulted in reduced investigation time during reexposure to the same juvenile at both 30 and 120 min. (c) Original time-response relations in the investigation appeared 6 weeks after the termination of estradiol treatment. These findings suggest that the presence of estradiol may be crucial for female recognition of males 120 min after a brief encounter.(ABSTRACT TRUNCATED AT 250 WORDS)

[Sabeluzole and flunarizine in memory processes: animal studies]. / Sabeluzol a flunarizin v pametových procesech: animální studie.

The memory enhancing properties of sabeluzole nad flunarizine were evaluated in two experimental paradigms in male rats. First, we studied the protective action of both drugs against a chlordiazepoxide-induced impairment of habituation. Sabeluzole (5 or 25 mg/kg) or flunarizine (10 mg/kg) were administered sc 1 hr before and chlordiazepoxide (20 mg/kg) immediately after the acquisition session. In the retention session 72 hr later, chlordiazepoxide treated animals displayed higher locomotor and exploratory activities and this effect was blocked by pretreatment with sabeluzole or flunarizine. The results suggest that both drugs prevented amnesic effect of chlordiazepoxide. The second paradigm was the social memory test in which the time spent in social investigation behaviour toward a familiar or a novel juvenile conspecific was used to measure the duration of the memory that the animal forms of the juvenile. Sabeluzole (25 mg/kg) or flunarizine (3 mg/kg) were injected to the adults immediately after the initial exposure. Reexposure to the same or a novel juvenile was done 2 hr later. In contrast to controls, sabeluzole-treated animals showed a significant reduction in social investigation during reexposure to the same juvenile. Since there was no effect on investigation of a novel juvenile, results suggest that sabeluzole-treated rats are able to remember longer the individual characteristics of juvenile rats obtained through olfactory cues during a short social interaction. The time spent by adults treated with flunarizine in the investigation the same juvenile during reexposure was similar to that observed during the initial exposure. It means that flunarizine was ineffective in enhancing short-term olfactory memory.

[Flunarizine and sabeluzole improves behavior disorders caused by cold-induced cortical lesions in mice]. / Flunarizin a sabeluzol zlepsují behaviorální poruchu indukovanou chladovou kortikální lézí u mysí.

The present paper reports two experiments is which an effect of sabeluzole and flunarizine upon behavioural consequences reflecting ischemic damage following cortical freezing lesions was evaluated in NMRI female mice. The parietal lesion was performed by applying a flat (2 mm in diameter) of a metal probe cooled to -75 degrees C on the exposed skull for 5 s. Flunarizine (15 mg/kg) was administered sc 1 hr before and 4 hr after performing the lesion and then, 1 mg/kg p.o. once daily for 14 days. Sabeluzole (5 mg/kg) was administered p.o. 1 hr before and 5 hr after performing the lesion and then, 5 mg/kg p.o. once daily for 14 days. Hole--board method was used to evaluate the exploratory head-dips activity of an animal in 5 sessions separated by 24 hr intervals during the postlesion testing from the 20th to the 24th day, i.e. from day 6 to 10 after finishing the treatment. The session lasted 5 min. In both experiments, the mean number of exploratory hole visits in lesioned female mice was significantly increased. Both flunarizine and sabeluzole reduced high hole exploration of lesioned mice to levels corresponding to those of the controls. Neither flunarizine nor sabeluzole affected significantly exploratory hole visit of control animals. Results showed that flunarizine as well as sabeluzole ameliorated behavioural disturbances reflecting the brain impairment induced through cortical freezing lesion. This effect is most probably related to the protective effect of both drugs against hypoxia induced in laboratory animals by several experimental procedures. The hole--board method seems to be suitable for the screening of compounds considered as cerebroprotective drugs.

Prolonged social recognition in male rats treated with alaptide or oxiracetam.

Male rats form short-term memory for the olfactory characteristics of juvenile conspecifics. Alaptide, a synthetic derivative of the hypothalamic MIF, given subcutaneously at doses of 0.5 and 1.0mg/kg immediately after the initial exposure to an adult male, reduced the time spent by adults in social investigation of the same juvenile upon re-exposure 4h, 24h and 72h after the initial exposure. Oxiracetam (30 and 60mg/kg) had a similar effect. Both drugs were ineffective in animals re-exposed to a novel juvenile. Thus, both alaptide and oxiracetam improved an animal's capacity to recognize the juvenile. The findings may be interpreted in terms of a prolonged retention of memory traces based on olfactory information received during a short social interaction.

Sabeluzole improves social recognition and antagonizes chlordiazepoxide's effect on habituation in the rat.

The memory enhancing properties of sabeluzole were evaluated in two experimental paradigms in rats. First, we determined the protective action of sabeluzole against a chlordiazepoxide-induced impairment of habituation. Sabeluzole (5 or 25 mg/kg, SC) was administered 1 h before and chlordiazepoxide (20 mg/kg, SC) immediately after the acquisition session. In the retention session 72 h later, chlordiazepoxide-treated animals displayed higher locomotor and rearing activities and this effect was blocked by pretreatment with sabeluzole. The results suggest that sabeluzole prevented the amnesic effect of chlordiazepoxide. The second paradigm was a social recognition test in which the behaviour toward a familiar or a novel conspecific was investigated. Time spent in social investigation and time spent sniffing of scent traces left on the floor was estimated during exposure of an adult to a juvenile male rat. Sabeluzole (25 mg/kg, SC) was injected into the adults immediately after the first exposure. Reexposure to the same or a novel juvenile was performed 120 min later. In contrast to control, sabeluzole-treated animals showed a significant reduction in social investigation during the second exposure to the same juvenile. Time spent sniffing the floor was significantly decreased in sabeluzole-treated males. Since there was no effect on investigation of a novel juvenile, results suggest that sabeluzole-treated rats are able to remember longer the individual characteristics of juvenile rat obtained through olfactory cues.

Modulation of social memory in rats by alaptide, a derivative of MIF.

The effect of alaptide, a synthetic derivative of the hypothalamic MIF, upon social memory of intact adult males (Experiment 1), castrated males (Experiment 2), ovariectomized females (Experiment 3) and aged females (Experiment 4) in rats was studied. Social investigation oriented toward a juvenile male (22-24 days old) was used as the measure of social recognition. In addition, sniffing behaviour by adult animals was evaluated during the exposure. Alaptide at the dose of 1.0 mg/kg, and 0.5 mg (Experiment 1), was injected sc immediately after the initial exposure. Reexposure of animals to the same or a novel juvenile was performed 120 min later. Time spent in social investigation by alaptide-treated intact males as well as by ovariectomized females was significantly reduced upon reexposure to the same juvenile. This reflects memory specific effect of alaptide, i.e., the animal is able to recognize individual olfactory characteristics of the juvenile. On the contrary, alaptide was ineffective in enhancing social recognition in castrated males and in aged females. Because the alaptide-treated animals spent less time in social investigation if reexposed both to the same and to a novel juvenile, the finding is considered as reflecting a non-specific effect. The results are discussed from a point of view of the importance of androgens or estrogens in the modulation of social recognition and of a male's or female's capacity to process and to retain olfactory information under the influence of alaptide. With the exception of intact adult males, all tested animals devoted less time to sniffing behaviour during reexposure so that habituation to the experimental environment took place in them. Thus, social investigatory behaviour and sniffing behaviour seem to be two different behavioural systems with different neurobiological mechanisms.