Opposite action of oxytocin to vasopressin in passive avoidance behavior in rats

The effect of oxytocin and lysine-8-vasopressin on step-down passive avoidance behavior has been studied in rats. Step-down latency was considerably shortened after treatment with oxytocin and lengthened by vasopressin. The data suggest an opposite action of oxytocin to vasopressin on step-down latency.     

Effects of retention interval and gonadectomy on sex differences in passive avoidance behavior

Female rats show more response suppression in aversively motivated learning when the effect of presentation of an aversive stimulus upon subsequent responding is measured immediately, whereas males show more suppression in procedures in which the effect of an aversive stimulus is measured after longer intervals. To test whether this divergence can indeed be attributed to temporal parameters, step through passive avoidance was studied using various intervals between shock and retention trial. In contrast to the hypothesis, males showed more response suppression than females when tested directly after shock presentation. This sex difference was also observed at longer intervals. The highest levels of passive avoidance was observed at a 15 minute interval in all groups. Ovariectomy had no effect on the performance of females, but castration of males significantly decreased their performance. These findings demonstrate that the presence of testosterone in adulthood is critical for the masculine pattern of this behavior.     

Fear behavior and passive avoidance deficits in mice with amygdala lesions

Mice with lateral amygdala lesions showed a deficit in passive avoidance behavior during a 10-min test of shock-contingent activity. Although these mice received more shocks than controls they displayed little or no evidence of fear behavior and continued to make punished responses throughout the test period. These results, together with those of previous studies, suggest that the impairment in shock motivated behavior in animals with amygdala lesions is due to a decrement in fear arousal.     

Combined effects of ECS and Metrazol on passive avoidance learning

The combined effects of a non-convulsant dosage (10 mg/kg of body weight) of Metrazol and 60 min ECS were investigated in order to find out if the interaction of the two would produce an amnesic effect upon passive avoidance learning. The main group of rats was given FS, with an immediate posttrial injection of Metrazol, followed by ECS at 60 min. Four other groups were given footshock (FS) followed by saline injection. Three of these 4 groups received ECS following FS at 30, 45, and 60 min respectively, leaving one group receiving only footshock. The footshock only and 60 min ECS groups had the same mean starting and running times, indicating no amnesia with 60 min ECS. The Metrazol 60 min ECS group had a significant retention deficit, falling between the 45 and 30 min groups. The results support the consolidation disruption hypothesis of ECS induced amnesia, and are contrary to the incubation interpretation of these effects.     

Effects of septal lesions on passive avoidance behavior using ice water as the aversive stimulus

Passive avoidance behavior following septal lesions was studied using an aversive stimulus which consisted of dropping the rat into ice water. In contrast to the inferior passive avoidance acquisition and retention when electric shock is used as the aversive stimulus, in the present study rats with septal lesions displayed superior retention of the passive avoidance response.     

Sexual dimorphism in passive avoidance behavior of rats: Relation to body weight,age, shock intensity and retention interval

Female rats were inferior to age- and weight-matched males in the retention of a step-through type passive avoidance response 24 and 48 hr after the learning. This sex difference could be observed at different intensities of foot shock which was used as aversive stimulus during the single learning trial. Additionally, unlike in males, retention of the passive avoidance response in the females was not the function of shock intensity. Male and female rats, however, showed similar passive avoidance if tested immediately after the learning trial. The results suggest the existence of sexual dimorphism in memory processes.     

Time-dependent effects of post-trial reinforcement,punishment or ECS on passive avoidance learning

Three studies were performed to assess the effects of posttrial food reinforcement, ice-water punishment, and ECS on step-down passive avoidance learning in mice. The treatments were each administered at <5, 30, 60 and 90 sec after the footshock. One-half min of feeding beginning either 10 or 30 sec after the footshock increased the step-down latencies 24 hr later. This was considered to support the hypothesis that reinforcement facilitates learning by a direct influence on short-term memory processes. Posttrial ice-water punishment (10 sec immersion) disrupted learning only in the 60 sec postshock delay group. ECS (5.4 mA, 0.35 sec, across the ears) disrupted learning at all posttrial delays except 90 sec, with maximal effects immediately and at 60 sec, and minimal disruption at 30 sec. Similarities in the topography of the ECS and punishment curves suggested that some of the effects of posttrial ECS could be due to aversive properties of the ECS (acting directly on memory processes).     

Deficits in passive avoidance and fear behavior following bilateral and unilateral amygdala lesions in mice

Bilateral amygdala lesions severely disrupt passive avoidance and fear behaviors. The effects of unilateral amygdala lesions on these behaviors are unclear, though unilateral lesions in other structures produce deficits similar to those produced by bilateral lesions. In the present experiment, female mice with unilateral or bilateral amygdala lesions manifested similar patterns of passive avoidance and fear behavior deficits. The results are discussed in light of previous passive avoidance and unilateral lesion studies.     

Effects of hippocampal lesions on passive avoidance and taste aversion conditioning

Rats with electrolytic lesions of the posteroventral hippocampus failed to perform a simple passive avoidance of footshock but showed conditioned aversion to a saccharin solution paired with apomorphine induced gastrointestinal distress. On the other hand, anterodorsal hippocampal lesions interfered with performance on both tasks. The more general deficit produced by the dorsal lesions is attributed to the fact that such lesions extended into the fimbria, and thus destroyed outputs from a larger area of the hippocampus.     

Septal lesions,cue availability,and passive avoidance acquisition by hooded male rats of two ages

When a clearly relevant cue contingency was available, the performance of young adult hooded male septal rats did not statistically differ from that of cued or noncued control animals in the acquisition of a shock passive avoidance task. Noncued young adult septal rats did, however, display the septal deficit classically observed under these conditions. The provision of cues did not improve the performance of older septal rats in terms of number of shocks to criterion; but cued rats with septal lesions in both age groups did require fewer daily sessions to meet the acquisition criterion than their control counterparts. These results suggest important age-related attentional differences between septal and control rats.     

The number of pre-shock trials affects sex differences in passive avoidance behavior

Different groups of male and female Wistar rats were exposed to a standard passive avoidance procedure in which the number of pre-shock trials was experimentally manipulated (1, 3 or 9 trials). Sexually dimorphic passive avoidance behavior was observed after 1 and 3 pre-shock trials. Entrance latencies on the pre-shock trials did not differ for males and females after 1 trial. In the 3 trial condition, latencies differed between the sexes and were also a function of repeated trials for male subjects, as their latencies increased over trials, while those of females did not. When 9 pre-shock trials were presented, the sex difference in entrance latencies was still observed, but latencies increased for both males and females. Although the results of the experiment suggest that sex differences in passive avoidance behavior might be attributable to sex differences in habituation processes to the stimuli associated with exposure to the platform, correlations between the latencies on the final pre-shock trial and behavior on the post-shock trial were not significant. The variables responsible for the occurrence of sexual dimorphism in passive avoidance behavior remain, therefore, largely unknown. The interpretation of this behavioral difference in terms of more general differences between males and females should proceed very cautiously.     

Microinjection of arginine8-vasopressin antiserum into the dorsal hippocampus attenuates passive avoidance behavior in rats

Antiserum to arginine⁸-vasopressin was microinjected bilaterally into the dentate gyrus of the dorsal hippocampus and the effect on passive avoidance behavior was studied. After the single learning trial of a passive avoidance response, immediate bilateral injection of 1 μl antiserum (diluted to $\text{1}\text{50}$) attenuated passive avoidance responding 24 hr later. In immunocytochemical control studies with injection of undiluted antiserum into the dentate gyrus a spreading was observed towards the ventral hippocampus and the dorsal septum. Additionally, administration into the lateral ventricle of 2 μl of $\text{1}\text{50}$ dilution of the antiserum did not affect the behavior. For an attenuation of passive avoidance behavior via intraventricular injection, 2 μl of a $\text{1}\text{10}$ dilution of anti-AVP was required. These data suggest that endogenous vasopressin in the septo-hippocampal system might be involved in memory processes.     

The effect of a choice alternative on sex differences in passive avoidance behavior

A modified standard passive avoidance conditioning procedure was used to investigate whether or not "inferior" passive avoidance behavior of female Wistar rats could be attributed to memory deficits. Male and female Wistar rats were first adapted to two standard passive avoidance conditioning compartments, which were clearly different from one another. Both compartments were accessible from the same illuminated platform. Three learning trials in one compartment were alternated with three trials in the other compartment and unavoidable shock was presented on the last (6th) learning trial in one of the compartments. One hour after shock presentation, subjects were again placed on the platform. Significantly more females than males reentered one of the compartments. Of the subjects which reentered , significantly more females and males than would have been expected by chance, entered the compartment in which shock had not been presented. The data are interpreted to show that sexual dimorphism in passive avoidance behavior should not be attributed to differences in memory capacities of male and female rats. Therefore, it remains to be determined which variables associated with hormonal or genetic background of the subjects and which requirements of the experimental task, are responsible for the occurrence of the observed difference.     

Cue-induced recall of a passive avoidance response by rats with hippocampal lesions

Two experiments are reported in which a stimulus reminder technique was used in an attempt to compensate for the disruptive effects of hippocampal lesions on passive avoidance (PA) conditioning. Groups of hippocampal, cortical and operated control rats were trained to run down an alley for water reward. When the approach response had stabilized, shock was introduced in the goal-box, resulting in increased running times in the control groups and the characteristic PA impairment in the hippocampal group. A recall test was administered 24 hr later but 2 hr before the test, animals were reminded of the previous treatment by being exposed to: (1) shock and related stimuli, (2) related stimuli only, or (3) neutral stimuli. The PA performance of the hippocampus groups in the recall test improved to the level of controls following conditions 1 or 2; there was no effect of condition on Treatment 3. Performance of control groups was virtually unaffected by any of the reminder conditions. The similarities were noted between these results and those of partial cueing studies involving human amnesics with known or suspected damage to the hippocampal system.     

Sex,age and shock-intensity as factors in passive avoidance

Sex, age and shock-intensity were studied in a step-through passive avoidance test. In adult rats (140 days) males showed more inhibition of a previously punished approach response. No sex differences were observed in young adult animals (60 days). In prepuberal animals (30 days), on the other hand, it was the females which showed more response inhibition. In prepuberty females showed far more response inhibition than in adulthood. Even when using 1.6 mA as a reinforcer, only 17% of the adult females showed inhibition after punishment of the entering response.     

Effects of amygdaloid lesions on the performance of rats in four passive avoidance tasks

The effects of amygdaloid lesions on shock punished step-down and rearing responses, quinine punished drinking, and ice water punished step-through responses were investigated in 4 experiments. Amygdaloid lesions impaired the suppression of step-down, rearing, and step-through responses but had no effect on the suppression of quinine consumption. Various interpretations of the response disinhibitory effects of amygdaloid damage are considered. It is concluded that no unitary explanation adequately explains this phenomenon. More extensive investigations of the conditions producing response disinhibition and their anatomical organization are suggested.     

Effect of lithium on morphine state-dependent memory of passive avoidance in mice

In the present study, effects of lithium chloride (LiCl) on morphine induced state-dependent memory of passive avoidance task were examined in mice. One-trial step-down paradigm was used for the assessment of memory retention in adult male NMRI mice. Administration of morphine (5 mg/kg) subcutaneously (s.c.) 30 min before training or testing induced impairment of memory performance. Injection of the same dose of the drug 30 min before testing restored memory retention impaired under pre-training morphine effect. Intraperitoneal (i.p.) injection of lithium, 60 min before training or prior to testing also impaired memory performance. Under the pre-training of morphine, the response of the opioid was restored when animals received LiCl (80 and 160 mg/kg) as pre-test injection. Pre-training administration of lower dose of lithium (20 mg/kg), but not the higher doses of the drug (80 and 160 mg/kg) impaired memory retention in passive avoidance test. LiCl-induced impairment of memory retention was restored by pre-test administration of morphine. In the animals receiving pre-training morphine, combined pre-test morphine and LiCl administration increased the restoration of memory by the opioid. It can be concluded that there may be a cross-state dependency between morphine and lithium.     

Open-field behavior, habituation and passive avoidance learning: Effect of ACTH and hydrocortisone on Normal and adrenalectomized rats

Exploratory behavior (GMA) and habituation rate (IH) were studied in an open-field situation in normal and adrenalectomized rats. Following this procedure the rats were subjected to passive avoidance learning (PA). Wide-spreading individual differences were observed in the exploratory behavior and the tendency of habituation of normal rats. As compared to the normal values, either the adrenalectomy which was performed 24 hr, 7 days and 28 days prior to the experiments or the ACTH and hydrocortisone treatment failed to modify the GMA and the IH significantly. An improvement of PA was found in the normal rats following ACTH and hydrocortisone treatment. In the adrenalectomized animals the hydrocortisone proved to be effective, whereas ACTH did not influence PA. No correlation was found between GMA, IH versus PA values and the influence of ACTH and hydrocortisone administration on these parameters. It is concluded that the direction of PA is unpredictable on the basis of the open-field test performed on R-Amsterdam strain of rats, and the effect of ACTH on passive avoidance learning is mediated through the adrenal glands.     

Effects of olfactory bulb removal on fear responses and passive avoidance in the rat

Following complete bulbectomies, male hooded rats showed an increase in irritability and difficulty of handling, but a decrease in timidity or fear responses. After rats had learned to drink in an open field, a cat was confined in the center, and fear was defined by the behavior of controls, viz., almost total suppression of drinking and long periods of freezing, broken by brief bursts of high-speed activity. Bulb animals could not have differed more radically. Bulbs showed neither freezing nor suppression of drinking. The present results could not be attributed to differences in shock reactivity; nor could they be attributed to differences in learning or retention. Bulb animals also showed an impairment on the acquisition of step-down passive avoidance but no difference in step-downs after acquisition. These results argue against an impairment of response inhibition. The present study suggests that bulbectomy increases irritability and decreases timidity.     

Passive and active avoidance behavior in the light-dark box test

The temporal evolution of passive and active avoidance behaviors has been followed in rats, using the light-dark box test, by measuring step-through and exit latencies. The employed schedule consisted of three 7 day periods (free exploration, reinforced learning, forced extinction-retention). The data show clearly that the two learned behaviors are both rapidly established and exhibit significant differences only during extinction, active avoidance apparently depending on close temporal reinforcement. The diverse role of several behavioral and neurological mechanisms is hypothesized.