Aldo Giachetti

Effects of nucleus basolateralis amygdalae neurotoxic lesions on aversive conditioning in the rat

After bilateral stereotaxic administration of ibotenic acid on the n. basolateralis amygdalae, male adult rats were tested in the light-dark box apparatus to measure the time-course of the acquisition and retention of passive and active avoidance responses. The results show that after the lesions both passive avoidance and active avoidance acquisition were impaired. Passive avoidance responses were retained quite well, while active avoidance responses disappeared quickly. Conditioned freezing was almost completely absent. Thus it appears that the n. basolateralis plays a facilitatory role in all the conditioned responses which were investigated.

Effects of nucleus basolateralis amygdalae neurotoxic lesions on some spontaneous activities in the rat.

Drinking, feeding, locomotion and exploratory activity of male Wistar rats were assessed after bilateral stereotaxic administration of ibotenic acid in the nucleus basolateralis amygdalae. Feeding, drinking and locomotion were measured in an activity cage, while exploratory activity was determined in a multiple Y-maze. In the 24-hour cycle, lesioned animals exhibited unvaried feeding, decreased drinking and increased locomotion. Exploration was also increased. The results show that this nucleus is not involved in quantitative feeding control, while it does exert a significant facilitatory influence on drinking. It also exerts an inhibitory influence on exploration and on locomotion.

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.

Some factors influencing conditioned and spontaneous behavior of rats in the light-dark box test

Step-through and exit latencies in the light-dark box test were used to examine the effects of unconditioned exploration, the physical characteristics of the apparatus and detention on passive and active avoidance. Experiment 1, in which the subjects (Ss) received inescapable shocks in the dark chamber, shows that omission of the free exploration of the apparatus does not significantly affect acquisition and retention of either of the learned responses. Further, passive avoidance, compared with active avoidance is, by far, the better consolidated response. Experiment 2, which is the reverse of Experiment 1, (the dark chamber becomes the safe box, and the punishments are administered in the light chamber) emphasizes the role played by the physical characteristics of the two chambers of the apparatus. This role is shown by the improvement of the active avoidance response. Experiment 3 confirms the importance of detention in influencing the behavior of conditioned and control Ss. These results underscore the basic differences of active and passive avoidance responses.

The behavior of the homozygous and heterozygous sub-types of rats which are genetically-selected for diabetes insipidus: a comparison with Long Evans and Wistar stocks.

Several aspects of spontaneous and conditioned behavior (food and water intake, locomotion and emotionality, passive and active avoidance acquisition and retention) of standard (albino and pigmented) rats, and rats heterozygous (HEDI) and homozygous (HODI) for diabetes insipidus, are reviewed. As would be expected, HODI rats have been repeatedly found to consume far more fluid than either HEDI or control rats. Pigmented rats appear to be more active than albinos. HODI rats exhibit less marked emotional responses than do control rats, among which the pigmented ones exhibit the highest emotionality. Light aversion is more evident in albino than in pigmented rats. No differences are found among HEDI, HODI and normal Long Evans rats. It is quite difficult to provide a clear-cut statement concerning inter-strain differences in passive avoidance behavior, possibly because of the variety of techniques employed. In any case, HODI rats do not perform worse than normal controls do. In one-way active avoidance paradigms, pigmented rats perform better than albinos, and the performance of HODI rats does not differ from that of controls. In two-way avoidance paradigms, albinos appear to outperform pigmented rats. Once again, there are no obvious differences between HODI and control animals. In addition to indicating that HODI rats may actually be less emotional than the other groups of rats reviewed here, the studies described once again fail to confirm the previously alleged functions of vasopressin in memory consolidation.

Inhibition of exploratory behavior in the rat by handling

The effect of tail-handling on exploratory behavior of the rat, measured as step-through latency in a well-lighted, two-box apparatus, was investigated. Male adult Wistar rats, aged 60 days, were employed in all three experiments. Experiment 1, in which the subjects were handled at different times after entering the goal chamber (0, 10, 30, 60, 300, and 600 sec), showed that immediate handling, relative to detention in the goal chamber (delay of handling) had an inhibitory effect on exploration. Experiment 2 showed that groups handled immediately after entering the goal chamber but then detained there for different durations all showed the same progressive inhibition of exploration. Experiment 3 showed that the inhibition of exploration (very long step-through latencies) due to tail-handling immediately after entering the goal chamber could be significantly decreased by further trials in which handling was delayed for a sufficient duration (30 sec or more). Handling is discussed as a stimulus that is aversive enough to elicit conditioned passive-avoidance responses (inhibition of exploratory behavior), although it is subject to rapid extinction.

The rat's right-left preference during free exploration of a multiple Y-maze

The right-left preference of Wistar, Sprague-Dawley, and Long Evans rats of both sexes was investigated in a multiple Y-maze in which the animals had to perform three consecutive right-left choices in order to go from the common starting point to one of the eight goal arms. The rats were free to explore the maze without being subjected to punishments or rewards. Care was taken to minimize inhibitory influences on exploration (low illumination, no handling to return the rats to home cage). The statistical analysis of the total right-left choices performed by the rats showed that three groups (Wistar females, Sprague-Dawley females, and Long Evans males) exhibited a preference for the right. This preference was not related either to sex or strain, but was possibly a species characteristic.

Aversive conditioning of homozygous and heterozygous D.I. Brattleboro rats in the light-dark box.

Active and passive avoidance, and conditioned freezing acquisition and retention were studied in HODI and HEDI Brattleboro rats. All animals were from the same source and of the same age and sex. The light-dark box test was employed. 0.6 and 2.0 mA footshocks were administered for the same number (7) of daily trials. Extinction time-course was followed for seven consecutive daily trials. Passive avoidance: the conditioned response was acquired and retained equally well by all Ss and for both shock intensities. Active avoidance: for 0.6 mA shocks HODI Ss acquired and retained the response significantly better than HEDI Ss; for 2.0 mA shocks the response was acquired equally by both groups of Ss, and retained significantly better by HODI Ss. Freezing: in general, HODI Ss exhibited less freezing then HEDI Ss. The diverse conditioned behavior of HODI and HEDI Ss in this paradigm, which allows the contemporaneous investigation of several aversive responses, does not support the hypothesis that vasopressin deficiency impairs learning and memory in the rat.

Effects of detention and illumination on rats' exploratory behavior in a two-box apparatus

The effects of detention and lighting intensity on the exploratory behavior of male Wistar rats have been investigated by means of several types of two-box apparatus. Experiments consisted of six consecutive daily trials. Step-through latency values were taken up to 180 sec. Even a very short detention (10 sec) within the starting box exerted a powerful inhibitory influence on the exploratory behavior of the subjects. Uniformly well-lighted surroundings (both boxes) exerted an equally powerful inhibitory influence on the same behavior. This inhibition was only slightly decreased by the availability of visual cues. Only in the apparatus in which at least one box was dark was the exploratory behavior well maintained. Both detention and bright lighting inhibited selectively the exploratory, locomotor behavior of these animals and did not inhibit other motor activities. In fact, groomings and attempts (abortive passages from one box into the other) were repeatedly performed during the increased step-through latency. These activities are discussed as indicators of a conflict between drives.

Equivalent aversiveness of back- and tail-handling in the rat

Using a two-box apparatus, it was shown that back-handling, when temporally close to a step-through latency test, causes a conditioned avoidance response that inhibits the exploratory behavior of the rat. The amount of inhibition due to back-handling was compared with that due to tail-handling (previously published). No significant differences were found between the inhibitory effects of these two methods of handling rats. This result is discussed in relation to sensory input and predation simulation.