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PubMed1978

[Avoidance learning in rats treated with estrogens].

Male and female rats were treated with estradiol benzoate in the 5 degrees day of life. The avoidance conditioning, tested after 65 days, was significatively impaired in males treated with estradiol, a significative retardation was observed in females treated, but no significant end-difference versus no-treated females. It is supposed that a hormone induced synaptic shaft/spines ratio in preoptic area may be involved in avoidance conditioning.

Amygdala↗
PubMed1992

Ultrasonic vocalization as an indicator of emotional state during active avoidance learning in rats.

Adult male rats subjected to a two-way avoidance task emitted ultrasonic vocalizations (20-30 kHz) both during the presentation of the conditioned stimulus and the intertrial interval. The rate of ultrasonic calling decreased during the 75-trial session indicating that acquisition of the conditioned avoidance response (CAR) was inversely correlated with the rate of vocalization. The rate of acquisition of the CAR was most rapid in those rats that did not emit any vocalization during learning. These data suggest that ultrasonic calling during stressful situations may be sensitive indicator of underlying emotional states that interfere with the acquisition of a complex task.

Animals↗
PubMed1996

Active and passive avoidance learning in rats neonatally treated with intraventricular 6-hydroxydopamine.

To clarify the behavioral characteristics of rats neonatally treated with 6-hydroxydopamine (6-OHDA), their performance on 4 aversive learning tasks, 3 active (shuttle, one-way, and rearing) avoidance tasks and one passive (step-through) avoidance task, was examined. On days 2 and 4 after birth, each rat of F344/Du strain received bilateral intraventricular injections of 6-OHDA (35 micrograms x 2) or vehicle solution following desmethylimipramine (20 mg/kg, s.c.) pretreatment. From day 90, each rat was trained in one of the 4 avoidance tasks. 6-OHDA-treated rats showed significantly less avoidance responses in the shuttle and the one-way avoidance tasks, but their performance on the rearing and the step-through passive avoidance tasks was not significantly different from that of control rats. The differential impairment of avoidance suggests that 6-OHDA treatment does not cause a general learning deficit, but facilitates rearing and/or jumping responses in aversive situations, which results in inappropriate escape responses.

Animals↗
PubMed1984

Stimulus selection in passive avoidance learning and retention: weanling, periadolescent, and young adult rats.

Periadolescent rats exhibit a number of behavioral differences in comparison with younger or older animals. For instance, periadolescents tend to show enhanced acquisition of simple active avoidance tasks, but impaired acquisition of more complex appetitive and aversive discriminations. In this experiment, rats were trained on a simple passive avoidance task at one of three ages, as weanlings (25 days), periadolescents (35 days), or young adults (45 days). Training occurred in the presence of both a redundant discriminative stimulus and a specified, redundant contextual stimulus. The periadolescents did not differ from either younger or older rats in rate of learning the passive avoidance task. The retention performance of these animals was then tested following a change in either, neither, or both of the redundant cues. When a measure of performance that controls for baseline activity was used, it was observed that periadolescents were not disrupted by a change in the redundant discriminative stimulus, a cue change that clearly disrupted performance in 25- and 45-day-old animals, and tended to be more disrupted by the contextual change than younger or older rats. It is hypothesized that the alterations in performance exhibited by periadolescents may be related to an ontogenetic alteration in stimulus selection modulated by the catecholaminergic systems.

Aging↗
PubMed1994

The disruptive effects of ketamine on passive avoidance learning in mice: involvement of dopaminergic mechanism.

The involvement of dopaminergic mechanisms in ketamine-induced disruption of one trial step-through passive avoidance performance was assessed through the coadministration with the dopamine D1 antagonist SCH 23390, the dopamine D2 antagonist YM-091512 and the dopamine autoreceptor agonist at low doses, apomorphine, in mice. Pretraining (10 min before) administration of ketamine (0; saline, 2.5, 5 and 10 mg/kg SC) dose-dependently reduced the latency in the retention trial conducted 24 h after the training. However, ketamine did not affect the retention latency when administered immediately after the training or prior to retention. YM-09151-2 (0.01 and 0.03 mg/kg SC) and apomorphine (0.01 and 0.03 mg/kg SC), but not SCH 23390 (0.01 and 0.03 mg/kg SC), ameliorated the impaired reduction by ketamine (10 mg/kg) in a dose-dependent manner. These results suggest that ketamine obstructs the acquisition of the passive avoidance task, and that this effect is induced by stimulation of dopamine D2 receptors through dopamine release from the presynaptic terminals.

Animals↗
PubMed1984

Disruption of passive avoidance learning in the rat by electrical stimulation of the hippocampus.

The effect of electrical stimulation to discrete regions of the dorsal hippocampus on passive avoidance was examined in five experiments. Rats stepped from a brightly lit, white compartment to a dark compartment. Following footshock in the dark compartment, step-through latencies were recorded 1 min, 24 hr, and 48 hr after footshock. When given 20 step-through trials prior to footshock, dentate-stimulated animals exhibited lack of passive avoidance with particularly short latencies at 1 min, and CA1 rats showed reduced latencies compared with latencies of cortical and nonoperated controls. In Experiment 2, rats given stimulation in the same regions performed the avoidance task without prior step-through experience. All groups showed less passive avoidance than the control group in Experiment 1, and there were no significant differences between groups. With a single step-through trial before the footshock trial, longer avoidance latencies were recorded, but again groups did not differ significantly. Dentate-implanted animals, given 20 prior exposure trials but with stimulation at different stages of the task sequence, demonstrated a passive avoidance deficit at 1 min after footshock. The results are discussed in terms of the generation of expectancy that the black compartment was a safe place and the effects of brain stimulation on the expectancy, with particular reference to Vinogradova's (1975) theory of hippocampal function.

Animals↗