CER suppression, passive-avoidance learning, and stress-induced suppression of drinking in the Syracuse high- and low-avoidance strains of rats (Rattus norvegicus).

The Syracuse strains of Long-Evans rats were selectively bred for good (SHA) or poor (SLA) avoidance learning in a two-way shuttle box, which resulted in a phenotypic difference that is correlated with behavior patterns indicative of emotional reactivity, SLA animals showing evidence of greater emotional reactivity than SHA animals. The first three experiments examined conditioned suppression of bar pressing and compared paired and unpaired conditioned- and unconditioned-stimulus presentations to evaluate the influence of conditioning versus primary aversive stimulation on baseline responding. SLA animals acquired conditioned suppression faster than SHA animals and also showed greater suppression of baseline responding than SHA animals. In Experiment 4, SLA animals learned a passive-avoidance task faster than SHA animals. In Experiment 5, SLA animals showed greater stress-induced suppression of drinking a weak quinine solution than SHA animals. These data are consistent with the hypothesis that SLA animals are more emotionally reactive than SHA animals.

Genetic differences in avoidance learning by Rattus norvegicus: escape/avoidance responding, sensitivity to electric shock, discrimination learning, and open-field behavior.

The behaviors of rats selectively bred for either good or poor shuttle box avoidance learning were studied. The results of Experiment 1 indicated that the phenotypic difference in avoidance learning is not associated with differences in speed of escape or avoidance responding. Differences between the lines in frequency of intertrial responses (ITRs), which appear during training but not during pretest, suggest that ITRs in animals of the low-avoidance (SLA) line are more suppressed by electric shock than in animals of the high-avoidance (SHA) line. This result suggests that SLA animals may be more emotionally responsive than SHA animals. Experiment 2 demonstrated that the animals of the two lines do not differ in absolute sensitivity to electric shock, and Experiment 3 showed that the poor performance of the SLA line is not due to an inability to learn. Experiment 3 also provided evidence which suggests that the poor avoidance learning by SLA animals is due to their emotional reactivity. Observations of open-field behavior in Experiment 4 are consistent with this hypothesis. The major consistent correlate of the phenotypic difference in avoidance learning is greater emotionality or emotional reactivity in SLA than in SHA animals.

Effects of differential interference with postnatal cerebellar neurogenesis on motor performance, activity level, and maze learning of rats: a developmental study.

The region of the cerebellum was X-irradiated in infant rats with selected exposure schedules designed to produce animals in which the cerebellar cortex was (a) essentially normal except for agenesis of late forming granule cells with axons situated in the uppermost molecular layer (12--15X), (b) lacking in stellate cells, with a severe reduction in granule cells with axons in the upper molecular layer (8--15X), (c) morphologically disorganized but had only intermediate cell agenesis (4--5X), or (d) disorganized and devoid of practically all postnatally forming interneurons (4--15X). In the first two experiments young adults had to traverse rotating rods that differed in texture and types of obstacles. The 8--15X animals showed no deficits on any of the rods tested. The third study dealt with spontaneous motor performance in the open field at three ages. The 4--5X and 4--15X animals were hypoactive as infants and young adults; this was attributed to their motor deficits. The 8--15X and 12--15X animals were hyperactive in the open field as young adults. The fourth experiment examined intra- and/or intersession habituation. No group differences were found in habituation patterns. In the fifth experiment, using activity wheels, the 4--15X group was hypoactive, and the 8--15X and 12--15X groups were hyperactive as young adults. In the sixth experiment young adults were tested for learning performance in a multiple-unit water maze. The 4--15X group was deficient on single alternation; the 4--5X and 12--15X groups on double alternation. The seventh experiment shed some light on the single alternation deficit of the 4--15X group; only these animals failed to alternate spontaneously in a nonaversive situation. In conclusion, these behavioral results, combined with those of recent morphological investigations, suggest that the cerebellar cortex is hierarchically organized: The basal domain of Purkinje cells and the lower molecular layer are implicated in the coordination of movements; the apical domain of Purkinje cells and the upper molecular layer, in the coordination of actions.

Characteristics of the pituitary-adrenal system in the Syracuse high- and low-avoidance strains of rats (Rattus norvegicus).

After many generations of selective breeding, rats of the high-avoidance strain (SHA) average 67% avoidance responses in a two-way shuttle box, whereas those of the low-avoidance strain (SLA) average 0%. Adrenal gland weights, both absolutely and relative to body weight, are 40-50% greater in adult SLA than SHA rats of both sexes. Females of both strains have larger adrenal glands than males. Morphometry revealed that the difference in adrenal size in adults is entirely in the three cortical zones. The strain difference occurs as early as 21 days of age, whereas the sex difference appears only after puberty. A 2-min exposure to either vapor induced an elevation in adrenal concentration of corticosterone which was significantly greater in SHA than SLA animals of both sexes at some time periods following the ether stress. Despite having smaller glands, older previously stressed SHA rats have higher basal adrenal concentrations of corticosterone than do SLA animals. The reduced steroidogenesis in the large adrenals of SLA rats suggests that there may be an enzymatic defect of genetic origin in those animals.