Biobehavioral responses to conditioned fear and restraint stress in borderline hypertensive rats (BHR)
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The purpose of this experiment was to determine the effects of an early environmental manipulation, handling (H), on cardiovascular (CV) reactivity, freezing behavior and corticosterone (CORT) responses to fear conditioning in the BHR, which is genetically susceptible to environmental stressors. H subjects were separated from the nest for 15 mins/day on post-natal days 1-14, while non-handled (NH) controls remained in the home cage. Adult BHR from each group were implanted with a femoral arterial catheter for mean arterial pressure (MAP) recording and blood sampling. Two days later, subjects were exposed to the fear conditioning procedure. Subjects were returned to the chamber the next day for 10 min during which time freezing behavior, CV responses and CORT measurements were taken. H subjects displayed significantly more freezing behavior compared to NH (92%±2.2 vs. 80.7%±5.7, p < .05). Although resting MAP did not differ between groups, H subjects had increased MAP reactivity when returned to the fear conditioning chamber (p < .01). Finally, H subjects had significantly lower CORT levels at the end of the 10 min test period (173±8 ng/ml vs. 217.7±22.2 ng/ml, p < .05). In a separate experiment, H subjects showed reduced CORT levels in response to acute restraint stress. These results indicate that neonatal H produces enhanced biobehavioral responses to fear conditioning in BHR and may suggest a useful model with which to study the interaction of genetics, emotionality, and heart disease.
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