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The effect of neonatal testosterone propionate (TP) injections in male rats on active and passive avoidance tasks during the prepubescent and adult periods of life Deol, Gurcharn Singh

Abstract

The effect of neonatal testosterone propionate (TP) (100 ug/day for the first 5 days of life or 1.25 mg. on day 1 of birth) injections on the acquisition of both active and passive avoidance was studied. Testing was initiated during both the prepubescent and adult periods of life. Neonatal TP injections facilitated the acquisition of active avoidance responding prior to puberty and also in adulthood. Neonatal TP injections had no effect on passive avoidance responding. A number of physiological (body, gonadal and adrenal weights) and behavioural (activity, shock sensitivity) measures were also studied to investigate their possible role in influencing our results. The TP injections led to significantly lower gonadal weights in the TP-injected group. Prior to puberty the TP-injected animals also possessed heavier adrenal glands, and were more active than the control group. The TP-injected group also had lower shock thresholds than the control group. The results suggest that excess neonatal TP injections affect an organism's ability to acquire an active avoidance response. The exact mechanism by which TP injections have their effect is unknown at this time. Future research would help to clarify whether the effect of excess neonatal TP is directly on the associative process or indirectly through a number of other factors, investigated in this article. Paradoxically, increased activity would be expected to interfere with the acquisition of passive avoidance behaviour, but this did not prove to be the case as TP injected animals acquired this response just as well or slightly better than controls. The observed differences between groups on shock reactivity measures suggest another plausible explanation of the results. Neonatal TP injections could facilitate acquisition of an active avoidance response by increasing sensitivity to the motivational stimulus. This possibility becomes even more tenable when we consider that other investigators have found a positive correlation between shock sensitivity and learning an active avoidance response (Beatty et. al. 1970, Pare, 1969). Specifically, these investigators have found that females acquire an active avoidance response faster than males and also have lower reactivity thresholds to footshock than males. Our finding of lowered shock sensitivity following neonatal TP injections would appear to parallel these observations and suggests shock sensitivity may be making an important contribution to the active avoidance data.

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