Gonadectomy and sensitivity to electric shock in the rat.

The effects of gonadectomy and hormone replacement on sex-typical responses to electric shock were assessed using a modification of the flinch-jump technique. Ovariectomy increased body weight but had no effect on any measure of sensitivity to shock. Gonadectomy in males at any age resulted in reduced weight gain but the effect of gonadectomy on shock thresholds in males varied with the age of operation: neonatal gonadectomy increased sensitivity to shock as reflected in lower thresholds on all measures; adult gonadectomy did not reliably affect any shock threshold and castration at 7 weeks of age lowered only flinch and shuffle thresholds without affecting jump thresholds. However, testosterone injections elevated shock thresholds depressed by gonadectomy and this effect was most evident in the neonatally castrated group. Hence, it is doubtful that neonatal gonadectomy removes an organizational influence of testicular hormones on pain sensitivity. Moreover, changes in body weight and reactivity to shock following gonadectomy can occur in a relatively independent fashion.