Gonadectomy enhances shock-induced behavioral inhibition in adult male rats: implications for impulsive behavior.

The effects of gonadectomy on shock-induced behavioral inhibition in a modified Vogel's drinking conflict model and on diazepam-induced disinhibition and sedation were investigated in adult male rats. Gonadectomy enhanced shock-induced behavioral inhibition when determined 9, 21, 45, and 65 days, but not 3 days, after operation, without affecting shock sensitivity or drinking motivation. Testosterone-substitution for 21 days following gonadectomy prevented this enhanced inhibition without significantly affecting the behavior in sham-operated rats. Diazepam produced behavioral disinhibition both in sham-operated and gonadectomized rats. However, after the highest dose (16 mg/kg, IP) the disinhibited behavior decreased only in sham-operated animals, most likely due to sedation. Moreover, whereas there was no difference in basal rotarod-performance between controls and gonadectomized rats, the latter animals were less sensitive to diazepam-induced disruption of rotarod walking ability. Sham-operated or gonadectomized animals did not differ with respect to serum diazepam levels at the postinjection times used in the behavioral tests. Taken together, gonadectomized rats were less sensitive towards diazepam-induced sedation, possibly due to a subsensitivity at or beyond GABA(A)/benzodiazepine receptors. Furthermore, the finding that lack of testosterone enhanced shock-induced inhibition could be interpreted to reflect increased impulse control and may involve an altered activation of GABA(A)/benzodiazepine receptors.