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 modi fied Vogel's drinking conflict model and on diazepam-induced disinhibition and sedation were investigated in adult male rats. Gonadectomy enhanced sho ck-induced behavioral inhibition when determined 9, 21, 45, and 65 days, bu t not 3 days, after operation, without affecting shock sensitivity or drink ing motivation. Testosterone-substitution for 21 days following gonadectomy prevented this enhanced inhibition without significantly affecting the beh avior in sham-operated rats. Diazepam produced behavioral disinhibition bot h in sham-operated and gonadectomized rats. However, after the highest dose (16 mg/kg, IP) the disinhibited behavior decreased only in sham-operated a nimals, most likely due to sedation. Moreover, whereas there was no differe nce in basal rotarod-performance between controls and gonadectomized rats, the latter animals were less sensitive to diazepam induced disruption of ro tarod walking ability. Sham-operated or gonadectomized animals did not diff er with respect to serum diazepam levels at the postinjection times used in the behavioral tests. Taken together. gonadectomized rats were less sensit ive towards diazepam-induced sedation, possibly due to a subsensitivity at or beyond GABA(A)/benzodiazepine receptors. Furthermore, the finding that l ack of testosterone enhanced shack-induced inhibition could be interpreted to reflect increased impulse control and may involve an altered activation of GABA(A)/benzodiazepine receptors. (C) 2000 Elsevier Science Inc.