To gauge the strength by which the testes influence stress-induced activation of neurosecretory neurons in the paraventricular nucleus, we studied within medial parvocellular neurons the effects of gonadectomy on restraint-induced Fos-immunoreactivity and on CRH (CRH) and arginine vasopressin (AVP) heteronuclear (hn) RNA expression levels. Relative to intact male rats with testes (sham-gonadectomized), gonadectomized rats showed a significantly greater number of medial parvocellular neurons recruited to express Fos protein evident at 0.5 h, and from 1 to 4 h following the onset of 30 min restraint exposure. Restraint provoked a transient increase in heteronuclear CRH levels that was maximal at the end of restraint, significant only in gonadectomized rats. Both intact and gonadectomized rats displayed an increase in AVP hnRNA expression levels in response to restraint exposure, however significantly greater in gonadectomized rats. All of these responses were accompanied by a higher corticosterone response in gonadectomized compared with intact rats, and negatively correlated with plasma testosterone concentrations, safe for stress-induced CRH transcription. These findings indicate an inhibitory role for testosterone on stress-induced indices of synaptic (Fos) and transcriptional (AVP hnRNA) activation among hypophysiotropic paraventricular neurons and provide meaningful endpoints with which to pursue how and where androgens operate on stress-related input to the PVN motor neurons.