Sleep loss mediates the effect of stress on nitrergic signaling in female mice.

Nitric oxide (NO) has been implicated as an important neurotransmitter in stress responses and sleep regulatory processes. However, the role of NO in the relationship between stress and sleep remains unclear. The medial septum (MS) and vertical diagonal band (VDB), regions of the basal forebrain involved in sleep regulation, contain nitric oxide synthase (NOS) producing neurons. Additionally, NOS neurons in the dorsal raphe nucleus (DRN) encode information about stress duration. The role of nitrergic neurons in these regions in subserving sex-specific responses to stress and sleep loss has yet to be elucidated. In this study, NADPH-d, an index of NOS activity, was used to examine the effects of acute restraint stress and sleep loss on NOS activity in the MS, VDB, and DRN. We show that NOS activity in response to restraint stress, total sleep deprivation (TSD), and partial sleep restriction (PSR) differs based on sex and region. Initial analysis showed no effect of restraint stress or TSD on NOS activity in the basal forebrain. However, investigation of each sex separately revealed that restraint stress and TSD significantly decrease NOS activity in the MS of females, but not males. Interestingly, the difference in NOS activity between restraint stress and TSD in females was not significant. Furthermore, PSR was not sufficient to affect NOS activity in males or females. These data suggest that restraint stress and sleep loss regulate NOS activation in a sex-dependent manner, and that the NOS stress response in females may be mediated by sleep loss.