Central nNOS is involved in restraint stress-induced fever: evidence for a cGMP pathway

It has been shown that the NO pathway plays a major role in restraint stress-induced fever, and that the neuronal nitric oxide synthase (nNOS) seems to be the NOS isoform that accounts for the pyretic effect of NO in psychological stress-induced fever. However, no information exists as to localization of the nNOS, i.e., in the peripheral or in the central nervous system (CNS). Thus, in the present study, we tested the hypothesis that NO arising from nNOS in the CNS participates in restraint stress-induced fever. Moreover, we also assessed the involvement of cyclic guanosine monophosphate (cGMP) in the mediation of the NO effects. To this end, intracerebroventricular S-methyl- l-thiocitrulline (SMTC; a selective nNOS inhibitor), sodium nitroprusside (an NO donor) or Rp-guanosine 3′,5′-cyclic monophosphothioate triethylamine (Rp-cGMPS; a specific membrane-permeable inhibitor of the activation by cGMP of cGMP-dependent protein kinase) were injected, and the colonic temperature ( T c) of restrained or unrestrained rats was recorded. Both SMTC (0.5 mg/μl) and Rp-cGMPS (10 μg/μl) intracerebroventricular injections enhanced restraint fever, whereas intracerebroventricular injections of sodium nitroprusside (100 μg/μl) reduced this response. These data indicate that NO produced in the CNS, arising from nNOS and acting via cGMP, plays an antipyretic role in the restraint stress-induced fever.