Localization of neuronal nitric oxide synthase-immunoreactivity (nNOS-
IR) in the median eminence of female rats (n = 4) was examined by elec
tron microscopy to explore the possibility that nitric oxide is involv
ed in the terminal regulation of neurosecretory peptides such as GnRH.
Under light microscopy, a dense distribution of nNOS-IR was observed
in this region. Electronmicroscopically, nNOS-IR was found in glial el
ements and nerve terminals containing dense-core vesicles. We also fou
nd a few nNOS-immunopositive synapses, in which intense immunoreactivi
ty was found on the postsynaptic density and mitochondrial membrane. T
he localization of nNOS-IR in nerve terminals and glial elements in th
e median eminence might indicate that nNOS plays a role in regulating
the release of neurosecretory peptide. (C) 1998 Elsevier Science B.V.