A functional role for nitric oxide in locus coeruleus: immunohistochemical and electrophysiological studies.

Immunohistochemical analysis of the localization of nitric oxide synthase-(NOS)-like immunoreactivity revealed the presence of this enzyme in a few neuronal cell bodies and in dendritic and axonal processes within the rat locus coeruleus (LC). Also cells in the pericoeruleus area were NOS-positive. Intracellular recordings were made from LC neurons in brain slices. Bath application of the NOS inhibitors nitro-L-arginine methyl ester (L-NAME) or NG-monomethyl-L-arginine (L-NMMA) potently enhanced the excitatory postsynaptic potential (EPSP) evoked by focal electrical stimulation of the slice. Hemoglobin, which binds extracellular NO, also enhanced the EPSP. This enhancement was reversed by coadministration of L-arginine, a precursor of neuronal nitric oxide (NO). Neither NOS inhibitors, L-arginine, nor hemoglobin had effects on the resting membrane potential or impedance. These results suggest a role for NO in synaptic transmission in the LC.