Nitric oxide synthase immunoreactive neurons anatomically define a longitudinal dorsolateral column within the midbrain periaqueductal gray of the rat: analysis using laser confocal microscopy.

Nitric oxide has recently been proposed as a neuronal messenger in both the central and peripheral nervous system. Antibodies against nitric oxide synthase (NOS), the synthesizing enzyme for nitric oxide, were used in combination with immunocytochemistry and confocal laser microscopy to analyze the distribution of this enzyme in the midbrain periaqueductal gray (PAG) of the rat. NOS immunoreactive neurons were localized predominantly in a longitudinally oriented column in the dorsolateral PAG. NOS immunoreactive fibers and processes were scattered throughout the PAG but were most prevalent in the dorsolateral column and in the juxta-aqueductal column. This study provides neurochemical support for the existence of longitudinal columns in the PAG which are postulated to underlie the functional organization of this complex brainstem region.