Nitric oxide synthesising neurons in the central subnucleus of the nucleus tractus solitarius in humans.

The central subnucleus of the nucleus tractus solitarius is an important central structure mediating esophago-esophageal reflexes. In experimental animals it contains a discrete group of nitric oxide synthase (NOS) neurons. The central subnucleus has not been described in the human. In the present study we mapped the distribution of NO synthesising neurons in the human nucleus tractus solitarius, using the NADPH diaphorase reaction and an antibody against NOS. We found a distinct group of small ovoid NO synthesising neurons, dorsomedial to the solitary tract and ventral to the gelatinous subnucleus, extending from 1 to 5 mm rostral to the obex, thus corresponding closely to the central subnucleus in experimental animals. Our study defines the anatomical location of the central subnucleus in the human nucleus tractus solitarius, and suggests the possible involvement of nitric oxide in the central regulation of esophageal reflexes in humans.