LOCALIZATION OF EFFERENT FUNCTION IN THE DORSAL MOTOR NUCLEUS OF THE VAGUS INVESTIGATED WITH ELECTRICAL BRAIN STIMULATION
Abstract
The present study utilized electrical stimulation of the medulla oblongata to investigate the organization of several different vagal responses. Monopolar stimulation of the dorsal motor nucleus of the vagus nerve (DMV) caused highly significant increases in gastric acid secretion, plasma insulin levels, and plasma glucagon levels. The same region was ineffective in eliciting bradycardia or changes in blood pressure and plasma glucose levels. Electrode placements immediately surrounding the DMV, and those along the path of the vagal motor neurons, evoked gastric acid responses which were much smaller than those from the DMV itself. Increases in insulin and glucagon levels of slightly smaller magnitude were seen following stimulation of these regions. Other regions sampled were ineffective in producing changes in these parameters. The "center-of-gravity" (centroid) was calculated for each of these responses using all of the electrode placements in the medulla (n = 205). The centroid points for the three responses which were evoked by brain stimulation are located at approximately the mid-anterior-posterior extent of the DMV. The centroid for gastric acid is located more medially in the DMV; those for insulin and glucagon are in the lateral pole of the nucleus. Four models of vagal efferent organization which can be abstracted from the anatomical literature were evaluated with the data from the present study (lateralized, anterior/posterior, columnar, and diffuse or "equipotential" representation of function). The longitudinal columnar type of organization best explained the results which were obtained. Medial DMV placements were more effective than lateral in eliciting gastric acid secretion and lateral placements were more effective than medial placements in eliciting insulin secretion. Increases in glucagon secretion were not significantly larger from lateral placements, although the trend was in that direction.
Degree
Ph.D.
Subject Area
Psychobiology
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