The morphology of identified preganglionic neurons in the dorsal motor nucleus of the vagus

Edward Alan Fox, Purdue University

Abstract

The dorsal motor nucleus of the vagus (dmnX) is composed of five topographically distinct, longitudinal columnar subnuclei. Each of these columns projects its axons through a different subdiaphragmatic vagal branch--the anterior or posterior gastric, anterior or posterior celiac, or the hepatic branch. Each cell column and its associated branch mediates a different set of preganglionic functions. The aims of the present study were to determine the location and extent of the dendritic fields associated with each column and to evaluate whether the different pools of preganglionic motor neurons displayed morphological specializations that might be associated with their functional specializations. Neurons of an individual dmnX column were retrogradely labeled by application of Fast blue to the associated subdiaphragmatic vagal branch. Fixed brain slices of 100$\mu$m thickness were prepared in coronal, sagittal and horizontal orientations. Randomly selected Fast blue labeled neurons were injected with Lucifer yellow and drawn with camera lucida, and then several of their morphological features were measured. Throughout the dmnX, the dendrites of preganglionic neurons were preferentially oriented. The predominant orientation was in the horizontal plane, and, consistent with an organizing role for the columns, most dendrites remained within their column of origin. Only a small percentage (5-30%) of the neurons in each of the columns projected dendrites into adjacent columns or brainstem nuclei, including the NTS. The cyto- and dendroarchitectural analyses did not support the idea that the dmnX was composed of several distinct neuron types. The most parsimonious interpretation of the data was that dmnX neurons are variants of a single preganglionic prototype with their dendrites varying widely in length and degree of ramification. Although they could not be categorized into discrete cell types, the preganglionic neurons did vary in the extent of their dendritic fields as a function of their location in the dmnX. Three factors which accounted for this distribution included rostrocaudal position, location within a frontal plane and column association. Neurons at rostral and mid-longitudinal levels of each column had more extensive dendritic arbors than those at caudal levels, ectopic neurons had the most extensive dendritic fields and dendrites of celiac column neurons were more extensive than those of hepatic and gastric column cells. This differential distribution of vagal preganglionics suggests that their structure and function are correlated.

Degree

Ph.D.

Advisors

Powley, Purdue University.

Subject Area

Psychobiology|Neurology

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