Dorsal motor nucleus of the vagus neurons: A multivariate taxonomy

The dorsal motor nucleus of the vagus (DMNX) contains neurons with differen t projections and discrete functions, but little success has been achieved in distinguishing the cells cytoarchitectonically. The present experiment e mployed multivariate analytical techniques to evaluate DMNX neuronal morpho logy. Male Sprague-Dawley rats (n = 77) were perfused, and the brainstems w ere stained en bloc with a Golgi-Cox protocol. DMNX neurons in each of thre e planes (coronal, sagittal, and horizontal; total sample = 607) were digit ized. Three-dimensional features quantified included dendritic length, numb er of segments, spine density, number of primary dendrites, dendritic orien tation, and soma form factor. Cluster analyses of six independent samples o f 100 + neurons and of three composite replicate pools of 200+ neurons cons istently identified similar sets of four distinct neuronal profiles. One pr ofile (spinous, limited dendrites, small somata) appears to correspond to t he interneuron population of the DMNX. In contrast, the other three distinc tive profiles (e.g., one is multipolar, with large dendritic fields and lar ge somata) are different types of preganglionic neurons. Each of the four t ypes of neurons is found throughout the DMNX, suggesting that the individua l columnar subnuclei and other postulated vagal motorneuron pools are compo sed of all types of neurons. Within individual motor pools, ensembles of th e different neuronal types must cooperatively organize different functions and project to different effecters within a target organ. By extension, spe cializations of the preganglionic motor peals are more likely to result fro m their afferent inputs, peripheral target tissues, neurochemistry, or phys iological features rather than from any unique morphological profiles. J. C omp. Neurol. 403:359-377; 1999. (C) 1999 Wiley-Liss, Inc.