MORPHOLOGY OF 2 CLASSES OF TARGET-SPECIFIC BULLFROG SYMPATHETIC PREGANGLIONIC NEURONS

These experiments took advantage of the unique ability to define targe t-specific sympathetic preganglionic neurons in the bullfrog spinal co rd in order to examine the morphologies of different classes of pregan glionic neurons. Sympathetic preganglionic neurons were identified by retrograde transport of fast blue from the sympathetic chain. Subseque ntly, fast blue-labelled sympathetic preganglionic neurons in fixed sp inal cord slices were filled with lucifer yellow and processed for vis ualization with lucifer yellow antiserum, biotinylated secondary antis erum, and avidin peroxidase. Target specificity of sympathetic pregang lionic neurons was determined by anatomical position; sympathetic preg anglionic neurons that control the vasculature (C-type sympathetic pre ganglionic neurons) lie in a position caudal to those that control non vascular targets [B-type sympathetic preganglionic neurons; Horn and S tofer (1988) J. Comp. Neurol. 268:71]. These two classes of sympatheti c preganglionic neurons have qualitatively similar morphologies. Howev er, they exhibit significant quantitative differences in total dendrit ic length and the rostrocaudal extent of dendrites. These differences are likely to be associated with differences in the number of synapses received by these two classes of sympathetic preganglionic neurons. M oreover, the segmental control of sympathetic preganglionic neurons by descending brainstem projections is likely to be finer for those invo lved in vascular control than for those that influence other targets. (C) 1994 WiIey-Liss, Inc.