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A light and electron microscopic analysis of the sacral parasympathetic nucleus after labelling primary afferent and efferent elements with HRP
Author(s) -
Mawe Gary M.,
Bresnahan Jacqueline C.,
Beattie Michael S.
Publication year - 1986
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.902500104
Subject(s) - efferent , biology , horseradish peroxidase , anatomy , ultrastructure , afferent , nucleus , axon , apposition , efferent neuron , postsynaptic potential , electron microscope , vesicle , sensory system , neuroscience , biochemistry , receptor , enzyme , physics , genetics , membrane , optics
Abstract Primary afferent input to the cat sacral parasympathetic nucleus (SPN) has been examined by injury filling sacral dorsal roots, ventral roots, or both with horseradish peroxidase (HRP). Appropriate spinal segments were processed for the demonstration of HRP with diaminobenzidine and prepared for sequential light (LM) and electron (EM) microscopy. At the LM level, a large fascicle of primary afferent fibers was observed passing ventrally along the lateral edge of the dorsal horn into the region of the SPN. Varicosities were seen throughout the course of the axons but were particularly abundant within the SPN. Injury filling of the ventral roots with HRP resulted in a Golgi‐like labelling of preganglionic neurons and their dendritic arbors, as well as ventral root afferent fibers. Swellings on both dorsal and ventral root afferent axons were observed in close apposition to labelled preganglionic neurons and their dendrites. At the ultrastructural level, labelled afferent terminals were found to contain clear spherical vesicles; 66% of these terminals also contained at least one dense‐cored vesicle. Of particular interest was the presence of labelled dorsal and ventral root afferent terminals synapsing on labelled preganglionic neurons. Preganglionic neurons were also pestsynaptic to unlabelled terminals containing clear spherical (79.7%) or pleomorphic vesicles (20.3%). These data indicate that preganglionic neurons receive direct input from several sources, and provide the first demonstration of direct input to these cells from sensory fibers in the dorsal and ventral roots. The connections described in the present study provide interesting and, as yet, unexplored possibilities for sensory and autonomic reflex integration.