title: Synaptic density, convergence, and dendritic complexity of prevertebral sympathetic neurons.
abstract: Prevertebral sympathetic ganglia contain a unique population of final motor neurons receiving convergent synaptic inputs not only from spinal preganglionic neurons, but also from peripheral intestinofugal neurons projecting from the gut. We used quantitative confocal and ultrastructural immunohistochemistry to determine how this increased synaptic convergence is accommodated by sympathetic final motor neurons in the celiac ganglion of guinea pigs. Terminals of intestinofugal neurons were identified by their immunoreactivity to vasoactive intestinal peptide. Stereologic analyses were based on transects and point counts at confocal and ultrastructural levels. The relative amount of dendritic neuropil in the medial regions of the ganglion was approximately 2.5 times greater than in the lateral regions of the ganglion, consistent with the 2 to 3 times difference in average dendritic field size of neurons in these regions. The total numbers of boutons and synaptic profiles showed significant positive correlations with the relative amount of neuropil in a region. However, the overall density of synaptic boutons was twice as high in the medial region of the ganglion compared with the lateral regions. Because the relative density of preganglionic synapses was similar in each region, this difference was due to the selective projection of intestinofugal inputs to neurons in the medial celiac ganglion, where they provided 45% of synaptic contacts. These results show that, compared with vasoconstrictor neurons, sympathetic neurons regulating gastrointestinal activity support a higher number of convergent inputs in two ways: in addition to having larger dendritic fields, they also have a twofold higher density of synapses.
authors.affiliation: Department of Anatomy & Histology, and Centre for Neuroscience, Flinders Medical Research Institute, Flinders University, Adelaide, SA, 5001, Australia. ian.gibbins@flinders.edu.au
authors.forename: Ian L
authors.initials: IL
authors.lastname: Gibbins
authors.forename: Ee Hiok
authors.initials: EH
authors.lastname: Teo
authors.forename: Phillip
authors.initials: P
authors.lastname: Jobling
authors.forename: Judy L
authors.initials: JL
authors.lastname: Morris
mesh_terms: D000818:Animals; D002795:Choline O-Acetyltransferase / Q000032:analysis; D003712:Dendrites / Q000502:physiology / Q000648:ultrastructure*; D004594:Electrophysiology; D005260:Female; D005728:Ganglia, Sympathetic / Q000737:chemistry / Q000166:cytology* / Q000502:physiology / Q000648:ultrastructure; D006168:Guinea Pigs; D007150:Immunohistochemistry; D008297:Male; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D008869:Microtubule-Associated Proteins / Q000032:analysis; D009474:Neurons / Q000502:physiology / Q000648:ultrastructure*; D009475:Neurons, Afferent / Q000502:physiology / Q000648:ultrastructure; D009478:Neuropeptide Y / Q000032:analysis; D019581:Neuropil / Q000502:physiology / Q000648:ultrastructure*; D013569:Synapses / Q000502:physiology / Q000648:ultrastructure*; D014660:Vasoactive Intestinal Peptide / Q000032:analysis
chemical_list: D008869:Microtubule-Associated Proteins; D009478:Neuropeptide Y; D014660:Vasoactive Intestinal Peptide; D002795:Choline O-Acetyltransferase