Ultrastructural observations of synaptic connections of vibrissa afferent terminals in cat principal sensory nucleus and morphometry of related synaptic elements.

摘要: Previous work suggests that slowly adapting (SA) periodontal afferents have different synaptic arrangements in the principal (Vp) and oral trigeminal nuclei structure associated with transmitter release may be related directly to bouton size. The present study examined ultrastructures of SA fast (FA) vibrissa their unlabeled axonal endings cat Vp by using intra-axonal labeling horseradish peroxidase a morphometric analysis. All FA afferent boutons contained clear, round, vesicles. most were presynaptic dendrites, but few axosomatic. Both types frequently postsynaptic ending(s) containing pleomorphic, vesicles (P-ending). size labeled was larger than afferents, dendrites for afferents. Large-sized made contacts small-diameter dendrites. P-endings. A analysis on pooled data indicated apposed surface area, active zone number, total vesicle mitochondrial volume highly correlated positive linear manner volume. These relationships also applicable P-endings, range each parameter smaller boutons. observations provide evidence two functionally distinct manifest unique differences share certain structural features organization ultrastructural "size principle" proposed Pierce Mendell ([1993] J. Neurosci. 13:4748-4763) Ia-motoneuron synapses is somatosensory system.