SYNAPTIC CONTACTS ESTABLISHED BY PRIMARY SENSORY FIBERS INNERVATING the TEETH of RATS - AN ULTRASTRUCTURAL-STUDY of the PARS INTERPOLARIS of the SPINAL TRIGEMINAL NUCLEUS

Abstract

Transganglionic degeneration was used in an electron microscopic study of afferent synaptic contacts in the dorsomedial region of the pars interpolaris of rats. in one experiment, the left inferior alveolar nerve was transected and in the other, partial pulpectomy of the first and second left lower molars was performed. Well defined degenerating terminals, almost completely occupied by round synaptic vesicle profiles were found in both ipsi and contralateral sides. in both experiments, approximately 70% of these terminals formed single asymmetric contacts with intermediate or distal dendritic segments. Fewer contacts were observed with proximal dendritic segments. dendritic spines, perikarya and other terminals. in addition, double and multiple synaptic contacts (synaptic glomeruli), accounting for 10% of the total, were also observed. Quantitative data regarding ultrastructural synaptic elements suggest that there is no preference for post-synaptic sites of fibers related to different sensory modalities such as pain, conveyed by dental fibers or other modalities, conveyed by the inferior alveolar nerve fibers.