title: The synaptic microcircuitry associated with primary afferent terminals in the interpolaris and caudalis of trigeminal sensory nuclear complex.
abstract: Previous ultrastructural studies indicating a higher number of axoaxonic contacts on individual low-threshold mechanoreceptive afferents in the principalis (Vp) than in the oralis (Vo) of cat trigeminal sensory nuclear complex (TSNC) suggest that the synaptic microcircuitry associated with primary afferents manifests unique differences across the sensory nuclei of TSNC. To address this issue, we analyzed synaptic microcircuits associated with fast adapting vibrissa afferent terminals in the interpolaris (Vi) and caudalis (Vc, laminae III/IV) by using intraaxonal injections of horseradish peroxidase (HRP) in cats. Forty-two and 65 HRP-labeled boutons were analyzed in the Vi and Vc, respectively. The labeled boutons contained clear, spherical vesicles. They most frequently formed asymmetric axodendritic synapses and were commonly postsynaptic to unlabeled axon terminals containing pleomorphic vesicles (p-endings) with symmetric junctions. The examination of synaptic contacts over the entire surface of individual boutons indicated that the afferent boutons made contacts with an average of two postsynaptic targets in the Vi and Vc. In contrast, axoaxonic contacts, and labeled boutons participating in synaptic triads, where p-endings contacted both the boutons and their postsynaptic targets, were, on average, higher in the Vi than in the Vc. These results suggest that the output of sensory information conveyed through low-threshold mechanoreceptive afferents is more strongly controlled at the level of the first synapse by presynaptic and postsynaptic mechanisms in the Vi responsible for sensory discriminative functions than in the Vc for sensorimotor reflexive functions.
authors.affiliation: Department of Oral Anatomy and Neurobiology, School of Dentistry, Kyungpook National University, Daegu 700-412, Korea.
authors.forename: Yong Chul
authors.initials: YC
authors.lastname: Bae
authors.forename: Hyung Joon
authors.initials: HJ
authors.lastname: Ahn
authors.forename: Kuk Pil
authors.initials: KP
authors.lastname: Park
authors.forename: Hyun Nam
authors.initials: HN
authors.lastname: Kim
authors.forename: Sang Kyoo
authors.initials: SK
authors.lastname: Paik
authors.forename: Jin Young
authors.initials: JY
authors.lastname: Bae
authors.forename: Hyun Won
authors.initials: HW
authors.lastname: Lee
authors.forename: Kyung Hwan
authors.initials: KH
authors.lastname: Kim
authors.forename: Atsushi
authors.initials: A
authors.lastname: Yoshida
authors.forename: Masayuki
authors.initials: M
authors.lastname: Moritani
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Shigenaga
mesh_terms: D000344:Afferent Pathways / Q000166:cytology / Q000648:ultrastructure; D000818:Animals; D002415:Cats; D046529:Microscopy, Electron, Transmission; D009475:Neurons, Afferent / Q000648:ultrastructure*; D017729:Presynaptic Terminals / Q000648:ultrastructure*; D014278:Trigeminal Nuclei / Q000166:cytology / Q000648:ultrastructure*; D014738:Vibrissae / Q000294:innervation