The synaptic microcircuitry associated with primary afferent terminals in the interpolaris and caudalis of trigeminal sensory nuclear complex.
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.
Bae
Yong Chul
YC
Department of Oral Anatomy and Neurobiology, School of Dentistry, Kyungpook National University, Daegu 700-412, Korea.
Ahn
Hyung Joon
HJ
Park
Kuk Pil
KP
Kim
Hyun Nam
HN
Paik
Sang Kyoo
SK
Bae
Jin Young
JY
Lee
Hyun Won
HW
Kim
Kyung Hwan
KH
Yoshida
Atsushi
A
Moritani
Masayuki
M
Shigenaga
Yoshio
Y
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