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The Journal of Neuroscience, August 15, 2001, 21(16):6298-6307

Quantitative Analysis of Synaptic Contacts Made between Functionally Identified Oralis Neurons and Trigeminal Motoneurons in Cats

Atsushi Yoshida¹, Hideyuki Fukami¹, Yoshitaka Nagase¹, Kwabena Appenteng², Shiho Honma¹, Li-Fen Zhang¹, Yong Chul Bae³, and Yoshio Shigenaga¹

¹ Department of Oral Anatomy and Neurobiology, Graduate School of Dentistry, Osaka University, Suita, Osaka 565-0871, Japan, ² Department of Physiology, University of Ghana Medical School, Accra 2086, Ghana, and ³ Department of Oral Anatomy, Kyungpook University School of Dentistry, Taegu 700-422, Korea

A previous study revealed that rostrodorsomedial oralis (Vo.r) neurons synapsing on trigeminal motoneurons use GABA and/or glycine as neurotransmitters. To determine the number and spatial distribution of contacts, injections of biotinamide and horseradish peroxidase were made into a Vo.r neuron and an -motoneuron in the jaw-closing (JC) and jaw-opening (JO) motor nucleus, respectively, in 39 cats. All Vo.r neurons responded to low-threshold mechanical stimulation of the oral tissues. Single Vo.r neurons terminating in the JC nucleus (Vo.r-dl neurons; n = 5) issued, on average, 10 times more boutons than Vo.r neurons terminating in the JO nucleus (Vo.r-vm neurons; n = 5; 4437 vs 445). The Vo.r-dl neuron-JC -motoneuron pairs (n = 4) made contacts on either the soma-dendritic compartment or dendrites, and the Vo.r-vm neuron-JO motoneuron pairs (n = 2) made contacts on dendrites, with a range of two to seven contacts. In five of the six pairs, individual or groups of two to three terminals contacted different dendritic branches of a postsynaptic cell. The Vo.r-dl neurons innervated a greater number of counter-stained motoneuronal somata than did the Vo.r-vm neurons (216 vs 26). Total number of contacts per Vo.r neuron was higher for the Vo.r-dl than Vo.r-vm neurons (786 vs 72). The present study demonstrates that axonal branches of Vo.r neurons are divided into two types with different innervation domains on the postsynaptic neuron and that they are highly divergent. The overall effect exerted by these neurons is predicted to be much greater within the JC than JO motoneuron pool.

Key words: trigeminal; contact; sensorineuron; motoneuron; neurobiotin; horseradish peroxidase

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Copyright © 2001 Society for Neuroscience  0270-6474/01/21166298-10$05.00/0

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