Opioid-mediated inhibition from the subnucleus caudalis of spinal trigeminal nucleus to the neurons in the subnucleus oralis.
The influence of enkephalin-containing neurons in the subnucleus caudalis of the spinal trigeminal nucleus (STN caudalis) on the subnucleus oralis of the STN (STN oralis) was examined using chloral hydrate-anesthetized rats. In the STN oralis, conditioning stimuli applied to the STN caudalis 10-50 ms preceding the test stimulus inhibited spikes produced by tooth pulp stimulation in type B interneuron, which was activated by orthodromic stimulation but not by thalamic stimulation, without affecting those of the relay neuron. When the type B interneurons were further classified into type B1 and type B2 neurons, which were characterized by the occurrence of the STN caudalis-induced inhibition with long and short latencies, respectively, microiontophoretically applied naloxone reduced the STN caudalis-induced inhibition of th orthodromic spikes of type B1 interneurons with little effects on type B2 interneuron. Furthermore, naloxone-reversible inhibition of tooth pulp-induced spikes of the type B1 interneurons were also observed during iontophoretic application of enkephalin. These results suggest that the type B1 interneurons in the STN oralis are inhibited by opioid peptides-containing neurons in the STN caudalis.
Ujihara
H
H
Department of Pharmacology, Faculty of Medicine, Kyoto University, Japan.
Sasa
M
M
Fujita
Y
Y
Takaori
S
S
D000200:Action Potentials; D000818:Animals; D004723:Endorphins / Q000378:metabolism / Q000502:physiology*; D007395:Interneurons / Q000187:drug effects / Q000502:physiology; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D009433:Neural Inhibition; D009475:Neurons, Afferent / Q000145:classification / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D014070:Tooth / Q000294:innervation; D014279:Trigeminal Nucleus, Spinal / Q000187:drug effects / Q000502:physiology*
D004723:Endorphins; D009270:Naloxone