Electrophysiological characterization of the rat trigeminal caudalis (Vc) neurons following intramuscular injection of capsaicin.
Extracellular single unit recording experiments were performed to examine response characteristics of wide dynamic range neurons in the Vc that receive masseter afferent input in Sprague-Dawley rats. Capsaicin, or its vehicle, was directly administered into the masseter muscle and changes in resting discharge, responses to mechanical stimulation on the cutaneous receptive field and the electrical threshold for masseter nerve stimulation were assessed. Intramuscular capsaicin induced significant increase in the background discharge and mechanical hypersensitivity to the cutaneous stimulation and lowered the threshold for masseter nerve stimulation-evoked responses in the majority of neurons. The capsaicin-induced increase in evoked responses, but not the resting discharge, was partially attenuated when the muscle was pretreated with a mGluR antagonist. The present study suggests that injury or inflammation in the masseter muscle induce generalized hyperexcitability of central trigeminal neurons and that the blockade of peripherally localized mGluR5 can effectively attenuate muscular hypersensitivity.
Chun
Yang H
YH
Kyung Hee University, School of Dentistry, Department of Oral Medicine, 1 Hoegi Dong, DongdaemunGu, Seoul, Republic of Korea.
Ro
Jin Y
JY
D000818:Animals; D002211:Capsaicin / Q000008:administration & dosage; D005071:Evoked Potentials / Q000187:drug effects; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D007273:Injections, Intramuscular; D008297:Male; D008406:Masseter Muscle / Q000187:drug effects / Q000503:physiopathology*; D008839:Microelectrodes; D009474:Neurons / Q000502:physiology*; D010146:Pain / Q000139:chemically induced / Q000188:drug therapy / Q000503:physiopathology*; D010812:Physical Stimulation; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate / Q000037:antagonists & inhibitors / Q000378:metabolism; D018689:Sensory System Agents / Q000008:administration & dosage; D014275:Trigeminal Caudal Nucleus / Q000503:physiopathology*
D018691:Excitatory Amino Acid Antagonists; C578937:Grm5 protein, rat; D011725:Pyridines; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate; D018689:Sensory System Agents; C121465:6-methyl-2-(phenylethynyl)pyridine; D002211:Capsaicin