Varieties of responses orofacial chronic pain information of modeled animal nociceptive neurons

2001 Fiscal Year Final Research Report Summary

• Project/Area Number: 11671999
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Surgical dentistry
• Research Institution: Kyushu Dental College
• Principal Investigator: IWAMOTO Masatsugu Kyusyu Dental College, Dentistry, Assistant, 歯学部, 助手 (20223430)
• Co-Investigator(Kenkyū-buntansha): NAKANISHI Osamu Kyusyu Dental College, Dentistry, Professor, 歯学部, 教授 (50137345) ; SAKAMOTO Eiji Kyusyu Dental College, Dentistry, Assistant, 歯学部, 助手 (00295859)
• Project Period (FY): 1999 – 2001
• Keywords: Trigeminal subnucleus caudalis / Ventro basal nucleus of thalamus / Thalamic intralaminar nucreus / Nociceptive neurons / Formalin test / Rat / Trigeminal nerve / Number of spike discharge

Research Abstract

Formalin test as nociceptive stimulation to facial receptive field were performed on rats with basal anesthesia by i.p. administration of urethane and α-chlorarose, dose of showing no response to facial skin pinch. This basal anesthesia could be regarded reliable on the behaviologicaly, and regarded as the chronic pain modeled animal of orofacial region.
Using this basal anesthesia, we investigated electrophysiological characteristics from Trigeminal subnucleus caudalis, Ventrobasal nucleus of thalamus and Intralaminar nucleus of thalamus. Sequential changes of maximal numbers of discharge spike histogram analysis from nociceptive single unit neurons were investigated on formalin test as nociceptive stimulation under basal anesthetized rats. As a result, the numbers of spike discharge from Trigeminal subnucleus caudalis and Ventrobasal nucleus of thalamus were classified to 3 petterns (Biphasic increase : increase just after injection and increase with a peak after 20-40 minutes, Monoph asic increase just after injection, Without characteristic change). Intralaminar nucleus of thalamus, the numbers didn't show characteristic tendency.
Same as above, these nucleuses were inserted microdialysis probe, and the quantity of glutamate as substance related to transmission of pain were measured after formalin test. As a result, the quantities of glutamate at Trigeminal subnucleus caudalis were classified to 2 petterns (Monophasic increase just after injection, Without characteristic change). Ventrobasal nucleus of thalamus and Intralaminar nucleus of thalamus,the quantities didn't show characteristic tendency.
Above results were obtained by practice of formalin test generally used as chronic pain model and sequential observation of 60 minutes. Increase of the numbers of spike discharges as reaction to chronic pain was recognized from Trigeminal subnucleus caudalis as a primary transmission nucleus, but from other superior nucleuses wasn't recognized. This is regarded as indication of the afferent transmission system on pain sensation above Trigeminal subnucleus caudalis.