Inhibitory actions of borneol on the substantia gelatinosa neurons of the trigeminal subnucleus caudalis in mice

• Published in: The Korean journal of physiology & pharmacology Vol. 24; no. 5; pp. 433 - 440
• Main Authors: Nguyen, Phuong Thao Thi, Jang, Seon Hui, Rijal, Santosh, Park, Soo Joung, Han, Seong Kyu
• Format: Journal Article
• Language: English
• Published: The Korean Physiological Society and The Korean Society of Pharmacology 01-09-2020; 대한약리학회
• Subjects: Original; 약리학
• ISSN: 1226-4512; 2093-3827
• DOI: 10.4196/kjpp.2020.24.5.433

The substantia gelatinosa (SG) of the trigeminal subnucleus caudalis (Vc) is the first relay site for the orofacial nociceptive inputs
via
the thin myelinated Aδ and unmyelinated C primary afferent fibers. Borneol, one of the valuable time-honored herbal ingredients in traditional Chinese medicine, is a popular treatment for anxiety, anesthesia, and antinociception. However, to date, little is known as to how borneol acts on the SG neurons of the Vc. To close this gap, the whole-cell patch-clamp technique was applied to elucidate the antinociceptive mechanism responding for the actions of borneol on the SG neurons of the Vc in mice. In the voltage-clamp mode, holding at –60 mV, the borneol-induced non-desensitizing inward currents were not affected by tetrodotoxin, a voltage-gated Na
+
channel blocker, 6-cyano-7-nitro-quinoxaline-2,3-dione, a non-
N
-methyl-d-aspartate (NMDA) glutamate receptor antagonist and DL-2-amino-5-phosphonopentanoic acid, an NMDA receptor antagonist. However, borneol-induced inward currents were partially decreased in the presence of picrotoxin, a γ-aminobutyric acid (GABA)
A
receptor antagonist, or strychnine, a glycine receptor antagonist, and was almost suppressed in the presence of picrotoxin and strychnine. Though borneol did not show any effect on the glycine-induced inward currents, borneol enhanced GABA-mediated responses. Beside, borneol enhanced the GABA-induced hyperpolarization under the current-clamp mode. Altogether, we suggest that borneol contributes in part toward mediating the inhibitory GABA and glycine transmission on the SG neurons of the Vc and may serve as an herbal therapeutic for orofacial pain ailments.