title: Participation of central GABAAreceptors in the trigeminal processing of mechanical allodynia in rats.
abstract: Here we investigated the central processing mechanisms of mechanical allodynia and found a direct excitatory link with low-threshold input to nociceptive neurons. Experiments were performed on male Sprague-Dawley rats weighing 230-280 g. Subcutaneous injection of interleukin 1 beta (IL-1β) (1 ng/10 µL) was used to produce mechanical allodynia and thermal hyperalgesia. Intracisternal administration of bicuculline, a gamma aminobutyric acid A (GABAA) receptor antagonist, produced mechanical allodynia in the orofacial area under normal conditions. However, intracisternal administration of bicuculline (50 ng) produced a paradoxical anti-allodynic effect under inflammatory pain conditions. Pretreatment with resiniferatoxin (RTX), which depletes capsaicin receptor protein in primary afferent fibers, did not alter the paradoxical anti-allodynic effects produced by the intracisternal injection of bicuculline. Intracisternal injection of bumetanide, an Na-K-Cl cotransporter (NKCC 1) inhibitor, reversed the IL-1β-induced mechanical allodynia. In the control group, application of GABA (100 µM) or muscimol (3 µM) led to membrane hyperpolarization in gramicidin perforated current clamp mode. However, in some neurons, application of GABA or muscimol led to membrane depolarization in the IL-1β-treated rats. These results suggest that some large myelinated Aβ fibers gain access to the nociceptive system and elicit pain sensation via GABAAreceptors under inflammatory pain conditions.
authors.affiliation: Department of Oral Physiology, School of Dentistry, Kyungpook National University, Daegu 41940, Korea.
authors.forename: Min Ji
authors.initials: MJ
authors.lastname: Kim
authors.affiliation: Department of Oral Physiology, School of Dentistry, Kyungpook National University, Daegu 41940, Korea.
authors.forename: Young Hong
authors.initials: YH
authors.lastname: Park
authors.affiliation: Department of Oral Physiology, School of Dentistry, Kyungpook National University, Daegu 41940, Korea.
authors.forename: Kui Ye
authors.initials: KY
authors.lastname: Yang
authors.affiliation: Department of Oral Physiology, School of Dentistry, Kyungpook National University, Daegu 41940, Korea.
authors.forename: Jin Sook
authors.initials: JS
authors.lastname: Ju
authors.affiliation: Department of Oral Anatomy, School of Dentistry, Kyungpook National University, Daegu 41940, Korea.
authors.forename: Yong Chul
authors.initials: YC
authors.lastname: Bae
authors.affiliation: Department of Oral Physiology, School of Dentistry and Institute of Oral Bioscience, Chonbuk National University, Jeonju 54896, Korea.
authors.forename: Seong Kyu
authors.initials: SK
authors.lastname: Han
authors.affiliation: Department of Oral Physiology, School of Dentistry, Kyungpook National University, Daegu 41940, Korea.
authors.forename: Dong Kuk
authors.initials: DK
authors.lastname: Ahn
keywords: GABAA receptor; IL-1β; Mechanical allodynia; NKCC1; Paradoxical anti-allodynic effect