Yoshinao Asahi1 and Norifumi Yonehara2,*
1Bobath Memorial Hospital, 1-6-5 Higashinakahama, Jyoto-ku, Osaka 536-0023, Japan
2Department of Pharmacology, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan
*Corresponding author. FAX: +81-6-6879-2914, E-mail: email@example.com
Abstract: We have conducted this study to elucidate the influence of GABAergic systems on manifestation of pharmacological activity of desipramine using both pharmacological and electrophysiological methods. Desipramine (20 mg/kg, i.p.) significantly blocked the adjuvant-induced thermal hyperalgesia, which was facilitated by treatment with the GABAA antagonist picrotoxin (2 mg/kg, i.p.) or the GABAB antagonist saclofen (2 mg/kg, i.p.). This analgesic effect of desipramine was antagonized by post-treatment with picrotoxin or saclofen. However, none of these compounds showed any effect in normal animals without adjuvant-induced inflammation. In a slice preparation of the hippocampus, treatment with GABA (10−5 - 5 × 10−4 M), baclofen (10−5 - 10−4 M) or muscimol (10−5 - 10−4 M) inhibited the field potential evoked in pyramidal neurons by Schaffer collateral stimulation. The inhibitory effect of GABA was facilitated by concurrent application of desipramine, carbamazepine or diazepam at a concentration of 5 × 10−5 - 2 × 10 −4 M. The rank of order of facilitation is: desipramine > carbamazepine > diazepam. Desipramine also enhanced the inhibitory effect of baclofen and muscimol. These results suggest that desipramine causes GABAergic systems to activate still more, and this phenomenon appears to be involved in manifestation of the pharmacological activity of desipramine such as antinociception.
Keywords: GABA, Desipramine, Analgesia, Hippocampus, Field potential
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