GABAergic modulation mediates antinociception produced by serotonin applied into thalamic nucleus submedius of the rat.
Our previous studies have indicated that the thalamic nucleus submedius (Sm) is involved in modulation of nociception as part of an ascending component of an endogenous analgesic system consisting of spinal cord-Sm-ventrolateral orbital cortex (VLO)-periaqueductal gray (PAG)-spinal cord loop and that microinjection of 5-hydroxytryptamine (5-HT) into Sm produces antinociception. The aim of the present study was to examine whether the gamma-aminobutyric acid (GABA)ergic modulation is involved in the Sm 5-HT-evoked antinociception. Experiments were carried out on lightly anesthetized rats with an implanted cannula targeting the Sm nucleus. The microinjection of GABA(A) receptor antagonist bicuculline dose-dependently depressed the tail flick (TF) reflex. A smaller dose (100 ng) of bicuculline enhanced the inhibition of TF reflex produced by 5-HT application into Sm, whereas application of GABA (2.5 microg) did not influence the TF reflex but significantly attenuated the 5-HT-evoked inhibition. These results indicate that GABA(A) receptor may be involved in mediating the 5-HT-induced antinociception in Sm possibly through a disinhibition mechanism.
Xiao
Dan-Qin
DQ
Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education, Xi'an Jiaotong University School of Medicine, Xi'an, Shaanxi 710061, People's Republic of China.
Zhu
Juan-Xia
JX
Tang
Jing-Shi
JS
Jia
Hong
H
D000704:Analysis of Variance; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D001931:Brain Mapping; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D018756:GABA Antagonists / Q000494:pharmacology; D008297:Male; D008959:Models, Neurological; D009619:Nociceptors / Q000187:drug effects*; D010147:Pain Measurement / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000494:pharmacology*; D013787:Thalamic Nuclei / Q000187:drug effects*; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D018756:GABA Antagonists; D012701:Serotonin; D005680:gamma-Aminobutyric Acid; D001640:Bicuculline