Ketamine abolishes cyclohexyladenosine induced antinociception on mononeuropathic rats

Abstract

Ketamine is known as a N-Methyl-D-Aspartate (NMDA) antagonist. Purine analogues attenuate pain transmission and also act as glutamate antagonists. The aim of the present study was to determine the antiallodynic effect of adenosine A1 receptor agonist, cyclohexyladenosine (CHA) and ketamine on thermal nociception in chronic constriction injury model in the rat. The present study was constituted on 32 male Sprague Dawley rats weighing 180-220 g. The right common sciatic nerve was exposed and ligated loosely with 4/0 chromic catgut under barbiturate anaesthesia. Drugs were administered after 7th postoperative day and given through four days. Treatment protocol was two injections/day performed by a 20 min interval through intraperitoneal route. Adenosine analogues were administered as the first drug. Doses were 1 mg/kg and 10 mg/kg for CHA and ketamine respectively. Doses were reduced to half when both of drugs were combined. Nociceptive tests were performed by Hot Plate Test (HPT) at 46°C through 120 min period every 30 minutes. Initiation time of jumping and licking movements at the operated side of the rats on the HPT was determined. Motor activity were increased on animals that received ketamine. Adenosine receptor analogue CHA clearly produced antinociception. Ketamine abolished CHA induced analgesia. The results were disappointing, antagonism was observed by two class of drugs known as glutamate antagonist and can be explained by excitatory phenomenon induced by ketamine. Future studies directed at other routes may show promise.