Type 1 and type 3 ryanodine receptors are selectively involved in muscarinic antinociception in mice: An antisense study

The importance of an intracellular calcium content increase to obtain cholinergic antinociception was demonstrated. The physiological and pathological role of ryanodine receptors (RyRs), receptors involved in the mobilization of intracellular calcium stores, at the CNS level is poorly understood. The aim of the present study was, therefore, to investigate the role of supraspinal endoplasmic type 1, 2 and 3 RyR subtypes in muscarinic antinociception in conditions of acute thermal (hotplate test) and inflammatory (abdominal constriction test) pain. In the absence of isoform selective RyR antagonists, types 1, 2 and 3 RyR knockdown mice were obtained. Western blotting experiments were performed to quantify the RyR isoform protein levels in knockdown mice demonstrating a selective protein level reduction in knockdown animals. I.c.v. pretreatment with an antisense oligonucleotide (aODN) against type 1 or type 3 RyR prevented cholinergic antinociception in the hotplate test shifting to the right of the physostigmine dose-response curve. This antagonistic effect disappeared 7 days after the end of the aODN administration. Conversely, the physostigmine analgesia remained unmodified in type 2 RyR knockdown mice. Similar results were obtained in the abdominal constriction test. Mice undergoing aODN treatments showed neither alteration of animals' gross behavior nor locomotor impairment (rota-rod and hole board tests). These results elucidate the intracellular mechanism underlying muscarinic antinociception. A selective involvement of RyR1 and RyR3 in supraspinal muscarinic analgesia was demonstrated whereas RyR2 appears not to play an essential role in acute thermal and inflammatory pain.