Comparative study of alpha2-adrenoceptors in Fischer 344 and Lewis rats. Evidence for clonidine-induced place aversion.
Fischer 344 (F344) and Lewis rat strains have been shown to exhibit different vulnerability to development or maintenance of opioid seeking behaviours probably due to differences in the endogenous opioid system. Since opioid and alpha(2)-adrenergic mechanisms closely interact in nociception and substance abuse, strain differences may be expected to affect alpha(2)-adrenoceptor-mediated events. The sensitivity of these two strains to alpha(2)-adrenoceptor-mediated antinociception has been reported to be markedly different. In this work we have further studied the function of alpha(2)-adrenoceptors in F344 and Lewis rats by means of several in vivo and in vitro procedures. Comparative studies of [(3)H]RX821002 and [(35)S]GTPgammaS binding revealed that alpha(2)-adrenoceptors could be slightly more responsive to agonist stimulation in the brain cortex of F344 rats, which is in agreement with previous antinociception studies. However, these differences were modest, not observed in the spinal cord and did not translate into functional differences concerning the effects of clonidine on vas deferens contractility and body temperature. Conditioning experiments showed that a moderate dose of clonidine, which is relevant in antinociceptive and opioid antiwithdrawal studies, induces a robust place aversion which is also equivalent in F344 and Lewis rats. This finding underlies the consistency of the effect and its independency of genetic differences between both rat strains. It seems therefore that the pharmacological properties of alpha(2)-adrenoceptors are similar in F344 and Lewis rats, and thus the previously reported differences in clonidine-induced antinociception could be attributed to other factors such as dissimilar endogenous function of specific noradrenergic pathways.
Herradón
Gonzalo
G
Lab. Pharmacology and Toxicology, University San Pablo CEU, Urb. Montepríncipe, 28668 Boadilla del Monte, Madrid, Spain. herradon@ceu.es
Morales
Lidia
L
Gramage
Esther
E
Alguacil
Luis F
LF
D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D001665:Binding Sites; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D003000:Clonidine / Q000494:pharmacology*; D003216:Conditioning, Operant / Q000187:drug effects*; D004558:Electric Stimulation; D008297:Male; D011485:Protein Binding; D051381:Rats; D011916:Rats, Inbred F344; D011917:Rats, Inbred Lew; D018341:Receptors, Adrenergic, alpha-2 / Q000502:physiology*; D013045:Species Specificity; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism; D014649:Vas Deferens / Q000187:drug effects / Q000378:metabolism
D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists; D018341:Receptors, Adrenergic, alpha-2; D003000:Clonidine