It has been suggested that analgesic effects of opioids can, at least in part, be mediated by cholinergic mechanisms. We have investigated the effects of the muscarinic agonist oxotremorine on the response to a brief thermal stimulus and to a long-lasting painful stimulus induced by formalin. Different groups of CD1 mice were injected with oxotremorine (from 0.005 to 0.05 mg/kg, i.p.). Some groups were tested 15, 30 and 60 minutes after injection in the tail-flick test; other groups received a subcutaneous injection in the dorsal part of the right hind paw of a diluted solution of formalin (5%) and the time spent in licking was recorded for the following 30 minutes. Oxotremorine induced dose and time dependent analgesic effects in both tests. In a second group of experiments it has been observed that ineffective doses of oxotremorine and morphine, when simultaneously administered, were able to enhance the nociceptive threshold in both tests. Naltrexone (1mg/kg) inhibited in part oxotremorine effects only in the second phase of the formalin test. These results show that both phasic and tonic pain can be affected by cholinergic stimulation and that this effect is at least in part mediated by the opioid system.
|Number of pages||1|
|Journal||Italian Journal of Neurological Sciences|
|Publication status||Published - 1997|
ASJC Scopus subject areas
- Clinical Neurology