[Effect of atropine on the inhibition of melatonin to the unit discharges evoked in the posterior group of thalamic nuclei in cats].
OBJECTIVE
To study the effect of atropine, muscarinic cholinergic antagonist, on the central analgesic action of melatonin (MT) and to explore the mechanism of MT analgesia.


METHODS
As an indicator of visceral pain, the unit discharges of the neurons in the posterior group of thalamic nuclei (PO) were caused by stimulating the great splanchnic nerve (GSN) of the cat. The cranial stereotaxic and extracellular glass microelectrode record technique were used. The drugs were given through the intra-cranial-ventricle (icv).


RESULTS
0.1% MT (10 micrograms.kg-1, icv) was shown to inhibit the unit discharge of the neurons in PO of the cat, whether the long latency or the short latency, which was evoked by stimulating GSN. The inhibition of 0.1% MT (10 micrograms.kg-1, icv) on the short latency discharge of neurons in PO was antagonized by 0.1% atropine (20 micrograms, icv). However, 0.1% atropine (20 micrograms, icv) did not show antagonistic effect on the inhibition of 0.1% morphine (5 micrograms, icv) at the same latency.


CONCLUSIONS
MT exhibited central analgesic action with mechanism different from morphine. It was suggested that the cholinergic system may be involved in analgesic process of MT.
Zou
Dan
D
School of Pharmacy, Shenyang Pharmaceutical University, Shenyang 110016, China.
Li
Jing-cai
JC
Zhang
Rui-de
RD
D000700:Analgesics / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001285:Atropine / Q000494:pharmacology*; D002415:Cats; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects; D005260:Female; D007276:Injections, Intraventricular; D008297:Male; D008550:Melatonin / Q000008:administration & dosage / Q000494:pharmacology*; D009020:Morphine / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009474:Neurons / Q000502:physiology; D013153:Splanchnic Nerves / Q000502:physiology; D013787:Thalamic Nuclei / Q000187:drug effects* / Q000502:physiology
D000700:Analgesics; D018727:Muscarinic Antagonists; D009020:Morphine; D001285:Atropine; D008550:Melatonin