Adenosine receptor link in an adrenal opioid-induced antinociception in the rat tail-flick test.

Abstract

Intrathecal administration of substance P at the lower thoracic spinal level has an antinociceptive effect on reaction time in the tail-flick test; this response is blocked by naloxone i.v. but not by i.v. administration of opiate antagonists which do not cross the blood-brain barrier. As morphine-induced analgesia is blocked by adenosine antagonists, to determine whether this substance P-induced, opioid-mediated antinociception also includes a purine link, the adenosine receptor antagonist, caffeine, was given systemically 10 min prior to substance P administration. In control rats pretreated with saline, substance P (6.5 nmol) produced an increase in reaction time to about 160% of preadministration values at one min after intrathecal injection. The effect could also be observed at 6 min after this injection. Pretreatment with 16 or with 32 mg/kg of caffeine i.p. blocked the response to substance P, and produced a hyperalgesia similar to that reported in studies at the lumbo-sacral spinal level. These results indicate that the adrenal opioid-induced antinociception observed upon intrathecal administration of substance P at the lower thoracic level occurs via an adenosine link. This is the first demonstration of a purine link in the expression of antinociceptive effects of an endogenously released opioid.

• Authors: K Yashpal, J L Henry
• Journal: Neuroscience letters (Neurosci Lett) Vol. 138 Issue 2 Pg. 253-6 (Apr 27 1992) ISSN: 0304-3940 [Print] Ireland
• PMID: 1376872 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Receptors, Purinergic
• Substance P
• Caffeine
• Adenosine

Topics

• Adenosine (antagonists & inhibitors)
• Analysis of Variance
• Animals
• Caffeine (pharmacology)
• Male
• Nociceptors (drug effects)
• Pain Measurement
• Rats
• Rats, Inbred Strains
• Reaction Time (drug effects)
• Receptors, Purinergic (physiology)
• Substance P (pharmacology)