PMID: 2492344Jan 1, 1989Paper

Morphine, capsaicin and K+ release purines from capsaicin-sensitive primary afferent nerve terminals in the spinal cord

The Journal of Pharmacology and Experimental Therapeutics
M I SweeneyJana Sawynok

Abstract

In the present study the neuronal source of adenosine released by K+, morphine and norepinephrine (NE) from the spinal cord was investigated. Intrathecal pretreatment with 5,7-dihydroxytryptamine and 6-hydroxydopamine reduced spinal 5-hydroxytryptamine and NE levels, respectively, but had no effect on adenosine release from dorsal spinal cord synaptosomes evoked by K+ or morphine. NE-evoked release of adenosine was unaffected by 5,7-dihydroxytryptamine but increased by 6-hydroxydopamine. Subcutaneous pretreatment of neonatal or intrathecal pretreatment of adult rats with capsaicin increased nociceptive thresholds and reduced the release of adenosine evoked by K+ and morphine but not NE from dorsal spinal cord synaptosomes. Intrathecal capsaicin also inhibited morphine-evoked release of adenosine in vivo. K+ and morphine released only small amounts of adenosine from ventral spinal cord synaptosomes whereas NE released significant amounts. Exposure of dorsal, but not ventral, spinal cord synaptosomes to capsaicin produced a dose- and Ca++-dependent release of adenosine, which was reduced by capsaicin pretreatment (neonatal and adult) and inhibition of ecto-5'-nucleotidase. Capsaicin also released endogenous ATP from dorsal spinal...Continue Reading

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