μ and δ opioid synergy between the periaqueductal gray and the rostro-ventral medulla

doi:10.1016/0006-8993(94)91155-X

Brain Research

Volume 665, Issue 1, 28 November 1994, Pages 85-93

https://doi.org/10.1016/0006-8993(94)91155-X Get rights and content

Abstract

Microinjection of [d-Ala², MePhe⁴, Gly(ol)⁵]enkephalin (DAMGO) into either the periaqueductal gray (PAG) or the rostral ventral medulla (RVM) elicts analgesia in the tailflick assay in the rat. Co-administration of DAMGO into both regions together results in a profound synergistic interaction similar to that we previously reported with morphine. U50,488H and DPDPE are inactive when given into either region. [d-Ala², Glu⁴]Deltorphin (deltorphin), on the other hand, elicits an analgesic response, although the maximal response is less than than μ agonists. Co-administration of DAMGO into one region with deltorphin in the other also results in a significant synergy. However, co-administration of DAMGO and deltorphin together in the same region gives only additive effects. These results confirm the existence of μ/μ synergy between the PAG and RVM. κ1 and δ1 agents are inactive, but theδ₂ agonist deltorphin is active in both regions. Our results indicate the presence ofμ/δ₂ synergy between the PAG and RVM which appears to involve interactions of pathways rather than receptori nteractions at the cellular level.

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μ and δ opioid synergy between the periaqueductal gray and the rostro-ventral medulla

Abstract

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Brain Res.

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Neuropharmacology

Eur. J. Pharmacol.

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Brain Res.

Afferent connections of the rostral medulla of the cat: a neural substrate for midbrain-medullary interactions

J. Comp. Neurol.