Regulation of cannabinoid and mu opioid receptors in rat lumbar spinal cord following neonatal capsaicin treatment

• Published in: Neuroscience letters Vol. 252; no. 1; pp. 13 - 16
• Main Authors: Hohmann, Andrea G, Herkenham, Miles
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier Ireland Ltd 07.08.1998; Elsevier
• Subjects: Analgesics, Opioid - pharmacology; Animals; Animals, Newborn; Autoradiography; Biological and medical sciences; C-fiber; Cannabinoid; Capsaicin; Capsaicin - pharmacology; Central nervous system; Central neurotransmission. Neuromudulation. Pathways and receptors; Cyclohexanols - pharmacology; Down-Regulation - drug effects; Enkephalin, Ala-MePhe-Gly; Enkephalins - pharmacology; Female; Fundamental and applied biological sciences. Psychology; Immunosuppressive Agents - pharmacology; Mu opioid; Nerve Fibers - chemistry; Nociceptors - physiology; Pregnancy; Rats; Rats, Sprague-Dawley; Receptors, Cannabinoid; Receptors, Drug - agonists; Receptors, Drug - analysis; Receptors, Opioid, mu - agonists; Receptors, Opioid, mu - analysis; Spinal Cord - chemistry; Tritium; Vertebrates: nervous system and sense organs; C-fiber; Mu opioid; Autoradiography; Cannabinoid; Capsaicin; Vertebrata; Spinal cord; Mammalia; Rat; Rodentia; Central nervous system; μ Opioid receptor; Nerve fiber C
• ISSN: 0304-3940; 1872-7972
• DOI: 10.1016/S0304-3940(98)00534-5

In vitro receptor binding and quantitative autoradiography were used to determine whether cannabinoid receptors in rat lumbar spinal cord are localized to the central terminals of nociceptive primary afferents. Rats were treated as neonates with capsaicin to destroy sensory C-fibers. The densities of cannabinoid and mu opioid receptors in the spinal cord of the adult rats were compared with age-matched vehicle controls. Neonatal capsaicin produced a moderate but reliable suppression (16%) of [ 3H]CP55,940 binding to cannabinoid receptors. By contrast, the binding of [ 3H][D-Ala 2-MePhe 4,Gly-ol 5]enkephalin (DAMGO) to mu receptors was depleted by approximately 60% in near adjacent sections. These data suggest that only a subpopulation of cannabinoid receptors is situated on the central terminals of primary afferent C-fibers. The present data provide anatomical evidence for a dissociation between cannabinoid and mu opioid modulation of sensory transmission at the level of the primary afferent inputs to the spinal cord.