Opioid binding sites in the fish brain: An autoradiographic study

Bird, David J.; Jackson, Marcus; Baker, Bridget I.; Buckingham, Julia C.

Abstract

Cryostat sections of trout brains were incubated with tritiated opioid ligands (5 nM [3H]etorphine or 4 nMd-[3H]Ala2, Met5 enkephalinamide) with the initial aim of locating opioid binding sites associated with the hypothalamo-pituitary axis. Naloxone-displaceable binding was observed in all regions of the brain, with a density ranking order of cerebellum > telencephalon > optic tectum > hypothalamus > brain stem > pituitary gland. Within the hypothalamus and pituitary gland binding was unexpectedly low, apart from a slightly enhanced binding anteriorly in the preoptic region and posteriorly associated with presumptive sensory fibres. A similar distribution of opioid binding sites was seen in the eel and lamprey brain. The high level of opioid binding in the cerebellum permitted a tentative identification of opioid subtypes using [3H]etorphine binding to membrane preparations from trout cerebellum. Scatchard analysis indicated the presence of a single class of high-affinity binding sites with a density of 0.38 pmol/mg protein and affinity constant (KD) of 2.6 nM. Displacement by unlabelled ligands suggested the existance of μ and/or κ receptors. © 1988.

• Journal Article Type: Article
• Publication Date: Jan 1, 1988
• Journal: General and Comparative Endocrinology
• Print ISSN: 0016-6480
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 70
• Issue: 1
• Pages: 49-62
• DOI: https://doi.org/10.1016/0016-6480%2888%2990093-7
• Public URL: https://uwe-repository.worktribe.com/output/1112265
• Publisher URL: http://dx.doi.org/10.1016/0016-6480(88)90093-7