Expression of ZFOR1, a delta-opioid receptor, in the central nervous system of the zebrafish (Danio rerio)

Opioid receptors, besides mediating the effects of analgesic compounds, are involved in drug addiction. Although a large amount of work has been done studying these receptors in mammals, little information has been obtained f rom nonmammalian vertebrates. We have studied the regional distribution in the central nervous system (CNS) of the zebrafish of the recently cloned de lta-opioid receptor homologue ZFOR1 using nonradioactive in situ hybridizat ion. Our findings show that different nuclei within the main subdivisions o f the brain displayed specific mRNA signal. The expression is widespread th roughout the brain, but only specific cells within each nucleus displayed Z FOR1. Stained cells were abundant in the telencephalon, both in the olfacto ry bulb and telencephalic hemispheres, and in the diencephalon, where expre ssion was observed in all the different subdivisions. In the mesencephalon, expression of ZFOR1 was abundant in the periventricular layer of the optic tectum. In the cerebellum, expression of ZFOR1 was detected in valvula cer ebelli, corpus cerebelli, and lobus vestibulolateralis in both granule and Purkinje cells. In the myelencephalon, cells expressing ZFOR1 were also dis tributed in the octavolateralis area, the reticular formation, and the raph e nuclei, among others. Also, ZFOR1 was detected in cells of the dorsal and ventral horn of the spinal cord. This work presents the first detailed dis tribution of a delta-opioid receptor in the CNS of zebrafish. Distribution of ZFOR1 expression is compared with that of the delta-opioid receptor desc ribed in mammals. (C) 1999 Wiley-Liss, Inc.