OPIOID RECEPTOR AND PEPTIDE MESSENGER-RNA EXPRESSION IN PROLIFERATIVEZONES OF FETAL-RAT CENTRAL-NERVOUS-SYSTEM

There is increasing evidence to suggest that opioid peptides may have widespread effects as regulators of growth. To evaluate the hypothesis that endogenous opioids control cellular proliferation during neural development, we have used in situ hybridization to examine opioid pept ide and receptor mRNA expression in neuroepithelial zones of fetal rat brain and spinal cord. Our data show that proenkephalin mRNA is widel y expressed in forebrain grerminal zones and choroid plexus during the second half of gestation. In contrast, prodynorphin mRNA expression i s restricted to the periventricular region of the ventral spinal cord. Little mu or delta receptor mRNA expression was detected in any regio ns of neuronal proliferation prior to birth. However, kappa receptor m RNA is widely expressed in hindbrain germinal zones during the 3rd wee k of gestation. Our present findings support the hypothesis that endog enous opioids ma; regulate proliferation of both neuronal and non-neur onal cells during central nervous system development. Given the segreg ated expression of proenkephalin mRNA in forebrain neuroepithelium and kappa receptor mRNA within hindbrain, different opioid mechanisms may regulate cell division in rostral and caudal brain regions.