Physical addiction to opiates is a problem of enormous social and economic significance in this country yet the molecular neuronal mechanisms which underlie this complex phenomenon are poorly understood. The recent cloning of the major subtypes of opioid receptors, as well as that of several genes encoding proteins closely related to the pharmacologically-defined opioid receptors, has greatly facilitated our understanding of cellular consequences associated with opioid receptor activation and signal transduction. In addition, elegant work done by others has clearly implicated noradrenergic neurons of the locus coeruleus (LC) and the mesolimbic dopamine system including the ventral tegmental area (VTA) and the nucleus accumbens (NA) in development of opiate tolerance, dependence and withdrawal. The LC, a well-defined neuronal cluster which is located near the wall of the fourth ventricle at the level of the pons, has been demonstrated to be exquisitely sensitive to the effects of chronic opiate treatment and opiate withdrawal. Several lines of evidence suggest that chronic treatment of rats with morphine alters the biochemical and electrophysiological phenotypes of noradrenergic neurons in the locus coeruleus and that these alterations are intimately linked to opiate tolerance, dependence and withdrawal. We have used CATHa cells, a locus coeruleus-like cell line, as a model system to study the effects of chronic morphine treatment on gene expression. Using the experimental technique of mRNA differential display, we have isolated two transcripts which appear to be regulated as a consequence of chronic morphine treatment, Morphine-Induced Transcript (MIT) and Morphine-Repressed Transcript (MRT). The experiments described herein are designed to characterize these transcripts by: (1) cloning full-length cDNAs corresponding to MIT and MRT, (2) elucidating the function of proteins encoded by MIT, MRT and other proteins encoded by morphine-regulated transcripts, (3) verifying that chronic morphine treatment modulates MIT and MRT expression in an animal model, and (4) studying the regional distribution of MIT and MRT in brain. We will then attempt to isolate transcripts from rat brain which are modulated as a consequence of chronic morphine treatment. Finally, we will clone and functionally dissect the promoter regions of genes corresponding to these morphine-modulated transcripts toward the goal of elucidation of the regulatory element(s) which confer morphine inducibility or repression upon these genes. These studies should facilitate our understanding of the molecular mechanisms which underlie neurobiological adaptation to chronic opiate exposure.
| Bouvier, C; Avram, D; Peterson, V J et al. (1998) Catecholaminergic CATH.a cells express predominantly delta-opioid receptors. Eur J Pharmacol 348:85-93 |
