DEVELOPMENTAL EXPRESSION OF CANNABINOID RECEPTOR MESSENGER-RNA

Cloning of the cannabinoid receptor affords the opportunity to examine its developmental expression. Other G-protein-coupled receptor system s, those for the opioids for example, exhibit distinct ontogenies. For the initial study, therefore, cannabinoid receptor mRNA expression wa s assessed in rat pups postnatal days 3, 5, 8, 10, 12, 15, 18 and 21. The brains were grossly dissected into cerebellum/brainstem and forebr ain, and total RNA was extracted by a modified acid-extraction method. Expression of the cannabinoid receptor was analyzed by two methods: p olymerase chain reaction (PCR) and Northern blot analysis. Oligonucleo tide primers based on bp 1-21 and bp 824-843 on the opposite strand we re chosen for use in the PCR. The probe used in the Northern blot anal ysis was a full length cDNA corresponding to the rat cannabinoid recep tor and was cloned in our lab based on published sequence information. Our results indicate that by postnatal day 3, cannabinoid receptor mR NA can be detected in the brain. Our results further indicate that can nabinoid mRNA expression steadily increases in the cerebellum/brainste m until postnatal days 18-21, while expression in the forebrain does n ot change. The findings from the present study indicate that cannabino id receptor mRNA is present in very young rats. Our data also suggest, however, regional differences in the relative expression of message w hich may parallel cerebellar proliferation and organization.