EXPRESSION OF THE CB1 AND CB2 RECEPTOR MESSENGER-RNAS DURING EMBRYONIC-DEVELOPMENT IN THE RAT

We mapped the distribution of CB1 and CB2 receptor messenger RNAs in t he developing rat to gain insight into how cannabinoids may affect emb ryogenesis. In situ hybridization histochemistry studies were done usi ng riboprobes specific for CB1 or CB2 receptor messenger RNAs. We foun d that CB1 and CB2 receptor messenger RNAs are expressed in the placen tal cone and in the smooth muscle of the maternal uterus at the earlie st gestational periods studied [from eight days of gestation (E8) thro ugh E12]. In the embryo, as early as E11, CB1 receptor messenger RNA i s expressed in some cells of the neural tube and, at later embryologic al stages (from E15 to E21), in several distinct structures within the central nervous system. In addition, high levels of CB1 receptor mess enger RNA were also found in areas of the peripheral nervous system su ch as the sympathetic and parasympathetic ganglia, in the retina and i n the enteric ganglia of the gastrointestinal tract. In addition to ne ural structures, high levels of the CB1 receptor messenger RNA were al so present in two endocrine organs, the thyroid gland and the adrenal gland. On the other hand, CB2 receptor messenger RNA is expressed excl usively in the liver of the embryo as early as E13. The region-specifi c expression of CB1 and CB2 receptor messenger RNAs suggests that thes e receptors have a functional role during embryogenesis. (C) 1997 IBRO . Published by Elsevier Science.