Elsevier

Neuroscience

Volume 82, Issue 4, 12 November 1997, Pages 1131-1149
Neuroscience

Expression of the CB1 and CB2 receptor messenger RNAs during embryonic development in the rat

https://doi.org/10.1016/S0306-4522(97)00348-5Get rights and content

Abstract

We mapped the distribution of CB1 and CB2 receptor messenger RNAs in the developing rat to gain insight into how cannabinoids may affect embryogenesis. In situ hybridization histochemistry studies were done using riboprobes specific for CB1 or CB2 receptor messenger RNAs. We found that CB1 and CB2 receptor messenger RNAs are expressed in the placental cone and in the smooth muscle of the maternal uterus at the earliest gestational periods studied [from eight days of gestation (E8) through E12]. In the embryo, as early as E11, CB1 receptor messenger RNA is expressed in some cells of the neural tube and, at later embryological stages (from E15 to E21), in several distinct structures within the central nervous system. In addition, high levels of CB1 receptor messenger RNA were also found in areas of the peripheral nervous system such as the sympathetic and parasympathetic ganglia, in the retina and in the enteric ganglia of the gastrointestinal tract. In addition to neural structures, high levels of the CB1 receptor messenger RNA were also present in two endocrine organs, the thyroid gland and the adrenal gland. On the other hand, CB2 receptor messenger RNA is expressed exclusively in the liver of the embryo as early as E13.

The region-specific expression of CB1 and CB2 receptor messenger RNAs suggests that these receptors have a functional role during embryogenesis.

Section snippets

Preparation of rat embryo tissue

Timed-pregnant Sprague–Dawley rats purchased from Taconic Farms (Germantown, NY, U.S.A.) were killed by CO2 inhalation. The uteri were dissected on ice. The day of the vaginal plug was designated as E1. Embryos plus uteri (E8–E13) or embryos alone (E13, E15, E17, E18, E19, E20 and E21) were frozen on dry ice and stored at −80°C until sectioning. Serial 12-μm-thick sections in sagittal and transversal planes were collected on silanized slides, briefly dried at 37°C and stored at −80°C until

Results

The following are the results obtained using the antisense probes. No signal was obtained when using the sense probes and are therefore not shown.

Discussion

Although exogenous cannabinoids have been associated with teratogenic effects, the role of endogenous cannabinoids remains largely unknown. In the present work, we have studied the fetal distribution of the two known cannabinoid receptor mRNAs, as well as the presence of these receptor mRNAs in the uterus and placenta. The expression of these receptor mRNAs during development suggests that exogenous as well as endogenous cannabinoids may affect fetal development. Recently, the presence of CB1

Conclusions

Our findings may provide some insight into the functional role of endogenous cannabinoids and into possible targets of exogenous cannabinoids during pregnancy.

In addition, our findings may also provide information for possible medicinal uses of CB1 versus CB2 agonists in a variety of known diseases where marijuana seems beneficial. Marijuana has been used for the treatment of ailments associated with cancer chemotherapy, glaucoma, AIDS, multiple sclerosis and other diseases (for a review see

Acknowledgements

We wish to thank Dr Stefen Lolait and Dr Tom Bonner for the the CB1 receptor plasmid templates, and Dr Sean Munro for the CB2 receptor plasmid template. We also thank Dr Ken Mackie for providing us with the rat CB1 antibody. Finally, we would like to thank Ricardo Dreyfuss for the photomicrography.

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