Expression of D1 receptor, D2 receptor, substance P and enkephalin messenger RNAs in the neurons projecting from the nucleus accumbens
Section snippets
Animal housing and surgery for FluoroGold
Male Sprague–Dawley rats (Simonsen Laboratories, Gilroy, CA) were housed in groups of four on a 12/12 h light/dark cycle. Food and water were available ad libitum. When the rats attained a weight of 250–300 g, they were anaesthetized with Equithesin (0.3 ml/100 g, i.p.) and mounted in a stereotaxic apparatus. 2% FluoroGold (Fluorochrome, Inc., Englewood, CO) was dissolved in 0.1 M cacodylate buffer (pH 7.2), and loaded into cleaned glass microfilament capillary pipettes with tips 20–40 μm in diameter.
FluoroGold iontophoretic deposits in the ventral pallidum and ventral tegmental area
Retrograde axonal transport of FluoroGold from deposits into the VP or VTA was used to label accumbal neurons. Fig. 2A shows a low magnification fluorescent photograph of coronal section illustrating an iontophoretic deposit of FluoroGold in the VP. The high density of FluoroGold in the core of the deposit was centred in the subcomissural VP, while the halo filled most of the VP. A composite drawing of the iontophoretic deposits in the VP from the four animals used for this study is shown in
Discussion
This study examined the distribution of mRNAs encoding D1 receptor, D2 receptor, substance P and enkephalin in the subpopulations of neurons in the nucleus accumbens projecting to the VTA or VP. Neurons innervating the VTA primarily express D1 receptor and substance P, with less than 3% of the retrogradely-labelled cells double-labelling for D2 receptor or PPE mRNAs. In contrast, between 35 and 46% of all cells retrogradely labelled from the VP expressed each of the four transcripts.
Conclusions
The present results provide a detailed analysis of the expression of D1 receptor, D2 receptor, PPT and PPE mRNAs in the projections from the nucleus accumbens to the VP and VTA. Preproenkephalin and D2 receptor mRNAs were exclusively expressed in neurons that project to the VP, whereas PPT and D1 receptor mRNAs were expressed in neurons projecting to both the VP and VTA. These results suggest that the projection from the nucleus accumbens to the VTA resembles striatal efferents to the ventral
Unlinked References
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Acknowledgements
This research was supported in part by the USPHS grants MH-40817, DA-03906 and a Research Career Development Award DA-00158 to P. W. Kalivas. We thank Dr Lynn Churchill for her technical assistance and helpful suggestions in the preparation of this manuscript. We also thank Dr Barbara A. Sorg for her expert advice in solving technical problems of the experiments.
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