Elsevier

Neuroscience

Volume 82, Issue 3, 24 October 1997, Pages 767-780
Neuroscience

Expression of D1 receptor, D2 receptor, substance P and enkephalin messenger RNAs in the neurons projecting from the nucleus accumbens

https://doi.org/10.1016/S0306-4522(97)00327-8Get rights and content

Abstract

In situ hybridization was combined with FluoroGold retrograde labelling to determine the distribution of messenger RNAs for the D1 dopamine receptor, D2 dopamine receptor, β-preprotachykinin or preproenkephalin in the neurons projecting from the nucleus accumbens to the ventral pallidum and the ventral tegmental area. Neurons were quantified in both the core and the shell of the nucleus accumbens to estimate the proportion of neurons projecting to the ventral pallidum or ventral tegmental area that contain transcripts for D1 receptors, D2 receptors, β-preprotachykinin or preproenkephalin. Following the deposition of FluoroGold into the central ventral pallidum, both the core and the shell of the nucleus accumbens were retrogradely labelled, while deposits into the ventral tegmental area selectively labelled cells in the shell. A high percentage of nucleus accumbens neurons innervating the ventral tegmental area expressed messenger RNAs for D1 receptors (72%) and β-preprotachykinin (62%), while less than 3% of the neurons contained messenger RNAs for preproenkephalin or D2 receptors. The neurons projecting to the ventral pallidum did not show the discrete distribution of transcripts as was observed in the accumbens-ventral tegmental area projection. Preproenkephalin messenger RNA was identified in 46% of the neurons innervating the ventral pallidum, and D2 receptor messenger RNA was found in approximately 40% of the cells. A large minority of neurons projecting from the nucleus accumbens to the ventral pallidum also expressed messenger RNAs for D1 receptors (37%) and β-preprotachykinin (35%). While a higher percentage of D1 receptor, and β-preprotachykinin messenger RNA expressing cells were located in the shell than in the core of the nucleus accumbens, the percentage tended to be higher in the core for cells expressing D2 receptors or preproenkephalin messenger RNA.

These data indicate that messenger RNAs for D2 receptors and enkephalin are selectively expressed in the accumbens-pallidal projection while transcripts encoding D1 receptors and substance P are contained in the efferent projections to both the ventral pallidum and ventral tegmental area. The presence of D1 receptors and β-preprotachykinin messenger RNA in both mesencephalic and pallidal projections contrasts output from the striatum where the expression of D1 receptors and β-preprotachykinin messenger RNA is primarily restricted to the mesencephalic projection.

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

[5]not cited in the text.[28]not cited in the text.[53]not cited in the text.

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.

References (75)

  • M.B Harrison et al.

    Selective localization of striatal D1 receptors to striatonigral neurons

    Brain Res.

    (1990)
  • M.B Harrison et al.

    Changes in D2 but not D1 receptor binding in the striatum following a selective lesion of striatopallidal neurons

    Brain Res.

    (1992)
  • L Heimer et al.

    Ventral striatum and ventral pallidum. Components of the motor system?

    Trends Neurosci.

    (1982)
  • L Heimer et al.

    Specificity in the projection patterns of accumbal core and shell in the rat

    Neuroscience

    (1991)
  • M Herkenham et al.

    Cell clusters in the nucleus accumbens of the rat, and the mosaic relationship of opiate receptors, acetylcholinesterase and subcortical afferent terminations

    Neuroscience

    (1984)
  • P.W Kalivas et al.

    GABA and enkephalin projection from the nucleus accumbens and ventral pallidum to VTA

    Neuroscience

    (1993)
  • H Maeno et al.

    Distribution of the substance P receptor (NK-1 receptor) in the central nervous system

    Molec. Brain Res.

    (1993)
  • A Mansour et al.

    A comparison of D1 receptor binding and mRNA in rat brain using receptor autoradiographic and in situ hybridization techniques

    Neuroscience

    (1991)
  • G.J Mogenson et al.

    Ventral pallidum projections to mediodorsal nucleus of the thalamus: an anatomical and electrophysiological investigation in the rat

    Brain Res.

    (1987)
  • T.C Napier et al.

    Substance P projection from the nucleus accumbens to the ventral pallidum. Anatomy, electrophysiology and behavior

    Neuroscience

    (1995)
  • W.J.H Nauta et al.

    Efferent connections and nigral afferents of the nucleus accumbens septi in the rat

    Neuroscience

    (1978)
  • R.D Oades et al.

    Ventral tegmental (A10) system: neurobiology. 1. Anatomy and connectivity

    Brain Res.

    (1987)
  • V.A Pieribone et al.

    The iontophoretic application of FluoroGold for the study of afferents to deep brain nuclei

    Brain Res.

    (1988)
  • G.S Robertson et al.

    D1 and D2 dopamine receptors differentially increase Fos-like immunoreactivity in accumbal projections to the ventral pallidum and midbrain

    Neuroscience

    (1995)
  • G.S Robertson et al.

    D1 and D2 dopamine receptors differentially regulate c-fos expression in striatonigral and striatopallidal neurons

    Neuroscience

    (1992)
  • R Tamiya et al.

    Substance P afferents have synaptic contacts with dopaminergic neurons in the ventral tegmental area of the rat

    Neurosci. Lett.

    (1990)
  • M Vankova et al.

    Enkephalin-containing nerve cell bodies in the substantia nigra of the rat: Demonstration by immunohistochemistry and in situ hybridization

    Brain Res. Bull.

    (1991)
  • K Yoshikawa et al.

    Rat brain preproenkephalin mRNA

    J. biol. Chem.

    (1984)
  • K.K.L Yung et al.

    Immunocytochemical localization of D1 and D2 dopamine receptors in the basal ganglia of the rat: Light and electron microscopy

    Neuroscience

    (1995)
  • D.S Zahm

    The ventral striatopallidal parts of the basal ganglia in the rat. II. Compartmentation of ventral pallidal efferents

    Neuroscience

    (1989)
  • D.S Zahm et al.

    On the significance of subterritories in the “accumbens” part of the rat ventral striatum

    Neuroscience

    (1992)
  • D.S Zahm et al.

    Evidence for the coexistence of glutamate decarboxylase and met-enkephalin immunoreactivities in axon terminals of rat ventral pallidum

    Brain Res.

    (1985)
  • H.W Berendse et al.

    Topographical organization and relationship with ventral striatal compartments of prefrontal corticostriatal projections in the rat

    J. comp. Neurol.

    (1992)
  • H.W Berendse et al.

    Compartmental distribution of ventral striatal neurons projecting to the mesencephalon in the rat

    J. Neurosci.

    (1992)
  • J.R Bunzow et al.

    Cloning and expression of a rat D2 dopamine receptor cDNA

    Nature

    (1988)
  • D.L Cameron et al.

    Dopamine D1 receptors facilitate transmitter release

    Nature

    (1993)
  • L Churchill et al.

    A topographically organized GABAergic projection from the ventral pallidum to the nucleus accumbens in the rat

    J. comp. Neurol.

    (1994)
  • Cited by (250)

    • Striatal circuits

      2022, Neurocircuitry of Addiction
    • Ventral pallidum cellular and pathway specificity in drug seeking

      2021, Neuroscience and Biobehavioral Reviews
    View all citing articles on Scopus
    View full text