Elsevier

Neuroscience

Volume 120, Issue 3, 1 September 2003, Pages 783-798
Neuroscience

Chemical organization of projection neurons in the rat accumbens nucleus and olfactory tubercle

https://doi.org/10.1016/S0306-4522(03)00326-9Get rights and content

Abstract

Projection neurons in the ventral striatum, the accumbens nucleus and olfactory tubercle, were examined by combining the retrograde tracing method and immunocytochemistry with antibodies against C-terminals of the preprodynorphin (PPD), preproenkephalin (PPE), preprotachykinin A (PPTA) and preprotachykinin B (PPTB). When the retrograde tracer was injected into the ventral pallidum, about 60% and 40% of retrogradely labeled neurons in the accumbens nucleus were immunoreactive for PPD and PPE, respectively. In contrast, all accumbens nucleus neurons projecting to the ventral mesencephalic regions including the substantia nigra and ventral tegmental area were immunopositive for PPD but not for PPE. Although no olfactory tubercle neurons projected fibers to the mesencephalic regions, 60% and 40% of olfactory tubercle neurons projecting to the ventrolateral portion of the ventral pallidum were immunoreactive for PPD and PPE, respectively, as were the accumbens nucleus neurons. About 70% of accumbens nucleus and olfactory tubercle neurons projecting to the ventral pallidum and all accumbens nucleus neurons projecting to the ventral mesencephalic regions showed PPTA immunoreactivity. A small population (2–12%) of accumbens neurons projecting to the ventral pallidum and mesencephalic regions displayed immunoreactivity for PPTB. Compared with the dorsal striatopallidal projection neurons that were reported to mostly express PPE, it was characteristic of the ventral striatum that only the smaller population (about 40%) of ventral striatopallidal projection neurons expressed PPE. This suggests that the ventral striatopallidal projection system is less specialized than the dorsal striatopallidal system in terms of peptide production, or that the ventral pallidum should be compared with a combined region of the globus pallidus and entopeduncular nucleus in the dorsal system.

Section snippets

Experimental procedures

The procedures of the present experiments were approved by the Animal Care and Use Committee at the Graduate School of Medicine in Kyoto University, Japan. In all the experiments of the present study, adult male Wistar rats (200–250 g body weight; Japan SLC, Shizuoka, Japan) were used. We tried to minimize the number of animals used and their suffering.

Distribution of immunoreactivities for PPD, PPE, PPTA and PPTB in the ventral pallidal and ventral mesencephalic regions

First, the distributions of neuropil immunoreactivities for PPD, PPE, PPTA and PPTB were examined in the regions that were known to receive axonal projection from the Acb and OT. The VP, one of the main targets of ventral striatal projection neurons, was roughly divided into three subregions according to Zahm (1989) and Zahm et al. (1996). In the subcommissural ventral pallidal regions, immunoreactivity for PPTA (Fig. 1c),

    Abbreviations used in the figures

    ac

    anterior commissure

    AcbC

    core region of the Acb

    AcbS

    shell region of the

Discussion

In the present study, we examined the chemical characteristics of ventral striatal projection neurons; the results were summarized and compared with those of the dorsal striatal projection neurons in Fig. 11. Although the data of PPTA- and PPTB-immunoreactive projection neurons were omitted from Fig. 11 for simplicity, the results of PPTA-immunoreactive projection neurons were similar to those of PPD-immunoreactive neurons. It was characteristic of the OT that no neurons project to the ventral

Acknowledgements

The authors gratefully acknowledge Mr. Akira Uesugi and Ms Keiko Okamoto for their photographic help. This work was supported by Grants-in-Aid from the Ministry of Education, Science, Sports and Culture of Japan (12308039, 13035026, 13041024, 14017050, 15700274 and 15029224), and a grant from Kyowa-Hakko Co., Ltd.

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