Cellular and Molecular NeuroscienceResearch PaperNeuronal localization of M2 muscarinic receptor immunoreactivity in the rat amygdala
Highlights
▶There is a high density of neuropilar M2 immunoreactivity in the amygdala, especially in rostral portions of the basolateral amygdala. ▶A subset of M2+ nonpyramidal neurons that express GABA, somatostatin, and neuropeptide Y were observed in the lateral nucleus and adjacent external capsule. ▶Large spiny and large aspiny neurons associated with the intercalated nuclei were M2R+. ▶Many neuropeptide Y containing axons in the basolateral amygdala were M2R+. ▶Discrete subpopulations of M2R+ neurons were also seen in the central and medial nuclei.
Section snippets
Tissue preparation
A total of 16 adult male Sprague–Dawley rats (250–350 g; Harlan, Indianapolis, IN, USA) were used in this study. All experiments were carried out in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals and were approved by the Institutional Animal Use and Care Committee (IACUC) of the University of South Carolina. All efforts were made to minimize animal suffering and to use the minimum number of animals necessary to produce reliable scientific data.
Immunoperoxidase studies
All of the immunoperoxidase studies were performed using the rabbit M2R antiserum. The pattern of M2R immunoreactivity (M2R-ir) in the forebrain at the level of the amygdala appeared to be identical to that obtained in previous studies using this antiserum (Levey et al., 1991, Levey et al., 1995b). Thus, staining in the cerebral cortex was predominately neuropilar and exhibited a bistratified configuration. M2R-ir in the striatum was mainly found in a population of large multipolar neurons. The
Discussion
This is the first detailed immunohistochemical investigation of M2R localization in the amygdala. Earlier immunohistochemical and in situ hydridization studies of muscarinic receptor protein and mRNA localization in the rat brain reported that M2R+ neurons were seen in low numbers in the amygdala, but they provided no details regarding their location within the nuclear complex (Levey et al., 1991). The present investigation found low numbers of M2R+ neurons in all nuclei of the amygdala,
Acknowledgments
The authors would like to thank Dr. John H. Walsh (CURE/Digestive Diseases Research Center, Antibody/RIA Core, NIH grant number DK41301, Los Angeles, CA) for the donation of the mouse anti-CCK antibody and Dr. Alison Buchan (University of British Columbia) for the donation of the mouse anti-somatostatin antibody. The authors would like to thank Dr. Jay F. Muller for his comments on an earlier version of this manuscript. This work was supported by NIH grant R01-DA027305.
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