Elsevier

Brain Research Bulletin

Volume 45, Issue 3, February 1998, Pages 261-268
Brain Research Bulletin

Articles
Neuropeptides in the Cat Amygdala

https://doi.org/10.1016/S0361-9230(97)00343-2Get rights and content

Abstract

The distribution of seven neuropeptides was studied in the cat amygdala using an indirect immunoperoxidase technique. No labeling was found for luteinizing hormone-releasing hormone or β-endorphin (1–27). Sparse α-melanocyte-stimulating hormone-immunoreactive fibers were found in the basomedial nucleus of the amygdala, whereas a low density of fibers containing α-neo-endorphin was observed in the anterior amygdaloid area. Neurotensin was observed in fibers of the anterior amygdaloid area (low density) and both the lateral (low density) and the medial part (moderate density) of the central nucleus. A low density of fibers containing neurokinin A was found in the anterior amygdaloid area, the basolateral nucleus, and the medial part of the central nucleus. A moderate density was observed in the basomedial nucleus and in the medial and cortical nuclei. Fibers containing somatostatin-28 (fragment 1–12) were observed in all the amygdaloid nuclei, whereas immunoreactive cell bodies were found in all the nuclei except in the medial part of the central nucleus and the medial nucleus. Perikarya containing neurokinin A were observed in the latter nucleus. The results point to a discrete distribution of peptidergic fibers in the cat amygdala, as well as the occurrence of neurons containing neurokinin A and somatostatin-28 (fragment 1–12). The distribution of the peptides studied in the cat is compared with the location of the same peptides in the amygdala of other species. The possible diencephalic origin of the peptidergic fibers is also discussed.

Introduction

The amygdala has been implicated in neuroendocrine, visceral, and pain mechanisms [11]as well as in behavioral mechanisms, such as ingestion, reproduction, defense 21, 22, aggression, memory, and learning (see [9]for a review). The amygdala has also been reported to be involved in several neurological disorders, including Alzheimer’s and Huntington’s diseases [9].

Few data are available on the distribution of peptides in the cat amygdala. Substance P has been detected in neurons of the medial amygdaloid nucleus [22], and adrenocorticotropin-like immunoreactivity has been observed in fibers of the anterior amygdaloid area, the medial division of the central nucleus, and the medial nucleus of the cat amygdaloid complex [20]. However, in other mammals (e.g., rat, monkey, humans) several immunocytochemical and radioimmunoassay studies of peptides in the amygdala have been performed 1, 2, 3, 4, 19, 26.

The aim of the present work was to determine the anatomical distribution of several peptides belonging to different families in the cat amygdala. These substances include tachykinins (neurokinin A), pro-dynorphin-derived peptides (α-neo-endorphin), pro-opiomelanocortin-derived peptides (β-endorphin, α-melanocyte-stimulating hormone), inhibitors of growth hormone (somatostatin), and releasing factors (luteinizing hormone-releasing hormone), as well as neurotensin. Our findings are discussed in light of previous studies on the distribution of the above-mentioned peptides in the amygdala of the rat, monkey, and humans.

Section snippets

Materials and Methods

Eight male adult cats (2–3 kg body weight), obtained from commercial sources (CRIFFA, Barcelona, Spain), were used in this study. Each animal was kept in a cage under standard conditions of light (lights on at 06.00, off at 20.00) and temperature (25°C) and had free access to food and water. The animals remained in their cages for 10 days before experiments, which were conducted following institutional approval.

Four animals were deeply anesthetized with ketamine (40–50 mg/kg intraperitoneally),

Results

Fig. 1, Fig. 2 show the distribution of the neuropeptides (SOM, NT, MSH, NEO-END, and NKA) studied in the cat amygdala based on the results obtained from both control and colchicine-treated cats. Colchicine treatment was necessary to visualize NKA-positive cell bodies. However, SOM-like-immunoreactive (ir) perikarya were observed without this treatment, although colchicine did increase the number of neurons containing SOM. The results were quantitatively the same with the DAB and

Discussion

We have described for the first time the distribution of NKA-like-ir fibers and perikarya in the mammalian amygdala. Moreover, the present work reports the distribution of MSH-, NT-, SOM-, NEO-END-like-ir fibers and cell bodies in the cat amygdala using an immunoperoxidase technique. A considerable diversity in the immunohistochemical distribution of the above-mentioned peptides has been reported in the amygdaloid complex of the cat.

Acknowledgements

P. Marcos is supported by the D. G.I.C.Y.T., Spain. The authors wish to thank N. Skinner and Prof. Cooper R. Mackin for revision of the English text. This work has been supported by the D. G.I.C.Y.T. (PB93/0992 and PB 96/1467), Spain.

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