ArticlesNeuropeptides in the Cat Amygdala
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.
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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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