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Hypophysial and meningeal melanocytes in the Zucker rat
S O Fetissov1, M A Barcza, M M Meguid
1Neuroscience Program, Surgical Metabolism and Nutrition Laboratory, Department of Surgery, SUNY HSC, Syracuse, NY 13210, USA. fetissos@mailbox.hscsyr.edu
Abstract:
Melanocytes have not been described in the pituitary of mammals or in the meninges of the rat. In this paper, we report the presence of the cluster of melanocytes in the intermediate lobe of the pituitary and around the median eminence of the hypothalamus forming an 'infundibulo-hypophysial circle', and also describe the characteristics of meningeal melanocytes in Zucker rats. In the leptomeninges, numerous melanocytes were found on the ventrolateral surface of cerebral hemisphere in the area of the middle cerebral artery. Pigment granules were also observed in the surrounding tissue outside the melanocytes as well as incorporated in the cytoplasm of neural and epithelial cells. Electron microscopy revealed that melanosomes in hypophysial and meningeal melanocytes were in different (II-IV) stages of maturity. In the leptomeninges of Zucker rats, HMB-45 immunoreactivity was found in round non-melanosome-containing cells, while no HMB-45 reaction was found in the leptomeninges of the albino rat. We conclude that both obese and lean Zucker rats possess functionally active melanocytes in the meninges and the pituitary and transfer pigment granules to neighboring cells. The distributions of melanocytes in proximity to blood vessels in the leptomeninges and in the 'infundibulo-hypophysial circle' suggest an endocrine secretory function.
Insights
This study identifies melanocytes in the rat pituitary and meninges, forming an
Area of Science:
- Neuroscience
- Cell Biology
- Endocrinology
Background:
- Melanocytes have not been previously documented in the mammalian pituitary or rat meninges.
- The presence and function of melanocytes in these locations remain largely unexplored.
Purpose of the Study:
- To investigate and characterize the presence of melanocytes in the pituitary and meninges of rats.
- To determine the maturity and potential function of these newly identified melanocyte populations.
Main Methods:
- Histological examination of pituitary and meningeal tissues.
- Electron microscopy to assess melanosome maturity.
- Immunohistochemistry using HMB-45 antibody.
Main Results:
- Melanocytes were identified in the pituitary intermediate lobe and around the hypothalamus, forming an 'infundibulo-hypophysial circle'.
- Meningeal melanocytes were abundant on the cerebral hemispheres, particularly near the middle cerebral artery.
- Pigment granules were observed within melanocytes and transferred to surrounding neural and epithelial cells.
- Melanosomes showed varying stages of maturity (II-IV) in both locations.
- HMB-45 immunoreactivity was present in meningeal melanocytes of Zucker rats but absent in albino rats.
Conclusions:
- Zucker rats possess functionally active melanocytes in the meninges and pituitary, capable of pigment transfer.
- The distribution of melanocytes near blood vessels suggests a potential endocrine secretory role.