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Melanin-concentrating hormone-like immunoreactive material in the rat hypothalamus; characterization and subcellular
1Department of Anatomy, Showa University School of Medicine, Tokyo, Japan.
Abstract:
Melanin-concentrating hormone (MCH) is a neurosecretory peptide that induces melanin concentration within teleost melanophores. Here, we characterized MCH-like substance in the rat brain by both an in vitro fish-scale melanophore bioassay and a radioimmunoassay with a salmon MCH antiserum that is directed toward the carboxy-terminus and requires the cyclic configuration for recognition. Furthermore, subcellular localization of the MCH in the rat brain was examined by immunocytochemistry using electron microscopy. We confirmed that MCH-immunoreactivity and MCH-bioactivity were present together in the same effluent fractions of the rat hypothalamic extracts by reverse-phase high-performance liquid chromatography (HPLC). At electron microscopic level, MCH-immunoreactivity was located specifically in secretory granules in MCH-positive cell bodies confined to the hypothalamus with their neuronal processes projecting widely in the rat brain. Although full characterization of substance must await its isolation, our results strongly support the notion that rat MCH-like substance may be homologous but not identical to salmon MCH, and simultaneously may serve some neurotransmitter and/or neuromodulator role in the brain of the rat.
Insights
Researchers identified a melanin-concentrating hormone (MCH)-like substance in rat brains using bioassays and radioimmunoassays. This substance, found in hypothalamic neurons, suggests a potential neurotransmitter role in rats, homologous but not identical to fish MCH.
Area of Science:
- Neuroendocrinology
- Comparative Physiology
- Molecular Biology
Background:
- Melanin-concentrating hormone (MCH) is a known neurosecretory peptide in fish, regulating melanin concentration in melanophores.
- Understanding MCH's role in mammals is crucial for comparative neurobiology and potential therapeutic applications.
Purpose of the Study:
- To characterize the MCH-like substance in the rat brain.
- To determine its localization within rat brain neurons.
- To investigate its potential homology and function compared to fish MCH.
Main Methods:
- In vitro fish-scale melanophore bioassay to detect MCH bioactivity.
- Radioimmunoassay using salmon MCH antiserum for MCH-immunoreactivity.
- Reverse-phase high-performance liquid chromatography (HPLC) for fraction analysis.
- Immunocytochemistry with electron microscopy for subcellular localization.
Main Results:
- MCH-immunoreactivity and MCH-bioactivity were co-eluted from rat hypothalamic extracts.
- MCH-immunoreactivity was localized to secretory granules in hypothalamic neurons.
- Neuronal processes containing MCH-like substance were observed projecting widely within the rat brain.
- Rat MCH-like substance demonstrated homology but not identity to salmon MCH.
Conclusions:
- The rat brain contains a substance with MCH-like bioactivity and immunoreactivity, primarily localized in the hypothalamus.
- This MCH-like substance is packaged in secretory granules, suggesting a neurosecretory function.
- The findings support the hypothesis that rat MCH is homologous to, but distinct from, salmon MCH.
- The study suggests a potential neurotransmitter or neuromodulator role for this substance in the rat brain.