Related Experiment Videos
Release of immunoreactive alpha-MSH by synaptosome-enriched fractions of homogenates of hypothalami
Abstract:
Immunoreactive alpha-melanocyte-stimulating hormone (alpha-MSH) was found to be concentrated in a synaptosome-enriched fraction prepared by differential centrifugation of rat hypothalamic homogenates. The release of the hormone from this preparation was investigated. After incubation, the synaptosomes were isolated by ultrafiltration and alpha-MSH in the ultrafiltrate was determined by radioimmunoassay. Particle-bound alpha-MSH, recovered by extraction with acid ethanol, and alpha-MSH released from the synaptosome preparation, were immunologically similar to synthetic alpha-MSH and had an accompanying melanotropic activity. Less than 10% of the particle-bound alpha-MSH was released during incubation in 0.32 M sucrose. However, in the presence of 2 mM Ca2+, alpha-MSH release increased with increasing concentrations (30-150 mM) of K+. The stimulatory effect of 60 mM K+ was complete within 2 min and was potentiated by increasing Ca2+ concentrations over the range of 0 to 2 mM. K+-induced release of alpha-MSH was independent of temperature from 1 to 30 degrees C, and neither glucose (10 mM) nor dopamine (10(-10)-10(-2) M) had any effect on the release of the peptide. It is concluded that a synaptosome-enriched fraction from the hypothalamus contains a releasable pool of immunoreactive alpha-MSH that is mobilized by depolarizing concentrations of K+ in a Ca2+-dependent manner.
Insights
Hypothalamic alpha-melanocyte-stimulating hormone (alpha-MSH) is stored in synaptosomes. Potassium and calcium ions trigger the release of alpha-MSH from these nerve endings.
Area of Science:
- Neuroendocrinology
- Molecular Neuroscience
Background:
- Alpha-melanocyte-stimulating hormone (alpha-MSH) is a peptide hormone with diverse functions in the central nervous system.
- Its precise localization and release mechanisms within hypothalamic synaptosomes are not fully elucidated.
Purpose of the Study:
- To investigate the presence and release of immunoreactive alpha-MSH from a synaptosome-enriched fraction of the rat hypothalamus.
- To characterize the conditions that modulate alpha-MSH release from hypothalamic synaptosomes.
Main Methods:
- Preparation of a synaptosome-enriched fraction from rat hypothalamic homogenates using differential centrifugation.
- Incubation of synaptosomes and isolation of released alpha-MSH via ultrafiltration.
- Quantification of alpha-MSH using radioimmunoassay.
- Assessment of melanotropic activity and immunological similarity to synthetic alpha-MSH.
Main Results:
- Immunoreactive alpha-MSH was concentrated in the hypothalamic synaptosome fraction.
- Alpha-MSH release was minimal in sucrose but significantly increased with elevated potassium (K+) concentrations in a calcium (Ca2+)-dependent manner.
- K+-induced release was rapid, temperature-independent, and unaffected by glucose or dopamine.
Conclusions:
- Hypothalamic synaptosomes contain a releasable pool of alpha-MSH.
- The release of this alpha-MSH is regulated by neuronal depolarization (via K+) and requires extracellular Ca2+.
- These findings suggest a role for alpha-MSH in synaptic signaling within the hypothalamus.