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MSG effects on beta-endorphin and alpha-MSH in the hypothalamus and caudal medulla
N E Alessi1, P Quinlan, H Khachaturian
1Department of Psychiatry, University of Michigan School of Medicine, Ann Arbor 48109.
Abstract:
Monosodium glutamate (MSG) was given to neonatal male rats to determine its effects on neurons containing beta-endorphin (beta-END) and alpha-melanocyte stimulating hormone (alpha-MSH) within the basal hypothalamus (arcuate nucleus) and caudal medulla [nucleus tractus solitarius (NTS)] and on the levels of beta-END and alpha-MSH within these areas. Immunocytochemical studies demonstrated a reduction in the number of cells within the medial hypothalamic area (arcuate nucleus) among MSG-treated animals versus saline controls. MSG did not reduce the number of cell bodies within the caudal medulla (NTS). MSG significantly reduced beta-END and alpha-MSH immunoreactive levels in the basal hypothalamus as determined by radioimmunoassay. Whereas a significant reduction in the level of beta-END occurred in the ventral caudal medulla (VCM), none occurred in the dorsal caudal medulla (DCM). In contrast, levels of alpha-MSH increased significantly in the DCM among animals receiving MSG compared to control animals. This study documents the contribution of beta-endorphin containing neurons of the basal hypothalamus to areas of the caudal medulla. The effect of MSG on beta-endorphin and alpha-MSH neurons in these areas and their differential effects on levels in the caudal medulla areas raises questions about the sites of origin of these peptides.
Insights
Monosodium glutamate (MSG) exposure in neonatal rats reduced beta-endorphin and alpha-MSH neurons in the hypothalamus. MSG also altered peptide levels in the caudal medulla, suggesting complex neuroendocrine effects.
Area of Science:
- Neuroendocrinology
- Neuroscience
- Peptide Research
Background:
- Neonatal exposure to substances can have long-lasting neuroendocrine effects.
- Monosodium glutamate (MSG) is known to affect hypothalamic neurons.
- Beta-endorphin (beta-END) and alpha-melanocyte stimulating hormone (alpha-MSH) are key neuropeptides involved in various physiological processes.
Purpose of the Study:
- To investigate the impact of neonatal MSG administration on beta-endorphin and alpha-MSH neurons.
- To examine the effects of MSG on peptide levels in the basal hypothalamus and caudal medulla.
- To elucidate the role of hypothalamic neurons in projecting to the caudal medulla.
Main Methods:
- Neonatal male rats were administered MSG or saline.
- Immunocytochemistry was used to assess cell numbers.
- Radioimmunoassay quantified peptide levels in specific brain regions (arcuate nucleus, nucleus tractus solitarius).
Main Results:
- MSG treatment reduced the number of beta-END and alpha-MSH neurons in the arcuate nucleus.
- MSG significantly decreased beta-END and alpha-MSH levels in the basal hypothalamus.
- MSG differentially affected peptide levels in the caudal medulla, reducing beta-END in the ventral part but increasing alpha-MSH in the dorsal part.
Conclusions:
- Neonatal MSG exposure disrupts hypothalamic neurons containing beta-END and alpha-MSH.
- MSG alters peptide levels in the caudal medulla, indicating complex neurochemical changes.
- The findings raise questions about the origins and regulation of these peptides in different brain areas.