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The effect of hypothalamic lesions on immuno-reactive alpha-melanocyte stimulating hormone secretion in the rat
Abstract:
We have examined the hypothesis that MSH secretion in the rat is under a tonic inhibitory control by the central nervous system. Electrothermic lesions were made in the medio-basal hypothalamus (m.b.h.) which destroyed the hypothalamo-hypophyseal connexions. Plasma and pituitary alpha-MSH wwere measured using a sensitive and specific radioimmunoassay technique. Pituitary alpha-MSH content decreased to 17% of control levels 24 hr after the lesion and returned to normal by 7 days. Plasma alpha-MSH was maximally elevated 15 min after the lesion, and returned to normal by 2 hr. No further change over control levels was found for the remainder of the experiment (98 days). The similarity of the plasma alpha-MSH response after m.b.h. lesions to that found previously after administration of long acting dopamine receptor blocking drugs suggests that these lesions may interrupt impulse flow in dopaminergic tubero hypophyseal neurones which are thought to be important in the inhibitory control of MSH secretion in the rat. From our present results it seems that the rat pituitary, unlike that of lower vertebrates, is able to re-establish basal MSH secretion very quickly after disconnexion from central control.
Insights
Central nervous system control of melanocyte-stimulating hormone (MSH) secretion in rats was investigated. Lesions disrupting hypothalamic connections showed rapid MSH level normalization, suggesting the rat pituitary quickly re-establishes basal secretion.
Area of Science:
- Neuroendocrinology
- Hormone regulation
Background:
- Melanocyte-stimulating hormone (MSH) secretion is influenced by central nervous system (CNS) control.
- The specific mechanisms of tonic inhibitory control on MSH secretion in rats are not fully elucidated.
Purpose of the Study:
- To test the hypothesis that MSH secretion in rats is under tonic inhibitory control by the CNS.
- To investigate the role of the medio-basal hypothalamus (m.b.h.) in regulating MSH secretion.
Main Methods:
- Electrothermic lesions were created in the m.b.h. of rats to disrupt hypothalamo-hypophyseal connections.
- Plasma and pituitary alpha-MSH levels were quantified using radioimmunoassay.
Main Results:
- Pituitary alpha-MSH content significantly decreased 24 hours post-lesion but normalized within 7 days.
- Plasma alpha-MSH showed a transient elevation peaking at 15 minutes and returning to baseline within 2 hours.
- These responses suggest interruption of dopaminergic tubero-hypophyseal pathways involved in MSH inhibition.
Conclusions:
- The rat pituitary rapidly re-establishes basal MSH secretion following disconnection from central inhibitory control.
- This contrasts with lower vertebrates, indicating a unique adaptation in the rat's neuroendocrine regulation of MSH.