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Effects of preoptic microinjections of alpha-MSH on fever and normal temperature control in rabbits
Abstract:
alpha-MSH within the septal region of the brain has been implicated in fever control; this peptide and ACTH (1-24), which contains the alpha-MSH amino acid sequence, reduce fever when given intracerebroventricularly (ICV) or peripherally. These peptides also cause hypothermia when given in doses larger than those required to reduce fever. Both peptides occur naturally within the preoptic PO region of the brain, the CNS locus of primary temperature control. alpha-MSH (350 ng) injected bilaterally into the PO region via chronic cannulas reduced fever caused in six rabbits by IV injection of IL-1 (interleukin 1, endogenous or leukocyte pyrogen) but had no effect in afebrile animals. A larger dose (1.5 micrograms) not only reduced fever but caused hypothermia in 12 rabbits. In separate experiments PO injections of ACTH (1-24) (1 microgram) reduced normal temperature. In the same six rabbits alpha-MSH (1 microgram) caused slightly smaller hypothermia. alpha-MSH (1.5 micrograms) also had no effect in 8 afebrile rabbits when injected into the septum. The primary conclusion is that alpha-MSH receptors within the PO region can contribute to both the antipyretic and hypothermic actions that are observed after ICV and peripheral administration of the peptide.
Insights
Alpha-melanocyte-stimulating hormone (alpha-MSH) in the brain
Area of Science:
- Neuroscience
- Endocrinology
- Physiology
Background:
- Alpha-melanocyte-stimulating hormone (alpha-MSH) and ACTH (1-24) are involved in fever regulation.
- These peptides are naturally present in the preoptic (PO) region of the brain, a key area for temperature control.
- Both peptides can reduce fever and induce hypothermia depending on dosage and administration route.
Purpose of the Study:
- To investigate the role of alpha-MSH receptors in the preoptic region of the brain in mediating fever control and hypothermia.
- To determine if direct administration of alpha-MSH into the preoptic region affects fever induced by interleukin-1 (IL-1).
Main Methods:
- Rabbits were injected with alpha-MSH or ACTH (1-24) directly into the preoptic (PO) region of the brain.
- Fever was induced using intravenous injections of interleukin-1 (IL-1).
- Body temperature changes were monitored following peptide administration in both febrile and afebrile animals.
Main Results:
- Alpha-MSH injected into the PO region reduced IL-1-induced fever in rabbits.
- Higher doses of alpha-MSH and ACTH (1-24) administered to the PO region induced hypothermia.
- Alpha-MSH in the septum did not affect afebrile rabbits, suggesting a specific role for the PO region.
Conclusions:
- Alpha-MSH receptors located within the preoptic region are crucial for both the fever-reducing and hypothermic effects of alpha-MSH.
- Direct action of alpha-MSH in the PO region contributes to the observed physiological responses to central and peripheral administration of the peptide.