GRF-induced feeding: evidence for protein selectivity and opiate involvement

Area of Science:

• Neuroendocrinology
• Neuroscience
• Behavioral Neuroscience

Background:

• Growth hormone-releasing factor (GRF) is a hypothalamic peptide regulating growth hormone release.
• GRF also functions as a neurotransmitter in the suprachiasmatic nucleus/medial preoptic area (SCN/MPOA), influencing feeding behavior.
• The role of opiate activity within the paraventricular nucleus of the hypothalamus (PVN) in GRF-induced feeding is not fully understood.

Purpose of the Study:

• To investigate the macronutrient selectivity of GRF-induced feeding.
• To determine the involvement of PVN opiate activity in GRF-stimulated feeding.
• To explore the relationship between GRF, opiates, and macronutrient intake.

Main Methods:

• Microinjections of GRF into the SCN/MPOA and methyl-naltrexone or naloxone into the PVN in rats.
• Assessment of chow and macronutrient diet intake following GRF administration.
• Microinjections of morphine into the PVN to assess its effect on macronutrient intake.

Main Results:

• GRF microinjection into the SCN/MPOA stimulated food intake, which was blocked by PVN methyl-naltrexone.
• GRF preferentially stimulated protein intake over carbohydrate intake in habituated animals.
• This selective protein intake was blocked by PVN naloxone, and PVN morphine microinjections also selectively stimulated protein intake.

Conclusions:

• GRF-induced feeding in the SCN/MPOA is selective for protein over carbohydrates.
• PVN opiate activity is essential for the expression of GRF-stimulated feeding.
• These findings suggest a neurobiological mechanism linking GRF and central opiate systems to macronutrient selection.