MSG lesions decrease body mass of suckling-age rats by attenuating circadian decreases of energy expenditure

Area of Science:

• Neuroendocrinology
• Developmental Biology
• Metabolic Regulation

Background:

• Suckling rats exhibit circadian rhythms in metabolic rate (MR) and core body temperature (Tc), featuring energy-saving drops.
• These rhythms are sympathetically controlled and can be modulated by leptin.
• Neonatal monosodium glutamate (MSG) treatment is known to damage the arcuate nucleus and induce adult obesity.

Purpose of the Study:

• To investigate the impact of neonatal MSG treatment on energy balance in rats during the first two postnatal weeks.
• To determine if MSG-induced arcuate nucleus damage affects early metabolic regulation and fat deposition.

Main Methods:

• Continuous monitoring of metabolic rate (MR) and core temperatures (Tc) in MSG-treated and control rat pups.
• Artificial and mother-reared pup comparisons to assess effects on nutrition and suckling.
• Analysis of plasma leptin levels in relation to body fat mass.

Main Results:

• MSG treatment disinhibited periodic, energy-saving drops in Tc and MR, leading to increased energy expenditure.
• MSG-treated pups showed reduced body fat despite normal lean body mass when artificially nourished.
• Mother-reared MSG-treated pups exhibited reduced lean body mass, suggesting impaired suckling.
• Plasma leptin levels were similar between groups but higher per unit of fat mass in MSG-treated pups.

Conclusions:

• Neonatal MSG treatment initiates a phase of increased energy expenditure and reduced fat deposition during suckling.
• This early metabolic alteration precedes the known postweaning obesity and depressed thermogenesis associated with MSG.
• Arcuate nucleus cell damage is hypothesized to underlie both the early metabolic changes and later obesity development.