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Perinatal MSG treatment attenuates fasting-induced bradycardia and metabolic suppression
Michelina M Messina1, Stephanie A Evans, Steven J Swoap
1Program in Neuroscience, Florida State University, Tallahassee, Florida, USA.
Abstract:
We studied the effect of arcuate nucleus (ARC) lesions induced pharmacologically by the perinatal treatment of monosodium l-glutamate (MSG) on the cardiovascular, metabolic, and behavioral responses to fasting. Saline and MSG-treated male Sprague-Dawley rats were instrumented with telemetry devices for measurement of mean arterial pressure (MAP) and heart rate (HR) and housed in room calorimeters at an ambient temperature (T(a)) of 23 degrees C for assessment of oxygen consumption (VO(2)). At baseline, controls and MSG-treated rats had similar MAP (control=95+/-4; MSG=91+/-2 mmHg), HR (control=323+/-4; MSG=324+/-2 bpm), and VO(2) (control=8.7+/-0.3; MSG=8.6+/-0.2 ml/min). There were no differences in fasting-induced reductions in body weight or in food intake upon refeeding. MSG-treatment significantly attenuated fasting-induced reductions in HR and VO(2). This effect was specific to reduced caloric availability, as MSG-treated rats exhibited intact capacity to both increase and decrease HR and VO(2) in response to cold (T(a)=15 degrees C) and to thermoneutrality (T(a)=30 degrees C). Additional studies were performed in saline- and MSG-treated rats chronically treated with beta(1)-adrenergic receptor blockade (atenolol) prior to and during fasting. In controls, the cardiovascular responses to fasting during beta(1)-blockade were blunted and generally mimicked the effects of MSG-treatment, while beta(1)-blockade had no additional effect on MSG-treated rats. The results are consistent with the hypothesis that ARC neuronal signaling is requisite for intact homeostatic responses to fasting and may participate in fasting-induced withdrawal of cardiac sympathetic activity.
Insights
Arcuate nucleus (ARC) lesions in rats reduced fasting-induced drops in heart rate and oxygen consumption. ARC signaling is vital for homeostatic responses to fasting and sympathetic activity.
Area of Science:
- Neuroscience
- Physiology
- Metabolism
Background:
- The arcuate nucleus (ARC) plays a crucial role in regulating energy balance and physiological responses.
- Understanding ARC's function during fasting is essential for metabolic and cardiovascular health.
Purpose of the Study:
- To investigate the impact of ARC lesions on cardiovascular, metabolic, and behavioral adaptations to fasting.
- To determine if ARC signaling is necessary for maintaining homeostasis during caloric restriction.
Main Methods:
- Pharmacological lesions of the ARC using monosodium l-glutamate (MSG) in Sprague-Dawley rats.
- Telemetry for measuring mean arterial pressure (MAP) and heart rate (HR).
- Room calorimetry for assessing oxygen consumption (VO(2)) at various ambient temperatures.
Main Results:
- MSG-induced ARC lesions attenuated fasting-induced reductions in HR and VO(2).
- These effects were specific to fasting, as responses to cold and thermoneutrality remained intact.
- Beta(1)-adrenergic receptor blockade mimicked MSG effects in controls, suggesting ARC's role in sympathetic withdrawal during fasting.
Conclusions:
- ARC neuronal signaling is essential for appropriate homeostatic responses to fasting.
- The ARC may mediate the withdrawal of cardiac sympathetic activity during periods of caloric deficit.
