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Food efficiency in rats following brain lesions which affect target body size: implications on the set point for
H D Mosier1, F M Crinella, J Yu
1Department of Pediatrics, University of California, Irvine 92717.
Abstract:
Target size, i.e. body size appropriate for age, may be reset by bilateral lesions of several brain areas. The mechanism for control of target body size is unknown, but some of the loci have marked effects on gustatory behavior and/or energy metabolism. We have tested the possibility that a disturbance in energy metabolism may be a common factor in resetting target size. Food efficiency for body weight gain and for metabolic size (the 0.75 power of body weight) was determined in rats that were experimentally stunted by neonatal head-irradiation or by bilateral electrolytic lesions produced soon after weaning in the dorsomedial hypothalamic nuclei (DMH) or the substantia nigra (SN). The irradiations were carried out in males and females; the surgical lesions were produced only in males. Observations were carried out from weaning through early adulthood. Subgroups of irradiated rats and controls were fasted for 48 hours at 40 days of age. Irradiated rats had reduced food efficiency for weight gain and for metabolic size, more marked in males than in females. DMH or SN lesions did not change food efficiency for weight gain. Food efficiency for metabolic size increased after DMH lesions and declined after SN lesions. During refeeding after a fast, irradiated rats showed a normal transient increase in food efficiency for weight gain, but not for metabolic size. The differences in food efficiency following different lesions tend to exclude altered energy metabolism as a common factor in the reset of target body size.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Altering target body size involves brain lesions, but energy metabolism changes are unlikely to be the common cause. Studies in rats show varied effects of lesions and irradiation on food efficiency and body weight regulation.
Area of Science:
- Neuroscience
- Endocrinology
- Metabolism
Background:
- Target body size regulation is complex and can be altered by brain lesions.
- Some brain regions involved in target size control also influence feeding behavior and metabolism.
Purpose of the Study:
- To investigate if altered energy metabolism is a common mechanism underlying target body size regulation.
- To examine the effects of neonatal head irradiation and specific brain lesions on food efficiency and body weight in rats.
Main Methods:
- Rats were stunted via neonatal head irradiation or lesions to the dorsomedial hypothalamic nuclei (DMH) or substantia nigra (SN).
- Food efficiency for body weight gain and metabolic size was measured from weaning to adulthood.
- Subgroups underwent fasting and refeeding protocols to assess metabolic responses.
Main Results:
- Irradiated rats exhibited reduced food efficiency, particularly males.
- DMH lesions increased metabolic size efficiency, while SN lesions decreased it; neither affected weight gain efficiency.
- Refeeding after fasting showed normal weight gain efficiency but not metabolic size efficiency in irradiated rats.
Conclusions:
- The differing effects of lesions on food efficiency suggest that altered energy metabolism is not a universal factor in resetting target body size.
- Brain regions like DMH and SN play distinct roles in regulating body size and metabolic processes.
