Timed hypocaloric food restriction alters the synthesis and expression of vasopressin and vasoactive intestinal peptide in the suprachiasmatic nucleus

Sep 9, 2004Brain research

Timed calorie restriction changes production of key signaling molecules in the brain's biological clock

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Abstract

Timed hypocaloric food restriction resulted in a significant decrease in the total number of vasopressin (AVP) and vasoactive intestinal peptide (VIP) neurons in adult rats.

The volume of the suprachiasmatic nucleus (SCN) and the total number of neurons remained unchanged between rats with free access to food and those on timed hypocaloric restriction.
Timed hypocaloric food restriction for 7 months decreased the total number of AVP- and VIP-immunoreactive neurons in the SCN.
Levels of AVP and VIP mRNA were significantly lower in the food-restricted group compared to controls.
Findings suggest a relationship between the food-entrainable oscillator and the light-entrainable pacemaker in regulating circadian rhythms.

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In mammals, the main circadian pacemaker is located in the suprachiasmatic nucleus (SCN) and its most potent synchronizer is the daily variation of the intensity of light. However, other nonphotic cues, such as timed food restriction, can induce changes in the circadian rhythms, leading also to the appearance of a food-entrained oscillator. The present study was designed to establish if the alterations of the circadian rhythms induced by timed hypocaloric food restriction are accompanied by structural changes in the SCN. Two groups of adult rats, both maintained on 12-h light/12-h dark cycles, were used; in one group, animals had permanent free access to food, whereas in the other they were subjected to a restricted hypocaloric early morning feeding during 7 months. Using stereological techniques and in situ hybridization, we have examined the structure of the SCN and the synthesis and expression of vasopressin (AVP) and vasoactive intestinal peptide (VIP). The volume of the SCN and the total number of neurons did not vary between the two groups. However, the total number of AVP- and VIP-immunoreactive neurons and the AVP and VIP mRNA levels were significantly decreased in timed hypocaloric food-restricted animals. The results indicate that timed hypocaloric food restriction has led to changes of AVP and VIP content of the neurons. They furthermore suggest the existence of a coupling between the food-entrainable oscillator and the light-entrainable pacemaker.

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Timed hypocaloric food restriction alters the synthesis and expression of vasopressin and vasoactive intestinal peptide in the suprachiasmatic nucleus

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