Leptin-sensitive neurons in the arcuate nucleus integrate activity and temperature circadian rhythms and anticipatory responses to food restriction.

Abstract

Previously, we investigated the role of neuropeptide Y and leptin-sensitive networks in the mediobasal hypothalamus in sleep and feeding and found profound homeostatic and circadian deficits with an intact suprachiasmatic nucleus. We propose that the arcuate nuclei (Arc) are required for the integration of homeostatic circadian systems, including temperature and activity. We tested this hypothesis using saporin toxin conjugated to leptin (Lep-SAP) injected into Arc in rats. Lep-SAP rats became obese and hyperphagic and progressed through a dynamic phase to a static phase of growth. Circadian rhythms were examined over 49 days during the static phase. Rats were maintained on a 12:12-h light-dark (LD) schedule for 13 days and, thereafter, maintained in continuous dark (DD). After the first 13 days of DD, food was restricted to 4 h/day for 10 days. We found that the activity of Lep-SAP rats was arrhythmic in DD, but that food anticipatory activity was, nevertheless, entrainable to the restricted feeding schedule, and the entrained rhythm persisted during the subsequent 3-day fast in DD. Thus, for activity, the circuitry for the light-entrainable oscillator, but not for the food-entrainable oscillator, was disabled by the Arc lesion. In contrast, temperature remained rhythmic in DD in the Lep-SAP rats and did not entrain to restricted feeding. We conclude that the leptin-sensitive network that includes the Arc is required for entrainment of activity by photic cues and entrainment of temperature by food, but is not required for entrainment of activity by food or temperature by photic cues.

• Authors: Michael F Wiater, Ai-Jun Li, Thu T Dinh, Heiko T Jansen, Sue Ritter
• Journal: American journal of physiology. Regulatory, integrative and comparative physiology (Am J Physiol Regul Integr Comp Physiol) Vol. 305 Issue 8 Pg. R949-60 (Oct 15 2013) ISSN: 1522-1490 [Electronic] United States
• PMID: 23986359 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)

Chemical References

• Leptin
• Ribosome Inactivating Proteins, Type 1
• Saporins

Topics

• Animals
• Arcuate Nucleus of Hypothalamus (drug effects, physiology)
• Circadian Rhythm (drug effects, physiology)
• Feeding Behavior (drug effects, physiology)
• Food Deprivation (physiology)
• Leptin (pharmacology)
• Male
• Motor Activity (drug effects, physiology)
• Neurons (drug effects, physiology)
• Rats
• Rats, Sprague-Dawley
• Ribosome Inactivating Proteins, Type 1 (pharmacology)
• Saporins
• Suprachiasmatic Nucleus (drug effects, physiology)