Feeding-entrained circadian rhythms are attenuated by lesions of the parabrachial region in rats.

Rats anticipate daily restricted meals with increased approaches to a feeder and an increase in core body temperature. Food anticipatory activity (FAA) is thought to be under the control of a feeding-entrained circadian oscillator. Although numerous forebrain lesions have failed to permanently abolish FAA, the hindbrain has not been investigated. The parabrachial nuclei (PBN) integrate information from visceral and gustatory afferents. This region is also innervated by neurons in the area postrema that have access to the peripheral circulation. Therefore, it is possible that this region plays a role in triggering FAA. In two experiments, a total of 19 rats were given ibotenic acid or electrolytic lesions targeted at the PBN. The PBN-lesioned animals showed a marked attenuation in anticipatory approaches to the food bin relative to sham-operated controls. Some animals did not anticipate the meal at all. In addition, the expected increase in core body temperature was severely attenuated in the PBN-lesioned animals compared with controls. The most likely interpretation of these data is that the PBN serve as a relay for information about the zeitgeber (food in the gut) or as a clock output pathway, but not as the site of the feeding-entrained circadian oscillator.