Circadian food anticipation persists in capsaicin deafferented rats

The feeding-entrained circadian oscillator (FEO) organizes locomotor activity and other variables to anticipate daily timed meals. Whether the biological substrate for the FEO is in the central nervous system or in the periphery, there must be communication between the gut and the brain to result in a behavioral output. To investigate potential neural routes of communication, rats with suprachiasmatic lesions were given systemic capsaicin (total dose: 100 mg/kg, ip) to produce visceral deafferentation. Deafferentation was confirmed using the phenyl-p-benzoquinone stretch test and the corneal irritation test. A 3-h meal was made available at the same time each day while wheel running was recorded for several weeks. Results indicated that rats with capsaicin lesions were somewhat more active overall and during nonanticipation times, but the onset time and the amount of anticipatory wheel running did not differ from vehicle-treated controls. In addition, reentrainment following a phase delay of mealtime and the persistence of anticipatory activity during food deprivation were similar between the groups. Since capsaicin deafferentation and subdiaphragmatic vagotomy do not prevent food-anticipatory activity, it is likely that communication between the gut and the brain is accomplished via a humoral route.