Anticipatory appetitive behavior of adrenalectomized rats under circadian salt-access schedules

Salt-hungry rats fail to develop anticipatory wheel-running activity when maintained under schedules of limited daily access to salt, in marked contrast to the robust anticipatory activity seen under food-access schedules. This suggests that the circadian oscillator underlying food-anticipatory activity is specifically related to food access and does not readily generalize to other scheduled resources. However, an alternative hypothesis is that rats are capable of anticipating daily salt-access periods, but that this anticipation is not manifest in wheel-running activity. In the present study, we maintained adrenalectomized rats under schedules of limited daily access to salt in which all salt was obtained by leverpressing. The results indicate that rats are capable of anticipating daily salt access by reference to an endogenous circadian timing mechanism. However, this behavior differs in several respects from that seen under food-access schedules.