Oral habituation in rat pups is in the brainstem

We have previously demonstrated a decremental, oral, experienced-based control of ingestion in rat pups that is potent, diet-specific, and long lasting. This control of ingestion is revealed in the decreases in mouthing responses of rat pups to repeated oral stimulation, a phenomenon that is well described as oral habituation. The present study examined the neural basis for oral habituation by examining the responses of decerebrate 10-day-old rat pups to repeated, brief infusions of a sucrose solution. Like neurologically intact pups, decerebrate pups showed distinct decreases in mouthing responses following a series of oral infusions. Thus, oral habituation is present in the hindbrain. Although intact pups demonstrated sensitization by showing increased responding to the first few stimulus presentations, decerebrates failed to show a sensitization to the stimulation. These results suggest that while the brainstem alone is sufficient for the expression of oral habituation, the forebrain also influences oral responsivity in intact animals.