Intracranial stimulation and one-drop licking in the rat

Abstract

The present study examined the effects of intracranial stimulation (ICS) of the lateral hypothalamic area (LH) on the lick response of the rat. Rewarding stimulation and/or a drop of water was presented contingent on a lick. Three rats were run on a three-ply multiple schedule. On separate components, licks were reinforced with water, water plus ICS, or ICS alone. For each component, the total number of licks was recorded as well as measures of the burst of licking that occurred after water reinforcement. Initially, nine ICS intensities were used from threshold (T) to threshold plus 400 μA (T + 400 μA). All animals were tested while water deprived, receiving their daily 12-cc ration after the testing session. Then the animals were retested at two ICS intensities (T and T + 200 μA), receiving their daily 12-cc ration of water either ½ h before being tested or at the end of the session. ICS intensities above threshold decreased the rate of responding when the stimulation was combined with water, both in terms of emitted and elicited licking. The operant lick rate for ICS alone was always lower than the lick rate for water alone or for water plus ICS. Water deprivation increased licking during the water component, marginally increased licking in the water-plus-stimulation component, and did not increase licking in the stimulation-only component.