Some effects of pimozide and of shifts in sucrose concentration on lick rate, duration, and interlick interval

Multiple dependent measures were employed to characterize the licking behavior of rats exposed to shifts in reward magnitude or injected with pimozide (PIM). Nondeprived rats licked either a 32% (n = 14) or 4% (n = 15) sucrose solution in daily 10 min sessions. Rats in the 32% condition were then down-shifted to either a 16% (n = 7) or 4% (n = 7) sucrose solution. Rats in the 4% condition were up-shifted to either 16% (n = 7) or 32% (n = 8) sucrose solution. The response profiles generated by those rats shifted to a lower reward magnitude were contrasted with either rats shifted from a 32% sucrose solution to a no-reward (plain tap water) condition, or with rats maintained on a 32% sucrose solution and administered the neuroleptic PIM (0.5 mg/kg or 1.0 mg/kg). Rats down-shifted from a 32% to 4% sucrose solution generated response profiles more similar to rats shifted to plain tap water than rats maintained on a 32% sucrose solution and administered PIM. These results suggested that PIM treatment is not functionally equivalent to either a shift to no-reward or to a shift to reduced reward conditions.