Accumbens activity during a multiple schedule for water and sucrose reinforcement in rats

Electrophysiological recording procedures were used to examine nucleus accumbens (Acb) cell firing during operant responding for water reinforcement vs. a highly palatable sweet solution (0.6 M sucrose). Rats (n = 8) were trained on a multiple schedule to press one lever for water (fixed ratio 1, FR1; 15 min) followed by a 20‐sec timeout period (chamber dark, levers retracted), and extension of a second spatially distinct lever that the animals pressed for sucrose reinforcement (FR1; 15 min). Of 84 cells, 55 neurons (65%) displayed one of three types of patterned discharges (increases or decreases in firing rate) immediately before or following the sucrose‐ or water‐reinforced response. The major finding of this report was that the majority of these neurons (36/55 cells; 65%) showed similar types of neuronal firing patterns across the two reinforcer conditions. The remaining cells (19/55; 35%) exhibited patterned activity specific to responding for one reinforcer only (water or sucrose). These findings are discussed with respect to how Acb neurons encode goal‐directed behaviors for “natural” reinforcers including food, water, and a palatable sweet solution. Synapse 43:223–226, 2002. © 2002 Wiley‐Liss, Inc.