MUSCIMOL INDUCES RETROGRADE-AMNESIA FOR CHANGES IN REWARD MAGNITUDE

These experiments examined the effect of the GABA, agonist, muscimol ( MUS), on memory for changes in reward magnitude. In Experiment 1 rats were trained to run a straight alley for either a large or small food reward. After reaching asymptotic performance rats in the high reward group were shifted to the small food reward. Half the animals received 1.0 or 3.0 mg/kg (ip) of MUS or the equivalent volume of saline immed iately after training. Shifted training continued for 3 more days and no further injections were given. Shifted saline animals displayed an increase in response latencies compared to unshifted controls with a s harp peak on the day after the shift. Shifted MUS receiving 1.0 mg/kg performed comparably to shifted saline animals. In contrast, Shifted M US animals receiving 3.0 mg/kg displayed performance comparable to shi fted saline animals on the day of the shift but displayed a sharp incr ease in response latencies on the second day after the shift. These fi ndings indicate that post-training systemic MUS injections delay the p eak increase in response latencies and suggest that MUS induces retrog rade amnesia for reward reduction. Experiment 2 examined the effect of MUS on the memory of a reward increase. Rats were first trained as in Experiment 1 and rats under the high reward condition were then shift ed to the small reward. On the next training session, the large food r eward was reinstated. Immediately after the session all animals were i njected with saline or 3.0 mg/kg of MUS. The large food reward was con tinued for the remainder of training and no further injections were gi ven. On the following session, the performance of the shifted saline a nimals was comparable to that of the unshifted controls while shifted MUS animals displayed significantly higher response latencies. The fin dings that MUS prevented the reduction in response latencies seen in s aline-injected animals suggest that MUS also induces retrograde amnesi a for reward increases, (C) 1995 Academic Press, Inc.