Modification of unit responses to gustatory stimuli by conditioned taste aversion in rats

Strong conditioned taste aversion (CTA) was established in rats by associating 0.1% saccharin drinking with subsequent LiCl (0.15 M, 2% body weight) poisoning. Unit reactions (n = 135) to mouth perfusion with saccharin (10 sec) and water (40 sec) were recorded in curarized animals and analysed with a spike detecting computer program. Saccharin induced reactions in the gustatory thalamus of naive and CTA trained rats were equally frequent. The percentage of saccharin induced reactions in lateral and ventromedial hypothalamus (LH and VMH) was affected by CTA training in a reciprocal manner: it decreased from 64 to 38% in LH neurons and increased from 40 to 70% in VMH neurons. It is argued that the modification of hypothalamic reactivity to saccharin reflects the changed signal significance of the sweet taste, which activates the feeding center and inhibits the satiety center in naive animals, but elicits opposite effects after CTA acquisition.