Fig. 1. The effect of gustatory experience on activation of ERK1–2 in the rat insular cortex. A, Activated ERK1–2 (dpERK1–2). B, Total ERK1–2. Three types of experimental groups were used. In group 1, rats were allowed to drink water. In group 2, rats were allowed to drink a solution of saccharin, a taste that they had never encountered before (the unfamiliar taste). In group 3, rats were allowed to drink the saccharin solution, which in this case was made familiar earlier by allowing them to drink it once for 10 min 3 d before presenting it again in the experiment (see Materials and Methods). Several sets of experiments were conducted in different combinations of the groups. Each graph depicts a “magnitude ratio,” which is the ratio of the combined intensity of the 42 + 44 kDa bands in one experimental group over another (groupi/groupj) as a function of time after the offset of drinking. A,Filled circles, Data from a set of experiments depicting group2/group1, i.e., the ratio of dpERK1–2 in the insular cortex of rats allowed to drink unfamiliar saccharin solution over that in rats allowed to drink water.A, Open circles, Data from another set of experiments depicting group2/group3, i.e., the ratio of dpERK1–2 in the insular cortex of rats allowed to drink unfamiliar saccharin over that in rats allowed to drink familiar saccharin.Inset, A representative blot of dpERK1–2 att = 30 min after drinking water (W), unfamiliar saccharin (S), or familiar saccharin (SF), and quantification of experiments similar to those depicted in the blot (activation in the water group, 1.0;n = 9–11 each). The results show that the effect of taste experience on the activation of ERK1–2 in the insular cortex is attributable to the unfamiliarity of the taste. B, Same as in A but depicting the results for total ERK1–2. (In this and all other figures, values are mean ± SEM, and *p < 0.05.)