Figure 1.
Repeated pavlovian conditioning results in increased activation of ERK2 in the NAcc. Samples from the NAcc and dorsal striatum were probed for ERK2 phosphorylation after either one pavlovian training session or four training sessions. A, Rats that received paired tone and food presentations demonstrated greater discriminated food-cup approach after four training sessions (n = 7) compared with rats that received a single training session (n = 8) or rats that received unrewarded tone presentations (1 session, n = 8; 4 sessions, n = 7). B, The normalized ratio of phosphoERK2 immunoreactivity to total ERK immunoreactivity (pERK/tERK) was greater in NAcc samples taken from rats after the fourth conditioning session compared with this ratio in NAcc samples taken from rats that received four sessions of unrewarded tone presentations (tone control) or from rats after a single pavlovian training session. ERK2 activation in NAcc samples taken from rats 3 h after they had completed the fourth training session (n = 8) did not differ from ERK2 activation in NAcc samples from the tone control group and was significantly lower than ERK2 activation in NAcc samples taken from rats immediately after they had completed the fourth training session. C, In contrast to ERK2 activation in the NAcc, no training-related changes in ERK2 activation were observed in the dorsal striatum. Similar data as shown in B for tissue samples harvested form the dorsal striatum. Representative pERK and tERK immunoblots are shown for each treatment group. The lower (p42) band was used for analysis. train, Trained; cont, control. *Significantly different from tone control; #significantly different from one session trained group; $significantly different from 3 h trained group, all at p < 0.05. All data are represented as mean ± SEM.
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