Figure 2. Baclofen inhibition reversal blocked by CGP35348.

A. Mean ratemeter graph of the effects of baclofen and CGP35348 on the firing rate of a single DA VTA. Vertical bars indicate the firing rate over 5 sec intervals. Horizontal bars indicate the duration of baclofen (0.3 μM) or baclofen+CGP35348 (10 μM) application. Initially, a 5 min baclofen (0.3 μM) administration produced inhibition of 53.0%. During the 40 min application of baclofen and CGP35348, there was a decrease in firing rate of 10% at 5 min that further decreased to 13% by the end of the 40 min period. Baclofen was administered for 5 min after the cessation of baclofen and CGP35348 treatment, producing an inhibition of 60.9% at 30 min.

B. The mean firing rate of DA VTA neurons in response to baclofen and CGP35348 in experiments similar to the one depicted in Figure 2A. The mean concentration of baclofen at 0.3 μM from experiments such as that shown in Figure 1 was used. The 5 min application of baclofen initially produced an inhibition in firing rate of 58.3%. In the presence of CGP35348 (10 μM), baclofen produced only 7% decrease in firing rate at 5 min, and this inhibition was further increased to 17% at 40 min. After the cessation of baclofen and CGP35348 treatment, baclofen produced an inhibition in firing rate of 61.6%. There was no significant reduction in baclofen-induced inhibition (paired t-test, p > 0.05).