Figure 3. PCA-switch experiment promotes a 5-HT release-dependent nicotine self-administration.

(a) Rats received an injection of either saline (1.5 ml/kg, i.p.) (saline PCA-nic) or tranylcypromine (3 mg/kg,i.p.) 20 hr prior to the three first self-administration sessions. On day 4 rats received PCA 1 hr prior to the self-administration session. Two other independant tra20hr pretreated group were tested for saline i.v. self-administration following PCA (tra20hr-PCA-sal) and for nicotine self-administration following saline (tra20hr-saline-nico). **p<0.01 versus NR and versus R and the saline PCA-nic group. n = 5–11/group. (b) PCA dose-response. On test day independent groups received three different doses of PCA (0.5, 1 or 1.5 mg/kg ip) or saline. Responses on day 4 at both the reinforced and non-reinforced holes are presented. *p<0.05 versus R saline; ##p<0.01 versus NR PCA 1mg/kg. n = 5–11/group. (c) MAO activity. Effect of tra20hr pretreatment given on the three first self-administration sessions on MAO-A and -B activities measured on day 4. Rats received 3 daily tranylcypromine (3 mg/kg, i.p.) (TraA and TraB) injections timed so that the last injection occurred 44 hours before sacrifices. The saline group (SalA and SalB) received 3 injections similarly timed. Tranylcypromine significantly reduced MAO activity. *p<0.05 and ***p<0.001 versus the corresponding Sal group. n = 4/group.