Application of nicotine acts as a “high-pass” filter facilitating burst release of DA (Exley and Cragg, 2008). Specifically, electrical stimulation frequencies ≤10 Hz elicit lower DA levels compared to control, while stimulation frequencies ≥25 Hz elicit higher DA levels compared to control (Rice and Cragg, 2004). We tested if this filtering phenomenon occurs following sustained CIN activation. To do this, we applied brief electrical stimulation at different frequencies, while long optical stimulation trains to CINs (50 pulses of 4 ms duration delivered at 5 Hz, 10 mW) were applied. Under these conditions, all of the tested protocols of electrical stimulation (1 pulse, 6 pulses at 30Hz and 6 pulses of 100Hz) evoked lower peak levels of DA release, compared to peak levels obtained in absence of optical stimulation (17.6 % at 1 pulse, p < 0.0001; 51.3% at 30Hz, p < 0.0001, 74.1% at 100Hz, p > 0.05; n= 3-6) (Fig. 2D). Therefore, endogenous cholinergic activity under the present experimental conditions does not produce the high-pass filtering elicited by bath application of nicotine. To confirm whether CINs follow high frequency
