A, Firing responses evoked by a depolarizing current pulse (3 nA, 50 ms duration) before (left) and after (right) extracellular application of 100 μM Dopamine. B, Near-threshold voltage response (2 nA, 50 ms duration) obtained before and after Dopamine application. The characteristic initial non-linear membrane response in the form of an apparent increase in the slope resistance, attributed to the activation of INa+P (Curti and Pereda, 2004; Curti et al, 2008) was substantially reduced by application of Dopamine, suggesting the down-regulation of INa+P by this modulator. C, This effect was quantified by comparing the ratio between early and late responses during control conditions and after Dopamine application. This ratio, estimated as (ΔV early − ΔV late)/ΔV early, averaged 0.33 ± 0.12 in control, and was significantly affected by dopamine application averaging 0.15 ± 0.05 (mean ± S.D.; p= 0.0002; n=8).