Striatal application of nicotine, but not of lobeline, attenuates dopamine release in freely moving rats.

We investigated the physiological role of native low- and high-affinity nicotinic acetylcholine receptors (nAChRs) in regulating dopamine (DA) release from striatal DA terminals. To evaluate the functional interactions of the two receptor subtypes, nicotine (which interacts with both high- and low-affinity nAChRs) and lobeline (which selectively interacts with high-affinity nAChRs) were perfused through a microdialysis probe implanted into the striatum of freely moving rats. The DA content of successive dialysates was quantified by HPLC with an electrochemical detector. A short-lasting (1-min) perfusion of nicotine or lobeline dose-dependently increased the DA content of striatal dialysates. A second application of the same dose of nicotine resulted in an attenuated DA increase, compared with the increase elicited by the first application; however, the DA increase elicited by a second application of lobeline was similar to that of the first lobeline application. The nicotine-induced response was not attenuated when it followed a lobeline perfusion; in contrast, if the nicotine perfusion preceded that of lobeline, the lobeline-induced response was attenuated. In the presence of mecamylamine (a noncompetitive nAChR antagonist), the increase in DA content of striatal dialysate samples induced by either nicotine or lobeline was attenuated. However, in the presence of methyllycaconitine (a preferential antagonist for low-affinity alpha7 homomeric nAChRs), the nicotine response was attenuated but that of lobeline was unaffected. These results suggest that the functional inactivation of striatal nAChRs requires the simultaneous activation of both low- and high-affinity nAChRs. Since lobeline is devoid of reinforcing properties, one might infer that the reinforcing properties of nicotine require the simultaneous activation of high- and low-affinity brain nAChRs.