Nicotine Administration in Rodents

Rats were treated SC with nicotine (nicotine-hydrogen-tartrate salt, 2 mg kg⁻¹ every 12 h; Sigma; St Louis, MO, USA)^{3 (link),4 (link)}. Mice were house individually and implanted subcutaneously with an osmotic minipump flow moderator (Model 1002, Alzet, DURECT Corporation; Cupertino, CA, USA) containing a daily dose of 25 mg kg⁻¹ of nicotine (nicotine-hydrogen-tartrate salt, Sigma; St Louis, MO, USA)^{46 (link)} due to their higher metabolism, or saline. Body weight was measured for 14 days. For the central nicotine experiments, intracerebroventricular (ICV) cannulae were stereotaxically implanted under ketamine/xylazine anesthesia^{3 (link),33 (link),47 (link)–50 (link)}. Animals were individually housed and used for experimentation four days later. Then, animals were subjected to a protocol of daily ICV injections of nicotine (nicotine-hydrogen-tartrate salt, 0.3 µg day⁻¹; Sigma; St Louis, MO, USA)^{51 (link)} or vehicle (3 µl of saline; control mice) using a 22-gauge needle (Hamilton; Reno, NV, USA) through the inserted cannulae for 7 days.