¹Department of Pharmacology, University of Tennessee Health Science Center, Memphis, TN, USA

Correspondence: Dr BM Sharp, Department of Pharmacology, University of Tennessee Health Science Center, 874 Union Avenue, Room 115, Memphis, TN 38163, USA, Tel: +1 901 448 6000; Fax: +1 901 448 7206, E-mail: bsharp@utmem.edu

Received 17 January 2006; Revised 30 March 2006; Accepted 15 May 2006; Published online 14 June 2006.

Abstract

As most human tobacco use begins during adolescence and ongoing development of the adolescent central nervous system could affect acquisition of nicotine self-administration (SA), our established rat SA procedure was modified to study adolescent acquisition of SA with prolonged access to nicotine (23 h/day). Postnatal age 43–45 female Lewis rats, without prior shaping, conditioning, or food deprivation, were housed in operant chambers equipped with two levers; pressing the active lever triggered an i.v. injection of nicotine. By the 10th day of SA, rats receiving 7.5, 15, 30, or 60 g/kg/injection nicotine (free base) obtained 2316, 508, 658, or 485 injections (meanSE), respectively. In the 30 g/kg/injection group, active : inactive ratio was greater than 2 after SA day 4; 92% of injections occurred during the 12-h active (dark) phase of the light cycle. Main effects (analysis of variance) were shown for day and lever (ie active vs inactive) (p<0.001). Adolescent males showed similar dose-dependent nicotine SA. With the increasing workload imposed by raising the fixed ratio (FR), less nicotine was self-administered at FR 5 and 7 compared to FR 1 and 3. In comparison to adult females self-administering 30 g/kg/injection of nicotine at FR 1, adolescents acquired nicotine SA at an accelerated rate (p<0.05) and received a greater number of injections (p<0.05) by day 10. In conclusion, when given prolonged access to the drug, both female and male adolescent Lewis rats rapidly acquire nicotine SA within the dosage range and FR constraints previously observed in adult Lewis rats. However, adolescent females acquired the behavior more rapidly and attained higher levels of stable nicotine SA than adults.