Prenatal nicotine and/or cocaine differentially alters nicotine-induced sensitization in aging offspring

Repeated exposure to psychostimulant drugs can result in behavioral sensitization, an amplified response in locomotor activity and stereotypy, which is used to model aspects of drug addiction. The expression of behavioral sensitization, induced by i.p. injections of nicotine once daily for 5 days, was examined in 450-day-old male rats exposed prenatally on GD 8-20 to one of the following conditions: (1) low nicotine: 2.5 mg/kg/day nicotine [LN]; (2) high nicotine: 5.0 mg/kg/day nicotine [HN]; (3) low nicotine/high cocaine: 2.5 mg/kg/day nicotine plus 40 mg/kg/day cocaine [LN/HC]; (4) high nicotine/low cocaine: 5.0 mg/kg/day nicotine plus 20 mg/kg/day cocaine [HN/LC]; (5) pair-fed controls: food intake yoked to HC dams [PF]; and (6) saline controls: daily injections of 0.9% NaCl solution[SAL]. Initial injection of nicotine did not alter activity or stereotypy in comparison to saline injections, with offspring in all prenatal treatment groups showing a desensitization to nicotine. Five consecutive daily nicotine injections resulted in behavioral sensitization in HN and HN/LC prenatal drug groups. Offspring exhibited an increase in horizontal activity that was evident on day 3, and still present after a 1.0 mg/kg i.p. nicotine challenge 72 hours after the last injection (day 8). SAL offspring exhibited attenuated sensitization. In contrast, nicotine sensitization was not seen in the LN, HC/LN, and the PF offspring; activity remained at the level seen after the initial injection of nicotine. Moreover, nicotine significantly reduced total activity in the LN and PF groups in comparison with their saline-injected counterparts. These data suggest that gestational exposure to high-dose nicotine, either alone or in combination with cocaine, may carry a greater risk than low-dose nicotine exposure of stimulant abuse in later life.