Nicotine-, tobacco particulate matter- and methamphetamine-produced locomotor sensitisation in rats.

RATIONALE: Repeated nicotine exposure produces a weak and transient sensitised locomotor response in rats. Since tobacco smoke contains thousands of non-nicotine chemical constituents, these could alter the sensitised response.
OBJECTIVES: This study aims to compare the magnitude, persistence and spatial distribution of locomotor sensitisation produced by repeated doses of nicotine, aqueous tobacco particulate matter (TPM) and a positive methamphetamine control.
METHODS: Male Sprague-Dawley rats received five nicotine (0.0, 0.2 or 0.4 mg/kg), TPM (containing 0.2 or 0.4 mg/kg nicotine) or methamphetamine (0.5 mg/kg) injections every second day, followed by a 4-day withdrawal before the first challenge (Challenge 1, C1). The animals were re-challenged again at 15 days post C1 to test for the persistence of sensitisation (Challenge 2, C2).
RESULTS: There were no major differences in sensitisation profile between nicotine and TPM. At the lowest 0.2 mg/kg nicotine/TPM dose, however, small differences emerged on select test days.
CONCLUSIONS: The results indicated that the non-nicotinic agents in TPM did not greatly impact the nicotine-produced locomotor-sensitised response. These findings might suggest that the differential pharmacological properties of TPM do not have major clinical significance. Alternatively, the locomotor model might not expose effects of non-nicotinic constituents, and furthermore, might not closely relate to human tobacco dependence. Different reward-related behavioural models should also be utilised to assess potential effects of non-nicotinic constituents before a role in dependence is discounted.