Evidence that mesoaccumbens dopamine and locomotor responses to nicotine in the rat are influenced by pretreatment dose and strain.
BACKGROUND
Sensitisation of the mesoaccumbens dopamine response to nicotine has been implicated in the development of nicotine dependence. This study explored the doses of nicotine that elicit the response in two strains of rats that differ in their baseline levels of activity.


METHODS
Male Sprague-Dawley and Lister hooded rats were pretreated with daily subcutaneous injections of (-)-nicotine for 7 days at doses ranging from 0.03 mg/kg to 0.90 mg/kg. Microdialysis studies were performed on day 9 in conscious freely moving rats, placed in an activity box and challenged with 0.4 mg/kg nicotine.


RESULTS
The acute administration of nicotine to drug-naive rats stimulated dopamine overflow in the accumbal shell but not the core. Sprague-Dawley rats, pretreated with nicotine (0.03 mg/kg/day and 0.10 mg/kg/day) showed increased basal overflow of dopamine in the accumbal core. Pretreatment with 0.10 mg/kg/day or 0.30 mg/kg/day, but not 0.03 mg/kg/day or 0.90 mg/kg/day, also caused sensitisation of the response to a nicotine challenge on the test day. Sensitisation of the locomotor response to nicotine exhibited a simple dose-response relationship, with the largest sensitisation being observed in animals pretreated with 0.90 mg/kg/day. In Lister hooded rats, pretreatment with nicotine reduced basal dopamine overflow in the accumbal core and did not cause sensitisation to a subsequent challenge with nicotine.


CONCLUSIONS
Sensitisation of the mesoaccumbens dopamine response to nicotine is influenced by pre-treatment dose and the strain of rats used. It is not related directly to the expression of sensitised locomotor responses to the drug and, therefore, may be implicated in other psychopharmacological properties of the drug, including dependence.
Iyaniwura
T T
TT
Biomedical Research Centre, University of Dundee Medical School, Ninewells Hospital, Dundee DD1 9SY, UK.
Wright
A E
AE
Balfour
D J
DJ
D000818:Animals; D004298:Dopamine / Q000378:metabolism / Q000502:physiology*; D007279:Injections, Subcutaneous; D008297:Male; D009043:Motor Activity / Q000187:drug effects* / Q000502:physiology; D009538:Nicotine / Q000008:administration & dosage*; D018722:Nicotinic Agonists / Q000008:administration & dosage*; D009714:Nucleus Accumbens / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013045:Species Specificity
D018722:Nicotinic Agonists; D009538:Nicotine; D004298:Dopamine