Response to novelty predicts the locomotor and nucleus accumbens dopamine response to cocaine.
The relationship between a rat's locomotor response to a novel environment and its behavioral and dopaminergic responses to cocaine was examined. Subjects were divided into two groups based on their locomotor response to a novel environment. Subjects who had a novelty response above the median were classified as high responders (HR), while those with a novelty response below the median were classified as low responders (LR). Following administration of cocaine-HCl (0, 2.5, 5.0, 10.0, or 15.0 mg/kg), HR rats showed a greater locomotor response than LR rats. Moreover, there was a significant correlation between a subject's locomotor response to the novel environment and the locomotor response to either 10.0 (r = 0.65) or 15.0 (r = 0.92) mg/kg cocaine. In a separate experiment, the extracellular concentration of dopamine in the nucleus accumbens (NACC) was monitored using microdialysis procedures. Following cocaine administration (15.0 mg/kg) HR rats showed a larger NACC dopamine response and greater locomotor activity than LR rats. In addition, there was a threefold greater locomotor activity to dopamine ratio in HR rats than in LR rats. A correlation between a subject's locomotor response to a novel environment and the dopaminergic response to cocaine was also evident. These results suggest that differences in the locomotor response to cocaine can, to some degree, be predicted by a rat's locomotor response to a novel environment, and that variations in dopamine-dependent mechanisms of the NACC may underlie these individual differences.
Hooks
M S
MS
Department of Chemistry, Emory University, Atlanta, Georgia 30322.
Jones
G H
GH
Smith
A D
AD
Neill
D B
DB
Justice
J B
JB
D000818:Animals; D003042:Cocaine / Q000494:pharmacology*; D003956:Dialysis; D004298:Dopamine / Q000378:metabolism*; D005106:Exploratory Behavior / Q000502:physiology*; D005110:Extracellular Space / Q000378:metabolism; D005544:Forecasting; D008297:Male; D009043:Motor Activity / Q000187:drug effects*; D009714:Nucleus Accumbens / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D003042:Cocaine; D004298:Dopamine