Individual differences in the propensity to approach signals vs goals promote different adaptations in the dopamine system of rats.
BACKGROUND
The way an individual responds to cues associated with rewards may be a key determinant of vulnerability to compulsive behavioral disorders.


OBJECTIVE
We studied individual differences in Pavlovian conditioned approach behavior and examined the expression of neurobiological markers associated with the dopaminergic system, the same neural system implicated in incentive motivational processes.


METHODS
Pavlovian autoshaping procedures consisted of the brief presentation of an illuminated retractable lever (conditioned stimulus) followed by the response-independent delivery of a food pellet (unconditioned stimulus), which lead to a Pavlovian conditioned response. In situ hybridization was performed on brains obtained either following the first or last (fifth) day of training.


RESULTS
Two phenotypes emerged. Sign-trackers (ST) exhibited behavior that seemed to be largely controlled by the cue that signaled impending reward delivery; whereas goal-trackers (GT) preferentially approached the location where the reward was delivered. Following a single training session, ST showed greater expression of dopamine D1 receptor mRNA relative to GT. After 5 days of training, GT exhibited greater expression levels of tyrosine hydroxylase, dopamine transporter, and dopamine D2 receptor mRNA relative to ST.


CONCLUSIONS
These findings suggest that the development of approach behavior towards signals vs goal leads to distinct adaptations in the dopamine system. The sign-tracker vs goal-tracker phenotype may prove to be a valuable animal model to investigate individual differences in the way incentive salience is attributed to environmental stimuli, which may contribute to the development of addiction and other compulsive behavioral disorders.
Flagel
Shelly B
SB
Molecular and Behavioral Neuroscience Institute, University of Michigan, 205 Zina Pitcher Place, Ann Arbor, MI, 48109-0720, USA. sflagel@umich.edu
Watson
Stanley J
SJ
Robinson
Terry E
TE
Akil
Huda
H
D000222:Adaptation, Physiological; D000818:Animals; D001522:Behavior, Animal; D001921:Brain / Q000378:metabolism*; D003192:Compulsive Behavior / Q000378:metabolism; D003213:Conditioning, Psychological; D003463:Cues; D004298:Dopamine / Q000378:metabolism*; D050483:Dopamine Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D005106:Exploratory Behavior; D006040:Goals; D017403:In Situ Hybridization; D008297:Male; D009042:Motivation; D010641:Phenotype; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017447:Receptors, Dopamine D1 / Q000235:genetics / Q000378:metabolism; D017448:Receptors, Dopamine D2 / Q000235:genetics / Q000378:metabolism; D012201:Reward; D017603:Signal Detection, Psychological; D013997:Time Factors; D014446:Tyrosine 3-Monooxygenase / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation
D050483:Dopamine Plasma Membrane Transport Proteins; D012333:RNA, Messenger; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; D014446:Tyrosine 3-Monooxygenase; D004298:Dopamine