Transcript Yates NS Day Poster - University of Kentucky

Conditioned Place Preference as a Function of Individual Differences in
Impulsivity
Justin Yates & Michael Bardo
University of Kentucky, Dept of Psychology
Introduction
• Impulsivity is a multifaceted construct that includes lack of
inhibitory control, lack of forethought, and inability to delay
gratification (Evenden, 1999).
• Amphetamine (AMPH) is a potent psychostimulant used to treat
attention deficit hyperactivity disorder (ADHD), narcolepsy, and
obesity and has high abuse potential (Berman et al., 2009).
• Past research has indicated a link between impulsivity and drug
abuse (Olmstead, 2006).
• The present experiment examined amphetamine conditioned
place preference (CPP) in high impulsive rats and low impulsive
rats.
• The purpose of this study was to determine if rats high in
impulsivity are more sensitive to the rewarding properties of
amphetamine measured by the CPP task.
• The hypothesis of this study was that rats high in impulsivity
would show greater CPP than rats low in impulsivity.
Methods
• Eighteen male Sprague-Dawley rats served as subjects.
• To measure individual differences in impulsivity, rats were
tested on a delay discounting procedure for 21 days.
• Rats were able to choose between a small, immediate reward
(1 food pellet) and a larger, delayed reward (3 food pellets).
• Mean adjusted delay (MAD) scores were calculated, and the
average MAD scores for the last 10 days were analyzed.
• Rats with MAD scores below the median were considered high
impulsives; rats with MAD scores above the median were
considered low impulsives.
• Following delay discounting, rats went through 10 days of CPP.
• On day 1, rats were allowed to explore all three compartments
of the CPP chamber for 15 minutes (pretest), and the time
spent in each compartment was calculated.
• On days 2 through 9, rats received injections of damphetamine (0.5 mg/kg, s.c.) and saline on alternating days,
and were confined to either the white or black compartment
(counterbalanced for drug) for 30 minutes. Activity was
measured by photobeams on each conditioning trial.
• After conditioning, rats were allowed to explore all three
compartments for 15 minutes (posttest) on day 10.
• A difference score was calculated as the difference in time
spent in the drug compartment on the pretest and posttest
sessions.
Results
Figure 4.
Figure 3.
• Across the 21 days of delay discounting sessions, there was an
overall increase in MAD scores that reached a plateau for high and
low impulsives after approximately 14 sessions (Figure 1).
• During CPP trials, both high and low impulsive rats experienced
increased locomotor activity when given amphetamine, but there
were no significant differences between groups collapsed across
trials (Figure 2).
• There was no significant difference between high and low
impulsives based on the CPP difference scores (Figure 3).
• However, when the CPP results were expressed as absolute
values, high impulsives spent significantly more time in the
amphetamine-paired compartment compared to the low
impulsives (t = 2.857, p < .05)(Figure 4).
*
Figure 1.
*p < .05 compared to Low AMPH
Discussion
Figure 2.
• AMPH produced a similar increase in locomotor
activity in both high and low impulsive rats.
• High impulsive rats spent significantly more time
in the compartment paired with AMPH during the
posttest compare to low impulsive rats.
• Even though there was no significant difference in
difference scores between the two groups, this
effect could be attributed to an outlier in the low
impulsive group. When this rat’s score was
removed, there is a significant difference between
these groups
• These results indicate that impulsivity in a delay
discounting task does not predict individual
differences in the locomotor stimulant effect of
AMPH.
• These results also indicate that impulsivity in a
delay discounting task does predict the rewarding
property of AMPH as measured by CPP.
• Thus, these findings provide further evidence
indicating that impulsivity is an antecedant risk
factor for drug abuse vulnerability.
Future Directions
• Another experiment will repeat this experiment
using a higher dose of AMPH (1.0 mg/kg).
• We plan to determine if dopamine and serotonin
systems in the orbitofrontal and medial
prefrontal cortices play a role in these behavioral
effects.
References
• Berman, SM, Kuczenski, R, McCracken, JT,
London, ED. (2009). Potential adverse effects
of amphetamine treatment on brain and
behavior: a review. Molecular Psychiatry, 14,
123-142.
• Evenden, JL. (1999). Varieties of impulsivity.
Psychopharmacology, 146, 348-361.
• Olmstead, MC. (2006). Animal models of
drug addiction: Where do we go from here?
The Quarterly Journal of Experimental
Psychology, 59, 625-653.
Acknowledgements
• Funding provided by NIH grant P50
DA05312.
• Thanks to Josh Beckmann, Julie Marusich,
and Cassie Gipson.