Delay discounting in C57BL/6J and DBA/2J mice: Adolescent-limited and life-persistent patterns of impulsivity.

Abstract

Impulsivity is a defining characteristic of adolescence. Compared to adults, for example, adolescents engage in higher rates of drug and alcohol experimentation, risky sexual practices, and criminal activity. Such behavior may reflect reduced sensitivity to long-term consequences for behavior during adolescence. Recently, our lab has attempted to refine mouse procedures to study developmental trends in decision making in the laboratory. In the present experiment, we examined sensitivity to delayed rewards in C57BL/6J (B6) and DBA/2J (D2) mice during adolescence and adulthood using an adaptation of a two-week delay discounting procedure developed by Adriani & Laviola (2003) [Behavioral Neuroscience, 117,[695][696][697][698][699][700][701][702][703]. During training, mice could choose between a 20-or 100-ul drop of milk delivered after a 1-s delay. During testing, the delay to the large drop of milk was increased from 1 to 100 seconds. As the delay to the larger volume increased, preference shifted to the smaller, more immediate option. In adolescence, both strains showed similar shifts in preference. In contrast, adult B6 mice were less sensitive to increasing delays than were adult D2 mice, who continued to perform much as their adolescent counterparts. A subsequent resistance-to-extinction test ruled out the possibility that the slower change in the adult B6 mice was due to perseverative responding. The present findings suggest that B6 and D2 strains may be differentially suited to uncovering the biological mechanism of short-term and long-term patterns of impulsive behavior. KeywordsImpulsivity; Delay Discounting; Development; Resistance to Extinction; C57BL6/6J; DBA/2JThe adolescent undergoes profound neural, physiological, behavioral, and social changes during in the transition from childhood to adulthood. Although the adolescent period is important for establishing the individual as an independent adult, it is also a period of developmental vulnerability (Casey, Jones, & Hare, 2008;Steinberg, 2005). Adolescent behavior is often described as impulsive, risky, and sensation-driven, reflecting increased tendencies for adolescents to engage in unsafe sexual practices, dangerous driving, criminal behavior, and experimentation with controlled substances (Arnett, 1992;Chambers, Taylor, & Potenza, 2003;Crews, He, & Hodge, 2007;Spear, 2000). In fact, potentially maladaptive Corresponding Author: Questions regarding this manuscript should be directed to Jonathan W. Pinkston, Department of Behavior Analysis, University of North Texas, Denton, TX 76209, jonathan.pinkston@unt.edu or Richard Lamb, Department of Psychiatry, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229 lamb@uthscsa.edu. Jonathan Pinkston is now at the University of North Texas. Publisher's Disclaimer:The following manuscript is the final accepted manuscript. It has not been subjected to the final copyediting, fact-checking, and proofreading required for formal publication. It is not the definitive, publisher-auth...

Spatial discrimination reversal and incremental repeated acquisition in adolescent and adult BALB/c mice

“…The present results suggest that sensitivity to effort and delay-of-reinforcement are important factors when characterizing adolescent behavior in response-initiated SDR and IRA procedures. The present findings may therefore extend those of recent studies using rodent models to quantify age-related differences in behavior (Adriani & Laviola, 2003; Pinkston & Lamb, 2011; Andrzejewski et al, 2011). Taken together, the rodent literature agrees with results from human adolescent studies of impulsivity using delay, probability, and time-based discounting paradigms (Green et al, 1994; Olson et al, 2008).…”

“…This suggests that the reinforcer captured lever-presses at chain links more temporally removed from reinforcement for adults than it did for adolescents, thus maintaining higher reinforcer rates despite the increase in response requirement as a function of chain length (Bizo & Killeen, 1997; Killeen & Sitomer, 2003). Stated another way, adolescent performance could be related to steepened delay-of-reinforcement gradients sometimes observed in adolescent rodents (Adriani & Laviola, 2003; Pinkston & Lamb, 2011). During IRA, there is a progressively increasing delay to reinforcement from the first link of the current chain as the number of links required to complete the chain increases.…”

“…The PFC has been implicated in processes ranging from behavior inhibition, task switching, attentional selection, and resistance to disruption in studies with rodents (Dalley et al, 2004; 2008). Imbalances in the development of brain regions like the PFC and NAcc during development may leave adolescents increasingly vulnerable to developing maladaptive patterns of behavior (Adriani & Laviola, 2004; Galvan et al, 2006; Moffit, 1993; Pinkston & Lamb 2011). Evidence from clinical and experimental studies implicate dysfunctions in fronto-striatal pathways, connecting frontal cortices with the basal ganglia, in a range of disorders, including ADHD and autism spectrum disorders (Cherkasova & Hechtman, 2009; Jentsch & Taylor, 1999; Langen et al, 2012).…”

“…Several behavior assays with rodents model characteristic patterns of adolescent behavior, including behavior rigidity, disinhibition, and impulsivity (Evenden, 1999; Madden & Johnson, 2010). Recent investigations have adapted these procedures to meet the time constraints presented by the rapid progression of rodent development (e.g., Adriani et al, 2003; Andrzejewski et al, 2011; Pinkston & Lamb, 2011; Sturman et al, 2010). Relative to adults, adolescent rodents spend more time exploring novel environments, develop an exaggerated sensitization response to psychostimulants, and discount delayed and probabilistic reinforcers more steeply (Adriani et al, 1998; Laviola et al, 2001; Pinkston & Lamb, 2011; Zoratto et al, 2013).…”

“…Recent investigations have adapted these procedures to meet the time constraints presented by the rapid progression of rodent development (e.g., Adriani et al, 2003; Andrzejewski et al, 2011; Pinkston & Lamb, 2011; Sturman et al, 2010). Relative to adults, adolescent rodents spend more time exploring novel environments, develop an exaggerated sensitization response to psychostimulants, and discount delayed and probabilistic reinforcers more steeply (Adriani et al, 1998; Laviola et al, 2001; Pinkston & Lamb, 2011; Zoratto et al, 2013). Also, adolescents learn to discriminate multiple stimuli more slowly (Spear & Brake, 1983) and display greater persistence under extinction compared to adults (Andrzejewski et al, 2011; Myslivecek & Hassmannova, 1979).…”