Effects of central 5-hydroxytryptamine depletion on sensitivity to delayed and probabilistic reinforcement

Abstract

These results provide additional evidence that central 5-HTergic mechanisms are involved in time discounting, but provide no evidence for a similar role of 5-HT in rats' sensitivity to probabilistic reinforcement.

Deficits in Impulse Control Associated with Tonically-elevated Serotonergic Function in Rat Prefrontal Cortex

“…Disruption of 5-HT function by intra-raphé injections of 5,7-dihydroxytryptamine promotes impulsive choice for the smaller immediate reward (Wogar et al 1993;Ho et al 1998;Mobini et al 2000). Similar effects of 5-HT depleting lesions on impulsivity have been inferred from other operant paradigms, including a conditional go/no-go visual discrimination task (Harrison et al 1999) and reinforcement schedules with low response rates (Wogar et al 1993).…”

“…Post-mortem analysis revealed that 5-HT utilization (ratio of the 5-HT metabolite, 5-hydroxyindoleacetic acid to 5-HT) in the right frontal cortex increased proportionally with impulsive responding during the intertrial interval. These data are apparently at odds with studies where profound and global central depletion of 5-HT following lesions of the ascending 5-HTergic projections induced by the selective neurotoxin, 5,7-dihydroxytryptamine, increase impulsive behavior on both a 5-CSRT task (Harrison et al 1997a,b) and a delayof-reward choice procedure (Wogar et al 1993;Mobini et al 2000).…”

“…There is now a substantial body of evidence implicating impaired functioning of brain serotonergic systems in impulsive behavior (Linnoila et al 1983;Harrison et al 1997a;Puumala and Sirviö 1998;Evenden 1999b;Mobini et al 2000). An enduring hypothesis underpinning research in this area is that reduced central serotonin (5-HT) activity, either directly or indirectly, predisposes a subject to impulsive tendencies (Linnoila et al 1983;Wogar et al 1993;Fairbanks et al 2001;Mobini et al 2000).…”

“…An enduring hypothesis underpinning research in this area is that reduced central serotonin (5-HT) activity, either directly or indirectly, predisposes a subject to impulsive tendencies (Linnoila et al 1983;Wogar et al 1993;Fairbanks et al 2001;Mobini et al 2000). However, the precise nature of the 5-HT impairment in impulsivity remains poorly understood because indirect indices of 5-HT function are often used in clinical and experimental studies (Linnoila et al 1983;Fairbanks et al 2001;Evans et al 2000).…”

Tryptophan Depletion Disrupts the Motivational Guidance of Goal-Directed Behavior as a Function of Trait Impulsivity

“…Furthermore, recent studies with human volunteers have found that ATD increases impulsive and aggressive behavior, although these effects appear to depend on individual differences in impulsive personality traits (Cherek and Lane, 1999;LeMarquand et al, 1999;Dougherty et al, 1999;Bjork et al, 2000;Marsh et al, 2002;Crean et al, 2002). Findings from studies with clinical human populations are corroborated by an extensive number of animal studies, which suggest that impulsive choice in delaydiscounting paradigms and premature responding in choice reaction-time tasks implicate changes in the 5-HT system (Wogar et al, 1993;Harrison et al, 1997a, b;Puumala and Sirvio, 1998;Koskinen et al, 2000;Mobini et al, 2000;Dalley et al, 2002;Passetti et al, 2003;Winstanley et al, 2003;Liu et al, 2004).…”