Waiting in DRL tests is impaired by serotonin depletion141 and is improved by manipulations that elevate serotonergic transmission.61 Systemic administration of serotonin-1A agonists and serotonin-2 antagonists improve waiting in DRL schedules.142, 143 The role for subtypes of serotonin-2 receptors is complex, with systemic activation of serotonin-2C receptors or antagonism of serotonin-2A receptors improving waiting.144, 145 This opposing influence of serotonin-2C and 2A receptors on DRL performance is similar to that observed for 5CSRTT.131
