Benzodiazepines reduce the tolerance to reward delay in rats

This study investigated whether benzodiazepines reduce the capacity of animals to wait for food reward. Rats trained in a T-maze were allowed to choose between two magnitudes of reward: immediate, but small (two pellets) vs delayed, but large (eight pellets). The rats learned within ten sessions to select (80–100%) the arm leading to the largest reward. Separate groups of rats were then confined for 15, 30 or 60 s in the arm associated with the largest reward before gaining access to the spacially contiguous goal-box. The choice of the other arm was not followed by a period of waiting. Under these conditions, the frequency with which the small-reward arm was chosen increased linearly as a function of the duration of the waiting period. Diazepam (2–4 mg/kg IP) dose-dependently increased the number of times the small-reward arm was chosen during the sessions for which the waiting period was fixed at 15 or 30 s. Nitrazepam (2 mg/kg IP), chlordiazepoxide (16 mg/kg IP) and clobazam (16 mg/kg IP) had similar effects. The action of diazepam was counteracted by simultaneous administration of flumazepil (Ro 15-1788, 8 mg/kg PO). In the absence of confinement, these benzodiazepines, diazepam (4 mg/kg) excepted, did not modify selection of the large-reward arm. Conversely, the serotonin uptake blockers indalpine (2–4 mg/kg IP) and zimelidine (8–16 mg/kg IP) dose-dependently increased preference for the arm leading to the delayed (25 s) but large reward.