EFFECTS OF DESIPRAMINE AND FLUVOXAMINE ON TIMING BEHAVIOR INVESTIGATED WITH THE FIXED-INTERVAL PEAK PROCEDURE AND THE INTERVAL BISECTION TASK

Acute treatment with antidepressant drugs is known to increase the mea n interresponse time (IRT) in the IRT>72-s schedule of reinforcement. In order to examine the possibility that this effect may reflect an ac tion of the antidepressants on timing processes, we tested the effects of two antidepressants, desipramine and fluvoxamine, on behaviour mai ntained under two other timing schedules in rats. In the fixed-interva l peak procedure (fixed-interval 30-s), acute treatment with desiprami ne (8 mg kg(-1)) reduced response rate, whereas acute treatment with f luvoxamine (8 mg kg(-1)) increased it. Neither drug significantly alte red the time to attainment of peak response rate or the Weber fraction . In the interval bisection task (standard durations 2 s and 8 s); the bisection point was not significantly altered by acute treatment with either drug. Chronic treatment with desipramine (8 mg kg(-1) b.d.) ha d no effect on any of the indices of timing under either schedule. Chr onic treatment with fluvoxamine (8 mg kg(-1) b.d.) reduced the time to attainment of peak response rate but had no effect on the Weber fract ion under the fixed-interval peak procedure. and did not alter the bis ection point or Weber fraction under the interval bisection procedure. The failure of desipramine and fluvoxamine to increase the time to pe ak response rate or the bisection point at doses that significantly al tered operant response rate suggests that the effect of these drugs on IRT schedule performance is unlikely to reflect an interaction with t iming processes.