Influences of Drug and Toxicant Exposure on the Microstructure of Responding

Abstract

A recent quantitative model has been used to examine the microstructure of behavior, and has described a bout of responding by three separate measures: within-bout response rate, bout initiation rate, and bout length. These measures have been shown to be affected by different types of variables. The studies that follow use this model as a tool to examine the microstructure of behavior. The first study examined the microstructure of behavior after haloperidol administration aiming to differentiate the anhedonic and motor effects of haloperidol. Both wheel running and nose-poking behavior was examined for BALB/c and C57BL/6 mice. Haloperidol decreased nose poking in a dose-dependent fashion with BALB/c mice being more sensitive to the rate depressing effects. The bout parameter most affected by haloperidol administration was bout initiation rate, which mirrored the decrease of overall nose poking. However, the same strain difference did not exist for wheel running. Wheel running was relatively unaffected by haloperidol administration for both strains. The statistical technique was also used to examine the microstructure of behavior after methylmercury (MeHg) exposure. Male BALB/c mice were exposured to 0 or 15ppm of Hg as methylmercuric chloride dissolved in drinking water. Nose-poking was maintained under a multiple schedule arrangement using two approaches to establishing high-rate responding. MeHg lowered within-bout response rate after about three months of exposure in both schedules. Effects on bout initiation rate were less consistent and appeared to have interacted with time of day and schedule type. The partitioning technique is a promising way of separating motor and motivational influences.