AUTOMATING THE GENERATION AND COLLECTION OF RATE-FREQUENCY FUNCTIONS IN A CURVE-SHIFT BRAIN-STIMULATION REWARD PARADIGM

The electrical self-stimulation paradigm has proven to be very useful in research aimed at delineating the neural substrates involved in rew ard-related learning. Of the procedures currently employed the curve-s hift method is among the more useful since it distinguishes between tr eatment effects on reward and performance. This method involves genera ting and plotting rate-frequency functions and quantifying the effects of experimental manipulations on reward by measuring the degree of la teral shift in these functions. We have designed a computerized system that automatically generates and collects descending rate-frequency f unctions from self-stimulating rats. The 3 main units of this system c onsisted of a 6809 micro-controller, a programmable timer logic board and a constant current source. The micro-controller and programmable t imer operated on custom written software that monitored lever pressing in the operant chambers and controlled stimulation parameters to gene rate and record rate-frequency functions. The present report describes this system and presents some typical data collected from rats self-s timulating on ventral tegmental electrodes before and after the admini stration of intra-accumbens vehicle (0.5 mu l distilled H2O), (+)-amph etamine (20.0 mu g/0.5 mu l), quinpirole (10.0 mu g/0.5 mu l) and syst emic quinpirole (1.0 mg/kg), all dopamine agonists. Stimulation consis ting of 300-ms trains of cathodal rectangular pulses (0.1 ms) was avai lable in 50-s trials. The number of pulses per train was decreased log arithmically from a value that sustained maximal responding to one tha t would not sustain responding. Self-stimulation thresholds were obtai ned by fitting the Gompertz growth model to the data and calculating t he point of maximal acceleration of the sigmoidal curve. It was found that the present system generated and collected rate-frequency functio ns similar to those that have been obtained manually in previous exper iments. The data showed that the system was sensitive to both central and systemic pharmacological manipulations by producing lateral and ve rtical shifts of the rate-frequency functions, indications of reward a nd motor effects, respectively. It was concluded that the present desi gn was useful in conducting entire self-stimulation sessions that requ ired minimal monitoring by the experimenter.