Development of a method and software for modeling gambling and risk states in rodents during intracranial self-stimulation

Introduction. Intracranial self-stimulation is widely used to investigate the neural mechanisms of reward and addiction in laboratory animals. Objective. To develop an integrated hardware–software system for self-stimulation experiments in rats that offers flexible stimulation schedules mimicking human gambling and risk-taking situations. Materials and methods. A real-time C# (.NET) application was written to control a microcontroller-based stimulator via USB. Male Wistar rats were implanted with electrodes in the ventral tegmental area (VTA) at the following coordinates: AP = –5.0 mm from bregma; L = –0.9 mm; H = –8.4 mm from the skull surface (Paxinos Watson, 2005). Animals were trained to self-stimulate in a two-pedal Skinner box under a fixed-ratio schedule (FR1-3) at threshold current intensity. After training, one lever was switched to a variable-ratio schedule (VR3-6) while the stimulation current was increased by 15 %. Once responding stabilized, rat behaviour was analysed. Results. The new program enabled prolonged, stable generation of bipolar pulses (1–1000 µA, 100 Hz) with precise time-stamping. Depending on stimulation parameters, rats preferred either the VR3-6 or the FR1-3 schedule. Reducing the probability of reinforcement on the variable-ratio lever shifted preference toward the fixed-ratio lever. A 7-day course of intraperitoneal administration of the SSRI antidepressant paroxetine (1 mg/kg/ day) produced shift in lever pressing, favouring the FR1-3 schedule. Conclusion. The developed system can successfully model rodent states analogous to human gambling and risk, facilitating the study of gambling-like behaviour. Repeated paroxetine administration attenuated gambling- and risk-like behaviour in this paradigm.