A self-adjusting, progressive shock magnitude procedure to investigate resistance to punishment: characterization in male and female rats

Indifference to harmful consequences is one of the main characteristics of compulsive behaviors and addiction. Animal models that provide a rapid and effective measure of resistance to punishment could be critical for the investigation of mechanisms underlying these maladaptive behaviors. Here, analogous to the progressive ratio (PR) procedure widely used to evaluate appetitive motivation as the response requirement is increased, we developed a self-adjusting, progressive shock magnitude (PSM) procedure. The PSM provides, within a single session, a break point that quantifies the propensity to work for a reward in spite of receiving electric footshock that progressively increases in duration. In both male and female rats, the PSM break point was sensitive to 1) the hunger drive; and 2) changes in the qualitative, but not quantitative, incentive value of the reward. In systematic comparisons between PSM and PR procedures in the same rats, we found that both measures are sensitive to manipulations of motivational states, but they are not correlated, suggesting that they measure overlapping but distinct processes. Importantly, the PSM procedure represents a refinement in the 3Rs principles of animal research because animals can control the magnitude of shock that they are willing to tolerate. This self-adjusting PSM procedure may represent a useful tool to investigate mechanisms underlying maladaptive behavior that persists in certain individuals despite harmful consequences.