Behavioral and pharmacological variables affecting risky choice in rats

The effects of manipulations of response requirement, intertrial interval ( ITI), and psychoactive drugs (ethanol, phencyclidine, and d-amphetamine) on lever choice under concurrent fixed-ratio schedules were investigated in r ats. Responding on the "certain" lever produced three 45-mg pellets, wherea s responding on the "risky" level produced either 15 pellets (p = .33) or n o pellets (p = .67). Rats earned all food during the session, which ended a fter 12 forced trials and 93 choice trials or 90 min, whichever occurred fi rst. When the response requirement was increased from 1 to 16 and the ITI w as 20 s, percentage of risky choice was inversely related to fixed-ratio va lue. When only a single response was required but the ITI was manipulated b etween 20 to 120 s (with maximum session duration held constant), percentag e of risky choice was directly related to length of the ITI. The effects of the drugs were investigated first at an ITI of 20 s, when risky choice was low for most rats, and then at an ITI of 80 s, when risky choice was highe r for most rats. Ethanol usually decreased risky choice. Phencyclidine did not usually affect risky choice when the ITI was 20 s but decreased it in h alf the rats when the ITI was 80 s. For d-amphetamine, the effects appeared to be related to baseline probability of risky choice: that is, low probab ilities were increased and high probabilities were decreased. Although incr ease in risky choice as a function of the ITI is at variance with previous ITI data, it is consistent with foraging data showing that risk aversion de creases as food availability decreases. The pharmacological manipulations s howed that drug effects on risky choice may be influenced by baseline proba bility of risky choice, just as drug effects can be a function of baseline response rate.