Drugs and punished responding VI: body weight as a determinant of drug effects.

Pigeons were rewarded with grain for pecking a key under a fixed-interval schedule of food presentation. After responding stabilized, each key-peck produced a 3.5 mA electric shock, about 50 msec in duration. Dose-effect curves for pentobarbital, d-amphetamine and chlordiazepoxide on punished responding were determined in these pigeons when their body weights were adjusted to 70%, 90% or 100% of their free-feeding weights. The lower the body weight, the higher the rate of punished responding before drugs were given. Pentobarbital increased punished responding in all three body weights, but it produced the largest increases in punished responding over the widest dose range when the body weight was maintained at 90% of the free-feeding weight. Chlordiazepoxide also tended to produce rate increases at all three body weights, but d-amphetamine increased the rate only when the birds were maintained at 100% of their free-feeding weights.