COCAINE AND FOOD-DEPRIVATION - EFFECTS ON FOOD-REINFORCED FIXED-RATIOPERFORMANCE IN PIGEONS

Key pecking by 6 pigeons was maintained by a fixed-ratio 30 schedule o f food presentation while body weights were 80% of free-feeding weight s. Acute administration of cocaine (0.3 to 13.0 mg/ kg, i.m.) dose-dep endently decreased response rates. Dose-effect curves were shifted to the right when 3 of the 6 pigeons were maintained at 70% of free-feedi ng weights and were shifted to the left when the other 3 pigeons were maintained at 90% of free-feeding weights. Then a dose of cocaine that initially decreased response rates by more than 95% of control rates was administered before each daily session. Comparable degrees of tole rance to these rate-decreasing effects developed in the two groups. Th e rate at which responding recovered was relatively rapid for pigeons in the 70% free-feeding-weight group and was slower for 2 of the 3 pig eons in the 90% free-feeding-weight group. When body weights were then increased from 70% to 80% or were decreased from 90% to 80% of free-f eeding weight, performance was disrupted initially only for pigeons wh ose weight went from 70% to 80% of free feeding. In the present experi ment the degree of deprivation may have indirectly influenced the degr ee of tolerance that developed to cocaine's response rate-decreasing e ffects because it directly influenced the dose chosen to be administer ed chronically. The degree of deprivation appeared to have a more dire ct influence on the rate at which tolerance developed.