Chronic effects of lead on schedule-controlled pigeon behavior

Abstract

Pigeons were trained to peck a response key under a multiple fixed ratio 30 response (FR 30) fixed-interval 5-min (FI 5) schedule of food presentation. When rates of responding stabilized, lead acetate (6.25, 12.5, and 25 mg/kg body weight) or sodium acetate solutions were given daily by gastric intubation. Blood-lead concentrations were measured weekly by atomic absorption spectrometry, and responding under the multiple schedule was measured Monday through Friday. Control intubations of sodium acetate did not affect responding under either component of the schedule. The 25-mg/kg dose of lead decreased rates of responding after 3 to 10 days of administration and usually was lethal between 18 and 35 days. Post mortem examination of the birds showed obvious esophageal dilatation, damage to the crop, weight loss, and subarachnoid hemorrhages. Administration of the 25-mg/kg dose was discontinued in some birds after responding had ceased. Responding gradually began to recover, but rates of responding remained low and variable under both components of the schedule for many days. Daily administration of the 12.5-mg/kg dose of lead caused one death, but no obvious signs of intoxication occurred in the other birds. However, three of the four birds surviving daily 12.5-mg/kg doses of lead showed decreased rates of responding under both schedule components within 30 days of the initial intubation. The fourth bird showed a highly variable rate under the FI component of the schedule during lead administration; however, when lead administration was discontinued, dramatic increases in rates of responding above lead pretreatment levels occurred, particularly under the FI component. These rate increases persisted for 75 days thereafter. The 6.25-mg/kg dose of lead produced only small changes in rates of responding during 70 days of intubation. Blood-lead concentrations were very high (150–3470 <g/dl) during treatment with all doses of lead. Increasing doses produced increasing blood concentrations which were correlated with increasing behavioral effects, although correlations between blood-lead concentrations and behavioral changes were low within individual birds.