RESUMO
Acute and chronic effects of mephenytoin (30-360 mg/kg) were examined in pigeons responding under a multiple fixed-ratio 50 fixed-interval 90-sec schedule of food delivery. The highest dose administered acutely (240 mg/kg) produced substantial reductions in rate of responding under both components of the multiple schedule; the effects of other doses were small and inconsistent. With chronic exposure tolerance appeared to develop to the rate-decreasing effects of the drug.
Assuntos
Hidantoínas/farmacologia , Mefenitoína/farmacologia , Animais , Columbidae , Alimentos , Mefenitoína/administração & dosagem , Tempo de Reação , Esquema de ReforçoRESUMO
Acute and chronic effects of methsuximide (25, 50, 75, and 100 mg/kg), a succinimide with anticonvulsant properties, were examined in pigeons responding under a multiple fixed-ratio 50 fixed-interval 90-sec schedule of food delivery. The clearest acute effect of methsuximide was a substantial reduction in response rates under both components of the multiple schedule when the drug was administered at 100 mg/kg. Detailed analysis of the temporal distribution of responding under the fixed-interval failed to reveal rate-dependent drug effects. Tolerance appeared to develop to the effects of methsuximide when the drug was administered chronically.
Assuntos
Condicionamento Operante/efeitos dos fármacos , Succinimidas/farmacologia , Animais , Anticonvulsivantes/farmacologia , Columbidae , Tolerância a Medicamentos , Feminino , Esquema de ReforçoRESUMO
Pigeons were exposed to schedules of food delivery that consisted of two sequential fixed ratios. When alternative sequences provided two food deliveries per 50 responses, the schedule with the shorter initial fixed-ratio value was consistently preferred. Progressively reducing from 1.0 to .25 the probability of food delivery following completion of the second fixed ratio of the sequence with the shorter initial fixed ratio did not reduce preference for this sequence. Moreover, the sequence with the shorter initial fixed ratio also was preferred when the probability of food delivery following completion of the initial ratio in that sequence was progressively reduced from 1.0 to .5, although preference shifted to the alternative when the probability was reduced to 0. These findings suggest that the length of the initial fixed ratio was a primary determinant of choice. Subsequent manipulations demonstrated, however, that when the initial fixed ratios of the two alternatives were equal, changes in the ratio value and probability of food delivery following completion of the second fixed ratio lawfully affected choice.
