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Behavioural history effects
on the maintenance of schedule-induced polydipsia in rats
Juan Ardoy and Ricardo
Pellón
Universidad Católica
San Antonio de Murcia and Universidad Nacional de Educación
a Distancia, Spain
Rats were trained during 15 sessions to press a lever according
to a fixed-interval 30-s food reinforcement schedule, and concurrently
they developed schedule-induced polydipsia (Stage A). Animals
were then divided in two treatments, being equated the rates
of lever pressing and licking the bottle spout. Exposure to
the fixed-interval 30-s schedule continued during another 30
sessions for experimental rats, but now water was not available
(Stage B). Control rats remained throughout in their home-cages.
Initial conditions were reinstated during the last phase of the
experiment (Stage A); during 10 sessions all rats were exposed
to the fixed-interval 30-s food schedule and they were allowed
to drink from the bottle. Experimental rats significantly increased
the rate of lever pressing when the opportunity to drink was
removed during Stage B, and lever pressing returned to baseline
levels when the water bottle was again reintroduced during the
last phase of the experiment. Data from the rate of licking are
more interesting, however. When initial conditions were reverted
during the last Stage A, experimental rats showed an initial
decline in licks per minute which recovered as sessions progressed.
Control rats, however, did not show significant changes in the
licking rate along this latter phase of the experiment. These
results prompt to the conclusion that a reinforcement experience
without the opportunity to perform the adjunctive behaviour of
licking transitorily interferes with the previous learning of
adjunctive patterns of behaviour, and this effect cannot be attributed
to the mere passage of time. The present results will be presented
in the context of data from our laboratory which suggest that
reinforcement acts by strengthening behavioural chains which
include distal elements to the reinforcer.
Keywords: schedule-induced polydipsia,
operant lever-pressing, behavioural history, rats |