Effect of central 5-hydroxytryptamine depletion on tolerance of delay of reinforcement: evidence from performance in a discrete-trials “time-left” procedure |
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Authors: | A S A Al-Ruwaitea T-J Chiang S S A Al-Zahrani M-Y Ho C M Bradshaw E Szabadi |
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Institution: | (1) Department of Psychiatry, University of Nottingham, Queen’s Medical Centre, Nottingham NG7 2UH, UK, GB |
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Abstract: | This experiment examined the effect of destruction of the ascending 5-hydroxytryptaminergic (5HTergic) pathways on performance
on a new discrete-trials version of the “time-left” procedure. Rats received either injections of 5,7-dihydroxytryptamine
into the dorsal and median raphe nuclei or sham lesions. They were trained in a discrete trials schedule in which reinforcers
were provided for responding on either of two levers, A and B. At a random time point, t s after the start of each trial, the two levers were inserted into the operant chamber; a response on A resulted in the delivery
of one food pellet after d
A s, whereas a response on B resulted in the delivery of two pellets after 84-t s. The value of d
A was varied between 1 and 12 s in different phases of the experiment. Both groups showed an increasing tendency to respond
on lever B as a function of time within the trial. Logistic functions were fitted to the data from each group, and a value
of the “indifference point” (T
50: the time within the trial at which proportional choice of B attained a value of 50%) was derived for each rat. For each
value of d
A, the values of T
50 were significantly greater in the lesioned rats than in the control rats, reflecting a rightward shift of the logistic function
in the lesioned group. The levels of 5HT and 5-hydroxyindoleacetic acid were reduced in the brains of the lesioned rats, but
the levels of noradrenaline and dopamine were not significantly altered. The results provide further evidence for the involvement
of the ascending 5HTergic pathways in the control of operant behaviour by delayed positive reinforcers.
Received: 12 January 1998/Final version: 6 May 1998 |
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Keywords: | 5-Hydroxytryptamine 5 7-Dihydroxytryptamine Operant behaviour Timing Delayed reinforcement |
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