Effect of destruction of the 5-hydroxytryptaminergic pathways on temporal memory: quantitative analysis with a delayed interval bisection task |
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Authors: | S S A Al-Zahrani M-Y Ho A S A Al-Ruwaitea 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 memory
for duration, using a delayed interval bisection task. Rats that had received injections of 5,7-dihydroxytryptamine into the
dorsal and median raphe nuclei, and sham-lesioned control rats, were trained in a series of discrete trials to press lever
A following a 2-s presentation of a light stimulus, and lever B following an 8-s presentation of the same stimulus. Following
stimulus offset a response on a panel placed midway between the two levers was required in order to initiate lever presentation;
a single response on either lever resulted in withdrawal of both levers and, in the case of a ‘correct’ response, reinforcer
delivery. When > 90% correct choices had been attained, an 8-s (phase I) or a 12-s (phase II) delay was interposed between
stimulus offset and lever presentation in 50% of the trials, and probe trials (10% of both non-delay and delay trials) were
introduced in which the light was presented for intermediate durations. Logistic functions were derived relating percent choice
of lever B to stimulus duration. In both groups, the imposition of post-stimulus delays displaced the bisection point (duration
yielding 50% choice of lever B) towards longer durations; this effect was significantly greater in the lesioned group than
in the control group. Imposition of post-stimulus delays resulted in increases in the Weber fraction, which did not differ
significantly between the two groups. 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 altered.
Received: 30 April 1996 / Final version: 20 August 1996 |
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Keywords: | 5-Hydroxytryptamine 5 7-Dihydroxytryptamine Operant behaviour Time discrimination Memory for duration Interval bisection procedure Rat |
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