Effect of destruction of the 5-hydroxytryptaminergic pathways on the acquisition of temporal discrimination and memory for duration in a delayed conditional discrimination task |
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Authors: | S S A Al-Zahrani M -Y Ho D N Velazquez Martinez M Lopez Cabrera C M Bradshaw E Szabadi |
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Institution: | (1) Department of Psychiatry, University of Nottingham, Queen's Medical Centre, NG7 2UH Nottingham, UK;(2) Present address: Faculty of Psychology, National University of Mexico, 04510 Mexico, D.F., Mexico;(3) Present address: Faculty of Medicine, National University of Mexico, 04510 Mexico DF, Mexico |
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Abstract: | This experiment examined the effect of destruction of the ascending 5-hydroxytryptaminergic (5HTergic) pathways on the acquistion of a temporal discrimination and on memory for duration, using a delayed conditional discrimination task. In phase I, rats that had received injections of 5,7-dihydroxytryptamine into the dorsal and median raphe nuclei, and shamlesioned 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 intiate lever presentation; a single response on either lever resulted in withdrawal of both levers and, in the case of a correct response, reinforcer delivery. Both groups gradually acquired accurate discrimination, achieving >90% correct choices within 20–30 sessions; the lesioned group acquired accurate performance significantly faster than the control group. In phase II, delays were interposed between stimulus offset and lever presentation in 50% of the trials (2, 4, 8, 16 and 32 s; 10% of trials in each case). Accuracy declined as a function of post-stimulus delay in both groups, and there was no significant difference between the performances of the two groups. Both groups showed an increasing tendency to respond on lever A following longer post-stimulus delays ( choose-short effect); this effect was somewhat enhanced 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 altered. |
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Keywords: | 5-Hydroxytryptamine 5 7-Dihydroxytryptamine Operant behaviour Time discrimination Memory for duration |
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