Effect of destruction of the 5-hydroxytryptaminergic pathways on the acquisition of temporal discrimination and memory for duration in a delayed conditional discrimination task.
This experiment examined the effect of destruction of the ascending 5-hydroxytryptaminergic (5HTergic) pathways on the acquisition 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 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. 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.
Al-Zahrani
S S
SS
Department of Psychiatry, University of Nottingham, Queen's Medical Centre, UK.
Ho
M Y
MY
Martinez
D N
DN
Cabrera
M L
ML
Bradshaw
C M
CM
Szabadi
E
E
D000818:Animals; D001921:Brain / Q000378:metabolism*; D004192:Discrimination, Psychological / Q000502:physiology*; D004298:Dopamine / Q000378:metabolism; D005260:Female; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D008568:Memory / Q000502:physiology*; D009434:Neural Pathways; D051381:Rats; D017208:Rats, Wistar; D012701:Serotonin / Q000494:pharmacology*; D013997:Time Factors
D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D004298:Dopamine