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  • 1
    Electronic Resource
    Electronic Resource
    Effect of central 5-hydroxytryptamine depletion on tolerance of delay of reinforcement: evidence from performance in a discrete-trials “time-left” procedure (1999)
    Springer
    Psychopharmacology 141 (1999), S. 22-29 
    Details
    ISSN: 1432-2072
    Keywords: Key words 5-Hydroxytryptamine ; 5 ; 7-Dihydroxytryptamine ; Operant behaviour ; Timing ; Delayed reinforcement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050802
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of central 5-hydroxytryptamine depletion on performance in the free-operant psychophysical procedure: facilitation of switching, but no effect on temporal differentiation of responding (1999)
    Springer
    Psychopharmacology 143 (1999), S. 166-173 
    Details
    ISSN: 1432-2072
    Keywords: Key words 5-Hydroxytryptamine ; 5 ; 7-Dihydroxytryptamine ; Operant behaviour ; Timing ; Switching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract This experiment examined the effect of destroying the ascending 5-hydroxytryptaminergic (5-HTergic) pathways on timing and switching behaviour in the free-operant psychophysical procedure. Rats received injections of 5,7-dihydroxytryptamine into the dorsal and median raphe nuclei or sham lesions. They were trained to press levers for sucrose reinforcement; sessions consisted of fifty 50-s trials in which reinforcers were available on a variable-interval 30-s schedule. In the first 25 s, of each trial, reinforcement was only available for responses on lever A; in the last 25 s, it was available only for responses on lever B. In phase 1 (70 sessions) repetitive switching between the levers was prevented by withdrawal of lever A after the first response on lever B in each trial; in phase 2 (40 sessions) this constraint on switching was removed; in phase 3 (40 sessions) the constraint was reinstated. Data were collected from probe trials (four per session) in which no reinforcers were delivered, during the last ten sessions of each phase. In all phases, both groups showed declining response rates on lever A and increasing response rates on lever B as a function of time from the onset of the trial. Response rate on lever B, expressed as percentage of overall response rate, could be described by a two-parameter logistic function. Removal of the constraint on switching reduced the slope of the function without changing the indifference point (time corresponding to 50% responding on lever B). The parameters of the timing function did not differ between the groups in any of the phases. However, the lesioned group showed a greater enhancement of switching rate during phase 2 than the control group. The levels of 5-HT and 5-hydroxyindoleacetic acid were reduced in the brains of the lesioned rats, but the levels of noradrenaline and dopamine were not altered. The results provide further evidence for the involvement of the ascending 5-HTergic pathways in switching between response alternatives, but cast doubt on our previous suggestion that the effects of 5-HT depletion on temporal differentiation of behaviour are mediated by facilitated switching.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050932
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of central 5-hydroxytryptamine depletion on inter-temporal choice: a quantitative analysis (2000)
    Springer
    Psychopharmacology 149 (2000), S. 313-318 
    Details
    ISSN: 1432-2072
    Keywords: Key words 5-HT ; 5 ; 7-Dihydroxytryptamine ; Operant behaviour ; Inter-temporal choice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Rationale: It has been proposed that the ascending 5-hydroxytryptaminergic (5-HTergic) pathways are involved in ”impulse control”. Previous experiments have shown that rats whose 5-HTergic pathways have been destroyed are more liable than intact rats to select a smaller, immediate reinforcer rather than a larger, delayed reinforcer (impulsive choice). However, it remains unclear whether this effect of central 5-HT depletion reflects a change in the rate of time discounting (i.e. a change in the rate at which reinforcers become devalued as a function of delay) or a change in sensitivity to reinforcer size. Objective: We examined the effect of central 5-HT depletion on time discounting using a quantitative model of inter-temporal choice (multiplicative hyperbolic model), which enables effects on time discounting to be differentiated from effects on sensitivity to reinforcer size. Methods: Rats received injections of 5,7-dihydroxytryptamine into the dorsal and median raphe nuclei or sham lesions. They were trained to press two levers for food-pellet reinforcers in a discrete-trials adjusting-delay schedule. In free-choice trials, selection of lever A resulted in a brief fixed delay (d A ) followed by delivery of one pellet; selection of lever B resulted in a longer variable delay (d B ) followed by delivery of two pellets; d B was adjusted in accordance with the subject’s choices. The value of d A was varied (0.5–8.0 s) in successive phasesof the experiment, and the indifference value of d B was determined in each case. Results: In both groups, the indifference value of d B was linearly related to the value of d A ,in accordance with the multiplicative hyperbolic model. The lesioned group showed shorter indifference delays than the sham-lesioned group, this being reflected in a parallel displacement of the linear indifference function. In both experiments, the levels of 5-HT and 5-hydroxyindole-acetic acid were reduced in the brains of the lesioned rats, but the levels of noradrenaline and dopamine were not altered. Conclusions: According to the multiplicative hyperbolic model, parallel displacement of the linear indifference function uniquely specifies a change in time discounting. Thus these results indicate that central 5-HT depletion results in an increase in the rate of time discounting for food reinforcers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130000385
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of destruction of the 5-hydroxytryptaminergic pathways on temporal memory: quantitative analysis with a delayed interval bisection task (1997)
    Springer
    Psychopharmacology 129 (1997), S. 48-55 
    Details
    ISSN: 1432-2072
    Keywords: Key words 5-Hydroxytryptamine ; 5 ; 7-Dihydroxytryptamine ; Operant behaviour ; Time discrimination ; Memory for duration ; Interval bisection procedure ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050161
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of destruction of the 5-hydroxytryptaminergic pathways on behavioural timing and “switching” in a free-operant psychophysical procedure (1996)
    Springer
    Psychopharmacology 127 (1996), S. 346-352 
    Details
    ISSN: 1432-2072
    Keywords: Key words 5-Hydroxytryptamine ; 5 ; 7-Dihydroxytryptamine ; Operant behaviour ; Timing ; Behavioural switching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract This experiment examined the effect of destruction of the ascending 5-hydroxytryptaminergic (5HTergic) pathways on performance in a free-operant timing schedule. Rats received either injections of 5,7-dihydroxytryptamine into the dorsal and median raphe nuclei or sham lesions. They were trained to press levers for a sucrose reinforcer. Training sessions consisted of 40, 50-s trials in which reinforcers were available on a variable-interval 25-s schedule; in the first 25 s of each trial, reinforcers were only available for responses on lever A, whereas in the last 25 s reinforcers were available only for responses on lever B. Data were collected from probe trials (four per session) in which no reinforcers were delivered, during the last ten of 50 training sessions. Both groups showed decreasing response rates on lever A and increasing response rates on lever B as a function of time from the onset of the trial. Response rate on lever B, expressed as a percentage of overall response rate, could be described by a two-parameter logistic function; neither the indifference point (i.e. the time corresponding to 50% responding on lever B) nor the slope of the function differed between the two groups. However, the lesioned group showed a higher rate of switching between response alternatives than the sham-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 confirm previous findings that behaviour in timing schedules is sensitive to destruction of the central 5HTergic pathways, and suggest that these pathways may contribute to the inhibitory regulation of switching between behavioural states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050096
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of central 5-hydroxytryptamine depletion on performance in the “time-left” procedure: further evidence for a role of the 5-hydroxytryptaminergic pathways in behavioural “switching” (1997)
    Springer
    Psychopharmacology 134 (1997), S. 179-186 
    Details
    ISSN: 1432-2072
    Keywords: Key words 5-Hydroxytryptamine ; 5 ; 7-Dihydroxytryptamine ; Operant behaviour ; Timing ; Behavioural switching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract This experiment examined the effect of destruction of the ascending 5-hydroxytryptaminergic (5HTergic) pathways on performance in a free-operant timing schedule: 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, 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 60-t s. The value of d A was varied between 1 and 8 s in different phases of the experiment. Both groups showed decreasing response rates on lever A and increasing response rates on lever B as a function of time within the trial. An index of timing (T 75: the time within the trial at which relative response rate on B attained a value of 75%) was systematically related to the value of d A, but did not differ significantly between lesioned and control rats. However, the lesioned group showed significantly higher rates of switching between response alternatives than the sham-lesioned group at all values of d A. 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 that the ascending 5HTergic pathways may contribute to the inhibitory regulation of switching between behavioural states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050440
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of central 5-hydroxytryptamine depletion on changeover behaviour in concurrent schedules of reinforcement (1999)
    Springer
    Psychopharmacology 144 (1999), S. 264-271 
    Details
    ISSN: 1432-2072
    Keywords: Key words 5-Hydroxytryptamine ; 5 ; 7-Dihydroxytryptamine ; Operant behaviour ; Concurrent schedules ; Switching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract   Rationale: Previous experiments have shown that rats whose 5-hydroxytryptaminergic (5-HTergic) pathways have been destroyed exhibit higher rates of switching between response alternatives on various temporal differentiation schedules. Objective: This paper reports two experiments investigating the effect of central 5-HT depletion on switching between concurrent schedules of reinforcement which do not entail temporal differentiation of behaviour. Methods: Rats received injections of 5,7-dihydroxytryptamine into the dorsal and median raphe nuclei or sham lesions. They were trained to press levers for sucrose reinforcement. In experiment 1, the rats were exposed to concurrent pairs of variable-time (VT) schedules specifying equal inter-reinforcement intervals; responses on a single ”changeover lever” alternated between the two VT schedules. In experiment 2, the rats were exposed to concurrent pairs of variable-interval (VI) schedules specifying equal inter-reinforcement intervals; responses on one lever (”VI lever”) earned reinforcers, while responses on the other lever (”changeover lever”) alternated between the two VI schedules. Results: In experiment 1, both groups showed longer ”dwell-times” (intervals between successive changeover responses) when a reinforcer was delivered in the ”dwell” than when no reinforcer was delivered (”win-stay” effect). The lesioned rats showed higher rates of changeover responding and shorter dwell-times (with and without reinforcer delivery) than the sham-lesioned group. In experiment 2, the rate of responding on the VI lever did not differ significantly between the two groups; however, the lesioned rats showed higher rates of changeover responding, shorter dwell-times (with and without reinforcer delivery) and smaller numbers of inter-changeover responses on the VI lever than the sham-lesioned group. In both experiments, the levels of 5-HT and 5-hydroxyindoleacetic acid were reduced in the brains of the lesioned rats, but the levels of noradrenaline and dopamine were not altered. Conclusions: These results provide further evidence for the involvement of the ascending 5-HTergic pathways in behavioural ”switching”, and indicate that this is not restricted to temporal differentiation schedules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130051002
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