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  • 1
    ISSN: 1432-2072
    Keywords: Operant behaviour ; Neuroleptics ; Pimozide ; “Anhedonia” hypothesis ; Herrnstein's equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A quantitative behavioural test system based on Herrnstein's (1970) equation was used to test a prediction derived from the “anhedonia” hypothesis of neuroleptic action, that pimozide should increase the value of the behavioural parameter K H (the reinforcement frequency needed to maintain the half-maximal response rate in variable-interval schedules). On the basis of theoretical considerations, it was shown that the equation implies that a drug which exerts such an effect on K H must have a more profound suppressant effect on performance maintained by low reinforcement frequencies than on performance maintained by high reinforcement frequencies. Fifteen rats were trained under variable-interval 10-s and variable-interval 100-s schedules, and the effect of pimozide (0.125, 0.25, 0.33, and 0.5 mg/kg) was tested on performance maintained under each schedule. The drug suppressed performance maintained under both schedules in a dose-dependent manner, and there was no tendency for the drug to exert a greater effect on performance maintained under the lower reinforcement frequency. These results do not provide any evidence that the effect of pimozide on variable-interval performance is due to an “anti-hedonic effect”; rather, they are compatible with the hypothesis that pimozide impairs the capacity to respond.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2072
    Keywords: d-Amphetamine ; Operant behaviour ; Variable-interval schedules ; Herrnstein's equation ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Dose-response curves were obtained for the effects of d-amphetamine sulphate (0.1–3.2 mg/kg) on the operant performance of rats in variable-interval 4-min and variableinterval 20-min schedules of reinforcement. Response rates maintained under variable-interval 4-min were suppressed in a dose-dependent manner. Response rates maintained under variable-interval 20-min schedules tended to be elevated by low doses and suppressed by higher doses. The degree of response rate suppression was greater in the case of the variable-interval 4-min schedule. The results are consistent with the previously reported effect of d-amphetamine on the values of the two constants of Herrnstein's (1970) equation: the drug reduces the reinforcement frequency needed to maintain the half-maximum response rates (K h) and lowers the maximum response rate (R max) (Bradshaw et al. 1981 b). It is suggested that the effects of d-amphetamine on operant performance may involve two processes: an enhancement of motivation and a reduction of the capacity to respond.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2072
    Keywords: Operant behaviour ; Variable-interval schedules ; Pentobarbitone ; Herrnstein's equation ; Rats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Six rats were exposed to a series of variable-interval schedules of reinforcement, each schedule specifying a different reinforcement frequency. The effects of two doses of pentobarbitone (24.16 and 40.27 μmol/kg) upon performance maintained under each schedule were examined. The data were analyzed in terms of the goodness of fit of Herrnstein's (1970) equation. Under control conditions (so injection or injection of vehicle alone) response rate was an increasing negatively accelerated function of reinforcement frequency, the data obtained from each rat conforming closely to Herrnstein's equation. In the presence of pentobarbitone there was a reduction in the value of R max (the theoretical maximum response rate) in all six rats. The effect of pentobarbitone upon the value of K H (the reinforcement frequency needed to obtain the half-maximal response rate) differed between animals, the value being increased in some rats and decreased in others. This was shown to reflect a systematic relationship between the baseline value of K H and the change in K H produced by pentobarbitone, high baseline values being associated with reductions, and low baseline values with elevations, in the presence of the drug. The data were also analyzed using conventional rate-dependency analysis. In some animals there was a tendency for lower response rates to be suppressed to a greater degree than higher rates, while the reverse was true in other animals. In general, rate-dependency functions provided poor descriptions of the data obtained from individual subjects.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-2072
    Keywords: Noradrenaline ; DSP4 ; Operant behaviour ; Herrnstein's equation ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effect of the selective noradrenaline neurotoxin DSP4 on steady-state operant behaviour was examined using a quantitative behavioural paradigm based on Herrnstein's (1970) equation, which defines a hyperbolic relationship between steady-state response rate and reinforcement frequency in variable-interval schedules. Eleven rats received injections of DSP4 (two doses of 50 mg/kg, intraperitoneally), and 12 rats received injections of the vehicle alone. The rats were trained to steady state in a series of six variable-interval schedules of sucrose reinforcement, affording scheduled reinforcement frequencies of 4–360 reinforcers per hour. Herrnstein's equation was fitted to the data obtained from each rat and to the averaged data obtained from the two groups. The value ofK H (the parameter expressing the reinforcement frequency needed to maintain the half-maximal response rate) was higher in the DSP4-treated rats than in the control rats; the value ofR max (the parameter expressing the maximum response rate) did not differ significantly between the two groups. At the end of the behavioural experiment the rats were sacrificed for determination of the concentrations of catecholamines in the brain by high-performance liquid chromatography. The levels of noradrenaline in the parietal cortex, hippocampus and cerebellum of the DSP4-treated rats were less than 20% of those of the control rats. The results provide further evidence that central noradrenergic neurones are involved in the maintenance of operant behaviour by positive reinforcement.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-2072
    Keywords: Noradrenaline ; Dorsal noradrenergic bundle ; 6-Hydroxydopamine ; Operant behaviour ; Herrnstein's equation ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The possible role of the dorsal noradrenergic bundle (DNAB) in the maintenance of operant behaviour by positive reinforcement was examined using a quantitative behavioural paradigm based on Herrnstein's (1970) equation which defines a hyperbolic relationship between steady-state response rate and reinforcement frequency in variable-interval schedules. Twelve rats received bilateral injections of 6-hydroxydopamine (4 μg/2 μl) into the DNAB; ten rats received sham injections. The rats were trained to steady state in a series of six variable-interval schedules of sucrose reinforcement affording reinforcement frequencies of 8–350 reinforcers per hour. Herrnstein's equation was fitted to the data obtained from each rat and to the averaged data obtained from the two groups. The values of both R max (the parameter of the equation expressing the theoretical maximum response rate) and K H (the parameter expressing the reinforcement frequency needed to maintain the half-maximal response rate) were significantly higher in the DNAB-lesioned group than in the sham-lesioned group. At the end of the behavioural experiment the rats were sacrificed for determination of catecholamine levels in the brain by high-performance liquid chromatography. The levels of noradrenaline in the neocortex and hippocampus of the DNAB-lesioned rats were approximately 10% of those of the sham-lesioned rats. The results indicate that destruction of the DNAB reduced the “value” of the reinforcer without impairing the animals' capacity to respond.
    Type of Medium: Electronic Resource
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