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  • 1
    ISSN: 1432-2072
    Keywords: Amphetamine ; Apomorphine ; Dopamine ; Exploration ; Locomotor activity ; Hole-board ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In the present experiments, the effects of a wide range of doses of d-amphetamine and apomorphine were studied on investigatory behavior in an automated eight-hole box. Amphetamine (0.125, 0.25, 0.5, 1.0, 3.0, 5.0 mg/kg) increased frequency and total duration of responses, and decreased mean duration in a dose-dependent manner. The strategy and organization of responses, as measured by the order of hole-visits and hole-switching, were unchanged at lower doses of amphetamine but were altered at higher doses. Perseverative hole-poking was observed at the highest dose (5.0) as indicated by increased number of hole-pokes per hole-visit. Apomorphine (0.05, 0.1, 0.2, 0.4, 0.8, 1.6, 3.2 mg/kg) decreased mean duration of responses, but in contrast to amphetamine markedly diminished frequency. Locomotor activity was also measured at all doses of both drugs. Our observations indicate that these two stimulant drugs both of which increase motor activity, have markedly different effects on investigatory responses. It is likely that amphetamine increases prepotent response tendencies (i.e., hole-poking), although this does not necessarily reflect enhanced exploration. Further, the results obtained with amphetamine support predictions made by the Lyon-Robbins behavioral theory of amphetamine effects.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2072
    Keywords: Opiates ; Nucleus accumbens ; Supersensitivity ; Chronic neuroleptic ; 6-OHDA lesion ; Mesolimbic dopamine neurones ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In the present study the functional relationship between enkephalinergic and dopaminergic neurones at the level of the nucleus accumbens was investigated. The study consisted of two experiments in which dopaminergic (DA) transmission was chronically inhibited, and the behavioural locomotor response to intra-accumbens opiate injections analysed. First, specific 6-OHDA lesion of the DA-A10 neurones (either in nucleus accumbens or ventral tegmental area) was found markedly to increase the behavioural excitatory effects induced by nucleus accumbens injection of opioid peptides or morphine. Specific lesion of the central noradrenergic neurones had no such effect. Second, chronic pharmacological blockade of DA activity either with reserpine or a neuroleptic (pipothiazine palmitate) similarly induced a strong enhancement of the behavioral response to intra-accumbens opiate injection. The results are discussed in terms of novel mechanisms underlying denervation supersensitivity, and may have important implications for the relation between dopamine dysfunction in mental illness and opiate addiction.
    Type of Medium: Electronic Resource
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