Effects of early handling on amphetamine-induced locomotor activation and conditioned place preference in the adult rat |
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Authors: | James Campbell L P Spear |
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Institution: | (1) Department of Psychology and Center for Developmental Psychobiology, Binghamton University, Box 6000, Binghamton, NY 13902-6000, USA, e-mail: lspear@binghamton.edu, Fax: +1-607-777-6418, US |
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Abstract: |
Rationale: Altered hormonal stress responsiveness has been implicated in psychostimulant responsivity, and early handling represents
a mild environmental manipulation which alters the hormonal profile following stress exposure. Objective: The present experiments examined whether early handling in rats would alter locomotor effects of amphetamine, as well as
cross-sensitization of locomotor responsiveness after chronic stress. Conditioned place preference (CPP) for amphetamine was
also measured. Methods: Handling consisted of daily 15-min isolation periods from days 1–12 postnatally. Novelty- and amphetamine (0, 1.5 mg/kg)-induced
locomotion were examined using circular corridors in adult rats that were either restrained repeatedly over 8 days or not
disturbed prior to testing. The effects of handling on amphetamine (0, 1, 2, 5 mg/kg) conditioned place preference (CPP) were
also examined following 3 days of drug-compartment pairings. Results: Early handling produced a more rapid post-stress recovery in corticosterone levels. Handled animals also exhibited a significant
attenuation in amphetamine-induced CPP compared to non-handled controls. Locomotor responsiveness to novelty and amphetamine
was not altered by early handling. Although no cross-sensitization was observed, evidence for stress sensitization was seen,
but was unaffected by early handling. Conclusions: Handled animals showed an attenuated CPP for amphetamine, data suggesting that sensitivity to the reward value of drugs
of abuse in adulthood may be susceptible to relatively minor environmental manipulations early in life. This effect of handling
on CPP does not seem to reflect differences in locomotor sensitivity to amphetamine.
Received: 5 August 1998 / Final version: 2 November 1998 |
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Keywords: | Early handling CPP Reward Stress Sensitization Locomotion |
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