ISSN:
1432-2072
Keywords:
Amphetamine
;
Apomorphine
;
Chronic treatment
;
Dopamine
;
Locomotor activity
;
Noradrenaline
;
Supersensitive receptors
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract Mice administered dexamphetamine (4 mg/kg i.p.) once daily for 20 days displayed an enhanced locomotor response (compared to that of vehicletreated mice) to dexamphetamine when challenged 4 to 16 days but not when challenged 32 days after withdrawal. In the experiments described a 20-day dexamphetamine administration followed by an 8-day withdrawal period was used. Pimozide or haloperidol not only completely antagonised the enhanced response to dexamphetamine (2 mg/kg i.p.) in dexamphetamine-treated mice, but also antagonised all dexamphetamine-induced stimulation. Reserpine, in contrast, preferentially blocked the difference in the response to dexamphetamine of dexamphetamine-and vehicle-treated mice, without antagonising all the dexamphetamine-induced locomotion. The stimulation produced in dexamphetamine-(but not in vehicle-) treated mice by dexamphetamine was partially blocked by phentolamine, phenoxybenzamine, and propranolol. FLA-63 did not significantly influence the response to dexamphetamine in either group. That a dopaminergic mechanism plays a major role in the enhanced response to dexamphetamine was shown by the significantly greater response in dexamphetamine-treated mice to apomorphine challenge. The treatment of mice with apomorphine (10 mg/kg/day i.p. for 20 days), produced a greater response to apomorphine challenge in the apomorphine-treated mice than in vehicle-treated mice 8 days after withdrawal. The data show that with long-term administration both dexamphetamine and apomorphine are able to produce in mice what appear to be supersensitive dopamine receptors. Moreover, the enhanced response to dexamphetamine after withdrawal from long-term dexamphetamine treatment appears to require the presence of reserpine-sensitive amine stores and, to a lesser extent, the presence of unblocked α-adrenergic receptors.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00432856
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