Ljmj. Vanderschuren et al., A single exposure to morphine induces long-lasting behavioural and neurochemical sensitization in rats, EUR J NEURO, 14(9), 2001, pp. 1533-1538
Repeated exposure to drugs of abuse causes persistent behavioural sensitiza
tion and associated adaptations in striatal neurotransmission, which is tho
ught to play an important role in certain aspects of drug addiction. Remark
ably, even a single exposure to psychostimulant drugs such as amphetamine o
r cocaine can be sufficient to elicit long-lasting sensitization. The prese
nt study was designed to evaluate whether long-lasting behavioural and neur
ochemical sensitization can also be evoked by a single exposure to morphine
, an opiate drug of abuse. Rats were pretreated once with morphine (2, 10 o
r 30 mg/kg). Three weeks later, the locomotor effects of morphine and amphe
tamine, as well as the electrically evoked release of [H-3]dopamine and [C-
14]acetylcholine from slices of nucleus accumbens and caudate-putamen, was
assessed. In morphine-p retreated rats, the psychomotor effects of morphine
and amphetamine were sensitized. In addition, the electrically evoked rele
ase of [H-3]dopamine and [C-14]acetylcholine was augmented in slices of nuc
leus accumbens and caudate-putamen from morphine-p retreated animals. Altho
ugh the sensitization of the locomotor effect of morphine was less profound
than previously observed after repeated intermittent morphine treatment, t
he enduring behavioural and neurochemical consequences of a single and repe
ated intermittent morphine treatment appear to be highly comparable. We the
refore conclude that a single exposure to morphine induces longlasting beha
vioural sensitization and associated neuroadaptations.