“School of Cognitive Sciences”
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| Paper IPM / Cognitive Sciences / 8567 |
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| Abstract: | |||||||||||
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In the present study, involvement of the N-methyl-d-aspartate (NMDA) receptors
of the CA1 region of dorsal hippocampus (intra-CA1) in the acquisition or
expression of morphine-induced conditioned place preference in rats was
studied. Male Wistar rats were used in these experiments. NMDA-receptor
agonist (NMDA) and antagonist (MK-801) were injected into the CA1 region of
the dorsal hippocampus (intra-CA1) and morphine was injected subcutaneously.
An unbiased conditioned place preference paradigm was used to study the effect
of these agents. In the first set of experiments, the drugs were used during the
development of conditioned place preference by morphine or they were used
alone in order to see if they induce conditioned place preference or conditioned
place aversion. Our data showed that subcutaneous (s.c.) injection of morphine
sulphate (2.5-10 mg/kg) induced conditioned place preference in rat. NMDA (0.1-
1 microg/rat) or MK-801 (1-4 microg/rat) did not induce conditioned place
preference or conditioned place aversion. Intra-CA1 administration of different
doses of NMDA (0.1-1 microg/rat) increased, while MK-801 (1-4 microg/rat)
decreased morphine-induced place preference. MK-801 reversed the effect of
NMDA on morphine response. In the second set of experiments, when the drugs
were used before testing on Day 5, in order to test their effects on the expression
of morphine (7.5 mg/kg)-induced place preference, intra-CA1 administration of
NMDA or MK-801 did not alter the morphine response. None of the drugs
influenced locomotion. It is concluded that NMDA receptor of the CA1 region of
hippocampus are involved in the acquisition but not expression of morphineinduced
place preference
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