Behavioural pharmacology
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Behavioural pharmacology · Oct 2011
Influence of N-methyl D-aspartate receptor mechanism on WIN55,212-2-induced amnesia in rat dorsal hippocampus.
In this study, we investigated the effects of both N-methyl D-aspartate (NMDA) and MK-801 on WIN55,212-2(WIN)-induced amnesia in rats. Step-through inhibitory avoidance of memory was used to examine the retrieval of memory, 24 h after training. All drugs were injected bilaterally into the dorsal hippocampus (intra-CA1) of rats. ⋯ In addition, pretest administration of different doses of the antagonist (2 and 4 µg/rat) induced full recovery of WIN-induced amnesia, but did not influence memory recovery in the subjects, which had received posttraining (0.5 µg/rat) and pretest WIN (0.25 and 0.5 µg/rat). Pretesting coadministration of ineffective doses of WIN (0.1 µg/rat) with NMDA (0.1 µg/rat), but not with MK (1 µg/rat), restored WIN-induced (0.5 µg/rat) amnesia. It can be concluded that the NMDA receptor mechanism located in the dorsal hippocampus may be involved in WIN-induced amnesia.
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Behavioural pharmacology · Oct 2011
Some determinants of morphine effects on intracranial self-stimulation in rats: dose, pretreatment time, repeated treatment, and rate dependence.
Intracranial self-stimulation (ICSS) is a procedure used to evaluate the abuse liability of drugs. The μ opioid receptor agonist morphine is an acknowledged drug of abuse, and this study examined factors that may influence expression of abuse-related morphine effects on ICSS in rats. Adult male rats were equipped with intracranial electrodes targeting the medial forebrain bundle, and 10 stimulus frequencies (56-158 Hz in 0.05 log increments) were available during each daily session under a continuous reinforcement schedule. ⋯ Repeated morphine (3.2-18 mg/kg/day×7 days at each dose) produced tolerance to rate-decreasing effects, enhanced expression of rate-increasing effects, and enhanced rate dependency of morphine effects. Withdrawal from repeated morphine produced small but significant dose-dependent decreases in ICSS. These results show that the magnitude and valence of morphine effects on rates of ICSS in rats are strongly influenced by morphine dose and pretreatment time, history of morphine exposure, and baseline ICSS rate.