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Morphine conditioned place preference in the hamster
Abstract:
Two experiments investigated the ability of morphine to produce a conditioned place preference in the hamster. In Experiment 1, it was found that a 15 mg/kg dose of morphine produced a conditioned place preference after eight conditioning trials. In addition, naloxone (0.4 mg/kg blocked the development of the morphine-conditioned place preference and itself produced a conditioned place aversion after four conditioning trials. In Experiment 2, the effects of four doses of morphine (0, 2.5, 5 and 15 mg/kg) on the acquisition of a conditioned place preference were studied. Only the 15 mg/kg dose produced a significant place preference. Compared to similar findings in the rat, the present results indicate that a relatively high dose of morphine is required to produce a conditioned place preference in the hamster.
Insights
High doses of morphine induce conditioned place preference in hamsters, unlike in rats. Naloxone blocks this effect and causes aversion, indicating morphine
Area of Science:
- Neuroscience
- Pharmacology
- Behavioral Science
Background:
- Opioid drugs, such as morphine, are known to produce rewarding effects.
- Conditioned place preference (CPP) is a behavioral paradigm used to assess the rewarding properties of drugs.
- Previous research has established CPP in various species, but data in hamsters is limited.
Purpose of the Study:
- To investigate the dose-dependent effects of morphine on conditioned place preference in hamsters.
- To examine the role of opioid receptors in morphine-induced CPP using naloxone.
- To compare CPP findings in hamsters with those reported in rats.
Main Methods:
- Two experiments were conducted using male hamsters.
- Experiment 1: Hamsters received either morphine (15 mg/kg) or saline, followed by testing in a two-compartment chamber to assess place preference. Naloxone (0.4 mg/kg) was used to block morphine effects.
- Experiment 2: Hamsters were conditioned with four different doses of morphine (0, 2.5, 5, and 15 mg/kg) to determine the effective dose for CPP.
Main Results:
- A significant conditioned place preference was observed in hamsters receiving a 15 mg/kg dose of morphine.
- Naloxone (0.4 mg/kg) successfully blocked the development of morphine-induced CPP and induced a conditioned place aversion.
- Only the highest dose of morphine (15 mg/kg) produced a significant place preference, while lower doses did not.
Conclusions:
- A relatively high dose of morphine is required to establish a conditioned place preference in hamsters.
- Opioid receptor antagonism by naloxone prevents morphine CPP and induces aversion, supporting the involvement of opioid pathways.
- These findings highlight species-specific differences in the rewarding effects of morphine, with hamsters requiring higher doses compared to rats.