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The effect of morphine on monoamine release and content in guinea-pig brain slices
Abstract:
The effect of morphine on the efflux of (3H) monoamines as well as the endogenous monoamine contents in electrically stimulated brain slices was investigated. Only at a concentration at high as 30 microM did the drug reduce the tritium efflux and counteracted the monoamine depletion caused by prolonged electrical stimulation. This effect was antagonized by Naloxone 10 microM. Besides the good agreement between the two methods used to evaluate drug effects the discrepancy between morphine concentrations active on the neurosecretory process and those effective in the whole animal is stressed. The opioids may act in vivo either by modulating the firing rate of the monaminergic neurons or by affecting other related neuronal pools.
Insights
Morphine at high concentrations reduces monoamine release and depletion in brain slices, an effect blocked by naloxone. This suggests opioids may modulate neuronal firing rates or related pools in vivo.
Area of Science:
- Neuroscience
- Pharmacology
Background:
- Opioids, such as morphine, are known to affect neurotransmitter systems.
- Monoamines play crucial roles in neuronal signaling and are implicated in various physiological processes.
Purpose of the Study:
- To investigate the effects of morphine on monoamine efflux and content in brain slices.
- To explore the mechanism of opioid action on monoaminergic neurons.
Main Methods:
- Electrically stimulated brain slices were used to measure (3H) monoamine efflux.
- Endogenous monoamine levels were quantified following prolonged electrical stimulation.
- The effects of morphine and naloxone were assessed at specific concentrations.
Main Results:
- Morphine (30 microM) significantly reduced tritium efflux and counteracted monoamine depletion.
- Naloxone (10 microM) antagonized the effects of morphine.
- A discrepancy was noted between in vitro and in vivo effective concentrations of morphine.
Conclusions:
- Morphine exhibits inhibitory effects on monoamine release and synthesis in the central nervous system.
- Opioid modulation of neuronal firing rates or related neuronal pools may explain in vivo effects.
- Naloxone confirms the opioid-specific nature of these observed effects.