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Increased probability of GABA release during withdrawal from morphine
1Vollum Institute, Oregon Health Sciences University, Portland 97201, USA.
Summary
Chronic morphine treatment increases GABA release during withdrawal, potentially contributing to drug abuse. This occurs via an upregulated cAMP-dependent pathway in the ventral tegmental area.
Area of Science:
- Neuroscience
- Neuropharmacology
- Addiction Research
Background:
- Opioid receptors in the ventral tegmental area (VTA) modulate GABAergic inhibition of dopamine neurons.
- This disinhibition is implicated in drug abuse, but the effects of chronic morphine on the GABA synapse are not well understood.
Purpose of the Study:
- To investigate how chronic morphine treatment affects GABA release during acute withdrawal.
- To elucidate the role of the cAMP-dependent pathway in these changes.
Main Methods:
- Electrophysiological recordings of GABA(A)-mediated inhibitory postsynaptic currents (IPSCs) in VTA dopamine neurons from guinea pigs.
- Acute withdrawal was induced after 6-7 days of morphine treatment.
- Pharmacological manipulation of adenylyl cyclase and cAMP-dependent protein kinase activity.
Main Results:
- Increased amplitude of evoked IPSCs and frequency of spontaneous miniature IPSCs in slices from morphine-treated animals compared to controls.
- Enhanced potentiation of IPSCs by forskolin and Sp-cAMPS in morphine-treated slices.
- Greater inhibition of IPSCs by kinase inhibitors staurosporine and Rp-CPT-cAMPS after chronic morphine treatment.
Conclusions:
- Chronic morphine withdrawal upregulates the cAMP-dependent cascade, increasing the probability of GABA release.
- Increased GABA release from opioid-sensitive synapses during acute withdrawal may be an adaptive response to prolonged morphine exposure.
- These findings offer insights into the neurobiological mechanisms underlying opioid addiction.