Possible association of alcohol tolerance with increased synaptic Ca2+ sensitivity

Area of Science:

• Neuroscience
• Neuropharmacology

Background:

• Ethanol's inhibitory effect on neurotransmitter release is debated, with theories suggesting reduced Ca2+ entry or increased intracellular Ca2+ removal.
• Investigating these mechanisms is crucial for understanding ethanol's neurobiological impact.

Purpose of the Study:

• To elucidate the precise mechanism by which ethanol inhibits neurotransmitter release.
• To determine whether ethanol affects Ca2+ entry or Ca2+ removal in presynaptic terminals.
• To explore the neurochemical basis of ethanol tolerance.

Main Methods:

• Utilized rat striatal slices to study 3H-dopamine release.
• Employed K+ depolarization and the Ca2+ ionophore A23187 to evoke neurotransmitter release.
• Compared release characteristics in control and ethanol-tolerant rats.

Main Results:

• Ethanol (50 mM) inhibited K+-evoked 3H-dopamine release but enhanced A23187-evoked release.
• Ethanol-tolerant rats showed increased 3H-dopamine release with both K+ depolarization and A23187 stimulation compared to controls.
• These findings indicate ethanol reduces depolarization-induced release by decreasing Ca2+ entry.

Conclusions:

• Ethanol inhibits depolarization-induced neurotransmitter release primarily by reducing presynaptic Ca2+ entry.
• Tolerance to ethanol's inhibitory effects on neurotransmitter release may involve adaptive changes in presynaptic terminal sensitivity to Ca2+.
• The study provides insights into the neurochemical mechanisms underlying ethanol's action and tolerance development.