Competing presynaptic and postsynaptic effects of ethanol on cerebellar purkinje neurons.
BACKGROUND
Ethanol has actions on cerebellar Purkinje neurons that can result either in a net excitation or in inhibition of neuronal activity. The present study examines the interplay of presynaptic and postsynaptic mechanisms to determine the net effect of ethanol on the neuronal firing rate of cerebellar Purkinje neurons.


METHODS
Whole-cell voltage-clamp recording of miniature inhibitory postsynaptic currents (mIPSCs) from Purkinje neurons in cerebellar slices was used to examine the effect of ethanol on presynapticsynaptic release of gamma-aminobutyric acid (GABA) and glutamate. Extracellular recording was used to examine the net action of both presynaptic and postsynaptic effects of ethanol on the firing rate of Purkinje neurons.


RESULTS
Under whole-cell voltage clamp, the frequency of bicuculline-sensitive miniature postsynaptic currents (mIPSCs) was increased dose-dependently by 25, 50, and 100 mM ethanol without any change in amplitude or decay time. Despite this evidence of increased release of GABA by ethanol, application of 50 mM ethanol caused an increase in firing in some neurons and a decrease in firing in others with a nonrandom distribution. When both glutamatergic and GABAergic influences were removed by simultaneous application of 6-cyano-7-nitroquinoxaline-2,3-dione and picrotoxin, respectively, ethanol caused only an increase in firing rate.


CONCLUSIONS
These data are consistent with a dual action of ethanol on cerebellar Purkinje neuron activity. Specifically, ethanol acts presynaptically to increase inhibition by release of GABA, while simultaneously acting postsynaptically to increase intrinsic excitatory drive.
Ming
Zhen
Z
Department of Psychiatry, Center for Alcohol Studies, UNC Neuroscience Center, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599-7178, USA.
Criswell
Hugh E
HE
Yu
Guozhong
G
Breese
George R
GR
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D002531:Cerebellum / Q000187:drug effects / Q000502:physiology; D000431:Ethanol / Q000494:pharmacology*; D066298:In Vitro Techniques; D009433:Neural Inhibition / Q000187:drug effects* / Q000502:physiology; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D017729:Presynaptic Terminals / Q000187:drug effects* / Q000502:physiology; D011689:Purkinje Cells / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley
D000431:Ethanol