Competing Presynaptic and Postsynaptic Effects of Ethanol on Cerebellar Purkinje Neurons

University of North Carolina at Chapel Hill, North Carolina, United States
Alcoholism Clinical and Experimental Research (Impact Factor: 3.21). 09/2006; 30(8):1400-7. DOI: 10.1111/j.1530-0277.2006.00167.x
Source: PubMed


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.
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.
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.
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.

Download full-text


Available from: George R Breese, Mar 13, 2014
  • Source
    • "We hypothesize that the source of this input could be the Lugaro cell or PC collaterals (Jorntell et al., 2010). The effect of ethanol on mIPSC frequency at MLI–MLI synapses (~20% with 80 mM ethanol) is similar to its effect on MLI–PC synapses (10–50% with 50–100 mM) (Ming et al., 2006; Kelm et al., 2007; Mameli et al., 2008; Hirono et al., 2009). The mechanism of action of ethanol at MLI axonal terminals has been previously determined to be complex, involving effects on the phospholipase C/inositol-1,4,5-trisphosphate/Ca 2+ /protein kinase C and cAMP/protein kinase A pathways (reviewed in Kelm et al., 2011). "
    [Show abstract] [Hide abstract]
    ABSTRACT: This study assessed the acute effect of ethanol on GABAergic transmission at molecular layer interneurons (MLIs; i.e. basket and stellate cells) in the cerebellar cortex. The actions of ethanol on spontaneous firing of these pacemaker neurons were also measured. Transgenic mice (glutamic acid-decarboxylase 67-green fluorescent protein knock-in mice) that express green fluorescence protein in GABAergic interneurons were used to aid in the identification of MLIs. Parasagittal cerebellar slices were prepared and whole-cell patch-clamp electrophysiological techniques were used to measure GABA(A) receptor-mediated spontaneous and miniature inhibitory postsynaptic currents (sIPSCs and mIPSCs). Loose-seal cell-attached recordings were used to measure spontaneous action potential firing. Stellate cells received spontaneous GABAergic input in the form of a mixture of action potential-dependent events (sIPSCs) and quantal events (mIPSCs); ethanol increased sIPSC frequency to a greater extent than mIPSC frequency. Ethanol increased spontaneous action potential firing of MLIs, which could explain the increase in sIPSC frequency in stellate cells. Basket cells received GABAergic input in the form of quantal events only. Ethanol significantly increased the frequency of these events, which may be mediated by a different type of interneuron (perhaps, the Lugaro cell) or Purkinje cell collaterals. Ethanol exposure differentially increases GABA release at stellate cell vs. basket cell-to-Purkinje cell synapses. This effect may contribute to the abnormalities in cerebellar function associated with alcohol intoxication.
    Full-text · Article · Nov 2011 · Alcohol and Alcoholism
  • Source
    • "Basolateral amygdala PPR Decreased PPR Silberman et al. (2008) Brainstem motor mIPSC Increased mIPSC frequency Sebe et al. (2003) Central nucleus of the amygdala mIPSC Increased mIPSC frequency Roberto et al. (2003), Kang-Park et al. (2007), Nie et al. (2009) Central nucleus of the amygdala PPR Decreased PPR Roberto et al. (2003), Nie et al. (2004) Cerebellar Purkinje (MDN and slice) mIPSCs Increased mIPSC frequency Ming et al. (2006), Kelm et al. (2007), Mameli et al. (2008), Hirono et al. (2009) Cerebellar Purkinje (MDN and slice) sIPSCs Increased sIPSC frequency Criswell et al. (2008), Mameli et al. (2008), Hirono et al. (2009) Cerebellar Purkinje PPR Decreased PPR Kelm et al. (2007), Criswell et al. (2008), Mameli et al. (2008) Cerebellar granule mIPSCs Increased mIPSC frequency Carta et al. (2004) Cerebellar granule sIPSCs Increased sIPSC frequency Carta et al. (2004) Cerebrocortical (MDN) sIPSCs No effect Criswell et al. (2008) Hippocampal CA1 pyramidal mIPSCs Increased mIPSC frequency Li et al. (2006) Hippocampal CA1 pyramidal sIPSCs Increased sIPSC frequency Ariwodola and Weiner (2004), Li et al. (2006) Lateral septal (MDN) sIPSCs No effect Criswell et al. (2008) Lateral septal PPR No effect Criswell et al. (2008) Spinal cord motor mIPSCs Increased mIPSC frequency Ziskind-Conhaim et al. (2003) Spinal cord motor sIPSCs Increased sIPSC frequency Cheng et al. (1999) "
    [Show abstract] [Hide abstract]
    ABSTRACT: While research on the actions of ethanol at the GABAergic synapse has focused on postsynaptic mechanisms, recent data have demonstrated that ethanol also facilitates GABA release from presynaptic terminals in many, but not all, brain regions. The ability of ethanol to increase GABA release can be regulated by different G protein-coupled receptors (GPCRs), such as the cannabinoid-1 receptor, corticotropin-releasing factor 1 receptor, GABA(B) receptor, and the 5-hydroxytryptamine 2C receptor. The intracellular messengers linked to these GPCRs, including the calcium that is released from internal stores, also play a role in ethanol-enhanced GABA release. Hypotheses are proposed to explain how ethanol interacts with the GPCR pathways to increase GABA release and how this interaction contributes to the brain region specificity of ethanol-enhanced GABA release. Defining the mechanism of ethanol-facilitated GABA release will further our understanding of the GABAergic profile of ethanol and increase our knowledge of how GABAergic neurotransmission may contribute to the intoxicating effects of alcohol and to alcohol dependence.
    Full-text · Article · Jan 2011 · Brain Research Reviews
  • Source
    • "After confirming that ethanol increases mIPSC frequency at the cerebellar interneuron- Purkinje cell synapse (Kelm et al., 2007, 2008a; Ming et al., 2006), we performed experiments to establish the source of this increase in mIPSC frequency. We have previously shown that ethanol increases mIPSC frequency at the interneuron-Purkinje cell synapse in the mechanically dissociated neuron preparation (Kelm et al. 2007), where communication from nearby neurons and glia is eliminated. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Research on the actions of ethanol at the GABAergic synapse has traditionally focused on postsynaptic mechanisms, but recent data demonstrate that ethanol also increases both evoked and spontaneous GABA release in many brain regions. Using whole-cell voltage-clamp recordings, we previously showed that ethanol increases spontaneous GABA release at the rat interneuron-Purkinje cell synapse. This presynaptic ethanol effect is dependent on calcium release from internal stores, possibly through activation of inositol 1,4,5-trisphosphate receptors (IP(3)Rs). After confirming that ethanol targets vesicular GABA release, in the present study we used electron microscopic immunohistochemistry to demonstrate that IP(3)Rs are located in presynaptic terminals of cerebellar interneurons. Activation of IP(3)Rs requires binding of IP(3), generated through activation of phospholipase C (PLC). We find that the PLC antagonist edelfosine prevents ethanol from increasing spontaneous GABA release. Diacylglycerol generated by PLC and calcium released by activation of the IP(3)R activate protein kinase C (PKC). Ethanol-enhanced GABA release was blocked by two PKC antagonists, chelerythrine and calphostin C. When a membrane impermeable PKC antagonist, PKC (19-36), was delivered intracellularly to the postsynaptic neuron, ethanol continued to increase spontaneous GABA release. Overall, these results suggest that activation of the PLC/IP(3)R/PKC pathway is necessary for ethanol to increase spontaneous GABA release from presynaptic terminals onto Purkinje cells.
    Full-text · Article · Mar 2010 · Neuropharmacology
Show more