Ethanol-Sensitive Pacemaker Neurons in the Mouse External Globus Pallidus

Abstract

Although ethanol is one of the most widely used drugs, we still lack a full understanding of which neuronal subtypes are affected by this drug. Pacemaker neurons exert powerful control over brain circuit function, but little is known about ethanol effects on these types of neurons. Neurons in the external globus pallidus (GPe) generate pacemaker activity that controls basal ganglia, circuitry associated with habitual and compulsive drug use. We performed patch-clamp recordings from GPe neurons and found that bath application of ethanol dose-dependently decreased the firing rate of low-frequency GPe neurons, but did not alter the firing of high-frequency neurons. GABA or glutamate receptor antagonists did not block the ethanol effect. The GPe is comprised of a heterogeneous population of neurons. We used Lhx6-EGFP and Npas1-tdTm mice strains to identify low-frequency neurons. Lhx6 and Npas1 neurons exhibited decreased firing with ethanol, but only Npas1 neurons were sensitive to 10 mM ethanol. Large-conductance voltage and Ca2+-activated K+ (BK) channel have a key role in the ethanol effect on GPe neurons, as the application of BK channel inhibitors blocked the ethanol-induced firing decrease. Ethanol also increased BK channel open probability measured in single-channel recordings from Npas1-tdTm neurons. In addition, in vivo electrophysiological recordings from GPe showed that ethanol decreased the firing of a large subset of low-frequency neurons. These findings indicate how selectivity of ethanol effects on pacemaker neurons can occur, and enhance our understanding of the mechanisms contributing to acute ethanol effects on the basal ganglia.

Titrating Tipsy Targets: The Neurobiology of Low-Dose Alcohol

“…The sensitivity of BK channels to alcohol is tightly controlled by β auxiliary subunits, such that β subunits significantly reduce amplitudes of BK channels and that β4 containing BK channels are more sensitive to alcohol than those containing the β1 subunit [70]. In addition to their role in mediating alcohol tolerance [72], BK channels may also play an important role in the effects of alcohol on pacemaker activity in the external globus pallidus (GPe) [73]. Alcohol at 10 mM decreased the firing rate of low-frequency firing GPe neurons in GPe slices in a BK channel-dependent manner, an observation that is supported by alcohol - induced enhancement of BK channel open probability recorded in cell-attached mode of Npas1-expressing neurons [73].…”

“…In addition to their role in mediating alcohol tolerance [72], BK channels may also play an important role in the effects of alcohol on pacemaker activity in the external globus pallidus (GPe) [73]. Alcohol at 10 mM decreased the firing rate of low-frequency firing GPe neurons in GPe slices in a BK channel-dependent manner, an observation that is supported by alcohol - induced enhancement of BK channel open probability recorded in cell-attached mode of Npas1-expressing neurons [73]. Multiple amino acid residues in the cytosolic tail domain of the α subunit of BK channels have been implicated in forming the potential binding pocket for alcohol, among which K361 forms a hydrogen bond with the alcohol molecule (Figure 3D) [74].…”

Alcohol and basal ganglia circuitry: Animal models

“…Neurons within the GPe are inhibited during acute ethanol exposure (Criswell, Simson et al 1995, Abrahao, Chancey et al 2016). A recent study has described ethanol inhibition of the activity of a subset of neurons in the GPe.…”

“…10 mM). The ethanol sensitive GPe neurons exhibit firing rates in the low frequency range, and are characterized by the expression of the transcription factors NPAS1 and Lhx6 (Abrahao, Chancey et al 2016). The mechanism underlying this inhibitory ethanol action appears to be potentiation of the function of large-conductance (BK) potassium channels, a well-known target for acute ethanol actions (Dopico, Bukiya et al 2014).…”

“…The mechanism underlying this inhibitory ethanol action appears to be potentiation of the function of large-conductance (BK) potassium channels, a well-known target for acute ethanol actions (Dopico, Bukiya et al 2014). In vivo , ethanol administration also inhibited firing in neurons with low baseline firing rates in the GPe of awake, freely-moving mice (Abrahao, Chancey et al 2016). Interestingly, GPe neurons that project back to striatum (the “arkypallidal” neurons) appear to be among those inhibited by ethanol.…”