Figure 4. Inhibition of VTA GABA neuron firing rate is reduced in Cx36 KO mice.

(A) This ratemeter record shows a representative VTA GABA neuron in a WT mouse recorded in vivo with a baseline firing rate of approximately 15 Hz before and after IP administration of 0.75 g/kg ethanol. Intraperitoneal administration of 1.0 g/kg ethanol reduced this neuron’s activity ~50% at approximately 10 min after injection. Transient increases in firing rate are often associated with systemic administration of ethanol (Steffensen et al., 2009). (B) This ratemeter record shows a representative VTA GABA neuron recorded in a separate WT mouse with a baseline firing rate of approximately 40 Hz before and after IP administration of 0.75 g/kg ethanol. Intraperitoneal administration of 1.0 g/kg ethanol suppressed this neuron’s activity at approximately 10 min after injection. (C) The ratemeter record shows a representative VTA GABA neuron in a KO mouse, with a baseline firing rate that was similar to that of the neuron in the WT mouse in (B), before and after IP administration of 0.75 g/kg ethanol. Ethanol did not alter the firing rate of this neuron in a KO mouse. (D) This graph compares the effects of IP administration of 0.75-4.0 g/kg ethanol on the firing rate of VTA GABA neurons recorded in KO vs WT mice. Ethanol reduced firing rate in both WT and KO mice. However, the IC₅₀ for ethanol inhibition was 0.25 g/kg in WT mice and 1.4 g/kg in KO mice. Wild-type mice were significantly more sensitive to ethanol than KO mice at all doses tested.