Fig. 9.
Proposed model of seasonal regulation of GABAAR expression in the VRC in 13-lined ground squirrels. A: excitatory neurons in the VRC express GABAAR ε-subunits (red) at low levels during the summer active period. In summer, inhibitory interneurons (blue) lacking δ-subunit GABAARs (presumably expressing γ-subunit-containing GABAARs) modulate VRC neuron excitability from nearby peripheral locations (P, yellow). B: during hibernation (T and IBA), excitatory VRC neurons upregulate GABAAR ε-expression (bright red). These neurons are modulated by inhibitory interneurons expressing δ-subunit-containing GABAARs (green) that are sensitive to allosteric positive modulation by EtOH. This season-specific plasticity that allows survival of normally lethal doses of barbiturate and EtOH may represent a shift from synaptic inhibition (C) to extrasynaptic inhibition (D).