Cognitive dysfunction occurs in many debilitating conditions including Alzheimer's disease, Down syndrome, post-traumatic stress disorder, and anxiety-related disorders. The hippocampus is a key anatomic substrate of cognition. While inhibitory G protein-dependent signaling in the hippocampus is a powerful modulator of cognitive processes, the relevance of specific G protein-modulated enzymes and ion channels is unclear. G protein-gated inwardly-rectifying K+ (GIRK) channels are activated by inhibitory G protein signaling, and mediate postsynaptic inhibition throughout the nervous system. Gain- or loss-of-function mutations impacting GIRK channel activity impair associative learning and memory, and alter plasticity of excitatory neurotransmission. To date, however, our understanding of the contribution made by GIRK channels to these processes derives from mice with constitutive genetic mutations. The goal of this project is to probe the contribution of GIRK channels in the hippocampus to associative learning and memory. The driving hypothesis is that GIRK channels in CA1 pyramidal neurons of the dorsal hippocampus are required for normal associative learning and memory, and the underlying plasticity of excitatory neurotransmission. This hypothesis will be tested using an interdisciplinary approach involving new genetic and pharmacologic tools, as described in three Specific Aims: (1) To understand how loss of GIRK channels in defined hippocampal neurons impacts cognition. GIRK channels will be selectively ablated from pyramidal or GABA neurons using transgenic Cre driver mice and a novel conditional GIRK2 knockout mouse line. Following validation of GIRK channel ablation, mice will undergo contextual fear conditioning, a test of associative learning and memory that is dependent on the dorsal hippocampus. A complementary conditional viral shRNA knockdown approach will be used to selectively suppress GIRK signaling in defined cell types within the dorsal CA1 region of the hippocampus. (2) To examine the impact of acute modulation of hippocampal GIRK channel activity on cognition. A novel family of small-molecule GIRK channel modulators will be used to acutely manipulate GIRK channel activity in the dorsal hippocampus before, during, and after fear conditioning. In addition, a DREADD- based approach will be used to acutely manipulate the excitability of selective cell types within the dorsal hippocampus. Collectively, these studies will complement efforts in AIM 1, while shedding light on the temporal nature of the GIRK channel contribution(s) to associative learning and memory. (3) To probe the influence of GIRK channel activity on synaptic plasticity in the hippocampus. The hypothesis that GIRK channels in CA1 pyramidal neurons are required for normal plasticity of excitatory neurotransmission in the dorsal hippocampus will be tested using genetic and pharmacologic manipulations of GIRK channels. These studies will yield new insights into the relevance of GIRK channels in the hippocampus to associative learning and memory, knowledge that could translate into new approaches for the treatment of disorders involving cognitive deficits.