The execution of complex functions and their breakdown in disease involves the interplay between an animal's genetics and environment. The overall goals of this proposal are to reveal how Ras-family GTPases influence signaling networks that control synaptic plasticity, and how an "enriched environment" (EE) alters these networks to change the way synaptic plasticity is induced in adolescent mice and remarkably, across generations. One focus of this proposal is on GRF1 and GRF2, which form a family of multi-catalytic, calcium- stimulated, guanine nucleotide exchange factors that have the potential to activate both Ras and Rac GTPases. Despite these similarities, we found that GRF1 and GRF2 promote opposing forms of synaptic plasticity induced by NMDA-type glutamate receptors (NMDA-Rs) beginning at early adolescence. GRF1 promotes long-term depression (LTD), while GRF2 promotes long-term potentiation (LTP), at least in part, because they regulate different MAP kinases. The experiments outlined below combine genetic, biochemical and electrophysiological studies to reveal how GRF1 and GRF2 respond to different upstream signals, and how signaling downstream from their Ras- and Rac-activating domains is differentially regulated in the hippocampus. These experiments will add new insight into how specificity is achieved in neuronal signal transduction. They will also add significantly to our understanding of the molecular basis of LTP and LTD induction. Defects in these well-established cellular paradigms of learning and memory are thought to contribute to a variety of neurological and mental health disorders. A second focus of this proposal is how environmental stimulation, involving exposure to novel objects, enhanced socialization and voluntary exercise particularly during pre-adolescence, changes the way LTP is induced. We discovered that adolescent enrichment unlocks a previously unidentified latent signaling pathway that promotes LTP in mice and rescues defective LTP and contextual fear memory in GRF knockout mice. Even more dramatic is our finding that these effects of pre-adolescent enrichment are passed on to the next generation through their adolescence. The experiments described will use multiple approaches to reveal how this novel EE-gated signaling pathway promotes LTP, and how EE unlocks this cascade to affect synaptic plasticity and memory across generations. A better understanding of the trans-generational effects of the environment on brain function may reveal new approaches to overcome neurological and mental health disorders.
Although a person's genetic blueprint strongly contributes to his/her susceptibility to disease, it is clear that the environment in which one lives influences how that blueprint is read. Our study investigates how Ras proteins contribute to biochemical pathways in the brain that mediate learning and memory. It also explores how a stimulating enriched environment, particularly during pre-adolescence, changes these biochemical pathways in normal animals, and compensates for a genetic defect in Ras signaling. Remarkably, we find that juvenile enrichment affects not only animals directly exposed to it, but also their future offspring through adolescence. A full understanding of the trans-generational effects of the environment on brain function may reveal new approaches to overcome neurological and mental health disorders.
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