Joy Sebe - US grants

[unreadable] DESCRIPTION (provided by applicant): The transplantation of neuronal precursor cells is a novel and promising therapeutic approach with the potential to treat neurodegenerative disorders, such as epilepsy. Epilepsy, a neurological disorder afflicting nearly 2 million Americans, results from an increase in neuronal excitability that is often due to reduced GABAergic transmission. Recently, we demonstrated that embryonic medial ganglionic eminence (MGE) precursor cells transplanted into a postnatal rodent brain not only migrate widely in the cortex and differentiate into GABAergic interneurons, but increase synaptic inhibition recorded from neurons in the host brain. The overall goal of the proposed study is to enhance the efficacy of this transplantation strategy by transplanting embryonic MGE cells that are fated to become "super" GABAergic interneurons, or interneurons that receive less GABAergic inhibition and are therefore likely to fire more action potentials in response to the same excitatory input. Prior to producing modified GABAergic interneurons, we will first characterize the inhibitory inputs received by native and grafted GABAergic interneurons to determine whether the transplantation process changes the inhibitory inputs onto grafted interneurons. Next, we will produce "super" GABAergic interneurons by transplanting MGE cells from mice lacking the GABAAR 8 subunit, a subunit that mediates tonic inhibition in the brain, including in the hippocampus and cerebellum. We hypothesize that the GABAergic interneurons that differentiate from such GABAAR 6 subunit knockout (KO) mice will receive less tonic inhibition and therefore release more GABA onto the surrounding host cells. We will record GABAergic currents and assess the input-output properties from host cortical neurons that are surrounded by grafted wild-type or "super" interneurons to test the hypothesis that MGE cells derived from receptor KO mice increase GABAergic inhibition in the host brain. [unreadable] [unreadable]

DESCRIPTION (provided by applicant): There is a fundamental gap in our understanding of the mitochondrial functions that are activated in afferent neurons during mechanotransduction and prolonged glutamate receptor activation. Our current objectives are 1.) to determine the extent to which the zebrafish lateral line afferent neurons phenocopy one the hallmarks of glutamate excitotoxicity observed in mammalian cochlea; and 2.) to identify the mitochondrial processes that may change their signaling during moderate levels of mechanotransduction vs. prolonged glutamate receptor activation. Our central hypotheses are that: 1.) prolonged glutamate receptor application will lead to swelling of afferent terminals and a disruption in afferent neuron firing in zebrafish; and 2.) moderate levels of mechanotransduction increase mitochondrial activity while prolonged glutamate receptor activation leads to mitochondrial stress and damage. The rationale for the proposed research is that protection of afferent neurons following noise overexposure requires an understanding of how normal levels of mechanotransduction and potentially excitotoxic insults trigger homeostatic and cytotoxic mechanisms in afferent neurons. Guided by preliminary data, this hypothesis will be tested by pursuing two specific aims: 1.) determine the extent to which prolonged glutamate receptor activation disrupts afferent neuron firing and compromises afferent terminal morphology; and 2.) identify mitochondrial processes that are activated in response to varying degrees of afferent neuron stimulation. To address these aims, we are using a combination of electrophysiology, immunohistochemistry, transmission electron microscopy and in vivo time-lapse imaging of zebrafish lateral line afferent neurons, which receive inputs from mechanosensory hair cells. The approach is innovative because it utilizes fluorescence reporters of cytoplasmic and mitochondrial function to visualize how afferent terminals vs. cell bodies respond to mechanotransduction and AMPA exposure in real time in an intact vertebrate. The proposed research is significant, because it will expand our understanding of how afferent neurons respond to the metabolic demands of mechanotransduction and will likely identify mitochondrial markers that are activated in response to AMPA exposure.