The reversibility and limits of homeostatic synaptic plasticity

<p>To experience the world, we depend on the ability of our brains to process information. Problems can occur when communication between neurons is not regulated, and a significant enough loss of stability could lead to conditions such as migraine and epilepsy. Homeostatic plasticity is thought to constrain activity within physiologically useful ranges. Our lab uses the fruit fly neuromuscular junction as a model synapse to study homeostatic plasticity.</p> <p>Homeostatic potentiation and homeostatic depression are two forms of homeostatic synaptic plasticity. Expression of a dominant negative glutamate receptor subunit in the muscle impairs its sensitivity to glutamate and triggers an increase in the number of vesicles released per evoked potential, or quantal content. This increase in quantal content is called homeostatic potentiation. We found that homeostatic potentiation is a reversible process: quantal content returns to normal levels when expression of the dominant negative ceases. We additionally found that homeostatic potentiation can be ablated at high temperature.</p> <p>Overexpression of the Vesicular Glutamate transporter (VGlut) causes an increase in the amplitude of spontaneous events, leading to a corresponding decrease in quantal content, called homeostatic depression. It is unknown to what degree homeostatic potentiation and homeostatic depression may share regulatory machinery. We screened genes required for homeostatic potentiation in the neuron for additional roles in homeostatic depression. We found that certain genes involved in calcium regulation, such as the IP3 receptor and ryanodine receptor, showed a substantial decrease in evoked potential amplitude in a VGlut overexpression background.</p>