Activity dependent synaptic plasticity and microfluidics

The visual cortex of the brain is one of the fundamental preparations to study critical periods and activity dependent changes in the brain. During development, when sensory input from one eye is prevented, visual acuity and brain connectivity is lost in favour of inputs from the active eye. Because of the brain’s complexity, it is difficult to perform thorough analyses of synaptic mechanisms that exist during development. Therefore, the development of simpler in vitro models would be advantageous. In our studies, we used a 3-compartment microfluidic device and created a new model for dual input in vitro activity dependent synaptic plasticity. Microfluidics offered the advantage of being able to physically and chemically isolate neurons in distinct environments. In chapter 2, we optimized previously developed microfluidic devices for use in our cell culture experiments and demonstrated that their application can create a dual input activity dependent system. Using a 3-compartment microfluidic device, the activity of one neuronal group was reduced by application of tetrodotoxin or the GABA agonist, muscimol. Treatment caused the formation of a greater number of synaptic contacts between the target ‘postsynaptic’ neurons and the ‘presynaptic’ inputs at normal working activity levels compared to the opposing ‘presynaptic’ inputs with reduced activity. In chapter 3, we established that ‘critical periods’ exist in our in vitro model by varying the ages at which we reduced neuronal input activity. Muscimol treatment had an earlier time window to induce activity dependent synaptic changes compared to inhibition by tetrodotoxin. By the fourth week in culture, neither treatment induced any synaptic difference between inputs. In chapter 4, we examined the mechanisms involved in our model. We manipulated NMDAR activity, CamKII activity, or GluR2 internalization postynaptically under the same conditions that we previously established. In our model, both treatments were NMDAR activity dependent while the requirement for CamKII activity and GluR2 internalization was dependent on the application of either muscimol or tetrodotoxin respectively. Taken together, we showed the ability to create a new in vitro model for activity dependent synaptic plasticity and that even in a simple system multiple mechanisms can exist.Medicine, Faculty ofGraduat