Britta Hornback

Optimizing Optogenetic Stimulation Frequency and Duration for Recording of Activity in the Infralimbic Cortex to Nucleus Accumbens Shell Pathway

Optogenetics is a technique that allows the direct manipulation of neuronal activity by virally introducing light-sensitive channelrhodopsins into a cell. Pulses of LED light from an optic fiber are used to stimulate the opsin proteins, allowing a net positive charge to flow into the neuron and induce action potentials, eventually leading to release of neurotransmitters. The purpose of this experiment was to determine the optimal frequencies and durations of light stimulation pulses in vivo to activate the neuronal projections from the infralimbic cortex (IL) to the nucleus accumbens shell (NAcS), a pathway important in the brain’s reward circuitry and addiction. An electrode was inserted in the NAcS of two Long Evans rats to measure changes in local field potentials (the strength of the electric fields surrounding active neurons) in response to optical stimulation of the IL. Though data collection is still in progress, we are testing short-duration stimulation (one to six milliseconds) to obtain reliable optogenetically-induced local field potential recordings from the IL-NAcS pathway. After collecting the recordings, histology and fluorescence microscopy will be used to verify the expression of opsins and the placement of optic fibers and electrodes in this pathway.