Real-time in vivo optogenetic neuromodulation and multielectrode electrophysiologic recording with NeuroRighter

Optogenetic channels have greatly expanded neuroscience’s experimental capabilities, enabling precise genetic targeting and manipulation of neuron subpopulations in awake and behaving animals. However, many barriers to entry remain for this technology – including low-cost and effective hardware for combined optical stimulation and electrophysiologic recording. To address this, we adapted the open-source NeuroRighter multichannel electrophysiology platform for use in awake and behaving rodents in both open and closed-loop stimulation experiments. Here, we present these cost-effective adaptations, including commercially available LED light sources; custom-made optical ferrules; 3D printed ferrule hardware and software to calibrate and standardize output intensity; and modifications to commercially available electrode arrays enabling stimulation proximally and distally to the recording target. We then demonstrate the capabilities and versatility of these adaptations in several open and closed-loop experiments, demonstrate spectrographic methods of analyzing the results, as well as discuss artifacts of stimulation.Emory University. School of Medicine (Emory Neurosciences Initiative seed grant)American Epilepsy SocietyEpilepsy Foundation of America (Predoctoral fellowship)National Science Foundation (U.S.) (NSF GRFP Fellowship 08-593)National Science Foundation (U.S.) (NSF IGERT Fellowship DGE-0333411)National Science Foundation (U.S.) (NSF EFRI #1238097)National Institutes of Health (U.S.) (NIH 1R01NS079757-01)American Society for Engineering Education (SMART Fellowship

Optogenetic dissection of septohippocampal neural circuitry for the treatment of epilepsy

Over 50 million people worldwide suffer from epilepsy. Of these, nearly a third will be refractory to medical therapy, and many will be poor candidates for surgical resection. Thus there is a need for novel targets and therapies, the former of which will require a greater understanding of neural networks involved in epilepsy, and the latter of which demands the development of novel therapeutic techniques. Seizures are less frequent during periods where theta – a 3-12Hz oscillatory rhythm in the hippocampal local field potential – is present. Theta is thought to originate in the medial septum, a basal forebrain structure that projects to the site of origin for the most common form of intractable epilepsy, the hippocampus. As has been demonstrated with pharmacologic and electrical stimulation, theta generation via the medial septum is consequently an ideal target for intervention. However, of the three neuron populations within the medial septum – cholinergic, GABAergic, and glutamatergic – it is unclear which is responsible for theta, or indeed if a single population is driving the oscillation. Optogenetics, a novel technique that enables activation and inhibition of genetically-defined neurons on a millisecond time-scale, provides the means to functionally dissect this septohippocampal axis and leverage the results for seizure therapy. In this thesis, I detail the current state of deep brain stimulation for epilepsy, and describe our motivation for targeting the medial septum and the importance of the hippocampal theta rhythm. I describe new technologies, software, and adaptations to our electrophysiology platform, NeuroRighter, to enable concurrent optogenetic neuromodulation and electrophysiology in awake and behaving animals, and demonstrate how these technologies and techniques can be used in several experimental approaches. I next use this system to show that both the GABAergic and glutamatergic neurons of the medial septum can drive and pace hippocampal oscillatory rhythms, but only the glutamatergic neurons are necessary to maintain phase relationships between successive theta cycles. I also demonstrate that activating and inhibiting the cholinergic neurons of the medial septum does not alter hippocampal local field potential activity, but does alter single-unit firing rates. These results shed light on the function of the medial septum in generating and modulating theta, and provide clear targets for optogenetic modulation of epilepsy.Ph.D