Optical Dissection of Information Flow in single neurons within brain – OpticNeuron
Optical approach to the study of how neurons in the brain compute information
Information processing in the brain involves the summation, integration, and propagation of electrical and chemical signals. We use optical methods to identify fundamental rules by which neurons process and/or compute such signals.
Application of novel optical methods for studying how neurons communicate via synapses.
Synapses are the fundamental computation unit of neurons, but are extremely small and inaccessible by classical studies using electrodes. We have developed and characterized molecules that indicates changes in voltage and calcium be increasing their fluorescence. We expect these tools and methods to be useful for other investigators and are suitable for the study of neuronal function in models of human neurological disorders.
1. We further characterized an optical reporter of membrane voltage that we developed in the laboratory a few years previously. We demonstrated that it can be used for detecting single synaptic responses in remote parts of the cell and can be used with the advanced optical microscopy (multi-photon excitation) which enables imaging in live animals.
2. Using multi-photon excitation (deep tissue imaging of single neurons) and optical activation of synapses to study, for the first time, how dendrites of cerebellar interneurons compute incoming information.
3. We are currently combining the optical sensors of voltage (see point 1) and calcium, using the deep tissue imaging methods to extend the study of dendritic computations.
1. We further characterized an optical reporter of membrane voltage that we developed in the laboratory a few years previously. We demonstrated that it can be used for detecting single synaptic responses in remote parts of the cell and can be used with the advanced optical microscopy (multi-photon excitation) which enables imaging in live animals.
2. Using multi-photon excitation (deep tissue imaging of single neurons) and optical activation of synapses to study, for the first time, how dendrites of cerebellar interneurons compute incoming information.
3. We found that calcium ions are summated differently than the synaptic voltage, resulting in differential signaling that is capable of changing the strength or efficacy of synapses –potentially important for storing motor memories in the cerebellum.
While optical strategies for making such measurements hold great promise, optical sensors generally lack the speed and sensitivity necessary to record neuronal activity on a single-trial, single-neuron basis. Here we show that our voltage sensitive indicator is sufficiently fast and sensitive that we can monitor the flow of electrical signals between and within neurons within living brain tissue, and may be applicable to the study in live animals.
Interneurons are important for regulating information flow in the brain, and defects in their signaling produce runaway excitation resulting in epileptic episodes. Our findings that cerebellar interneurons serve to signal sparse patterns of electrical activity because of dendrite computations are important for understanding how the cerebellum cortical circuit functions, and may contribute to such behaviors as motor coordination. Finally, our findings indicate computational rule that could pervade in neurons of other brain regions.
1. Abrahamsson, T., Cathala, L., Matsui, K., Shigemoto, R., and DiGregorio, DA. Thin dendrites of cerebellar interneurons confer sublinear synaptic integration and a gradient of short-term plasticity. Neuron, 73: 1159-1172 (2012).
2. Fink AE., Bender, KJ., Trussell, LO., Otis, TS. and DiGregorio, DA. Two-photon compatibility and single-voxel, single-trial detection of subthreshold neuronal activity by a two-component optical voltage sensor. PLoS One, 7(8):e41434 (2012).
Within the brain there are billions of neurons that communicate with each other via specialized contacts called synapses. Defects in the communication between synapses are thought to be at the heart of the memory deficits associated with neuropathological disorders such as Alzheimer’s disease. We propose here a set of experiments designed to identify and characterize the cellular and physiological mechanisms influencing synaptic transmission and integration in neurons within intact brain circuits. The study of such mechanisms is difficult because of the inaccessibility of the signaling within small neuronal subcompartments. We will combine recently developed confocal and holographic optical methods into a state of the art microscope suitable for imaging [Ca2+] and membrane potential within small inaccessible compartments of neurons, simultaneous with photoactivation of single and multiple synapses. By monitoring and manipulating synaptic signaling in thin dendrites, single spines, dendritic branches and even in presynaptic boutons we will identify new cellular mechanisms fundamental for understanding information flow, and the computation power, of neurons within the brain.
Project coordination
David DIGREGORIO (INSTITUT PASTEUR)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
Partnership
IP INSTITUT PASTEUR
Help of the ANR 481,077 euros
Beginning and duration of the scientific project:
- 36 Months
