A holistic approach to studying synapses, circuits and learning

Our abilities to combine mouse genetics with electrophysiology, two-photon imaging, and behavior and manipulate selective inputs with optogenetic and pharamacogenetic approaches have allowed us to go beyond examining local circuitry in slices towards probing how long-range circuits across many brain areas sculpt dendritic integration and somatic plasticity in brain slices and impact learning behavior in the live animal.

methods_overview

Electrophysiology

We use somatic and dendritic patch clamp electrophysiology in acute brain slices to gain access into compartmentalized intracellular dynamics of the neuron. We measure intrinsic and extrinsic properties of various cell types to examine synaptic physiology and functional connectivity. Our experimental designs especially cater to looking at spatio-temporal integration of inputs, coincidence detection and plasticity.

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Imaging

Two-photon functional imaging in brain slices and in awake behaving mice is a technical driving force for several of our projects. This method provides high spatial and temporal resolution in monitoring activity in genetically defined neuronal populations and their subcellular compartments. Until recently it was difficult to image deep structures like the hippocampus in moving animals. With the advent of head-fixed virtual navigation systems and cranial windows lodged inside the cortex we can now image cortico-hippocampal activity during learned behavior.

We have also delved into the world of inter-molecular and intra-molecular interactions within synaptic boutons with live cell fluorescent imaging techniques such as FRET, FRAP and FLIM.

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Behavior

In our quest to link synaptic activity in neural circuits with learning we are beginning to explore the realms of mouse behavior. Our behavioral testing comes in two flavors that of:

  • classical freely moving behavioral paradigms such as operant fear conditioning, spatial working and reference memory and
  • head-fixed behavioral tests in a virtual reality environment. We like mixing these tasks with electrophysiology and imaging.

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Molecular and genetic manipulation of neurons

Our combinatorial genetics strategies rely on cell-type specific recombinase expressing transgenic driver mouse lines and stereotaxic delivery of recombinant viruses to selectively target and express genetically encoded proteins.

  • Optogenetics – Light gated ion channels and pumps for functional manipulations.
  • Fluorescent reporter molecules and genetically encoded Ca2+ indicators for optical tracking.
  • Pharmacogenetics – ligand gated ion channels for functional manipulations.
  • Anatomical mapping with monosynaptic retrograde labeling with pseudo-typed rabies.
  • Intersectional and promoter specific genetic targeting.