Titel: Two Depko Talks
Startdatum: Sep 19 2018
Startzeit: 09:30 am
Endzeit: 11:30 am
Ort: Max Planck House Lecture Hall

Speaker: Dr. Michael Lippert
Title: Behaviorally Matched Optogenetic and Electrical VTA Stimulation Leads to Similar Patterns of Brain-Wide Functional Activity in Mice
Abstract: Optogenetic stimulation has become a dominant method in neurophysiology to stimulate neurons with high genetic precision. While it is a common method in current rodent studies, its clinical applicability and application in non-human primates are still subject of intense research. In these fields, however, electrical stimulation is the most common brain stimulation method, a method often viewed as inherently inferior in terms of stimulation specificity. This view has further been strengthened by functional imaging studies reporting large differences in activity patterns evoked by electrical or optogenetic stimulation. In our work we explore the influence of matching stimulation strength across stimulation modality in a mouse VTA self-stimulation paradigm. We adjusted stimulation intensity in either modality to the point of behavioral equality, i.e. equal self-stimulation rates. Subsequent cerebral blood flow sensitive SPECT imaging in the awake mice showed highly similar patterns of activity across modalities, in stark contrast to the previously reported differences. By investigating the required stimulation intensity we conclude that those results are likely the result of overstimulation by electrical current. Reducing stimulation current to a level where it evokes similar self-stimulation behavior as optogenetic stimulation leads to almost indistinguishable activations.

Speaker: Dr. Jürgen Goldschmidt
Title: SPECT-imaging of cerebral blood flow - a new tool for mapping brain-wide neural activation patterns in behaving rodents
Abstract: In vivo imaging of brain-wide neural activation patterns in behaving rodents still poses problems. Optical methods suffer from limited penetration depths and field-of-views, while fMRI requires the animals to be restrained inside scanners severely limiting the repertoire of behavioral tests that can be performed.Single-photon emission computed tomography (SPECT) imaging of cerebral blood flow is a new tool for mapping brain-wide neural activation patterns in behaving rodents. Awake unrestrained animals are intravenously injected during ongoing behavior with 99mTc-HMPAO, a blood flow tracer labeled with the gamma-emitter 99m-technetium. After flow-dependent accumulation, the tracer is trapped within the brain. The distribution of the trapped tracer - reflecting the average blood flow during the injection time - can be mapped in anesthetized animals after injection.The spatial resolution of SPECT-imaging in rodents is substantially higher than in humans and higher than that of small-animal-PET imaging. In our lab we map the distribution of the blood-flow tracer at (isotropic) spatial resolutions of up to 400 µm and image the same animals repeatedly under different behavioral conditions. Examples will be presented illustrating the value of this approach for studying neural activation patterns in unrestrained rodents.

Host: Oxana Eschenko