Voltage Sensitive Dye Imaging
Voltage-sensitive dye (VSD) imaging allows population patterns of cortical activity to be recorded with high temporal resolution, and recent findings ascribe potential significance to these spatial propagation patterns - both for normal cortical processing and in pathologies such as epilepsy. We routinely perform high signal-to-noise ratio imaging on a single-trial basis. For VSD, we use a WuTech 464II photodiode array, and more recently, a MiCAM02. We mainly use the dye RH1691 from Optical Imaging. Over the past decade, we have accumulated a large amount of experience in in vivo rodent imaging. Feel free to contact us for potential collaborations or methodological questions.
Figure Propagating waves in barrel and visual cortices. Top traces in A and B are signals from a single detector in recording field. Bars under each trace mark time of a spontaneous event (spt) and an evoked response (evk) during recording trial. Vertical broken lines mark time of stimulation. Bottom images in each panel are frames showing spatiotemporal patterns of evoked (top row) and spontaneous events (bottom row). Imaging field is 4 mm in diameter. Each image is a 0.625-ms snap shot, with every 8th frame displayed (5-ms frame intervals). Bars under top trace mark duration of images. A: in barrel cortex, evoked response started from principal barrel and spread as a propagating wave to entire imaging field within 15 ms. Spontaneous event started from bottom of the field and propagated as a slow wave across field.B: in visual cortex, sensory-evoked wave is slower than that in the barrel cortex. Note that spontaneous wave in visual cortex was initiated from the bottom of the field, propagated upward, and reflected near the top to propagate downward.
Intrinsic Signal Imaging/Calcium Imaging
These signals have a much higher amplitude and are easier to measure, but lack temporal resolution. In addition to our VSD devices above, we also use an Andor camera and custom-made implantable optical fibers for these recordings.
We use both custom-built amplifiers/Labview scripts and Neuralynx recording systems.
We perform standard optogenetics in mice, rats and gerbils with vectors pioneered by Karl Deisseroth, and obtained from the University of North Carolina Vector Core.
Figure Optogenetic stimulation of gerbil cortex. A. Fluorescence micrograph showing areas of channelrhodopsin (ChETA) expression, two weeks after viral transduction. B. Peristimulus time histogram showing unit recording from an optogenetically stimulated cell in Gerbil cortex in vivo. A transient phasic response and lower-level tonic response is seen.
Bioelectronic Engineering and Image Analysis Protocols
Michael tinkers with electronics and makes gadgets in his spare time. Kenta programs in his spare time.
Tim is an expert in Thallium autometallography, and works in collaboration with Jürgen Goldschmidt.
Thallium autometallography (TlAMG) is a novel method for high-resolution mapping of neuronal activity that utilizes the close coupling of neuronal potassium (K+) uptake and electrical activity. Intravenous injection of a trace amount of the K+ analogue thallium (Tl+) in awake behaving animals allows for simultaneous mapping of cerebral K+/Tl+-uptake within a time frame of 5 min. Tl+ content in neurons (including in the dendrites and proximal axons), is visualized using a modified Timm-staining protocol in brain sections. This fine resolution allows identification of neuron types.
Figure Layer-specific cellular Tl+-uptake in primary auditory cortex (A1) for a rat that was mapped during awake behaviour (left, WK) and a rat that was mapped during non-rapid eye movement sleep (right, NREMS). Under both conditions, a considerably higher fraction of intensely stained cells can be found in infragranular layers V and VI as compared to supragranular layers I, II and III. Note, however, the reduced number of labelled cells in granular layer IV of the NREMS animal. Scale bar is 50 µm.
fMRI and SPECT
We perform fMRI imaging in collaboration with Prof. Frank Angenstein and SPECT imaging in cooperation with Jürgen Goldschmidt to study the influence of dopaminergic projections.
To monitor rodent behavior, we use the following: