The University of California, Berkeley laboratory of Professor Stephan Lammel elucidates the mechanisms of neural circuit malfunction in neuropsychiatric diseases and the influence of pharmaceutical intervention. Dopamine midbrain neurons are associated with pathological conditions, including substance abuse disorders and depression. Investigating neural circuit organization and function in healthy and diseased brains provides an understanding of the underlying pathology as well as the potential efficacy of novel therapeutic approaches.
Han de Jong, postdoctoral fellow in the Lammel lab, uses fiber photometry to investigate dopamine neurons expressing GCaMP6, a genetically encoded green fluorescent calcium indicator. Within the past few years, technical advances in fiber photometry have allowed researchers to monitor circuit-specific activity by visualizing calcium dynamics in freely moving mice. Cellular network dynamics are monitored by capturing calcium fluorescence traces from neural activity millimeters deep within the brain through a brain-implanted optical fiber. Although fiber photometry lacks cellular resolution, it can detect synchronous neuronal activity dynamics from multiple regions simultaneously during behavioral paradigms or after external stimuli, such as sensory tasks or drug injections, respectively.
CGaMP6 fluorescence traces are dim and were previously recorded using a one fiber position paired to a dedicated photodetector. Comparable sensitivity between photodetectors and sCMOS cameras is necessary to measure GCaMP activity in vivo. In addition to sensitivity, speed is necessary for high frequency sampling between 20-40 Hz for up to two hours to capture calcium dynamics.
Replacing photodetectors with a sCMOS camera, frame projected independent-fiber photometry (FIP) has been able to simultaneously capture multiple regions of the brain1. The Prime sCMOS camera has a high speed PCI-express interface that can record up to 100 frames per second to capture dynamic calcium signaling in vivo.
GCaMP fluorescence signals are robust with 470-nm excitation, but there are non-calcium-dependent charges that are observed with the 410-nm excitation, which are motion-related artifacts and used as the isosbestic GCaMP control signal. The Prime sCMOS has great sensitivity and low read noise, which maximizes the ability to detect faint fluorescence.
Imaging multiple cell populations was not possible with a single photodetector, but with a sCMOS camera coupled to a Dual View Λ emission splitting system, it is now possible to acquire two spatially identical but spectrally distinct images simultaneously. The DVΛ enables dual-color imaging of different cell populations expressing GCaMP and R-CaMP where their emission is split into separate halves of the sensor.
Dual fiber recording in freely moving mice.
A. Schematic representation of the experimental setup including the Prime CMOS camera and the Dual View Lambda. This setups allows for simultaneous recordings of up to 7 fibers of both GCaM and RCaMP at high framerates.
B. 50ms exposure of two fiber implants in the brain of a freely moving mouse.
C. Simultaneously collected GCaMP6 fluorescence on two fibers. Excitation of GCaMP6 with 470nm light is alternated with 405nm at 40hz. GCaMP6 emission when exited with 405nm is used to correct for movement artifacts.
Additional information about the Lammel Lab and their work is available at: