Microendoscopy for awake animal imaging and for deep imaging

In vivo micro-endoscopy is a rapidly growing field, and many efforts are developed in particular towards the objective of imaging awake and freely moving animals. To reach this goal, two alternatives have been followed. A first solution made use of a fibre bundle as a relay between a widefield microscope and the studied animal [1, 2]. This technique is robust and fast (as it doesn’t involve scanning), but provides no capacity for optical sectioning. To solve this problem, many groups are developing head-mounted two-photon (2P) microscopes which involve strong technological efforts to miniaturize 2P microscopes elements. Imaging in awake and resting adult rats have been demonstrated with such a device [3]; however, because 2 photon-imaging is a scanning technique, image acquisition was not fast enough and relative motion between the microscope and brain was apparent during animal movements.

For this research project, we are currently building a structured illumination endoscope using a high resolution fiber bundle similar to the one that N. Bozinovic, C. Ventalon et al. developed in Boston University [4]. This will be an intermediate solution combining the advantages of both previously mentioned techniques: it will fast and robust (as a non-scanning technique) but will still provide sectioning and have a resolution comparable to the one of head-mounted two-photon microscopes.

Such an endoscope will also permit to access brain regions that cannot be imaged with standard 2ph microscopy (such as the thalamus or deep layers of the cortex). In addition, by transporting arbitrary shaped illumination patterns within the endoscope, we will be able to combine in vivo photo-activation and imaging in deep tissue.

References
[1] M. Murayama, E. Pérez-Garci, H.R. Lüscher & M.E. Larkum, J. Neurophysiol. 98, 1791-1805 (2007).
[2] B.A. Flusberg, A. Nimmerjahn, E.D. Cocker, E.A. Mukamel, R.P. J Barretto1, T.H. Ko, L.D. Burns, J.C. Jung & M.J. Schnitzer, Nat. Methods 5, 935–938 (2008).
[3] F. Helmchen, M.S. Fee, D.W. Tank & W. Denk, Neuron 31, 903–912 (2001).
[4] N. Bozinovic, C. Ventalon, T. Ford, J. Mertz, Opt. Express 16, 8016–8025 (2008).