The functional dynamics and structure of both larval and adult Drosophila melanogaster muscle were
investigated with a nonlinear multimodal microscope. Imaging was carried out using a home built microscope capable of
recording the multiphoton excitation fluorescence, second harmonic generation, and third harmonic generation signals
simultaneously at a scanning rate of up to ~12 frames/sec. The sample was excited by a home built femtosecond
Ti:Sapphire laser at 840 nm, or by a Yb-ion doped potassium gadolinium tungstate (Yb:KGW) crystal based oscillator at
1042 nm. There was no observable damage detected in the myocyte after prolonged scanning with either of the lasers.
Microscopic second harmonic generation (SHG) appears particularly strong in the myocytes. This allows the
fast contraction dynamics of the myocytes to be followed. The larger sarcomere size observed in the larvae myocytes is
especially well suited for studying the contraction dynamics. Microscopic imaging of muscle contractions showed
different relaxation and contraction rates. The SHG intensities were significantly higher in the relaxed state of the
myocyte compared to the contracted state. The imaging also revealed disappearance of SHG signal in highly stretched
sarcomeres, indicating that SHG diminishes in the disordered structures. The study illustrates that SHG microscopy,
combined with other nonlinear contrast mechanisms, can help to elucidate physiological mechanisms of contraction. This
study also provides further insight into the mechanisms of harmonic generation in biological tissue and shows that
crystalline arrangement of macromolecules has a determining factor for the high efficiency second harmonic generation
from the bulk structures.
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Catherine Greenhalgh, Bryan Stewart, Richard Cisek, Nicole Prent, Arkady Major, Virginijus Barzda, "Dynamic investigation of Drosophila myocytes with second harmonic generation microscopy," Proc. SPIE 6343, Photonics North 2006, 634308 (8 September 2006);