News item: Photostimulation of astrocytes with femtosecond laser pulses

On Jan 21, 2009, Optics Express published online an original paper entitled “Photostimulation of astrocytes with femtosecond laser pulses”, http://www.opticsinfobase.org/abstract.cfm?URI=oe-17-3-1291 from Britton Chance Center for Biomedical Photonics, Huazhong University of Science and Technology, China. This work was carried out by graduate students Yuan Zhao and Yuan Zhang, under the supervision of Drs. Shaoqun Zeng and Wei Zhou. Later on February 2, this paper is selected as “image of the week, February 2 2009” in OpticsInforBase http://www.opticsinfobase.org/, the website of the OSA publications.

Astrocytes are the major electrically non-excitable cells in the central nervous system. Accumulative evidences have proved that astrocytes are actively involved in brain functions, serving as a bridge in the communication between neurons and other brain cells. However, due to the ineffectiveness of existing stimulating methods, including mechanical stimulation, electrical stimulation, uncaging and pharmacological applications, the essential roles of astrocytes have not yet been resolved.

In this paper, 800-nm near infrared femtosecond laser pulses were focused onto the cell membrane of astrocytes, evoking remarkable intercellular Ca2+ wave spreading radially from the stimulated point (see the movie below). Localized transient photoporation was demonstrated to be induced on the cell membrane by laser irradiation, through which extracellular Ca2+ entry into the cytoplasma was necessary for Ca2+ elevations in the stimulated cell and subsequent propagation across others. This process could be regarded as simulating physiological Ca2+ influx from ion channels in plasma membrane. In virtue of the facility of manipulating laser, repetitive photostimulation of astrocytes was actually performed with well-controlled laser intensity and targeting, resulting in similar responses in the stimulated cell. Because of the high peak intensity of femtosecond laser pulses to reduce the energy threshold, minimum laser intensity was adopted. Furthermore, the results confirmed the viability of astrocytes upon laser irradiation. Therefore, noncontact photostimulation of astrocytes employing femtosecond laser is demonstrated to be non-disruptive, reproducible, and with high spatiotemporal precision. This versatile optical tool is promisingly efficient and helpful for resolving problems that traditional approaches are difficult to touch, especially for studies in vivo or in live animals.