© 2004 Society for Neuroscience
Scientists at Carnegie Mellon University in Pittsburgh have created a transgenic mouse that will allow researchers to visualize patterns of activity directly in individual neurons in vivo.1 To create the animals, Alison Barth and colleagues coupled the c-fos promoter, which is typically activated during neural activity, to a green fluorescent protein (GFP) marker. "By coupling c-fos activation to the expression of GFP, I could now see cells that were specifically implicated by particular stimuli, and specifically stimuli in vivo," Barth explains.
Barth was interested in locating individual neurons engaged in a behavior (such as learning) or affected by a drug. Previously, studying these cells required fixing the tissue and using a fos-specific antibody to identify cells that have been activated. But these experiments provided limited knowledge about cellular behavior simply because the cells being studied were dead, Barth explains. "By that time you can't really investigate how the neurons are behaving," says Matt Wachowiak, an assistant professor of biology at Boston University who was not involved with the study.
Barth points out that her method allows investigators to look at long-term (minutes-to-hours) changes in neural activity. Another method, the synapto-pHluorin-based imaging technique developed by Wachowiak and colleagues,2 highlights neural activity occurring at the millisecond-to-second time scale, providing information about neurons that are firing in real time in response to a stimulus. Looking at longer time-scale events provides information not only about active cells, but also about changes in gene expression that result from the activity.
"If you want to look at very immediate events, you probably [should] change to using another technique. But if you want to look at the recent history of activation, in the past hour or so, [Barth's technique] is a good way of doing it," says Mark Murphy, senior research fellow, Department of Anatomy and Cell Biology, University of Melbourne, Australia, who also did not participate in the study.
Barth has licensed the technology to large pharmaceutical companies and currently is developing mice with longer-lasting markers to study events that occur over days or weeks.
- Aileen Constans