Probing neural circuits in the zebrafish: a suite of optical techniques

The ability to image neural activity in populations of neurons inside an intact animal, while obtaining single-cell or subcellular spatial resolution, has led to several advances in our understanding of vertebrate locomotor control. This result, first reported in a 1995 study of motoneurons in larval zebrafish, was the beginning of a series of technical developments that exploited the transparency and simplicity of the larval CNS. Presented here, in chronological fashion, is a suite of imaging techniques that have extended the ability to probe and optically dissect neural control systems. Included are methodological details pertaining to: (1). the in vivo optical recording of neural activity, (2). the optical dissection of complex neural architectures, and (3). additional fluorescence imaging-based techniques for the anatomical and physiological characterization of these systems. These approaches have provided insights into the descending neural control of escape and other locomotive behaviors, such as swimming and prey capture. The methods employed are discussed in relation to complementary and alternative imaging techniques, including, for example, the Nipkow disk confocal. While these methodologies focus on descending motor control in the larval zebrafish, the extension of such approaches to other neural systems is viewed as a promising and necessary step if neurobiologists are to bridge the gap between synaptic and brain region levels of analysis. The efficiency of optical techniques for surveying the cellular elements of intricate neural systems is of particular relevance because a comprehensive description of such elements is deemed necessary for a precise understanding of vertebrate neural architectures.