Light-activated serotonin for exploring its action in biological systems.

Serotonin (5-HT) is a neuromodulator involved in regulating mood, appetite, memory, learning, pain, and establishment of left-right (LR) asymmetry in embryonic development. To explore the role of 5-HT in physiology, we have created two forms of "caged" 5-HT, BHQ-O-5HT and BHQ-N-5HT. When exposed to 365 or 740 nm light, BHQ-O-5HT releases 5-HT through one- or two-photon excitation, respectively. BHQ-O-5HT mediated changes in neural activity in cultured mouse primary sensory neurons and the trigeminal ganglion and optic tectum of intact zebrafish larvae in the form of high-amplitude spiking in response to light. In Xenopus laevis embryos, light-activated 5-HT increased the occurrence of LR patterning defects. Maximal rates of LR defects were observed when 5-HT was released at stage 5 compared with stage 8. These experiments show the potential for BHQ-caged serotonins in studying 5-HT-regulated physiological processes.

Electrophysiological recording in the brain of intact adult zebrafish.

Previously, electrophysiological studies in adult zebrafish have been limited to slice preparations or to eye cup preparations and electrorentinogram recordings. This paper describes how an adult zebrafish can be immobilized, intubated, and used for in vivo electrophysiological experiments, allowing recording of neural activity. Immobilization of the adult requires a mechanism to deliver dissolved oxygen to the gills in lieu of buccal and opercular movement. With our technique, animals are immobilized and perfused with habitat water to fulfill this requirement. A craniotomy is performed under tricaine methanesulfonate (MS-222; tricaine) anesthesia to provide access to the brain. The primary electrode is then positioned within the craniotomy window to record extracellular brain activity. Through the use of a multitube perfusion system, a variety of pharmacological compounds can be administered to the adult fish and any alterations in the neural activity can be observed. The methodology not only allows for observations to be made regarding changes in neurological activity, but it also allows for comparisons to be made between larval and adult zebrafish. This gives researchers the ability to identify the alterations in neurological activity due to the introduction of various compounds at different life stages.