Voltage and Calcium Imaging of Brain Activity.

Sensors for imaging brain activity have been under development for almost 50 years. The development of some of these tools is relatively mature, whereas qualitative improvements of others are needed and are actively pursued. In particular, genetically encoded voltage indicators are just now starting to be used to answer neurobiological questions and, at the same time, more than 10 laboratories are working to improve them.

Monitoring brain activity with protein voltage and calcium sensors.

Understanding the roles of different cell types in the behaviors generated by neural circuits requires protein indicators that report neural activity with high spatio-temporal resolution. Genetically encoded fluorescent protein (FP) voltage sensors, which optically report the electrical activity in distinct cell populations, are, in principle, ideal candidates. Here we demonstrate that the FP voltage sensor ArcLight reports odor-evoked electrical activity in the in vivo mammalian olfactory bulb in single trials using both wide-field and 2-photon imaging.

Experience-dependent versus experience-independent postembryonic development of distinct groups of zebrafish olfactory glomeruli.

Olfactory glomeruli are innervated with great precision by the axons of different olfactory sensory neuron types and act as functional units in odor information processing. Approximately 140 glomeruli are present in each olfactory bulb of adult zebrafish; these units consist of either highly stereotypic large glomeruli or smaller anatomically indistinguishable glomeruli. In the present study, we investigated developmental differences among these types of glomeruli.

Expression of sall4 in taste buds of zebrafish.

We characterized the expression of sall4, a gene encoding a zinc finger transcription factor involved in the maintenance of embryonic stem cells, in taste buds of zebrafish (Danio rerio). Using an enhancer trap line (ET5), we detected enhanced green fluorescent protein (EGFP) in developing and adult transgenic zebrafish in regions containing taste buds: the lips, branchial arches, and the nasal and maxillary barbels. Localization of EGFP to taste cells of the branchial arches and lips was confirmed by co-immunolabeling with antibodies against calretinin and serotonin, and a zebrafish-derived neuronal marker (zn-12).

Distribution and functional organization of glomeruli in the olfactory bulbs of zebrafish (Danio rerio).

Odor molecules are transduced by thousands of olfactory sensory neurons (OSNs) located in the nasal cavity. Each OSN expresses a single functional odorant receptor protein and projects an axon from the sensory epithelia to an olfactory bulb glomerulus, which is selectively innervated by only one or a few OSN types. We used whole-mount immunocytochemistry to study the neurochemistry and anatomical organization of glomeruli in the zebrafish olfactory system.

Olfactory conditioning in the zebrafish (Danio rerio).

The zebrafish olfactory system is an attractive model for studying neural processing of chemosensory information. Here we characterize zebrafish olfactory behaviors and their modification through learning, using an apparatus consisting of a circular flow-through tank that allows controlled administration of odorants. When exposed to the amino acids l-alanine and l-valine, naive zebrafish responded with appetitive swimming behavior, which we measured as the number of >90 degrees turns made during 30s observation periods.

Neural control of the velum in larvae of the gastropod, Ilyanassa obsoleta.

Larval molluscs commonly use ciliated vela to swim and feed. In this study we used immunohistochemistry to demonstrate innervation of velar cilia and muscles by monoaminergic and peptidergic fibres in the caenogastropod, Ilyanassa obsoleta. Photoelectric recordings from pre-oral cilia on isolated pieces of velum revealed that serotonin increased, whereas catecholamines (dopamine and norepinephrine) decreased beat frequency at concentrations of 10(-6) to 10(-9) mol l(-1).