Disruption of Eaat2b, a glutamate transporter, results in abnormal motor behaviors in developing zebrafish.

Analysis of zebrafish mutants that have defects in motor behavior can allow entrée into the hindbrain and spinal cord networks that control locomotion. Here, we report that zebrafish techno trousers (tnt) locomotor mutants harbor a mutation in slc1a2b, which encodes Eaat2b, a plasma membrane glutamate transporter. We used tnt mutants to explore the effects of impaired glutamate transporter activity on locomotor network function. Wild-type larvae perform robust swimming behavior in response to touch stimuli at two and four days after fertilization. In contrast, tnt mutant larvae demonstrate aberrant, exaggerated body bends beginning two days after fertilization and they are almost paralyzed four days after fertilization. We show that slc1a2b is expressed in glial cells in a dynamic fashion across development, which may explain the abnormal sequence of motor behaviors demonstrated by tnt mutants. We also show that tnt larvae demonstrate enhanced excitation of neurons, consistent with the predicted effects of excessive glutamate. These findings illustrate the dynamic regulation and importance of glutamate transporters during development. Since glutamate toxicity caused by EAAT2 dysfunction is thought to promote several different neurological disorders in humans, including epilepsy and neurodegenerative diseases, tnt mutants hold promise as a new tool to better understand these pathologies.

Modular laboratory exercises to analyze the development of zebrafish motor behavior.

The embryonic zebrafish is an excellent research model to examine the neural networks that coordinate locomotive behavior. It demonstrates robust locomotive behavior early in development, its nervous system is relatively simple and accessible compared to mammalian systems, and there are mutants available with specific molecular and motor deficits. We have developed a series of four exercises that provide students with a basic understanding of locomotive behavior development, nervous system organization, development of neurotransmitter responsiveness, and genetics. The first two exercises can be performed in one 3-h laboratory period, and the third and fourth exercises, which build on the first two, can be completed in one or two subsequent periods. In the first exercise, students observe and quantify two distinct behaviors that characterize different developmental stages, spontaneous movement, and touch-evoked tail coiling. In the second, the students use a pharmacological approach to determine if the neurotransmitter glycine is required for the embryo to perform each behavior. In the third, they use simple lesions to assess whether the brain is required for each type of behavior. In the fourth, the students examine bandoneon, a zebrafish motility mutant that has a glycine receptor defect, by observing its behavior during spontaneous movement and touch-evoked tail coiling, performing lesions, and applying pharmacological drugs. These exercises are readily adaptable, such that portions can be omitted or expanded to examine other neurotransmitter systems or later stages of locomotive behavior development.