Ethanol exposure during gastrulation alters neuronal morphology and behavior in zebrafish

Ethanol (EtOH) exposure during development has been shown to lead to deficits in fine and gross motor control. In this study we used zebrafish embryos to determine the effects of EtOH treatment during gastrulation. We treated embryos in the gastrulation stage (5.25 hours post fertilization (hpf) to 10.75 hpf) with 10 mM, 50 mM or 100 mM EtOH and examined the effects on general animal morphology, the c-start reflex behavior, Mauthner cell (M-cell) morphology and motor neuron morphology. EtOH treated fish exhibited a minor but significant increase in gross morphological deformities compared with untreated fish. Behavioral studies showed that EtOH treatment resulted in an increase in the peak speed of the tail during the escape response. Furthermore, there was a marked increase in abnormally directed c-starts, with treated fish showing greater incidences of c-starts in inappropriate directions. Immunolabeling of the M-cells, which are born during gastrulation, revealed that they were significantly smaller in fish treated with 100 mM EtOH compared with controls. Immunolabeling of primary motor neurons using anti-znp1, showed no significant effect on axonal branching, whereas secondary motor axons had a greater number of branches in ethanol treated fish compared with controls. Together these findings indicate that ethanol exposure during gastrulation can lead to alterations in behavior, neuronal morphology and possibly function.