Glycinergic neurons (a subtype of neurons which use glycine as a signalling protein) in a 48 hour old zebrafish embryo, viewed from a lateral aspect. Glycine is a major inhibitory neurotransmitter in the spinal cord and hindbrain. This embryo is labelled to show glycinergic neurons in green and axonal tracts in red. The first glycinergic neurons in the zebrafish spinal cord start to differentiate cordally and a wave of differentiation spreads rostrally (near the front end of the body) between 24 and 48 hours post fertilisation. By 48 hours post fertilisation glycinergic neurons are evident throughout the spinal cord and hindbrain. Width of image is 2 millimetres.