Color threshold and ratio of S100 beta, MAP5, NF68/200, GABA & GAD. I. Distribution in inner ear afferents.

Afferents of chick embryos (Gallus domesticus) VIIIth nerve were examined at E3, E6, E9, E13, El7, and hatching (NH) for anti-S100 beta, anti-MAP5, anti-GABA, anti-GAD and anti-NF68/200 stain. Different ages were processed together to determine if the distribution of these antibodies changed during synaptogenesis and myelination. Color thresholding showed that saturation of pixels changed for S100 beta only 5%, for NF68/200 10%, and for MAP5, 10%, between E9-NH. Color ratio of NF68/200 over MAP5 was 1.00 at E13 and 0.25 at E16 and NH. S100 beta, GABA and GAD were co-expressed on nerve endings at the edge of the maculae and center of the cristae, whereas hair cells in the center of the maculae expressed either S100 beta or GABA, but not both. S100 beta/NF68/200 shared antigenic sites on the chalices, but NF68/200 expression was higher than S100 beta in the chalices at hatching. MAP5 was expressed in more neurons than NF68/200 at E11, whereas NF68/200 was more abundant than MAP5 at hatching. The results suggest that: 1) the immunoexpression of these neuronal proteins is modulated concomitantly with the establishment of afferent synapses and myelination; 2) S100 beta may serve a neurotrophic function in the chalices where it is co-expressed with the neurotransmitter GABA and its synthesizing enzyme GAD.