A light and transmission electron microscope study of the neural processes within the pigeon anterior semicircular canal neuroepithelium.

This report addresses two questions. First, what is the incidence and distribution of multiple type I hair cells within a single NC in the pigeon's anterior semicircular canal crista? Second, are the synaptic structures found in the avian anterior crista similar to those found in the mammalian crista and if so are they different for single and multiple hair cell calyxes? Three pigeon anterior cristae were studied using interference LM and one pigeon anterior crista was studied using TEM. The light microscope studies showed that about 28% of the NCs studied contained a single type I hair cell; 64% contained 2-5 type I hair cells; and about 8% contained 6-12 type I hair cells. It was noted that the largest number of type I hair cells/unit area was located on the lower slopes of the crista while the smallest number of type I hair cells/unit area was located on the upper slopes and apex of the crista. The TEM studies showed that of 51 hair cells studied, 35% were type II hair cells and 65% were type I hair cells. These studies also showed that synaptic structures described in mammals are also seen in the pigeon. So far, in our preliminary studies we have been unable to demonstrate any difference in synaptic structures associated with single calyxes and those associated with multiple calyxes.