Fetal development of primate chemosensory corpuscles. I. Synaptic relationships in late gestation.

Fetal macaque chemosensory corpuscles during the last part of gestation contained chemosensory, sustentacular, and undifferentiated basal cells. Sustentacular cells had apical secretory granules and no specialized contacts with axons. Chemosensory cells contained basal collections of 80-100 nm dense core granules, and specialized axonal contacts of three types--afferent synapses, efferent synapses, and subsurface cisternae. Afferent synapses were commonly present on electron opaque cells with many 80-100-nm granules, typical 40-60-nm synaptic vesicles, and a few cisternae of smooth or granular endoplasmic reticulum. Cells with subsurface cisternae and/or efferent synapses were usually electron lucent, lacked vesicles and granules, and contained numerous intracytoplasmic cisternal elements. A continuum of intermediate forms was observed. It is postulated that transition of synaptic arrays accompanies the maturation of individual chemosensory cells.