Quantitative studies of rat carotid body type I cell nerve endings.

The results of a stereological and morphometric analysis of rat carotid body type I cell nerve endings are described. 66.9% of endings possessed symmetrical junctions. Of the remaining endings, 3.6% were presynaptic and 26% were postsynaptic to type I cells; 3.6% of endings had a reciprocal configuration. Apart from membrane specialisations, no other ultrastructural criteria were found to distinguish the different types of endings. Ventilation with 100% and 10% oxygen showed that the hypoxic mixture reduced synaptic vesicle concentration in the nerve endings; this effect was independent of the innervation to the carotid body.