Presence of reciprocal synapses in the rabbit carotid body.

The synaptic junctions between glomus cells and nerve endings in the rabbit carotid body were studied by electron microscopy. Many of them were morphologically of afferent type, glomus cells being presynaptic to nerve endings; occurrence of efferent synapses was less common than that of afferent synapses. In addition, reciprocal synapses in which two or more junctions of opposite polarity were lying side by side were frequently seen particularly between large nerve endings and glomus cells. Some single synapses were discovered to be part of reciprocal synapses through examination of serial sections. The results support possible participation of dopamine in a modulatory feedback loop through reciprocal synapses in the rabbit carotid body.