SOMATIC ACETYLCHOLINE-RELEASE IN RABBIT NODOSE GANGLION

In the rabbit, as in various other species, the presence of a cholinergic vagal afferent contingent has been demonstrated previously using biochemical and immunohistological approaches at the nodose ganglion level, where vagal afferent cell bodies are located. This structure is completely devoid of synaptic contacts. In the present study, somatic acetylcholine release is demonstrated on different types of in vitro rabbit nodose ganglion preparations (fragments of nodose tissue or isolated cell bodies) using chemiluminescent detection. Acetylcholine endogenous content was measured and was shown to be greater in the right nodose ganglion compared to the left. This difference was also observed when spontaneous and potassium chloride-evoked acetylcholine release was measured in extracellular fluid after a 15-min incubation of nodose ganglion fragments. Calcium removal totally blocked this somatic release. A kinetic study of acetylcholine release was also performed by placing the samples (nodose ganglion fragments or isolated cell bodies) directly in front of the photomultiplier, allowing the direct monitoring of (acetylcholine + choline) and choline effluxes. The net acetylcholine release was then deduced by subtraction. Identical kinetics was obtained with the two different nodose ganglion preparations used. This somatic release is calcium-dependent. The occurrence of acetylcholine release at the nodose ganglion level is discussed in comparison with the events occurring in the cholinergic nerve endings. These mechanisms could be implicated in the premodulation of the vagal afferent messages conveyed from the periphery to the central nervous system.