PRESYNAPTIC ADENOSINE A(2A) RECEPTORS ON SOMA AND CENTRAL TERMINALS OF RAT VAGAL AFFERENT NEURONS

The dorsal vagal complex of the medulla oblongata is a key centre involved in the regulation of numerous autonomic functions, including cardiovascular control. Adenosine has been implicated as a potential neuromodulator of the baroreceptor reflex, and therefore the current study has investigated the presence and characteristics of adenosine receptors on rat vagal afferent neurons. In the nodose-vagal grease gap preparation, the adenosine A(2a) agonist CGS-21680 evoked a depolarisation only in the presence of the selective adenosine A(1) antagonist PACPX. Autoradiography using [H-3]NECA (4 nM) with suppression of A(1) binding enabled the first visualisation of high affinity adenosine A(2) receptors in the nucleus tractus solitarius (NTS). Unilateral nodose ganglionectomy resulted in over 90% reduction in binding in the lesioned (ipsilateral) NTS compared to a sham control. Furthermore, local administration of CGS-21680 increased evoked glutamate release in the NTS, as measured by in vivo microdialysis. These data suggest the presence of presynaptic adenosine A(2a) receptors on both the soma and central terminals of rat vagal afferent neurons, and thereby support the hypothesis that adenosine may have a modulatory role in the baroreceptor reflex.