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 invo lved in the regulation of numerous autonomic functions, including card iovascular control. Adenosine has been implicated as a potential neuro modulator of the baroreceptor reflex, and therefore the current study has investigated the presence and characteristics of adenosine recepto rs on rat vagal afferent neurons. In the nodose-vagal grease gap prepa ration, 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) bindi ng enabled the first visualisation of high affinity adenosine A(2) rec eptors in the nucleus tractus solitarius (NTS). Unilateral nodose gang lionectomy resulted in over 90% reduction in binding in the lesioned ( ipsilateral) NTS compared to a sham control. Furthermore, local admini stration of CGS-21680 increased evoked glutamate release in the NTS, a s measured by in vivo microdialysis. These data suggest the presence o f presynaptic adenosine A(2a) receptors on both the soma and central t erminals of rat vagal afferent neurons, and thereby support the hypoth esis that adenosine may have a modulatory role in the baroreceptor ref lex.