INCREASED ACETYLCHOLINE CONTENT INDUCED BY ANTIDROMIC STIMULATION OF A SYMPATHETIC-GANGLION - A POSSIBLE RETROGRADE ACTION OF ADENOSINE

Prolonged high-frequency orthodromic stimulation of superior cervical ganglia is known to result in increased acetylcholine (ACh) synthesis and ACh content after the period of stimulation. In a previous study, we provided evidence to suggest that adenosine acts as an extracellula r signal to activate this increased ACh synthesis and we proposed that the source of that adenosine might be postsynaptic. Thus, the purpose of the present study was to test whether direct stimulation of the po stganglionic nerves could affect ganglionic ACh content. Antidromic co nditioning of ganglia (15 Hz, 45 min) did not affect significantly the ir ACh content. However, if ganglia were allowed a 15-min rest period after this antidromic conditioning, their ACh stores were increased by 20%; a similar increase was induced by 4-Hz stimulation before the re st period. During the 15-Hz antidromic stimulation, ACh release was no t clearly increased above the basal level, suggesting that preganglion ic nerve endings were not stimulated to an extent that could explain t he increased ACh content. Orthodromic stimulation (5 Hz) of ganglia 15 min after they had been subjected to antidromic conditioning (15 Hz, 45 min) showed increased ACh release in comparison with that from cont rol unconditioned ganglia. Moreover, the extra ACh released by the con ditioned ganglia was quantitatively similar to the increase in the ACh stores, as if most, or all, of the additional ACh was released by pre ganglionic stimulation. If the antidromic conditioning and the rest pe riod were done during perfusion with Ca2+-free medium, the ganglia did not accumulate extra ACh. The ACh content was also not changed if gan glia were conditioned in the absence of Ca2+ but rested with normal Ca 2+. However, ACh content was increased by 23% when the antidromic stim ulation was done with normal Ca2+ but the rest period was without Ca2. To test the role of adenosine in this retrograde effect, the effect of nucleoside transport inhibitors was tested. Dipyridamole blocked th e antidromic stimulation-induced increase, but nitrobenzylthioinosine did not. Overall, these results are consistent with the idea that a di ffusible retrograde messenger activates ACh synthesis. The sensitivity to blockade by dipyridamole suggests that adenosine might be that sig nal.