Tonic adenosine neuromodulation is preserved in motor nerve endings of aged rats

Neuromuscular transmission is decreased in aged subject. Since endogenous a denosine is a potent neuromodulator at motor nerve endings, either inhibiti ng via A(1) receptors or facilitating via A(2A) receptors acetylcholine rel ease, we now investigated if the tonic effect of endogenous adenosine was m odified at phrenic nerve endings of aged rats. The A(2A) receptor antagonis t (ZM241385, 50 nM) inhibited (77 +/- 9%) and the A(1) receptor antagonist (DPCPX, 50 nM) facilitated (74 +/- 13%) acetylcholine release from young ad ult (6 weeks old) rat preparations, indicating a simultaneous tonic activat ion of A(2A) and A(1) receptors. Tonic modulation by adenosine was unaltere d in aged (24 months old) rats, since ZM241385 (50 nM) inhibited (73 +/- 8% ) and DPCPX (50 nM) facilitated (91 +/- 20%) acetylcholine release in aged animals similarly to young rats. This indicates that, in contrast to the ce ntral nervous system where adenosine neuromodulation is modified in aged an imals, the control by adenosine of phrenic nerve function is preserved in a ged animals (C) 2000 Elsevier Science Ltd. All rights reserved.