Spinal NMDA receptor activation is necessary for de novo, but not the maintenance of, A2a receptor-mediated phrenic motor facilitation.
Adenosine 2a (A2a) receptor agonists elicit persistent increases in phrenic nerve activity by transactivating the neurotrophin receptor, TrkB, near phrenic motoneurons. Our working model proposes that A2a receptor-mediated TrkB receptor activation strengthens glutamatergic synapses onto phrenic motoneurons. Activation of glutamate N-methyl d-aspartate (NMDA) receptors has been implicated in other models of phrenic motor plasticity. Thus we hypothesized that NMDA receptor activation also would contribute to A2a receptor-mediated phrenic motor facilitation. Adult male Sprague-Dawley rats were anesthetized with urethane, mechanically ventilated, neuromuscularly paralyzed, and bilaterally vagotomized. The A2a receptor agonist CGS-21680 and the NMDA receptor-channel blocker MK-801 were administered intrathecally over the C4 spinal segment. Phrenic nerve activity was recorded before, during, and after drug administration. MK-801 (concentration range 0.1, 1.0, 10.0, and 100 microM) was administered 30 min before CGS-21680 (50 microM). MK-801 dose-dependently blocked A2a receptor-mediated phrenic motor facilitation. When administered at 60 min post-CGS-21680, MK-801 prevented further increases in phrenic nerve activity compared with the CGS-21680 alone (CGS-21680 alone at 120 min: 114 +/- 19%; CGS-21680 and MK-801 at 60 min post-CGS-21680: 61 +/- 11%, above baseline, P < 0.05) but did not return phrenic motor output to baseline values. Our data suggest that NMDA receptor activation is necessary for de novo A2a receptor-mediated phrenic motor facilitation and that the maintenance of preexisting phrenic motor facilitation does not involve NMDA receptor-dependent mechanisms.
Golder
F J
FJ
Dept. of Clinical Studies-Philadelphia, School of Veterinary Medicine, Univ. of Pennsylvania, 3900 Delancey St., Philadelphia, PA 19104, USA. golderf@vet.upenn.edu
D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D058917:Adenosine A2 Receptor Antagonists; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology; D004195:Disease Models, Animal; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004347:Drug Interactions; D008297:Male; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D018696:Neuroprotective Agents / Q000494:pharmacology; D010627:Phenethylamines / Q000494:pharmacology; D010791:Phrenic Nerve / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D043705:Receptor, Adenosine A2A / Q000378:metabolism*; D020813:Receptor, trkB / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism*; D013119:Spinal Cord Injuries / Q000188:drug therapy / Q000209:etiology / Q000378:metabolism*
D058917:Adenosine A2 Receptor Antagonists; D000959:Antihypertensive Agents; D018696:Neuroprotective Agents; D010627:Phenethylamines; D043705:Receptor, Adenosine A2A; D016194:Receptors, N-Methyl-D-Aspartate; C061282:2-(4-(2-carboxyethyl)phenethylamino)-5'-N-ethylcarboxamidoadenosine; D016291:Dizocilpine Maleate; D020813:Receptor, trkB; D000241:Adenosine