Non-NMDA and NMDA receptors transmit area postrema input to aortic baroreceptor neurons in NTS

Abstract

We sought to determine whether glutamate acting at both N-methyl-D- aspartate (NMDA) and non-NMDA receptors transmits area postrema (AP) excitatory inputs to nucleus tractus solitarii (NTS) neurons in the aortic baroreceptor or vagal afferent pathways in vivo. In α-chloralose- anesthetized rabbits, we recorded extracellular NTS neuronal responses to low-frequency aortic depressor nerve (ADN), vagus nerve, and AP stimulation and to iontophoresis of α-amino-3-hydroxy-5-methylisoxazole-4-prepionic acid and NMDA during control, iontophoresis of 2,3-dihdroxy-6-nitro-7- sulfamoylbenzo(f)quinoxaline (NBQX), DL-2-amino-5-phosphonovaleric acid (AP5), or both, and recovery conditions. In neurons receiving AP and ADN inputs, NBQX attenuated AP- and ADN-evoked responses by 46 (P = 0.0206) and 49% (P = 0.0042). AP5 attenuated AP- and ADN-evoked responses by 39 (P = 0.0270) and 40% (P = 0.0157). NBQX + AP5 attenuated AP- and ADN-evoked responses by 74 (P = 0.0040) and 75% (P = 0.0028). In neurons receiving AP and vagal inputs, AP transmission was attenuated by 58, 60, and 98%; vagal transmission was attenuated by 62, 35, and 83% during NBQX, AP5, and both antagonists, respectively. These data suggest that both non-NMDA and NMDA receptors transmit AP input to NTS neurons in aortic baroreceptor or vagal afferent pathways.