Electrophysiological evidence for the presence of NR2C subunits of N-methyl-D-aspartate receptors in rat neurons of the nucleus tractus solitarius

Abstract

The nucleus tractus solitarius (NTS) plays an important role in the control of autonomic reflex functions. Glutamate, acting on N-methyl-D-aspartate (NMDA) and non-NMDA ionotropic receptors, is the major neurotransmitter in this nucleus, and the relative contribution of each receptor to signal transmission is unclear. We have examined NMDA excitatory postsynaptic currents (NMDA-EPSCs) in the subpostremal NTS using the whole cell patch clamp technique on a transverse brainstem slice preparation. The NMDA-EPSCs were evoked by stimulation of the solitary tract over a range of membrane potentials. The NMDA-EPSCs, isolated pharmacologically, presented the characteristic outward rectification and were completely blocked by 50 µM DL-2-amino-5-phosphonopentanoic acid. The I-V relationship of the NMDA response shows that current, with a mean (± SEM) amplitude of -41.2 ± 5.5 pA, is present even at a holding potential of -60 mV, suggesting that the NMDA receptors are weakly blocked by extracellular Mg 2+ at near resting membrane potentials. This weak block can also be inferred from the value of 0.67 ± 0.17 for parameter δ obtained from a fit of the Woodhull equation to the I-V relationship. The maximal inward current measured on the I-V relationship was at -38.7 ± 4.2 mV. The decay phase of the NMDA currents was fitted with one exponential function with a decay time constant of 239 ± 51 and 418 ± 80 ms at a holding potential of -60 and +50 mV, respectively, which became slower with depolarization (e-fold per 145 mV).

Frequency‐dependent facilitation of synaptic throughput via postsynaptic NMDA receptors in the nucleus of the solitary tract

“…First, we used a depolarizing ‘flip’ protocol that has been used extensively to study the relative contributions of AMPA‐Rs vs . NMDA‐Rs (Baptista & Varanda, ; Balland et al . ).…”

Memantine effects on liver and adrenal gland of rats exposed to cold stress

“…Drugs that block N-methyl-d-aspartate (NMDA) glutamate receptors are known to be neuroprotective in animal models for studying these acute brain injury conditions [11,12]. Memantine is a non-competitive antagonist at NMDA receptors and it is currently used to treat subjects with moderate to severe Alzheimer's disease to improve cognitive symptoms [13].…”

Peptide and Lipid Modulation of Glutamatergic Afferent Synaptic Transmission in the Solitary Tract Nucleus

“…Remote ST activation rarely activates NMDA receptors even using rapid bursts of ST shocks in low magnesium conditions (Jin et al, 2003). In transverse NTS slices, NMDA receptor mediated synaptic responses were reported in 3–4-week-old animals (Aylwin et al, 1997; Baptista et al, 2005a) or a subset of second order, adult NTS neurons with myelinated afferents (Jin et al, 2003). In transverse slices, the ST and recipient neurons are in close proximity (often 200–300 μm) but the contributions of the spread of the electrical stimulus beyond the ST or the developmental state of the animals are difficult to assess.…”