Developmental Study of N‐Methyl‐d‐Aspartate‐induced Firing Activity and Whole‐cell Currents in Nucleus Tractus Solitarii Neurons

Abstract

Whole-cell recordings of rat nucleus tractus solitarii (NTS) neurons were performed on a slice preparation. We investigated possible postnatal changes in firing activities and currents induced by N-methyl-D-aspartate (NMDA) application. A total of 42 neurons were selected and fell into the following age groups: 0-5 days (n = 15), 10-15 days (n = 9) and 30-60 days (adult, n = 18). During this period, input resistance and spike duration decreased by approximately 40%. At all ages, bath application of NMDA elicited a bursting firing activity when the membrane potential was held between -60 and -75 mV. However, in the youngest cells the rhythmic bursting activity was irregular and was characterized by a progressive firing inactivation during a burst. In a tetrodotoxin-containing saline, NMDA-induced oscillations of membrane potential were retained in all age groups. The membrane current-voltage relationship of the NMDA-induced inward current (INMDA) was characterized by a region of negative slope conductance which was similar in all age groups. Thus the voltage-dependent block of INMDA is present in NTS neurons from birth, allowing NTS neurons to display membrane potential oscillations. However, postnatal maturation of repolarizing conductances, as suggested by changes in spike characteristics, could render the oscillatory activity more stable than at birth.

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

“…Specifically, we found that in 70% of NTS neurons NMDA-Rs contributed to 70% of the total charge transfer when recordings were made at +40 mV. Our observation is consistent with a previous report in young animals using this protocol (Balland et al 2008); these results suggest that NMDA-Rs play a functional role in the NTS well beyond early developmental stages (Vincent et al 1996). Consistent with previous reports we found that, when slices were incubated in Mg 2+ -free aCSF, the majority of NTS neurons exhibited an NMDA-R component as part of their ST-evoked glutamatergic EPSCs (Aylwin et al 1997;Smith et al 1998;Yen et al 1999;Jin et al 2003).…”

“…); these results suggest that NMDA‐Rs play a functional role in the NTS well beyond early developmental stages (Vincent et al . ). Consistent with previous reports we found that, when slices were incubated in Mg 2+ ‐free aCSF, the majority of NTS neurons exhibited an NMDA‐R component as part of their ST‐evoked glutamatergic EPSCs (Aylwin et al .…”

Vagally evoked synaptic currents in the immature rat nucleus tractus solitarii in an intact in vitro preparation

“…The relatively robust inhibitory tone we observed could have been due in part to developmental differences in GABAergic circuitry in the NTS. Although most intrinsic membrane properties of NTS neurones tend to be largely mature by the end of the first postnatal week (Kalia et al 1993; Nabekura et al 1994; Bao et al 1995; Vincent et al 1996), dendritic and axonal morphologies may not reach their full complexity until the end of the third postnatal week (Lasiter et al 1989). Such findings suggest that differences in synaptic density or efficacy might explain the relatively robust synaptic responses we observed.…”

Postnatal Development of Glutamate Receptor-Mediated Responses in the Neostriatum

“…In other regions of the brain, previous studies have reported that the magnitude of NMDA current increases Ujihara and Albuquerque, 1992], decreases [Hori and Kanda, 1996] or is unaltered [Burgard and Hablitz, 1994;Vincent et al, 1996] throughout postnatal development. In both the neocortex and spinal cord, there is evidence that NMDA receptor function develops before that of AMPA/KA receptors [Burgard and Hablitz, 1993;Kim et al, 1995;Ziskind-Conhaim, 1990;Zona et al, 1994].…”