Developmental profiles of glutamate receptors and synaptic transmission at a single synapse in the mouse auditory brainstem

Abstract

Using whole-cell recordings from presynaptic terminals and postsynaptic principal neurons in the mouse medial nucleus of the trapezoid body (MNTB), we have characterized properties of the calyx of Held synapse during the first three postnatal weeks. We observed that evoked excitatory postsynaptic currents (EPSCs) mediated by NMDA receptors (NMDAR) increased until postnatal day 11/12 (P11/12) after which they declined to very low or undetectable levels at P16. Meanwhile, EPSCs mediated by AMPA receptors (AMPAR) showed an approximate three-fold increase in amplitude. These changes were paralleled by NMDAR and AMPAR currents evoked by exogenous NMDA and kainate to MNTB neurons except that whole-cell kainate currents remained constant after P7/8 while AMPAR-EPSCs continued to increase. We found that the decay time constant t for NMDAR-EPSCs and AMPAR-EPSCs declined by about 30 % and 70 %, respectively. Analyses of NMDAR-EPSCs with subunit-specific pharmacological agents including ifenprodil, N,N,N‚,N‚-tetrakis(2-pyridylmethyl)-ethylenediamine (TPEN), zinc and Mg 2+ revealed subtle developmental changes in subunit composition. As maturation progressed, this synapse displayed a reduction in the number of presynaptic spike failures and the extent of synaptic depression in response to trains of stimuli (50-300 Hz) while the recovery rate from depression accelerated. These results demonstrate profound changes in the size and kinetics of postsynaptic glutamate receptors and in the spike-firing capability of presynaptic terminals at the calyx of Held-MNTB synapse during early development. We suggest that these concurrent presynaptic and postsynaptic adaptations represent important steps for synapse consolidation and refinement and ultimately for the development of fast high-fidelity transmission at this synapse. synaptic properties of the mouse calyx of Held-MNTB synapse within the first three postnatal weeks. We found that synaptic NMDARs were present only transiently within the first 2 weeks, and exhibited a unique developmental profile. Although synaptic AMPARs exhibited a nearly linear growth in density over the same period, the total population of functional AMPARs (i.e. whole-cell kainate currents) reached a maximum by the end of the first postnatal week. We suggest that these changes, along with concurrent alterations in kinetic properties of EPSCs and in synaptic depression and recovery, contribute significantly to the development of high-fidelity synaptic transmission at this synapse. Part of this study had been previously published in abstract form (Joshi & Wang, 2000). METHODS Slice preparationMice were housed in the facility certified by the Canadian Council of Animal Care and used for this study according to a protocol approved by the Hospital for Sick Children Animal Care Committee. Brainstem slices were prepared from P3-P18 mice (CD1/C57 black) as previously described (Forsythe & BarnesDavis, 1993). Mice were decapitated with a small guillotine and brains were rapidly dissected and immersed in ice-cold artif...

Development of NMDA R1 expression in chicken auditory brainstem

“…Similarly, in the mouse, where the early postnatal developmental period corresponds to a late embryonic stage in chick (Kubke and Carr, 2000), synaptogenesis in the calyx of Held is marked by both AMPAand NMDAR-mediated currents (Hoffpauier et al, 2006). The mean amplitude of NMDA EPSCs in calicine terminals in the mouse medial nucleus of the trapezoid body (MNTB) decreases in a stepwise fashion between P5 and P13, whereas the mean amplitude of AMPA EPSCs increases steadily from P5 to P15 (Futai et al, 2001;Joshi and Wang, 2002;Youssoufian et al, 2005). In rat MNTB, AMPA receptor-mediated EPSCs as well as quantal synaptic currents acquire progressively faster kinetics, whereas NMDAR-mediated EPSCs diminish with age, as indicated by a 50% reduction in mean amplitude and faster decay kinetics from P5 to P14 (Taschenberger and von Gersdorff, 2000).…”

“…In rodent cortex, NR2B is highly expressed before birth and remains roughly constant into adulthood, whereas NR2A is expressed after birth and increases with age (Watanabe et al, 1992;Sheng et al, 1994;Wenzel et al, 1997). During postnatal development, NR2C is expressed at low levels in cortex but at high levels in cerebellum, whereas NR2D is expressed at high levels in brainstem of mice (Watanabe et al, 1992), rats (Wenzel et al, 1997), and zebra finches (Wada et al, 2004).NMDAR contribute to auditory nerve responses during development (Zhou and Parks, 1992; Zhang and Trussell, 1994a,b;Futai et al, 2001;Joshi and Wang, 2002;Hoffpauir et al, 2006). In the chick vestibulocochlear nuclei, NMDAR emerge at E6, with functional synapses apparently generated at E7 (Sato and Momose-Sato, 2003).…”

Roles of the Fast-Releasing and the Slowly Releasing Vesicles in Synaptic Transmission at the Calyx of Held

“…The presynaptic patch pipette contained a low Ca 2ϩ buffer (0.05 mM EGTA), and the extracellular solution contained cyclothiazide and kynurenic acid to prevent postsynaptic AMPA receptor desensitization and saturation Joshi and Wang, 2002;Scheuss et al, 2002;Taschenberger et al, 2002). In Figure 1 A, the presynaptic terminal was depolarized to ϩ40 mV for 1 ms to mimic an AP.…”

Mechanisms Underlying Developmental Speeding in AMPA-EPSC Decay Time at the Calyx of Held

“…Developmental switches of postsynaptic receptor subunits underlie speeding in the decay time of synaptic currents mediated by nicotinic acetylcholine receptors (Mishina et al, 1986), glycine receptors (Takahashi et al, 1992), GABA A receptors (Okada et al, 2000), and NMDA receptors (NMDARs) Takahashi et al, 1996). Like other synaptic currents, the decay time of AMPA-EPSCs at the calyx of Held becomes faster during postnatal development (Taschenberger and von Gersdorff, 2000;Futai et al, 2001;Iwasaki and Takahashi, 2001;Joshi and Wang, 2002;Wall et al, 2002;Yamashita et al, 2003). However, it is not known whether the switch of AMPA receptor (AMPAR) subunits underlies this developmental speeding.…”