Research report
AMPA and NMDA receptor-mediated currents in developing dentate gyrus granule cells

https://doi.org/10.1016/j.devbrainres.2004.12.002Get rights and content

Abstract

Granule cells (GCs) of the hippocampal dentate gyrus (DG) undergo postnatal neurogenesis such that cells at different maturational stages can be studied within an anatomically restricted region and a narrow animal age epoch. Using whole cell patch clamp recordings in hippocampal slices, we have previously found that input resistance (IR) correlates inversely with morphometric indicators of GC maturity. Using IR as an index of maturity we measured developmental changes in synaptic currents mediated by N-methyl-d-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in GCs from 5- to 12-day rats. Peak NMDA and AMPA EPSC amplitudes increased, and the NMDA/AMPA ratio reversed with advancing cell age. NMDA EPSCs showed a maturational decrease in rise time but no change in decay time, whereas AMPA EPSCs showed neither rise nor decay time changes with development. Ifenprodil, a high affinity selective inhibitor of NR1/NR2B diheteromeric NMDA receptors, blocked approximately 50% of the peak amplitude of evoked NMDA EPSCs in all tested GCs regardless of their maturity and did not affect the measured kinetic properties. These data suggest that development of glutamatergic synapses follows distinct schedules. AMPA receptors possessed mature kinetics and became the dominant glutamatergic current within the age epoch studied, whereas NMDA receptors showed maturational changes in rise times but not decay kinetics. The reported modifications of EPSC properties are consistent with changes in receptor and synapse number, and relative quantities of AMPA and NMDA receptors. Changes in the subunit composition that determines NMDA decay kinetics may occur beyond the early neonatal period.

Introduction

The hippocampal dentate gyrus (DG) is vital to normal learning and memory [21] and is implicated in neurodevelopmental disabilities such as epilepsy, schizophrenia, and autism [20], [30] as well as neurodegenerative disorders such as Alzheimer disease [24]. Granule cells (GCs) of dentate gyrus undergo postnatal neurogenesis in many mammalian species including humans [6], [10]. Both clinical and experimental data suggest that newly born GCs may contribute to functional recovery from brain injury of diverse etiologies [3], [18], [25], [34] and/or serve as a source of replacement for cells lost in disease [13], [32]. Thus, the study of GC integration in the hippocampal network is of potential therapeutic importance.

Because of postnatal neurogenesis and stratification within DG, GCs with staggered birthdates can be studied in situ over a narrow animal age epoch and even within a given hippocampal slice. Using patch clamp recordings of biocytin-filled GCs in rat hippocampal slices in the first postnatal month, we have previously shown that cells with input resistance (IR) ranging from 0.250 to 3.0 GΩ can be found within an anatomically restricted region in the middle third of the suprapyramidal limb, and that the cells with highest IR are the least mature by morphometric criteria such as dendritic length and degree of penetration of the dendritic arbor into the molecular layer [17], [19]. In a subsequent qualitative electrophysiologic study of very immature GCs (IR ≥ 1 GΩ) from young rat DG (postnatal days 5–12), we demonstrated a maturational progression of the response to medial perforant path stimulation that paralleled morphometric advances in cell age: glutamatergic currents were absent in the youngest cells, exclusively NMDA-mediated in somewhat older cells, and both α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and NMDA-mediated in the oldest cells in the population [37]. In the present study, we examined GCs from 5- to 12-day rats (IR range 0.350–2.200 GΩ) that had both AMPA and NMDA-mediated currents. Using IR as an index of maturity, we examined the relative maturation of amplitude and kinetics of these currents, and determined the response of the NMDA currents to the selective NR2B antagonist ifenprodil.

Section snippets

Materials and methods

Hippocampal slices (300–350 μm) from Sprague–Dawley rats of both genders (6–12 days) were prepared as previously described [37] and were maintained at 35 °C for at least 30 min, allowed to cool to room temperature and transferred as needed to a small volume perfusion chamber (32 °C). ACSF composition was (in mM): NaCl 124, KCl 3, CaCl2 2.4, MgSO4 1.3, NaH2PO4 1.25, NaHCO3 26, and glucose 10 (gassed with 95% O2/5% CO2, pH = 7.4). Recording pipettes were pulled from borosilicate glass capillaries

Amplitude and kinetics of NMDA and AMPA currents

NMDA and AMPA currents were compared in 39 GCs (Table 1). In this population, IR ranged from 0.350 GΩ (most mature) to 2.200 GΩ (least mature), and RMP became more hyperpolarized with advancing cell maturity as we have previously shown [19]. Both NMDA and AMPA peak currents increased with advancing cell maturity (Fig. 1) with mean peak AMPA current ranging from −53.0 ± 17.5 to −434.0 ± 134.7 pA, and mean peak NMDA current ranging from 65.2 ± 19.3 to 336.8 ± 117.0 pA. The ratio of peak NMDA/AMPA

Discussion

Using input resistance (IR) as an indicator of cell maturity, we characterized developmental properties of evoked AMPA and NMDA EPSCs in GCs from early postnatal rat DG. We report that the peak amplitudes of both types of current increased with advancing cell age and that the NMDA/AMPA amplitude ratio reversed from >1 in younger cells to <1 in older cells. NMDA EPSCs showed a maturational decrease in rise time but no change in decay time, whereas AMPA EPSCs showed neither rise nor decay time

Acknowledgments

Northwestern University Buehler Center on Aging, Crown Family, Mr. and Mrs. William J. White (BLT); Open Hearts for Retarded Children (JFP).

References (37)

  • A.W. Dunah et al.

    Regional and ontogenic expression of the NMDA receptor subunit NR2D protein in rat brain using a subunit-specific antibody

    J. Neurochem.

    (1996)
  • G.M. Durand et al.

    Long-term potentiation and functional synapse induction in developing hippocampus

    Nature

    (1996)
  • P.S. Eriksson et al.

    Neurogenesis in the adult human hippocampus

    Nat. Med.

    (1998)
  • D. Feldmeyer et al.

    Functional consequences of changes in NMDA receptor subunit expression during development

    J. Neurocytol.

    (1996)
  • J.M. Fritschy et al.

    Synapse-specific localization of NMDA and GABA(A) receptor subunits revealed by antigen-retrieval immunohistochemistry

    J. Comp. Neurol.

    (1998)
  • S.N. Gomperts et al.

    Distinct roles for ionotropic and metabotropic glutamate receptors in the maturation of excitatory synapses

    J. Neurosci.

    (2000)
  • E. Gould et al.

    Neurogenesis in adult mammals: some progress and problems

    J. Neurosci.

    (2002)
  • S. Hestrin

    Developmental regulation of NMDA receptor-mediated synaptic currents at a central synapse

    Nature

    (1992)
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