AMPA receptor involvement in 5-hydroxytryptamine2A receptor-mediated pre-frontal cortical excitatory synaptic currents and DOI-induced head shakes

The development of glutamatergic synapses involves a sequence of events that are still not well understood. We have studied the time course of the development of glutamatergic synapses in cultured spinal neurons by characterizing spontaneous synaptic currents recorded from cells maintained in vitro for different times. At short times in culture (2 days in vitro; DIV2), spontaneous synaptic activity consisted almost solely of N-methyl-d-aspartate (NMDA) receptor (NMDAR) openings. In contrast, older neurons (DIV5 to DIV8) displayed clear α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor (AMPAR)–mediated synaptic currents, while the NMDAR-mediated activity remained small. Between 8 and 14 days in vitro there was a large increase in the density of synaptically activated NMDARs, although there was no significant increase in the density of the NMDAR-mediated current activated by exogenous glutamate. The results indicate that there is a switch in NMDAR targeting from somatic to synaptic regions during the course of the second in vitro week. Finally, our results support the conclusion that the spontaneous synaptic activity displayed in culture depends on ongoing NMDAR-mediated activity, even when the expression of synaptic NMDARs is low.

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Theta-Frequency Facilitation of AMPA Receptor-Mediated Synaptic Currents in the Principal Cells of the Medial Septum

Journal of Neurophysiology ◽

10.1152/jn.2001.85.4.1709 ◽

2001 ◽

Vol 85 (4) ◽

pp. 1709-1718 ◽

Cited By ~ 15

Author(s):

John N. Armstrong ◽

Brian A. MacVicar

Keyword(s):

Ampa Receptor ◽

Ampa Receptors ◽

Laser Scanning ◽

Medial Septum ◽

Laser Scanning Microscopy ◽

Projection Neurons ◽

Synaptic Currents ◽

External Application ◽

Septal Neurons ◽

Current Facilitation

Recent evidence suggests that Ca2+-permeable AMPA receptors display rapid, short-lasting current facilitation. In this study, we investigated the properties of AMPA receptor-mediated synaptic currents in medial septal neurons of the rat in an in vitro slice preparation. Immunocytochemistry with a selective antibody to the GluR2 subunit revealed that both choline acetyltransferase-containing and parvalbumin-containing neurons of the medial septum express no detectable GluR2 subunit immunoreactivity. We used whole cell voltage-clamp recordings to measure synaptically evoked AMPA receptor-mediated currents from medial septal neurons following stimulation of midline afferents. The GYKI 52466 (50 μM)- and 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide (NBQX) (20 μM)-sensitive AMPA receptor-mediated component of the synaptic response was isolated by blocking GABAA- and N-methyl-d-aspartate receptor-mediated currents with 30 μM bicuculline and 100 μM 2-amino-5-phosphonovaleric acid, respectively. In some cases, patched cells were filled with Lucifer yellow (0.1%) and imaged using 2-photon laser scanning microscopy. AMPA receptor-mediated currents that were observed in large medial septal neurons (20–30 μm) displayed rectification. These currents were sensitive to external application of philanthotoxin-343 (PhTx-343, 50 μM), a potent, high-affinity antagonist of Ca2+-permeable, GluR2-lacking AMPA receptors. Rectifying AMPA receptor-mediated currents also displayed a rapid increase in amplitude when evoked five times at low frequency such as 6 Hz. In contrast to currents observed in large medial septal neurons, AMPA-receptor mediated currents evoked in the remaining small (8–11 μm) neurons were nonrectifying and displayed rapid synaptic depression when stimulated five times at 6 Hz. The currents evoked in these cells were unaffected by external application of PhTx-343 and were therefore GluR2-containing AMPA receptors. The results of the present study demonstrate that the principal projection neurons of the medial septum contain PhTx-343-sensitive, GluR2-lacking AMPA receptors that display rapid current facilitation when stimulated at low frequencies.

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