High- and low-conductance NMDA receptors are present in layer 4 spiny stellate and layer 2/3 pyramidal neurons of mouse barrel cortex

TL;DR

This study identifies both high- and low-conductance NMDA receptors in layer 4 spiny stellate and layer 2/3 pyramidal neurons of mouse barrel cortex, providing insights into their roles in synaptic plasticity and neuronal excitability.

Contribution

It provides electrophysiological evidence of both NMDA receptor subtypes in these neurons, expanding understanding of their functional roles in sensory processing.

Findings

Both neuron types contain high- and low-conductance NMDA receptors.

Layer 4 cells express both receptor types, supporting their role in excitation amplification.

Layer 2/3 pyramidal neurons also have low-conductance NMDA receptors, indicating shared functions.

Abstract

NMDA receptors are ion channels activated by the neurotransmitter glutamate in the mammalian brain and are important in synaptic function and plasticity, but are also found in extrasynaptic locations and influence neuronal excitability. There are different NMDA receptor subtypes which differ in their single-channel conductance. Recently, synaptic plasticity has been studied in mouse barrel cortex, the primary sensory cortex for input from the animal's whiskers. Pharmacological data imply the presence of low-conductance NMDA receptors in spiny stellate neurons of cortical layer 4, but of high-conductance NMDA receptors in pyramidal neurons of layer 2/3. Here, to obtain complementary electrophysiological information on the functional NMDA receptors expressed in layer 4 and layer 2/3 neurons, single NMDA receptor currents were recorded with the patch-clamp method. Both cell types were found to contain high-conductance as well as low-conductance NMDA receptors. The results are consistent with the reported pharmacological data on synaptic plasticity, and with previous claims of a prominent role of low-conductance NMDA receptors in layer 4 spiny stellate neurons, including broad integration, amplification and distribution of excitation within the barrel in response to whisker stimulation, as well as modulation of excitability by ambient glutamate. However, layer 4 cells also expressed high-conductance NMDA receptors. The presence of low-conductance NMDA receptors in layer 2/3 pyramidal neurons suggests that some of these functions may be shared with layer 4 spiny stellate neurons.