NMDA receptors | How do NMDA receptors work? What happens when you block NMDA receptors? NMDA in LTP

NMDA Receptors: Function and Importance

NMDA (N-methyl-D-aspartate) receptors are ionotropic, ligand-gated glutamate receptors found at glutamatergic synapses. They help regulate synaptic strength and plasticity and contribute to memory formation. The channels conduct sodium, potassium, and calcium ions.

How the Magnesium Block Works

At resting, negative membrane potentials, a magnesium ion blocks the NMDA receptor’s channel pore and prevents substantial ion flow. Glutamate released by a presynaptic neuron binds to the receptor, but binding alone is not enough to open the channel.

Nearby AMPA receptors also bind glutamate. Their activity allows sodium to enter the postsynaptic neuron, making the inside more positive. When the postsynaptic membrane becomes sufficiently depolarized, it repels the magnesium ion from the NMDA channel. With glutamate bound and the magnesium block removed, ions can flow through the channel, including a substantial influx of calcium.

Electrophysiological Properties

The video describes whole-cell patch-clamp recording in voltage-clamp mode, where the membrane voltage is held at set values while current is measured.

NMDA receptor currents are small or nearly absent at strongly negative voltages because magnesium blocks the channel. As the membrane becomes more positive, the block is relieved and current increases. Current direction reverses near the receptor’s reversal potential, stated as approximately 0 mV. Current–voltage (I–V) and conductance–voltage (G–V) plots illustrate these voltage-dependent properties.

The video gives a single-channel conductance of about 50 picosiemens and describes NMDA currents as relatively sustained compared with those of other ionotropic receptors.

Subunits and Receptor Configurations

NMDA receptors can be assembled from different subunits, including NR1, NR2 subtypes, and NR3 subtypes. The video presents NR1 as a consistent component and describes receptor assemblies containing NR1 together with other subunits.

Coincidence Detection and Synaptic Plasticity

NMDA receptors require both glutamate binding and relief of the magnesium block to conduct effectively. Glutamate binding signals presynaptic activity, while depolarization and magnesium-block removal signal postsynaptic activity. This allows the receptor to respond when presynaptic and postsynaptic activity coincide.

Calcium entering through the receptor can raise postsynaptic calcium levels and activate calcium-dependent kinases such as CaMKII. These enzymes affect downstream targets and can change synaptic strength.

Memory and Long-Term Potentiation

The video describes a mouse Morris water maze task in which a hidden platform is associated with a spatial landmark. Mice that learn the task tend to navigate toward the platform’s location. When NMDA receptors are blocked, the mice described fail to show the same preference for the platform’s quadrant, illustrating the receptors’ importance in this memory-related task.

The video also demonstrates long-term potentiation (LTP) by applying high-frequency (100 Hz) stimulation to a presynaptic neuron and measuring the postsynaptic response. After stimulation, a similar test stimulus produces a larger response. The increased response, reflected in a greater postsynaptic-potential slope, can persist for minutes to hours and represents lasting synaptic strengthening.

Blocking NMDA receptors prevents the described protocol from producing the potentiated response, highlighting their role in this form of synaptic plasticity.

Speakers and Sources

• Speaker: The video’s narrator/presenter, associated with the channel Animated biology With arpan.
• Other speakers: None identified. The narrator describes the water-maze and electrophysiology examples; no separate researchers or sources are named.