Timing Mechanisms Underlying Gate Control by Feedforward Inhibition.

Area of Science:

• Neuroscience
• Pain research
• Spinal cord physiology

Background:

• The gate control theory of pain suggests mechanoreceptor inputs are modulated by spinal cord inhibitory circuits.
• A key question is how early excitatory inputs are gated by later inhibitory inputs.

Purpose of the Study:

• To elucidate the mechanisms underlying the gating of Aβ mechanoreceptor inputs by disynaptic inhibition in T neurons.
• To investigate the role of potassium channel activity and glutamate receptor kinetics in pain gating.

Main Methods:

• Electrophysiological recordings in T neurons.
• Investigation of potassium channel currents (I_A) and N-methyl-D-aspartate receptor (NMDAR) activation.
• Modulation of inhibitory neuron activity and nociceptor input.

Main Results:

• Aβ-evoked excitatory postsynaptic potentials (EPSPs) in T neurons are subthreshold, allowing time for inhibitory inputs.
• Potassium channel activity (I_A) filters or reduces Aβ inputs, creating permissive conditions for gating.
• Capsaicin-activated nociceptor input reduces I_A, sensitizing T neurons and enabling Aβ input to evoke firing before inhibition.

Conclusions:

• Distinct kinetics of glutamate receptors and electrical filtering by potassium channels resolve the timing issue in feedforward inhibition-mediated pain gating.
• Modulation of these mechanisms offers potential strategies to bypass pain gate control.