Activity-dependent changes in the pain matrix.

Area of Science:

• Neuroscience
• Pain Research
• Cellular Signaling

Background:

• Multireceptive neurons in the dorsal horn and trigeminal nucleus exhibit increased excitability and receptive field expansion upon stimulation.
• Similar receptive field alterations occur in response to various injuries, suggesting a common mechanism in pain processing.
• These neurons integrate non-nociceptive and nociceptive inputs, implicating their altered activity in referred pain.

Purpose of the Study:

• To investigate the mechanisms underlying increased neuronal excitability and receptive field expansion in pain pathways.
• To explore the role of glutamate and substance P in modulating neuronal activity in the central nervous system.
• To examine the time-dependent processing of noxious stimulation in a model of chronic pain.

Main Methods:

• Electrophysiological studies (in vivo and in vitro) to assess neuronal activity.
• Quantitative autoradiography using 14C-2-deoxyglucose technique in a rat model of chronic monoarthritis.
• Analysis of molecular mechanisms including membrane receptor phosphorylation and gene expression.

Main Results:

• Repetitive synaptic excitation and L-glutamate application lead to increased neuronal excitability and receptive field expansion.
• Co-activation of glutamate and substance P receptors significantly contributes to this facilitatory effect.
• Chronic pain models show spontaneously active dorsal horn neurons that maintain activity without peripheral noxious input, indicating central sensitization.

Conclusions:

• Increased excitability of dorsal horn neurons, driven by glutamate and substance P, is a key mechanism in receptive field expansion and potentially referred pain.
• Central sensitization, characterized by sustained neuronal activity, occurs in chronic pain states.
• Understanding these mechanisms offers insights into pain perception and potential therapeutic targets.