Isolectin B(4)-positive and -negative nociceptors are functionally distinct.

Area of Science:

• Neuroscience
• Pain research
• Sensory neuron biology

Background:

• Small-diameter sensory neurons, crucial for pain (nociceptors), are categorized as IB(4)-positive nonpeptidergic or IB(4)-negative peptidergic.
• Postnatal development shows IB(4)-positive neurons require glial-derived neurotrophic factor (GDNF), while IB(4)-negative neurons depend on nerve growth factor (NGF).
• These nociceptor populations project to different spinal cord areas, but their functional roles in pain remain unclear.

Purpose of the Study:

• To investigate potential functional differences between IB(4)-positive and IB(4)-negative nociceptors.
• To explore how neurotrophic factors influence these neuronal populations and their response to noxious stimuli.

Main Methods:

• Whole-cell voltage and current-clamp recordings were performed on acutely isolated adult mouse dorsal root ganglion neurons.
• Neurons were labeled with fluorescent IB(4) to distinguish between the two populations.
• Electrophysiological properties, including action potential duration, sodium currents, and heat-activated currents, were measured.

Main Results:

• IB(4)-positive neurons exhibited longer action potentials and higher TTX-resistant sodium current densities compared to IB(4)-negative neurons.
• IB(4)-positive neurons showed smaller currents activated by noxious heat.
• Nerve growth factor (NGF) significantly increased the number of heat-responsive neurons, whereas GDNF did not.

Conclusions:

• Distinct electrophysiological properties, including differential heat sensitivity, exist between IB(4)-positive and IB(4)-negative small neurons.
• These findings suggest that these two nociceptor populations may transmit different aspects of noxious stimuli.
• The differential response to NGF further supports distinct functional roles in acute pain and after injury.