Ascending multisynaptic pathways from the trigeminal ganglion to the anterior cingulate cortex

Area of Science:

• Neuroscience
• Pain Research
• Somatosensory System

Background:

• The anterior cingulate cortex (ACC) is involved in pain perception.
• Ascending pathways from the trigeminal system to the ACC are not fully understood.

Purpose of the Study:

• To identify multisynaptic ascending pathways from the trigeminal ganglion (TG) to the ACC in rats.
• To characterize the types of primary afferent fibers involved in these pathways.
• To investigate the functional role of these pathways in pain processing.

Main Methods:

• Retrograde transneuronal transport of rabies virus for neuronal tracing.
• Extracellular unit recordings in the ACC.
• Electrophysiological recording and stimulation of trigeminal nerve pathways.
• Retrograde labeling with fluorogold.

Main Results:

• Multisynaptic pathways from the TG to the ACC were identified, involving the medial thalamus and spinal trigeminal nucleus.
• Neurons in the TG projecting to the ACC predominantly originated from medium- to large-sized cells with myelinated Aδ or Aβ afferent fibers.
• In contrast, TG neurons projecting to the primary somatosensory cortex had smaller cell sizes associated with unmyelinated C afferent fibers.
• ACC neurons responded to trigeminal nerve stimulation with short latencies (<20ms).

Conclusions:

• Somatosensory information reaches the ACC via multisynaptic pathways primarily from myelinated primary afferents, forming the medial nociceptive system.
• These pathways likely contribute to the affective-motivational aspects of pain.
• The distinct pathways suggest separate functions for the medial and lateral nociceptive systems in pain processing.