Presynaptic interactions between trigeminal and cervical nociceptive afferents supplying upper cervical lamina I neurons

Cervical and trigeminal afferents innervate neighboring cranial territories, and their convergence on upper cervical dorsal horn neurons provides a potential substrate for pain referral in primary headache syndromes Lamina I neurons are central to this mechanism as they relay convergent nociceptive input to supraspinal pain centers. Unfortunately, little is known about the interactions between trigeminal and cervical afferents supplying lamina I neurons. Here we used rats of both sexes to show that cervical and trigeminal afferents interact via presynaptic inhibition, where monosynaptic inputs to lamina I neurons undergo unidirectional as well as reciprocal presynaptic control. This means that afferent-driven presynaptic inhibition shapes the way trigeminal and cervical A delta- and C-fiber input reaches lamina I projection and local-circuit neurons. We propose that this inhibition provides a feedforward control of excitatory drive to lamina I neurons that regulates their convergent and cervical- or trigeminal-specific processing modes. As a consequence, disruption of the trigeminal and cervical afferent-driven presynaptic inhibition may contribute to development of primary headache syndromes.

Automated summary

Cervical and trigeminal afferents interact via presynaptic inhibition, shaping the way sensory input reaches neurons. Disruption of this inhibition may contribute to the development of primary headache syndromes.