Papers of the Week

Nociceptive trigeminal afferents innervating craniofacial area, e.g. facial skin and cranial meninges, project to a broad region in the medullary and upper cervical dorsal horn designated as the trigeminocervical complex. Lamina I neurons in the trigeminocervical complex integrate and relay peripheral inputs, thus playing a key role in both cranial nociception and primary headache syndromes. Because of the technically challenging nature of recording, the long-range trigeminal afferent inputs to the medullary and cervical lamina I neurons were not intensively studied so far. Therefore, we have developed an ex vivo brainstem-cervical cord preparation with attached trigeminal nerve for the visually-guided whole-cell recordings from the medullary and cervical lamina I neurons. Two-thirds of recorded neurons generated intrinsic rhythmic discharges. The stimulation of the trigeminal nerve produced a complex effect; it interrupted the rhythmic discharge for hundreds of milliseconds but, if the neuron was silenced by a hyperpolarizing current injection, could elicit a discharge. The monosynaptic inputs from the trigeminal Aδ-, high-threshold-Aδ-, low-threshold-C- and C-afferents were recorded in the medullary neurons, as well as in the cervical neurons located in the segments C1-C2 and, to lesser degree, in C3-C4. This pattern of supply was consistent with our labelling experiments showing extensive cervical projections of trigeminal afferents. Excitatory inputs were mediated, although not exclusively, via AMPA/kainate and NMDA receptors, while inhibitory inputs via both GABA and glycine receptors. In conclusion, the trigeminocervical lamina I neurons receive a complex pattern of long-range mono- and polysynaptic inputs from a variety of the trigeminal nociceptive afferents.