Ultrastructural Basis for Craniofacial Sensory Processing in The Brainstem

The study of projections and synaptic connectivity of trigeminal sensory and proprioceptive afferents in the 1 ^st relay nucleus of the brainstem, helps us to understand where and how the specific craniofacial neural information is transmitted and processed in the CNS. This paper reviews recent findings on the synaptic connectivity of specific craniofacial sensory and proprioceptive afferents in the brainstem. It also deals with neurotransmitters and receptors involved in the presynaptic modulation of the trigeminal primary afferents. Here, we will also review recent findings on the projection and synaptic connectivity of the axons, and terminals in the trigeminal sensory nuclei that express nociceptive markers such as theromosensitive TRP channels TRPV1 and TRPA1, and the purinergic receptor P2X3. The dental pulp is a good model for the study of peripheral pain because it is densely innervated by nociceptive afferents. Finally, we describe the axons innervating the dental pulp and the morphological changes that the myelinated axons undergo during their intradental course.