Information on the frequency and spatial distribution of axonal varicosities associated with release of neurotransmitters in the dental pulp is important to help elucidate the peripheral mechanisms of dental pain, mediated by myelinated versus unmyelinated fibers. For this, we investigated the distribution of axonal varicosities in the human dental pulp using light- and electron-microscopic immunohistochemistry for the vesicular glutamate transporter 2 (VGLUT2), which is involved in the glutamatergic transmission, and syntaxin-1 and synaptosomal nerve-associated protein 25 (SNAP-25), combined with parvalbumin (PV), which is expressed mostly in myelinated axons, and substance P (SP) and calcitonin gene-related peptide (CGRP), which are expressed mostly in unmyelinated axons. We found that the varicosities of the SP- and CGRP-immunopositive (+) axons were uniformly distributed throughout the dental pulp, whereas those of PV+ axons were only dense in the peripheral pulp, and that the expression of PV, VGLUT2, syntaxin-1, SNAP-25, SP and CGRP was significantly higher in the varicosities than in the axonal segments between them. These findings are consistent with the release of glutamate and neuropeptides by axonal varicosities of SP+ and CGRP+ unmyelinated fibers, involved in pulpal pain throughout the human dental pulp, and by varicosities of PV+ fibers, arising from parent myelinated fibers, and involved in dentin sensitivity primarily in the peripheral pulp.

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This study investigated the effects of distraction tasks, such as Sending Text Message (STM) task with cellphone and Searching Navigation (SN) task with car navigation system, on driving performance and Skin Conductance Level (SCL) of experienced taxi drivers. Twelve male taxi drivers (age 56.3±4.4 years, taxi driving experience 28.4±6.4 years) and fourteen female taxi drivers (age 55.5±3.5 years, taxi driving experience 19.4±5.0 years) were instructed to drive at a constant speed (90 km/hr) for 2 min while keeping a distance of 30 m from the front car also running at a speed of 90 km/hr. Subjects performed driving only for the first 1 min (Control phase). For an additional 1 min (Task phase), they performed Driving Only, Driving + STM, or Driving + SN while driving. For all events, driving performance during the Task phase was evaluated by car control data such as average following distance and speed deviation. For Driving Only, Driving + STM, and Driving + SN, change of SCL from the Control phase to the Task phase, relative change of SCL, was calculated. Compared to Driving Only, during Driving + STM or Driving + SN, relative change of SCL was increased. Compared to Driving Only, during Driving + STM or Driving + SN, average following distance and speed deviation increased. It can be concluded that, even for experienced taxi drivers, distraction tasks increase workload, increased the difficulty to control a car, and detracted from safe driving.