In this study we used immunocytochemistry to investigate whether autonomic fibres sprouted in the skin of the lower lip in a rat model of neuropathic pain. We used a bilateral chronic constriction injury (CCI) of the mental nerve (MN), a branch of the trigeminal nerve. In this model, we also studied the accompanying changes in peptidergic [calcitonin gene-related peptide (CGRP)-immunoreactive] sensory fibres, as well as in trkA receptor immunoreactivity in the sensory nerves. Autonomic (sympathetic and parasympathetic) fibre sprouting was first observed 1 week post-injury with a peak in the number of sprouted fibres occurring at 4 and 6 weeks post-CCI. CGRP-IR fibres almost disappeared at 2 weeks post-CCI, but quickly sprouted, leading to a significant peak above sham levels 4 weeks post-injury. trkA receptor expression was found to be up-regulated in small cutaneous nerves 4 weeks post-CCI, returning to sham levels by 8 weeks post-CCI. There was no sympathetic fibre sprouting in the trigeminal ganglion following CCI. At 4 weeks post-CCI, rats displayed spontaneous, directed grooming to the area innervated by the MN that was not seen in sham animals, which we interpreted as a sign of spontaneous pain or dysesthesiae. Collectively, our findings indicate that as a result of autonomic sprouting due to CCI of the MN, remaining intact nociceptive fibres may potentially develop sensitivity to sympathetic and parasympathetic stimulation, which may have a role in the generation of abnormal pain following nerve injury.

Improving the sense of 'presence' is a common goal of 3D display technology for film, television and virtual reality. However, there are instances in which 3D presentation may elicit unanticipated negative responses. For example, it is well established that violations of interpersonal space cause discomfort in real-world situations. Here we ask if people respond similarly when viewing life-sized stereoscopic images. Observers rated their level of comfort in response to animate and inanimate objects in live and virtual (stereoscopic projection) viewing conditions. Electrodermal activity was also recorded to monitor their physiological response to these stimuli. Subjects exhibited significant negative reactions to violations of interpersonal space in stereoscopic 3D displays, which were equivalent to those experienced in the natural environment. These data have important implications for the creation of 3D media and the use of virtual reality systems.

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