Journal of Neuroscience, Vol 15, 2972-2984, Copyright © 1995 by Society for Neuroscience
Anterograde tracing of trigeminal afferent pathways from the murine tooth pulp to cortex using herpes simplex virus type 1
EM Barnett, GD Evans, N Sun, S Perlman and MD Cassell
Neuroscience Program, University of Iowa, Iowa City 52242, USA.
Due to its predominantly nociceptive innervation, viral tracing from the
tooth pulp provides a potential means for tracing central pain pathways.
The neural pathways from the tooth pulp to cortex were determined using in
situ hybridization to detect the anterograde transneuronal spread of herpes
simplex virus type 1 strain H129 following inoculation into the murine
mandibular incisor pulp. Virus first appeared in the brain at day 3 in the
dorsomedial region of all three subnuclei of the spinal trigeminal nucleus
and the principal sensory nucleus. By days 5-6 virus had spread to the
contralateral medial nucleus of the medial geniculate complex, posterior
thalamus, and ventroposteromedial thalamus. At days 7-8 virus was detected
in laminae IV and Va of the primary somatosensory cortex and lamina IV of
the secondary somatosensory cortex in regions previously shown to receive
input from the lower jaw. Several mice also showed infection of laminae
II/III of the ipsilateral dysgranular insular cortex, along with labeling
for virus in the ipsilateral external lateral parabrachial nucleus,
posterior thalamus, and posterior basolateral amygdala. Our results are
highly consistent with previous tracing and electrophysiological studies
utilizing the tooth pulp and with studies implicating the infected
structures in nociception. Viral spread appeared to define two separate
afferent systems with infection of structures which have been implicated in
the sensory-discriminative aspects of pain, such as the ventroposteromedial
thalamus and somatosensory cortex, as well as in the dysgranular insular
cortex and related subcortical nuclei which may have a role in the
affective- motivational aspects of pain.
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