Distribution of herpes simplex virus type 1 in human geniculate and vestibular ganglia: implications for vestibular neuritis.

Vestibular neuritis is a common cause of partial unilateral vestibular paralysis, which usually spares posterior semicircular canal function. The cause is assumed to be a viral reactivation of latent herpes simplex virus type 1 (HSV-1) in human vestibular ganglia. The existence of an anastomosis between the intermediate nerve and the superior vestibular nerve suggests the question of whether selective affliction of the superior vestibular nerve is the result of migration of HSV-1 from the geniculate ganglion along this faciovestibular anastomosis. We determined the distribution of HSV-1 among geniculate ganglia, vestibular ganglia, and within Scarpa's ganglion by examining 35 human temporal bones by polymerase chain reaction. HSV-1 was found in 66% of geniculate ganglia and 60% of vestibular ganglia; all examined parts of vestibular ganglia were almost equally HSV-1 infected. Our data provided no support for viral migration along this anastomosis or for a preferential latency of HSV-1 in the superior vestibular nerve. We suggest that the common double innervation of the posterior ampulla by two nerves running in two separate bony canals could offer an alternative explanation for the regular sparing of posterior canal function in vestibular neuritis.

Pseudorabies virus-induced leukocyte trafficking into the rat central nervous system.

When the swine alphaherpesvirus pseudorabies virus (PRV) infects the rat retina, it replicates in retinal ganglion cells and invades the central nervous system (CNS) via anterograde transynaptic spread through axons in the optic nerve. Virus can also spread to the CNS via retrograde transport through the oculomotor nucleus that innervates extraocular muscles of the eye. Since retrograde infection of the CNS precedes anterograde transynaptic infection, the temporal sequence of infection of the CNS depends on the route of invasion. Thus, motor neurons are infected first (retrograde infection), followed by CNS neurons innervated by the optic nerve (anterograde transynaptic infection). This temporal separation in the appearance of virus in separate groups of neurons enabled us to compare the immune responses to different stages of CNS infection in the same animal. The data revealed focal trafficking of peripheral immune cells into areas of the CNS infected by retrograde or anterograde transport after PRV Becker was injected into the vitreous body of the eye. Cells expressing the leukocyte common antigen, CD45(+), entered the area of infection from local capillaries prior to any overt expression of neuropathology, and quantitative analysis demonstrated that the number of cells increased in proportion to the number of infected neurons within a given region. Recruitment of cells of monocyte/macrophage lineage began prior to the appearance of CD8(+) cytotoxic lymphocytes, which were, in turn, followed by CD4(+) lymphocytes. These data demonstrate that PRV replication in CNS neurons stimulates the focal infiltration of specific classes of CD45(+) cells in a time-dependent, temporally organized fashion that is correlated directly with the number of infected neurons and the time that a given region has been infected.

Highly variable distribution of HSV-1-specific DNA in human geniculate, vestibular and spiral ganglia.

Viral reactivation in temporal ganglia is the suspected cause of Bell's palsy, vestibular neuritis and sudden hearing loss. Since the distribution of latent herpes simplex type 1 (HSV-1) in geniculate, vestibular and spiral ganglia of individual human temporal bones could have implications for the explanation of isolated as well as combined disorders of these three cranial nerves, we examined these ganglia in 18 human temporal bones of adults by nested polymerase chain reaction. In all of the temporal bones HSV-1 specific DNA was detected: 10/18 (56%) of the geniculate, 11/18 (61%) of the vestibular and 9/18 (50%) of the spiral ganglia samples were positive. All combinations of positive and negative ganglia were found in individual temporal bones at roughly equal frequencies. These data support a viral etiology of all three conditions, especially their occasional combinations.

Anterograde tracing of trigeminal afferent pathways from the murine tooth pulp to cortex using herpes simplex virus type 1.

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.