Central nervous system innervation of the penis as revealed by the transneuronal transport of pseudorabies virus.

Transneuronal tracing techniques were used in order to identify putative spinal interneurons and brainstem sites involved in the control of penile function. Pseudorabies virus was injected into the corpus cavernosus tissue of the penis in rats. After a four day survival period, rats were perfused with fixative and virus-labelled neurons were identified by immunohistochemistry. Postganglionic neurons were retrogradely labelled in the major pelvic ganglia. In the spinal cord, sympathetic and parasympathetic preganglionic neurons were labelled transneuronally. Presumptive interneurons were also labelled in the lower thoracic and lumbosacral spinal cord in locations consistent with what is currently known about such interneurons. In the brainstem, transneuronally labelled neurons were found in the medulla, pons and hypothalamus. Regions consistently labelled included the nucleus paragigantocellularis, parapyramidal reticular formation of the medulla, raphe pallidus, raphe magnus, A5 noradrenergic cell group, Barrington's nucleus and the paraventricular nucleus of the hypothalamus. This study confirmed previous studies from our lab and others concerning the preganglionic and postganglionic neurons innervating the penis. The number, morphology and location of these neurons were consistent with labelling seen following injection of conventional tracers into the penis. The brainstem nuclei labelled in this study were also consistent with what is currently known about the brainstem control of penile function. The labelling appeared to be highly specific, in that descending systems involved in other functions were not labelled. These results provide further evidence that the pseudorabies virus transneuronal tracing technique is a valuable method for identifying neural circuits mediating specific functions.

Immunohistochemical and behaviour pharmacological analysis of rats inoculated intranasally with vesicular stomatitis virus.

A temperature-sensitive mutant of vesicular stomatitis virus was inoculated intranasally into infant Sprague-Dawley rats aged 9 to 17 days. Rats receiving the virus at 9 days of age had an extensive spread of infection throughout the brain and the animals died after a few days. Rats inoculated at day 11 postnatally survived and the infection was limited to the olfactory pathways, hypothalamus, diagonal bands and the anterior raphe nuclei. Stereological measurements showed that the volume of infected neurons constituted 67 +/- 10% of the total neuronal volume in the dorsal raphe nucleus. Double-labelling experiments revealed that both 5-hydroxytryptamine- and substance P-immunoreactive neurons contained the virus antigen. The motor stimulant effect of amphetamine was studied at 3 months post infection. The increase in amphetamine-induced frequency and duration of rearing was significantly attenuated in infected rats and the amphetamine-induced locomotion was slightly reduced.

Transneuronal transport of herpes simplex virus from the cervical vagus to brain neurons with axonal inputs to central vagal sensory nuclei in the rat.

The recent introduction of live viruses as intra-axonal tracing agents has raised questions concerning which central neurons are transneuronally labelled after application of the virus to peripheral organs or peripheral nerves. Since the central connections of the vagus nerve have been well described using conventional neuronal tracing agents, we chose to inject Herpes Simplex Virus Type 1 into the cervical vagus of the rat. After survival times of up to 3 days the rat brains were processed immunohistochemically using a polyclonal antiserum against herpes simplex virus. Two days after injection of the virus we observed viral antigen in the area postrema and in the nucleus tractus solitarius and the dorsal motor nucleus of the vagus (dorsal vagal complex), principally ipsilaterally. At this survival time the viral antigen in the dorsal vagal complex was largely confined to glial cells. After 3 days the viral antigen was localized both in glia and in nerve cells within the dorsal vagal complex and in brain regions previously demonstrated, using conventional tracing procedures, to contain neurons with axonal projections to the dorsal vagal complex. This was true for medullary, pontine, midbrain and hypothalamic regions and for telencephalic regions including the amygdala, the bed nucleus of the stria terminalis, and the insular and medial frontal cortices. Many of the nerve cells containing viral antigen were displayed in a Golgi-like manner, with excellent visualization of the dendritic tree. Axonal processes, in contrast, were not visualized. We used co-localization studies to confirm previous findings concerning monoamine neurotransmitter-related antigens present in medullary and pontine neurons projecting to the dorsal vagal complex. After 3 days there were many Herpes Simplex Virus Type 1-containing glial cells along the intra-medullary course of the vagal rootlets. However, no viral antigen was found in brain regions containing neurons whose axons pass through the region of glial cell-labelled rootlets. Glial cells containing viral antigen were particularly numerous in brain regions known to receive an input from neurons in the area postrema and the dorsal vagal complex. Taken together with our observation concerning the early appearance of viral antigen within glial cells in the dorsal vagal complex, this suggests that when the virus reaches the axon terminal portion it is transferred to nearby glial cells and possibly enters central neurons by way of these structures.