Article Figures & Data
Figures
- Fig. 1.
The circuitry analyzed in the present study is diagrammed schematically in a sagittal view of the rodent brain. Retrograde, transsynaptic infection of the CNS by PRV can take place via two pathways following injection of virus into stomach muscles. Neurons from two subdivisions of the autonomic nervous system innervate the stomach. Axon terminals provide sites of entry, and the axons provide conduits for viral infection of the cell bodies of these neurons in the brain stem. The most direct infection is achieved by retrograde infection of caudal brain stem neurons in the DMV. However, retrograde transsynaptic passage of virus through a disynaptic circuit involving pseudounipolar neurons in the celiac ganglion also leads to infection of sympathetic preganglionic neurons in the intermediolateral cell group (IML) in the spinal cord. Retrograde transsynaptic passage of virus from the DMV and IML produces an infection of other cell groups in the brain stem and forebrain. The organization of this circuitry is described in greater detail in the Materials and Methods section. The lines labeled A, B, and C define the planes of section used in subsequent illustrations. Abbreviations: AP, area postrema; BNST, bed nucleus of stria terminalis; CeAm, central nucleus of the amygdala; NTS, nucleus of the solitary tract; PT, paratrigeminal nucleus; PVN, paraventricular hypothalmic nucleus; IC, insular cortex; RF, reticular formation. The subfornical organ (SFO) lies in the C-plane, just above the BNST.
- Fig. 2.
Low-power photomicrographs illustrate the progression of infection in the caudal brainstem 60, 72, and 96 h following injection of strains of PRV. Negative images, where viral immunoreactivity is revealed as a white signal on a dark background, are shown. PRV-Becker (PRV-Be), a wild-type strain of PRV, infects a large number of neurons in the DVC (DMV, NTS, and AP) 60 h postinoculation, but only scattered neurons are infected in the ventrolateral portion of the medulla. Animals infected by this virus did not survive beyond 67 h in this study. Photomicrographs in other rows illustrate the patterns of infection produced by PRV-91, PRV-25, PRV-26, and PRV-Bartha (PRV-Ba). PRV-Ba, an attenuated vaccine strain harboring a number of deletions and mutations, produces the most-extensive infection at all postinoculation intervals. PRV-25, PRV-26, and PRV-91 infect a subset of the circuitry infected by PRV-Ba, but they still produce extensive retrograde infections. RF, reticular formation.
- Fig. 3.
The extents of retrograde transsynaptic infection of the forebrain produced by injection of PRV mutants into the wall of the stomach are illustrated. Low-power, negative images, where circumscribed areas of viral immunoreactivity are revealed as a white signal on a dark background, are shown. Vertical columns illustrate selected coronal-plane sections obtained at the levels of B (right column) and C (left column) illustrated in Fig. 1. Horizontal rows illustrate the pattern of infection produced by PRV-25, PRV-26, PRV-91, and PRV-Bartha (PRV-Ba) 96 h following stomach inoculation. Animals injected with PRV-Becker did not survive that long and could not be analyzed. The most-extensive infection is produced by PRV-Ba. The other mutants infect a subset of the neurons infected by PRV-Ba. IC, insular cortex.
- Fig. 4.
High-power photomicrographs illustrate the extents of infection in primary neurons of the DMV and synaptically connected second-order neurons of the NTS 60 h after inoculation of the stomach with different strains of PRV. Positive images, where viral immunoreactivity in individual neurons is detected as a black signal on a light background, are shown. The most-extensive infection is observed in animals infected with PRV-Becker (Be), which also produces the most-pronounced neuropathology, indicated by extensive cytopathic effect. PRV-Bartha (Ba) also infects a large number of DMV and NTS neurons at this time after inoculation, but both the extent of infection and the degree of cytopathology are reduced relative to those produced by PRV-Becker. PRV-25, PRV-26, and PRV-91 infect a subset of the neurons infected by PRV-Ba. The schematic diagram in the lower right corner illustrates the organization of synaptic connections through which this circuitry is infected. CC, corpus callosum; XII, 12th cranial nerve. Calibration bar = 100 mm.
- Fig. 5.
The distributions of infected neurons in the PVN observed 60 h following inoculation of the stomach with PRV-Becker (Be), PRV-91, PRV-25, PRV-26, and PRV-Bartha (Ba) are illustrated. Positive images, where viral immunoreactivity in individual neurons is detected as a black signal on a light background, are shown. PRV-Ba produces the most-extensive infection of neurons in the medial parvicellular subdivision of the PVN (mpPVN) that give rise to descending projections to autonomic cell groups in the brain stem (DMV) and spinal cord (IML). The schematic diagram in the lower right panel illustrates the subdivisions of this hypothalamic nucleus that is synaptically connected to the DMC in the brain stem. Other strains of virus produce a more restricted pattern of infection. Calibration bar = 200 mm. dpPVN, dorsal parvicellular subdivision of the PVN (dpPVN).
- Fig. 6.
The distributions of infected neurons in the PVN observed 72 h following inoculation of the stomach with PRV-91, PRV-25, PRV-26, and PRV-Bartha (Ba) are illustrated. Positive images, where viral immunoreactivity in individual neurons is detected as a black signal on a light background, are shown. Animals infected with PRV-Becker (Be) did not survive beyond 67 h in this study and could not be analyzed at this time after infection. All of the mutants infect a substantial number of neurons in the medial parvicellular subdivision of the PVN (mpPVN) as well as scattered neurons in the dorsal parvicellular subdivision (dpPVN). Both of these cell groups give rise to descending projections to autonomic nuclei in the brain stem and spinal cord. The schematic diagram illustrates the subdivisions of this hypothalamic nucleus. Calibration bar = 200 mm.
- Fig. 7.
The distributions of infected neurons in the PVN observed 96 h following inoculation of the stomach with PRV-91, PRV-25, PRV-26, and PRV-Bartha (Ba) are illustrated. Positive images, where viral immunoreactivity in individual neurons is detected as a black signal on a light background, are shown. Animals infected with PRV-Becker (Be) did not survive beyond 67 h in this study and could not be analyzed at this late time after infection. All of the mutants infect large numbers of neurons throughout the medial and dorsal parvicellular subdivisions of the nucleus (mpPVN and dpPVN, respectively) at this postinoculation interval. The schematic diagram illustrates the subdivisions of this hypothalamic nucleus. Calibration bar = 200 mm.
Tables
- Table 1.
Animals used in this study
Virus Stock titer No. of animalsa examined at: 60 h 72 h 84 h 93 h 96 h PRV-Be 3.5 × 108 4 Noneb None None None PRV-Be 4.0 × 108 2 3 1 2 1 PRV-25 3.5 × 108 2 3c 4 2 1 PRV-26 2.3 × 108 2 3d 3 2 3 PRV-91 3.0 × 108 1 3 1 1 1 a Numbers of animals that were euthanized and brains that were analyzed at the indicated times postinfection.
b No animals infected with PRV-Becker survived more than 67 h postinfection.
c Four animals infected with PRV-25 died unexpectedly at approximately 72 h postinfection, and these tissues were not suitable for processing. They are not included in the numbers shown in the table.
d One animal infected with PRV-26 died unexpectedly at approximately 72 h postinfection, and this tissue was not suitable for processing. This animal is not included in the number shown in the table.
