Multi-factorial specification of virus-host interactions: studies with strains of Venezuelan equine encephalomyelitis virus in mice

Cerebral serotonin in viral encephalitis

In order to evaluate central serotonergic function during viral encephalitis biochemical, behavioural and immunohistofluorescence studies were carried out. Mice were inoculated with the moderate virulent strain of venezuelan equine encephalomyelitis virus, Pixuna. Signs of encephalitis were observed in 50-60% of infected animals. Levels of serotonin and 5-hydroxyindolacetic acid, and the ratio of the indolamine and its metabolite in raphe and cortex did not change with respect to sham-inoculated mice. A differential decrease in turnover rate by pharmacological methods, such as pargyline, p-chlorophenylalanine and probenecid administration, was observed in raphe and cortex. The ratio serotonin turnover rate/steady state concentration of serotonin was only decreased in the raphe of sick animals. The response to 5-methoxy-N,N-dimethyltryptamine was greater in infected animals. The duration of immobility in the swim test was shorter in the infected group. A greater number of viral antigen particles was localized in raphe and periraphe areas than in cortex, brain stem or striatum. The results suggest a serotonin presynaptic deficit, a postsynaptic hyperreactivity of serotonin system, and a region-selective distribution of the virus.

Behavioural effects produced in mice infected with venezuelan equine encephalomyelitis virus

Pixuna, a strain of intermediate virulence of venezuelan equine encephalomyelitis virus, was inoculated intracranially to 24-day-old mice. Signs of encephalitis were present in 60% of the animals between 6 and 9 days with a maximum at 7 days postinoculation. The rest of the infected mice did not show clinical signs of encephalitis. In order to study the functional state of serotonergic systems a series of tests susceptible to modifications by serotonin activity were carried out. Locomotor activity was measured in an open field test. Virus-inoculated animals presented a variety of changes in their locomotor behavior at various days postinoculation with respect to the sham-inoculated group, however, they were not significant. Central serotonergic function was examined by the production of the serotonergic syndrome with the receptor agonist, 5-methoxy-N,N-dimethyltryptamine and the precursor, 5-hydroxytryptophan, both administered 4 days after the inoculation. The dose of the agonists was established by a prior drug-response analysis. Intensity of the syndrome was significantly higher in infected mice than in the sham-inoculated group only in 5-methoxy-N,N-dimethyltryptamine-treated animals. The behaviour in the swim test was also measured. Duration of immobility was much shorter in infected than in control mice. The decrease in central serotonin turnover previously reported might be responsible for the modification in locomotor behaviour and for the supersensitivity of serotonin receptors observed in infected mice.

Serotonin turnover rate in raphe and cortex of mice infected with Venezuelan equine encephalomyelitis virus

The turnover of serotonin (5HT) was determined in the raphe area and cortex of mice infected with Pixuna, a strain of intermediate virulence of Venezuelan equine encephalomyelitis virus (VEEV). NMRI-mice, 24 days old, were inoculated intracerebrally (ic) with 300 LD50 of the virus. The animals were sacrificed 4, 7, 15, 21, 30, and 60 days postinoculation. 5HT and 5-hydroxyindoleacetic acid (5HIAA) in raphe and cortex were determined by high performance liquid chromatography (HPLC) with electrochemical detection. Turnover rate of 5HT was determined by the administration of pargyline, p-chlorophenylalanine, and probenecid. The content of 5HT or 5HIAA and 5HT/5HIAA ratios were not significantly different in infected compared with control mice. However, a decrease of 5HT turnover rate, determined after pargyline treatment, was observed in the raphe and not in the cortex of infected mice at 4 and 7 days after the inoculation. The turnover rate/(5HT)0 in raphe is decreased in infected mice with signs of illness, suggesting a lower density of 5HT innervation in this brain area. The administration of p-chlorophenylalanine and probenecid showed that the cortex is also affected, but the synthesis is less modified than metabolism or elimination. Cell bodies of 5HT neurons seem to be more susceptible than projections to infection by Pixuna strain of VEEV.

Replication of alphaviruses in cultures of donkey monocytes

Representative strains of Venezuelan equine encephalitis virus (VEEV) and Eastern equine encephalitis virus (EEEV) were compared for their ability to grow in cultures of unstimulated leucocytes and monocytes derived from donkey peripheral blood. Replication of epizootic and vaccine strains of VEEV, but not of enzootic strains was observed in this system. Only a minority of monocytes supported virus replication as detected by immunofluorescence, electron microscopy and infectious center assays. EEEV did not appear to replicate in this cell system although virus attached to and was internalized by monocytes.

Influence of Venezuelan equine encephalomyelitis virus on catecholamine metabolism in mouse CNS: early changes in turnover rates and content

The influence of two strains of Venezuelan equine encephalomyelitis virus on catecholamine metabolism in the central nervous system (CNS) of the mouse was studied by the intracranial inoculation of NMRI-IVIC mice, 24 days old. Doses of 300 LD50 of the moderately virulent Pixuna strain and 10(4) LD50 of the nonvirulent TC-83 strain were used. The animals were sacrificed 4, 7, 12, and 18 days after the inoculation, and the CNS contents of dopamine, norepinephrine, and adrenaline were determined by a radioenzymatic method. The turnover of these compounds was studied with the aid of the enzymatic inhibitors pargyline and alpha-methyl tyrosine. With the Pixuna strain a decrease in the level and turnover of catecholamines was observed in all eight brain areas studied: cerebellum, pons-medulla, hypothalamus, mesencephalon, striatum, olfactory bulb-tuberculum, hippocampus, and cerebral cortex. In some regions the levels returned to normal in 12-18 days, but in the striatum, mesencephalon, hypothalamus, and olfactory bulb-tuberculum, recovery was slower and required at least 18 days after inoculation. The levels of catecholamines in the brain of mice inoculated with the nonvirulent TC-83 strain were not modified, but there was a decrease in the turnover.

Virion polypeptide heterogeneity among virulent and avirulent strains of eastern equine encephalitis (EEE) virus

Comparative analysis of structural virion polypeptides of 24 selected EEE virus strains, representing North and South American types, was performed by one-dimensional discontinuous sodium dodecyl sulfate (SDS)-polyacrylamide-gel electrophoresis (PAGE). The structural proteins of different EEE virus isolates, resolved by this method, exhibited mol.wts. values in the range of 57-60 X 10(3) for (E-1), 51-54 X 10(3) for (E-2) and 35-38 X 10(3) daltons for the core (NP) nucleocapsid. The exception was the South American human lethal virus, TRVL-89287 strain, which was shown to possess only a single envelope glycoprotein. The high molecular weight envelope (E-1) glycoprotein species was absent or co-migrated adjacent to the smaller envelope (E-2) glycoprotein. Results indicated similarities in the core (NP) proteins, however greater variability in the envelope (E-/ and/or E-2) glycoproteins. Based on these variations seven distinct profiles could be observed among the EEE virus strain studied. The classification based on the patterns of structural polypeptides obtained by SDS-PAGE of these strains does not correlate well with any other previously reported in vitro characteristics (antigenic subtypes, HTP elution profiles) nor with the in vivo virulence markers.