Contrasting patterns of virus spread and neuropathology following microinjection of herpes simplex virus into the hippocampus or cerebellum of mice.

Two strains of herpes simplex virus type 1 (HSV) were microinjected into either the hippocampus or cerebellum of two different mouse strains. Immunoperoxidase staining revealed rapid and extensive spread of virus within the hippocampus and certain of its afferent connections. In contrast, only scattered peroxidase positive cells were observed following cerebellar inoculation. Extensive lesions were observed only in animals surviving intrahippocampal inoculations. These results suggest that localization of the pathological process in HSV encephalitis is due in part to a selective vulnerability of telencephalic or limbic structures.

The production of focal herpes encephalitis in mice by stereotaxic inoculation of virus. Anatomical and behavioral effects.

A low virulence strain of herpes simplex type 1 was microinjected into the hippocampus of BALB/c mice. Intense replication of virus at the inoculum site was followed by spread of viral antigen to the afferent connections of the hippocampus. Surviving animals showed focal damage of limbic structures and specific behavioral abnormalities generally consistent with hippocampal damage. This procedure thus produces an animal model which more closely resembles human herpes encephalitis than those previously reported.

Host genetics and the behavioral sequelae to herpes encephalitis in mice.

The effects of intracerebral infection with herpes simplex virus on the subsequent behavior of two strains of mice were examined. Infected Nya:NYLAR mice were hyperactive and did not show any deficits in the acquisition or reversal of a spatial learning task. In contrast, infected Nya:(SW) mice were hypoactive and made more errors than controls during both phases of the learning tasks. These differences in the nature of the sequelae to infection were related to an overall higher virus titer in the brains of Nya:(SW) mice, an effect particularly marked in the cerebral hemispheres. The results suggest that herpes encephalitis may produce a variety of behavioral syndromes, depending in part on the genetic background of the host. The relevance of these findings to clinical disorders produced by viral infection is discussed.

Disappearance of scrapie virus from tissues of the mouse.

Examination of newborn mice, inoculated intraperitoneally with high doses of scrapie virus, revealed that the virus could not be reisolated from their tissues after about 1 week following inoculation, until almost 1 year later. The inoculum was rapidly removed and was not detectable, although the animals became latently infected. Homogenization of whole inoculated newborn animals showed that only about 3% of virus could be recovered by the 2nd day postinoculation (p.i.). During the first 6 days p.i. the half-life of titratable scrapie was about 15 h. A further study of the rate of disappearance of clarified scrapie virus from blood after intravenous inoculation showed an even more rapid disappearance, with a half-life of 5.16 min. Prior treatment of the recipient mice with either carbon black or silica to block the reticuloendothelial system (RES) did not affect the rate of disappearance. It was concluded that the mouse possesses a very efficient means of scrapie virus removal from the blood which is not dependent upon an active RES. However, after 1 h the rate of disappearance changed dramatically; the residual virus level was very stable, with no significant drop during the next 21 h. This finding was compatible with the possibility that two forms of scrapie virus, with different removal rates, coexisted in the inoculum. Silica treatment caused a shortened scrapie incubation period.

Binding of herpes simplex virus to regional areas of the rodent brain.

The binding of 3H-thymidine labeled herpes simplex virus to homogenates of rodent brain regions and liver was examined. The results indicated that binding sites in the brain are distributed in a non-uniform manner, the specific pattern observed depending upon the age of the animal. In addition, binding was found to be reduced by pretreatment of the labeled virus with specific antiserum or trypsin. These results suggest that the distribution of herpes simplex virus receptors is one of the factors determining neurotropism and the localization of infection within the brain.

Behavioral effects of low-level perinatal exposure to toluene in mice.

The effects of toluene on several behavioral measures were examined in mice exposed pre- and postnatally and continuously through behavioral testing. The test animals were the offspring of dams given solutions of toluene in drinking water (16,80 or 400 ppm) during pregnancy and lactation. After weaning, the test mice were maintained at the same toluene exposure concentrations. At 35 days of age decreased habituation of open-field activity was seen in the 400-ppm group. This effect was not found in mice which received a single intraperitoneal injection of toluene (14.4 or 72 mg/kg) in sesame seed oil. Rotorod performance, measured at 45-55 days of age, was depressed in all exposed groups. No effects of toluene exposure were seen on maternal fluid consumption, offspring mortality rate, development of eye or ear openings, or surface-righting response.

Regional tyrosine hydroxylase and choline acetyltransferase concentrations in the brains of lymphocytic choriomeningitis-infected mice.

The neurotransmitter biosynthesis enzymes tyrosine hydroxylase and choline acetyltransferase were investigated in selected brain areas of Nya : NYLAR mice infected with lymphocytic choriomeningitis (LCM) virus. Statistically significant alterations in the concentrations of both enzymes occurred in the olfactory, caudate, and neocortical regions at 5 days postinfection. No such alterations occurred in mice given cytoxan (150 mg/kg) 3 days postinfection and examined 5 days postinfection. At 10 days postinfection, however, the cytoxan-treated animals had significantly altered enzyme concentrations in the olfactory region, though not in the caudate or neocortex. This alteration appeared to be transitory, since it was not found in cytoxan-treated animals 60 days postinfection. A possible explanation is that virus production or interference in a brain region cycles over a period of hours or days. Still undetermined is whether these neurochemical changes are a primary effect of the virus or a secondary effect due to the immune response. It is noteworthy that cytoxan caused a marked increase in the enzyme activities studied in most of the brain areas.

Early behavioral abnormalities in mice due to scrapie virus encephalopathy.

The behavioral effects of scrapie virus infection, a slow degenerative disease of the central nervous system, were examined in mice. Testing was conducted at 50, 100, and 150 days postinfection and included open-field behavior, Y-maze alternation and activity, and two-way shuttle-box avoidance. The behavioral pathology was found to be task-specific rather than of a global nature. Furthermore, the effects observed could be classified as either early or late components of the disease. The relevance of this animal model to human presenile dementias is discussed.

Locomotor effects of catecholaminergic drugs on herpes-infected mice.

Changes in spontaneous, amphetamine (AMP) and apomorphine (APO) induced locomotor activity were used to assess the effects of central nervous system (CNS) infection with herpes type 1 virus. A dual herpesvirus inoculation procedure was used in which the animals received an immunizing footpad inoculation followed at 2 weeks by an identical intracerebral challenge. Four weeks later the animals were tested with intraperitoneal injections of saline or d-l-amphatmine (0.5 and 2.0 mg/kg). When footpad herpes-virus was given via one or two injections, it had no effect on spontaneous or AMP induced activity. When food-pad-intracerebral herpes mice were tested 28-33 days post intracerebral inoculation, they demonstrated depressed AMP-induced but not spontaneous activity. AMP at a dosage of 5.0 mg/kg overcame the herpesvirus blockage of 0.5 and 2.0 mg/kg AMP induced activity. Intraperitoneal injection of APO in day 3 post-IC animals produced less suppression of activity in the virus group than in the controls. These results suggest that non-fatal CNS herpes infection produces hypoactivity, in contrast to thehyperactivity during acute fatal CNS herpes encephalitis (Lycke & Roos, 1975), and that the effect may be due to alterations in postsynaptic receptor sensitivity.

Effects of herpes virus and amphetamines on locomotor activity.

Altered levels of catecholamines (dopamine or norepinephrine) or perturbations in their relationship to other neurotransmitter systems (particularly the cholinergic system) have been suggested as causal factors in several human mental disorders. Herpes simplex virus infection of the central nervous system alters catecholamine metabolism and has been suggested to be a causative factor in certain forms of mental illness. As a means of studying chronic HSV infection, we have developed a dual inoculation procedure employing footpad inoculation followed at a 2-week interval by intracerebral challenge with an identical HSV inoculation. In addition, we have employed daily, peripheral injections of d-l-amphetamine to further aid in the study of HSV effects on behavior. Central HSV infection, in the immunized animal, led to a significant decrease in locomotor activity and to an alteration in the response of the infected animal to amphetamine (a shifting of the dose response curve to the right). These results suggest that chronic HSV infection of the CNS leads to a decrease in activity of the catecholaminergic system that may involve either alterations in the release of dopamine and norepinephrine or their effect on postsynaptic receptors.

Alterations in behavior resulting from persistent lymphocytic choriomeningitis virus infection.

We have studied behavioral change in mice persistently infected as neonates with lymphocytic choriomeningitis virus. Open-field, electric shock startle, and locomotor behavior were measured on these persistently infected mice and normal controls when they were 2--6 months of age. The infected mice exhibited significantly greater latency to move in the open-field, were more sensitive to low current electric shock and were slightly less active when tested for 4 days in running wheels. Immunofluorescent examination of adult mouse brain 14 days after the initiation of persistent infection with cyclophosphamide (given 3 days after virus) demonstrated viral antigen in hippocampal and olfactory tissue. Behavioral results were interpreted in terms of direct effects of virus on the brain, perhaps altering certain critical neurophysiologic and neurochemical parameters. The possible relationship between limbic system pathology and human mental disorder is raised.

Virus-induced behavioral alteration of mice.

Neonatal mice were inoculated intracerebrally with lymphocytic choriomeningitis virus (LCM). These mice developed long-term persistent tolerant infections and when tested at 3.5 to 6.0 months of age they showed significant increases in behavioral latency when subjected to open-field tests, and significant decreases in the current level required to elicit to startle response and in locomotor activity in a running wheel. Comparable results were obtained with mice in which persistent infection was induced at 8 weeks of age and which were tested at 3.5 to 6.0 months of age. It was concluded that mice infected with LCM at birth or as adults exhibited long-lasting behavioral abnormalities.

Latent form of Scrapie virus: a new factor in slow-virus disease.

Scrapie is an unusual slow-virus disease of sheep which is very much like kuru and Creutzfeldt-Jakob disease, both fatal, slow neuological diseases of man. In mice, scrapie usually has an incubation period of about 6 months. Intraperitoneal inoculation of virus particles into newborn mice caused no disease, and there was no detectable virus replication for 1 year, but high titers of scrapie were present in the spleen and brain at 18 months. Virus replication occurred in mice injected from 4 days after birth by all inoculation routes, wheter or not they were injected with scrapie virus on day 0. The results suggest that scrapie virus replicates peripherally only in thymocytes, which are not present in mice until a few days after birth. The latent state suggests that the comparable human diseases could appear in later life as a result of perinatal infection. In some respects these diseases resemble premature senility.

Experimental animals and in vitro systems in the study of lymphocytic choriomeningitis virus.

The history of lymphocytic choriomeningitis (LCM) research is reviewed from the point of view of whether the main discoveries concerning LCM pathogenesis have stemmed from animal or in vitro research methods. Most of the results initially stemmed from animal experiments, but in recent years recourse has increasingly been made to in vitro techniques to confirm and amplify the animal-based conclusions.Different research approaches are discussed and an attempt is made to assess the role of in vitro versus animal methods in obtaining knowledge on this virus. The same analysis is applied to the future needs and trends in arenavirus research.