A Model of Methotrexate Encephalopathy: Neurotransmitter and Pathologic Abnormalities

Methotrexate may cause seizures, dementia, and leukoencephalopathy when given in toxic doses to children with leukemia or solid tumors. Even in therapeutic doses, treatment with this drug is associated with an increased incidence of seizures in children with leukemia. To study mechanisms of injury, juvenile rats were given multiple intraventricular injections of methotrexate and the brains were analyzed for histopathology and biogenic amine metabolites of dopamine and serotonin. Disruption of monoamine metabolism has been proposed as a cause of brain dysfunction from this chemotherapy. Multiple injections (1 or 2 mg/kg) produced convulsions in an increasingly larger percentage of animals at higher cumulative doses, and five doses produced the neuropathological changes seen in human leukoencephalopathy. A single dose reduced the concentration of brain metabolites of dopamine, but not serotonin, six hours later. The effect was less pronounced after five doses. This rodent model should be useful for studying the metabolic basis of methotrexate encephalopathy. (J Child Neurol 1986;1:351-357)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67332/2/10.1177_088307388600100406.pd

Impact of indolent inflammation on neonatal hypoxicâ ischemic brain injury in mice

This report describes a new experimental model to evaluate the effect of a recurrent systemic inflammatory challenge, after cerebral hypoxiaâ ischemia in immature mice, on the progression of brain injury. Treatment with a low dose of lipopolysaccharide (E. coli O55:B5, 0.2 mg/kg for 3 days, then 0.1 mg/kg for 2 days) daily for 5 days after unilateral cerebral hypoxiaâ ischemia (right carotid ligation followed by 35 min in 10% O2) in 10â dayâ old mice resulted in increased right forebrain tissue damage (35.6% reduction in right hemisphere volume compared to 20.6% reduction in salineâ injected controls), in bilateral reductions in corpus callosum area (by 12%) and myelin basic protein immunostaining (by 19%), and in suppression of injuryâ related right subventricular zone cellular proliferation. The postâ hypoxicâ ischemic lipopolysaccharide regimen that amplified brain injury was not associated with increased mortality, nor with changes in body temperature, weight gain or blood glucose concentrations. The results of the present study demonstrate that systemic inflammation influences the evolution of tissue injury after neonatal cerebral hypoxiaâ ischemia and may also impair potential recovery mechanisms.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152966/1/jdnjijdevneu200708005.pd

Hypoxic–ischemic injury results in acute disruption of myelin gene expression and death of oligodendroglial precursors in neonatal mice

Studies of ischemic brain injury in neonatal rodents have focused upon the pathophysiology of neuronal damage. Much less consideration has been given to white matter injury, even though it is a major contributor to chronic neurological dysfunction in children. In the human neonate, particularly in those born prematurely, periventricular white matter is highly susceptible to hypoxic–ischemic (H–I) injury. To understand the basis for this selective vulnerability, we examined myelin gene expression and cell death in the subventricular layer and the surrounding white matter of neonatal mice following H–I insult. Using an in situ hybridization technique that gives high resolution and is very sensitive, we examined myelin basic protein and proteolipid protein gene expression three and twenty‐four hours after a H–I insult. To elicit unilateral forebrain hypoxic and ischemic injury, 9–10‐day‐old mice underwent right carotid artery ligation followed by timed (40–70 min) exposure to 10% oxygen. Twenty‐four hours following H–I, myelin basic protein and proteolipid protein transcripts were markedly reduced in striatum, external capsule, fornix, and corpus callosum in the injured side. Three hours after lesioning (ligation+70 min hypoxic exposure) myelin basic protein gene transcripts were visibly reduced in the ipsilateral white matter tracts. Interestingly, some cells in the subventricular layer expressed proteolipid protein transcripts, and 3 h after a H–I insult they were degenerating in the injured but not contralateral side. TUNEL staining showed an increase in the number of positive cells in the injured subventricular layer and corpus callosum but the adjacent striatum did not show a corresponding change in the number of TUNEL labeled cells. Ultrastructural studies of the subventricular zone and corpus callosum 3 h after H–I revealed that many subventricular cells, glial cells in the corpus callosum, and callosal axons in the injured side had already degenerated. However, the subventricular cells, glia and axons in the contralateral corpus callosum were spared. Many cells in the injured corpus callosum exhibited a apoptotic morphology; yet more mature oligodendrocytes in this region appeared normal. Our results show that a H–I insult causes a surprisingly swift and dramatic degenerative response in the subventricular layer and adjacent white matter. Within 3 h after H–I, the programmed cell death cascade was initiated; internucleosomal DNA degradation took place in subventricular and glial cells; oligodendrocyte progenitors died and axonal degeneration in the ipsilateral corpus callosum was extensive. The swiftness of the subventricular and glial cell degeneration suggests the H–I insult directly targets glia, as well as neurons, and raises the provocative question of whether glia exert damaging effects upon neurons and axons. Since the severity of the H–I insult can be modulated by varying the duration of hypoxia, the model is ideal to study whether oligodendrocyte progenitors are more susceptible to death than mature oligodendrocytes, whether mature oligodendrocytes de‐differentiate and then are induced to remyelinate surviving axons, and/or whether oligodendrocyte progenitors in the subventricular layer can be stimulated to proliferate, migrate, and remyelinate the surviving axons.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152542/1/jdns0736574800000757.pd

Impact of indolent inflammation on neonatal hypoxic‐ischemic brain injury in mice

This report describes a new experimental model to evaluate the effect of a recurrent systemic inflammatory challenge, after cerebral hypoxia-ischemia in immature mice, on the progression of brain injury. Treatment with a low dose of lipopolysaccharide (E. coli O55:B5, 0.2 mg/kg for 3 days, then 0.1 mg/kg for 2 days) daily for 5 days after unilateral cerebral hypoxia-ischemia (right carotid ligation followed by 35 min in 10% O(2)) in 10-day-old mice resulted in increased right forebrain tissue damage (35.6% reduction in right hemisphere volume compared to 20.6% reduction in saline-injected controls), in bilateral reductions in corpus callosum area (by 12%) and myelin basic protein immunostaining (by 19%), and in suppression of injury-related right subventricular zone cellular proliferation. The post-hypoxic-ischemic lipopolysaccharide regimen that amplified brain injury was not associated with increased mortality, nor with changes in body temperature, weight gain or blood glucose concentrations. The results of the present study demonstrate that systemic inflammation influences the evolution of tissue injury after neonatal cerebral hypoxia-ischemia and may also impair potential recovery mechanisms