Cathy Housman

Neuropathology of remote hypoxic-ischemic damage in the immature rat

SummaryThis study was undertaken to determine: (a) the duration of hypoxia required to produce brain damage in immature rats with unilateral carotid artery ligation (Levine technique); (b) the regions of immature brain most vulnerable to hypoxia-ischemia (HI); and (c) the neuropathology of the remote HI insult. To this end, 7-day postnatal rats, subjected to unilateral carotid artery ligation combined with hypoxia of varying durations (45, 60, 75 or 90 min), were killed at 30 days of postnatal age and their brains examined by light microscopy. The results indicated that a longer duration of HI was more likely to produce brain lesions and that the extent and severity of the lesions closely correlated with the length of HI. Shorter intervals of HI primarily damaged the cerebral cortex and hippocampus, while longer periods resulted in more extensive damage and were often associated with cavitary lesions of the cerebral hemisphere. Comparison of HI brain damage produced by the Levine technique in immature and adult rats suggested that in immature rats: (a) the cavitary lesions were common; (b) the non-cavitary cortical lesions had a tendency to show a vertical band-like distribution — a pattern never seen in adults; and (c) the lesions often showed mineralization. The similarities between these experimentally produced HI cerebral lesions and those observed in the developing human brain, such as ulegyria and porencephaly, are discussed.

The Role of Neutrophils in the Production of Hypoxic-Ischemic Brain Injury in the Neonatal Rat

Neutrophils contribute to ischemic brain injury in adult animals. The role of neutrophils in perinatal hypoxic-ischemic (HI) brain injury is unknown. Allopurinol reduces neutrophil accumulation after tissue ischemia and is protective against HI brain injury. This study was designed to investigate how neutrophils contribute to perinatal hypoxic ischemic brain injury and how neutropenia compared with allopurinol in its neuroprotective effects. A HI insult was produced in the right cerebral hemisphere of 7-d-old rats by right common carotid artery ligation and systemic hypoxia. Half the rats were rendered neutropenic with an anti-neutrophil serum (ANS). At 15 min of recovery from hypoxia, half the neutropenic and nonneutropenic rats received allopurinol (135 mg/kg, s.c.). The protective effect of the four treatment combinations was determined on brain swelling at 42 h of recovery. Neutropenia reduced brain swelling by about 70%, p < 0.01. Allopurinol alone produced similar protection so that the relatively small number of animals studied did not permit assessment of an additive effect. Neutrophil accumulation in cerebral hemispheres was measured by myeloperoxidase (MPO) activity assay and by neutrophil counts in 6-μm sections stained by MPO and ANS immunostaining. MPO activity peaked between 4 and 8 h of recovery in both hemispheres. Hemispheric neutrophil counts peaked at the end of the HI insult and again at 18 h of recovery. Neutrophils were stained within blood vessels and did not infiltrate the injured brain before infarction had occurred. We conclude that neutrophils contribute to HI brain injury in the neonate and that neutrophil depletion before the insult is neuroprotective.

Temporal evolution of neuropathologic changes in an immature rat model of cerebral hypoxia: a light microscopic study

The sequential evolution of neuropathologic changes was studied in an immature model of cerebral hypoxia-ischemia. Accordingly, 7-day postnatal rats were subjected to unilateral common carotid artery ligation combined with 2 h of hypoxia (breathing in 8% oxygen) and their brains were examined by light microscopy at recovery intervals ranging from 0 to 3 weeks. Immediately following hypoxia, a large area with a pale staining border was noted occupying most of the cerebral hemisphere ipstlateral (IL) to the occluded common carotid artery; in approximately half of the brains the dorsomedial cortex of the contralateral (CL) hemisphere was also involved. Most neurons in the pale area had nuclei containing a coarse granular condensation of chromatin. Within a few hours, the majority of neurons in the IL hemisphere had developed pyknotic nuclei and clear or eosinophilic perikarya. After 24 h these changes had evolved in the majority of brains into coagulation necrosis (infarction) in the IL hemisphere sphere and foci of selective neuronal necrosis in the CL ortex. Within a few days infarcts became partially cavirated, and by 3 weeks a smooth-walled cystic infarct had developed. Activated microglia/macrophages and reactive astrocytes were first seen at 4 and 24 h, respectively. No parenchymal neutrophilic infiltrate was seen at any time point.

Autoimmune basis for visual paraneoplastic syndrome in patients with small cell lung carcinoma. Retinal immune deposits and ablation of retinal ganglion cells

Recently, patients with visual paraneoplastic syndrome (VPS) were described, a binocular loss of vision found in patients with small cell carcinoma of the lung (SCCL). The patients have serum antibodies against a small number of discrete antigens which are shared by the retina and small cell carcinoma cells, and which are associated with cells and processes of the ganglion cell layer of the retina. Pathologic findings are presented with regard to the presence of immunoglobulins in, and the nature of the lesions in, the central nervous system of a VPS patient. The patients blood‐brain barrier was shown to be compromised, as demonstrated by the finding of high immunoglobulin levels in the cerebrospinal fluid and immune deposits in the retina. It is further shown that within the central nervous system only the retina and optic nerve show any tissue damage with the specific loss of retinal ganglion cells and their processes. The findings support the hypothesis of an autoimmune cause for this remote effect of cancer.

Effect of seizures on cerebral hypoxic–ischemic lesions in immature rats

The present investigation was designed to study the effect of chemically induced seizures on cerebral hypoxic-ischemic (HI) damage in immature animals. Accordingly, cerebral HI was produced in 7-day postnatal (p7) rats and p13 rats by combined unilateral common carotid artery ligation and hypoxia with 8% oxygen. Seizures were induced chemically by the subcutaneous injection of kainic acid (KA) or inhalation of flurothyl vapor. Three types of experiments were conducted in each age group and for each convulsant. In some animals (group 1), seizures were produced at 24 h and again at 6 h prior to HI. In groups 2 and 3, seizures were induced 2 h or 24 h post HI, respectively. The results indicate that in group 1 animals, the first seizure significantly reduced duration of the second seizure challenge 18 h later at both p7 and p13 (p=0.001). Histologic examination of brains of animals in group 1 subjected to seizures prior to HI and their HI-only controls showed that seizures prior to HI conferred protection against cerebral damage. This effect was significant for flurothyl seizures in p13 rats for all cerebral regions, especially hippocampal CA1 (p=0.0004), and in p7 rats for hippocampus (p=0.04) and particularly cerebral cortex (p=0.007). For KA seizures, the protective effect was only significant in p13 rats and was limited to hippocampal CA regions and subiculum (p=0.0009). Histologic assessment of cerebral lesions of p7 and p13 rats in the other two groups showed no significant difference between the animals subjected to seizures 2 h or 24 h post HI and their HI-only controls (p>0.05). In conclusion, the results of the present study provide no evidence that seizures in early postnatal development aggravate pre-existing cerebral HI damage. They do suggest that seizures prior to HI or prior to a second seizure confer tolerance to both conditions.

The effect of focal cerebral cooling on perinatal hypoxic-ischemic brain damage

We describe a method of focal cooling of the head and its effects on hypoxic-ischemic cerebral damage in neonatal rat. Focal cooling of the head was obtained by positioning a catheter under the scalp ipsilateral to the ligated common carotid artery and by running cold water through the catheter during 2 h of systemic hypoxia. Hypoxia was produced in neonatal rats by breathing 8% oxygen for 2 h in a 37°C chamber. Animals underwent focal cooling with ipsilateral scalp temperatures ranging from 22°C to 35°C. Temperature recordings from the ipsilateral scalp, cerebral hemisphere (dorsal hippocampus) and core (rectal) were obtained. The results suggest that the method is effective in cooling of brain and also to a lesser extent in lowering of the core temperature. At a mean scalp temperature of 28°C, mean hippocampal temperature in hypoxic rat was 29.5°C and mean core temperature in hypoxic rat was 32.8°C. At a lower scalp temperature of 22°C, mean hippocampal temperature in hypoxic rat was 24.7°C and mean core temperature was 31.3°C. Neuropathologic examination 3–4 days following hypoxia-ischemia showed that focal cooling with a scalp temperature of lower than 28°C completely protected from brain damage, and that there was a trend towards greater damage with higher scalp temperatures.

Spinal cord abnormalities in caudal regression syndrome

SummaryCaudal regression syndrome includes malformations ranging from mild forms of sacral agenesis to severe limb anomalies referred to as sirenomelia. The latter, in addition to sacral anomalies, shows malformed single lower limb and agenesis of rectum and genitourinary tracts. We report the neuropathologic examination in four infants, three with sirenomelia and one with lumbosacral agenesis. Brain and spinal cord were normal except for the structures in the caudal region of the spinal cord that were abnormal in all four cases. The first sirenomelic case with a mild sacral hypoplasia had only minor fusion of a few sacral roots and a slightly low-positioned conus medullaris. The second sirenomelic case with an intermediate degree of sacral hypoplasia had fusion of some of the sacral roots and ganglia, spinal ganglion cell heterotopias, filar lipoma and absence of the last sacral roots and ganglia. The third sirenomelic case with a severe degree of sacral hypoplasia showed additional tethering of the spinal cord. Case four with the agenesis of the lumbosacral spine had a total lack of the lumbosacral spinal cord, and dysplasia of the T11 and T12 cord segments. These findings suggest that the extent of anomalies of the caudal spinal cord structures in the caudal regression syndrome are roughly proportional to the anomalies of the vertebral column, and that they may constitute some of the main components of this syndrome.

Effect of anesthetics on neuropathologic sequelae of status epilepticus in rats

&NA; We compared the efficacy of four different classes of anesthetics to arrest the progression of brain damage after chemoconvulsant‐induced seizures in rats. In two series of experiments, ventilated, paralyzed Long‐Evans rats were subjected to 30 or 45 min of continuous seizures induced by intravenous (IV) mercaptopropionic acid (MPA) or inhaled flurothyl, respectively. In the first series, seizures produced with MPA were treated with: 1) thiopental, 15 mg/kg IV bolus (controls); 2) thiopental, 27 mg/kg IV followed by 20.9 mg·kg−1·h−1 for 2 h; 3) isoflurane 4% inhaled concentration for 1 min followed by 1%‐2% for 2 h; 4) ketamine 30 mg/kg IV followed by 9.12 mg·kg−1·h−1 for 2 h; 5) midazolam 25 mg/kg IV followed by 9.7 mg·kg−1·h−1 for 2 h. In a second series, seizures were produced by flurothyl and, based on suggestive results in the MPA series, control rats were compared with rats receiving midazolam 25 mg/kg IV followed by 9.7 mg·kg−1·h−1. In all instances, seizure activity, recorded by electroencephalograph, stopped with anesthetic treatment. In MPA‐treated rats extranigral damage was mild, with no differences apparent between anesthetics. Control animals sustained severe lesions in the substantia nigra pars reticulata (SNPR). No statistically significant differences between anesthetic groups were present, although an effect was suggested for midazolam to decrease SNPR lesional area (P = 0.06). In flurothyl‐treated rats, there were significant reductions in SNPR neuropathologic grade (P = 0.025) and lesional area (P = 0.025) with midazolam. We conclude that midazolam attenuates postseizure SNPR damage in rats. (Anesth Analg 1993;77:330‐7)

Substantia nigra lesions in mercaptopropionic acid induced status epilepticus a light and electron microscopic study

SummaryLight microscopic and ultrastructural changes of substantia nigra were studied in paralyzed ventilated rats with status epilepticus induced by mercaptopropionic acid. Some rats were killed at the end of seizure activity and others were examined in varying intervals after the arrest of seizure. The earliest changes were reduction in the size of the neuronal nuclei and chromatin clumping followed by simultaneous distention of axons and dendrites. There was also enlargement of the neuronal perikarya associated with microvacuolation. This neuronal microvacuolation corresponded ultrastructurally to swollen mitochondria with disrupted cristae. These changes were followed by progressive neuronal shrinkage and astrocytic swelling. The swollen astrocytic processes together with swollen neurites gave a spongy appearance to the involved area. The lesion thereafter progressively enlarged and evolved into an area of frank necrosis containing abundant macrophages. This lesion is morphologically different from that produced in cortex and hippocampus by seizure activity or due to the direct effect of excitotoxins. The significance of substantia nigra pars reticularis changes and their pathogenesis are discussed.