Epilepsy is resistant to drug treatment in about one-third of cases, but the mechanisms underlying this drug resistance are not understood. In cancer, drug resistance has been studied extensively. Amongst the various resistance mechanisms, overexpression of drug resistance proteins, such as multi-drug resistance gene-1 P-glycoprotein (MDR1) and multidrug resistance-associated protein 1 (MRP1), has been shown to correlate with cellular resistance to anticancer drugs. Previous studies in human epilepsy have shown that MDR1 and MRP1 may also be overexpressed in brain tissue from patients with refractory epilepsy; expression has been shown in glia and neurones, which do not normally express these proteins. We examined expression of MDR1 and MRP1 in refractory epilepsy from three common causes, dysembryoplastic neuroepithelial tumours (DNTs; eight cases), focal cortical dysplasia (FCD; 14 cases) and hippocampal sclerosis (HS; eight cases). Expression was studied immunohistochemically in lesional tissue from therapeutic resections and compared with expression in histologically normal adjacent tissue. With the most sensitive antibodies, in all eight DNT cases, reactive astrocytes within tumour nodules expressed MDR1 and MRP1. In five of eight HS cases, reactive astrocytes within the gliotic hippocampus expressed MDR1 and MRP1. Of 14 cases of FCD, MDR1 and MRP1 expression was noted in reactive astrocytes in all cases. In five FCD cases, MRP1 expression was also noted in dysplastic neurones. In FCD and DNTs, accentuation of reactivity was noted around lesional vessels. Immunoreactivity was always more frequent and intense in lesional reactive astrocytes than in glial fibrillary acidic protein-positive reactive astrocytes in adjacent histologically normal tissue. MDR1 is able to transport some antiepileptic drugs (AEDs), and MRP1 may also do so. The overexpression of these drug resistance proteins in tissue from patients with refractory epilepsy suggests one possible mechanism for drug resistance in patients with these pathologies. We propose that overexpressed resistance proteins lower the interstitial concentration of AEDs in the vicinity of the epileptogenic pathology and thereby render the epilepsy caused by these pathologies resistant to treatment with AEDs.

No abstract

Neuronal heterotopia are seen in various pathologies and are associated with intractable epilepsy. We examined brain tissue from four children with subcortical or periventricular nodular heterotopia of different aetiologies: one with severe epilepsy following focal brain trauma at 17 weeks gestation, one with hemimegalencephaly and intractable epilepsy, one with focal cortical dysplasia and intractable epilepsy, and one dysmorphic term infant with associated hydrocephalus and polymicrogyria. The connectivity of nodules was investigated using histological and carbocyanine dye (DiI) tracing techniques. DiI crystal placement adjacent to heterotopic nodules revealed numerous DiI-labelled fibres within a 2-3 mm radius of the crystals. Although we observed labelled fibres closely surrounding nodules, the majority did not penetrate them. Placement of DiI crystals within nodules also identified a limited number of projections out of the nodules and in one case there was evidence for connectivity between adjacent nodules. The cellular and neurochemical composition of nodules was also examined using immunohistochemistry for calretinin and neuropeptide Y (NPY), which are normally expressed in GABAergic cortical interneurons. Within heterotopic nodules from all cases, numerous calretinin-positive neurons were identified, along with a few cell bodies and many processes positive for NPY. Calretinin-positive neurons within nodules were less morphologically complex than those in the cortex, which may reflect incomplete differentiation into an inhibitory neuronal phenotype. There were also abnormal clusters of calretinin-positive cells in the overlying cortical plate, indicating that the migratory defect which produces heterotopic nodules also affects development of the cortex itself. Thus, heterotopic nodules consisting of multiple neuronal cell types are associated with malformation in the overlying cortical plate, and have limited connectivity with other brain regions. This abnormal development of connectivity may affect neuronal maturation and consequently the balance of excitation and inhibition in neuronal circuits, leading to their epileptogenic potential.

We have used a porcine model of global hypoxia-ischaemia to examine the mode and extent of cell damage to the newborn brain. Apoptosis and necrosis were observed in neurons and glial cells following transient cerebral hypoxic-ischaemic injury (HII) by haematoxylin and eosin staining and by in situ end labelling (ISEL). Quantitative neuropathological analysis of the cingulate gyrus, the hippocampus and the cerebellum showed that the degree of both apoptosis and necrosis increased with the severity of injury in these brain areas. The hippocampus and cerebellar cortex were particularly sensitive to HII. Furthermore, some cell types were more susceptible to a particular mode of cell death. In the cerebellum. Purkinje cells died by necrosis but never by apoptosis. In contrast, cerebellar granule cells were frequently apoptotic, but never necrotic. In the hippocampus, apoptosis occurred in the inner layer neurons of the dentate fascia and necrosis in the more mature outer layer neurons. This suggests that immature neurons may be more prone to apoptotic death while terminally differentiated neurons die by necrosis. Apoptosis but not necrosis was seen in cerebral white matter. This model may help to elucidate the factors that determine cell fate following HII and aid the development of cerebroprotective strategies.

Drug resistance in epilepsy due to malformations of cortical development (MCD) is unexplained. P-glycoprotein is a mediator of drug resistance, and we propose that MCD lesions over-express P-glycoprotein. Because P-glycoprotein expression may be induced by some antiepileptic drugs (AEDs), we studied brain samples from MCD cases before the onset of seizures or treatment with AEDs. Sixteen MCD cases and 16 age-matched controls were examined using immunohistochemistry. Glial labelling, representing over-expression, was seen in 10 of 16 MCD samples and in two of 16 control samples (p = 0.003). Semiquantitative assessment showed many immunoreactive glia in five of 16 MCD and one of 16 controls. We conclude that there is constitutive over-expression of P-glycoprotein in many MCD.

It is not known whether the post-irradiation lower motor neuron syndrome results from radiation damage to motor neuron cell bodies or from damage to the nerve roots of the cauda equina. We studied six cases who had presented with testicular neoplasms, subsequently undergoing irradiation that encompassed inter alia para-aortic nodes with co-irradiation of the distal spinal cord and cauda equina. A predominantly motor disorder affecting the legs ensued after variable and often prolonged latencies (3-25 years). However, all patients also developed mild sensory features either initially or on prolonged follow-up. Sural sensory nerve action potentials (SNAPs) were normal in five. Mild sphincter symptoms occurred in three of five surviving cases after a mean of 7.9 years. MRI showed gadolinium enhancement of the cauda equina in two of three patients. The first reported neuropathological study, uncomplicated by metastatic disease, of the conus and cauda equina was performed in one patient who died. This showed a radiation-induced vasculopathy of the proximal spinal roots, with preservation of motor neuronal cell bodies and spinal cord architecture. These clinical, radiological, neurophysiological and pathological findings all point to a predominantly, but not exclusively, motor radiculopathy affecting the irradiated portion of the cauda equina proximal to the dorsal root ganglia. Radiation exposure exceeded 40 Gy both in our series and in previous reports. The natural history of this disorder is one of relentless deterioration occasionally punctuated by 1-2-year periods of stability. Post-irradiation lumbosacral radiculopathy is a more accurate name for this condition.

There is an association between quality of intrapartum care and death. The findings also suggest an association between suboptimal care and cerebral palsy, but this seems to have a role in only a small proportion of all cases of cerebral palsy. The contribution of adverse antenatal factors in the origin of cerebral palsy needs further study.

No abstract