Neuropathological analysis of the brainstem and cerebral cortex lesions on epileptogenesis in hereditary dentatorubral-pallidoluysian atrophy

Epileptic baboons have lower numbers of neurons in specific areas of cortex

Epilepsy is characterized by recurrent seizure activity that can induce pathological reorganization and alter normal function in neocortical networks. In the present study, we determined the numbers of cells and neurons across the complete extent of the cortex for two epileptic baboons with naturally occurring seizures and two baboons without epilepsy. Overall, the two epileptic baboons had a 37% average reduction in the number of cortical neurons compared with the two nonepileptic baboons. The loss of neurons was variable across cortical areas, with the most pronounced loss in the primary motor cortex, especially in lateral primary motor cortex, representing the hand and face. Less-pronounced reductions of neurons were found in other parts of the frontal cortex and in somatosensory cortex, but no reduction was apparent in the primary visual cortex and little in other visual areas. The results provide clear evidence that epilepsy in the baboon is associated with considerable reduction in the numbers of cortical neurons, especially in frontal areas of the cortex related to motor functions. Whether or not the reduction of neurons is a cause or an effect of seizures needs further investigation.

Lesions of acetylcholine neurons in refractory epilepsy

We have examined brainstem lesions in patients with refractory epilepsy disorders, including West syndrome (WS), Lennox-Gastaut syndrome (LGS), and dentatorubral-pallidoluysian atrophy (DRPLA). Acetylcholinergic neurons (AchNs) in the pedunculopontine tegmental nucleus (PPN) are involved in mental development, and disruption of neuronal nicotinic acetylcholine receptors can lead to epilepsy. In order to investigate the involvement of lesions of AchNs in refractory epilepsy, we performed immunohistochemical analyses of AchNs in the PPN in autopsy cases who had a past history of WS and/or LGS and in DRPLA cases who showed progressive myoclonic epilepsy. In addition, we performed a preliminary quantification of the levels of acetylcholine, neuropeptides, and monoamine metabolites in the cerebrospinal fluid (CSF) of patients with WS and benign convulsions associated with mild gastroenteritis (CwG). In the PPN analysis, the total number of neurons and the number of AchNs were reduced in WS/LGS and WS cases, while DRPLA cases showed a decrease in the number and percentage of AchNs. In the CSF analysis, WS patients demonstrated a reduction in the levels of inhibitory neuropeptides, while CwG patients showed increased levels of acetylcholine and decreased levels of serotonin metabolites. These data suggest the possible involvement of lesions of AchNs in WS and DRPLA.

Lesions of cortical GABAergic interneurons and acetylcholine neurons in xeroderma pigmentosum group A

Xeroderma pigmentosum (XP) is a rare genetic disorder caused by inherited disturbances in the nucleotide excision repair system; patients with XP groups A (XP-A), B, D, and G were shown to have progressive neurological disturbances. Particularly, XP-A patients, which account for approximately half of Japanese XP patients, show severe neurological disorders, including mental retardation and epilepsy. Herein, we performed an immunohistochemical analysis of the number of GABAergic interneurons (GABAis), including calbindin-D28K, parvalbumin, and calretinin, in the cerebral cortex and acetylcholinergic neurons (AchNs) in the nucleus basalis of Meynert (NM) and in the pedunculopontine tegmental nucleus (PPN) in six autopsy cases of XP-A in order to investigate the relationships between mental dysfunction and GABAis and AchNs. The density and percentages of neurons that were immunoreactive for calbindin-D28K and parvalbumin were significantly reduced in the frontal and temporal cortices in XP-A cases, although the density of neurons that were immunoreactive for MAP2 did not differ from that in controls. Additionally, XP-A cases showed reduced AchNs in both the NM and the PPN. The observed reductions of cortical GABAis and AchNs may be involved in the mental disturbances, the higher occurrence of epilepsy, and/or the abnormalities in rapid eye movement sleep in patients with XP-A.

Lesions in the central tegmental tract in autopsy cases of developmental brain disorders

We retrospectively analyzed central tegmental tract (CTT) lesions in 120 consecutive autopsy cases of developmental brain disorders to investigate the significance of symmetrical CTT lesions. Magnetic resonance imaging (MRI) findings of CTT lesions have been sporadically reported in various cases of child neurological diseases. In this study, symmetrical CTT lesions were observed in 25 (20.8%) among 120 cases of developmental brain disorders. These 25 cases were classified into three groups (groups I-III) in decreasing order of the severity of the lesion. Compared to five cases of group I in which CTT lesions were accompanied by diffuse tegmental damage, 20 cases of groups II or III developed relatively selective CTT lesions in which the medial longitudinal fasciculus and/or medial or lateral lemniscus were preserved. The causes of brain disorders in all three groups seemed to be different, and lysosomal disorders and congenital brain anomalies were frequently seen in cases in groups II and III, respectively. The dentato-rubro-olivary system is known to be involved in palatal myoclonus, and five out of 13 cases in group II showed myoclonic epilepsy. Compared with 95 cases without the CTT lesion, the changes in the pontine reticular formation were more closely associated with the CTT lesion than those in the inferior olivary nucleus. In conclusion, in cases of developmental brain disorders, the neuropathology of the symmetrical CTT lesion should be investigated.

Forebrain ischemia triggers GABAergic system degeneration in substantia nigra at chronic stages in rats

The long-term consequences of forebrain ischemia include delayed Parkinson's syndrome. This study revealed delayed neurodegeneration in the substantia nigra 8 weeks after 12.5 minutes of global ischemia in rat brain. Following neuronal loss of 30-40% in central and dorsolateral striatum at day 3, neuronal damage in the substantia nigra (SN) was assessed at 4-8 weeks using immunohistochemistry for glutamate decarboxylase 67 (GAD67), vesicular GABA transporter (VGAT), and calretinin (CR). At day 56, the optical density of GAD67-, but not VGAT-, immunoreactivity in substantia nigra pars reticulata (SNR)-significantly decreased. CR-neurons concentrated in substantia nigra pars compacta (SNC) were reduced by 27% from day 3 (n = 5) to day 56 (n = 7, ANOVA, p < .01). Movement coordination was impaired at day 56, as evaluated using beam-walking test (time-to-traverse 5.6 ± 1.2 sec versus 11.8 ± 5.4 sec; sham versus ischemia, p < .05, n = 5, and 7, resp.). Our results demonstrate delayed impairment of the GABAergic system components in SN and associated with movement deficits after global ischemia.

Reassessment of phenytoin for treatment of late stage progressive myoclonus epilepsy complicated with status epilepticus

In order to find an effective treatment option for status epilepticus in progressive myoclonus epilepsy (PME), we reviewed the clinical course of 9 patients with PME. Initially, epilepsy was successfully treated with antiepileptics. However, it gradually became refractory to medication, and status epilepticus emerged 3-19 years after the onset of epilepsy. In these patients, status epilepticus in PME was classified into (1) myoclonic status epilepticus (MSE), (2) myoclonic-generalized status epilepticus (MGSE), and (3) generalized status epilepticus (GSE). MSE was common in patients with neuronal ceroid lipofuscinosis, and GSE was common in those with dentatorubral-pallidoluysian atrophy. MGSE was characterized by the mixture of escalating myoclonus and generalized seizures, and was observed in patients with Gaucher disease or unspecified PME. All patients were often refractory to infusion of benzodiazepines and barbiturates but phenytoin was able to terminate status epilepticus in 7 patients. Oral phenytoin administration as preventive therapy was effective in 6 patients. Aggravation of myoclonus was not provoked by these treatments. We propose that phenytoin should be considered as a treatment choice for PME patients at late stages to prevent the detrimental effects of prolonged or repeated status epilepticus on the brain tissues.

Mechanisms of neurodegeneration in mucopolysaccharidoses II and IIIB: analysis of human brain tissue

Mucopolysaccharidoses (MPS) are inherited disorders caused by the deficiency of lysosomal enzymes. Sanfilippo syndrome (MPS III) and Hunter syndrome (MPS II) are characterized by severe and mild neurological disorders, respectively, in which the neurodegenerative mechanisms remain to be clarified. We immunohistochemically examined the involvement of tauopathy/synucleinopathy, cell death and oxidative damage in the brains of three cases each of MPS IIIB and MPS II and age-matched controls. In cases of MPS IIIB, the density of GABAergic interneurons in the cerebral cortex immunoreactive for calbindin-D28K and parvalbumin was markedly reduced when compared with age-matched controls. The swollen neurons showed immunoreactivity for phosphorylated alpha-synuclein but not for phosphorylated tau protein or beta-amyloid protein; those in the cerebral cortex demonstrated nuclear immunoreactivity for TUNEL, single-stranded DNA and 8-OHdG. Neither lipid peroxidation nor protein glycation was marked in MPS cases. The expression levels of superoxide dismutases (Cu/ZnSOD and MnSOD) and glial glutamate transporters (EAAT1 and EAAT2) were reduced in two MPS II cases. The disturbance of GABAergic interneurons can be related to mental disturbance, while synucleinopathy and/or DNA impairment may be implicated in the neurodegeneration of swelling neurons due to storage materials in MPS IIIB cases. These findings suggest the possibility of neuroprotective therapies other than enzyme replacement in MPS patients.