Keisuke Iwanaga

Variability of brain lesions in rats administered methylmercury at various postnatal development phases

The effect of methylmercury chloride (MMC) on the developing rat nervous system was studied by light microscopy. Rats on postnatal day 2 (P2), P15 and P60 were administered 10 mg/kg/day MMC orally for 10 days. In newborn (after P2) rats, there was no abnormal activity or body weight loss. Young (after P15) rats showed weight loss on the 9th day after starting MMC, and subsequently unsteadiness, gait disturbance and paroxysmal convulsions appeared. In adult rats, weight loss began on the 6th day after starting MMC, and the hind-limb crossing phenomenon was induced on the 13th day. Histopathologically, minimal damage was found in the hippocampus and brainstem in newborn rats. In young rats, widespread neuronal degeneration was observed in the cerebral neocortex, CA3 and CA4 regions of the hippocampus, neostriatum, red nucleus, and various brainstem nuclei. In adult rats, neuronal damage was most extensive in the cerebellum and spinal dorsal nerve roots. These findings indicate that neuronal vulnerability to MMC exposure differs depending on the postnatal developmental stage and the brain region in the rat.

Sporadic four-repeat tauopathy with frontotemporal lobar degeneration, Parkinsonism, and motor neuron disease: a distinct clinicopathological and biochemical disease entity

Tau is the pathological protein in several neurodegenerative disorders classified as frontotemporal lobar degeneration (FTLD), including corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP). We report an unusual tauopathy in three Japanese patients presenting with Parkinsonism and motor neuron disease (neuroimaging revealed frontotemporal cerebral atrophy in two patients who were examined). At autopsy, all cases showed FTLD with the most severe neuronal loss and gliosis evident in the premotor and precentral gyri. Although less severe, such changes were also observed in other brain regions, including the basal ganglia and substantia nigra. In the spinal cord, loss of anterior horn cells and degeneration of the corticospinal tract were evident. In addition, the affected regions exhibited neuronal cytoplasmic inclusions resembling neurofibrillary tangles. Immunostaining using antibodies against hyperphosphorylated tau and 4-repeat tau revealed widespread occurrence of neuronal and glial cytoplasmic inclusions in the central nervous system; the astrocytic tau lesions were unique, and different in morphology from astrocytic plaques in CBD, or tufted astrocytes in PSP. However, immunoblotting of frozen brain samples available in two cases revealed predominantly 4R tau, with the approximately 37-kDa and 33-kDa low-molecular mass tau fragments characteristic of CBD and PSP, respectively. No mutations were found in the tau gene in either of the two cases. Based on these clinicopathological, biochemical, and genetic findings, we consider that the present three patients form a distinct 4R tauopathy associated with sporadic FTLD.

Dysembryoplastic neuroepithelial tumor: report of a case without typical glioneuronal elements

We studied a temporal lobe lesion found in a 44-year-old woman with a 25-year history of intractable complex partial seizures. Histologically, the lesion contained several nodular areas differing in cellular composition within the disarranged uncal cortex; in each area, neuronal and small round cells, mature ganglion cells and fibrillary astrocytic cells predominated. Ultrastructurally, the small round cells demonstrated neuronal, astrocytic or oligodendrocytic features. The astrocytic cell processes were occasionally covered by basal laminae. The mature ganglion cells had well-developed rough endoplasmic reticulum, many mitochondria and lipofuscin granules in their cytoplasm. No dense-cored vesicles were evident. We diagnosed this temporal lobe lesion as a dysembryoplastic neuroepithelial tumor (DNT), although no areas of typical glioneuronal elements with mucinous matrix were evident. This case suggests that a glioneuronal element is not always a constant feature of DNT, and that although mature ganglion cell nodules may be present, they may differ from those of gangliocytomas and gangliogliomas in lacking intracytoplasmic dense-cored vesicles. The presence of occasional astrocytic cell processes covered by basal laminae strongly suggests that some of the constituent astrocytic cells were of subpial astrocytic origin.

Ultrastructural Relationship between Lewy Bodies and Pale Bodies Studied in Locus Ceruleus Neurons of a Non-Parkinsonian Patient

The Lewy body (LB) is a hallmark of Parkinsons disease (PD). The pale body (PB) also represents a characteristic intracytoplasmic alteration of the neurons of the substantia nigra and locus ceruleus of PD patients. We recently had the opportunity to study a non‐parkinsonian patient (a 66‐year‐old man) who had numerous LBs and PBs in the neurons of the locus ceruleus. However, there was no evidence of neuronal loss in this region. We performed a detailed ultrastructural study of these inclusions for which multiple serial sections were used. Our results revealed that the constituent filamentous structures of the LBs and PBs were indistinguishable from each other, that transitions occasionally occurred between PBs and LBs, and that presynaptic structures entrapped in the cytoplasm were frequently present in the vicinity of both types of inclusion bodies. These findings suggest that PBs, at least those of the present type, actually represent early LBs. In addition, the entrapment of presynaptic structures by the cytoplasm of neurons of the locus ceruleus may indicate the existence of certain degenerative (or regressive) processes in these cells and that postsynaptic areas in particular, may have a role in PB and LB formation.

Corticobasal degeneration with neither argyrophilic inclusions nor tau abnormalities : a new subgroup ?

In corticobasal degeneration (CBD), cerebral cortical neuronal loss with achromasia and degeneration of the subcortical nuclei, particularly the substantia nigra, are common. Recent studies have suggested that the occurrence of argyrophilic nigral inclusions, resembling the neurofibrillary tangles found in progressive supranuclear palsy, and widespread tau abnormalities may be features of CBD. We studied brain tissues from two patients in whom CBD was suspected clinically. From the distribution of their cortical and subcortical lesions, the patients were diagnosed as having CBD. However, Gallyas/taupositive neuronal and glial structures were not found, which suggests there may be a subgroup of CBD with neither argyrophilic inclusions nor tau abnormalities.

Bunina bodies in motor and non-motor neurons revisited: A pathological study of an ALS patient after long-term survival on a respirator

Bunina bodies (BBs) are small eosinophilic neuronal cytoplasmic inclusions (NCIs) found in the remaining lower motor neurons (LMNs) of patients with sporadic amyotrophic lateral sclerosis (SALS), being a specific feature of the cellular pathology. We examined a case of SALS, unassociated with TDP‐43 or C9ORF72 mutation, of 12 years duration in a 75‐year‐old man, who had received artificial respiratory support for 9 years, and showed widespread multisystem degeneration with TDP‐43 pathology. Interestingly, in this patient, many NCIs reminiscent of BBs were observed in the oculomotor nucleus, medullary reticular formation and cerebellar dentate nucleus. As BBs in the cerebellar dentate nucleus have not been previously described, we performed ultrastructural and immunohistochemical studies of these NCIs to gain further insight into the nature of BBs. In each region, the ultrastructural features of these NCIs were shown to be identical to those of BBs previously described in LMNs. These three regions and the relatively well preserved sacral anterior horns (S1 and S2) and facial motor nucleus were immunostained with antibodies against cystatin C (CC) and TDP‐43. Importantly, it was revealed that BBs exhibiting immunoreactivity for CC were a feature of LMNs, but not of non‐motor neurons, and that in the cerebellar dentate nucleus, the ratio of neurons with BBs and TDP‐43 inclusions/neurons with BBs was significantly lower than in other regions. These findings suggest that the occurrence of BBs with CC immunoreactivity is intrinsically associated with the particular cellular properties of LMNs, and that the mechanism responsible for the formation of BBs is distinct from that for TDP‐43 inclusions.

Pick's disease: selective occurrence of apolipoprotein E-immunoreactive Pick bodies in the limbic system

Abstract We carried out immunohistochemical examination of apolipoprotein E (apoE) in brains from two patients with Pick’s disease. In these cases 1 and 2, the APOE genotypes were ɛ3/4 and ɛ3/3, respectively. In both cases, numerous argyrophilic globular intraneuronal inclusions, Pick bodies (PBs), were distributed widely throughout the brain, and immunohistochemically were occasionally positive for apoE. Interestingly, such apoE-immunoreactive PBs were virtually restricted to neurons in the limbic system; in the dentate gyrus, the proportion of apoE-immunoreactive PBs relative to the total number of argyrophilic PBs was 5.0% in case 1 and 2.7% in case 2, whereas in the frontal and temporal neocortices it was less than 0.1% in both cases. Diffuse cytoplasmic immunoreactivity for apoE was found in only a few limbic system neurons without PBs in both cases. In conclusion, it is considered that apoE may not be positively involved in the process of PB formation and that the preferential distribution of apoE-immunoreactive PBs in the limbic system may reflect the presence of certain regional factors associated with the synthesis or metabolism of apoE in this particular system.

A newly discovered age-related synaptic change in the human locus ceruleus: morphometric and ultrastructural studies

Abstract We have recently found that in the human locus ceruleus (LC) some pigmented neurons contain granules in their cytoplasm that are immunoreactive (IR) for the 38-kDa synaptic vesicle-specific protein (SVP). These represent synaptic terminals enveloped in the somatic cytoplasm. In the present study we analyzed LC pigmented neurons morphometrically in 48 autopsied individuals, whose ages at death ranged from 5 to 94 years, and also examined LC pigmented neurons ultrastructurally in 4 of these individuals. The number and incidence of LC pigmented neurons containing SVP-IR intracytoplasmic granules became significantly higher with age. The mean somatic area of the neurons was significantly higher than that of neurons without SVP-IR intracytoplasmic granules. Ultrastructurally, the synaptic terminals, which contained many round or flattened clear vesicles and sometimes dense-cored vesicles, were found to be enveloped by the somatic cytoplasm of some pigmented neurons and occasionally formed synaptic contacts with the cytoplasm. These enveloped synaptic terminals showed no apparent degenerative features. Our results strongly suggest that the enveloping of synaptic terminals by the somatic cytoplasm of human LC pigmented neurons is a phenomenon associated with the aging brain, and that this phenomenon may be related to intrinsic adaptive mechanisms of the LC pigmented neurons to certain environmental changes associated with aging.

Synaptic terminals wrapped in the somatic cytoplasm of pigmented neurons in the human locus ceruleus

We examined the locus ceruleus (LC) of 59 autopsied individuals whose ages at death ranged from 5 to 108 years. Immunocytochemistry with synaptic vesicle-specific 38-kDa protein (SVP) revealed that clusters of SVP-like immunoreactive coarse granules were present in the somatic cytoplasm of some pigmented neurons in all individuals examined. These SVP-like immunoreactive granules were confirmed electron microscopically to be contained in synaptic terminals which were wrapped in the somatic cytoplasm of pigmented LC neurons.