Elizabeth O'Hearn

Neurotoxicity of MDMA and related compounds: Anatomic studies

The cytotoxic effects of amphetamine derivatives were studied by immunocytochemistry to identify the cellular compartments affected by these drugs, to obtain morphologic evidence of neuronal degeneration, and to assess the potential for regeneration. The substituted amphetamines, MDA, MDMA, PCA, and fenfluramine, all release serotonin and cause acute depletion of 5-HT from most axon terminals in forebrain. (1) Unequivocal signs of axon degeneration were seen at 36-48 hour survivals: 5-HT axons exhibited increased caliber, huge, swollen varicosities, fragmentation, and dilated proximal axon stumps. (2) Fine 5-HT axon terminals were persistently lost after drug administration, while beaded axons and raphe cell bodies were spared. These two types of 5-HT axons, which arise from separate raphe nuclei and form distinct ascending projections, are differentially vulnerable to psychotropic drugs. (3) From 2-8 months after treatment, there was progressive serotonergic re-innervation of neocortex along a fronto-occipital gradient. Longitudinal 5-HT axons grew into layers I and VI from rostral to caudal, before sprouting into middle cortical layers; this bilaminar pattern of growth simulates perinatal development of 5-HT innervation. This study demonstrates differential vulnerability of 5-HT projections, evidence for axonal degeneration, and sprouting of 5-HT axons leading to re-innervation of forebrain. While the sprouting axons are anatomically similar to the type that was damaged, it is not known whether a normal pattern of innervation is re-established.

Organization of raphe-cortical projections in rat: A quantitative retrograde study

Retrograde transport of a fluorescent dye was employed to study the projections from raphe nuclei to neocortex in the rat. The spatial distributions of labeled raphe cells were analyzed quantitatively to determine whether the nuclei are topographically organized with respect to different cortical targets. The dorsal raphe nucleus (DRN), exclusive of the lateral wing regions, has a predominantly (3:1) ipsilateral projection with decreasing numbers of cells projecting to frontal, parietal, and occipital cortex. Overlapping cell groups within the DRN project differentially to these three cortical areas: DRN cells innervating frontal cortex extend more rostrally and laterally than those to either parietal or occipital cortex. The medium raphe and B9 projections are bilaterally symmetric, with equal cell numbers projecting to frontal, parietal, and occipital cortex. The rostro-caudal distributions of cells that project to disparate cortical areas differ in B9 but not in MR. The percentage of cortically projecting cells that are serotonergic is 80% for the DRN, 60% in the MR and 33% in the B9 cell group. The dorsal raphe nucleus and the B9 cell group are organized heterogeneously, and overlapping sets of neurons project differentially upon particular areas of neocortex. In contrast, the median raphe nucleus projects uniformly upon the neocortex and does not exhibit topographic organization. The three rostral raphe nuclei (DR, MR and B9) are each organized according to different rules with regard to their efferent projections to cortex. The differential organization of the raphe nuclei suggests that groups of cells within these three raphe nuclei are likely to innervate different combinations of cortical targets and thus to have different functional effects.

A disorder similar to Huntington's disease is associated with a novel CAG repeat expansion.

Huntingtons disease (HD) is an autosomal dominant disorder characterized by abnormalities of movement, cognition, and emotion and selective atrophy of the striatum and cerebral cortex. While the etiology of HD is known to be a CAG trinucleotide repeat expansion, the pathways by which this mutation causes HD pathology remain unclear. We now report a large pedigree with an autosomal dominant disorder that is clinically similar to HD and that arises from a different CAG expansion mutation. The disorder is characterized by onset in the fourth decade, involuntary movements and abnormalities of voluntary movement, psychiatric symptoms, weight loss, dementia, and a relentless course with death about 20 years after disease onset. Brain magnetic resonance imaging scans and an autopsy revealed marked striatal atrophy and moderate cortical atrophy, with striatal neurodegeneration in a dorsal to ventral gradient and occasional intranuclear inclusions. All tested affected individuals, and no tested unaffecteds, have a CAG trinucleotide repeat expansion of 50 to 60 triplets, as determined by the repeat expansion detection assay. Tests for the HD expansion, for all other known CAG expansion mutations, and for linkage to chromosomes 20p and 4p were negative, indicating that this mutation is novel. Cloning the causative CAG expansion mutation for this new disease, which we have termed Huntingtons disease‐like 2 (HDL2), may yield valuable insight into the pathogenesis of HD and related disorders.

Phenotypic features of Huntington's disease-like 2.

Huntingtons disease‐like 2 is an autosomal dominantly inherited disorder due to an expansion of trinucleotide repeats. It resembles classic Huntingtons disease in clinical phenotype, inheritance pattern, and neuropathological features. We highlight the clinical features of this disorder, including chorea, dystonia, parkinsonism, and cognitive deficits.

Spinocerebellar Ataxia Type 12

SCA12 is a late-onset, autosomal dominant, slowly progressive disorder. Action tremor is the usual presenting sign. Subsequent development of ataxia and hyperreflexia suggests spinocerebellar ataxia. In the index SCA12 kindred, which resides in North America and is of German ancestry, parkinsonism, anxiety, depression, and cognitive dysfunction are not uncommon. SCA12 is linked to a CAG repeat expansion mutation in exon 7 of PPP2R2B, a gene that encodes Bβ, a regulatory subunit of protein phosphatase 2A (PP2A). CAG repeats number 7-28 in normal individuals and 55-78 in SCA12 patients. The mechanism by which this mutation leads to SCA12 has not been determined. The CAG expansion in PPP2R2B has promoter function in vitro. CAG length correlates with increased Bβ expression. There is no evidence that this CAG expansion results in polyglutamine production. In addition to the North. American SCA12 kindred, multiple SCA12 families have been found in Northern India that are not related to the index SCA12 kindred. SCA12 has been reported, rarely, in Singapore and China. Action tremor, anxiety, and depression in SCA12 have responded to usual treatments for these disorders. SCA12 may be considered in patients who present with action tremor and later develop signs of cerebellar and cortical dysfunction.

Clinical signs and symptoms in a large hereditary spastic paraparesis pedigree with a novel spastin mutation

The most common form of autosomal dominant hereditary spastic paraparesis (HSP), SPG4, is caused by mutations in the spastin gene on chromosome 2p. This disease is characterized by intra‐ and interfamilial phenotypic variation. To determine the predictive values of clinical signs and symptoms in SPG4, we examined 43 members of a large pedigree with autosomal dominant HSP. We then identified the genetic etiology of the disorder in this family, a novel nonsense mutation in exon 1 of spastin, carried by 24 of the examined family members. The best clinical predictors of positive gene status were the presence of hyperreflexia in the lower extremities, >2 beats of ankle clonus, pes cavus, bladder symptoms and increased tone in the legs. The mean age of onset was 32.2 ± 7.4 years, but the age of onset was earlier in children from 10 of 12 child–parent gene‐positive pairs, with a mean difference of 10.8 ± 3.3 years. The finding of leg weakness was especially common in older‐onset affected family member with leg hyperreflexia. These results suggest that specific clinical signs and symptoms may be of value in differentiating individuals affected with SPG4 from family members with nonspecific neurological findings.

Neuropathology and Cellular Pathogenesis of Spinocerebellar Ataxia Type 12.

SCA12 is a progressive autosomal‐dominant disorder, caused by a CAG/CTG repeat expansion in PPP2R2B on chromosome 5q32, and characterized by tremor, gait ataxia, hyperreflexia, dysmetria, abnormal eye movements, anxiety, depression, and sometimes cognitive impairment. Neuroimaging has demonstrated cerebellar and cortical atrophy. We now present the neuropathology of the first autopsied SCA12 brain and utilize cell models to characterize potential mechanisms of SCA12 neurodegeneration.

The alkylating agent penclomedine induces degeneration of purkinje cells in the rat cerebellum.

Purpose. Penclomedine (PEN), a multichlorinated α-picoline derivative which is metabolized to highly reactive alkylating species, was selected for clinical development due to its prominent activity against a wide range of human tumor xenografts when administered either parentally or orally. Its principal dose-limiting toxicity in preclinical and clinical studies has been neurocerebellar toxicity, which has been related to the magnitude of peak plasma PEN concentrations, but not to plasma concentrations of its putative principal alkylating metabolite, 4,o-demethylpenclomedine (DMPEN). These observation, as well as PENs toxicologic, pharmacologic, and tissue distribution profiles, have suggested that the parent compound is primarily responsible for cerebellar toxicity. The studies described in this report were undertaken to characterize the neuropathology of PEN neurotoxicity, with a long-term goal of developing strategies to maximize its therapeutic index. Design. Male Sprague–Dawley rats were treated with therapeutically relevant doses of PEN, orally and intraperitoneally (i.p.), on various administration schedules, and DMPEN administered i.p. The animals were monitored for neurotoxicity, and brain sections were examined for neuropathology, particularly Purkinje cell loss and neuronal injury. Brain sections were stained using standard histochemical techniques and immunostained with OX-42 to detect microglial cells that are activated following neuronal damage, and calbindin D28K, a calcium-binding protein expressed by cerebellar Purkinje cells. Results. Dose-related neurocerebellar toxicity associated with parasagittal bands of Purkinje cell degeneration and microglial activation in the cerebellar vermis were evident in rats treated with PEN 100–400 mg/kg i.p. as a single dose. Neuronal injury was not observed in other regions of the brain. Furthermore, neither clinical nor histopathological evidence of cerebellar toxicity was apparent in rats treated with similar total doses of PEN administered i.p. on a daily×5-day dosing schedule. Similar histological findings, in an identical neuroanatomical distribution, were observed in rats treated with PEN orally; however, the magnitude of the neuronal toxicity was much less than in animals treated with equivalent doses of PEN administered i.p. Although acute lethality occurred in some rats treated with equimolar doses of DMPEN as a single i.p. treatment, surviving animals exhibited neither signs nor histopathological evidence of neurocerebellar toxicity. Conclusions. PEN produces selective dose- and schedule-dependent Purkinje cell degeneration in the cerebellar vermis of rats, whereas therapeutically relevant doses of PEN administered orally are better tolerated and produce less neurocerebellar toxicity. In addition, roughly equivalent, albeit intolerable, doses of the major active metabolite DMPEN, which was lethal to some animals, produced neither clinical manifestations of neurocerebellar toxicity nor Purkinje cell loss. These results support a rationale for investigating whether PEN administered orally, which may undergo significant first-pass metabolism to DMPEN and other less toxic intermediates, or treatment with DMPEN, itself, may result in less neurocerebellar toxicity and superior therapeutic indices than PEN administered parenterally.