Long-term cortical atrophy after excitotoxic striatal lesion: effects of intrastriatal fetal-striatum grafts and implications for Huntington disease

Cortical Fluoro-Jade staining and blunted adrenomedullary response to hypoglycemia after noncoma hypoglycemia in rats

Intensive insulin therapy in patients with type 1 diabetes mellitus reduces long-term complications; however, intensive therapy is also associated with a three-fold increase in hypoglycemic episodes. The present study in conscious rats characterizes the physiologic and neuropathologic consequences of a single episode of moderate hypoglycemia. In this model, intravenous insulin is used to reduce plasma glucose to 30 to 35 mg/dL for 75 mins. This single hypoglycemic insult acutely induces hypoglycemia-associated autonomic failure (HAAF), with epinephrine responses to hypoglycemia reduced more than 36% from control. Neuropathology after this insult includes the appearance of dying cells, assessed with the marker Fluoro-jade B (FJ). After hypoglycemic insult, FJ+ cells were consistently seen in subdivisions of the medial prefrontal cortex, the orbital cortex, and the piriform cortex. There was a significant correlation between depth of hypoglycemia and number of FJ+ cells, suggesting that there is a critical threshold below which vulnerable cells begin to die. These data suggest that there is a population of cells that are vulnerable to moderate levels of hypoglycemia commonly experienced by patients with insulin-treated diabetes. These cells, which may be neurons, are primarily found in cortical regions implicated in visceral perception and autonomic control, raising the possibility that their loss contributes to clinically reported deficits in autonomic and perceptual responses to hypoglycemia.

Glial overexpression of heme oxygenase-1: a histochemical marker for early stages of striatal damage

The level of heme oxygenase-1 (HO-1) in the normal striatum is below the limit of immunodetection. However, HO-1 is overexpressed in both neural and non-neural cells in response to a wide range of lesions. We induced different types of lesions affecting the striatal cells or the main striatal afferent systems in rats to investigate if overexpression of HO-1 could be a useful histochemical marker of striatal damage. Thirty-six hours after intrastriatal or intraventricular injection of excitotoxins that affect striatal neurons (ibotenic acid) or of neurotoxins that affect striatal dopaminergic (6-hydroxydopamine) or serotonergic (5,7-dihydroxytriptamine) afferent terminals, or after surgical lesioning of cortico-striatal projections, there was intense induction of striatal HO-1 immunoreactivity (HO-1-ir). Double immunolabeling revealed that the HO-1-ir was located in glial cells. After intrastriatal injection of ibotenic acid, a central zone of neuronal degeneration contained numerous round and pseudopodic HO-1-ir cells, and was surrounded by a ring of HO-1-ir cells, most of which were immunoreactive for astroglial markers. Intraventricular injection of neurotoxins induced astroglial HO-1-ir cells which were more evenly distributed throughout the lesioned or denervated areas. HO-1-ir microglial cells were also observed in areas subjected to mechanical damage. The HO-1-ir was markedly lower or absent 1 week after lesion, and even more so 3 weeks after, although some HO-1-ir cells were still observed after intrastriatal injection of ibotenic acid or surgical corticostriatal deafferentation. The results indicate that determination of glial HO-1-ir is a useful histochemical marker for early stages of striatal damage.

Systemic administration of N-acetylcysteine protects dopaminergic neurons against 6-hydroxydopamine-induced degeneration

The results of several in vitro studies have shown that cysteine prodrugs, particularly N-acetylcysteine, are effective antioxidants that increase the survival of dopaminergic neurons. N-acetylcysteine can be systemically administered to deliver cysteine to the brain and is of potential use for providing neuroprotection in the treatment of Parkinson's disease. However, it has also been reported that an excess of cysteine may induce neurotoxicity. In the present study, we injected adult rats intrastriatally with 2.5 microl of 6-hydroxydopamine (7.5 microg) and N-acetylcysteine (240 mM) or cysteine (240 mM) or intraventricularly with 6-hydroxydopamine (200 microg) and subcutaneously with N-acetylcysteine (10 and 100 mg/kg). We studied the effects of these compounds on both the nigrostriatal dopaminergic terminals and the surrounding striatal tissue. The tissue was stained with fluoro-jade (a marker of neuronal degeneration) and processed by immunohistochemistry to detect tyrosine hydroxylase, neuronal and glial markers, and the stress protein heme-oxygenase-1. After intrastriatal injection, both cysteine and N-acetylcysteine had clear neuroprotective effects on the striatal dopaminergic terminals, but also led to neuronal degeneration (as revealed by fluoro-jade staining) and astroglial and microglial activation, as well as intense induction of heme-oxygenase-1 in astrocytes and microglial cells. Subcutaneous administration of N-acetylcysteine also induced significant reduction of the dopaminergic lesion (about 30% reduction). However, we did not observe appreciable N-acetylcysteine-induced fluoro-jade labeling in striatal neurons or any of the above-mentioned changes in striatal glial cells. The results suggest that low doses of cysteine prodrugs may be useful neuroprotectors in the treatment of Parkinson's disease.

Behavioral and neurological correlates of ALS-parkinsonism dementia complex in adult mice fed washed cycad flour

Consumption of cycad seed products (Cycas circinalis) is one of the strongest epidemiological links to the Guamian neurological disorder amyotrophic lateral sclerosis-parkinsonism-dementia complex (ALS-PDC), however, the putative toxin which causes neurodegeneration has never been identified definitively. To reexamine this issue, 6-7-mo-old, male CD-1 mice were assessed for motor and cognitive behaviours during and following feeding with pellets made from washed cycad flour. Cycad-fed animals showed early evidence of progressive motor and cognitive dysfunctions. Neurodegeneration measured using TUNEL and caspase-3 labeling was found in neocortex, various hippocampal fields, substantia nigra, olfactory bulb, and spinal cord. In vitro studies using rat neocortex have identified toxic compounds in washed cycad flour that induce depolarizing field potentials and lead to release of lactate dehydrogenase (LDH), both blocked by AP5. High-performance liquid chromatography (HPLC)/mass spectrometry of cycad flour samples failed to show appreciable amounts of other known cycad toxins, cycasin, MAM, or BMAA; only trace amounts of BOAA were present. Isolation procedures employing these techniques identified the most toxic component as beta-sitosterol beta-D-glucoside (BSSG). The present data suggest that a neurotoxin, or a toxic metabolite, not previously identified in cycad, is able to gain access to central nervous system (CNS) resulting in neurodegeneration of specific neural populations and in motor and cognitive dysfunctions. These data are consistent with a number of major features of ALS-PDC in humans.

Pyramidal Cell Loss in Motor Cortices in Huntington's Disease

Patterns of huntingtin protein aggregation and cortical neuronal loss suggest early involvement of corticostriatal pathways in Huntington's disease. However, theories of pathogenesis of chorea rely on the motor cortices being intact. The motor cortices have not previously been studied at a cellular level in Huntington's disease. We analyzed the neuronal number in the caudate, putamen, and three motor cortical areas in five cases of Huntington's disease and five controls. For each motor cortical region the total neuronal number, number of interneurons, and number of SMI32 immunopositive pyramidal neurons were quantified using previously published techniques and any relationship between cell loss and severity or duration of chorea was examined. The results showed a loss of long projecting SMI32 immunopositive pyramidal neurons in the primary motor cortex with associated morphological changes and suggest a loss of short projecting pyramidal neurons in the premotor cortex. Degeneration in the primary motor cortex correlated with subcortical degeneration. These findings indicate pyramidal cell involvement in Huntington's disease and implicate the degeneration of corticostriatal pathways in the production of chorea.