Effect of nitrogen on cellular production and release of the neurotoxin anatoxin-a in a nitrogen-fixing cyanobacterium.

Anatoxin-a (ANTX) is a neurotoxin produced by several freshwater cyanobacteria and implicated in lethal poisonings of domesticated animals and wildlife. The factors leading to its production in nature and in culture are not well understood. Resource availability may influence its cellular production as suggested by the carbon-nutrient hypothesis, which links the amount of secondary metabolites produced by plants or microbes to the relative abundance of nutrients. We tested the effects of nitrogen supply (as 1, 5, and 100% N of standard cyanobacterial medium corresponding to 15, 75, and 1500 mg L(-1) of NaNO(3) respectively) on ANTX production and release in a toxic strain of the planktonic cyanobacterium Aphanizomenon issatschenkoi (Nostocales). We hypothesized that nitrogen deficiency might constrain the production of ANTX. However, the total concentration and more significantly the cellular content of anatoxin-a peaked (max. 146 µg/L and 1683 µg g(-1) dry weight) at intermediate levels of nitrogen supply when N-deficiency was evident based on phycocyanin to chlorophyll a and carbon to nitrogen ratios. The results suggest that the cellular production of anatoxin-a may be stimulated by moderate nitrogen stress. Maximal cellular contents of other cyanotoxins have recently been reported under severe stress conditions in another Nostocales species.

Triaging transient ischemic attack and minor stroke patients using acute magnetic resonance imaging.

We examined whether the presence of diffusion-weighted imaging (DWI) lesions and vessel occlusion on acute brain magnetic resonance images of minor stroke and transient ischemic attack patients predicted the occurrence of subsequent stroke and functional outcome. 120 transient ischemic attack or minor stroke (National Institutes of Health Stroke Scale < or = 3) patients were prospectively enrolled. All were examined within 12 hours and had a magnetic resonance scan within 24 hours. Overall, the 90-day risk for recurrent stroke was 11.7%. Patients with a DWI lesion were at greater risk for having a subsequent stroke than patients without and risk was greatest in the presence of vessel occlusion and a DWI lesion. The 90-day risk rates, adjusted for baseline characteristics, were 4.3% (no DWI lesion), 10.8% (DWI lesion but no vessel occlusion), and 32.6% (DWI lesion and vessel occlusion) (p = 0.02). The percentages of patients who were functionally dependent at 90 days in the three groups were 1.9%, 6.2%, and 21.0%, respectively (p = 0.04). The presence of a DWI lesion and a vessel occlusion on a magnetic resonance image among patients presenting acutely with a transient ischemic attack or minor stroke is predictive of an increased risk for future stroke and functional dependence.

Fulminating adult-onset subacute sclerosing panencephalitis in a 49-year-old man.

CONTEXT: Subacute sclerosing panencephalitis (SSPE) is a rare, slow viral infection caused by a defective measles virus. It is characterized by progressive mental deterioration associated with motor impairment and prominent myoclonus. In about 10% of all cases, the disease can progress rapidly and lead to death within a few months. The oldest previously reported fulminating case was in a 25-year-old man. OBJECTIVE: To emphasize the relationship between retinal involvement and acute SSPE by reporting the case of a 49-year-old man with clinical, laboratory, and pathological evidence of acute SSPE. SETTING: Hôpital de l'Enfant-Jésus, Quebec, Quebec. REPORT OF A CASE: This man was referred to the Department of Neurological Sciences on March 21, 2001, because of recent behavioral changes and progressive cognitive impairment over the past few months. Medical history was unremarkable except for an episode of measles in his childhood. Neurological examination showed bilateral myoclonic jerks. Ophthalmic examination revealed bilateral macular swelling and papilledema. Electroencephalography showed periodic sharp and slow-wave discharges. Magnetic resonance imaging showed bilateral diffuse T2-signal hyperintensities in both periventricular and subcortical white matter. Cerebrospinal fluid antimeasles antibody titers were highly positive. An Omaya reservoir was inserted and therapy using a combination of high-dose intrathecal interferon alfa and oral isoprinosine were administered for 6 weeks. Despite transient subjective improvement in the patient's condition, it continued to deteriorate, he became bedridden, and he died on June 26, 2001. CONCLUSION: To our knowledge, this patient is the oldest case of SSPE reported in the literature. This patient and other patients with acute SSPE associated with bilateral macular swelling described in the literature raised the possibility of measles virus-acquired virulent neurotropism in the retina before invading the central nervous system.