MR imaging of postischemic neuronal death in the substantia nigra and thalamus following middle cerebral artery occlusion in rats.

The goal of this study was to investigate apparent diffusion coefficient (ADC) and T(2) relaxation time (T(2)) in the substantia nigra and thalamus after middle cerebral artery occlusion in rats. In the substantia nigra ipsilateral to infarct, ADC was significantly lower and T(2) was significantly higher on the third and fourth days, but they did not change significantly on the first, second, eighth and 15th days. In the ipsilateral thalamus, ADC and T(2) did not change significantly between the first and fourth days, but were significantly lower on the eighth and 15th days. This combination of MR findings suggested that secondary degeneration in the thalamus was different from that in the substantia nigra.

MRI of secondary changes in the thalamus following a cerebral infarct.

We investigated acute secondary degeneration in the thalamus following a cerebral infarct in 21 patients with an infarct in the territory of the middle cerebral artery, using serial MRI at various time after the stroke. Secondary degeneration in the ventral nuclei of the thalamus was seen as regions of slightly low signal on proton-density and/or T2-weighted images, mostly obtained a few weeks after the onset. An area of slightly high signal was observed in the dorsomedial nucleus of the thalamus on T2-weighted images about 6 weeks after the onset. Damage to the superior and anterior thalamic radiation caused degeneration in the ventral and dorsomedial nucleus, respectively. Thus, the time of detection and the abnormalities seen on MRI in secondary degeneration vary depending upon which area of the thalamus is involved. The mechanism underlying the degeneration is therefore also likely to differ in these areas.

MR detection of secondary changes remote from ischemia: preliminary observations after occlusion of the middle cerebral artery in rats.

PURPOSE: To determine whether secondary MR changes occur in the thalamus or the substantia nigra after middle cerebral artery (MCA) occlusion in rats. METHODS: Sprague-Dawley rats were subjected to MCA occlusion. At varying intervals, proton density-, T1-, and T2-weighted images were obtained with a 4.7-T superconductive MR unit. RESULTS: T2-weighted images revealed an area of high signal intensity in the ipsilateral substantia nigra 4 days after occlusion. A lesion of low signal intensity appeared in the ipsilateral thalamus 7 days after surgery on proton density- and/or T2-weighted images. CONCLUSION: MR showed secondary changes in the thalamus and the substantia nigra after MCA occlusion in rats. MR imaging should provide more information on the neuropathology of the delayed neuronal degeneration after cerebral ischemia.

Functional expression of three isoforms of human nitric oxide synthase in baculovirus-infected insect cells.

Complementary DNAs encoding three human isoforms (neuronal, inducible, and endothelial) of nitric oxide synthase were cloned into the baculovirus expression vector pVL1392/1393. Transfection of Sf-9 insect cells with the recombinant baculovirus resulted in the expression of high levels of nitric oxide synthases. The expressed proteins of neuronal and inducible nitric oxide synthase were predominantly soluble, whereas the endothelial enzyme was for the most part, particulate. Recombinant enzymes were purified with 2',5'-ADP Sepharose affinity chromatography. The effects of reference enzymatic inhibitors (NG-methyl-L-arginine, NG-nitro-L-arginine and N-iminoethyl-L-ornithine) on recombinant expressed proteins were not significantly different from native nitric oxide synthase enzyme preparations. L-aminoguanidine was found to be much less potent in inhibiting recombinant or native human inducible nitric oxide synthase compared to the murine isoform. These findings indicate previously unappreciated interspecies differences in the action of nitric oxide synthase enzymatic inhibitors. The functional expression of human nitric oxide synthase isoforms in a heterologous expression system allowed screening of novel inhibitors. Studies indicated that S-ethylisothiourea and 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine were potent novel inhibitors of human nitric oxide synthases.