Fluorescent imaging of nitric oxide production in neuronal varicosities associated with intraparenchymal arterioles in rat hippocampal slices

The fluorescent indicator 4,5-diaminofluorescein (DAF-2) has been used to i nvestigate the production of nitric oxide in the vicinity of intraparenchym al cerebral blood vessels. Slices of rat hippocampus 300-350 mum thick, wer e loaded with 5 muM DAF-2 diacetate. On exposure to light of 450-490 nm wav elength, point sources of fluorescence, 1.8 +/- 0.2 mum in diameter (mean /- SEM), were observed in close apposition to the outer surface of the vasc ular smooth muscle wall of 10/15 arterioles. In fixed slices, resectioned a nd processed for nicotinamide adenine dinucleotide phosphate-dependent diap horase, stained varicose fibres were also seen in close association with th e smooth muscle wall of small arterioles. These findings suggest that tonic activity in perivascular nitrergic nerve fibres lying in close proximity t o intraparenchymal microvessels may be a source of dilator tone within the parenchyma. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.