Nitric oxide generators produce accumulation of chelatable zinc in hippocampal neuronal perikarya

While zinc is essential for health, it has also been implicated in the neuropathology of several disease states such as Alzheimer's disease, epilepsy and cerebral ischemia. Recent studies have shown that oxidative and nitrosylative stresses can liberate zinc from metalloproteins in vitro. Thus, nitric oxide (NO.), a radical molecule which serves as a retrograde messenger, was studied for its effects on the in vivo accumulation of zinc in neurons. Three NO.-donors, sodium nitroprusside (SNP; greater than or equal to 5 nmol), spermine-nitric oxide complex (SPER-NO; less than or equal to 200 nmol), and 3-morpholino-sydnonimine (SIN-1; less than or equal to 200 nmol) were administered into the dorsal hippocampus of rats. Brain tissue was stained by both the Timm's method, and with N-(6-methoxy-8-quinolyl)-para-toluenesulfonamide (TSQ), a histochemical stain for metal ions and a selective fluorescent probe for zinc ions, respectively. A sporadic pattern of zinc accumulation within the perikarya, axons, and dendritic processes of certain pyramidal neurons, interneurons, and dentate granule cells was found 2 h after administrations of SNP and SPER-NO, but not with SIN-1. With SNP, sporadic perikaryal zinc staining of the pyramidal neurons and interneurons at strata oriens (SO), pyramidale (SP), and radiatum (SR) was consistently observed, but with SPER-NO, the granule cells of the dentate gyrus were preferentially stained. Administration of sodium ethylenediamine tetraacetic acid (NaEDTA, 10 nmol) 10 min before SNP resulted in a marked reduction of sporadic perikaryal zinc staining in the SO and SR. The more selective metal chelator, N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN, 10 nmol) injected 10 min before SNP abolished the staining of neuronal perikarya and surrounding neuropil. In addition, SNP, but not SPER-NO, induced convulsive activity. Groups of rats that manifested continuous wet dog shakes and/or generalized convulsions for at least 4-5 h after SNP were found to have generalized perikaryal Timm's staining of all neurons in the pyramidal cell layer of the subicular and cornu ammonis regions, similar to the staining found after seizures induced by kainic acid. However, after kainic acid-, but not SNP-induced seizures, Timm's staining of neuronal perikarya in the piriform cortex and amygdala was also observed. This is the first evidence that NO. can induce accumulation of zinc in neuronal perikarya and processes in the hippocampus in vivo. As a mechanism underlying the possible involvement of zinc in neurodegenerative disorders caused by excitotoxicity and/or oxidative stress, it is an alternative to release of synaptic vesicle zinc and uptake by damaged hippocampal neuronal perikarya. (C) 1998 Elsevier Science B.V. All rights reserved.