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 oxidat ive 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 ac cumulation 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-sydnonimin e (SIN-1; less than or equal to 200 nmol) were administered into the d orsal hippocampus of rats. Brain tissue was stained by both the Timm's method, and with N-(6-methoxy-8-quinolyl)-para-toluenesulfonamide (TS Q), a histochemical stain for metal ions and a selective fluorescent p robe for zinc ions, respectively. A sporadic pattern of zinc accumulat ion within the perikarya, axons, and dendritic processes of certain py ramidal neurons, interneurons, and dentate granule cells was found 2 h after administrations of SNP and SPER-NO, but not with SIN-1. With SN P, sporadic perikaryal zinc staining of the pyramidal neurons and inte rneurons at strata oriens (SO), pyramidale (SP), and radiatum (SR) was consistently observed, but with SPER-NO, the granule cells of the den tate gyrus were preferentially stained. Administration of sodium ethyl enediamine tetraacetic acid (NaEDTA, 10 nmol) 10 min before SNP result ed in a marked reduction of sporadic perikaryal zinc staining in the S O and SR. The more selective metal chelator, N,N,N',N'-tetrakis(2-pyri dylmethyl)ethylenediamine (TPEN, 10 nmol) injected 10 min before SNP a bolished 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 generalize d perikaryal Timm's staining of all neurons in the pyramidal cell laye r of the subicular and cornu ammonis regions, similar to the staining found after seizures induced by kainic acid. However, after kainic aci d-, but not SNP-induced seizures, Timm's staining of neuronal perikary a in the piriform cortex and amygdala was also observed. This is the f irst evidence that NO. can induce accumulation of zinc in neuronal per ikarya and processes in the hippocampus in vivo. As a mechanism underl ying the possible involvement of zinc in neurodegenerative disorders c aused 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 .