͑1981͔͒ were used to characterize the spatial patterns of pitting sites on AISI 316 stainless steel. Populations of artificial pitting sites were generated ͑e.g., clustered, anti-clustered, random, or periodic͒ to test the ability of the selected spatial statistics methods to characterize these patterns. Experimental pitting patterns on AISI 316 stainless steel analyzed by the same methods indicated that interactions occur between micrometer scale pits over multiple micrometer distances. Spatial statistics results indicated that positive ͑e.g., clustering of pit sites͒ occur between pitting sites when they are grown potentiodynamically. Processes associated with the acid/halide pitting mechanism have been shown to promote interactions between pit sites that give rise to such spatial patterns ͓J.

The electrochemical noise resulting from the corrosion of Type 410 stainless steel under open circuit conditions in solutions of widely different corrosivity has been examined. Parameters derived from electrochemical noise measurements and conventional electrochemical measurements were correlated with one another and with post-test examination of the specimens. Both the noise resistance and the polarization resistance increased with decreases in solution corrosivity. In all of the solutions studied, the noise resistance was found to be consistently higher than the polarization resistance. In solutions in which pitting occurred, the open circuit potential of the electrode versus a true reference electrode was more sensitive to the transition to stable pitting than was the pitting index.

The ability of grafted fetal ventral mesencephalic dopaminergic (DAergic) neuroblasts to reinnervate the unilaterally DA denervated rat striatum and improve motoric asymmetry has been well documented in several laboratories. The importance of host target specificity, and catecholamine (CA) neurotransmitter species, in the ability of grafts to ameliorate rotational responses to apomorphine and to affect electrophysiological characteristics of striatal neurons has not been systematically studied. We unilaterally lesioned Sprague-Dawley rats with 6-hydroxydopamine (6-OHDA) and verified the lesions using apomorphine (0.05 mg/kg, s.c.)-induced rotational behavior. Some of the animals subsequently received, intrastriatally, either DA neuroblasts from ventral mesencephalon that normally innervate the striatum, or from arcuate nucleus that do not. Additionally, two other groups were included that received either a CAergic graft from the noradrenergic nucleus locus coeruleus or a graft of cerebral cortex, which normally projects to the striatum but does not contain CAergic neurons. Only the fetal ventral mesencephalic grafts were able to reduce apomorphine- induced rotations and normalize striatal cell firing rates; striatal cell firing rates with ventral mesencephalic grafts were 1.43 Hz +/- 0.22, with arcuate nucleus grafts were 6.03 +/- 0.73, with locus coeruleus grafts were 4.71 +/- 0.74, and with cerebral cortex grafts were 4.36 +/- 0.45. Moreover, only the ventral mesencephalic grafts produced a dense tyrosine hydroxylase (TH)-immunoreactive nerve terminal network in the striatum; in contrast, the arcuate nucleus grafts did not reinnervate the striatum. In locus coeruleus grafted striata, few very long TH-positive axons were seen. We thus conclude that target specificity and neurotransmitter type are critically important in the ability of a graft to functionally reinnervate the 6- OHDA denervated striatum.

No abstract