Patients with several inherited human encephalomyopathies exhibit systemic and neurological symptoms in association with specific mitochondrial mutations. The mechanisms by which these mitochondrial mutations result in cellular injury have not been elucidated. One potential cause of neuronal vulnerability is an inability to effectively buffer intracellular calcium. We report that fibroblasts from patients with one specific inherited encephalomyopathy, MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) syndrome, have elevated levels of ionized calcium and cannot normally sequester calcium influxes. Quantitative fluorescence imaging demonstrated that this abnormality was associated with a relative decrease in mitochondrial membrane potential compared to control fibroblasts. This documentation of pathological calcium homeostasis in a genetic neurological disease extends the calcium hypothesis of toxic cell injury to human mitochondrial encephalomyopathies.

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Development of the noradrenergic fiber innervation of the rat hippocampus by the locus coeruleus was examined immunohistochemically in fixed tissue from animals aged 4 days through 55 days postnatal. The presence of tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) immunoreactive cells and fibers was evaluated in sections of hippocampus and locus coeruleus. Large, multipolar TH- and DBH-positive cells with long beaded fibers were visible within locus coeruleus at all ages; no immunopositive cell bodies were found in hippocampus. In hippocampal sections from mature animals (PN55), the highest density of DBH-stained fibers was found in stratum lucidum of CA3 and in the hilus and inner molecular layer of the dentate gyrus. Whereas similar patterns of fiber positivity were found at PN21 and PN10 (although with somewhat reduced density of immunopositive fibers), the pattern was quite different at PN4. Although fiber staining was relatively sparse at PN4, relative density of DBH fibers was highest in stratum radiatum of CA1 and subiculum. This change in staining pattern suggests that noradrenergic function in hippocampus may change as the rat matures. Double immunofluorescence techniques showed an overlap of DBH and TH positive fibers in all hippocampal regions at all ages. DBH immunostaining appeared to be somewhat more sensitive than the TH staining. These data made it impossible to confirm the presence of significant numbers of nonnoradrenergic, catecholamine-containing fibers in hippocampus.

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A study of the onset of cation and guanine nucleotide regulation of delta, mu, and kappa rat brain opioid receptors during postnatal development was undertaken. Site-specific binding assays were utilized for each receptor type and the effects of 0.5 mM MnCl2, 100 mM NaCl, and/or 50 microM guanosine-5'-(beta, gamma-imido) triphosphate [Gpp(NH)p] were assessed. The most pronounced changes of opioid binding were seen in the presence of Mn2+. In adults, agonist binding to delta sites was stimulated by Mn2+, whereas that to mu sites was not affected and kappa binding was inhibited. The postnatal development of Mn2+ regulation for the three receptor subtypes was distinctly different. The largest effects were seen on delta sites detected in the early neonatal period, Mn2+ eliciting a 68% stimulation of binding over controls at day 1. Significant inhibition of kappa site binding by Mn2+ was detected only after the third postnatal week. Mn2+ caused a significant reversal of Gpp(NH)p inhibition of delta binding in the early neonatal period, exceeding that in the absence of regulators. Inhibition of mu and delta receptor binding by Na+ was greater, and the Mn2+ reversal of this effect was smaller, in the first 2 postnatal weeks than in adults. Gpp(NH)p + Na+ regulation did not change appreciably during the postnatal period. However, Mn2+ reversal of the considerable inhibition elicited by the combination of Na+ and Gpp(HN)p was developmental time-dependent. The data are discussed in terms of multiple sites of interaction for guanine nucleotides and cations.(ABSTRACT TRUNCATED AT 250 WORDS)