ELECTRON HISTOCHEMICAL EXAMINATION OF OXIDATIVE ENZYMES AND MITOCHONDRIA

Morphological and cytochemical characteristics of periodontal Ruffini ending under normal and regeneration processes

Current knowledge on the Ruffini endings, primary mechanoreceptors in the periodontal ligament is reviewed with special reference to their cytochemical features and regeneration process. Morphologically, they are characterized by extensive ramifications of expanded axonal terminals and an association with specialized Schwann cells, called lamellar or terminal Schwann cells, which are categorized, based on their histochemical properties, as non-myelin-forming Schwann cells. Following nerve injury, the periodontal Ruffini endings of the rat incisor ligament can regenerate more rapidly than Ruffini endings in other tissues. During regeneration, terminal Schwann cells associated with the periodontal Ruffini endings migrate into regions where they are never found under normal conditions. Also during regeneration, alterations in the expression level of various bioactive substances occur in both axonal and Schwann cell elements in the periodontal Ruffini endings. Neuropeptide Y, which is not detected in intact periodontal Ruffini endings, is transiently expressed in their regenerating axons. Growth-associated protein-43 (GAP-43) is expressed transiently in both axonal and Schwann cell elements during regeneration, while this protein is localized in the Schwann sheath of periodontal Ruffini endings under normal conditions. The expression of calbindin D28k and calretinin, both belonging to the buffering type of calcium-binding proteins, was delayed in periodontal Ruffini endings, compared to their morphological regeneration. As the importance of axon-Schwann cell interactions has been proposed, further investigations are needed to elucidate their molecular mechanism particularly the contribution of growth factors during the regeneration as well as development of the periodontal Ruffini endings.

The Ruffini ending as the primary mechanoreceptor in the periodontal ligament: its morphology, cytochemical features, regeneration, and development

The periodontal ligament receives a rich sensory nerve supply and contains many nociceptors and mechanoreceptors. Although its various kinds of mechanoreceptors have been reported in the past, only recently have studies revealed that the Ruffini endings--categorized as low-threshold, slowly adapting, type II mechanoreceptors--are the primary mechanoreceptors in the periodontal ligament. The periodontal Ruffini endings display dendritic ramifications with expanded terminal buttons and, furthermore, are ultrastructurally characterized by expanded axon terminals filled with many mitochondria and by an association with terminal or lamellar Schwann cells. The axon terminals of the periodontal Ruffini endings have finger-like projections called axonal spines or microspikes, which extend into the surrounding tissue to detect the deformation of collagen fibers. The functional basis of the periodontal Ruffini endings has been analyzed by histochemical techniques. Histochemically, the axon terminals are reactive for cytochrome oxidase activity, and the terminal Schwann cells have both non-specific cholinesterase and acid phosphatase activity. On the other hand, many investigations have suggested that the Ruffini endings have a high potential for neuroplasticity. For example, immunoreactivity for p75-NGFR (low-affinity nerve growth factor receptor) and GAP-43 (growth-associated protein-43), both of which play important roles in nerve regeneration/development processes, have been reported in the periodontal Ruffini endings, even in adult animals (though these proteins are usually repressed or down-regulated in mature neurons). Furthermore, in experimental studies on nerve injury to the inferior alveolar nerve, the degeneration of Ruffini endings takes place immediately after nerve injury, with regeneration beginning from 3 to 5 days later, and the distribution and terminal morphology returning to almost normal at around 14 days. During regeneration, some regenerating Ruffini endings expressed neuropeptide Y, which is rarely observed in normal animals. On the other hand, the periodontal Ruffini endings show stage-specific configurations which are closely related to tooth eruption and the addition of occlusal forces to the tooth during postnatal development, suggesting that mechanical stimuli due to tooth eruption and occlusion are a prerequisite for the differentiation and maturation of the periodontal Ruffini endings. Further investigations are needed to clarify the involvement of growth factors in the molecular mechanisms of the development and regeneration processes of the Ruffini endings.

Impaired succinic dehydrogenase activity of rat Purkinje cell mitochondria during aging

The perikaryal Purkinje cell mitochondria positive to the copper ferrocyanide histochemical reaction for succinic dehydrogenase (SDH) have been investigated by means of semiautomatic morphometric methods in rats of 3, 12 and 24 months of age. The number of organelles/microm3 of Purkinje cell cytoplasm (Numeric density: Nv), the average mitochondrial volume (V) and the mitochondrial volume fraction (Volume density: Vv) were the ultrastructural parameters taken into account. Nv was significantly higher at 12 than at 3 and 24 months of age. V was significantly decreased at 12 and 24 months of age, but no difference was envisaged between adult and old rats. Vv was significantly decreased in old animals vs. the other age groups. In young and old rats, the percentage of organelles larger than 0.32 microm3 was 13.5 and 11%, respectively, while these enlarged mitochondria accounted for less than 1% in the adult group. Since SDH activity is of critical importance when energy demand is high, the marked decrease of Vv supports an impaired capacity of the old Purkinje cells to match actual energy supply at sustained transmission of the nervous impulse. However, the high percentage of enlarged organelles found in old rats may witness a morphofunctional compensatory response.

Age-dependent decrease in the activity of succinic dehydrogenase in rat CA1 pyramidal cells: a quantitative cytochemical study

A computer-assisted morphometric study has been carried out on the ultrastructure of perikaryal CA1 pyramidal cell mitochondria positive to the copper ferricyanide cytochemical reaction for succinic dehydrogenase (SDH) in rats of 3, 12 and 23 months of age. The cytoplasmic volume fraction occupied by the positive mitochondria (Volume density: Vv), the number of organelles/micron 3 of CA1 pyramidal cell cytoplasm (Numerical density: Nv) and the average mitochondrial volume (V) were automatically calculated by means of computer-assisted morphometry. Vv was significantly decreased in 23-month-old animals versus the other age groups. Nv was unchanged between 3 and 12 months of age, but was decreased to a significant extent in old animals. V did not undergo significant changes in the three age groups taken into account. In the old animals the percent of organelles smaller than 0.16 micron 3 is above 20%, while in the young and adult groups the same size of mitochondria accounts for 7 and 3%, respectively. Thus, a reduction in the number of medium sized organelles appears to be responsible for the decrease in Vv due to age. Since SDH activity is known to support maximum rates of respiration, quantitative estimation of the active mitochondria provides information on the metabolic competence of the cells investigated when energy demand is high. In this context, our present findings document that a significant impairment in the efficiency to match actual energy provisions occurs in old CA1 pyramidal cells.

Cytochrome oxidase activity as a marker for periodontal sensory receptors in the rat

Cytochrome oxidase activity was explored histochemically in axon terminals of periodontal Ruffini endings of rat upper incisors at both the light- and electron-microscopic levels. Staining clearly demonstrated ramified structures in the alveolar half of the periodontal ligament. These structures resembled the profiles of the axon terminals of the periodontal Ruffini ending previously demonstrated by an immunohistochemical method for neurofilament protein. Histochemically at the electron-microscopic level, the ramified structures were identified as true Ruffini endings in which each axon terminal was filled with reactive mitochondria. Two types of mitochondria were distinguished with respect to the localization pattern of reaction products; almost all mitochondria were positive for cytochrome oxidase activity, with only a few negative. As the enzyme activity did not decrease after demineralization, the findings suggest that cytochrome oxidase is a useful marker enzyme for demonstrating sensory receptors in the periodontal ligament. Histochemical methods for cytochrome oxidase may contribute to the light- and electron-microscopic morphological analysis of periodontal sensory receptors.

Succinate dehydrogenase and mitochondria in the hair cells in the organ of Corti of mature and old shaker-1 mice

The activity of succinate dehydrogenase in the sensory hair cells in the organ of Corti of mature and old shaker-1 mice described as the animals grew older, the outer hair cells being the most effected. The decrease inactivity of this enzyme was closely linked with the degeneration of the mitochondria. When mitochondria were absent or grossly degenerated there was no enzyme activity. It is possible that this defect is linked with the deafness in these mice.

Triphenyltetrazolium and its derivatives are anisotropic inhibitors of energy transduction in oxidative phosphorylation in rat liver mitochondria

Triphenyltetrazolium and its derivatives inhibited energy transduction in mitochondria but not in submitochondrial particles, which are inside-out relative to the membranes of mitochondria. Triphenyltetrazolium incorporated into the inside of submitochondrial particles inhibited ATP synthesis in the particles. Triphenyltetrazolium also inhibited the reduction of NAD by succinate coupled with oxidation of succinate by O2 and hydrolysis of ATP. Energization of mitochondrial inner membranes with succinate and with ATP induced sites on the membranes for triphenyltetrazolium and its derivatives. The maximum amounts of energy-dependent binding sites for triphenyltetrazolium on membranes energized with succinate and ATP, respectively, were 14 and 4 nmol/mg protein. Triphenyltetrazolium also induced H+ ejection from the energized membranes. The maximum amounts of H+ ejection from membranes energized with succinate and ATP, respectively, were 4 and 2.4 nmol/mg protein. Triphenyltetrazolium also decreased the membrane potential up to about half the control value and caused shrinkage of mitochondria in an energy-dependent fashion. Comparison of the Hammett's sigma constants of triphenyltetrazolium derivatives with various substituents on the 3-benzene ring showed that lower concentrations of triphenyltetrazolium derivatives with a stronger positive charge were required for inhibition of energy transduction. The present findings show that triphenyltetrazolium and its derivatives act as anisotropic inhibitors of energy transduction by binding to negative charges created on the outer side (C-side) of energized mitochondria, and that the positive charge of these inhibitors is one of important factors for their inhibitory activity. These negative charges may be an essential part of the H+ pump.

Nephrotoxicity following acute administration of N-(3,5-dichlorophenyl)succinimide in rats

The acute renal effects of the fungicide N-(3,5-dichlorophenyl)succinimide (NDPS) were studied in male Sprague-Dawley rats. NDPS (50 mg/kg, i.p.) increased urine volume and decreased food intake and body weight at 24 h but not 48 h. No change in urine content or the accumulation by renal cortical slices of the organic anion p-aminohippurate (PAH) or the organic cation tetraethylammonium (TEA) was observed with 50 mg/kg NDPS when compared to control animals. Rats receiving 100 or 200 mg/kg NDPS (i.p.) exhibited increased urine volume, proteinuria, glucosuria, decreased food intake and body weight, increased BUN and decreased accumulation of PAH and TEA at both 24 h and 48 h. These effects were generally more pronounced at the 200 mg/kg dose level. Pair-fed control experiments demonstrated that renal effects were NDPS-induced and not related to daily food consumption. NO change in water intake was observed with any dose of NDPS used. The results demonstrate that NDPS alters renal function in a dose-dependent manner. In addition, NDPS (50 mg/kg) is capable of producing diuresis without apparent nephrotoxicity while doses of 100 mg/kg or more produce diuresis and nephrotoxicity.

Light and electron-microscopic studies on guinea pig hearts after perfusion with nitro-blue tetrazolium (NBT)

Guinea pig hearts isolated by the Langendorff technique were perfused with a nitro-blue tetrazolium salt solution. In spite of a homogeneous dark-blue staining at the macroscopic examination, light-microscopic studies showed a spotty staining of the myocardial fibers. Since no microscopic alterations were found which could explain the unstained areas, ultramicroscopic studies were undertaken. At ultrastructural level, striking alterations of myocardial cells were observed. They consisted of mitochondrial lesions, alterations of the transversal tubuli, and intercalated discs. Arteriolar narrowing and capillary edema were found, suggesting that pathological changes in the microcirculation could be a possible reason for the spotty staining of the myocardial fibers. Some speculations on the nature and localization of the formazan granules are also reported.

Tetrazolium salts and formazans

The history of the tetrazolium salts and formazans goes back 100 years, to when Friese (1875) reacted benzene diazonium nitrate with nitromethane, to produce a cherry-red "Neue Verbindung". This was the first formazan. 19 years later, Von Pechmann and Runge (1894) oxidised a formazan to produce the first tetrazolium salt. Many hundreds of tetrazolium salts and formazans were prepared in the following years, but only a handful have found applications in biological research. This article has attempted to describe the properties of these compounds, and to illustrate how the tetrazolium salt-formazan reaction has been exploited to serve an extremely wide variety of functions.

Electron-microscopic-histochemical demonstration of succinic-dehydrogenase activity in root cells of yellow lupine

Succinic dehydrogenase (SDH) activity was demonstrated in unfixed root segments from Lupinus luteus at the ultrastructural level by the use of ferricyanide as electron acceptor. The specificity of the reaction was proven by malonate inhibition. The reaction product was found to be localized in the mitochondria and to a lesser extent on the membranes of plastids. Different mitochondria of the same cell often showed different intensity of the staining reaction. Different cells of the same tissue exhibited varying degrees of enzyme activity. An increase was found in the number of cells exhibiting the SDH reaction, as well as in the intensity of the reaction itself, from the meristematic zone of the root to the more differentiated regions.

Mitochondrial antibodies in primary biliary cirrhosis. I. Localization of the antigen to mitochondrial membranes

The antigen reacting with complement-fixing antibodies in the sera of patients with primary biliary cirrhosis was localized predominantly in the mitochondrial fraction of tissue homogenates obtained by differential centrifugation. Purified mitochondrial preparations had a high content of the antigen whereas purified lysosomes failed to fix complement with PBC sera. Analysis of a number of fractionation experiments showed a high correlation between antigen content and the mitochondrial enzyme succinic dehydrogenase in all fractions. There was much poorer correlation with lysosomal and micrososomal enzyme markers. The patterns of staining obtained with a fluorescein conjugate of IgG from a PBC patient closely paralleled those obtained with a histochemical method for the demonstration of succinic dehydrogenase, further confirming the mitochondrial localization of the antigen. Staining was brightest in cells containing mitochondria with well-developed cristae. Studies on mitochondria fragmented by osmotic lysis, hexane, lysolecithin, and ultrasound suggest that the antigen is associated with the mitochondrial inner membranes.

The demonstration of the succinic dehydrogenase system in Bacillus subtilis using tetranitro--blue tetrazolium combined with techniques of electron microscopy

Activity of the succinic dehydrogenase system was studied in Bacillus subtilis utilizing combined techniques of cytochemistry and electron microscopy. Organisms were incubated in a medium containing tetranitro-blue tetrazolium (TNBT) which served as an electron acceptor. Enzymatic activity, as evidenced by deposition of TNBT-formazan, was found on membranous organelles associated with the cytoplasmic membrane and septal plasma membrane, the nuclear area, and the plasma membrane. Flagella, approximately 190 A in diameter, with thorn-like projections protruded through the cell wall. Tangential-oblique sections of the cell wall showed many pores approximately 220 A in diameter with a center-to-center spacing of approximately 450 A.

ACRIFLAVINE INDUCTION OF DIFFERENT KINDS OF "PETITE" MITOCHONDRIAL POPULATIONS IN SACCHAROMYCES CEREVISIAE

Avers, Charlotte J. (Rutgers, The State University, New Brunswick, N. J.), Cynthia R. Pfeffer, and Martha W. Rancourt. Acriflavine induction of different kinds of "petite" mitochondrial populations in Saccharomyces cerevisiae. J. Bacteriol. 90:481-494. 1965.-Mutant frequencies induced by 1 or 2 hr in 16 and 64 mug/ml of acriflavine were significantly higher during acceleration and log-phase exposures than during lag or stationary phases. From these induced petites, 59 colonies were selected at random and established in pure culture. All strains were analyzed histochemically for mitochondrial cytochrome oxidase and succinic dehydrogenase (SDH) reactions. On the basis of counts of stained mitochondria per cell obtained by light microscopy, four different cell phenotypes were recognized among the mutant strains: (i) reduced cytochrome oxidase, wild-type SDH; (ii) reduced cytochrome oxidase, high SDH; (iii) absent cytochrome oxidase, high SDH; and (iv) absent cytochrome oxidase, wild-type SDH. The last group was the most common, characterizing 43 of the 59 strains. Electron microscopy showed differences in mitochondrial ultrastructure for the various cell phenotype classes. Electron histochemical localizations showed cytochrome oxidase reaction product only on mitochondrial membranes of respiration-competent cells. Both reactive and unreactive mitochondria occurred in the same cell in mutants with partial respiratory competence. Different mitochondrial subpopulation mixtures characterized the mutant strains, many of which had at least two kinds of respiratory-competent types per chondriome. The diverse chondriomes comprised a stable feature of the mutants, since they have been maintained unchanged during serial transfer for more than 1 year in culture. Together with earlier reports of at least two kinds of mitochondria in wild-type cells, the evidence indicated that mitochondria were capable of regulating some portion of their phenotype. The recognition of mitochondrial phenotypes was proposed as an initial step in a formal analysis of organelle heredity.