Histochemical studies on monoamine oxidase in the midbrain of the mouse

The enteric nervous system in tissue culture. III. Studies on neuronal survival and the retention of biochemical and morphological differentiation

The maintenance of differentiated properties and survival rates of enteric neurons, grown in explant cultures for periods of up to 3 weeks, was studied. Using catecholamine fluorescence, immunohistochemistry and autoradiography, it was found that adrenergic neurons, VIP-containing neurons and putative GABAergic neurons, which constitute small subpopulations of guinea pig myenteric neurons in vivo, were all represented in plexus explants after maintenance in culture for 2-3 weeks. The pattern of expression of the transmitter-related enzymes, acetylcholinesterase and monoamine oxidase, paralleled that found in in situ studies. Investigation of neuronal structure by intracellular injection of horseradish peroxidase revealed that the cultured neurons continue to express the wide diversity in gross morphology which characterizes these cells in vivo. Employing autoradiography following uptake of [3H]GABA to label putative GABAergic neurons, their survival rate from days 1 to 15 of culturing was determined. No neuronal death was detected between days 1 and 5, while the number of neurons decreased between days 5 and 15. These observations suggest that enteric neurons maintained in explant cultures survive well and maintain to a high degree their histochemical and morphological properties.

Histochemical detection of monoamine oxidase activity in smooth muscle and epithelial tissues of Mytilus edulis L. and Mytilus galloprovincialis Lmk

Monoamine oxidase (MAO) activity was detected in the glio-interstitial tissue of the anterior byssus retractor muscle (ABRM) of Mytilus by the use of either dopamine or 5-HT as substrate and nitro blue tetrazolium salt as an electron receptor. Both substrates gave superimposable patterns. However, dopamine reactivity was very weak. Discrete but clear MAO activity was detected in the periphery of the smooth muscle cell, i.e., at the level of the peripherally localized mitochondria. The presence of MAO in the epithelium of the buccal palps was also demonstrated. These histochemical observations can be correlated with certain ultrastructural aspects, in particular the presence electron dense organelles profiles in glio-interstitial cells. This MAO activity is discussed in relationship with the high 5-HT content of ABRM and the control of its relaxation. Pigment formation and/or collagen tanning are discussed in terms of a possible relationship with inactivation of biogenic amines. These results complement previous data concerning the glio-interstitial tissue found in close association with muscle and nerve structures.

Enzyme-cytochemistry of the saccus dorsalis of the rainbow trout, Salmo gairdneri Richardson

In the saccus dorsalis of the rainbow trout, Salmo gairdneri Richardson, the activity of various enzymes (transferase, lyases, oxidoreductases, hydrolases) have been studied in detail. The results of this enzyme-cytochemical study firmly demonstrate that the organ is metabolically highly active. The epithelial cells have a strong energy metabolism. Energy production can take place under aerobic as well as under anaerobic conditions. Evidence is presented that glucose from blood is directly utilized for energy demands. The epithelial cells show also high synthetic activities. The moderate amino acid metabolism may participate in the synthesis of an acid mucopolysaccharide-protein complex, especially in the so-called dark cells. Lipid metabolism appears to be restricted to the mitochondria, indicating a high turnover of lipid moieties in the membranes. In contrast to the normal looking mitochondria, the macromitochondria--besides shape and localization--have an extremely high lipid and monoamine metabolism, which may point to a special function in the cellular economy. The high activity of enzymes involved in the degradation of monoamines and in the hydration of CO2 is of particular physiological interest. The significance of the observations is discussed in relation to formerly obtained indications on the involvement of the saccus dorsalis in fluid secretion, extrusion of organic substances of low molecular weight into the ventricular system and uptake of organic substances from the cerebrospinal fluid. The hypothesis of the saccus dorsalis being an analogue of the choroid plexus is supported by several relevant data.

On the method of Glenner for the histochemical demonstration of the monoamine oxidase (MAO)

The method of Glenner et al. for the histochemical demonstration of MAO activity was studied by means of scanning microdensitometry and discrete measurement of optical density (lambda=590 nm) of the liver and brain tissues sections. The experiments indicated that: (1) The optimal time of incubation (the thickness of sections is 15 mum) is 60-90 min. (2) The histochemical reaction proceeds with the following substrates: dopamine, noradrenalin, serotonin, and tryptamine. (3) Iproniazid is the best inhibitor for preincubation whereas for simultaneous inhibition the substrate semicarbazide is better. (4) The incubation under the anaerobic conditions caused a considerable decrease of the stain intensity of the sections. We consider these data to indicate that both the aldehydes and acids formed under oxidation may take part in direct reduction of NBT to diformazan. (5) The histochemical reaction for MAO without substrates testifies to the presence of endogenous amines or other redox reactions leading to the reduction of NBT.