Ca(2+)-ATPase and Mg(2+)-ATPase in Aplysia glial and interstitial cells: an EM cytochemical study.

The localization of Ca(2+)- and Mg(2+)-ATPases was determined in Aplysia central and peripheral nervous system, using an electron microscopic cytochemical method. The enzyme activity appeared localized to the membrane of glial granules (gliagrana), particularly in the peripheral nervous system of the esophagus, and on the plasma membrane of central glial cells adjacent to neuronal cell bodies. No calcium- and/or magnesium-ATPase activity was detectable on the plasma membrane of glial cells surrounding nerve axons in the pleuro-visceral connectives. These findings are discussed along two main lines: (a) the calcium-ATPase of the gliagrana coincides with a high intragranular calcium and/or proton concentration; and (b) the presence of a calcium-ATPase activity at the glio-neuronal interface around the neuronal cell bodies coincides with the use of calcium ions as charge carriers of the action potential, and its absence at the level of the axon with the concurrent functional use of sodium ions.     

Histochemical and cytochemical demonstration of Ca++-ATPase activity in the stellate cells of the adenohypophysis of the guinea pig

The histo- and cytochemical localization of Ca++-ATPase activity in the adenohypophysis of the guinea pig was studied utilizing a newly developed method (Ando et al. 1981). An intense reaction was observed in the wall of the blood vessels and between non-secretory cells (stellate cells) and endocrine cells of the pars distalis. Under the electron microscope the Ca++-ATPase reaction product was located extracellularly in relation to the plasmalemma of the stellate cells. This reaction was dependent on Ca++ and the substrate, ATP, and reduced by the addition of 0,1 mM quercetin to the standard incubation medium. Preheating of the sections before incubation completely inhibited the enzyme activity. When Mg++ in different concentrations were substituted for Ca++ in the incubation medium the reaction was always reduced. Both Ca++ and Mg++ in the incubation medium also reduced the reaction. The plasmalemma of the endocrine cells contains no demonstrable amount of Ca++-ATPase activity. The function of the Ca++-ATPase activity is discussed in relation to the regulation of the extracellular Ca++ concentration which seems to be important with respect not only to the secretory process of the endocrine cells but also to the metabolism of the adenohypophysis.     

Microglial cells in the central nervous system of the rabbit and rat: cytochemical identification using two different lectins

Microglial cells were selectively demonstrated in the central nervous system of adult rabbits and rats using lectin histochemistry. Biotinylated Ricinus communis agglutinin-120 (RCA-1) and biotinylated Griffonia simplicifolia B4 isolectin (GSA I-B4) were used as histochemical markers on sections of Bouin-fixed paraffin-embedded cerebrum and cerebellum. Results were quite similar using both lectins and both species. GSA I-B4 resulted in a better staining in the rat, while RCA-1 labelling was superior in the rabbit. Neither neurons nor glial cells other than microglia were stained with our technique. Lectin histochemistry applied for the detection of microglial cells appears to be of sufficient selectivity and may be considered as an important tool in the morphological and neurobiological study of these cells.     

An endogenous inhibitor of Ca++-ATPase from human placenta

Intracellular free calcium is regulated by Ca(++)-ATPase, one form present on the plasma membrane (PM Ca(++)-ATPase) and the other on sarcoplasmic (endoplasmic) reticulum (SR/ER Ca(++)-ATPase). An endogenous inhibitor of SR Ca(++)-ATPase from human placenta was shown to be present in normal placenta and the activity was not detectable in placenta from preeclamptic patients. The inhibitor was distributed in cytosol and microsomes. The inhibition of Ca(++)-ATPase by this inhibitor was concentration- and time-dependent. The inhibitor neither bound to DEAE- nor CM-sepharose resins at pH 7.5 and 8.5. Furthermore, it was heat stable for 15 min up to 55 degrees C and completely destroyed at 80 degrees C in a few minutes. It was also observed to be stable at room temperature for at least 3 months. The purification and characterization of this inhibitor would be valuable in achieving an understanding of the normal regulation of Ca(++)-ATPase in the placenta during pregnancy.     

An Endogenous Inhibitor of Ca++-ATPase from Human Placenta

Intracellular free calcium is regulated by Ca⁺⁺-ATPase, one form present on the plasma membrane (PM Ca⁺⁺-ATPase) and the other on sarcoplasmic (endoplasmic) reticulum (SR/ER Ca⁺⁺-ATPase). An endogenous inhibitor of SR Ca⁺⁺-ATPase from human placenta was shown to be present in normal placenta and the activity was not detectable in placenta from preeclamptic patients. The inhibitor was distributed in cytosol and microsomes. The inhibition of Ca⁺⁺-ATPase by this inhibitor was concentration-and time-dependent. The inhibitor neither bound to DEAE-nor CM-sepharose resins at pH 7.5 and 8.5. Furthermore, it was heat stable for 15min up to 55°C and completely destroyed at 80°C in a few minutes. It was also observed to be stable at room temperature for at least 3 months. The purification and characterization of this inhibitor would be valuable in achieving an understanding of the normal regulation of Ca⁺⁺-ATPase in the placenta during pregnancy.     

Tenascin-R: role in the central nervous system

Tenascin-R (TN-R), a member of the tenascin family of extracellular matrix glycoproteins, is exclusive to the nervous system. It affects cell migration, adhesion and differentiation, although no remarkable clinical consequences have been shown in knock-out animal models. TN-R's expression pattern suggests a possible primary or secondary role in certain neurological problems including malformations, tumors and neurodegenerative disorders. This review summarizes the structure and molecular interactions of this molecule and discusses its function and possible roles in the central nervous system.     

Anti-idiotypic antibodies as a tool for cytochemical identification of substance P receptors in the central nervous system

Anti-idiotypic antibodies may serve as valuable probes for cytological identification of peptide receptors in the CNS. We have previously described the preparation of anti-substance P (SP) anti-idiotypic antibodies (anti-Id Ab) and have shown that they recognize SP receptors. These anti-Id Ab can be used in cytology to label SP receptors in CNS. We chose rat cervical spinal cord as a model because SP is present in large amounts in the dorsal and ventral horns, where it is implicated in pain and in motor function, respectively. After application of an indirect immunoperoxidase technique to tissue sections from perfused animals, immunolabeling was seen in the two superficial layers of the dorsal horn, the area surrounding the central canal, extending along the white matter in lamina VII, and in part of the ventral horn. This localization is in accordance with the classical distribution of SP receptors as seen by autoradiography with labeled SP. In the light of control experiments, as well as of biochemical and pharmacological arguments, we discuss the specificity of the immunolabeling. We conclude that anti-Id Ab recognize NK-P receptors, although crossreaction with NK-A or NK-B receptors cannot be totally ruled out.     

Use of the analytical electron microscope (AEM) in cytochemical studies of the central nervous system.

Central nervous tissues (median eminence and arcuate nucleus) were studied by means of energy dispersive x-ray analysis using electron optical systems (analytical electron microscopy). These studies were conducted after the tissue had been treated specifically for localized biogenic amines (BA). The results indicate that not only is the BA cytochemical reaction highly specific, and that BAs can be localized intraneuronally in areas not previously identified, but also that the analytical electron microscope is a very valuable and potentially powerful tool in the studies of inclusion bodies and organelles in the central nervous system and other tissues. Thus, the nonspecific density production by osmium tetroxide can be elucidated from the specific BA reaction plus other areas of the nervous system containing density producing heavy metals, i.e., iron are readily identifiable.     

Ultracytochemical study of Ca++-ATPase and K+-NPPase activities in retinal photoreceptors of the guinea pig

Summary Ca⁺⁺-ATPase activity was demonstrated histochemically at light- and electron-microscopic levels in inner and outer segments of retinal photoreceptor cells of the guinea pig with the use of a newly developed one-step lead-citrate method (Ando et al. 1981). The localization of ouabain-sensitive, K⁺-dependent p-nitrophenylphosphatase (K⁺-NPPase) activity, which represents the second dephosphorylative step of the Na⁺-K⁺-ATPase system, was studied by use of the one-step method newly adapted for ultracytochemistry (Mayahara et al. 1980). In retinal photoreceptor cells fixed for 15 min in 2% paraformaldehyde the electron-dense Ca⁺⁺-ATPase reaction product accumulated significantly on the inner membranes of the mitochondria but not on the plasmalemma or other cytoplasmic elements of the inner segments. The membranes of the outer segments remained unstained except the membrane arrays in close apposition to the retinal pigment epithelium. The cytochemical reaction was Ca⁺⁺- and substrate-dependent and showed sensitivity to oligomycin. When Mg⁺⁺-ions were used instead of Ca⁺⁺-ions, a distinct reaction was also found on mitochondrial inner membranes.In contrast to the localization of the Ca⁺⁺ -ATPase activity, the K⁺-NPPase activity was demonstrated only on the plasmalemma of the inner segments, but not on the mitochondria, other cytoplasmic elements or the outer segment membranes. This reaction was almost completely abolished by ouabain or by elimination of K⁺ from the incubation medium.Fellow of the Alexander von Humboldt Foundation, Bonn, Federal Republic of Germany     

Endocannabinoids in the central nervous system

The major psychoactive component of cannabis derivatives, delta9-THC, activates two G-protein coupled receptors: CB1 and CB2. Soon after the discovery of these receptors, their endogenous ligands were identified: lipid metabolites of arachidonic acid, named endocannabinoids. The two major main and most studied endocannabinoids are anandamide and 2-arachidonyl-glycerol. The CB1 receptor is massively expressed through-out the central nervous system whereas CB2 expression seems restricted to immune cells. Following endocannabinoid binding, CB1 receptors modulate second messenger cascades (inhibition of adenylate cyclase, activation of mitogen-activated protein kinases and of focal-adhesion kinases) as well as ionic conductances (inhibition of voltage-dependent calcium channels, activation of several potassium channels). Endocannabinoids transiently silence synapses by decreasing neurotransmitter release, play major parts in various forms of synaptic plasticity because of their ability to behave as retrograde messengers and activate non-cannabinoid receptors (such as vanilloid receptor type-1), illustrating the complexity of the endocannabinoid system. The diverse cellular targets of endocannabinoids are at the origin of the promising therapeutic potentials of the endocannabinoid system.     

Emergence in the central nervous system

“Emergence” is an idea that has received much attention in consciousness literature, but it is difficult to find characterizations of that concept which are both specific and useful. I will precisely define and characterize a type of epistemic (“weak”) emergence and show that it is a property of some neural circuits throughout the CNS, on micro-, meso- and macroscopic levels. I will argue that possession of this property can result in profoundly altered neural dynamics on multiple levels in cortex and other systems. I will first describe emergent neural entities (ENEs) abstractly. I will then show how ENEs function specifically and concretely, and demonstrate some implications of this type of emergence for the CNS.     

Glial repair in the cultured central nervous system of an insect

Summary Insect glial cells are capable of division and repair in organ culture after selective damage with the toxin ethidium bromide. The repair is slower and less organised than seen in vivo after similar treatment and is still incomplete after one month. Granule-containing cells, which play an important role in the early stages of repair in vivo, are never seen in cultured connectives. This observation adds further support to the hypothesis that these cells are derived from haemocytes and that their presence is necessary for rapid and orderly repair. The uptake of ³H-thymidine into perineurial glial cells in vitro, both in control and ethidiumtreated connectives, shows that there is a considerable proliferation of cells in this region. Some uptake of thymidine is also seen in subperineurial glia but division alone cannot account for the large increase in the number of glial nuclei found at the early stages of repair in this region. Further, glial cells with diverse morphologies suggest that subpopulations are present. We conclude that cell migration from undamaged areas, as well as cell proliferation, is necessary for CNS repair in vitro.