摘要:

AbstractThe early or “instantaneous” current‐voltage relationship for the light‐activated potassium current inAplysiagiant neurons was linear during the first second of illumination. However, the light current was greatly reduced or abolished by prolonged hyperpolarization. It was also greatly reduced by the injection of calcium EGTA buffers having calcium activities of 5.6 × 10−8Mand simulated by injecting buffers with calcium activities of 2.8–5.6 × 10−7M. Removal of calcium from the extracellular fluid had no effect. Both the light‐and calcium‐activated outward potassium currents were reduced by tetra‐ethylammonium (TEA) ions. The light current was not affected by substituting rubidium for potassium nor by substituting either lithium or Tris for sodium. The calcium‐activated potassium current persisted when the neuron was cooled to 5°C. However, the light response could no longer be elicited. Light hyperpolarizesAplysianeurons probably by increasing intracellular calcium activity two‐to six‐fold which activates a membrane potassium conductance. Calcium levels appear to be restored within the cell and are energy dependent. The light‐activated release of calcium is inhibited by cooling. The body wall ofAplysiatransmits enough visible or 500‐nm light to hyperpolarize someAplysiagiant neurons under ambient conditions. These neurons may be involved in the extraretinal light e

ISSN:0022-3034    

DOI:10.1002/neu.480080102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

摘要:

AbstractThe ultrastructure, absorbance, and elemental content of lipochondria present in the cytoplasm ofAplysiagiant neurons have been investigated before and after 30–1,200 sec doses of white light at intensities which produce saturated light responses. The effects of exposure to the calcium ionophore A‐23187 and to EGTA were also examined. The lipochondria of nonilluminated neurons are membrane‐bound, and contain lipids, protein, Na, K, Mg, Ca, Si, Cl, Br, P, and a pigment which is probably β‐carotene. The cytoplasm appeared to have little pigment. When neurons were illuminated for 20 min, 60–70% of the lipochondria showed marked ultrastructural alterations, the most notable being the appearance of membranous material. Earlier changes which occur after 30 sec of illumination include the appearance of paracrystalline arrays and mottling. Less than 10% of lipochondria in nonilluminated neurons have a similar appearance. These effects were greatly enhanced in illuminated neurons exposed to the calcium ionophore or EGTA. In nonilluminated neurons, the ionophore also produced ultrastructural changes. In frozen specimens, the calcium content of the most electron dense lipochondria of illuminated neurons was reduced. Other elements which were counted were also reduced. The lipochondria are the main intracellular site of photopigment. They may also act as an intracellular source for calcium which, as the accompanying paper indicated, may mediate phototransduction inAply

ISSN:0022-3034    

DOI:10.1002/neu.480080103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

摘要:

AbstractThe role of extracellular calcium in monoamine responses of central neurons was investigated using explant cultures of tuberal hypothalamus. The spontaneous activity of neurons in cultures was recorded in balanced salt and calcium‐deficient salt solutions. The firing rate was reversibly augmented during perfusion with calcium‐free salt solutions. This increased firing rate was counteracted by the addition of magnesium. Addition of magnesium also regularized the pattern of firing. Iontophoretic application of putative monoamine neurotransmitters reversibly decreased the rate of firing in both normal and calcium‐deficient salt solutions. These results suggest that monoamine inhibitions are not primarily mediated by transmembrane calcium f

ISSN:0022-3034    

DOI:10.1002/neu.480080104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

摘要:

AbstractThe effects of chick brain–spinal cord extract on morphological development and cyclic nucleotide levels of cultured chick embryo skeletal muscle cells were determined. It had previously been shown that the extract stimulated morphological differentation, protein synthesis, and cholinesterase activity of muscle cells. Myoblasts fused earlier and an increase in number as well as diameter of myotubes were seen in the extract treated cultures. Cyclic nucleotides levels were higher (almost twice the controls for both adenosine 3′, 5′ ‐cyclic monophosphate and guanosine 3′, 5′ ‐cyclic monophosphate) and preceded their occurence in the control cultures. It was suggested that factor(s) in the extract interact with membrane receptor(s) to alter nucleotide levels which, in turn, allow the effects to

ISSN:0022-3034    

DOI:10.1002/neu.480080105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

摘要:

AbstractMyelin isolated from three areas of mouse brain, from whole brain at several ages in normal mice, and from whole brain of adult quaking mutant mice was separated into seven bands and a pellet on discontinuous density gradients using 0.32, 0.45, 0.55, 0.60, 0.70, 0.75, and 0.85Msucrose. The distribution of myelin in the subfractions was independent of homogenization and shocking conditions employed to isolate the myelin preparations, but was related to the type of myelin applied to the gradient. Compared to myelin isolated from older animals, myelin isolated from 18–24 day old mice displayed a distribution pattern with greater proportions of material banding at lesser sucrose densities. Similarly, myelin obtained from hindbrain contained proportionately more material layering at lesser sucrose densities compared to myelin isolated from cerebral cortex. Myelin subfraction patterns observed for 8–12 day old control mice and quaking mutants were unlike each other or any other myelin preparation examined.In the 18–90 day old animals, the markers studied were not uniformly distributed among the myelin subfractions. The pellet and the layer banding at the 0.75/0.85Msucrose interface contained the highest specific concentrations of sialic acid, nucleic acid, and total adenosine triphosphatase activity. In contrast, the specific activity of 2′,3′ ‐cyclicnucleotide‐3′‐phosphohydrolase was lowest in the pellet as well as the three bands obtained above 0.60Msucrose and was highest in the fraction banding at the 0.65/0.70Msucrose interface.The results obtained were not consistent with an artifactual origin of the myelin subfractions, but instead suggested that the subfractions have physiological significance. One explanation for the different banding patterns observed between young and mature myelin may be the different amount of myelin in various brain regions d

ISSN:0022-3034    

DOI:10.1002/neu.480080106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

ISSN:0022-3034    

DOI:10.1002/neu.480080107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

ISSN:0022-3034    

DOI:10.1002/neu.480080101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY