Hidden receptors for nerve growth factor in PC12 cells

The binding of nerve growth factor (NGF) to its receptors in PC12 cells was studied in two experimental conditions: (a) cell fixation with paraformaldehyde followed by permeabilization of the plasma membrane with methanol and (b) metabolic poisoning of living cells with sodium azide. Paraformaldehyde fixation of PC12 cells causes a 60-70% reduction of NGF binding capacity; the original binding capacity is restored following permeabilization with methanol. A kinetic analysis of NGF binding under these conditions reveals a single homogeneous population of receptors at variance with experiments performed in living cells where two kinetically distinct types of NGF receptors were demonstrated [Landreth, G. E. and Shooter, E. M. (1980) Proc. Natl Acad. Sci. USA, 77, 4751-4755; Schechter, A. L. and Bothwell, M. A. (1981) Cell, 24, 867-874]. Our results suggest that a proportion of the NGF receptors in PC12 cells is hidden, i.e. not available for binding to the ligand, and in a dynamic equilibrium with exposed receptors. The existence of hidden receptors is confirmed by treatment of PC12 cells with sodium azide, which causes a 50% reduction in NGF binding capacity and protection from trypsin digestion of the remaining pool of hidden receptors. The latter become exposed at the cell surface following removal of sodium azide. Our data provide an interpretation for the as yet unsatisfactorily explained data on NGF receptors.

A macromolecular structure favouring microtubule assembly in NGF-differentiated pheochromocytoma cells (PC12)

Cellular extracts derived from pheochromocytoma cells (PC12-) inhibit the assembly of calf brain tubulin, while those derived from nerve growth factor-differentiated cells (PC12+) do not display this effect. Incubation with RNase abolishes the inhibition by PC12- extracts and reveals the presence of an activating effect exerted by PC12+ extracts. Activation of microtubule assembly is enhanced when extracts are prepared from PC12+ cells exposed for 1 day to 1.0 microM taxol and is abolished when PC12+ extracts are: (a) prepared from cells incubated for 1 day with 1 microM colchicine, (b) treated with the non-ionic detergent Nonidet P-40 or (c) centrifuged at 100 000 g instead of 80 000 g. 2D gel electrophoresis of the proteins of the 100 000 g pellet responsible for the activating effect (referred to as 100 K g pellet) reveals the presence of 100 K, 88 K and 32 K proteins which are markedly enriched in PC12+ extracts. The 88 K protein is further enriched in taxol-treated cells and markedly reduced in the same cells incubated with colchicine. A correlation between the differential protein composition of the 100 K g pellets and their effect on microtubule formation is postulated.

Correlation between the preferred orientation and spatial frequency of neurones in visual areas 17 and 18 of the cat

1. In seventy-six penetrations through areas 17 and 18 of the cat, neurones were regularly sampled at intervals of 100 micrometers and preferred orientation, optimal spatial frequency and resolving power were determined for each neurone in response to drifting sinusoidal gratings. 2. As already shown for area 17, in tangential penetrations through area 18, whenever the preferred orientation rotates progressively from cell to cell, the optimal spatial frequency tends to remain constant. 3. A statistical analysis on 1574 cells in areas 17 and 18 showed that for pairs of cells separated 200-300 micrometers along a track the difference in preferred orientation delta alpha and the difference in optimal spatial frequency delta f are not randomly distributed: cell pairs with small delta alpha are most likely to have large delta f and vice versa. 4. These findings indicate that in areas 17 and 18 neurones with the same optimal frequency are aligned along a direction orthogonal to the orientation columns. 5. The optimal spatial frequency, resolving power and the velocity cut-off were averaged for cells from different penetrations located in the same cortical layer or sublayer of area 18: mean optimal spatial frequency and acuity are highest in layer IV and lowest in layers II and V, while the velocity cut-off is highest in layers II and V and lowest in layer IV. 6. Our data suggest that the layering of cells according to optimal spatial frequency is a more subtle subdivision than the six histological layers.

Contrast influence on perceived orientation

When two gratings of slightly different orientation and equal contrast are presented dichoptically the observer perceives a unique fused grating at an orientation intermediate between the two (cyclofusion). We show here that if the contrast of the two gratings is different the perceived orientation of the fused grating depends on the relative contrast of the two monocular images. The results show that the perceived orientation varies linearly with the contrast difference, provided that the contrast values of the gratings presented to each eye are such as to give rise to a fused image. In these conditions, the perceived orientation is the average of the two monocular orientations, weighted with their contrast.

Patterns in the discharge of simple and complex visual cortical cells

The activity of visual cortical neurons (area 17) was recorded in anaesthetized cats in response to sinusoidal drifting gratings. The statistical structure of the discharge of simple and complex cells has been studied as a function of the various parameters of a drifting grating: spatial frequency, orientation, drifting velocity and contrast. For simple cells it has been found that the interspike interval distributions in response to drifting gratings of various spatial frequencies differ only by a time scale factor. They can be reduced to a unique distribution by a linear time transformation. Variations in the spatial frequency of the grating induce variations in the mean firing rate of the cell but leave unchanged the statistical structure of the discharge. On the contrary, the statistical structure of the simple cell activity changes when the contrast or the velocity of the stimulus is varied. For complex cells it has been found that the invariance property described above for simple cells is not valid. Complex cells present in their activity in response to visual stimuli two different firing patterns: spikes organized in clusters and spikes that do not show this organization ('isolated spikes'). The clustered component is the only component of the complex cell discharge that is tuned for spatial frequency and orientation, while the isolated spike component is correlated with the contrast of the stimulus.

Two firing patterns in the discharge of complex cells encoding different attributes of the visual stimulus

The activity of complex neurones of area 17 was recorded in anaesthetized cats in response to sinusoidal drifting gratings of various orientations, spatial frequencies and contrasts. The responses of complex cells present two different firing patterns: spikes organized in clusters and spikes which do not show this organization ("isolated spikes"). The clustered component is the only one in the complex cell discharge which is tuned for spatial frequency and orientation, while the isolated spike component is correlated with the contrast of the stimulus.

[Calcium nephrolithiasis and phosphate therapy. Long term study (65 cases) (author's transl)]

Protected phosphate therapy was used in 65 cases of recurrent calcium nephrolithiasis. Mean duration treatment was 2 years and 1 month (more than 3 years in 17 cases). Mean lithiasis episodes by year-patients were 1,55 renal colics and 0.34 stone formation before phosphate treatment, versus 0.66 renal colics and 0.10 stone formation (more than 60% reduction), during treatment. There was simultaneously decrease of hypercalciuria (24 cases out of 42), of asthenia (16 cases out of 19), of signs of spasmophilia (12 cases out of 18) and disappearing of bone pains (4 cases out of 6). Side effects were rare. Minor digestive troubles were observed in 11 cases: diarrhea (3 cases) or gastralgias (9 cases). These side-effects necessitated discontinuation of thiazide therapy in only two cases and reduction of doses in 6 other cases. From our data, phosphate therapy appears an efficient drug in recurrent calcium nephrolithiasis. It acts in reducing levels of calciuria and enhancing urinary pyrophosphates excretion, inhibitors of calcium crystallization.

Ureteral reimplantation in children with neurogenic bladder

The treatment of urologic complications from myelomeningocele and especially of vesico-renal reflux is a controversial problem. A series of 26 reimplanted ureters in 17 children, with good results in more than 85%, is reported. Ureteroneocystostomy, carried out with a few technical innovation, may represent a useful method for the treatment of vesico-renal reflux and obstruction of the uretero-vesical junction in neurogenic bladder associated with myelomeningocele. This surgical approach leads to the disappearance of the reflux, decrease of dilatation of the upper urinary tract and preservation of renal function in most cases; moreover, infection can be more easily controlled. Ureteral reimplantation should be preceded by periodic urethral dilatation, external transurethral sphincterotomy, and pharmacologic regulation in order to attempt to decrease urethral resistance. After successful surgery, it is possible to try to reeducate the bladder. Reimplantation should be preferred to permanent urinary diversion even if there is gross reflux.

[Acute respiratory insufficiency caused by posttraumatic pulmonary metabolic disorder]

Six cases of acute respiratory insufficiency are presented. Particular reference is made to the pathogenetic mechanisms of the syndrome and the term ARDS is examined. The definition "acute respiratory insufficiency due to post-aggressive pulmonary dysmetabolism" is proposed. An account is also given of satisfactory results obtained by interdepartmental along-to-date lines. It is hoped that knowledge of this often fatal syndrome will not be confined to resuscitation services, but extended to other hospital departments.

Rare phenotypes of the PGM 1 and PGM 2 loci and a new PGM 2 variant allele in the Indians

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