Racial and cultural differences in sensitivity to flickering light

Latin America has been registering a fast decrease in fertility rates since the mid-twentieth century. This change can be linked to the modernization process these populations have been undergoing. However, research with Latin American indigenous populations, which are undergoing relatively similar lifestyle changes, shows very different trends in fertility. The aim of this study was to analyze fertility patterns in the indigenous Toba community of Cacique Sombrero Negro, which is experiencing a rapid process of economic and social Westernization. Fertility patterns were analyzed between 1981 and 1999, the period for which the most accurate records were found. Results showed an overall increase in fertility rates and changes in the age of peak fertility across time periods. It is hypothesized that the lifestyle transition this population is experiencing leads to better access to resources that, in the absence of contraception, allow for a higher number of offspring. Nevertheless, this higher resource availability would be differential, affecting mostly the fertility of younger mothers.     

Reactions of neural elements of neocortex to action of hypoxia at the early neonatal period in rats

We studied reactions of neural elements from different neocortex regions (sensorimotor, visual, auditory) to acute normobaric hypoxia on the model of human incomplete pregnancy (the 2-day-old rat pups) and revealed similar and unidirectional reorganization in all these regions. The chosen parameters of hypoxia induced the earliest detectable changes as fast as in a day since exposure: a decrease in cell body size and cytoplasmic volume, intensification of apoptotic cell death. By the end of the neonatal period (day 5), several ultrastructural changes were observed by indicating deceleration of processes of nerve cell differentiation: arrest of complication of smooth and rough endoplasmic reticulum and Golgi apparatus, the reduced number of free ribosomes and polysomes in cytoplasm as well as of axonal and dendritic growth cones in neuropil, delayed and disordered myelination of nerve fibers. All these morphofunctional abnormalities may be the structural basis for development of neonatal encephalopathies.     

Effect of rhythmical light flickering on the stability of the human body

Influence of photostimulation upon the man's movements biomechanics (stabilogram, goniogram, electromiogram etc) according to the one-leg toe balance model was investigated on 500 persons. Lowering of the exercise biomechanical efficiency at the background of light gleams was established. Light gleams with the frequency of 8-12 Hz which violated movement control processes (the correction of the body GWC) had maximal confusing effect.     

Galactosyltransferase activity of intact neural retinal cells from the embryonic chicken

Permeability of electrotonic junctions between isolated and reaggregated Fundulus blastomeres was evaluated with a new fluorescent dye, Lucifer yellow CH. The dye is readily shown to pass between coupled cells. It does not enter from the bathing medium, nor does it move between cells via the enlarged extracellular space sometimes seen between them. Thus, we conclude that passage is via a private pathway, presumably provided by the gap junctions described for this tissue. In contrast to previous findings, fluorescein (as the sodium salt, uranine) also passes between coupled Fundulus cells. Although it can enter from the bathing medium, it may be less concentrated in the space between a cell pair than in the uninjected cell. Again, passage via gap junctions is indicated. Molecular models demonstrate that Lucifer yellow and fluorescein are similar in size. Thus, similarity in ability to permeate junctional membranes is to be expected.     

Responses of retinal rods of the frog to light

To study the effect of the intensity, duration, spectral composition, and diameter of the light spot on the amplitude and shape of the response of single rods of the frog retina, potentials were recorded intracellularly. The rods tested could be divided into two groups on the basis of their responses to light spots of different spectral composition: those with maxima of sensitivity at 507 ± 8 nm and 442 ± 8 nm. With an increase in the intensity of light the response amplitude rose gradually and the time for the response to rise to its maximum was shortened. A bright flash temporarily inhibited the sensitivity of the cell to subsequent test flashes. If light spots of larger diameter (1000–1500 µ) were presented a delayed depolarization wave, due to illumination of the distant surroundings of the receptor, was observed in the course of recovery of the photic response; this effect was maximal for stimulation with red light and it was evidently induced by horizontal cell activity. The possible functional role of the depolarizing effect of illumination of the distant surroundings of the receptor is discussed.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 7, No. 1, pp. 84–92, January–February, 1975.     

A functional statistical analysis of the action potentials in the brain multineuronal activity of waking cats

In the present work a method is substantiated of the correction of singled out impulses series by identification of parameters of neurones discharges (PD) during a long period of recording (up to 120 days) of the neuronal activity by means of chronically implanted nichrome semimicroelectrode in different brain part of alert cats.     

Remodeling of retinal ganglion cell dendrites in the absence of action potential activity.

The dendrites of ganglion cells in the retina have an excess number of spines and branches that are normally lost during the first postnatal month of development. We investigated whether this dendritic remodeling can be prevented when the action potential activity of ganglion cells is abolished by chronic intraocular injections of tetrodotoxin (TTX) during the first 4 or 5 postnatal weeks in the cat. Dendritic tree morphologies of alpha and beta ganglion cells from TTX-treated, non-TTX-treated (contralateral eye), and normal control retinae were compared after intracellular filling with Lucifer yellow. Qualitative observations and quantitative measurements indicate that TTX treatment does not prevent the normally occurring loss of spines and dendritic branches. Indeed, the dendritic trees of both alpha and beta cells in TTX injected eyes actually have even fewer spines and branches than normal cells at equivalent ages. However, because the total dendritic lengths of these cells are also reduced after TTX blockade, spine density is indistinguishable from untreated animals at the same age. In addition, although dendritic field areas are not altered with treatment, the complexity of the dendritic trees is reduced. These observations suggest that dendritic remodeling can occur in the absence of ganglion cell action potential activity. Thus, the factors that influence the dendritic and axonal development of retinal ganglion cells must differ, because similar TTX treatment during the period of axonal remodeling does have profound effects on the final pattern of terminal arborizations.     

Blinking suppresses the neural response to unchanging retinal stimulation

Blinks profoundly interrupt visual input but are rarely noticed, perhaps because of blink suppression, a visual-sensitivity loss that begins immediately prior to blink onset. Blink suppression is thought to result from an extra-retinal signal that is associated with the blink motor command and may act to attenuate the sensory consequences of the motor action. However, the neural mechanisms underlying this phenomenon remain unclear. They are challenging to study because any brain-activity changes resulting from an extra-retinal signal associated with the blink motor command are potentially masked by profound neural-activity changes caused by the retinal-illumination reduction that results from occlusion of the pupil by the eyelid. Here, we distinguished direct top-down effects of blink-associated motor signals on cortical activity from purely mechanical or optical effects of blinking on visual input by combining pupil-independent retinal stimulation with functional MRI (fMRI) in humans. Even though retinal illumination was kept constant during blinks, we found that blinking nevertheless suppressed activity in visual cortex and in areas of parietal and prefrontal cortex previously associated with awareness of environmental change. Our findings demonstrate active top-down modulation of visual processing during blinking, suggesting a possible mechanism by which blinks go unnoticed.     

Regulation of retinal dopamine biosynthesis and tyrosine hydroxylase activity by light

Dopamine (DA)-containing neurons of the rat retina are apparently activated transsynaptically by photic stimulation. Exposure of dark-adapted rats to light increases retinal DA biosynthesis and metabolism. Associated with the light-evoked increase of DA biosynthesis is a rapid activation of tyrosine hydroxylase (TH), the rate-limiting enzyme of catecholamine biosynthesis. The activation of TH is characterized by an increased affinity of the enzyme for the pteridine cofactor. Because TH in dark-adapted retinas is apparently not saturated with cofactor, the light-evoked increase of affinity is probably responsible for the observed stimulation of DA biosynthesis. Cyclic AMP (cAMP)-dependent protein phosphorylation in vitro activates TH extracted from dark-adapted retinas, and phosphorylation-induced TH activation is very similar and not additive with light-evoked activation of the enzyme. Incubation of viable cell suspensions of dissociated retinas with 8-bromo cAMP also activates TH, which indicates the availability of sufficient cAMP-dependent protein kinase in the proper subcellular compartment to regulate the enzyme in situ. The DA-containing neurons of the rat retina are tonically inhibited in darkness, and evidence is presented that this tonic inhibition involves direct synaptic input to the DA neurons from gamma-aminobutyric acid-containing amacrine cells. The DA-containing neurons are also subject to feedback inhibition through DA receptors, and to modulation by alpha 2-adrenergic receptors.     

Some characteristics of adrenal steroidogenesis and their possible relationships to the action of the adrenocorticotropic hormone.

An attempt to define in quantitative terms the characteristics of the biphasic rate curve for pregnenolone synthesis in cell-free systems from the adrenal using male Sprague-Dawley rats is reported. When adrenocorticotropic hormone (ACTH) was used 2 units of .2 ml of .9% saline were injected ip 15 minutes before killing the rats. The effect of ACTH on adrenal steroidogenesis is in the stimulation of the rate of conversion of cholesterol to pregnenolone. This reaction sequence is thought to occur in the mitochondria. Methods of preparing subcellular fractions are described. Incubation of pregnenolone with mitochondria for 20 minutes at 20 degree C resulted in a 70% disappearance of the pregnenolone. This loss does not occur if the mitochondria are boiled, indicating an enzymatic process. The rate of pregnenolone synthesis characteristically shows a biphasic curve with a rapid primary rate and a slower secondary rate. ACTH administration in vivo increased both rates but the percentage increase was greater for the secondary rate. In addition an increase in the duration of the primary rate resulted. Different explanations are offered for these characteristics. Pregnenolone may act as an inhibitor of its own synthesis from cholesterol but not from 20alpha-hydroxycholesterol. Substances that cause mitochondria to swell may stimulate pregnenolone synthesis. Another theory proposes that the limiting ACTH-sensitive step is the rate at which mitochondrial cholesterol is transported to or binds to the cholesterol side-chain cleavage enzyme. The possible role of an inhibitor in the regulation of steroidogenesis is indicated. Data are consistent with the observation that the transition from the primary rate to the slower secondary rate shows the accumulation of an inhibitory substance. The action of ACTH would then be to modify the structure of the cholesterol side-chain cleavage enzyme so that there is a decreased susceptibility of the enzyme to the inhibitor.     

Analysis of gene expression in neural cells subject to chronic proteasome inhibition

A number of studies have suggested that proteasome inhibition plays a causal role in the neuropathological processes observed in aging, Alzheimer's disease (AD), and Parkinson's disease (PD). Although the effects of acute and toxic proteasome inhibition on neural viability are well documented, at present little is known about the effects of chronic low-level proteasome inhibition on neural homeostasis. In order to address this issue we have established clonal lines of neural SH-SY5Y cells, which were generated after continual exposure to low concentrations of a pharmacological proteasome inhibitor. We have recently utilized these clonal cell lines to demonstrate that chronic low-level proteasome inhibition induces neural alterations that are highly relevant to aging, AD, and PD. The focus of this study was to elucidate the alterations in gene expression that occurred in our clonal cell lines after chronic low-level proteasome inhibition. Taken together, data presented in this report indicate that, although chronic low-level proteasome inhibition alters the expression of a limited number of genes (less than 0.8%), it is observed to significantly alter the expression of genes within specific categories that are highly relevant to aging, AD, and PD. Perhaps just as importantly, our analysis revealed that the vast majority of genes altered by chronic low-level proteasome inhibition have not been significantly characterized, suggesting that proteasome inhibition may mediate effects on neural homeostasis through as yet unidentified cellular processes.