Neural mechanisms of recovery following early visual deprivation

Natural patterned early visual input is essential for the normal development of the central visual pathways and the visual capacities they sustain. Without visual input, the functional development of the visual system stalls not far from the state at birth, and if input is distorted or biased the visual system develops in an abnormal fashion resulting in specific visual deficits. Monocular deprivation, an extreme form of biased exposure, results in large anatomical and physiological changes in terms of territory innervated by the two eyes in primary visual cortex (V1) and to a loss of vision in the deprived eye reminiscent of that in human deprivation amblyopia. We review work that points to a special role for binocular visual input in the development of V1 and vision. Our unique approach has been to provide animals with mixed visual input each day, which consists of episodes of normal and biased (monocular) exposures. Short periods of concordant binocular input, if continuous, can offset much longer episodes of monocular deprivation to allow normal development of V1 and prevent amblyopia. Studies of animal models of patching therapy for amblyopia reveal that the benefits are both heightened and prolonged by daily episodes of binocular exposure.     

Effects of early monocular deprivation because of leukoma or cataract on the development of the retina

The development of a normal retina and a retina with an early one-side occlusion in consequence of a cataract or a wall-eye was studied. Autoradiographically and with the help of a scanning cytophotometry method a normal maturing of a retina was shown to be finished in fourteen days of postnatal development without any significant changes. The degenerative changes of ganglion-cells ensuing the maturity of retina were discovered during the experiment. The depression of a protein metabolism of neurons in the deprived eye passes ahead the marked morphological changes. The gangliocytes of the intact eye don't differ much from the normal ones.     

Recovery from monocular deprivation in the monkey. III. Reversal of anatomical effects in the visual cortex

Transneuronal autoradiography was used to study the effects of visual deprivation on the ocular dominance stripes in layer IVc of the striated cortex of Erythrocebus patas (Old World) monkeys. The animals were studied after: (a) 21-28 days of monocular deprivation starting at, or within, a few days of birth; (b) the same treatment followed by a further 3, 6, 15 or 126 days of monocular vision through both eyes (reopening). One other monkey was monocularly deprived from birth to 1890 days. In most cases the behaviour of the ocular dominance stripes formed by the initially closed eye was studied. After 24 days of monocular deprivation from birth, the input from the normal eye was distributed uniformly within layer IVc, with no periodicity evident. After 21 days of deprivation, the deprived eye's input formed narrow stripes occupying about 38% of layer IVc in the operculum. Seven months of monocular deprivation reduced this to about 29%. Opening the closed eye after the deprivation produced no change in the area innervated: when periods of 15 or 96 days of binocular vision followed the deprivation, the areas innervated by the initially deprived eye were 26 and 30% respectively. However, in both cases the deprived eye's input formed blobs and spots, rather than uniformly narrow stripes. In contrast to reopening, reverse suturing increased the fraction of layer IVc occupied by input form the initially deprived eye. In the operculum, the effects of reverse suturing appeared to be fully developed after only 6 days of reversal: the initially deprived eye's stripes having expanded to occupy about 50% of layer IVc. A further 9 days' reversal produced little change in this. In the visual cortex in the calcarine fissure, the effect of the initial deprivation ws more severe, and the expansion induced by reverse suturing more pronounced. The initial deprivation caused the stripes to shrink to occupy 24% of layer IVc; after 6 days of reverse sulture the proportion increased to 52%, while after 15 days of reverse suture about 88% of IVc was occupied. These results show that reverse suturing can cause fresh growth of afferent axons in regions of layer IVc from which they had been at least partially removed, either by the normal process of segregation, or as a consequence of monocular deprivation. Taken in conjuction with the findings of the accompanying two papers (Blackemore et al...     

Recovery from monocular deprivation in the monkey. I. Reversal of physiological effects in the visual cortex

This is a study of the effects of monocular deprivation, reverse suturing (opening the deprived eye with closure of the other) and reopening of the deprived eye alone (without closing the other) on the physiological organization of the primary visual cortex in monkeys (Erythrocebus patas). All animals were initially monocularly deprived by suture of the lids of the right eye from soon after birth until about 4 weeks of age (24-29 days). In a monocularly deprived animal, recordings were taken from area 17 at 24 days. Already most neurons recorded outside layer IVc, were strongly or completely dominated by functional input from the left eye. The Non-oriented cells of layer IVc, where the bulk of the afferent input terminates, were also mainly dominated by the left eye. Although segregation of input from the two eyes was not complete, large areas of layer IVc were already monocularly dominated by the left eye. Four animals were reverse-sutured at about 4 weeks and recorded 3, 6, 15 and 126 days later. In each animal the pattern of ocular dominance was fairly similar within and outside layer IVc. Even with only 3 days of forced usage of the initially deprived right eye, about half of all cells recorded had become dominated by it, and the process of "recapture' of cortical cells by the initially deprived eye was apparently complete within 15 days. In layer IVc, the recovery took the form of an expansion of zones dominated by the deprived eye, as if the originally shrunken stripes of afferent termination had become enlarged. Binocularly driven neurons were rare at all stages, in all layers, but when present and orientation-selective, they had similar preferred orientations in the two eyes. Likewise the "columnar' sequences of preferred orientation continued without obvious disruption on shifting from regions dominated by one eye to those dominated by the other. Simply reopening the deprived eye at about 4 weeks, for 15 to 96 days caused no detectable change in the overall ocular dominance of cortical cells and, on average, no expansion of right-eye dominance columns in layer IVc. Therefore the recovery seen after reverse suturing depends not just on the restoration of normal activity to axons carrying information from the right eye, but on the establishment of a competitive advantage, through the right eye being made more active than the left.     

Recovery from monocular deprivation in the monkey. II. Reversal of morphological effects in the lateral geniculate nucleus

The cross-sectional area was measured of neurons in the lateral geniculate nucleus (l.g.n.) of monkeys (Erythrocebus patas) subjected to monocular deprivation by unilateral eyelid suture, and of others in which the closed lids had been subsequently opened (either alone, "reopening', or together with closure of the previously open eye, "reverse suture'). Monocular deprivation for the first month of the monkey's life retards l.g.n. cell growth such that neurons in the laminae innervated by the closed eye are about 15% smaller in cross-sectional area than those in normally innervated laminae. This failure of normal growth can be countered by reverse suture for even short periods of time, the size difference between laminae being abolished within 6 days after reverse suture performed at the age of 1 month. Simply reopening the closed eye has little or no effect on l.g.n. neuronal recovery. These morphological results in the l.g.n. correlate closely with studies on the width of ocular dominance "stripes' in layer IVc of the visual cortex of the same animals: the stripes, narrower than normal after monocular deprivation, "expand' with a time course similar to that of l.g.n. cell recovery, as judged by single unit recording and by autoradiography in the cortex after transneuronal transport of labelled tracers injected in an eye.     

Effects of phosphate sorptivity on long-term plant recovery and effectiveness of fertilizer phosphate in soils

Summary A greenhouse experiment was carried out on 30 soils of eastern Australia in the first year and 15 soils in the following years to determine the effects of soil phosphate sorptivity and phosphate removal in harvested material on effectiveness and recovery of fertilizer phosphate by white clover during a four year period.Phosphate recovery by the clover and fertilizer effectiveness were primarily negative functions of phosphate sorptivity. After the first year there was a progressive decrease in the sorptivity effect such that the subsequent decreases in phosphate recovery and effectiveness were largest on weakly sorptive soils and smallest on strongly sorptive soils. In the long term the cumulative effects of the apparently slow immobilizing reactions on the weakly sorptive soils tended to equalize the effects of faster reactions on strongly sorptive soils so that the actual recovery and effectiveness in the final year were similar on all soils regardless of their sorptivities. The cumulative recovery and cumulative effectiveness in the long term, however, remained strongly negative functions of sorptivity. Phosphate removal in harvested material caused large decreases in phosphate effectiveness on all soils and particularly on weakly sorptive soils.     

The effect of different temperature regimens in reperfusion on the recovery of myocardial contractile function after hypothermic cardiac ischemia]

The changes of the contractile function of the heart and cAMP content in myocardium depending on the temperature conditions of reperfusion (28 degrees C, 32 degrees C, 37 degrees C) after 90 minutes of hypothermal ischemia have been investigated on isolated hearts of rats. The comparative analysis of the investigation results has shown that, after cooling a cardial muscle to 8-12 degrees C, reperfusion with initial temperature of perfusate of 32 degrees C promotes fast restoration of independent cardiac activity, does not cause formation of reperfusion contracture, normalizes processes of synthesis and cAMP utilization in cardiomyocytes.     

How monocular deprivation shifts ocular dominance in visual cortex of young mice

We used a chronic recording method to document the kinetics of ocular dominance (OD) plasticity induced by temporary lid closure in young mice. We find that monocular deprivation (MD) induces two separate modifications: (1) rapid, deprivation-induced response depression and (2) delayed, deprivation-enabled, experience-dependent response potentiation. To gain insight into how altering retinal activity triggers these cortical responses, we compared the effects of MD by lid closure with monocular inactivation (MI) by intravitreal injection of tetrodotoxin. We find that MI fails to induce deprived-eye response depression but promotes potentiation of responses driven by the normal eye. These effects of MI in juvenile mice closely resemble the effects of MD in adult mice. Understanding how MI and MD differentially affect activity in the visual system of young mice may provide key insight into how the critical period ends.     

Cytochemical features of cortical neurons during the recovery period following early visual deprivation]

It was shown interferometrically that 10 days after the removal of rabbits, that had been exposed to early (from the virth till 2.5 month of life) visual deprivation, to the ordinary light conditions, a reliable increase in the neuron size could be noted in addition to the reliably increased protein content in the cytoplasm of the visual cortex neurons. Degrees of the above changes in neurons of laminae III, IV and V are not similar, no complete normalization occurring in any lamina. A question of the reversibility of changes caused by early visual deprivation and of the compensatory capacities of neuron in particular lamina is discussed.     

The recovery of terminal lymph flow following occlusion

The effects of external pressure on the relative terminal lymphatic flow rate following occlusion of the lymph system were studied. Sulfur colloid tagged with 99mTc was injected into the hind thigh of dogs prior to compressive loading. Initially, the lymphatic clearance of the tracer was measured for approximately forty minutes with no applied external pressure. The terminal lymph vessels were then occluded for thirty minutes with the application of an applied external pressure of 75 mm Hg. Finally, the lymphatic clearance following occlusion was measured with the application of a nonocclusive pressure. External pressures of 0, 30, and 45 mm Hg were tested to determine the effects of post-occlusive pressure application on terminal lymphatic clearance. Results indicated that terminal lymphatic clearance did not resume for an applied pressure of 45 mm Hg following occlusion. The relative lymphatic clearance rate at an external pressure of 30 mm Hg following occlusion was 54% of the clearance rate for a 0 mm Hg applied pressure prior to lymph occlusion. The results for a 0 mm Hg external pressure following occlusion indicated a 23 percent clearance rate compared to the pre-occlusive state. A two compartment model was utilized to determine the lymphatic clearance rate per unit tissue volume of subcutaneous tissue from the experimental data for each pressure phase.     

Effects of selective sleep deprivation on ventilation during recovery sleep in normal humans.

To assess the effects of selective sleep loss on ventilation during recovery sleep, we deprived 10 healthy young adult humans of rapid-eye-movement (REM) sleep for 48 h and compared ventilation measured during the recovery night with that measured during the baseline night. At a later date we repeated the study using awakenings during non-rapid-eye-movement (NREM) sleep at the same frequency as in REM sleep deprivation. Neither intervention produced significant changes in average minute ventilation during presleep wakefulness, NREM sleep, or the first REM sleep period. By contrast, both interventions resulted in an increased frequency of breaths, in which ventilation was reduced below the range for tonic REM sleep, and in an increased number of longer episodes, in which ventilation was reduced during the first REM sleep period on the recovery night. The changes after REM sleep deprivation were largely due to an increase in the duration of the REM sleep period with an increase in the total phasic activity and, to a lesser extent, to changes in the relationship between ventilatory components and phasic eye movements. The changes in ventilation after partial NREM sleep deprivation were associated with more pronounced changes in the relationship between specific ventilatory components and eye movement density, whereas no change was observed in the composition of the first REM sleep period. These findings demonstrate that sleep deprivation leads to changes in ventilation during subsequent REM sleep.