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PubMed1979

Light adaptation in cone photoreceptors: the occurrence and significance of unitary adaptive strength.

The behavior of "peak response-log intensity" functions generated by the "dark glasses model" is examined and is shown to describe previously observed light adapted behavior in cone photoreceptors. The models of Boynton and Whitten (1970) and Norman and Werblin (1974) are closely related to the dark glasses model--the Boynton-Whitten model being more specific and the Normann-Werblin model more general. For the models, a certain parameter relationship will produce systems which have optimal intensity discriminative capacities. When the data are fitted, this parameter relationship--unitary adaptive strength--seems to emerge. Possible evolutionary and psychophysical implications are discussed.

Adaptation, Ocular↗
PubMed1975

Ion conductance changes associated with spike adaptation in the rapidly adapting stretch receptor of the crayfish.

The time course of the repetitive impulse discharges has been investigated for two high intensities of maintained depolarizing currents, 30 nA and 50 nA, for which the receptor adaptation was complete within 70 msec. The changes in sodium and potassium conductance associated with the decline in spike activity have been analyzed at different instances of time by interrupting in successive experiments the various action potentials in the pulse trains either at the early phase by holding the potential at about -60 mV and recording the inward current (upstroke-gNa) or by evaluating the delayed outward current flowing as the result of a depolarizing voltage pulse which at the end of the action potential re-increased the membrane potential by mV (after potentialgK). At the higher current intensity of 50 nA the discharge frequency was increased, while larger reductions in upstroke-gNa and after potential-gK during receptor adaptation became apparent. The progressive decrease in pulse amplitude from 99 mV to 63 or 55 mV is paralleled by a gradual reduction in upstroke-gNa from 97 mmho/cm-2 to 37 or 27.5 mmho/cm-2 and in after potential-gK from 11.5 mmho/cm-2 to about 7 mmho/cm-2. When under a stimulus of 30 nA the sodium conductance decreases to an average value of 37 mmho/cm-2 only a distorted spike can be elicited, while the spike activity was completely suppressed at upstroke-gNa equals 27.5 mmho/cm-2 was essentially the same under both conditions. The results have been interpreted in terms of the model for impulse generation formulated by Michaelis and Chaplain (1973). According to the model both sodium and potassium inactivation reduce the pulse amplitude. However, while Na-inactivation reduces the frequency of impulse discharge, the K-inactivation actually leads to an increase in spike frequency. As the frequency of the short train of pulses recorded under high-intensity current stimulation remained essentially unaltered, it is suggested that the coupling between Na- and K-inactivation actually leads to an increase in spike frequency. As the frequency of the short train of pulses recorded under high-intensity current stimulation remained essentially unaltered, it is suggested that the coupling between Na- and K-inactivation ensures a constancy of the information-carrying parameter, i.e. the average impulse density.

Action Potentials↗
PubMed2024

Adaptive or non-adaptive? Cranial evolution in a radiation of miniaturized day geckos.

Lygodactylus geckos represent a well-documented radiation of miniaturized lizards with diverse life-history traits that are widely distributed in Africa, Madagascar, and South America. The group has diversified into numerous species with high levels of morphological similarity. The evolutionary processes underlying such diversification remain enigmatic, because species live in different ecological biomes, ecoregions and microhabitats, while suggesting strikingly high levels of homoplasy. To underscore this evolutionary pattern, here we explore the shape variation of skull elements (i.e., cranium, jaw and inner ear) using 3D geometric morphometrics and phylogenetic comparative methods on computed tomography scans (CT-scan) of a sample encompassing almost all recognized taxa within Lygodactylus. The results of this work show that skull and inner ear shape variation is low (i.e., there is high overlapping on the morphospace) across geographic regions, macrohabitats and lifestyles, implying extensive homoplasy. Furthermore, we also found a strong influence of allometry shaping cranial variation both at intra and interspecific levels, suggesting a major constraint underlying skull architecture, probably as a consequence of its miniaturization. The remaining variation that is not allometric is independent of phylogeny and ecological adaptation and can probably be interpreted as the result of intrinsic developmental plasticity. This, in turn, supports the interpretation that speciation in this group is largely concordant with a non-adaptive hypothesis, which results mainly from vicariant processes.

Animals↗
PubMed1977

[Influence of adaptation to altitude hypoxia and subsequent de-adaptation on the retention of a temporary connection].

Adaptation to simulated altitude hypoxia was followed by a significant increase of the degree of retention of active avoidance of the conditioned reflex. Twenty four hours after the reflex elaboration the adapted rats required only half of conditioned and unconditioned stimulus combinations in the reflex retention test than control ones. This effect was reproduced 1 and 5 days after the cessation of hypoxic training. The obtained increase in the degree of the conditioned reflex retention disappeared during deadaptation 10 and 27 days after the cessation of hypoxic training.

Adaptation, Physiological↗
PubMed1977

The role of the parathyroids for the adaptation to a low calcium intake. 5. The long-term effect of parathyroidectomy on the adaptation to a low calcium intake in adult rats with special reference to the metabolism of vitamin D.

One-year-old selectively parathyroidectomized rats showed a normalization of their plasma calcium level to above 4.1 mEq/l in 38% within 18 weeks on a normal dietary intake of calcium and inorganic phosphate but low in vitamin D. On a low level of dietary calcium, normalization did not occur in any of the parathyroidectomized animals. The conversion of 25-hydroxycholecalciferol into the active metabolite of vitamin D, 1,25-dihydroxycholecalciferol, by the kidneys was stimulated by a low dietary intake of calcium in intact animals and the accumulation of this metabolite was increased in small intestine mucosa. This adaptory increase in the level of intestinal 1,25-dihydroxycholecalciferol was not disturbed by selective parathyroidectomy, nor the synthesis by the kidneys. The synthesis reached a limit above which no further increase occurred despite the prevailing hypocalcemia possibly through an influence of the concomitant hyperphosphatemia. The renal synthesis and intestinal accumulation of 1,25-dihydroxycholecalciferol were directly related to the intestinal net absorption of dietary calcium, which we have reported on previously. Although increased, the endogenous level of 1,25-dihydroxycholecalciferol was too low to accomplish mobilization of skeletal calcium necessary for adaptation to a low calcium intake, as we have reported elsewhere. Thus, for adaptation skeletal calcium reserves must become mobilized through stimulated parathyroid activity with resulting osteoporosis. The parathyroids were found to have no direct regulatory influence upon the synthesis of 1,25-dihydroxycholecalciferol.

Adaptation, Physiological↗
PubMed1977

Cold adapted variants of influenza A. II. Comparison of the genetic and biological properties of ts mutants and recombinants of the cold adapted A/AA/6/60 strain.

The genetic and biological properties of 13 recombinant influenza A clones derived at 25 degrees C from the A/AA/6/60-cold variant (by crosses with 4 different wild type strains) were compared with a set of 5-FU induced ts-mutants. The 5-FU mutants had previously been placed into 7 complementation-recombination groups; the A/AA/6/60-cold parent (PI-7) and the 12 cold recombinant clones which were ts were shown to share a lesion with only one of these groups. The parental strain and 5 recombinant clones were evaluated for replication in the lungs and nasal turbinates of hamsters. Each virus appeared to be attenuated; genetic stability correlated with the level of viral replication in the hamster lung, i.e., viruses which grew best showed a tendency to revert to the ts+ phenotype. Characterization of the ts+ revertants for the presence of the cold adaptation property revealed that these viruses exhibited a spectrum of cold adaptation properties. Two viruses, PI-7 (the parental cold variant) and the CR6 recombinant (A/Queensland/6/72) did not revert in either the lungs or nasal turbinates of hamsters.

Animals↗
PubMed1976

[Altitude adaptation. Part II. Altitude adaptation as a problem of human biology. I. Growth)].

There are 3 main components influencing the mean stature of high altitude natives. The lower mean birthweight, which seems to result from the impossibility of complete adaptation during the last trimenon of gestation, which cannot be fully compensated during life. The general protein deficiency, or the habits of nutrition which are not comparable with the food-composition in industry-nations may be important. A definitive undernourishment has not been observed in those nations with longtime adaptation to the available food since generations, but several deficiencies of substances which specially influence growth, cannot be outruled. We also have to recognize the generally lower mean stature of the population in whole (South America Indians), that means of the both parents of a child. In the presence of low gene flow from one to the other generation this may influence also individual body measurement.

Acclimatization↗
PubMed1975

Adaptation and failure of adaptation to extreme natural environments.

Although the environmental stresses to which man is subjected on the ground are less than those commonly encountered in aviation or under water, they may still exceed an individual's powers of adaptation. Extremes of temperature, commonly encountered in the Arctic or the tropics, may occur in regions of normally temperate climate and lead to failure of temperature regulation, resulting in hypothermia, frostbite, heat exhaustion, or heat stroke. High mountains impose additional hazards due to high winds and lack of oxygen, and deep mines are dangerous work-places because of high temperature and humidity. Some physiological acclimatization occurs in extreme natural environments and the dangers may be reduced by appropriate clothing, diet and behaviour.

Adaptation, Physiological↗
PubMed1975

Effects of ingestion of organic selenium in adapted and non-adapted rats.

1. Rats were given moderate-selenium (4-5 mg/kg) or low-Se (0-5 mg/kg) diets during gestation and lactation. Their young were given diets with high (10 mg/kg), moderate or low Se contents from weaning, and groups of rats were killed at intervals during the 14-week experimental peroid. 2. Compared with young rats which received the low-Se diet, those which received the moderate- or high-Se diets had a high incidence of liver lesions and there were changes in liver Se content, haemoglobin concentration, packed cell volume, prothrombin activity, fibrinogen content, spleen weight, body water and serum glutamic-oxaloacetic and glutamic-pyruvic transaminas (L-aspartate : 2-oxoglutarate aminotransferase; EC 2.6.1.1 and L-alanine : 2-oxoglutarate aminotransferase; EC 2.6.1.2 respectively) and alkaline phosphatase (EC 3.1.3.1) activities. In those rats which received the high-Se diet the changes were more pronounced than in those which received the moderate-Se diet. 3. In young rats from dams given moderate-Se diets, which were themselves given the moderate-Se diet, the liver Se content decreased continuously, whereas rats given the same diet but from dams which had received the low-Se diet, the liver Se content increased continuously. There was a slight improvement of symptoms of Se toxicity in all groups by the 5th week of the experimental peroid. 4. The results suggest that there was an adaptation to chronic Se intake.

Adaptation, Physiological↗
PubMed1975

The role of the parathyroids for the adaptation to a low calcium intake. 4. The long-term effect of parathyroidectomy on the adaptation to a low calcium intake in adult rats with special reference to calcium metabolism.

One-year-old selectively parathyroidectomized rats showed, on a normal dietary intake of calcium, phosphorus and vitamin D, a reduction in plasma calcium to below 4.1 mEq./1 in 86 per cent and on restricted calcium intake in 100 per cent. On the normal level of dietary calcium, normalization of plasma calcium occurred 17 per cent within 8 weeks and in another 40 per cent between the 8th and 27th week of observation while on the low level only 10 per cent of the animals normalized their plasma calcium and first after the long-term period of observation. This was most probably accomplished by successively restored parathyroid activity from aberrant parathyroid tissue as deducted from data regarding the metabolism of calcium, magnesium and inorganic phosphate. Adaptation, viz. normalization of plasma calcium, was brought about by mobilization of skeletal calcium with resulting osteoporosis, as reported in our previous study on the same animals. Intestinal net absorption of calcium showed no significant difference between normocalcemic normophosphatemic intact and hypocalcemic hyperphosphatemic parathyroidectomized animals at the respective level of dietary calcium. Thus, parathyroidectomized animals with persistently reduced plasma calcium showed a normal adaptory increase in intestinal calcium absorption upon chronically restricted calcium intake. In the discussion of the regulation of this adaptory system the possible effects of the plasma concentrations of both calcium and inorganic phosphate upon the intracellular Ca22+concentration in the kidney tubules must be considered. Plasma magnesium did not appear to have a primary influence. Intestinal absorption of inorganic phosphate was not dependent upon the presence of the parathyroids but followed that of calcium suggesting a regulation by the action of 1,25-dihydroxycholecalciferol.

Adaptation, Physiological↗
PubMed1978

Effects of cold adaptation and re-adaptation upon the mitochondrial phospholipids of brown adipose tissue.

1. A study of the mitochondrial phospholipids, phospholipid fatty acid patterns and enzyme activities was investigated in brown tissue (B.A.T.) from rats chronically exposed to cold and/or treated with thyroxine. 2. The total activities of the oxidative enzymes were increased after cold exposure, but not after thyroxine treatment. 3. Cold exposure increased the amount of phosphatidylethanolamine, phosphatidylcholine, cardiolipin and lysophospholipids, the effect being greatest for phosphatidylethanolamine. At the same time, there were marked alterations in the fatty acid composition of the mitochondrial phospholipids (decrease of palmitic, palmitoleic and oleic acids ; increase of stearic, linoleic and arachidonic acids). 4. All these cold-induced alterations were reversed by re-adaptation of the animal to a normal temperature range. 5. The alterations of the fatty acid composition of phospholipids could be explained by changes in the rate of individual fatty acid biosynthesis.

Adaptation, Physiological↗
PubMed1977

Impulse dependent adaptation in Helix pomatia neurones: demonstration of the adaptation conductance.

By conventional voltage clamp methods an increase in membrane conductance after a depolarizing pulse is demonstrated in neurones of Helix pomatia. This increase decays exponentially with a time constant in the range of 5--20 s. The rise of the conductance during the depolarization can be represented by 3 exponentials with time constants from 12 ms to 1 s. The steady state value of the conductance depends on the membrane potential in a sigmoid manner. The conductance gives rise to an outward current, which appears to be carried by potassium ions. The firing pattern of the cell is governed by the conductance. A short, rectangular potential change, a pulse clamp, is used to disturb the firing pattern of the freely firing cell. The effect on the firing pattern depends on the height and duration of the clamp pulse in the same manner as the conductance increase. The normal firing produces similar changes in the membrane conductance.

Adaptation, Physiological↗
PubMed1976

Visual adaptation: effects of externally applied retinal on the light-adapted, isolated skate retina.

Incubation with externally applied 11-cis retinal induces a marked increase of visual sensitivity within partially bleached skate photoreceptors. This activity of 11-cis retinal is duplicated by 9-cis retinal, but not by all-trans retinal. The sensitization of photoreceptors promoted by 11-cis and 9-cis retinal is accompanied by the formation of rhodopsin and isorhodopsin, respectively.

Adaptation, Ocular↗