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PubMed2003

Alpha-melanophore-stimulating hormone in the brain, cranial placode derivatives, and retina of Xenopus laevis during development in relation to background adaptation.

The amphibian Xenopus laevis can adapt the color of its skin to the light intensity of the background. A key peptide in this adaptation process is alpha-melanophore-stimulating hormone (alpha-MSH), which is derived from proopiomelanocortin (POMC) and released by the endocrine melanotrope cells in the pituitary pars intermedia. In this study, the presence of alpha-MSH in the brain, cranial placode derivatives, and retina of developing Xenopus laevis was investigated using immunocytochemistry, to test the hypothesis that POMC peptide-producing neurons and endocrine cells have a common embryonic origin and a common function, i.e., controlling each other's activities and/or being involved in the process of physiological adaptation. The presence of alpha-MSH-positive cells in the suprachiasmatic nucleus, ventral hypothalamic nucleus, epiphysis, and endocrine melanotrope and corticotrope cells, which are all involved in regulation of adaptation processes, has been detected from stage 37/38 onward. This is consistent with the presumed common origin of these cells, the anterior neural ridge (ANR) of the neural-plate-stage embryo. The olfactory epithelium and the otic and epibranchial ganglia also contain alpha-MSH, indicating that these placodal derivatives originate from a common placodal domain continuous with the ANR. Furthermore, we demonstrate the presence of alpha-MSH in a subpopulation of retinal ganglion cells (RGCs), which is possibly also derived from the ANR. Immunoreactivity for alpha-MSH in RGCs that are located in the dorsal part of the retina is dependent on the background light intensity, suggesting that these cells are involved in the regulation of background adaptation. Taken together, the results support the hypothesis that POMC peptide-producing cells have a common embryonic origin and are involved in adaptation processes.

Adaptation, Physiological↗
PubMed1986

Renal adaptation to phosphorus deprivation: characterization of early events.

Renal adaptation to low dietary phosphorus (P) can occur within 4 h. To characterize events preceding adaptation, rats were gavaged with 0.6% P (+P) or 0.03% P (-P) diet and killed 1, 2, or 4 h later. Brush border membrane vesicles were prepared and Na-dependent phosphate (Pi), glucose, and 1-proline transport were measured. In intact rats, 1 h after gavage, serum P in +P was 8.0 +/- 0.5 and in -P, 6.1 +/- 0.4 mg/dl, p less than 0.01. One and 2 h after gavage, Pi uptake was similar between groups; at 4 h, 0.25 min Pi uptake was increased by 59.3% +/- 14.8 in -P, p less than 0.02, n = 11. In thyroparathyroidectomized rats, Pi uptake increased in -P by 40.1% +/- 7.4 compared to +P at 2.5 h after gavage, and by 51.3 +/- 9.3 at 4 h, p less than 0.025, n = 11. When actinomycin D or cycloheximide were administered both 16 h prior to and at gavage, 0.25 min Pi uptake 4 h after gavage was 59.1% +/- 14 and 60.6% +/- 19 higher in -P than +P, respectively, p less than 0.025. The adaptation was detected only when measured with an inward-directed Na-gradient. Na-dependent glucose and proline uptakes were not changed by -P diet. These studies demonstrate that early renal adaptation to low dietary P is preceded by a fall in serum P, is independent of parathyroid hormone, and does not require protein synthesis. Early adaptation may represent an increased rate of carrier movement or a change in availability of already synthesized carrier. The signal for adaptation may be the decrease in serum P, or filtered load of phosphorus.

Adaptation, Physiological↗
PubMed1998

Temperature adaptation of house keeping and heat shock gene expression in Neurospora crassa.

Adaptation of house keeping and heat shock gene expression was determined in Neurospora crassa during continuous exposure to different temperatures. Steady-state values of total protein synthesis differed little after incubation for 24 h at temperatures between 15 and 42 degreesC. Adaptation kinetics at 42 degreesC showed an initial, transient inhibition of total protein synthesis. Similar kinetics were observed with actin synthesis and tubulin mRNA. A priming 1-h heat shock of 42 degreesC 2 h prior to a second continuous exposure to 42 degreesC abolished the inhibitory effect of the second treatment and resulted in "acquired translational tolerance." Steady-state values of HSP70 synthesis rates revealed increasing levels with increasing temperatures after incubation for 24 h at different temperatures. Adaptation kinetics of the synthesis rates of different HSPs in vivo revealed maximal rates after 2 h and then a decrease to the elevated steady-state levels. The total amount of the major constitutive and inducible HSP70 isoform as determined by Western blots reached a maximum 2 h after the beginning of 42 degreesC exposure and only a slight decrease (25%) of the maximal value after 24 h. The inducible isoform of HSP70, in contrast, reached a maximum after 4-8 h and then decreased strongly after 24 h. HSP mRNAs reached maximal amounts 45-60 min after the beginning of 42 degreesC exposure and then declined after 8 h as determined by in vitro translation. Northern blots revealed maximal mRNA amounts of the inducible HSP70 after 30 min and zero amounts after 4 h exposure to 42 degreesC. After a shift to 42 degreesC HSP70 isoforms were immediately translocated into the nucleus and reshuttled into the cytoplasm during the following 6 h. The nuclear content of HSP70 remained elevated during the adapted steady state at 24 h. It is concluded that the adapted state after 24 h is based on enhanced amounts of constitutive isoforms in the cytoplasm and in the nucleus, whereas the inducible isoforms of HSP70 show faster adaptation kinetics.

Adaptation, Physiological↗
PubMed1994

Characterisation of angiotensin II binding to glomeruli from rainbow trout Oncorhynchus mykiss adapted to fresh water and seawater.

Specific binding of 125I-[Asn1, Val5]-angiotensin II to isolated glomeruli of freshwater-adapted and seawater-adapted rainbow trout, Oncorhynchus mykiss, reached a plateau after 20 min at 10 degrees and was displaced by nonradiolabelled [Asn1, Val5]-angiotensin II. Seawater adaptation increased the rate of dissociation of 125I-[Asn1, Val5]-angiotensin II from putative receptors. Competitive binding experiments revealed a single population of high-affinity receptors with a KD 0.3-0.4 x 10(-10) M, which was unchanged by seawater adaptation. Seawater adaptation did, however, reduce the density (Bmax) of the binding sites, which may reflect down-regulation by the higher plasma concentration of angiotensin II in seawater-adapted trout.

Adaptation, Physiological↗
PubMed1999

Effects of prolactin and growth hormone on strategies of hypoosmotic adaptation in a marine teleost, Sparus sarba.

Silver seabream (Sparus sarba) held in seawater (33 per thousand) or acclimated to a hypoosmotic environment of 6 per thousand were given intraperitoneal injections of saline (0.8% NaCl), recombinant bream growth hormone (rbGH, 1 microg/g), or ovine prolactin (oPRL, 6microg/g) for 7 consecutive days. Serum Na+ levels were unaffected by hypoosmotic acclimation and rbGH and oPRL treatment. Treatment of seawater fish with oPRL resulted in hyperchloremia. In 6 per thousand, saline-treated fish exhibited elevated branchial chloride cell (CC) numbers and exposure indices, all of which were markedly reduced by oPRL. CC numbers and morphometrics were unaffected by oPRL in seawater fish. In contrast, rbGH treatment of seawater fish resulted in elevated CC numbers, apical area, and fractional area and, in 6 per thousand fish, elevated CC fractional area and exposure numbers. Branchial Na+-K+-ATPase activity reduced in saline-treated fish adapted to 6% but was unaffected by rbGH regardless of salinity. oPRL reduced activity in both seawater and 6 per thousand-adapted fish. Neither hypoosmotic adaptation nor oPRL had any effect on renal Na+-K+-ATPase activity whereas rbGH reduced activity in both 33 and 6 per thousand. Saline-treated fish adapted to 6 per thousand exhibited reduced Na+-K+-ATPase activity in most regions of the intestine. Treatment with rbGH did not change intestinal Na+-K+-ATPase activity of seawater fish but elevated activity in the anterior regions (esophagus and stomach) of 6 per thousand-adapted fish. Treatment with oPRL elevated Na+-K+-ATPase activity throughout the gastrointestinal tract of seawater fish and in the anterior reaches of 6 per thousand-adapted fish. The data indicated that the as yet uncharacterized osmoregulatory roles of PRL and GH in seabream may warrant further attention as the present study connoted differing responses to that of other teleosts studied.

Adaptation, Physiological↗
PubMed2002

Selective inhibition of the epidermal growth factor receptor impairs intestinal adaptation after small bowel resection.

BACKGROUND: Prior indirect studies have suggested that a functional epidermal growth factor receptor (EGFR) appears to be indispensable for the adaptive response of the remnant intestine to massive small bowel resection (SBR). The recent availability of a specific pharmacologic EGFR inhibitor enabled us to more directly test the hypothesis that EGFR signaling is required for postresection intestinal adaptation. METHODS: Mice (C57B1/6, n = 26) underwent a 50% SBR or sham operation and were then given orogastric EGFR inhibitor (ZD1839, 50 mg/kg/day) or vehicle. After 3 days, indices of adaptation (wet weight, crypt depth, and villus height) and apoptotic index (number of apoptotic bodies per crypt) were calculated in the ileum. The expression of proliferating cell nuclear antigen (PCNA) and activated EGFR was measured by Western blotting. RESULTS: ZD1839 prevented EGFR activation and the normal postresection increases in ileal wet weight, villus height, and crypt depth. Enterocyte proliferation was reduced twofold in the SBR group by ZD1839. Although not statistically significant, rates of enterocyte apoptosis were the highest in the inhibitor-treated mice. CONCLUSION: Following massive SBR, pharmacologic inhibition of the EGFR attenuates proliferation and the normal adaptive response of the intestine. These results more directly confirm the requirement of a functional EGFR as a mediator of the postresection adaptation response. This study demonstrates an in vivo application of a novel selective EGFR inhibitor and offers a unique experimental model to gain mechanistic insight into understanding postresection intestinal adaptation.

Adaptation, Physiological↗
PubMed2003

A minimum on the mean number of steps taken in adaptive walks.

I consider the adaptation of a DNA sequence when mutant fitnesses are drawn randomly from a probability distribution. I focus on "gradient" adaptation in which the population jumps to the best mutant sequence available at each substitution. Given a random starting point, I derive the distribution of the number of substitutions that occur during adaptive walks to a locally optimal sequence. I show that the mean walk length is a constant:L = e-1, where e approximately 2.72. I argue that this result represents a limit on what is possible under any form of adaptation. No adaptive algorithm on any fitness landscape can arrive at a local optimum in fewer than a mean of L = e-1 steps when starting from a random sequence. Put differently, evolution must try out at least e wild-type sequences during an average bout of adaptation.

Adaptation, Biological↗
PubMed1999

NO-dependent mechanisms of adaptation to hypoxia.

In studying NO-dependent mechanisms of resistance to hypoxia, it was shown that (1) acute hypoxia induces NO overproduction in brain and leaves unaffected NO production in liver of rats; (2) adaptation to hypoxia decreases NO production in liver and brain; and (3) adaptation to hypoxia prevents NO overproduction in brain and potentiates NO synthesis in liver in acute hypoxia. Dinitrosyl iron complex (DNIC, 200 microg/kg, single dose, iv), a NO donor, decreases the resistance of animals to acute hypoxia by 30%. Nomega-nitro-L-arginine (L-NNA, 50 mg/kg, single dose, ip), a NO synthase inhibitor, and diethyl dithiocarbamate (DETC, 200 mg/kg, single dose, iv), a NO trap, increases this parameter 1.3 and 2 times, respectively. Adaptation to hypoxia developed against a background of accumulation of heat shock protein HSP70 in liver and brain. A course of DNIC reproduced the antihypoxic effect of adaptation. A course of L-NNA during adaptation hampered both accumulation of HSP70 and development of the antihypoxic effect. Therefore, NO and the NO-dependent activation of HSP70 synthesis play important roles in adaptation to hypoxia.

Adaptation, Physiological↗
PubMed1999

Production and storage of nitric oxide in adaptation to hypoxia.

Adaptation to hypobaric hypoxia is known to exert multiple protective effects related with nitric oxide (NO). However the effect of adaptation to hypoxia on NO metabolism has remained unclear in many respects. In the present work we studied the interrelation between NO production and storage in the process of adaptation to hypoxia. The NO production was determined by the total nitrite/nitrate concentration in rats plasma. The volume of NO store was evaluated in vitro by the magnitude of isolated aorta relaxation to diethyldithiocarbamate. It was shown that both the nitrite/nitrate level and the NO store increased as adaptation to hypoxia developed. Furthermore, the NO store volume significantly correlated with plasma nitrite/nitrate. Therefore, adaptation to hypoxia stimulates NO production and storage and these effects can potentially underlie NO-dependent beneficial effects of adaptation.

Adaptation, Physiological↗
PubMed2000

Bipartite geminivirus host adaptation determined cooperatively by coding and noncoding sequences of the genome.

Bipartite geminiviruses are small, plant-infecting viruses with genomes composed of circular, single-stranded DNA molecules, designated A and B. Although they are closely related genetically, individual bipartite geminiviruses frequently exhibit host-specific adaptation. Two such viruses are bean golden mosaic virus (BGMV) and tomato golden mosaic virus (TGMV), which are well adapted to common bean (Phaseolus vulgaris) and Nicotiana benthamiana, respectively. In previous studies, partial host adaptation was conferred on BGMV-based or TGMV-based hybrid viruses by separately exchanging open reading frames (ORFs) on DNA A or DNA B. Here we analyzed hybrid viruses in which all of the ORFs on both DNAs were exchanged except for AL1, which encodes a protein with strictly virus-specific activity. These hybrid viruses exhibited partial transfer of host-adapted phenotypes. In contrast, exchange of noncoding regions (NCRs) upstream from the AR1 and BR1 ORFs did not confer any host-specific gain of function on hybrid viruses. However, when the exchangeable ORFs and NCRs from TGMV were combined in a single BGMV-based hybrid virus, complete transfer of TGMV-like adaptation to N. benthamiana was achieved. Interestingly, the reciprocal TGMV-based hybrid virus displayed only partial gain of function in bean. This may be, in part, the result of defective virus-specific interactions between TGMV and BGMV sequences present in the hybrid, although a potential role in adaptation to bean for additional regions of the BGMV genome cannot be ruled out.

Adaptation, Physiological↗
PubMed1991

The neurophysiological correlates of colour and brightness contrast in lateral geniculate neurons. II. Adaptation and surround effects.

We report on experiments which were undertaken in an attempt to clarify mechanisms underlying the contrast effects of chromatic surround illumination on spectral responsiveness of cells in the parvocellular layers of the LGN (P-LGN-cells), that had been demonstrated under standard conditions in the preceding companion paper. The experiments were done in anesthetized macaques (Macaca fascicularis). In some neurons, S-potentials were recorded together with the post-synaptic action potentials, and all effects seen in P-LGN-cells were present already in their retinal afferents indicating their retinal origin. The responsiveness of the cells for center stimuli of different wavelengths and during illumination of the receptive field center or the outer surround was determined. Continuous outer surround illumination altered maintained discharge rate (MDR), sensitivity and gain of P-LGN and retinal ganglion cells in the same way and empirically not distinguishable from direct illumination of the receptive field. Responses to surround flashes showed the same dependence on spectral composition as those to center flashes. Adaptation and excitation caused by outer surround illumination (inner diameter 5 degrees, outer diameter 20 degrees) were, in the average, ten times weaker than those exerted by light of the same spectral composition shone directly into the receptive field. Surround effects decreased proportional to r-2. Excitation by outer surround flashes was reduced by adaptation of the receptive field center in the same manner as responses to center flashes. The findings indicate that outer surround light has a direct excitatory and adaptive effect on the excitatory or inhibitory cones feeding into the receptive field. This indicates that straylight from the surround into the center could be responsible for the adaptive and excitatory effects of surround illumination. The straylight fraction from the remote surround into the receptive field must be higher, however, than that estimated from the psychophysically determined point spread function. It comes closer to earlier direct straylight measurements in excised eyes, but may be enhanced by chromatic aberration. If a surround of excitatory colour is flashed simultaneously with an excitatory center stimulus, additivity of center and surround excitation is observed only at low center intensities, while at higher center intensities the gain for center excitation is reduced similar to adaptive gain control. This could be explained by lateral interaction through horizontal connections in the retina, which decays within seconds, while adaptation of the cones feeding into the receptive field center is fully effective only after about 3 s.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Ocular↗
PubMed1992

Differences in adaptive stabilization of structures in response to stress and hypoxia relate with the accumulation of hsp70 isoforms.

The phenomenon of adaptive stabilization of structures (PhASS) develops during adaptation of the organism to intermittent restraint stress. The PhASS manifests itself in a considerably increased resistance of the heart to a broad spectrum of harmful factors. In the present work, the content of hsp70 and their role in the development of PhASS during adaptation to intermittent restraint stress and to intermittent hypoxia were studied. In adaptation to restraint stress, five hsp70 isoforms with pI ranging from 5.7 to 6.3 were accumulated in the myocardium. The heart simultaneously became strikingly resistant to reperfusion paradox and heat shock. In adaptation to hypoxia, only two hsp70 isoforms with pI about 5.8 were accumulated. The resistance to reperfusion paradox was not increased and the resistance to heat shock was increased only moderately. These data suggest a role of different hsp70 isoforms in the mechanism of PhASS as well as adaptive protection of the heart.

Adaptation, Physiological↗
PubMed1977

Dark adaptation and receptive field organisation of cells in the cat lateral geniculate nucleus.

The receptive fields of LGN cells were investigated with stationary light and dark spot and annulus stimuli. Stimulus size and background intensity were varied while stimulus/background contrast was kept constant. The speed of dark adaptation vaired considerably from cell to cell. Dark adaptation made responses more sustained in all neurones and eliminated the oscillatory on-responses evoked under some conditions in the light-adapted cells. Dark adaptation led also to a disappearance of early phasic inhibition in on-responses, and increased response rise time and latency. The power of surround responses to inhibit centre responses decreased slightly at low levels of light adaptation in LGN cells but much less than in retinal ganglion cells. Some other traces of changing retinal surround effects also appeared inthe LGN on dark adaptation. For example, the functional size of receptive fields increased at low levels of illuminance as has been observed in retinal ganglion cells and the receptive fields as estimated from response peaks were larger than those estimated from sustained components.

Animals↗
PubMed1977

Adaptation and habituation characteristics of tectal neurons in the pigeon.

The adaptation and habituation characteristics produced by the repeated presentation of a moving visual stimulus were studied in single cells in the pigeon's optic tectum. Units located near the surface in the stratum opticum showed little adaptation. However, cells located in deeper layers exhibited varying rates and degrees of adaptation and recovery. Approximately two thirds of the units that adapted, individually showed different rates of adaptation to different directions of movement, thus revealing different receptive field profiles in their adapted and recovered states. Some units were described as habituating since a change in the path of the stimulus through the receptive field or a change in the type of stimulus, resulted in the reinstatement of the initial level of responsiveness.

Adaptation, Physiological↗
PubMed1983

Adaptive sensitivity of the surround mechanism of cat retinal ganglion cells.

The spatial distribution of the surround's adaptation mechanism was studied in X- and Y-cells in the cat's retina. Adaptive sensitivity was assessed with adapting annuli with equal-area, but variable position and with adapting annuli with variable size. The results provide evidence that adaptive sensitivity of the surround's adaptive mechanism is higher in the center of the receptive field of Y-cells than of X-cells.

Adaptation, Ocular↗
PubMed1995

Are arm trajectories planned in kinematic or dynamic coordinates? An adaptation study.

There are several invariant features of point-to-point human arm movements: trajectories tend to be straight, smooth, and have bell-shaped velocity profiles. One approach to accounting for these data is via optimization theory; a movement is specified implicitly as the optimum of a cost function, e.g., integrated jerk or torque change. Optimization models of trajectory planning, as well as models not phrased in the optimization framework, generally fall into two main groups-those specified in kinematic coordinates and those specified in dynamic coordinates. To distinguish between these two possibilities we have studied the effects of artificial visual feedback on planar two-joint arm movements. During self-paced point-to-point arm movements the visual feedback of hand position was altered so as to increase the perceived curvature of the movement. The perturbation was zero at both ends of the movement and reached a maximum at the midpoint of the movement. Cost functions specified by hand coordinate kinematics predict adaptation to increased curvature so as to reduce the visual curvature, while dynamically specified cost functions predict no adaptation in the underlying trajectory planner, provided the final goal of the movement can still be achieved. We also studied the effects of reducing the perceived curvature in transverse movements, which are normally slightly curved. Adaptation should be seen in this condition only if the desired trajectory is both specified in kinematic coordinates and actually curved. Increasing the perceived curvature of normally straight sagittal movements led to significant (P < 0.001) corrective adaptation in the curvature of the actual hand movement; the hand movement became curved, thereby reducing the visually perceived curvature. Increasing the curvature of the normally curved transverse movements produced a significant (P < 0.01) corrective adaptation; the hand movement became straighter, thereby again reducing the visually perceived curvature. When the curvature of naturally curved transverse movements was reduced, there was no significant adaptation (P > 0.05). The results of the curvature-increasing study suggest that trajectories are planned in visually based kinematic coordinates. The results of the curvature-reducing study suggest that the desired trajectory is straight in visual space. These results are incompatible with purely dynamic-based models such as the minimum torque change model. We suggest that spatial perception--as mediated by vision--plays a fundamental role in trajectory planning.

Adaptation, Physiological↗
PubMed1987

Simultaneous opposing adaptive changes in cat vestibulo-ocular reflex direction for two body orientations.

The specificity of adaptation of vestibulo-ocular reflex direction was examined by exposing cats to combined pitch vestibular rotation and horizontal optokinetic motion at 0.25 Hz, while alternating body position between lying on the left side and lying on the right. The direction of optokinetic motion relative to head motion was reversed when the cat's body posture was changed so that, for example, if head upward rotation was coupled to leftward visual world motion when the cat was lying on its left side, then head upward rotation was coupled to rightward visual world motion when the cat was on its right side. Body position and optokinetic motion direction were changed every 10 min for a total of 2 h of adaptation on each side. Horizontal and vertical electrooculographic recordings were made during pitch rotations in darkness before and after adaptation. Saccades were removed from the records and vestibulo-ocular reflex gain was measured in the direction of optokinetic motion. In every case, the adaptation procedure produced a directional change in the vestibulo-ocular reflex specific to the posture during measurement and appropriate to reduce the retinal image motion caused by the combined vestibular and optokinetic stimuli. That is, adaptive horizontal eye movements measured on the two sides were in opposite directions for the same direction of head motion. This specificity suggests that adaptation of vestibulo-ocular reflex direction involves specific neural pathways that are controlled by body orientation signals which most likely arise from the otolith organs.

Adaptation, Physiological↗
PubMed1988

A model system for motor learning: adaptive gain control of the blink reflex.

An important aspect of the control of movement is how the nervous system produces adaptive gain modification. To investigate this problem in a simple motor system, we studied lid movement and orbicularis oculis muscle activity in human and rabbit subjects during adaptation of reflex eye blinks. The gain of the reflex could be increased or decreased, depending upon the nature of the adaptive stimulus. Since these gain changes could persist upon removal of the adapting stimulus, adaptation appears to result from a modification of the neural program subserving the blink reflex. The orbicularis oculis electromyogram revealed that the neural modifications producing adaptive gain changes predominantly altered the longer latency components of the reflex, while the short latency components remained unchanged. Moreover, in two other paradigms that modulate the gain of reflexes, habituation and reflex modification, similar changes also occurred primarily in the longer latency components of the blink reflex. This result suggests that modification of neurons in longer latency, indirect pathways, may underlie different forms of motor learning.

Adaptation, Physiological↗