scholarly journals The pigmentary effector system VIII—The dual receptive mechanism of the amphibian background response

1936 ◽  
Vol 120 (817) ◽  
pp. 158-173 ◽  
Keyword(s):  
Normal Animal ◽  
The Other ◽  
White Background ◽  
Pars Intermedia ◽  
Pars Tuberalis ◽  
General Hypothesis ◽  
Common Path ◽  
Black Background ◽  
To Come ◽  
Stimulation Of

In a previous contribution (Hogben and Slome, 1931) evidence was brought forward to show that the white background response does not depend on the same mechanism of coordination as the black background response, which is produced by reflex liberation of a hormone (“B” substance) of the pars intermedia in the pituitary gland; and experiments pointing to the existence of another internal secretion (“W” substance), connected directly or indirectly with the activity of the pars tuberalis, were described. The existence of separate receptor components of the retina controlling the two systems was left for subsequent enquiry. Of two possible hypotheses concerning the nature of the receptive mechanism, the most likely one is illustrated diagrammatically in fig. 1. In normal situations, when an animal is illuminated on a black background, light can only fall on the floor of the retina. If it is aquatic, the maximum divergence of any two rays which strike the eye is twice the critical angle for air and water, so that in the absence of reflexion of rays from sur­rounding objects below the surface of separation all rays will presumably be brought to a sharp focus in shallow water. There are thus three distinct possibilities which arise from the way in which the animal is illuminated if, as in Xenopus , the eyes are situated on the top of the head: ( a ) in darkness no part of the retina is stimulated, the same being true of the eyeless animal; ( b ) when the animal is exposed to a black background only a sharply localized region of the retina is stimulated; ( c ) when the animal is exposed to a white background the whole of the retina is illuminated owing to the scattering of rays in all directions from the surroundings. For convenience of description the usual black back­ground situation will be described hereafter as one in which only the “floor” of the retina is stimulated, and the white background situation as one in which the floor and the “ periphery ” of the retina are both stimulated together. If then, the receptor elements of the floor and periphery initiate different systems of reflex arcs the phenomena of the background response in Amphibia and Reptiles may be interpreted as follows. In Reptiles we may suppose that stimulation of floor reflexly excites the melanophores to expand, while stimulation of peripheral photoreceptors excites them to contract, being presumably prepotent in the final common path. In Amphibia two alternatives may be con­sidered: ( a ) that floor elements reflexly excite liberation of “B” and that peripheral photoreceptors, being prepotent, reflexly inhibit libera­tion of “B"; ( b ) that floor elements reflexly excite liberation of “B”, and peripheral photoreceptors reflexly excite production of the antago­nistic substance “W” in quantity sufficient to over-ride the effect of “B”. The crucial test of the truth of the general hypothesis that the floor and peripheral elements of the retina initiate different processes of coordina­tion was suggested by Keeble and Gamble (1904-6) in their experiments on Crustacea. If it is true, a normal animal illuminated from below in a black tank with a white top should react in exactly the same way as a normal animal when illuminated in a black tank from above. On the other hand, a normal animal illuminated from below in a black tank with a black top should react like an eyeless animal in the same situation, because the floor elements would not be subject to stimulation. The experiment may be varied as indicated below. In order to obtain signi­ficant results two classes of precautions must be carefully observed. One is that the physical dimensions of the tank must not exceed certain limits, since the maximal divergence of two rays is rigidly fixed when an animal is illuminated from above. The other is that there must be no air-water interface to permit reflexion of the incident rays downwards. Aside from the fact that no bubbles must be allowed to collect, this condition presents a practical difficulty if the animal has to come to the surface to breathe.

RATES OF INCORPORATION OF [3H]LEUCINE INTO PROTEIN OF THE PARS INTERMEDIA OF THE PITUITARY IN THE AMPHIBIAN XENOPUS LAEVIS AFTER CHANGE OF BACKGROUND COLOUR

1971 ◽  
Vol 51 (3) ◽  
pp. 521-532 ◽  
Author(s):  
P. WHUR ◽  
B. WEATHERHEAD
Keyword(s):  
Trichloroacetic Acid ◽  
Liquid Scintillation ◽  
Background Level ◽  
Scintillation Counting ◽  
The Other ◽  
White Background ◽  
Pars Intermedia ◽  
Melanocyte Stimulating Hormone ◽  
Black Background ◽  
Pars Nervosa

SUMMARY Xenopus were kept on, and transferred between, black or white back-grounds before incubating the pars intermedia and sometimes other parts of the pituitary with [3H]leucine. The rates of incorporation of label were assessed either by liquid scintillation counting of trichloroacetic acid precipitates or quantitative analysis of autoradiographs. Inhibition of incorporation of label was achieved after incubation with puromycin, showing that the label was associated with newly synthesized peptide material. The rates of incorporation of label into pars distalis and pars nervosa were not significantly different in animals from black or white back-grounds. However, pars intermedia from animals on a black background incorporated label at three to six times the rate of animals from a white background. In animals kept for some days on a white background and then transferred to a black background the rate of incorporation began to rise within a few minutes and reached the new higher level after several hours. In animals transferred from a black to a white background, however, no decline in rate was detected until 2 days after the transfer, but by 3 days the rate had returned to the white background level. The timing of these changes bears no relationship to the timing of changes, reported elsewhere, in the ultrastructure of pars intermedia cells after changes in background colour. They are, on the other hand, similar to the timing of changes in the melanocyte-stimulating hormone content of pars intermedia and also to changes in the melanophore index.

scholarly journals The chromatic behaviour of the eel ( Anguilla vulgaris L.)

1940 ◽  
Vol 128 (852) ◽  
pp. 343-353 ◽  
Keyword(s):  
Blood Supply ◽  
White Background ◽  
Posterior Lobe ◽  
Pituitary Extract ◽  
Present Communication ◽  
Nervous Stimulation ◽  
Black Background ◽  
The Times ◽  
Stimulation Of

Neil (1939) has described the chromatic response of normal and blinded eels to various condition of illumination. From the times taken to equilibrate when passing from white to black “background” and vice versa with overhead illumination, he concluded that co-ordination is humoral. The time taken to equilibrate after transference to darkness from an illuminated white background or vice versa implies that control is bihumoral. Apart form Neill's work and an early comment by Petersen the chromatic behaviour of the eel has engaged little attention. Lode (1890) described contraction of the melanophores after faradic stimulation of the cord. Odiorne (1933) found that injection of posterior lobe pituitary extract caused expansion of the melanophores. The present communication deals with experiments designed to elucidate the mechanism of co-ordination more fully. It includes observations on ( a ) modification of normal chromatic behaviour by total or partial hypophysectomy; ( b ) effect of total and partial hypophysectomy on tolerance to pituitary extracts; ( c ) influence of nervous stimulation in the presence or absence of an intact blood supply. They are based chiefly on the behaviour of the dermal melanophores for recording which the melanophore index ( μ ) of Hogben and Slome (1931) is used throughout.

scholarly journals The pigmentary effector system - IX. The receptor fields of the teleostean visual response

1940 ◽  
Vol 128 (852) ◽  
pp. 317-342 ◽  
Keyword(s):  
Colour Change ◽  
Primary Response ◽  
Senior Author ◽  
The Other ◽  
White Background ◽  
Visual Response ◽  
Local Response ◽  
Black Background ◽  
Effector System ◽  
The Difference

Both among vertebrates and among Crustacea one commonly meets with two co-existent modes of chromatic response to photic stimulation. One is the dispersion (“expansion”) of melanophores and certain other chromatophores under the local (primary) influence of light on the skin. The other is aggregation (“contraction”) of melanophores and of certain other chromatophores when light reflected from the surroundings impinges on the organs of vision, in contradistinction to dispersion (“expansion”) when only overhead illumination strikes the eye. Though the primary (local) response is usually subordinate to and is more or less overruled by the secondary or visual response, the relative importance of the two components varies within wide limits. In particular species either may be negligible in comparison with the other. When, as more commonly, both contribute significantly to the observed result, a blinded animal is necessarily more pale in darkness than in light. Probably this fact influenced all the earlier investigators who, including the senior author (1924), paid little attention to the otherwise paradoxical fact that animals kept on a “black background” (i. e. under conditions of overhead illumination in light absorbing surroundings) are much darker than animals kept in similar conditions with no light at all. Subsequent analysis of the normal course of colour change, both in vertebrates and in Crustaces, has shown that this is also true of species which have no appreciable primary response, and that the difference generally exceeds the limits of variation consistent with the co-existence of a detectable primary response. It is therefore clear that the difference between the “white background” response and the “black background” response is not due to intensity alone.

Synthesis, storage, and release of MSH in the pars intermedia of the pituitary gland of Xenopus laevis during background adaptation

1977 ◽  
Vol 55 (6) ◽  
pp. 922-927 ◽  
Author(s):  
B. G. Jenks ◽  
A. P. VanOverbeeke ◽  
B. F. McStay
Keyword(s):  
Protein Synthesis ◽  
Xenopus Laevis ◽  
De Novo ◽  
Synthetic Activity ◽  
White Background ◽  
Pars Intermedia ◽  
Black Background ◽  
Background Adaptation ◽  
Initial Stage ◽  
Simultaneous Decrease

Pituitary levels of melanophore-stimulating hormone (MSH), release of MSH, and protein synthetic activity in the pars intermedia were determined in Xenopus laevis during background adaptation. MSH was measured using a radioimmunoassay to α-MSH; uptake of [3H]lysine, determined autoradiographically, was used to assess protein synthesis; changes in melanophore index indicated changes in release of MSH. Adaptation to black background led to eventual depletion of MSH and increased protein synthetic activity. Conversely, during adaptation to a white background MSH levels increased and protein synthesis decreased. Changes in synthesis lagged considerably behind changes in release. During the initial stage of black-background adaptation, release of MSH was not accompanied by simultaneous decrease in levels of MSH in the gland from which it is concluded that replenishment of MSH took place. Our results indicated that this replenishment in the gland could not be accounted for by de novo synthesis of the hormone. It is proposed that a stored precursor to MSH exists, conversion of which provides for rapid replenishment of MSH. It is suggested that the factor(s) controlling MSH release affect synthesis of this hormone only indirectly.

QUANTIFICATION OF ULTRASTRUCTURAL CHANGES IN THE 'MELANOCYTE-STIMULATING HORMONE CELL' OF THE PARS INTERMEDIA OF THE PITUITARY OF XENOPUS LAEVIS, PRODUCED BY CHANGE OF BACKGROUND COLOUR

1972 ◽  
Vol 53 (2) ◽  
pp. 303-NP ◽  
Author(s):  
B. WEATHERHEAD ◽  
P. WHUR
Keyword(s):  
Endoplasmic Reticulum ◽  
Rough Endoplasmic Reticulum ◽  
Ultrastructural Level ◽  
Ultrastructural Changes ◽  
White Background ◽  
Pars Intermedia ◽  
Black And White ◽  
Melanocyte Stimulating Hormone ◽  
Black Background ◽  
Stimulating Hormone

SUMMARY The fact that the transfer of amphibians between black and white backgrounds causes the 'melanocyte-stimulating hormone (MSH) cells' of the pars intermedia of the pituitary to undergo considerable morphological change has been established for some time. The application of morphometric techniques to the 'MSH cells' of Xenopus has permitted the quantitative analysis of these changes at the ultrastructural level. Of the nine classes of organelle selected for analysis in these cells, three, namely nucleus, plasma membrane and dense bodies, showed no statistically significant changes. The remaining classes of organelle all showed significant changes in the percentage of the total cell volume that they occupied, although not all the organelles changed at the same rate. Transfer of animals from a white to a black background for up to 12 days was associated with increase in the percent volume of rough endoplasmic reticulum, Golgi membranes, Golgi granules and mitochondria and with a decrease in the percent volume of the fibrous granules. Return of animals to a white background after 6 days on a black background produced a reversal of the above changes with return to, or close to, white background (control) levels. This quantitative ultrastructural approach also highlights discrepancies in both the rate and magnitude of the changes in some of the organelles and related non-morphological parameters previously reported, e.g. the size of the rough endoplasmic reticulum and the rate of incorporation of labelled amino acid into protein; or the numbers of fibrous granules and the levels of detectable pituitary MSH. Some possible interpretations of these discrepancies are discussed.

The processing of β-endorphin and α-melanotrophin in the pars intermedia of Xenopus laevis is influenced by background adaptation

1992 ◽  
Vol 135 (3) ◽  
pp. 469-478 ◽  
Author(s):  
K. Maruthainar ◽  
Y. Peng-Loh ◽  
D. G. Smyth
Keyword(s):  
Ion Exchange ◽  
Xenopus Laevis ◽  
Molecular Size ◽  
Ion Exchange Chromatography ◽  
Exchange Chromatography ◽  
Proteolytic Processing ◽  
White Background ◽  
Pars Intermedia ◽  
Black Background ◽  
Background Adaptation

ABSTRACT β-Endorphin-and α-melanotrophin (α-MSH)-related peptides were extracted from the pars intermedia of Xenopus laevis maintained for 2, 4 or 6 weeks on a white background and for the same periods on a black background. The peptides were resolved under dissociating conditions by gel exclusion chromatography on Sephadex G-50 and they were detected by radioimmunoassay with antibodies to β-endorphin, α,N-acetyl β-endorphin and α-MSH. The β-endorphin-related peptides separated into two fractions of different molecular size. Further purification of the peptides in each fraction was by ion exchange chromatography on SP-Sephadex C-25 and by high-pressure liquid chromatography. The α-MSH-related peptides were resolved by gel exclusion and ion exchange chromatography. The purified β-endorphin- and α-MSH-immunoreactive peptides were identified by comparison of their chromatographic properties with the corresponding peptides from porcine pituitary or by comparison with synthetic peptides. The major form of β-endorphin in the pars intermedia of the frog adapted to a white background was identified as α,N-acetyl β-endorphin (1–8); it was accompanied by a small quantity of acetylated peptides with molecular size similar to β-endorphin. In contrast, the pars intermedia of the frogs adapted to a black background contained approximately equal amounts of α,N-acetyl β-endorphin (1–8) and the larger forms of β-endorphin. The higher molecular weight forms were identified as the α,N-acetyl derivatives of β-endorphin (1–26), (1–27) and (1–31); however after 6 weeks of white adaptation the sole remaining peptide in this group was the 26-residue peptide. An additional β-endorphin immunoreactive peptide, provisionally identified as β-endorphin (10–26), was present in both black- and white-adapted animals; the amounts of this peptide increased during white adaptation. Major differences in the processing of α-MSH were also observed. In the frogs adapted to a black background des-acetyl α-MSH greatly predominated over the acetyl form whereas after 6- weeks adaptation to a white background the acetylated peptide proved to be the principal component. The results demonstrate that the proteolytic processing of β-endorphin and the acetylation of α-MSH in Xenopus laevis are influenced by background adaptation. The formation of β-endorphin (1–8) appears to reflect the action of an endopeptidase that acts at the single arginine residue present at position 9. This cleavage does not appear to take place in mammalian β-endorphins where position 9 is occupied by lysine. Journal of Endocrinology (1992) 135, 469–478

The Relation between Target Localisation in Strings of Letters, Contrast, and Refresh Rate

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 167-167
Author(s):  
N van Kruysbergen ◽  
A Hendriks
Keyword(s):  
Target Location ◽  
The Other ◽  
White Background ◽  
Original Experiment ◽  
Refresh Rate ◽  
Black Background ◽  
Target Localisation ◽  
The Subject ◽  
The Right ◽  
The Relationship

Jacobs (1987, Vision Research27 1953 – 1966) obtained psychometric curves to investigate the relationship between target localisability and the latency of primary saccades. These psychometric curves show correct scores as a function of string length, target location, and target-background similarity. They were obtained with white text on a black background. We repeated this experiment, with a few extensions. First, we did not only use white text on a black background, but we used black text on a white background as well. The stimuli were also presented with the use of isoluminant colours. Second, we varied the refresh rate of the screen (from 60 Hz up to 150 Hz). Third, we used two different instructions for the subjects: in one the subject was instructed to indicate the position of the target relative to the beginning of the string; in the other the position of the target relative to the fixation point. When the string was presented to the right of the fixation point, the results of these two instructions were predicted to be similar; in the other case the results might be different. The results of our experiments show a clear effect of the amount of contrast between text and background, and an influence of the screen refresh rate. We also found that the results differ depending on the instruction used. Sadly, we were not able to replicate all of the results of the original experiment by Jacobs.

scholarly journals Dynamics of proopiomelanocortin and prohormone convertase 2 gene expression in Xenopus melanotrope cells during long-term background adaptation

1998 ◽  
Vol 159 (2) ◽  
pp. 281-286 ◽  
Author(s):  
CH Dotman ◽  
F van Herp ◽  
GJ Martens ◽  
BG Jenks ◽  
EW Roubos
Keyword(s):  
Skin Color ◽  
Control Level ◽  
Maximum Level ◽  
White Background ◽  
Pars Intermedia ◽  
Black Background ◽  
Background Adaptation ◽  
Processing Enzyme

The toad Xenopus laevis is able to adapt its skin color to background light intensity. In this neuroendocrine reflex, the proopiomelanocortin (POMC)-derived peptide alpha-melanophore-stimulating hormone (alphaMSH) is a key regulatory factor. In animals adapting to a black background, release of alphaMSH from the pituitary pars intermedia causes dispersal of melanin in skin melanophores. To investigate the long-term in vivo dynamics of alphaMSH production during black background adaptation, the biosynthetic rate of POMC and the contents of POMC, alphaMSH and the POMC processing enzyme precursor convertase 2 (PC2) have been studied in the pars intermedia using pulse-labeling, Western blot and radioimmunoassay. In control animals, adapted to a white background, the rate of POMC biosynthesis and the POMC content were low, while high alphaMSH and PC2 contents were found. After 1 week of adaptation to a black background, the rate of POMC biosynthesis and the POMC protein content had increased 19- and 3.7-fold respectively. These parameters attained a maximum level (28- and 5. 8-fold higher than control) after 3 weeks and remained at these elevated levels for at least 12 weeks. After 1 week, the pars intermedia content of alphaMSH was only 30% of the control level, but after 6 and 12 weeks, the alphaMSH level had increased to the control level. The PC2 content decreased to 52% of control after 1 week and stabilized after 3 weeks at a level slightly lower than the control value. The results show that during long-term background adaptation a steady-state situation is reached, with a balance between the biosynthesis, enzymatic processing and release of alphaMSH. The in vivo dynamics of the processing enzyme PC2 suggest a parallel storage and release of alphaMSH and mature PC2 in the Xenopus pituitary pars intermedia.

scholarly journals Sensations from a single M-cone depend on the activity of surrounding S-cones

2018 ◽  
Author(s):  
Brian P. Schmidt ◽  
Ramkumar Sabesan ◽  
William S. Tuten ◽  
Jay Neitz ◽  
Austin Roorda
Keyword(s):  
Adaptive Optics ◽  
Relative Activity ◽  
The Other ◽  
White Background ◽  
Coarse Scale ◽  
Retinal Position ◽  
Natural Movement ◽  
Short Wavelength Light ◽  
Wavelength Light ◽  
Stimulation Of

ABSTRACTColor vision requires the activity of cone photoreceptors to be compared in post-receptoral circuitry. Decades of psychophysical measurements have quantified the nature of these comparative interactions on a coarse scale. How such findings generalize to a cellular scale remains unclear. To answer that question, we quantified the influence of surrounding light on the appearance of spots targeted to individual cones. The eye’s aberrations were corrected with adaptive optics and retinal position was precisely tracked in real-time to compensate for natural movement. Subjects reported the color appearance of each spot. A majority of L-and M-cones consistently gave rise to the sensation of white, while a smaller group repeatedly elicited hue sensations. When blue sensations were reported they were more likely mediated by M- than L-cones. Blue sensations were elicited from M-cones against a short-wavelength light that preferentially elevated the quantal catch in surrounding S-cones, while stimulation of the same cones against a white background elicited green sensations. In one of two subjects, proximity to S-cones increased the probability of blue reports when M-cones were probed. We propose that M-cone increments excited both green and blue opponent pathways, but the relative activity of neighboring cones favored one pathway over the other.

The Kidney and Fibrinolysis

1970 ◽  
Vol 24 (01/02) ◽  
pp. 026-032 ◽  
Author(s):  
N. A Marsh
Keyword(s):  
Molecular Weight ◽  
Plasminogen Activator ◽  
Enzyme System ◽  
Normal Animal ◽  
Fibrinolytic Enzyme ◽  
The Other ◽  
Exclusion Chromatography ◽  
Normal Urine ◽  
Renal Origin ◽  
Molecular Exclusion Chromatography

SummaryMolecular exclusion chromatography was performed on samples of urine from normal and aminonucleoside nephrotic rats. Normal urine contained 2 peaks of urokinase activity, one having a molecular weight of 22,000 and the other around 200,000. Nephrotic urine contained three peaks of activity with MW’s 126,000, 60,000 and 30,000. Plasma activator determined from euglobulin precipitate had a MW. in excess of 200,000. The results indicate that in the normal animal, plasma plasminogen activator does not escape into the urine in substantial quantities but under the conditions of extreme proteinuria there may be some loss through the kidney. The alteration in urokinase output in nephrotic animals indicates a greatly disordered renal fibrinolytic enzyme system.The findings of this study largely support the hypothesis that plasma plasminogen activator of renal origin and urinary plasminogen activator (urokinase) are different molecular species.

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