Clark S. Donley

Johns Hopkins University, Baltimore, Maryland, United States

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Publications (5)10.48 Total impact

  • Hilmar Meissl · Clark S. Donley ·
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    ABSTRACT: The adaptive performance of the chromatic response of the distal part of the pineal organ (frontal organ, stirnorgan) of the frog. Rana esculenta, was studied by recording from pineal nerve fibres.Following exposure to strong red light the excitatory component increases sensitivity in darkness for about 60 min, its time course being comparable to the first portion of the dark-adaptation curve of the achromatic response of the proximal part of the frog's pineal organ. The determination of threshold of the excitatory component required weak ultraviolet background illumination in order to depress the maintained discharge of the excitatory response elicited by the test stimulus.The evidence presented indicates that the impulse rate of pineal nerve fibres carrying the chromatic response of the organ depends on the balance between opposing inhibitory and excitatory processes.
    Vision Research 02/1980; 20(5):379-83. DOI:10.1016/0042-6989(80)90027-9 · 1.82 Impact Factor
  • Clark S. Donley · Hilmar Meissl ·
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    ABSTRACT: In situ recorded responses (electropinealogram or EPG) are: (1) not color coded: (2) composed of a fast (lasting < 1sec) photopic component (λmax > 500 nm) and a slower (lasting 1 sec to 1 min) scotopic component (λmax ≈- 500 nm): (3) able to dark-adapt over at least 3.5 log units over a few half hours; (4) dominated by the scotopic (slow) component even at light levels where the spike activity is photopic; (5) show light integration according to Bloch's law up to ≈-5 sec in the dark-adapted state, up to ≈-500 msec in the light-adapted state; (6) also slow in light adapting requiring up to 30 min. The contention that they represent receptor potentials is based on: (a) the lack of a knee in the two-component dark-adaptation curve, (b) the dominance of a scotopic spectral sensitivity curve at photopic adaptation levels and (c) the limited number of cells and cell types in the organ.
    Vision Research 02/1979; 19(12):1343-9. DOI:10.1016/0042-6989(79)90206-2 · 1.82 Impact Factor
  • C S Donley · H Meissl ·

    The Journal of Physiology 12/1978; 284:115P. · 5.04 Impact Factor
  • H Meissl · C S Donley · J H Wissler ·
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    ABSTRACT: 1. The relative content of free amino acids was measured in the pineal organ of the rainbow trout using a [14C]dansylation assay procedure and a two-dimensional microchromatography for separation.2. The main compounds of low molecular weight have been identified as taurine, glycine, alanine, arginine, histidine, glutamic acid and aspartic acid. γ-Aminobutyric acid and the indoleamine serotonin were present only in small quantities.3. Differences in the amino acid patterns between day and night in a daily photoperiod of 12:12 hr (light: dark) were only slight.4. Continuous light for 7 days significantly decreased the amount of taurine and increased ornithine, lysine, tryptophan, tyrosine and 5-hydroxyindole. Serotonin was not detectable under these conditions.
    Comparative Biochemistry and Physiology Part C Comparative Pharmacology 02/1978; 61 C(2):401-5. DOI:10.1016/0306-4492(78)90077-1
  • Clark S. Donley ·
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    ABSTRACT: Slow potentials recorded from the frog (Rana pipiens) Stirnorgan in response to a step stimulus of dim violet light, can increase linearly for at least a minute. Such a long integration time is remarkable. Either a violet or a green conditioning stimulus will cause a reduction in the response to a subsequent violet test stimulus, even with separation times of up to 2 min. The decay time constant of this effect is about 35 sec, twice as long as the decay of the response to the violet conditioning flash itself. Such interaction can be accounted for by a proposed model in which transmitters block post synaptic sites as well as directly inactivate opponent transmitter. In the absence of conditioning stimuli, the stimulus-response curve for violet stimuli is linear with log intensity over the two log units recordable. Possibly, the violet-green interaction in the frog Stirnorgan permits time of day (or season) estimation by determining the angle of the sun.
    Vision Research 03/1975; 15(2):245-51. DOI:10.1016/0042-6989(75)90214-X · 1.82 Impact Factor