No abstract

Melanophores were studied in tadpoles of the South African clawed toad, Xenopus laevis, during the first week after hatching (stages 46-49) at 25 degrees C. The tadpoles had melanophores with dispersed melanosomes in the light and punctate melanophores in the dark in LD 12:12. The melanophores remained punctate in constant dark and the melanosomes remained dispersed in constant light. Lights-out (in the light-time of LD 12:12) caused the melanophores to become punctate, which occurred more quickly than the dispersion of melanosomes, which commenced when the lights were turned on (in the dark-time of LD 12:12). Melanophores with dispersed melanosomes in tadpoles (in constant light) became punctate in response to a series of melatonin concentrations (0.2-5 ng/ml) in their bathing water irrespective of the time of day melatonin was administered. An image-analysis technique for assessing melanophore responses was tested.

Circadian responses to photoperiod were studied in house sparrows (Passer domesticus) by subjecting them to 4-h light pulses and measuring the subsequent phases of their circadian rhythms. The direction and magnitude of phase shifts in response to 4-h light pulses following pretreatment with light-dark cycles (LD) 16:8 or LD 8:16 varied with time of day; advances (3.4 h) occurred when pulses were imposed in the late subjective night on both groups of birds; delays (-2.1 h) occurred when the pulses were imposed in the early subjective night on the LD 8:16 birds. The time profiles for responses to light pulses that scanned 24 h (phase-response curves) were modified by long and short photoperiod. Short photoperiod 1) increased amplitude (1.7 h), 2) increased time from the prior lights-out to the peak of advances (6 h), and 3) decreased the mean phase shift (0.9 h).

No abstract

N-Acetyltransferase (NAT) is an enzyme whose rhythmic activity in the pineal gland and retina is thought to be responsible for melatonin circadian rhythms. The enzyme has circadian properties--its rhythm persists in constant conditions, and it is precisely controlled by light and dark. Experiments are reported in which 4-h light or dark pulses were imposed on chicks (Gallus domesticus) over a 24-h period. Pineal NAT profiles were measured during and subsequent to the pulses. The phase of the NAT cycle following pulses was plotted to obtain phase-response curves. Light pulses produced a maximum phase shift (advance of 5 h) 8 h after the expected time of lights-out; dark pulses produced a maximum phase shift (advance of 4 h) 3 h after the expected time of lights-out. Maximum phase delays (-2 h) occurred 1-2 h after the expected lights-out for light pulses and 8 h after expected lights-on for dark pulses.

Circadian responses were studied using the perching activity of house sparrows (Passer domesticus). The sparrows were subjected to single or double 4-hr light pulses (the single pulses or the second pulses of the doublets scanned 24 hr) in the first cycle after previous entrainment to a light-dark cycle (LD 12:12). The differences in times at which the birds commenced perch-hopping in LD 12:12 before the pulses and in the five cycles immediately following the pulses were determined (phase shifts). A 24-hr time profile for phase shifts in response to single light pulses replicated our previous study: Early-night pulses delayed the rhythm (-1.7 hr), while late-night pulses advanced the rhythm (+3.8 hr). After pretreatment with a light pulse that advanced the birds +2.7 hr, the resetting curve was advanced. There were no delays; the range of average shifts was +0.1 hr to +6.2 hr. After pretreatment with a light pulse that delayed the birds -1.7 hr, the resetting curve was delayed. Average delays as much as -1.1 hr and advances up to +2.1 hr were measured. The data for double pulses were interpreted from predictions made from single-pulse data.

Abstract— Sparrows (Passer domesticus) are day‐active birds which exhibit circadian rhythms of perch‐hopping activity. The phases of sparrow's circadian rhythms were studied following single 4 h light pulses, single 4 h dark pulses, doublet treatments of light and dark pulses, and a 10 h light pulse. The sparrows exhibited a phase response curve to 4 h light pulses with maximum phase advances (3.8 h) at CT20 and maximum phase delays(–1.3 h) at CT16. The sparrows also displayed a phase response curve to dark pulses with maximum phase advances (2.2 h) at CT16 and maximum phase delays at CTO(–0.7 h). The remaining pulses were imposed during the subjective dark‐time. The 10 h pulse beginning 1 h after lights‐out produced a 2.2 h phase shift. The doublet of 2 h pulses that were the “skeleton” of the 10 h pulse produced a 2.5 h phase shift. The early 2 h pulse, applied by itself resulted in a ‐0.4 h delay; the late 2 h pulse applied singly produced a 3.1 h advance. When an early 3 h dark pulse was imposed together with a late light pulse, the phase was advanced 3.6 h; singly the pulses produced 1.8 h and 2.7 h advances.

Above 24 h the values diminish slightly as a function of T. The critical number of short night signals depends on the light regime. The clock-counter system works better with very long cycles. Below 24 h it loses its efficiency. If there were a circadian element in the system (either for clock or for counter), a higher efficiency would be expected as one approaches the natural period of 24 h. The measure of time provided by the Zeitgeber is determined by a circadian system for the induction at the larval stage while it is apparently accomplished according to an hour-glass model for diapause termination in the pupa. This change in operation during development is indicated here for the first time. Metamorphosis in holometabolous insects involves the almost total restructuring of the tissues and organs, including the central nervous system. Two situations may occur: either there is a single clock to control entry into and exit from diapause, and metamorphosis provokes a change in its operation, or induction is controlled by a larval clock operating with a circadian oscillator and diapause termination by another, anatomically different pupal clock, working according to the hour-glass model.Summary. In two arctiid species, Holomelina lamae and H. aurantiaca, which rhythmically extrude and retract their abdominal tips during pheromone emission, pheromone glands contain up to three orders of magnitude more of the major component than in most Lepidoptera examined to date. Using an effluent collection technique, relatively high rates of pheromone emission were obtained from freely calling females. In contrast, volatilization rates from forcibly extruded glands were about 25 times lower for both species, suggesting that pulsation of the gland functions to increase the release rate.