Zeitschrift für vergleichende Physiologie

We investigated efferent neurotransmission in theLimulus lateral eye by studying the action of pharmacological agents on responses of photoreceptor cells in vitro. We recorded transmembrane potentials from single cells in slices of retina that were excised during the day and maintained for several days in a culture medium. Potentials recorded in the absence of pharmacological agents resemble those recorded from cells in vivo during the day. Octopamine, a putative efferent neurotransmitter, induced changes in photoreceptor potentials that mimicked in part those generated at night by a circadian clock located in the brain. Specifically, octopamine (100 to 500 μM) decreased the frequency of occurrence of quantum bumps in the dark and increased the amplitude of photoreceptor responses to intermediate and high light intensities. Similar actions were produced by naphazoline (25 to 100 (μM, potent agonist of octopamine), forskolin (8 to 400 μM, activator of adenylate cyclase), IBMX (1 mM, inhibitor of phosphodiesterase), and 8-bromo-cAMP (500 μM, analogue of cAMP). 8-bromo-cGMP (500 μM, analogue of cGMP) decreased the rate of spontaneous quantum bumps only. Our results support the hypothesis that (1) octopamine is an efferent neurotransmitter of circadian rhythms in theLimulus eye and that (2) it activates adenylate cyclase to increase levels of the second messenger, cAMP, in photoreceptor cells. Circadian changes in photoreceptor responses to moderate intensities may be a specific action of cAMP, since cGMP has no effect. Circadian changes in the rate of spontaneous quantum bumps may involve a less specific intermediate, since both cAMP and cGMP reduce bump rate. Characteristics of the retinal slice preparation precluded a detailed study of the effects of pharmacological agents on retinal morphology.

The eye of the marine mollusk Aplysia californica contains a photo-entrainable circadian pacemaker that drives an overt circadian rhythm of spontaneous compound action potentials in the optic nerve. Both light and serotonin are known to influence the phase of this ocular rhythm. The current study evaluated the effect of FMRFamide on both light and serotonin induced phase shifts of this rhythm. The application of FMRFamide was found to block serotonin induced phase shifts but, by itself, FMRFamide did not cause significant phase shifts. Furthermore, the effects of FMRFamide on light-induced phase shifts appeared to be phase dependent (i.e., the application of FMRFamide inhibited light-induced phase delays but actually enhanced the magnitude of phase advances). As in Aplysia, the eye of Bulla gouldiana also contains a circadian pacemaker. In Bulla, FMRFamide prevented light-induced phase advances and delays. Although FMRFamide alone generated phase dependent phase shifts, it did not cause phase shifts at the phases where it blocked the effects of light. These data demonstrate that FMRFamide can have pronounced modulatory effects on phase shifting inputs to the ocular pacemakers of both Aplysia and Bulla.

Oxygen consumption was measured in slices of dogfish (Scyliorhinus canicula) rectal gland tissue and compared with spleen and kidney. Concentrations of dibutyryl cAMP and theophylline that have previously been shown to stimulate secretion from the perfused gland and to produce a large increase in ouabain binding in this tissue, greatly increased oxygen consumption in the rectal gland but were without effect on oxygen consumption in the spleen and the kidney. Addition of theophylline alone increased rectal gland oxygen consumption and no further increase was detected on addition of cAMP at the concentration used (0.05 mmol l−1). Ouabain (10−4 M) significantly decreased oxygen consumption in all three tissues studied and completely abolished the increase in oxygen consumption of the rectal gland produced as a result of the addition of cAMP and theophylline. These findings are discussed in relation to the apparent specific effect of cAMP on the rectal gland and its possible mode of action in this tissue.

Um den Grad der Ausnutzung der Sonnenwärme durch wechselwarme Tiere kennenzulernen, wurde — als eine Teilfrage dieses Problems — die Reflexion verschiedener Tieroberflächen im kurzwelligen Ultrarot untersucht. Es zeigte sich bei Käferelytren und Schmetterlingsflügein eine ausgesprochen selektive Reflexion mit einem Maximum bei 1μ und einem Minimum bei 1,9–2,2μ, bzw. 2,6 bis 3μ. Das Maximum ist, da es in einem Bereich liegt, in dem die Sonnenstrahlung ziemlich hohe Intensität besitzt, von Bedeutung. Zwischen der Reflexion im sichtbaren Bereich und im Ultrarot ist kein deutlicher Zusammenhang. — Bei den Schneckenschalen verläuft die Reflexionskurve ähnlich, aber unregelmäßiger, Frosch- und Eidechsenhäute haben eine von den kurzen zu den langen Wellen gleichmäßig ansteigende Kurve. Die Strahlungsausnutzung ist hier größer. Zwischen den einzelnen Arten innerhalb jeder Tiergruppe bestehen in der Reflexion erhebliche Unterschiede. Irgendwelche Gesetzmäßigkeiten — etwa ein Zusammenhang zwischen dem Reflexionsvermögen der Tiere und dem in ihrem Lebensraum vorherrschenden Strahlungsklima (Sonne oder Schatten) — sind nicht zu erkennen.

The results of this study demonstrate that trout (Salmo gairdneri) are capable of orienting to polarized light fields. The spectral composition of the polarized light fields can significantly influence the orientation of trout. Rainbow trout exhibit ontogenetic losses in orientation to polarized light fields which appears coincident with the ontogenetic loss of the UV-sensitive cones. Trout were trained to swim to a refuge located at one end of the training tank under a polarized light field. The E-vector of the polarized light field was oriented parallel or perpendicular to the long axis of the training tank. Trained fish were released in a circular test tank and their angular response scored. Under a white plus ultraviolet polarized light field, trout oriented in the trained E-vector orientation. For instance, fish trained under a parallel E-vector orientation exhibited angular responses close to parallel in the test tank. However, when the spectral composition of the polarized light field was manipulated, the accuracy of spatial orientation of the trout varied. Trout weighing about 30 g exhibited accurate orientation to the white plus UV polarized light field. The trout were incapable of orientation at a body weight of 50 to 60 g.

Individual bumblebees were tested on a task of walking along a test tunnel to collect sucrose solution in an initial training illumination condition that simulated natural daylight, and in two spectrally different illumination conditions. Compared to the training condition the bees took a significantly longer time to complete the task in conditions that simulated either an ultraviolet negative illumination environment, or an illumination environment that represented blue skylight. In a control condition, bees did not derive this cue from spectral information reflected from the dark background material. This result shows that bees can directly perceive spectral changes in illumination conditions, even in the context of a task that does not require colour processing. This potentially enables the visual system of bees to have prior knowledge about the spectral quality of illumination conditions in which they may forage. The findings are discussed in relation to both theoretical models and empirical evidence of colour constancy, and it is concluded that bees can use multiple mechanisms to solve the dilemma posed by having to find colour targets in the spectrally different illumination conditions that exist for insects visiting flowers.

Postinhibitory rebound (PIR) is an intrinsic property often exhibited by neurons involved in generating rhythmic motor behaviors. Cell DE-3, a dorsal excitatory motor neuron in the medicinal leech exhibits PIR responses that persist for several seconds following the offset of hyperpolarizing stimuli and are suppressed in reduced Na+ solutions or by Ca2+ channel blockers. The long duration and Na+ dependence of PIR suggest a possible role for persistent Na+ current (I NaP). In vertebrate neurons, the neuroprotective agent riluzole can produce a selective block of I NaP. This study demonstrates that riluzole inhibits cell DE-3 PIR in a concentration- and Ca2+-dependent manner. In 1.8 mM Ca2+ solution, 50–100 µM riluzole selectively blocked the late phase of PIR, an effect similar to that of the neuromodulator serotonin. However, 200 µM riluzole blocked both the early and late phases of PIR. Increasing extracellular Ca2+ to 10 mM strengthened PIR, but high riluzole concentrations continued to suppress both phases of PIR. These results indicate that riluzole may suppress PIR via a nonspecific inhibition of Ca2+ conductances and suggest that a Ca2+-activated nonspecific current (I CAN), rather than I NaP, may underlie the Na+-dependent component of PIR.