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W H Krul

Publications and source records attributed to W H Krul.

4 recordsLinked to original sources
PubMed1978

Diurnal changes in the rabbit's visual evoked potential.

Rabbits that have been exposed to the natural cycles of day and night exhibit marked diurnal changes in the shape of their Visual Evoked Potential in constant environmental conditions. The results of exposure to artificial 24 hr light-dark cycles strongly suggest that it is the regular alternation of daylight and darkness which acts as the synchronizing "Zeitgeber" for the V.E.P. rhythm which exists after exposure to the natural cycles of day and night. It would seem further that the V.E.P. changes reflect a square-wave like rhythm in the sensitivity of the visual system to photic stimuli, in which the sensitivity is much higher at night than in the day-time. The probable importance of the diurnal V.E.P. rhythm for the occurrence of daily fluctuations in behaviour is discussed.

Animals↗
PubMed1978

Photoperiodic programming of diurnal changes in rabbit visual evoked potentials.

Rabbits which have been exposed for several weeks to the natural cycles of daylight and darkness, or to various fixed 24 hr light-dark alternations, exhibit in constant environmental conditions large diurnal changes in the shape of the Visual Evoked Potential. These changes run a square-wave like time course and seem to reflect a similar diurnal rhythm in the sensitivity of the visual system to photic stimuli. The relation between the durations of the two phases of the rhythm can, within wide limits, be changed by variations in length of the artificial or natural photoperiod. It further appears that after exposure to continuous illumination or darkness rabbits have either a free-running V.E.P. rhythm or no such rhythm at all. The probable importance of the diurnal changes in the visual system for the occurrence of seasonal fluctuations in behaviour is discussed.

Animals↗
PubMed1978

Seasonal fluctuations of the circadian changes in rabbit visual evoked potentials.

Two rabbits were exposed for more than a year to the natural cycles of daylight and darkness. At intervals of 2 months and less records were taken of the time course of the 24 hr rhythm appearing in constant conditions in their cortical flash-evoked responses. It appeared that the rhythm can be programmed as well by the natural light-dark alternations as by artificial cycles. In temperate zones this "natural programming" causes large seasonal fluctuations in the time course of the rhythm which reflects, over the major part of the year and with remarkable precision, the times of sunrise and sunset and, in consequence, the length of the day. The possible significance of fixing daylength temporarily in the nervous system is discussed in connection with Bünning's hypothesis on the causation of seasonal photoperiodism.

Animals↗