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R J Wubbels

Publications and source records attributed to R J Wubbels.

6 recordsLinked to original sources
PubMed2000

Vestibular-induced behaviour of rats born and raised in hypergravity.

One group of rats were bred and kept under hypergravity (HG) conditions (2.5 g) in a centrifuge. Another group were bred and kept under normal gravity conditions (1 g). Rats from both groups were dropped from a supine position into a water basin under infrared illumination leaving only gravity (1 g for both groups) for orientation. The airrighting reflex and reappearance at the water surface were examined. The success rate for airrighting of HG rats is 47% versus 45% for controls, and is performed about equally fast by both groups. The success rate of HG and control hamsters is </=25% and >/=80%, respectively [22]. This interspecific difference does not appear to support the conjecture that altered behaviour is caused by a structural change of vestibular end organs during ontogenetic development under HG. The success rate for surfacing of control rats is 100%. Surfacing of young HG rats is less successful (36% at age 6 weeks) and requires more time. On average, surfacing of adult rats of both groups is about the same. Apparently, the repeated stay of centrifuge-bred rats at 1 g for experiments and daily care suffices to recalibrate and improve their orientation, which is essential for surfacing.

Adaptation, Physiological↗
PubMed1997

Neuronal encoding of sound direction in the auditory midbrain of the rainbow trout.

Acoustical stimulation causes displacement of the sensory hair cells relative to the otoliths of the fish inner ear. The swimbladder, transforming the acoustical pressure component into displacement, also contributes to the displacement of the hair cells. Together, this (generally) yields elliptical displacement orbits. Alternative mechanisms of fish directional hearing are proposed by the phase model, which requires a temporal neuronal code, and by the orbit model, which requires a spike density code. We investigated whether the directional selective response of auditory neurons in the midbrain torus semicircularis (TS; homologous to the inferior colliculus) is based on spike density and/or temporal encoding. Rainbow trout were mounted on top of a vibrating table that was driven in the horizontal plane to simulate sound source direction. Rectilinear and elliptical (or circular) motion was applied at 172 Hz. Generally, responses to rectilinear and elliptical/circular stimuli (irrespective of direction of revolution) were the same. The response of auditory neurons was either directionally selective (DS units, n = 85) or not (non-DS units, n = 106). The average spontaneous discharge rate of DS units was less than that of non-DS units. Most DS units (70%) had spontaneous activities < 1 spike per second. Response latencies (mode at 18 ms) were similar for both types of units. The response of DS units is transient (19%), sustained (34%), or mixed (47%). The response of 75% of the DS units synchronized to stimulus frequency, whereas just 23% of the non-DS responses did. Synchronized responses were measured at stimulus amplitudes as low as 0.5 nm (at 172 Hz), which is much lower than for auditory neurons in the medulla of the trout, suggesting strong convergence of VIIIth nerve input. The instant of firing of 42% of the units was independent of stimulus direction (shift <15 degrees), but for the other units, a direction dependent phase shift was observed. In the medial TS spatial tuning of DS units is in the rostrocaudal direction, whereas in the lateral TS all preferred directions are present. On average, medial DS units have a broader directional selectivity range, are less often synchronized, and show a smaller shift of the instant of firing as a function of stimulus direction than lateral DS units. DS response characteristics are discussed in relation to different hypotheses. We conclude that the results are more in favor of the phase model.

Air Sacs↗
PubMed1995

Mapping of sound direction in the trout lower midbrain.

In the trout lower midbrain 35% of the auditory neurons are directionally selective (DS). Most of these neurons have a higher directional selectivity than the sensory hair cells. DS units and non-DS units occur in vertical clusters, with the former more dorsally. The direction of preference is topographically mapped. Apparently, auditory space mapping is a common feature in the midbrain of vertebrates.

Animals↗
PubMed1984

Photopic spectral sensitivities of the red and the yellow field of the pigeon retina.

The spectral sensitivities of the red field and the yellow field in the retina of the homing pigeon (Columba Livia) were determined on the basis of ERG responses. Between 450 and 550 nm the relative spectral sensitivity of the yellow field turned out to be higher than that of the red field. The results are in agreement with spectral sensitivity data, obtained by behavioural threshold procedures.

Action Potentials↗