Biomedical subjects

R M Santarelli

Publications and source records attributed to R M Santarelli.

4 recordsLinked to original sources

PubMed1991

Contribution of the maculo-ocular reflex to gaze stability in the rabbit.

The contribution of the maculo-ocular reflex to gaze stability was studied in 10 pigmented rabbits by rolling the animals at various angles of sagittal inclination of the rotation and/or longitudinal animal axes. At low frequencies (0.005-0.01 Hz) of sinusoidal stimulation the vestibulo-ocular reflex (VOR) was due to macular activation, while at intermediate and high frequencies it was mainly due to ampullar activation. The following results were obtained: 1) maculo-ocular reflex gain decreased as a function of the cosine of the angle between the rotation axis and the earth's horizontal plane. No change in gain was observed when longitudinal animal axis alone was inclined. 2) At 0 degrees of rotation axis and with the animal's longitudinal axis inclination also set at 0 degrees, the maculo-ocular reflex was oriented about 20 degrees forward and upward with respect to the earth's vertical axis. This orientation remained constant with sagittal inclinations of the rotation and/or longitudinal animal axes ranging from approximately 5 degrees upward to 30 degrees downward. When the longitudinal animal axis was inclined beyond these limits, the eye trajectory tended to follow the axis inclination. In the upside down position, the maculo-ocular reflex was anticompensatory, oblique and fixed with respect to orbital coordinates. 3) Ampullo-ocular reflex gain did not change with inclinations of the rotation and/or longitudinal animal axes. The ocular responses were consistently oriented to the stimulus plane. At intermediate frequencies the eye movement trajectory was elliptic because of directional differences between the ampullo- and maculo-ocular reflexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Auditory steady-state responses in the rabbit.

The authors have studied auditory brainstem (ABRs), middle latency (MLRs) and steady-state potentials (SSRs) in 15 adult male rabbits weighing between 2.5 and 3 kg in order to verify if SSRs are due to a mere superimposition of ABRs and MLRs or to a resonance phenomenon. Ten of them were awake while 5 were studied under urethane anesthesia. Acoustic stimuli consisted in 0.1-ms square-wave pulses delivered at presentation rates ranging between 1 and 80/s at a stimulus intensity of 80 dB p.e. SPL. Our data show that reliable auditory SSRs can be obtained in the rabbit at a presentation rate of 30 stimuli/s, probably due to the superimposition of ABRs and MLR Pb waves which show an interwave interval of about 35 ms. The nonlinear aspects which can be detected are probably due to the effect of decreasing interstimulus intervals on the duration and amplitude of the Pb wave. It can then be concluded that SSRs in the rabbit are due more to a superimposition of ABR and MLR waves than to a resonance phenomenon.

Acoustic Stimulation↗

PubMedDate not supplied

[Considerations on analysis time duration in a posturographic study in normal subjects].

In order to evaluate the importance of analysis time on posturographic parameters (average X, Y and R, Sway Path, Sway Area, Ellipse Area) both with eyes open and closed, 24 normal subjects were examined for an overall period of 60 seconds. Mean +/- 1 SD values of each parameter were obtained for each time interval (0-20, 20-40, 40-60 sec.) into which the overall period was divided. With the eyes open, the parameters for each time interval did not differ significantly and they were always lower than those obtained with the eyes closed. On the other hand, with the eyes closed, there was a significant reduction in the various parameters as analysis time progressed. In 4 out of 24 subjects an inverse behaviour was detected. The authors conclude that the open-eye analysis time could be limited to 20 sec while, due to changes observed in the various posturographic parameters, closed-eye analysis time should be extended to 60 seconds. The analysis time may prove important in identifying peripheral or central vestibular pathologies since it may be that some of them induce earlier alterations of posturographic parameters while in other pathologies such changes are observed later on.

Adult↗

PubMedDate not supplied

[Influence of static stimulation of cervical and otolithic receptors on posturographic parameters].

In the present work 30 normal adult subjects (20 males, 10 females; age range 25-40 years) having no signs or symptoms of vestibular involvement were studied in order to verify whether posturographic parameters could be influenced by the static stimulation of cervical and otolithic receptors. The posturographic evaluation was carried out using a stabilometric platform (Bertec) with the subject standing and the head in one of the following positions: median position, turned left (45 degrees), turned right (45 degrees), tilted left (40 degrees), tilted right (40 degrees), with eyes both opened and closed. The data obtained indicate that wide standard deviations exist in the observed parameters and no significant changes were observed with the head turned either to the right or left nor with the head tilted in either direction. Moreover, the posturographic data obtained with eyes open were slightly reduced in comparison to those obtained with the eyes closed. One can, thus, conclude that neither cervical nor otolithic inputs influence posturographic parameters under static conditions, while visual inputs modify significantly posturographic data, except the coordinates of the foot center of pressure.

Adult↗