Christer Liedgren

Limb Input to the Cat Vestibular Nuclei

The input from fore- and hindlimbs to the vestibular nuclear complex (VNC) was investigated in awake cats. Electrical stimulus was given to the sciatic, radial and vestibular nerves bilaterally and single unit responses were recorded in the VNC with extracellular technique. The position of the microelectrode was histologically confirmed. All four major vestibular nuclei received fore- as well as hindlimb input. Forty per cent of the neurons with limb input also received vestibular afferents. No major distinguishing features appeared between the different nuclei with regard to response characteristics. Certain differences in laterality of response, quantitative fore-hindlimb ratio and somatosensory-labyrinthine convergence were observed however. Response latencies to sciatic and radial nerve stimuli always exceeded a 3 msec and were grouped around 8 and 16 msec. A third population of vestibular neurons had latencies over 20 msec. Both excitatory and inhibitory responses were recorded, with the latter not always following an activation. The findings illustrate the complex nature of the ascending pathway to the VNC and the integrative properties of this complex.

Electronystagmographic Findings in Rats Exposed to Styrene Or Toluene

A previously described experimental model for studying the effect of industrial solvents in the vestibular system of rabbits has been applied to rats. To achieve a constant concentration, the solvent was infused intravenously, dissolved in a lipid emulsion. Arterial blood levels were estimated by gas chromatography. The vestibulo-oculomotor behaviour of rats during repeated rotatory acceleration was investigated by electronystagmography. The effect of two solvents-toluene and styrene-on the rotatory induced nystagmus was examined. Both solvents caused an exaggerated reaction at arterial blood levels above 75 ppm. The investigation indicated that the rat will be suitable species for further electronystagmographic investigation of the influence of organic solvents on the vestibular system, for example in screening studies of the toxicity of these solvents.

Effects of Trichloroethylene on the Human Vestibulo-Oculomotor System

Ten healthy volunteers were subjected to a vestibulo-oculomotor test battery before, during and 1 hour after trichloroethylene exposure. The concentration of trichloroethylene in inspiratory air was 32-78 ppm (176-429 mg/m3). The concentration of trichloroethylene in venous blood was followed throughout the experiment. The mean pulmonary uptake was estimated. Each test person was also subjected to a control experiment, breathing air free of trichloroethylene. A decreased ability to visually suppress the vestibulo-oculomotor reflex during sinusoidal stimulation was noticed during trichloroethylene exposure. One hour after exposure the test subjects showed a decreased maximum velocity of the voluntary saccade and a decreased ability to follow a sinusoidally moving target.