家兎の間・中脳の電気刺激により誘発される眼球運動

抄録

Electrical stimulation of the mesodiencephalon in 32 conscious rabbits was performed with the aim of elucidating its oculomotor function in the present experiments. For each animal a bipolar stimulating electrode was permanently implanted into one of the following structures : area pretectalis (Prt), nucleus pretectalis anterior (PA), nucleus lateralis posterior thalami (LP) nucleus ventralis basalis thalami (VB), tractus opticus (OT), nucleus medialis dorsalis thalami (MD), nucleus reticularis tegmenti (Tg), nucleus pretectalis (PR T) and lamina medullaris posterior thalami (Lmpth). Saccades were induced from these sites except for OT, some parts of PA or part of LP and central nystagmus was induced from OT, PA and LP. The most favourable stimulation condition for inducing saccades was a train of rectangular pulses of 0.5 msec in duration at a frequency of 400 Hz and that for the central nystagmus a train of rectangular pulses of 0.5 msec in duration at 50-100 Hz. Saccades occurred in the direction generally ipsilateral to the stimulation sites and were horizontal, oblique and vertical depending on stimulation sites. Threshold intensities ranged from 0.25V to 8V (av. 3 2V) and latencies for the oculomotor effects from 75 msec to 190 msec (av. 124 msec). There was a tendency that the threshold became progressively lower with deeper placement of the electrode at PA. Although patters of the induced saccades were greatly influenced by changing eye positions via the otolith reflex, there was no indication for the so-called goal directed eye movements.
In contrast, the threshold for the induced nystagmus was lowest at OT with the slow phase ipsilateral to the stimulation site. To clarify the neural pathway responsible for the central nystagmus, ablation of the flocculus and paraflocculus contralateral to the stimulation site was carried out but no consist-ent result was obtained. It seems that the flocculus is not involved in the main pathway for the central nystagmus. But the fact that the nystagmus was facilitated in darkness and with an eye blindfolded ipsilateral to the stimulation site suggests that the flocculus may be relevant to the nystagmus to some degree.