Fachbereich Veterinärmedizin



    Untersuchungen zum Blitzlicht-induzierten Nystagmus beim Meerschweinchen - eine Fallstudie anhand von Beobachtungen an drei Meerschweinchen (2002)

    Welbhoff, Jens U
    Berlin, 2002 — 151 Seiten
    Institut für Veterinär-Physiologie

    Oertzenweg 19 b
    14163 Berlin
    +49 30 838 62600

    Abstract / Zusammenfassung

    Phylogenetically, in the visual system the development of six types of eye movements enables visual perception in space. The anatomical basis are brain-stem located stuctures and areas of the visual cortex. Brain-stem nuclei of the lower mammals maintain the vestibulo-oculomotor reflex (VOR) and the optokinetic nystagmus (OKN) as well as formes of saccadic eye movements. In primates, including men, cortical centres establish important functions in controlling saccades, OKN and smooth pursuit eye movements (and also vergent and fixation).Due to the simple structure of retina and cortex in guinea pigs, these animals are most suitable when investigating cortex-not-influenced eye movements under the premission not to investigate operated or leasioned animals.The present investigation was restricted to optokinetic eye movements.In all animals we saw a slow built-up of the OKN, which is determined as the velocity of the slow phase of the rhythmic nystagmic eye movements.As it is well known that cortex creates a fast OKN built-up and brainstem-mediation creates a slow built-up, our observation of a slow built-up in guinea pigs rejects the assumtion of cortex-participation in OKNOur observation in the time course of the optokinetic after-nytagmus supports the assumption of a largely brain-stem mediation of optokinetic eye movements.Two particular types of optokinetic eye movements are previously defined throughelicitation without any real stimulus motion: they are called sigma-OKN ( so far in guinea pigs only investigated in out lab.) and flash-induced OKN ( for the fist time in guinea pigs described in the present study).We found that sigma OKN in guinea pigs exists. This observation is not in accordance with the so far published scientific opinion, that sigma OKN requires a loop via the cerebral cortex. As we proved in OKN and OKAN, that the cortical loop does not exist in guinea pigs, sigma OKN could not have been expected to exist. As working hypothesis we coined the term apparent-motion OKN for the observed type of eye in our study.Futhermore, in all animals nystagmic eye movements could be elicited by a simple presentation of flash light (flash-induced OKN).This has been shown for the first time. We could show that the presentation of flash light was initially responded with a slow nystagmus phase. This is an unconditioned requirement for optokinetic eye movements. In the further course of experiments, however, we failed to proof hat the socalled sigmaOKN is a subgroup of the brainstem-mediated flash-induced OKN.The present study gains more knowledge on the role of the cerebral cortex and the brainstem in execution of eye movements.