Elektrophysiologische Charakterisierung und morphologische Darstellung von Neuronen des tecto-bulbären und bulbo-tectalen Systems von lungenlosen Salamandern (Fam. Plethodontidae)

Abstract

In lungless salamanders (Fam. Plethodontidae), as in all vertebrates, the final integration of all exo- and endogenous information to behavior, takes place in the motor neurons of the medulla oblongata and medulla spinalis. During prey catching , the primary visual center, the tectum opticum analyses visual information and controls behavior via motor nuclei in the brainstem very fast, involving sometimes only a single synaptic layer. This study looked for mechanisms of information processing of this descending visual pathway and the ascending pathway of the medulla oblongata to the tectum opticum.Neurons of both brain regions were characterized by intracellular recording in vitro and in vivo. Input resistance, time constant, capacity and resting potential were determined. Input connections of neurons were determined by electrical stimulation of peripheral nerves. Observed rectifying characteristics and reverse potentials of isolated cell responses were used for an estimation of intracellular ionic concentration. The morphology of recorded cells was depicted by iontophoretic application of biocytin.In tectal cells different kinds of signals revealed mechanisms like gap junction coupling and active dendrites. In vivo, cells show action potential frequencies up to 30 Hz. Current injection in vitro showed that most neurons can generate action potential frequencies only up to 150 Hz. The tectum opticum as main visual center and integrator for somatosensoric and vestibular information is constituted by ~10:sup:5:/sup: neurons only. This indicates that analysis of the visual input is mostly analyzed by subthreshold mechanisms. Printversion via Verlag (http://www.tectum-verlag.de ) available.