Manley transition

The transition to Germany

My first sabbatical year (1976) I spent in Germany, living mostly in Munich, where my then wife was carrying out a postdoctoral year with Detlev Ploog at the Max-Planck Institute of Psychiatry. I worked together with Hans Leppelsack in the Department of Zoology (Prof. Johann Schwarzkopf) in Bochum, on starlings. I had decided that, since it was possible to record from the mammalian cochlear nerve within the cochlea, this should be possible in birds - indeed easier, since in birds the cochlear ganglion (which of course is not spiralled) is only separated from scala tympani by a membrane and not by bone. I therefore developed an approach to the cochlear ganglion in the starling in Bochum and - on the first try - the electrode popped into the ganglion and gave us beautifully large action potentials from ganglion cells. Thenceforth we studied the spontaneous and sound-driven activity of starling nerve fibres and characterized their behaviour (Manley, 1979; Manley and Gleich, 1984; Manley et al., 1985). Their spontaneous activity was different to that of mammals (only one broad class, no very low rates), as was their tuning selectivity (on average sharper than that of mammals). This was the beginning of a long series of studies on avian hearing, later including many species' anatomy, and electrophysiology in fewer species: starlings, chickens, emus (in Australia) and barn owls (see below). My students Otto Gleich, Christine Köppl, Alexander Kaiser and Jutta Brix, as well as my co-workers Horst Oeckinghaus and the late Franz-Peter Fischer carried out a huge range of anatomical and physiological studies on bird species (also summarised in my book: Manley, 1990).

Following my sabbatical year in Germany, I only returned briefly to McGill, having decided, for personal and career reasons, to return to Germany in 1977. There, I worked for two years with the remarkably energetic Prof. Eberhard Zwicker (Elektroakustik) and one of his assistants, Agnes Kronester-Frei. Both Zwicker, who was partly engaged in building cochlear models, and Agnes, who was a brilliant anatomist, were interested in the structure and particularly the function of the tectorial membrane. In her thesis work, Agnes had shown that under normal physiological conditions, the tectorial membrane formed a seal over the organ of Corti, both at the outer edge and on the inner side of the inner hair cells. Previously, fixation artefacts (that cause the tectorial membrane to shrink) had led to the notion that the upper surface of the organ of Corti was fully exposed to the endolymph fluids of scala media. In view of Agnes' results, we were no longer sure of this.

These colleagues invited me to use my operative and electrophysiological skills to work with them on the physiology of the subtectorial space. There was, in fact, a substantial literature on this topic already available, in which authors had pushed recording electrodes through the organ of Corti, generally from below (scala tympani). They recorded the contact of the electrode with various structures (which could only be guessed at) before the electrode penetrated the scala media and recorded the endocochlear potential, which in mammals is about +80mV relative to the rest of the body. However, the recording traces had been hard to interpret and the travel paths of the electrodes essentially unknown. To pursue this with a better technique, Agnes and I developed a method by which the electrode could be observed live during the penetration of the organ (Manley and Kronester-Frei, 1980). This involved using tiny galvanometer mirrors mounted on fine wires and held in scala tympani while illuminating the organ of Corti from above through scala vestibuli. This permitted a wonderfully clear view (if the mirrors were not contaminated by red blood cells!) of the entire width of the organ and made the identification of the cell types and rows possible and the visualisation of the electrode within the scalae and the tissues. We were able to show that without this visualization it was impossible to know where the electrode tip was located, since the electrode often pushed tissue layers forward before penetrating them and it was in fact extremely difficult to estimate the angles of the electrode to the organ without actually being able to see it.

Using this technique, both Agnes and my later co-worker Geerd Runhaar and I carried out a series of recordings through the organ of Corti, sometimes using stains to confirm electrode positions, sometimes using ion-specific electrodes to identify the nature of the fluids encountered. These were the first recordings that allowed an exact, three-dimensional and unequivocal localisation of the electrode tip during the penetrations. The data showed, for the first time, that the space within the inner sulcus (that lies below the tectorial membrane) was at zero potential and did not contain high levels of potassium. The endocochlear potential and high potassium levels were first encountered when the electrode touched the tectorial membrane. These results were published (Runhaar and Manley, 1987) but essentially ignored. Still today, "established wisdom" has it that the top of the organ of Corti is exposed to the endolymphatic fluid. Scientific work should, if incorrect for any reason, be publicly discussed and criticized. To be ignored is the worst fate possible, since it means the loss of all the work and of the funds that went into it and, possibly, needless repetition in the future. Apparently no one is interested in the electrophysiological profile of the organ of Corti - or perhaps the distributions of the fluids are not important?

During this time I also wrote a short review of hearing in reptiles (Manley, 1981).

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