Adventures in a submicron world
In addition to the glass micropipette electrodes (now often called sharp electrodes to distinguish them from the more blunt versions used for patch clamps of single ion channels), our submicron adventures were made possible by the availability of scanning electron microscopy (SEM), high-resolution optical fluorescence microscopy, the S100 bus computer and CP/M operating system, high quality servo sensors and actuators, high-quality acoustic sensors and actuators, and a high-mobility, ionic, fluorescent organic dye (Lucifer Yellow, designed and synthesized by Walter Stewart at NIH).
Through the decade of the 1970s, we had used SEM to examine the arrays of submicron transducer elements (stereovilli) on the surfaces of the sensory cells (hair cells) of the vertebrate inner ear and had speculated on the relationship between the conspicuous variations in the geometries of those arrays from hair cell to hair cell and the variations of signal properties from axon to axon in the VIIIth-nerve. At the end of that decade, we fabricated the glass electrodes, filled their tips with Lucifer Yellow, inserted them into VIIIth-nerve axons, used the actuators to provide stimulation to the ear, used precisely-calibrated sensors to monitor and quantify that stimulation, intercepted the neural responses being sent along those axons from the inner ear to the brainstem, used computers to analyze the relationships between those reponses and the quantified stimuli and to deduce the sensory functions implied by those relationships, injected Lucifer Yellow into each such functionally-identified axon, and then used fluorescence microscopy to trace the functionally-identified axons precisely to the hair cells they innervated (and, occasionally, precisely to their target neurons in the brainstem). With these tools and methods we confirmed our speculations about the relationships between inner-ear signal-processing properties and the geometries of those arrays of submicron transducers on inner-ear hair cells. What we were doing was reverse engineering the vertebrate ear. I guess we'd appropriately have been called bio-reverse-engineers. By the way, we were the first to trace individual, functionally-identified axons in any vertebrate cranial nerve (although one might not consider that to be a useful endeavor in any cranial nerve but VIII). And, in one phase of our studies, we actually got to the sub-nano level (thanks to the analysis available with our S100 bus computer): in single VIIIth-nerve acoustic axons we measured responses to mechanical vibrations with peak amplitudes below one-tenth of one nanometer (see Figures 5 and 7 in the reference at this link). This was another first.
The Colleagues involved in this mapping work included Ellen Leverenz (undergraduate physics graduate from MIT and doctoral student in Berkeley Biophysics, who worked with me on inner-ear acoustic sensors), Richard Baird (undergraduate EE graduate from MIT and doctoral student in Berkeley EECS, who worked on inner-ear otoconial position/motion sensors, e.g., utriculus and lagena, and with Ellen and me on acoustic sensors), Steve Myers (post-doc with a PhD in neuroanatomy from U. Michigan, who worked on inner-ear rotational motion sensors, e.g., semicircular canals and utriculus), Hironori Koyama (post-doc with a PhD in EE from the University of Tokyo who worked with Ellen and me on acoustic sensors), Kathryn Cortopassi (undergraduate EE graduate from Cal and doctoral student in Berkeley/UCSF Bioengineering who worked on acoustic and position/motion sensing in the lagena), Bob Capranica, Andrea Simmons and Gary Harned (Cornell neuroethologists who worked with Ellen and me on inner-ear acoustic sensors and taught us the art of closed-field stimulation), and Jean Caston (a visiting researcher from the University of Rouen, who worked on both motion and acoustic sensors of the inner ear).