We present single-ion-channel recordings performed with biomimetic lipid membranes which are directly attached to the surface of a complementary metal-oxide-semiconductor (CMOS) preamplifier chip. With this system we resolve single-channel currents from several types of bacterial ion channels, including fluctuations of a single alamethicin channel at a bandwidth of 1 MHz which represent the fastest single-ion-channel recordings reported to date. The platform is also used for high-resolution alpha-hemolysin nanopore recordings. These results illustrate the high signal fidelity, fine temporal resolution, small geometry, and multiplexed integration which can be achieved by leveraging integrated semiconductor platforms for advanced ion channel interfaces.

There are multiple populations of gonadotropin releasing hormone (GnRH) neurons that have distinct physiological and behavioral functions. Teleost fish have a population of GnRH3 neurons located in the terminal nerve (TN) associated with the olfactory bulb that is thought to play a neuromodulatory role in multiple physiological systems, including olfactory, visual, and reproductive. We used transgenic zebrafish in which the GnRH3 promoter drives expression of a green fluorescent protein to identify GnRH3 neurons during development in live embryos. Unlike with hypophysiotropic GnRH neurons of zebrafish, TN-GnRH3 neurons are of neural crest origin and are one of the first populations of GnRH neurons to develop in the early embryo. Using a combination of optical imaging and electrophysiology, we showed that during the first three days post-fertilization, TN-GnRH3 neurons increase in number, extend neural projections, move in association with tissue expansion, and acquire an adult-pattern of spontaneous action potential firing. Early during development, about half of the neurons were quiescent/non-firing. Later, at three days post-fertilization, there was an increase in the proportion of neurons showing action potential firing and an increase in the number of neurons that showed an adult-like tonic or beating pattern of action potential firing with a firing frequency similar to that seen in adult TN-GnRH3 neurons. This study represents the first neurophysiological investigation of developing GnRH neurons in live embryos -- an important advance in understanding their potential non-reproductive roles during embryogenesis.

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