Abstract
The brain stem contains neural circuits that mediate vital functions. Many studies have addressed the development of brainstem neurons using molecular genetic and anatomical techniques. Studies of the development of functional connections have lagged behind, partly because of the anatomical complexity of the brain stem and because electrophysiological techniques for assessing neuronal activity are limited in the number of cells that can be recorded simultaneously. Here we use an optical recording technique to visualize activity in emerging vestibular and auditory circuits in the intact brain stem of the chicken embryo. Dissected brain stems at embryonic days 5-9 were labeled with a voltage-sensitive dye, NK2761. Vestibular or cochlear afferents were stimulated with suction electrodes, and a 1020-element photodiode array recorded membrane potential changes in large areas of the brain stem. Signals related to synaptic potentials in first- and second-order vestibular and cochlear nuclei, and in ocular motoneurons involved in vestibulo-oculomotor reflexes, were visualized at appropriate latencies representative of conduction and synaptic delays. Inhibitory and excitatory potentials could be discriminated by pharmacological blockade of GABA and glutamate receptors. Activation of specific neuron groups emerged in a developmental sequence that matched the anatomical development of vestibular and auditory projections. [Jpn J Physiol 54 Suppl:S153 (2004)]
