LACK OF BIOCYTIN TRANSFER AT GAP-JUNCTIONS IN THE CHICKEN VESTIBULAR NUCLEI

In vivo experiments were designed to test for functional gap junctions at 'mixed' synapses that were morphologically characterized between t he large-diameter, primary vestibular fibers and second-order vestibul ar neurons in the chicken, Gallus gallus. In previous intracellular re cordings and dye injections into these neurons from brain slice prepar ations of chick embryos (E15/16) and also newborn hatchlings (H1-2), n o evidence was obtained for functional gap junctions. Therefore, biocy tin, a low molecular weight tracer that permeates gap junction channel s, was extracellularly applied to either the ampullary nerves or to th e vestibular ganglion of 3-6 day old hatchlings and adult chickens (9 months). This procedure resulted in the uptake of the dye and heavy st aining of both the thick and thin fibers composing the vestibular nerv e and in loading of vestibular efferent neurons. However, no dye trans fer was observed between the large-diameter, primary vestibular fibers and second-order vestibular neurons. This observation, which was perf ormed using a relatively non-invasive approach on intact animals, sugg ests that the gap junctions at these mixed synapses are probably not f unctional under the conditions of these experiments. (C) 1997 ISDN.