Bonness, Viola; (1999) The appearance of amino acid transmitters, their receptors and gap junctions in the developing chick retina. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

In the developing CNS the majority of neurons migrate to their final position, further differentiate and form synapses one with another. This highly orchestrated process requires intercellular communication from earliest times. This thesis investigates the appearance of amino acid transmitter release, the expression of amino acid transmitter receptors and gap junctional connections by ganglion cells in the embryonic chick retina. The release of the amino acid transmitters glutamate, aspartate, GABA and glycine from the retina was investigated using high performance liquid chromatography (HPLC). These experiments show the release of all four transmitters can be detected by HPLC from embryonic day four (E4) onwards, although in the case of GABA such release was only detectable when extracellular potassium was raised. The ratio of release under normal ionic conditions to that evoked by raising extracellular potassium increased towards synaptogenesis. High potassium evoked both Ca2+-dependent and Ca2+-independent release of transmitter. The developmental profile of the appearance of receptors for the four amino acid transmitters in ganglion cells was established in situ by whole-cell patch- clamping. The results show that ganglion cells respond to GABA and glycine at E6, while responses to AMPA and NMDA appear at E6 and E8, respectively. The time course of the development of gap junctional coupling between ganglion cells and other cells has been established using whole-cell patch- clamping as a means to introduce a mixture of gap junction permeant and impermeant dyes into their cytoplasm. Confocal microscopy of these preparations shows a general increase in the extent of coupling towards the time of synaptogenesis (~E12), which is followed by a marked decrease at E14. Throughout the period examined (E5-E14) some ganglion cells were coupled to cells that traverse the retina, which may represent neurons in the process of migration to their final destination.

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