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The Journal of Neuroscience, November 15, 1999, 19(22):10004-10013
Target-Specific Factors Regulate the Formation of Glutamatergic Transmitter Release Sites in Cultured Neocortical Neurons
Ralf Mohrmann, Markus Werner, Hanns Hatt, and Kurt Gottmann Lehrstuhl für Zellphysiologie, Ruhr-Universität Bochum, D-44780 Bochum, Germany
Synapse formation in the mammalian CNS is thought to involve specific target recognition processes between presynaptic and postsynaptic neurons leading to the establishment of defined neuronal circuits. To study the role of target neuron-specific factors in synaptogenesis, we used cocultures of presynaptic explants and dissociated target neurons from rat neocortex, which enabled us to selectively vary the postsynaptic target neurons. Cocultures containing target neurons that were obtained early during development [embryonic day 16 (E16)] were compared to cocultures containing target neurons that were obtained at a later embryonic stage (E19).
Postsynaptic currents (PSCs) were evoked in target neurons by maximal extracellular stimulation in the presynaptic explant. The mean amplitudes of AMPA and NMDA receptor-mediated PSCs were sixfold reduced in E16 target neurons, whereas the mean amplitudes of GABAA receptor-mediated PSCs did not differ between E16 and E19 target neurons. This reduction was in part caused by an apparently twofold reduction in mean quantal amplitude, as shown by recording AMPA receptor-mediated miniature PSCs. In addition, a reduced number of glutamatergic release sites in E16 target neurons was revealed by synapsin I immunostaining of dendritic presynaptic terminals. No differences in mean release probability were observed between E16 and E19 target neurons.
Thus, the formation of glutamatergic transmitter release sites was strongly influenced by target neuron-specific factors. The formation of functional GABAergic synapses, however, was independent of the type of target neurons, suggesting specific retrograde signaling during the establishment of glutamatergic synapses.
Key words: synapse formation; target neurons; glutamatergic synapses; GABAergic synapses; AMPA receptors; NMDA receptors; neocortical neurons
Copyright © 1999 Society for Neuroscience 0270-6474/99/192210004-10$05.00/0
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