The role of firing patterns in neuronal development of sensory systems

The emergence of precise and orderly sets of neuronal connections often depends upon coordinated electrical activity during the early stages of development. In recent years, an increasing number of reports have shown that neurons of immature sensory systems can spontaneously generate electrical activity that occurs synchronously amongst adjacent cells. These patterns of correlated activity seem to be well suited to the role of providing the cues that are necessary for the activity-dependent refinement of the neural connections in the developing visual, auditory and somatosensory pathways

Changing Patterns of Spontaneous Bursting Activity of On and Off Retinal Ganglion Cells during Development

AbstractIn adult ferrets, retinal ganglion cells (RGCs) responsive to increased (On) or decreased (Off) illumination convey information to different cellular layers of the dorsal lateral geniculate nucleus (dLGN). These dLGN sublaminae emerge during development when RGCs are found to undergo correlated spontaneous bursting activity. Using Ca2+ imaging and intracellular dye-filling techniques, we demonstrate here that in ferret neonates, morphologically identified On and Off β RGCs have similar burst frequencies prior to the segregation of their inputs in the dLGN, but during the segregation period, they develop distinct burst frequencies. Although the bursts of On cells and Off cells occur synchronously, On cells burst only 25%–35% of the time that Off cells do. This change in the temporal bursting patterns of On and Off RGCs may underlie the segregation of their inputs on dLGN neurons

Early appearance and transient expression of putative amino acid neurotransmitters and related molecules in the developing rabbit retina: An immunocytochemical study

We have studied, by immunocytochemistry, the ontogeny of GABA, glycine, glutamate, glutamine, and taurine-containing cells in the rabbit retina. Amacrine cells show GABA immunoreactivity by embryonic day 25 (E25) and throughout postnatal life. By contrast, ganglion cells and horizontal cells are only transiently GABA-immunoreactive (-IR); few appear GABA-IR by the third postnatal week. At maturity, glycine is present in amacrine cells and in some bipolar cells. During development, putative ganglion cells transiently contained glycine between E25 and postnatal day 3 (P3), whereas immunolabelling in presumed amacrine cells and bipolar cells persists after birth. Ganglion cells, bipolar cells, photoreceptors, and some amacrine cells are glutamate-IR in the adult retina. Glutamate immunoreactivity first appears in the somata and processes of cytoblastic cells by E20 and is prominent by E25. Surprisingly, ganglion cells are not strongly glutamate-IR until just before eye-opening, at postnatal day 10 (P10), coincident with the appearance of glutamine in their somata and in Muller glial cells. Bipolar cells are glutamate-IR before they or Muller cells contain high levels of glutamine (at P10). Glutamate immunoreactivity in photoreceptors is progressively restricted to the inner segments by eye-opening. At no stage are presumed horizontal cells glutamate-IR or glutamine-IR, but some amacrine cells show glutamate- and glutamine-IR by P10. Taurine is localized to photoreceptors and Müller glial in the adult retina. Some cytoblasts are taurine-IR at E20; with ensuing development, taurine labelling becomes restricted primarily to Müller cells and photoreceptors; some putative bipolar cells may also be labelled. However, for a few days around birth, cells resembling horizontal cells, also show taurine immunoreactivity. The early appearance and often transient expression of these amino acids in retinal cells suggests that these neuroactive molecules may be involved in the structural and functional development of the retina