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J. Qu, K.L. Myhr; The Development of Intrinsic Excitability in Mouse Retinal Ganglion Cell Subtypes . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3114.
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© ARVO (1962-2015); The Authors (2016-present)
The development of intrinsic excitability in retinal ganglion cells (RGCs) is critical to their function as the spiking output neurons of the retina. The unique intrinsic excitabilities (input–output functions) of subtypes of neurons contribute to their distinct functions. The mechanisms that underlie the development of these subtype–specific properties are not known. To determine these mechanisms in developing RGCs, we need to first describe the differentiation of intrinsic excitability in the subtypes. Some subtype–dependent differences in developing mammalian RGCs have been observed. In mouse RGCs, intrinsic excitability increases from prenatal to early postnatal ages, but it has not been measured at later postnatal ages as subtypes become distinct. The mouse retina provides experimental advantages as a model system; thus it is important to determine the development of intrinsic excitability of developing mouse ganglion cell subtypes.
The electrical properties of developing mouse RGCs were recorded using standard whole–cell patch clamp recordings from acutely dissected intact mouse retinas. The morphology of each cell was determined by imaging the Lucifer Yellow that diffused from the electrode. RGCs from mice that were between postnatal days 4 (P4) and P22 were studied.
The youngest cells (P4–6) had the most depolarized resting potentials. With maturation, the resting potentials shifted to a more hyperpolarized level. In addition, there was a significant hyperpolarizing shift of the action potential threshold between P4–6 and the older groups (P8–14, P20–22). The discharge patterns generated by depolarizing current injection changed from predominantly a single spike (P4–6) to repetitive firing (P8–14, P20–22). This indicated higher excitability in more mature cells. The significant differences between the excitabilities of ON and OFF subtypes of RGCs shown in other mammals were not observed in our studies.
Intrinsic properties changed with development, favoring excitation with maturation, but differences between ON versus OFF subtypes were not seen. Future studies may reveal differences among additional morphological classes.
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