2 results
Dendritic development of retinal ganglion cells after prenatal intracranial infusion of tetrodotoxin
- Gregor Campbell, Ary S. Ramoa, Michael P. Stryker, Carla J. Shatz
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- Journal:
- Visual Neuroscience / Volume 14 / Issue 4 / July 1997
- Published online by Cambridge University Press:
- 02 June 2009, pp. 779-788
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The dendritic form of a cell may be established by many factors both intrinsic and environmental. Blockade of action potentials along the course of axons and in their postsynaptic targets dramatically alters the development of axonal morphology. The extent to which blockade of target cell activity retrogradely alters the dendritic morphology of the presynaptic cells is unknown. To determine whether the establishment of dendritic form by developing retinal canclion cells depends on activity within their targets, the sodium channel blocker, tetrodotoxin (TTX), was administered via minipumps to the diencephalon of cat fetuses from embryonic day 43 (E43) to E57. At E57 retinae were removed and living retinal ganglion cells injected in vitro with Lucifer yellow to reveal their dendritic morphology. In the TTX-treated animals both alpha and beta types of retinal ganglion cells were present, as were putative gamma cells. Overall, the dendrites of retinal ganglion cells in TTX-treated animals appeared qualitatively and Quantitatively similar to those of untreated animals. The only significant change in the TTX-treated cases was a small increase in the number of dendritic spines on the non-beta cells. These results indicate that the acquisition of basic dendritic form of developing ganglion cells is not influenced by the action potential activity within their targets, and that it is also independent of the terminal branching patterns of their axons.
The role of spontaneous retinal activity before eye opening in the maturation of form and function in the retinogeniculate pathway of the ferret
- P. MILTON COOK, GLEN PRUSKY, ARY S. RAMOA
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- Journal:
- Visual Neuroscience / Volume 16 / Issue 3 / May 1999
- Published online by Cambridge University Press:
- 01 May 1999, pp. 491-501
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During early mammalian development, inputs from the two retinas intermix within the lateral geniculate nucleus (LGN), then segregate during the first postnatal week into layers that receive input from a single retina. Functionally, the LGN also changes markedly during the first postnatal month; early geniculate responses to retinal input are mainly excitatory, then inhibitory circuits mature within the LGN. These remarkable changes in form and function of the retinogeniculate pathway occur at a time when patterned visual activity is not present, but retinal ganglion cells already manifest spontaneous action potential activity. To examine the role of early retinal activity in these critical developmental processes, we placed the slow release polymer Elvax embedded with tetrodotoxin (TTX) into the vitreous chamber of one or both eyes of neonatal ferrets. Animals receiving monocular injection of TTX had the other eye treated with Elvax containing control citrate buffer. Intraocular injection of horseradish peroxidase was made at the end of the period of TTX treatment to reveal the retinal terminals in the LGN. Chronic monocular or binocular blockade of retinal activity during the first postnatal week did not prevent eye-specific segregation, although it made the boundaries between layers less distinct. Retinal terminals ended preferentially in the appropriate layer, but a large number of terminals were also present in the inappropriate layer. Further segregation was achieved during the second postnatal week of activity blockade, when most retinal terminals ended preferentially in the appropriate geniculate layer and sharper layer boundaries were present. However, a small but significant number of terminals still extended into the inappropriate layer. Together, these findings indicate that monocular as well as binocular blockade of retinal activity resulted in some anomalous retinogeniculate projections and delayed eye-specific patterning, but segregation was largely intact at the end of the second postnatal week. We also report here that intraocular tetrodotoxin had a marked effect on the maturation of intrinsic geniculate circuits prior to eye opening. Whole-cell patch-clamp recordings in the LGN slice preparation revealed that activity blockade prevented the maturation of the slow, but not the fast, hyperpolarizing potential of LGN neurons during the first postnatal month and up to P38, the oldest age studied. In conclusion, these results indicate that spontaneous retinal activity modulates the time course of binocular segregation but does not alone account for the segregation of retinogeniculate terminals. However, early retinal activity plays an important role in developing the intrinsic circuitry of the LGN.