Nd

Development of excitability in presynaptic motor neurons required synaptic activation of the postsynaptic muscle cells. The data suggested that muscle released a retrograde factor, perhaps NT-3.

During development, no changes in peak density or kinetics of ICa were noted. INa showed a twofold increase in its density with subtle changes in kinetics. In contrast, /Kv increased threefold in density and displayed changes in kinetic properties.

During this early developmental period, most outer hair cells expressed sodium current, in contrast to the situation in the adult.

During late embryonic and early postnatal periods, /Na density was upregulated in cortical plate neurons. IK density showed subtle changes. The AP acquired a larger amplitude, shorter duration, and more negative value of threshold.

Sodium current was developmentally upregulated. Morpholino antisense knockdown indicated that Nav1.1 and channels were more prevalent at early and late stages, respec-tively. Action potentials acquired larger overshoots and briefer dura-tions as both sodium and potassium currents increased in density.

A critical period for the maturation of the delayed rectifier current required mRNA synthesis during a 9 h critical period. After transcriptional blockade, A-current development recovered but delayed rectified current did not.

Maturation of A-current extended to times later than that for other voltage-dependent currents.

Extensive upregulation of /K current density occurred with changes in activation kinetics.

Changes in sodium channel mRNA and protein levels were followed, beginning during embryonic development. Although there were dramatic increases in sodium channel mRNA levels postnatally, the increase did not fully account for protein levels, suggesting other levels of regulation (translational or post-translational). Increased gene transcription and channel mRNA. Kinetic analysis suggests a requirement for a developmentally regulated translational or post-translational step in brain sodium channel expression.

Xenopus embryo spinal motor neurons in vitro

Xenopus spinal neurons in vitro

Xenopus spinal neurons, in vitro

Xenopus spinal neurons, in vitro

Xenopus embryonic myocytes, in vitro

Rat forebrain, E16-adult

Nick and Ribera (2000)

Rat outer hair cells, P0-11

Mouse cerebral cortex -intermediate zone and cortical plate, E14-P17

Zebra fish Rohon-Beard neurons, 16-48 h postfertilization

Oliver et al. (1997)

Picken-Bahrey and Moody (2003)

Ribera and Nusslein-Volhard (1998); Pineda et al. (2005)

Ribera and Spitzer (1989)

Ribera and Spitzer

(1990) Ribera and

Spitzer

(1991) Scheinman etal. (1989)

Table 2 (Continued)

VGIC type VGIC molecular identity Regulation Neuron type References

Sodium ND During development, /Na increased in Cat retinal ganglion cells, Skaliora etal.

density and displayed kinetic E30-E55 (1993)

changes. These developmental changes were largely restricted to the period of axon ingrowth (E30-38).

Calcium LVA and HVA The density of LVA Ca2+ currents Rat visual cortical Tarasenko decreased during early stages of neurons, P2-12 et al. (1998)

postnatal development, while the density of HVA increased.

HVA, high-voltage-activated; LVA, low-voltage-activated; ND, not determined; E, embryonic; P, postnatal.

b4-2

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