Neurotrophin-4/5 promotes dendritic outgrowth and calcium currents in cultured mesencephalic dopamine neurons.
Ca(2+) currents and their modulation by neurotrophin-4/5 were studied in cultured mesencephalic neurons. Tyrosine hydroxylase-positive neurons consistently had larger somas than tyrosine hydroxylase-negative neurons. Neurons with larger somas were therefore targeted for recording. In both control and neurotrophin-4/5-treated cultured neurons, isolation of Ca(2+) currents in cultured mesencephalic neurons revealed prominent low- and high-voltage-activated currents. These currents were separable based upon their voltage dependence of activation, the response to replacement of Ca(2+) with Ba(2+) and the response to Ca(2+) channel blockers. Replacement of Ca(2+) with Ba(2+) resulted in a slight reduction of low-voltage-activated currents and a significant enhancement of high-voltage-activated currents. Cd(2+) blocked a larger fraction of the high-voltage-activated current than Ni(2+). The synthetic conotoxins SNX-124 and SNX-230 selectively blocked high-voltage-activated currents. Morphological analysis of mesencephalic cultures pretreated with neurotrophin-4/5 revealed an increase in soma size and dendritic length in tyrosine hydroxylase-positive neurons. In agreement with the neurotrophin-4/5 induction of growth, neurotrophin-4/5 also increased cell capacitance in whole-cell recordings. Neurotrophin-4/5 significantly enhanced both low- and high-voltage-activated currents, but normalization for changes in capacitance revealed only a significant increase in high-voltage-activated current density. This study demonstrates the existence of low-voltage-activated and multiple classes of high-voltage-activated calcium currents in cultured mesencephalic neurons. Morphological and physiological data demonstrate that the increases in calcium currents due to neurotrophin-4/5 pretreatment are associated with somatodendritic growth, but an increase in high-voltage-activated Ca(2+) channel expression also occurred.
Ethel Percy Andrus Gerontology Center, USC Program in Neuroscience, University of Southern California, Los Angeles, CA 90089-0191, USA.
R A
RA
DeFazio
K
K
Pong
B
B
Knusel
J P
JP
Walsh
D000818:Animals; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism; D002478:Cells, Cultured; D003712:Dendrites / Q000187:drug effects* / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism; D004622:Embryo, Mammalian; D005260:Female; D008297:Male; D008636:Mesencephalon; D009414:Nerve Growth Factors / Q000494:pharmacology*; D018696:Neuroprotective Agents / Q000494:pharmacology*; D011247:Pregnancy; D051381:Rats; D017207:Rats, Sprague-Dawley; D013378:Substantia Nigra / Q000187:drug effects* / Q000378:metabolism
D015220:Calcium Channels; D009414:Nerve Growth Factors; D018696:Neuroprotective Agents; C071951:neurotrophin 5; C073922:neurotrophin 4; D004298:Dopamine