RT Journal Article
SR Electronic
T1 Local Directional Cues Control Growth Polarity of Dopaminergic Axons Along the Rostrocaudal Axis
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 4112
OP 4119
DO 10.1523/JNEUROSCI.20-11-04112.2000
VO 20
IS 11
A1 Shin-ichiro Nakamura
A1 Yasuko Ito
A1 Ryuichi Shirasaki
A1 Fujio Murakami
YR 2000
UL http://www.jneurosci.org/content/20/11/4112.abstract
AB The vertebrate CNS is composed of a variety of longitudinal axonal tracts extending rostrally and caudally. Although recent studies have demonstrated that chemoattraction and chemorepulsion play key roles in axon guidance along the circumferential axis in the neural tube of the vertebrate, mechanisms of axonal elongation along the longitudinal axis, and most importantly, what determines rostrocaudal polarity of axonal growth, remains unknown. Here, we examined the mechanism that guides midbrain dopaminergic axons rostrally, using flat whole-mount preparations of embryonic rat brain both in vivo and in vitro.At embryonic day 11 (E11) and early stage E12, dopaminergic neurons in the ventral midbrain extended short axons dorsally. By middle stage E12, these axons had increased in number, some deflecting rostrally and others caudally. At E13, almost all axons showed rostrally oriented growth heading toward the forebrain targets. In in vitrowhole-mount preparations prepared from an E12 embryo and cultured for 24 hr, these axons showed rostrally oriented growth, but when they were forced to grow on substratum of reversed rostrocaudal polarity, they turned abruptly and grew following the polarity of the reversed midbrain substratum. These results suggest that local directional cues in the midbrain guide these axons rostrally and support the idea that substratum-associated polarized cues play an important role in axon guidance along the longitudinal axis.