Neurotrophins, but not depolarization, regulate substance P expression in the developing optic tectum.
Neurotransmitter expression can be regulated by both activity and neurotrophins in a number of in vitro systems. We examined whether either of these factors was likely to play a role in the in vivo optic nerve-dependent regulation of a substance P-like immunoreactive (SP-ir) population of cells in the developing optic tectum of the frog. In contrast to our previous results with the adult system, blocking tectal cell responses to glutamate release by retinal ganglion cells with 6-cyano-7-nitroquinoxaline-2,3 dione (CNQX) did not affect the percent of SP-ir cells in the developing tectum. Treatment with d-(-)-2-amino-5-phosphonovaleric acid (d-AP-5) was also ineffective in this regard, although both it and CNQX treatment disrupted visual map topography. Chronic treatment with brain-derived neurotrophic factor (BDNF) and neurotrophin-4/5 (NT-4/5) produced increases in SP-ir cells in the treated lobes of normal animals, which were significant in the case of NT-4/5. Both substances also prevented the decrease of SP cells that would otherwise occur in the deafferented lobe of unilaterally optic nerve-transected tadpoles. These changes in the percent of SP-ir cells occurred without any detectable changes in the overall number of tectal cells. NGF had no effect on SP expression. Nor did it affect topographic map formation, which was disrupted by treatment with either BDNF or NT-4/5. Our results demonstrate that different mechanisms regulate SP expression in the developing and adult tectum. They indicate that neurotrophin levels in the developing optic tectum may selectively regulate a specific neuropeptide-expressing population of cells.
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School of Biological Sciences, University of Kentucky, Lexington, Kentucky 40506, USA.
Debski
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D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D001931:Brain Mapping; D019208:Brain-Derived Neurotrophic Factor / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005260:Female; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009414:Nerve Growth Factors / Q000494:pharmacology*; D009473:Neuronal Plasticity / Q000187:drug effects / Q000502:physiology; D018696:Neuroprotective Agents / Q000494:pharmacology; D011894:Rana pipiens; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology; D012165:Retinal Ganglion Cells / Q000187:drug effects / Q000378:metabolism; D013373:Substance P / Q000032:analysis / Q000096:biosynthesis*; D013477:Superior Colliculi / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism*; D014795:Visual Pathways / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism
D019208:Brain-Derived Neurotrophic Factor; D018691:Excitatory Amino Acid Antagonists; D009414:Nerve Growth Factors; D018696:Neuroprotective Agents; D016194:Receptors, N-Methyl-D-Aspartate; C071951:neurotrophin 5; D013373:Substance P; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate; C073922:neurotrophin 4