The calcitonin gene-related peptide (CGRP) phenotype is expressed early and up-regulated by resiniferatoxin (RTX) in mouse sensory neurons.
Calcitonin gene-related peptide (CGRP) immunoreactivity was detected at day 2 in vitro (embryonic day 15) in developing mouse dorsal root ganglion (DRG) neurons in primary culture. During 2 weeks of culture the proportion of CGRP-immunoreactive (CGRP-IR) neurons remained around 65-70%, much higher than usually found in adult animals (45-50%). Treatment of cultures with the capsaicin analog resiniferatoxin (RTX; 0.3-30 nM) significantly augmented CGRP immunoreactivity per neuron at all ages investigated without increasing the number of CGRP-immunoreactive cells. The increased CGRP immunoreactivity was observed both in the axonal varicosities and in the perinuclear region of cell bodies. This RTX-induced increase in CGRP immunoreactivity was completely blocked by Ruthenium red (RR). Treatment with the non-esterified form of RTX (resiniferol 9, 13, 14 orthophenylacetate, ROPA) produced no increase. These results suggest that: (1) early expression of the CGRP phenotype is regulated in a cell-autonomous way in developing mouse DRG neurons in vitro; and (2) the RTX-induced increase in CGRP biosynthesis is most likely the result of activating the capsaicin/RTX receptor rather than directly activating the protein kinase C (PKC) pathway in vitro. The results may also reflect qualitative and quantitative differences in capsaicin/RTX sensitivity of sensory neurons between embryonal and adult ages.
Laboratory of Experimental Neuropathology, NINDS, NIH, Bethesda, MD 20892.
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Jakab
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Szallasi
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Agoston
D000818:Animals; D001369:Axons / Q000187:drug effects / Q000648:ultrastructure; D015740:Calcitonin Gene-Related Peptide / Q000096:biosynthesis* / Q000235:genetics; D002211:Capsaicin / Q000494:pharmacology; D004224:Diterpenes / Q000494:pharmacology*; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D051379:Mice; D009475:Neurons, Afferent / Q000187:drug effects / Q000378:metabolism*; D009498:Neurotoxins / Q000494:pharmacology*; D010641:Phenotype; D011493:Protein Kinase C / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects*
D004224:Diterpenes; D009498:Neurotoxins; C024353:resiniferatoxin; D011493:Protein Kinase C; D015740:Calcitonin Gene-Related Peptide; D013755:Tetradecanoylphorbol Acetate; D002211:Capsaicin