CALCITONIN-GENE-RELATED PEPTIDE (CGRP) IN THE DEVELOPING MOUSE LIMB

The mitogenic effects of neuropeptides and their localization to devel oping tissues suggest an important role for these peptides during gest ation. We examined the expression and action of the neuropeptide calci tonin gene-related peptide (CGRP) in the developing mouse limb bud, an excellent model system for studying musculoskeletal development. CGRP immunoreactivity (CGRP-ir) was first detected in the developing limb at day 16.5 of gestation (E 16.5) and was limited to nerve fibers surr ounding blood vessels, within the developing muscle or in close proxim ity to the developing cartilaginous skeleton. Although CGRP-ir was not observed until E 16.5, limb buds were responsive to CGRP as early as E 11.5. Within 5 min of exposure to CGRP (10(-8) to 10(-7) M) a 2-3-fo ld increase in cyclic AMP (cAMP) levels was observed. This CGRP-induce d increase in cAMP was abolished by the addition of human CGRP(8-37), a CGRP receptor antagonist. This result suggests that the effect on cA MP was mediated by the interaction of CGRP with CORP receptors. Our fi ndings indicate that mouse limbs are responsive to CGRP when they are composed of primarily undifferentiated mesenchyme and that CGRP-ir app ears at a later stage of development in association with cartilage and muscle differentiation.