release of vasoactive intestinal peptide increased significantly by 91 % during descending relaxation only , whereas release of both substance p and substance k increased significantly by 107 % during ascending contraction only , supporting the participation of vasoactive intestinal peptide motor neurons in descending relaxation and tachykinin motor neurons as well as cholinergic motor neurons in ascending contraction .
C0038585
substance p
C0039241
tachykinin