Noradrenergic and peptidergic innervation of the extrinsic vessels and microcirculation of the rat cremaster muscle

The noradrenergic and peptidergic innervation of the extrinsic vessels and microcirculation of the rat cremaster muscle was examined. Catecholamine-containing nerves were identified histochemically by glyoxylic acid-induced fluorescence and tyrosine hydroxylase immunoreactivity (TH-IR). The extrinsic pudic-epigastric artery and vein as well as the entire intramuscular arteriolar network was innervated by noradrenergic axons. The capillaries and intramuscular venules of the cremaster muscle were devoid of a noradrenergic innervation. Immunohistochemical double-labeling demonstrated that most, if not all, of the TH-IR axons also possessed neuropeptide Y immunoreactivity (NPY-IR), implying colocalization of the norepinephrine and NPY in the perivascular nerves. No vasoactive intestinal peptide immunoreactivity (VIP-IR) was found, except for occasional VIP-IR axons associated with the pudic-epigastric artery. Substance P immunoreactive (SP-IR) axons formed a sparse plexus around the arteries and larger arterioles. Calcitonin generelated peptide immunoreactivity (CGRP-IR) had a similar distribution to the SP-IR axons. CGRP-IR was also observed in axons alongside some smaller arterioles and capillaries. The extrinsic vessels and intramuscular arteriolar network of the rat cremaster muscle are innervated by noradrenergic axons which contain NPY and by presumed sensory nerves containing SP and/or CGRP. Both types of nerves may contribute to regulation of microvascular function.