Adrenergic innervation in the microcirculation of the bat wing

The distribution of adrenergic nerves to the microcirculation of the wing web of the bat was studied in whole-mount preparations employing glyoxylic acid fluorescence histochemistry. A dense perivascular adrenergic nerve plexus consisting of various-sized nerve bundles surrounded the arteries. The accompanying veins were sparsely innervated by small nerve bundles or single axons. Arterioles also possessed a dense perivascular plexus comprised of a loose network of small axon bundles. Muscular venules accompanying most arterioles were supplied by a small number of varicose axons which surrounded these vessels in a loose network. The majority of the terminal arterioles were devoid of any direct innervation. The proximal segment of some terminal arterioles was innervated by one or two axons which were observed to diverge from the vessels and terminate in the tissue. The true capillaries, postcapillary venules, and lymphatics possessed no direct adrenergic innervation. Surgical sectioning of the appropriate nerve trunks or administration of 6-hydroxydopamine caused complete disappearance of all fluorescent adrenergic axons in the wing web. Faint acetylcholinesterase-positive staining was observed in a perivascular plexus surrounding the arteries and arterioles. A much diminished acetylcholinesterase activity was observed after treatment with 6-hydroxydopamine which implies that this enzymatic activity resides in the adrenergic nerves.