Developmental changes in the transmitter properties of sympathetic neuronsthat innervate the periosteum

During the development of sweat gland innervation, interactions with the ta rget tissue induce a change from noradrenergic to cholinergic and peptiderg ic properties. To determine whether the change in neurotransmitter properti es that occurs in the sweat gland innervation occurs more generally in symp athetic neurons, we identified a new target of cholinergic sympathetic neur ons in rat, the periosteum, which is the connective tissue covering of bone , and characterized the development of periosteal innervation of the sternu m. During development, sympathetic axons grow from thoracic sympathetic gan glia along rib periosteum to reach the sternum. All sympathetic axons displ ayed catecholaminergic properties when they reached the sternum, but these properties subsequently disappeared. Many axons lacked detectable immunorea ctivities for vesicular acetylcholine transporter and vasoactive intestinal peptide when they reached the sternum and acquired them after arrival. To determine whether periosteum could direct changes in the neurotransmitter p roperties of sympathetic neurons that innervate it, we transplanted periost eum to the hairy skin, a noradrenergic sympathetic target. We found that th e sympathetic innervation of the transplant underwent a noradrenergic to ch olinergic and peptidergic change. These results suggest that periosteum, in addition to sweat glands, regulates the neurotransmitter properties of the sympathetic neurons that innervate it.