Development of muscarinic receptors and regulation of secretory responsiveness in rodent sweat glands

Sweat glands are innervated by sympathetic neurons which undergo a change i n transmitter phenotype from noradrenergic to cholinergic during developmen t. As soon as the glands begin to differentiate, M3 muscarinic receptor mRN A and binding sites are detectable. Receptor expression appears in the abse nce of innervation and is maintained after denervation. While receptor expr ession is not responsiveness is. Muscarinic blockade during development or in adult animals results in the loss of responsiveness and its reappearance requires several days. Cholinergic muscarinic activation is most likely to regulate one or more steps in the signalling cascade that are downstream o f calcium mobilization. The anterograde regulation of sweat gland responsiv eness is one facet of the reciprocal interactions are required to establish a functional synapse in this system.