The neurohistology of quiescent mammary tissue in Lepus albus

The neurohistology of quiescent mammary tissue from adult female albino rabbits was investigated by cholinesterase histochemistry. Dense plexuses of nerve fibers enter the nipple in the dermis surrounding the lactiferous ducts, and unite at the summit of the nipple to form an apical plexus. From the plexuses at the base of the nipple nerves pass between deep epidermal invaginations, to form a basal nipple sub‐epidermal plexus, A sub‐epidermal plexus of fibers of small diameter arises from the apical dermal plexus. At the base of the nipple extensive nerve plexuses occur around smooth muscle. The only endings are intraepidermal nerve terminals from the apical sub‐epidermal plexus. In mammary skin outside the nipple area the dermal and sub‐epidermal plexuses are more attenuated. Longitudinally or circularly arranged nerves occur around hair follicles. Peri‐arterial plexuses are present throughout the mammary tissue. The myo‐epithelial cells and alveoli are not innervated. The neurohistological pattern suggests a spatio‐temporal sensory innervation concerned in neurohormonal reflexes of milk secretion and ejection, and neural reflexes of nipple erection. Autonomic motor innervation regulates blood flow and promotes nipple erection. The absence of myo‐epithelial cell and alveolar innervation indicates a solely endocrine effector regulation of milk ejection and secretion.