Observations of Nerve Terminals in Human Labial Salivary Glands

The existence of a motor innervation to the secretory and myoepithelial elements of salivary glands has been supported amply by physiological and pharmacological studies extending over a century (reviewed in Babkin, 1950 ; Emmelin, 1967) . However, the exact morphological nature of this innervation at the acinar level is less well established, and has been the subject of several conflicting reports . The earliest electron microscopic investigations of rodent salivary glands (Scott and Pease, 1959) demonstrated the presence of axons between parenchymal elements, deep to the basement membrane . These observations have been confirmed by Shackleford and Schneyer (1964) for the rodent salivary gland, by Ruskell (1968) for the monkey lacrimal gland, by Yamamoto (1966) for the guinea pig nasal gland, by Yamauchi and Burnstock (1967) for the sheep lacrimal gland, and by Watari (1968) for the exocrine pancreas of several different vertebrates . Tandler (1965) has illustrated a direct contact between an axon and a myoepithelial cell in the human submandibular gland . All of these studies have shown that a space of 200-250 A exists between the neural membrane and the effector cell membrane when they are in a "direct" contact (Grillo, 1966) . On the other hand, "indirect" contacts, with a space of 0 .1 .s or more between the neural element and the acinar element, together with the interposition of basement membrane, have been described in the salivary glands of dogs (Fujita et al ., 1964), cats (Garrett, 1966), rats (Tamarin, 1966), and man (Garrett, 1967) . The present report describes the appearance of several intra-acinar axons and axonal varicosities in human labial salivary glands and thus supports the concept of a direct-contact innervation of the secretory and contractile elements of these glands .