William E. Renehan

The development of meissner corpuscles in primate digital skin

Digital skin from fetal and neonatal primates was examined using light and electron microscopic techniques to document the development of the Meissner corpuscle. Generation of the receptor was initiated early in the third trimester by fine neurites which left the superficial dermal nerve plexus, ascended the dermal papillae and entered the basal epidermis. As maturation of the Meissner corpuscle continued, the axons were confined to the apex of the dermal papilla, where they were oriented parallel to the surface to the surface of the skin and terminated among cytoplasmic extensions of presumptive lamellar cells. During late fetal life the complexity of the lamellar cell stacking increased and the lamellar cell bodies were found solely at the base of the receptor. Numerous axon terminals were evident between the cytoplasmic lamellae. The appearance of the neonatal Meissner corpuscle was indistinguishable from that of the adult, indicating that the complete cycle of development is concluded before birth.

The target specificity of the extrinsic innervation of the rat small intestine.

The target specificity of the extrinsic innervation of the rat small intestine was examined by simultaneously injecting the proximal and distal small intestine with either wheat germ agglutinin-horseradish peroxidase (HRP) or fast blue. The number of single- and double-labeled cells in the nodose, dorsal root and coeliac-superior mesenteric ganglia and the dorsal motor nucleus of the vagus were counted and expressed as percentages of total labeled cells. Cells containing both HRP and Fast blue projected to both regions of the intestine. We found that the nodose and mesenteric ganglia contained significantly fewer double-labeled neurons (approximately 3 and 9% respectively) than the dorsal motor nucleus (19%) or dorsal root ganglion (20%). Presumably, a large number of double-labeled afferent or efferent neurons would limit the ability of a given component of the extrinsic innervation to control the activity of restricted regions of the small intestine (but might be important in overall regulation of intestinal function). In a separate series of experiments we examined the topography of neurons in the dorsal motor nucleus of the vagus labeled with HRP injection into either the proximal or distal small intestine. Both of these injections labeled neurons in the entire rostro-caudal extent of the nucleus, though approximately 75% of the cells were located between 720 microns caudal and 720 microns rostral to the obex. Cells in the rostral regions were found primarily in the lateral pole of the nucleus, whereas caudal regions contained labeled cells in both the medial and lateral poles.

Numbers of Axons Innervating Mystacial Vibrissa Follicles in Newborn and Adult Rats

Electron-microscopic techniques were used to determine the numbers of axons in the deep vibrissal nerves innervating the C1 and C4 follicles in newborn and adult rats. All counts were made from thin sections taken after the nerve had entered the follicle capsule (FC). In newborn animals, the nerves supplying the C1 (n = 10) and C4 (n = 10) follicles contained an average (means +/- standard deviation) of 355.0 +/- 40.0 and 233.9 +/- 19.2 axons, respectively. In the adult animals (n = 10 for C1 and n = 9 for C4), the respective values were 314.4 +/- 26.2 and 233.3 +/- 34.4 axons. There were no significant differences between the values for the counts from the neonates and adults for either follicle (p greater than 0.01, independent t tests). In the vibrissal nerves of neonates, both degenerating axons and occasional growth cones were visible. Such profiles were not observed in the nerves taken from adults.

An electron microscopic analysis of the morphology and connectivity of individual HRP-labeled slowly adapting vibrissa primary afferents in the adult rat

The ultrastructure of 4 slowly adapting vibrissa primary afferent central terminal arbors was examined following intracellular injection of horseradish peroxidase (HRP). The terminals were found to contain clear round vesicles and formed primarily asymmetric synapses on dendritic shafts and spines. Few examples of synaptic glomeruli, with the labeled axon as the central element, were identified.

Restoration of orbicularis oculi function by contralateral orbicularis oculi innervated muscle flap vs neuromuscular pedicle technique

In preliminary experiments with dogs and cats, unilateral paralysis of the orbicularis oculi muscle group was produced by a section of the seventh nerve that included the posterior auricular branch. Either one of two procedures was then employed in attempts to reinnervate the paralyzed eyelid. In one group of animals, a neuromuscular pedicle was employed and in another, a contralateral orbicularis innervated muscle flap was used. Both methods restored synchronous, reflex blinking to the denervated eyelid. Of the two procedures, neurotization appears to offer the greater promise because the use of a neuromuscular pedicle requires an expendable nerve that is functional, and no such suitable substitute is available in humans.