Fine structure of the neuro-insular complex type II in the cat.

Electron microscopy of a neuro-insular complex type II is described in the adult cat. A group of B-cells was recognized in the endoneurial space of a nerve provided with a continuous multi-layered perineurial sheath. The endocrine cells together with unmyelinated axons were enveloped by cytoplasmic processes of Schwann cells. A synaptic-like structure was occasionally noted on the surface of an endocrine cell. The neurotropism of endocrine cells (WATZKA, 1931) which leads to the formation of pancreatic neuro-insular complexes is compared with the neurotropism of Leydig cells and ovarial interstitial cells. It is suggested that such neuro-endocrine complexes generally communicate via vascular connections to the target organs or target tissues.