Neuroepithelial bodies (NEB) were identified in the lung of Bufo marinus. The characteristics of the cells and their innervation were studied with electron and fluorescence microscopy before and after close vagosympathetic denervation. The bodies consist of low columnar cells which rest on the epithelial basal lamina. The majority of the cells do not reach the lumen of the lung (basal cells); the few which do (apical cells) are bordered by microvilli and possess a single cilium. The neuroepithelial cell cytoplasm contains a variety of organelles the most characteristic of which are dense cored vesicles. Microspectrofluorometry and electron microscopic cytochemistry indicate significant quantities of 5-hydroxytryptamine in these cells. The neuroepithelial bodies could be divided into three groups on the basis of their innervation: 1) About 60% of the NEBs are innervated solely by nerve fibers containing agranular vesicles which form reciprocal synapses; 2) about 20% are innervated solely by adrenergic nerve fibres which from distinct synaptic contacts; and 3) the remaining 20% are innervated by both types of nerve fibres. It is proposed that the NEBs are receptors monitoring intrapulmonary P CO2 and so leading to modulation of activity in afferent nerve fibres (type containing a granular vesicles). The presence of NEBs soley with an adrenergic (efferent) innervation poses a problem with this interpretation.

An electrophysiological and anatomical study of the guinea pig taenia coli is reported. Changing the membrane potential of single cells cannot modulate the ratc of firing action potentials but does reveal electrical coupling between the cells during propagation. The amplitude of the junction potentials which occur during transmission from inhibitory nerves is unaffected in many cells during alteration of the membranc potential, indicating electrical coupling during transmission. The tacnia coli is shown to consist of smooth muscle bundles which anastomose. There are tight junctions between the cells in the bundles, and these probably provide the pathway for the electrical coupling. The smooth muscle cells towards the serosal surface of the taenia coli are shown electrophysiologically to have an extensive intramural inhibitory innervation, but a sparse sympathetic inhibitory and chotinergic excitatory innervation. These results are in accordance with the distribution of these nerves as determined histochemically. As single axons are only rarely observed in the taenia coli, it is suggested that the only muscle cells which undergo permeability changes during transmission are those adjacent to varicosities in the nerve bundles. The remaining muscle cells then undergo potential changes during transmission because of electrical coupling through the tight junctions.

1. The autonomic interstitial cells have been studied in the toad small and large intestine and guinea‐pig taenia coli by means of both the light and electron microscopes. The guinea‐pig superior cervical ganglion has also been examined. 2. Apart from muscle cells, neurons and Schwann cells, at least one other cell type has been observed. These cells have been designated connective tissue cells on the basis of their gross form, fine structure and relation to other cells. In many respects they resemble fibroblasts and macrophages. 3. These cells are in close relation to nerve fiber bundles and smooth muscle cells. They often form a complete sheath around bundles of axons and Schwann cells. Many of the processes of the connective tissue cells lie in grooves on the surface of the muscle cells; the distance between apposing cell membranes is about 200 Ä. 4. The processes of the connective tissue cells often interdigitate with each other in a most complex manner, the opposing cell membranes being about 200 Ä apart. Such a close relationship would appear with the light microscope to be a fusion forming a syncytium. 5. Observation with the light microscope on the terminal ramifications of the autonomic nervous system where small bundles of fine axons are enclosed by connective tissue cells could give rise to the impression that they contained “neurofibrils.” 6. It is suggested that the term autonomic interstitial cell covers a number of cell types which have been confused. The cells designated connective tissue cells along with Schwann cells have between them the characteristics of the autonomic interstitial cells as described by previous workers. Cajal's original description of sympathetic interstitial cells was actually a description of connective tissue cells.

No abstract

The cytological features and membrane specialisations of neuroepithelial cells (apical cells) in direct contact with the lumen of the lung were studied with transmission and scanning electron microscopy. The luminal surface of the apical cell is characterised by microvilli, a cilium with an 8 + 1 microtubular pattern and numerous coated vesicles. The cytoplasmic region immediately beneath the luminal plasma membrane contains numerous smooth-walled vesicles, tubules and microtubules, a few microfilaments and dense granules (15-20 nm in diameter). The luminal pole of the cell is marked off from the basal or vascular pole by a well-defined terminal web associated with junctional complexes. Protrusion of the luminal pole occurs as a transient phenomenon and is accompanied by a pinching in of the cell at the terminal web. It is proposed that the distinctive features of the luminal pole of the apical cell are comparable to those of recognised chemoreceptor cells. It is also proposed that in view of the common features of apical and basal cells the apical cell functions as a receptor/transducer and the basal cells served as an accessory source of peptides/5-hydroxytryptamine to be released on stimulation of the apical cell. Furthermore, we have drawn attention to the structural heterogeneity of the neuroepithelial bodies in various vertebrate classes.