D. C. Rogers

Innervation and cytochemistry of the neuroepithelial bodies in the ciliated epithelium of the toad lung (Bufo marinus).

SummaryNeuroepithelial 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 fibres containing agranular vesicles which form reciprocal synapses; 2) about 20% are innervated solely by adrenergic nerve fibres which form 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 PCO2 and so leading to modulation of activity in afferent nerve fibres (type containing agranular vesicles). The presence of NEBs solely with an adrenergic (efferent) innervation poses a problem with this interpretation.

Fine structure of smooth muscle and neuromuscular junctions in the foot of Helix aspersa

SummaryThe smooth muscle cells in the foot of Helix aspersa are arranged in bundles which interweave to form a complex mesh. In the peripheral cytoplasm of the muscle cells there is a system of interconnected obliquely and longitudinally orientated tubules. The full extent of this system has not been determined; its possible function in relation to Ca++ storage and excitation-contraction coupling is discussed. Longitudinal tubules are present among the myofilaments and in association with mitochondria. Distributed throughout the myofilaments are elliptically shaped dense bodies, the fine structure of which resembles an accumulation of thin filaments. Located on the plasma membrane of the muscle cells are dense areas; the fine structure and relationships of these cellular elements resemble desmosomes. They may serve as attachment points for thin, cytoplasmic filaments (not necessarily myofilaments). The muscle cells are innervated by axons which diverge from a coarse, neural plexus (the sole plexus). The axons initially come into close contact with the muscle cells and then pass over their surfaces for up to 35 μ before being gradually enveloped by flange-like protrusions of the muscle cells. These axons contain either, (i) agranular vesicles (600 Å in diameter), (ii) agranular and very dense granular vesicles (1000 Å in diameter) or (iii) agranular and less dense, granular vesicles (1000 Å in diameter). The possible role of these inclusions as sites of excitatory and inhibitory transmitters is discussed.

Fine structure of smooth muscle and neuromuscular junctions in the optic tentacles of Helix aspersa and Limax flavus

SummaryThe smooth muscle cells studied contain a central core of thick and thin myofilaments surrounded by a peripheral layer of myofilament-free cytoplasm. Numerous vesicles, tubules, microfilaments, mitochondria and fine granules are present in the peripheral cytoplasm. Glycogen particles are distributed in large or small groups in both the peripheral cytoplasm and among the myofilaments. In contracted muscle cells the peripheral cytoplasm bulges out at regular intervals into the intercellular connective tissue. Numerous close contacts between single, usually naked, axons and these cytoplasmic protrusions occur. The axons at these contacts contain numerous small (500 Å in diameter) and large vesicles (800–1000 Å in diameter). Sometimes a number of axons simultaneously form close contacts with a muscle cell. These close contacts are considered to be the sites at which transmitter is released and acts on the muscle cell membrane.

Fine structure of the epineural connective tissue sheath of the subesophageal ganglion in Helix aspersa

SummaryThe epineural connective tissue sheath investing the subesophageal ganglion of Helix aspersa consists of a superficial region and a deeper region. The superficial region contains masses of globular cells intermingled with smooth muscle cells and nerve fibers all embedded in a connective tissue matrix. The histochemical and fine structural features of the globular cells show seasonal changes. During autumn to winter glycogen accumulates in their cytoplasm; this accumulation is accompanied by the appearance of dense, cytoplasmic globules which fuse together and ultimately form large pools of granular material. All the organelles and cytoplasm are displaced towards the cell periphery. Various cell-membrane invaginations containing dense material are prominent but there is no direct evidence to link these structures with the uptake of metabolites for glycogenesis. In winter there is a concentration of homogeneous, membrane-bound inclusions in the vicinity of the Golgi bodies. It is suggested that these inclusions constitute a lipid store. They decrease in number during summer. The globular cells do not bear any intimate relation to neurons and there is no reason to include these cells in the neuroglia. The muscle cells often weave around the globular cells but there is no direct contact. Nerve fibers innervate at least some of the muscle cells. The connective tissue consists of large and small diameter fibers suggesting that maturation of the fibrous components of the intercellular matrix is taking place in the superficial regions of the epineural sheath.

Changes in the physiology and fine structure of the taenia of the guinea‐pig caecum following transplantation into the anterior eye chamber

1. The taenia of the guinea‐pig caecum has been used as a model to study the re‐establishment of autonomic innervation following transplantation into the anterior eye chamber. The ultrastructure, the histochemical localization of noradrenaline and acetylcholinesterase and the pharmacology of transmission to the taenia have been examined 1 day to 16 weeks following transplantation. Both ganglion‐free strips of the taenia and caecal wall segments including the underlying Auerbachs plexus were used.

Fine structural and cytochemical study of the innervation of smooth muscle in an amphibian (Bufo marinus) lung before and after denervation

SummaryThe innervation of the toad (Bufo marinus) lung was studied with transmission electron microscopy and fluorescence techniques, both before and after 12 or 20 days close vagosympathetic denervation. Four cytologically distinct types of neuronal processes were recognised, in relation to the visceral muscles of the lung. These were described as cholinergic, adrenergic, nonadrenergic/non-cholinergic (NANC) and sensory on the basis of the characteristics of their vesicular content and cytochemical reactions. An apparent efferent innervation of visceral smooth muscle was achieved by NANC (50%), cholinergic (25%) and adrenergic (25%) fibres. A few sensory fibres were also present. After denervation only NANC fibres persisted, showing that the cell bodies of these fibres were intrapulmonary. The vascular smooth muscle was supplied by cholinergic, adrenergic and sensory fibres. In the walls of the proximal branches of the pulmonary artery were fibres containing large dense-cored vesicles. These profiles, which were associated with the vasa vasorum, were similar to neurosecretory fibres. After denervation all neural profiles associated with the vasculature had degenerated. The observations suggest that vagal vasodepressor effects in the toad lung are mediated indirectly through relaxation of visceral muscle strands which in their contracted state compress vascular channels.

The ultrastructural characteristics of the apical cell in the neuroepithelial bodies of the toad lung (Bufo marinus)

SummaryThe 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 serve 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.

Surface specializations of the epithelial cells at the tip of the optic tentacle, dorsal surface of the head and ventral surface of the foot in Helix aspersa

SummaryMorphologically the surface specializations of the epithelium covering the dorsal head and ventral foot regions in Helix aspersa consists either of cilia or microvilli respectively. The epithelium at the tip of the optic tentacle is a simple one. Each epithelial cell has a number of cilia-like projections from their free surfaces. These projections usually branch at their tips into two or three slender, microvilli-like structures. From the bases of the cilia-like projections arise numerous, tubular processes which form a thick, spongy layer interspersed between these projections. The microvilli-like structures are immersed in a fine, fibrous mat; unlike the fibrous mats on the dorsal head and ventral foot epithelia this material does not autofluoresce. It is suggested that it arises from the collar cells and not from typical mucocytes. The functional relationship between these surface specializations of the optic tentacle epithelium and the abundance of sensory axons in this region is discussed. These epithelial cell projections on the tentacle probably function not only as a protective covering but also to create a fluid trap for odours in the ambient air. The various contacts between epithelial cells serve to maintain the integrity of the epithelium while allowing for stretching due to protrusion of the tentacle.

The fine structure of the collar cells in the optic tentacles of Helix aspersa.

SummaryAt the base of the optic tentacular ganglion there is a group of large monopolar cells containing numerous secretory inclusions. These are the collar cells. Secretory material can be seen accumulating in swollen portions of the granular endoplasmic reticulum. It is postulated that this material is transported to the Golgi bodies and thus the limiting membrane of the inclusions is derived from the Golgi membranes. The Golgi bodies appear to be polarized and small vesicles resembling secretory inclusions are associated with one face of these organelles. The secretory inclusions fuse together to form large membrane-bound secretory pools in the perikaryon. The collar-cell processes are packed with secretory inclusions. These processes traverse the digital extensions of the tentacular ganglion and pass into the epithelium covering the tip of the tentacle. The secretory inclusions do not resemble neurosecretory inclusions in other situations. The collar cell processes receive a nerve supply from single axons containing granular and agranular vesicles. The evidence that these cells may be modified neurons is only minimal.

Cell contacts and smooth muscle bundle formation in tissue transplants into the anterior eye chamber

SummarySegments of the taenia coli from guinea-pig were transplanted into the anterior chamber of the eye. Depending on such factors as the total volume of the transplant and the presence or absence of ganglion cells degeneration was either very extensive (90% or more of the total number of muscle cells) or localized (alternating regions of degenerating and normal structure). During days 1–2 muscle cells lost their plasma membranes so that their cytoplasmic contents were dispersed into the intercellular spaces. Many cells produced numerous small processes which were pinched off and dispersed in a similar manner. Following a period of intense mitotic activity (3–8 days) numerous cells with the characteristics of embryonic smooth muscle cells were evident. Within 10–14 days these differentiating cells produced bulbous protrusions and assumed more irregular outlines than at 3–8 days. The protrusions formed close contacts (50–100Å intercellular space) and tight junctions between adjacent muscle cells. Aggregation of muscle cells into bundles was under way between 14–28 days. At approximately 4–6 weeks these developing muscle groups were invaded by nerve fiber bundles. The pattern of the innervation and the form and size of the muscle bundles simulated the normal. These findings are discussed in relation to the possible functions of the intercellular contacts and cellular protrusions which characterise various periods of regeneration.