Some observations on the fine structure of the sympathetic ganglion of the toad, Bufo vulgaris japonicus

Synaptic organization of amphibian sympathetic ganglia

The synaptic organization of the amphibian sympathetic ganglia was studied, especially in the last two abdominal paravertebral ganglia of the frog. These ganglia appear to form a monosynaptic relay, not containing interneurons. They consist of two systems working in parallel: the principal neurons, by far the most numerous, and a small number of chromaffin (i.e., SIF) cells, usually arranged in clusters. Each principal neuron is innervated by a preganglionic branch forming a set of cholinergic synapses which exhibit classical ultrastructure. The only peculiarity is the presence of a subsynaptic apparatus in a variable percentage of synaptic complexes. Electrophysiological studies have demonstrated that synaptic transmission is due to ACh release and involves several postsynaptic potentials. Moreover, the principal neurons are of two types, B and C, whose preganglionic axons and their own axons have different conduction velocities. C neurons tend to be small in diameter, and B neurons are larger, but the size distribution of the two populations overlaps. More recently, it was demonstrated that these two neuronal systems have different immunocytochemical features. The C preganglionic fibers contain an LHRH-like peptide, which is responsible for late synaptic events. The B preganglionic fibers contain CGRP, whose role has not yet been established. The principal neurons all contain adrenaline, but neuropeptide Y is also present in C neurons and could be a second transmitter at peripheral junctions. SP-containing fibers also pass through the ganglia, but give rise to intraganglionic synapses only rarely, except in the celiac plexus. Galanin can coexist with neuropeptide Y in certain C neurons. Numerous principal neurons are immunoreactive for VIP. Chromaffin cells contain noradrenaline and metenkephalin, and some contain SP or LHRH; they are endocrine cells controlled by preganglionic fibers and can have a modulatory effect on principal neurons endowed with appropriate receptors. The accessibility of frog abdominal ganglia and the anatomical separation of B and C preganglionic fiber pathways provide interesting systems in which to carry out experimentation on the stability and specificity of synaptic contacts. After postganglionic axotomy, the majority of synapses disappear by disruption of synaptic contacts. There is a certain discrepancy between the recovery of synaptic transmission and the reappearance of morphologically identifiable synapses, suggesting that a certain amount of transmission is possible at contacts devoid of synaptic complexes. The selective deafferentation of B or C neurons showed that the subsynaptic apparati are mainly found at B neuron synapses. The course of reinnervation following selective deafferentation reveals the existence of different specificities at B and C synapses: C neurons are easily reinnervated by B preganglionic fibers, whereas C fibers appear fairly ineffective at reinnervating B neurons, even after a long interval. Attempts were made to reinnervate ganglionic neurons with somatic motor nerve fibers. Reinnervation was achieved only rarely, and it is concluded that the ganglionic synapses in the frog have a higher specificity and lower plasticity than in mammals.

Immunoelectron microscopy on the localization of endothelin in the umbilical vein of perinatal rabbits

Immunoelectron microscopic localization of endothelin (ET) using the mouse monoclonal anti-ET sera was performed on the pre- and postnatal rabbit umbilical vein during stages when Weibel-Palade (WP) bodies increase in number in the endothelial cells. The immunoreactions are localized in the rough endoplasmic reticulum, Golgi cisterns, and WP bodies that are actively segregated from the Golgi apparatus. After degranulation and extracellular release of WP bodies was induced by compound 48/80, heavy immunoreactions were seen in both vascular lumen and cytoplasm near the degranulated WP bodies. These results indicate that ET is stored in WP bodies after segregation from the Golgi apparatus and released from the endothelial cells concomitantly with other components of these granules by exocytosis. Because the immunoreactions are also seen in pinocytotic vesicles that are occasionally in contact with WP bodies, it seems likely that WP bodies are also involved in the uptake and storage of ET from blood plasma.

Vasocontractions of the in-vitro toad aortas induced by endothelin-1 and sarafotoxin-S6b

Dose-dependent tension curves were recorded from the in vitro toad aortas by administration of endothelin-1 and sarafotoxin-S6b. The maximal contractile tensions by both drugs were evoked at a 10(-8) M concentration. By a single dose application (10(-8) M) of endothelin-1 and sarafotoxin-S6b to both endothelium-preserved and denuded vessels, the induction of the endothelium-dependent vasocontraction occurs after 2 min of administration. Ultrastructural changes of Weibel-Palade bodies such as decrease in electron density, swelling with a wide peripheral halo, and expulsion of their contents in a manner of exocytosis become evident within 2 min after administration of these drugs. These findings indicate that some vasocontractile substances in Weibel-Palade bodies are extracellularly discharged by endothelin-1 and sarafotoxin-S6b.

Melanin storing cells in anuran gut

1. The location, distribution and morphological characteristics of the pigment cells found in the frog gut are described. 2. The pigment cells show long and large protoplasmic projections. At the ultrastructural level, the nucleus is elongated with prominent nucleolus and dense marginal chromatin. The cytoplasm is full with pigment granules (2500-7500 A) and typical premelanosome structures have been observed. 3. The pigment cells number is higher in the esophagus and large intestine than in the stomach or small intestine and the pigment cells are always located in close contact with blood vessels and nervous structures (ganglia and fibres). 4. We have observed that the pigment content depends upon seasonal variations, increasing during the cold months. 5. We have demonstrated by histological methods that the cells pigment content is melanin. 6. According to their morphological and tinctorial characteristics the anuran gut melanin storing cells are similar to the skin epidermal melanocytes.

Degranulation of endothelial specific granules of the toad aorta after treatment with compound 48/80

Incubation of isolated toad aortas in Ringer solution containing compound 48/80, a histamine liberator, resulted in marked degranulation of endothelial specific granules. Since incubation of these vessels in Ringer solution only did not show significant morphologic changes in these granules, these findings suggest that the degranulation was induced by histamine release from the granules, as in the case for mast cell degranulation, and that endothelial specific granules are a storage site of histamine in the toad aorta. The present morphologic data were supported by preliminary chromatography, which showed appreciable concentrations of histamine in the granule-containing pellets of subcellular fractions of homogenized toad aortas.

The structure of the coeliac ganglion of a teleost fish Myoxocephalus scorpius

In order to compare the structure of a teleost sympathetic ganglion with those of other vertebrates, light, fluorescence histochemical and electron microscopy were carried out on the coeliac ganglion of the scorpion fish, Myoxocephalus scorpius. In common with studies on other vertebrates, fluorescence h istochemistry distinguished two cell types: a) principal neurones which exhibited low levels of specific catecholamine fluorescence and comprise the majority of neurones in the ganglia, and b) smaller intensely fluorescent cells, some of which had processes tens of micrometers long. With the electron microscope, the principal cells were seen to make axodendritic and axosomatic synapses with axons containing mainly 30 nm agranular vesicles at the synaptic site while in other vertebrates usually only one or other synaptic association is present. Both the somata and the processes of intensely fluorescent cells contain 300-600 nm diameter vesicles many of which have electron dense cores. These cells are also innervated by axons containing 30 nm agranular vesicles.

The innervation and fine structure of paraneuronic cells in an amphibian pulmonary artery

The pulmonary artery of Bufo marinus contains large numbers of bipolar cells situated in the tunica adventitia and in the outer layers of the media. These cells show a bright green-yellow fluorescence (emission spectra 485 nm) after formaldehyde pre-treatment suggesting that they contain a primary monoamine. The most characteristic fine-structural feature of these cells is the presence of numerous dense-cored vesicles (80--300 nm diameter) in their cytopalsm. The cells are in close contact (20 nm gap) with both agranular and granular nerve fibres. Both EM-cytochemical and formaldehyde-induced fluorescence tests indicate that the granule-containing nerve fibres are adrenergic. The agranular nerve fibres form discrete synaptic contacts with pre and post-synaptic membrane thickenings on the cells. This was never observed with respect to the adrenergic fibres. Each process of the cells is about 45 micrometer long. The processes do not bear any special relationship to either vessels of the arterial vasa vasorum or medial smooth muscle cells. Their location in the wall of the artery suggests that they are functionally significant with respect to activity of the arterial media.

Postsynaptic specializations at excitatory and inhibitory cholinergic synapses

In serial sections of neurons in the paravertebral ganglia of the frog (Limmodynastes dumerili), the postsynaptic structures termed 'postsynaptic bar' (PSB) and 'junctional subsurface organ' (JSO) were never observed in the same ganglion cell. Further, PSBs were found mostly in small ganglion cells (less than 22 micrometer), while JSOs were found mostly in large ganglion cells (up to 45 micrometer). Between 10 and 22 PSBs were located at both 'spine' and 'non-spinous' somatic synapses of the smaller ganglion cells; while 8 to 16 JSOs were located largely in the axon hillock region of the larger ganglion cells. Based on these observations, it is suggested that the two ganglion cell populations represent the B and C cell types defined according to electrophysiological data. Further, since the nerve terminals adjacent to both these postsynaptic structures appear to be cholinergic according to their vesicular content, this provides some basis for suggesting that JSOs are associated with slow excitatory synapses, while PSBs are present at slow inhibitory synapses.

Identification of small intensely fluorescent (SIF) cells as chromaffin cells in bullfrog sympathetic ganglia

Small intensely fluoresent (SIF) cells were investigated in the ninth and tenth paravertebral sympathetic ganglia of the bullfrog using histochemical and electron microscopic techniques. Fluorescence histochemistry revealed that clusters of SIF cells are sparsely distributed in the ninth and tenth ganglia; the clusters were usually located in the vicinity of blood vessels. Fluorescent processes were not observed emanating from SIF cells. The clusters stained positively for the chromaffin reaction indicating that SIF cells are chromaffin cells. Ultrastructurally, the SIF-chromaffin cells in the sympathetic ganglia appeared virtually identical to the chromaffin cells in the adrenal gland; this includes two cell types that appear morphologically the same as the epinephrine and norepinephrine containing chromaffin cells in the adrenal gland. Efferent synapses from the SIF-chromaffin cells in sympathetic ganglia to sympathetic ganglia to sympathetic neurons were not observed. The SIF-chromaffin cells in bullfrog sympathetic ganglia did not have the morphological characteristics of interneurons; it is suggested that they may function as extra-adrenal chromaffin tissue.

Synaptic innervation of sympathetic ganglion cells in the bullfrog

The synaptic innervation of the ganglion cells in the ninth and tenth paravertebral sympathetic ganglia of the bullfrog was investigated by histochemical and electron microscopic techniques and by intracellular recording. The neurons were unipolar and most ganglion cells were innervated by a single preganglionic axon. The preganglionic fiber stained for acetylcholinesterase and was observed to spiral around the axon hillock of the ganglion cell before arborizing and making synaptic contact with the neuron. Most synapses were located on the soma near the axon hillock region, with features typical for cholinergic junctions. The axosomatic location of the synapses was manifested physiologically by a decrease in membrane resistance (increased conductance) at the peak of the fast EPSP (excitatory postsynaptic potential) and by a demonstrable reversal potential for the fast EPSP.

A special type of small granule-containing cell in the abdominal para aortic region of the frog

Light and electron microscopic studies have been made of a special type of small granule-containing cell (termed Type IV cell) in the frog abdominal para aortic region. These cells contain numerous dense granular vesicles (100--150 nm in diameter) and are considerably smaller (10--20 mu) than neighbouring nerve cells, although they have many features in common with them. They do not resemble chromaffin cells as do Types I, II and III cells. The cell bodies are completely ensheathed by satellite cells and are isolated from neighbouring cells of the same type. Type IV cells have long processes which usually become incorporated in bundles containing 2--20 processes, including some cholinergic nerve fibres, and are loosely enveloped by perineurium. The termination of the processes of Type IV cells do not appear to form efferent synapses on nerve cells at least within the para aortic region or in paravertebral sympathetic ganglia. A close topographical relationship is not found between these processes and blood vessels. It is suggested that the small Type IV granule-containing cells in the frog abdominal para aortic region are not interneurons or neurosecretory cells, but are a special type of sympathetic nerve cell.

Junctional subsurface organs in frog sympathetic ganglion cells

Subsurface cisternae in frog sympathetic ganglion cells were studied and shown to have similar features to those of the C.N.S. A number of special features were, however, revealed by high resolution microscopy. Highly flattened subsurface cisternae occurred in close proximity to the ganglion cell membrane and formed structures comparable to gap junctions. These subsurface cisternae appeared to be elongated plates (about 0.3 X 2.5 mum) specifically restricted to the area of the ganglion cell membrane adjacent to nerve endings, although often with the intervention of a thin satellite sheath. Thus they have been termed here 'junctional subsurface organs', although the nerve terminals opposing them did not show any synaptic specialization. The junctional subsurface organ was often accompanied by closely arrayed endoplasmic reticulum and/or mitochondria. Where the junctional subsurface organ intervened between plasma membrane and endoplasmic reticulum or mitochondria, faint particles appeared to traverse both sides and bridge the narrow spaces to the opposing plasma membrane and endoplasmic reticulum or mitochondria. The possible functional significance of the junctional subsurface organs is discussed.