Distribution of Noradrenaline Storing Particles in Peripheral Adrenergic Neurons as Revealed by Electron Microscopy

The cell bodies, the axons and the terminal parts of peripheral sympathetic neurons originating in the superior cervical ganglion and terminating in the dilator muscle of the iris were investigated in the rat by electron microscopy using potassium permanganate as a fixative. In all parts of the neuron granular vesicles were found. They were most numerous in the axonal enlargements of the nerve terminals, although also high numbers were found in some cell bodies, mostly localized in clusters in the peripheral parts of the cytoplasm. Two types of granular vesicles were found with a mean diameter of 495 Å (small) and 967 Å (large), respectively. The small granular vesicles were in majority, constituting about 98 per cent in the axonal enlargements in the dilator muscle of the iris. The number of vesicles in the axonal enlargements varied widely from 45 to 852 per enlargement. In all probability the small granular vesicles are the main storage site of noradrenaline in the peripheral adrenergic neurons. However, also the large ones probably contain an amine or at least are involved in the amine metabolism.     

Ultrastructure of the pineal gland of the monkey, Macaca fascicularis, with special reference to the presence of synaptic junctions on pinealocytes

Summary The present study described the normal ultrastructure of the monkey pineal gland. The gland was composed of the principal pinealocytes, intramural neurons and glial cells. The nucleus of the pinealocytes was deeply infolded with evenly distributed chromatin materials. The abundant cytoplasm was rich in organelles including the well-developed Golgi apparatuses, multivesicular bodies, dense-cored vesicles and widely scattered free and polyribosomes. A variety of axon terminals was observed and the majority of them contained pleomorphic agranular vesicles with a few large dense-cored vesicles. A few terminals showed flattened vesicles or small dense cored vesicles. Some of the axon terminals formed synaptic contacts with the cell bodies of pinealocytes. These synapses were mainly concentrated in the posterior third of the gland. The occasional intramural neurons observed were postsynaptic to axon terminals containing round agranular vesicles. The sources of the nerve fibres and terminals forming synaptic junctions with pinealocytes and intramural neurons were discussed.     

The fine structure of the monkey submandibular gland with a special reference to intra-acinar nerve endings

The secretory terminations of monkey submandibular gland were studied by electron microscopy. The acini are composed of two types of secretory cells which are presumably serous and mucous in type. Myoepithelial cells are present also in the acini. The peri-acinar connective tissue contains many unmyelinated nerve fibers. In some portions, the axons contain many synaptic vesicles of various types. These nerve endings partially lose their Schwann cell investment and reach the acinar basement membrane. In peri-acinar connective tissue two types of nerve endings may be recognized. They are thought to be adrenergic and cholinergic in type. On the other hand, only one type of nerve ending (cholinergic) is observed within the acini. The intra-acinar nerve endings are not surrounded by Schwann cell cytoplasm and make direct contact with plasma membranes of the myoepithelial and mucous cells, with a space about 200 Å wide intervening between the nerve and terminal cell. No nerve endings occur in the interspaces between the serous cells. Also, the ultrastructure of the secretory and myoepithelial cells is described.     

Calbindin immunoreactivity in sensory and autonomic ganglia in the guinea pig

Immunoreactivity (IR) for the calcium binding protein, calbindin, was localized in sensory ganglia (nodose, trigeminal and dorsal root), in parasympathetic ganglia (otic and sphenopalatine) in sympathetic chain ganglia and in sympathetic pre-vertebral ganglia of guinea pig. In sensory ganglia, fine nerve fibres with calbindin-IR surrounded the majority of cell bodies, a low proportion of which were themselves reactive. In cranial parasympathetic and in sympathetic chain ganglia, a small proportion of nerve cells was surrounded with baskets of calbindin-IR nerve fibres, but very few cell bodies were reactive. In prevertebral sympathetic ganglia, dense networks of terminals surrounded many cell bodies, but few somata were themselves reactive. In the coeliac and inferior mesenteric ganglia, the calbindin-IR nerve fibres surrounded somatostatin-IR cell bodies, but not those with neuropeptide Y-IR. It is concluded that specific subgroups of peripheral autonomic and sensory neurones have calbindin-IR.     

Fine structure of nerve terminals in the human gut

An electron microscopical investigation was made of neuronal terminals in operatively removed human duodenum and jejunum. No intraepithelial neuronal elements were found. The lamina propria mucosae, submucosa and muscular layer possessed, in addition to large bundles of unmyelinated nerve fibers, small ones consisting of three or four axons wrapped by infoldings of one Schwann cell. Some of these axons were light; others contained mitochondria and clear vesicles measuring 200–500 Å across. Still other axons had dense-cored vesicles with a diameter ～ 700 Å. The plasma membranes of vesiculated axons were not thickened and only in part invested by the Schwann cell, but were covered by a basement membrane. Such profiles were interpreted as nerve terminals, and were separated from fibers of the muscularis mucosae, bases of epithelial cells and submucous capillaries by interspaces measuring 5,000–6,800 Å. The gap between neuronal terminals and smooth muscle in the muscular wall was smaller (900 Å, more often 1,500–3,000 Å). The myenteric plexus contained nerve bundles consisting of the usual axons and of preterminals; some of the latter contained small clear vesicles, others predominantly larger granulated vesicles, and still others a mixture of both types of vesicles. The similarities and differences of neuronal terminals occurring in animals and in man were pointed out. The significance of the findings of this study was discussed in the light of current concepts of the physiology of autonomic nerve transmission.     

Adrenergic nerve elements in the hypogatric ganglion of the guinea pig

Adrenergic nerve elements in the hypogastric ganglion of the guinea pig were studied by fluorescence and electron microscopy. The ganglion contains two main elements exhibiting green to green-yellow fluorescence for catecholamines. One consists of basket-like, simple nerve endings around some of the ganglion cell bodies, and the other of small polyhedral cells with short axonic processes. Electron microscopy revealed the ultrastructure of these elements. The adrenergic nerve endings contain small granular vesicles, about 500 Å in diameter, as well as a few large granular and small agranular vesicles. They were more rare than the cholinergic endings, which contain numerous small agranular vesicles mixed with a few large granular vesicles. Both adrenergic and cholinergic endings submerge to a considerable depth into the cytoplasm of ganglion cells. The ganglion cells send spinous processes into these endings. The fluorescent polyhedral cells are probably in an intermediate position between adrenal medullary cells and ganglion cells. They contain numerous large granular vesicles. Their axonic processes extend for a short distance to end in close topographical relation to capillaries. According to the structure of the granulated vesicles, these cells were classified into four types. The function of the adrenergic elements in ganglionic transmission was discussed.     

The ultrastructure of the nucleus of the oculomotor nerve (somatic efferent portion) of the cat

Summary The ultrastructure, of the somatic efferent portion of the nucleus of the oculomotor nerve was studied in four adult cats. The neuronal population is composed of neurons of variable size. A continuous pattern of morphological aspects is evident between the large neurons, which show abundant cytoplasm with well developed organelles and the small neurons which have a reduced amount of cytoplasm. The dendrites are generally smooth, with few short spines. Axo-somatic and axo-dendritic synapses are numerous. Synaptic boutons are also present on the axon hillock.The neuropil is characterized by the occurrence of small groups of dendrites which may be in direct touch with their membranes. Direct membrane appositions may also occur between neighbouring neurons and between the cell somata and tangentially running dendrites. Generally beneath the site of apposition there is accumulation of mitochondria, multivesicular bodies, coated vesicles and moderately dense amorphous material. The morphological features suggest the possibility of cellular interchanges at the sites of direct membrane apposition.Five types of synaptic boutons were recognized on the basis of their vesicular content, the presence of abundant filaments in the pre-synaptic bag, the occurrence of post-synaptic specializations. The, different synaptic types and their distribution are similar to those reported in the spinal motor nuclei. Many of the synapses make synaptic contacts with two or more post-synaptic elements. Axo-axonic synapses were also observed.     

Spinal neurons involved in the control of the seminal vesicles: a transsynaptic labeling study using pseudorabies virus in rats

The seminal vesicles are male accessory sex glands that mainly contribute the seminal fluid of the ejaculate. Previous studies have suggested that seminal vesicles are supplied by both sympathetic and parasympathetic nerves. However, this conclusion was mainly based on studies in pelvic major ganglions and direct neuroanatomical evidence of spinal neurons innervating the seminal vesicles is still lacking. In order to map the spinal nerve circuit innervating the seminal vesicles, the present study used the pseudorabies virus (PRV) retrograde tracing technique in combination with immunohistochemistry. Three groups of rats were prepared: (1) nerves intact; (2) right hypogastric nerve and bilateral pelvic nerves sectioned; (3) right pelvic and bilateral hypogastric nerves sectioned. For the intact group, 3 to 5 days after injection of PRV into the left seminal vesicle in male rats, immunohistochemistry for PRV was performed to map the control circuit. Double immunofluorescence experiments against PRV and choline acetyltransferase (ChAT) were performed to discriminate preganglionic neurons and interneurons. Double detection of PRV and galanin (GAL) was also performed to identify lumbar spinothalamic (LSt) cells. Three days after virus injection, both sympathetic and parasympathetic preganglionic neurons were retrograde-labeled. Four days after injection of PRV into the seminal vesicles, PRV-infected neurons were found in the dorsal horn, ventral horn, dorsal gray commissure (DGC), medial gray matter and intermediolateral cell column (IML) from T13 to S1. For the group with an intact hypogastric nerve, 4 days after injection of PRV into the seminal vesicles, PRV-infected neurons were mainly located in DGC and IML of spinal lumbar segments (L) 1-L2. However, in the group with an intact pelvic nerve, PRV-infected neurons were mainly located in DGC of L5-S1 spinal segments. At the L3-L4 level, most of the virus-labeled neurons around the central canal expressed immunoreactivity for GAL, strongly suggesting that they could be LSt cells. These anatomical data support the idea that the sympathetic and parasympathetic nervous system are both involved in the control of the seminal vesicles and we demonstrated a connection between preganglionic neurons innervating the seminal vesicles and LSt cells which play a crucial role in coordinating the spinal control of ejaculation.     

FMRFamide-like immunoreactivity in the brain of the honeybee (Apis mellifera). A light-and electron microscopical study

Peptide-FMRFamide-like immunoreactivity in the brain and suboesophageal ganglion of the honeybee Apis mellifera L. is demonstrated with the peroxidase-antiperoxidase technique. Immunoreactivity is found in about 120 perikarya of the brain and in about 30 of the suboesophageal ganglion. These cells are distributed in 13 paired clusters representing neurons of different types including neurosecretory neurons projecting to neurohemal organs. Immunoreactivity of different intensity is found in the non-glomerular neuropil around the mushroom bodies, in the lateral protocerebrum, the central body, the optic tubercles, the lobula and medulla of optic lobe, the ocellar neuropil, in multiglomerular elements of the antennal lobes and in the dorsal deuterocerebrum. In the mushroom bodies, immunoreactivity is located in layers of the lobes and stalks, corresponding to intrinsic fibre bundles of some Kenyon cell types. The somata of these intrinsic cells did not show FMRFamide-like immunoreactivity. Electron microscopy of immunostained somata and nerve fibres was performed employing a pre-embedding peroxidase-antiperoxidase technique. Fibres of optic lobes and the non-glomerular neuropil contain immunoreactive dense core vesicles (diameter 50-165 nm) accumulated in boutons besides small synaptic vesicles and synaptic membrane specializations. Immunoreactive layers of the mushroom body neuropil were analysed at the ultrastructural level. Axon profiles with dense-core vesicles of a small type (diameter 35-75 nm) show only faint immunoreactive products. Immunoreactivity of intrinsic mushroom body neurons does not appear to be specifically correlated with synaptic organelles. Our results indicate that FMRFamide or related peptides peptides may be neuroactive compounds in different classes of nerve cells in the bee brain.     

Non-sympathetic synaptic innervation of the pinealocyte of the Mongolian gerbil (Meriones unguiculatus): an electron microscopic study

Summary Direct synaptic innervation of pinealocytes was observed in the superficial pineal gland of the Mongolian gerbil (Meriones unguiculatus) by electron microscopy. This innervation consisted of nerve fibres terminating in boutons with clear transmitter vesicles with a diameter of 40–60 nm. The boutons made synaptic junctions with the cell membrane of the pinealocyte displaying thickenings of both the pre- and postsynaptic membranes. Such boutons persisted in the gland 1 week after removal of both superior cervical ganglia. In contrast, all the sympathetic boutons containing transmitter vesicles with a small dense core disappeared after ganglionectomy. This direct synaptic innervation reveals a neuronal character of the pinealocyte and might underlie reports of action potentials in electrophysiological recordings from the gland.     

Ultrastructure of photoreceptors and circadian pacemaker neurons in the eye of a gastropod, Bulla

Each of the paired cephalic eyes of the marine gastropod, Bulla, is about 0.5 mm in diameter and contains about 1000 large photoreceptors, small photoreceptors, numerous pigmented support cells and about 130 neurons. The photoreceptors are of three types: large (90 micron X 20-30 micron) dense ones (PRLD) with elaborate narrow microvilli and aggregates of 650 A clear vesicles in the cytoplasm; large clear ones (PRLC) with elaborate wide microvilli and aggregates of 650A clear vesicles; small slender receptors (PRS) with a tuft of microvilli and lacking vesicle aggregates. Neurons (15-25 micron) containing dense-core 1000 A vesicles are in the periphery of the retina or grouped in a collar around the neuropil below the photoreceptor layer. The 4-5 largest neurons are in the collar area. Correlation of neuron morphology with electrical activity was done with intracellular recording and Lucifer yellow injection of some of the larger neurons in the collar area whose action potentials contribute to the optic nerve impulses. Each one has an axon in the optic nerve and processes that go to the neuropil. They are the pacemaker neurons of the circadian rhythm in impulse frequency that is recorded from the optic nerve, since only their action potentials are correlated 1:1 with the optic nerve impulses. Gap junctions (with pentalaminar structure) are common between photoreceptors, glial cells, photoreceptors and glial cells, and neuronal processes in the neuropil, providing a basis for electrotonic coupling among retinal cells. There are about 2000 axons (diameter less than 3 micron) in the optic nerve, possibly one from each retinal photoreceptor and neuron plus efferent fibres from the brain. Accessory nerves, containing a few large axons, are seen in the optic nerve sheath.     

Fine structure at the cut ends following section of the sensory component of the vagus nerve of mice

The fine structures at the cut ends following section of the sensory component of the midcervical vagus nerve of mice were examined. No changes were found in the fine structure of the neurons in the nodose ganglion or in that of the axons in the midcervical vagus nerve 14 d after supranodose vagotomy. After supranodose vagotomy followed 14 d later by midcervical vagotomy, the dilated axons present in the vicinity of the cut contained clear vesicles with a mean diameter of 69 nm and dense-cored vesicles with a mean diameter of 78 nm, vesiculotubular membranous structures, smooth endoplasmic reticulum (SER), mitochondria, multivesicular bodies, dense bodies, neurofilaments, and microtubules. The similarity between sensory axons interrupted by cutting and the presynaptic terminals of sensory neurons is discussed.     

Ultrastructure and immunocytochemistry of the neuroepithelial bodies in the lung of the tiger salamander,Ambystoma tigrinum (Urodela,amphibia)

Light and electron microscopy of the lungs of Ambystoma tigrinum (Urodela) revealed a relatively complex pattern of the neuroendocrine (NE) cells. In the apical parts of smaller septa single NE cells not associated with nerve fibres were covered and surrounded by pneumocytes. The larger septa possessed small areas of ciliated epithelium, in which the NE cells were grouped in a form of neuroepithelial bodies (NEB) consisting of 3–5 cells and covered by goblet cells. NE cells possessed a large nucleus with patches of condensed chromatin, clear cytoplasm, and membrane-bound vesicles of variable morphology and size, of these dense core vesicles (DCV) ranged from 70–140 nm, while rarely the larger ones exhibited a diameter of 300–600 nm. In some NEB a second type of NE cells was observed for the first time in an amphibian species: these cells communicated with the air space and exhibited on their surface microvilli and a single modified cilium with a 8+1 microtubule arrangement. Their cytoplasm contained two types of DCV: dense core granules with a diameter of 140–260 nm and vesicles 320–700 nm in diameter with a moderately electron dense interior. The NEB were associated with intracorpuscular, sensory nerve terminals morphologically afferent and efferent. By immunocytochemistry, the NE cells revealed the presence of serotonin, met-en-kephalin, and leu-enkephalin. A paracrine and chemoreceptor role is proposed for NEB of Ambystoma tigrinum.© Willey-Liss, Inc.     

国人皮肤麦克尔细胞及其颗粒和亮小泡的超微结构观察

本文首次报道了国人皮肤麦克尔细胞(MC)及其颗粒和亮小泡的超微结构。MC多分布在触盘增厚的表皮基底层,与神经终末接触并形成突触样结构,与角质形成细胞以桥粒相联系。ME具有一分叶状核。丰富的线粒体和许多直径80—120nm的膜包致密核心颗粒和直径70～90nm的亮小泡。这些颗粒和小泡不仅靠近突触样结构膜,也靠近与角质形成细胞相邻的胞膜。本文还讨论了MC分泌功能的可能性。     

Sensory components in the terminal innervation of the ovine cardiac conduction system

Neuromuscular relationships in the cardiac conduction system of the ovine heart were studied by means of light and electron microscopy. Fluorescence microscopy was used to demonstrate the distribution of adrenergic nerves. Histochemical methods demonstrated sites of acetylcholinesterase and nonspecific cholinesterase activity at both light and electron microscopic levels. Surgical denervation was used in an attempt to support the identification of different types of nerve endings. A dense plexus of nerves strongly positive for acetylcholinesterase was present in all parts of the conduction system. Nonspecific cholinesterase was found to be limited to large nerve bundles which were presumed to be preganglionic. A dense plexus of adrenergic nerve fibers was identified in both the SA and AV nodes, but such fibers were very sparsely distributed along the AV bundle and its branches. On the basis of morphology as demonstrated by electron microscopy, three types of nerve endings or varicosities associated with the specialized cells of the conduction system were identified. Cholinergic endings, presumably post-ganglionic parasympathetic, contained many nongranulated synaptic vesicles. Adrenergic or post-ganglionic sympathetic endings or varicosities contained granulated synaptic vesicles. Axonal enlargements containing numerous mitochondria and varying numbers of pleomorphic dense bodies were identified as sensory endings on the basis of their morphologic similarity to such endings found elsewhere in the animal body. These were found in 22% of the blocks examined by electron microscopy, were present in all parts of the conduction tissue, and were acetylcholinesterase positive. They did not show obvious signs of degeneration following vagotomies or thoracic sympathectomy, suggesting the possibility that they were endings of neurons intrinsic to the heart. No signs of degeneration were noted in the endomysial plexus following vagotomy either proximal or distal to the distal (nodose) ganglion. Degeneration of small fibers of the plexus was noted following thoracic sympathectomy. This study provides evidence suggesting a significant sensory innervation to the cardiac conduction system, with the cell bodies of the sensory neurons located in or near the heart.     

An ultrastructural study of nerve and glial cells by freeze-substitution

Summary The ultrastructure of nerve and glial cells in the cerebral and cerebellar cortices of mice was studied after rapid freezing followed by substitution fixation. The cerebral and cerebellar cortices were frozen by bringing them into contact with a polished pure copper block cooled at a temperature of about –196 ° C. The tissues were fixed and substituted in acetone containing 2–4% OsO₄ at –78 ° C for 2–3 days and then prepared for electron microscopy. Tissue fixed by this method displayed the following characteristics. (1) The contour of cells, processes and intracellular membrane systems was smooth. (2) The extracellular spaces were of variable widths. (3) Microtubules were well preserved and were often observed to extend into nerve terminals and to run close to presynaptic membranes. (4) The matrix of cytoplasm and mitochondria was electron dense. Dense granules, possibly binding sites of divalent cations, were often found in the mitochondrial matrix. (5) The plasma membrane of neuronal processes was thicker than that of glial processes. (6) The plasma membranes of nerve fibres and glial processes appeared asymmetrical, the inner leaflet being slightly thicker than the outer leaflet, whereas membranes of cell organelles such as smooth endoplasmic reticulum, Golgi bodies, lysosomes, multivesicular bodies, mitochondria and synaptic vesicles, were symmetrical.     

The fine structure of the submucous plexus of the guinea-pig ileum. I. The ganglia, neurons, Schwann cells and neuropil

Summary A fine structural study was made of the ganglia, neurons, Schwann cells and neuropil of the submucous plexus of the guinea-pig ileum. The arrangement of the plexus as seen by light microscopy is briefly described. Submucous ganglia are small, containing an average of eight neurons per ganglion (compared with 43 in myenteric ganglia) and are connected with each other by fine nerve strands.The cell bodies of neurons and Schwann cells and a neuropil consisting of neuronal and Schwann cell processes form the ganglia. No other cell types or blood vessels are found within the ganglia. Ganglia are surrounded by a continuous basal lamina but lack a well-defined connective tissue investment. The glial investment of neurons is incomplete: many neurons lie directly beneath the basal lamina with no intervening Schwann cell processes, and the plasma membranes of adjacent neurons are often directly apposed over large areas. Other areas of apposition occur between the cell bodies and processes of neurons and Schwann cells. Desmosome-like membrane specializations may be seen between neurons and other neurons or Schwann cells. Submucous neurons could not be categorized according to size, shape, organelle content or types of processes. Processes emerging from nerve-cell bodies were placed into four broad categories on the basis of shape and microtubule content.Many bundles of closely apposed small nerve profiles lacking intervening Schwann processes are found in the neuropil in addition to a large number of vesiculated varicosities, some of which are directly apposed to the plasma membranes of nerve-cell bodies. A small proportion of vesiculated profiles form synapses with nerve cell bodies, their processes and profiles in the neuropil. From their structure, submucous neurons appear to form a more homogeneous population than myenteric neurons. Because of their incomplete investment they are more likely to be freely exposed to substances diffusing in the extraganglionic tissue than are neurons of sympathetic ganglia.     

Selectivity of neuronal degeneration produced by chronic guanethidine treatment

Summary Chronic guanethidine treatment of rats produced extensive damage to sympathetic neurons of the superior cervical ganglion and pelvic plexus. No ultrastructural changes were observed in parasympathetic cholinergic neurons in the ciliary ganglion and pelvic plexus, nor in sensory neurons in nodose and dorsal root ganglia. A total of only six nerve cell bodies free of degenerative changes were observed in sections of superior cervical ganglia from 20 rats. This suggests either that the earlier estimates of 5% cholinergic neurons in the superior cervical ganglion based on acetylcholinesterase staining are too high, or implies that sympathetic cholinergic neurons, unlike parasympathetic neurons, are damaged by chronic guanethidine treatment.     

Electron microscopic observations of the mesencephalic nucleus of the fifth nerve in the Selachian brain

Summary The mesencephalic nucleus of the trigeminal nerve (mes V) in the brain of the skate (Raja oscellata) was studied by electron microscopy. Mes V neurons are large (40–80 m diameter) and are located in the periventricular grey matter. Their perikaryal cytoplasm is rich in Golgi apparatus, small mitochondria, rough endoplasmic reticulum, polysomes and bundles of neurofilaments. A striking feature is the presence of masses of glycogen granules, at times surrounded by membrane wrappings and lysosomal bodies.Two types of conventional synaptic contacts were made onto mes V perikarya and dendrites. One had round, agranular vesicles and usually also contained dense-cored vesicles, the other had flattened, pleomorphic, agranular vesicles and usually lacked dense-cored vesicles. Additional membrane complexes consisting of a region of gap junction flanked by sites of desmosomal attachment were observed to link neighbouring mes V neurons. Somato-somatic, dendro-somatic, axo-somatic, and dendro-dendritic junctions were noted. Except for the somato-somatic union, one or more chemical synapses were located close to the sites of gap junctions.     

Ultrastructure and immunocytochemistry of the neuroepithelial bodies in the lung of the tiger salamander, Ambystoma tigrinum (Urodela, Amphibia).

Light and electron microscopy of the lungs of Ambystoma tigrinum (Urodela) revealed a relatively complex pattern of the neuroendocrine (NE) cells. In the apical parts of smaller septa single NE cells not associated with nerve fibres were covered and surrounded by pneumocytes. The larger septa possessed small areas of ciliated epithelium, in which the NE cells were grouped in a form of neuroepithelial bodies (NEB) consisting of 3-5 cells and covered by goblet cells. NE cells possessed a large nucleus with patches of condensed chromatin, clear cytoplasm, and membrane-bound vesicles of variable morphology and size, containing an electron dense interior surrounded by a lucent space. The size of these dense core vesicles (DCV) ranged from 70-140 nm, while rarely the larger ones exhibited a diameter of 300-600 nm. In some NEB a second type of NE cells was observed for the first time in an amphibian species: these cells communicated with the air space and exhibited on their surface microvilli and a single modified cilium with a 8 + 1 microtubule arrangement. Their cytoplasm contained two types of DCV: dense core granules with a diameter of 140-260 nm and vesicles 320-700 nm in diameter with a moderately electron dense interior. The NEB were associated with intracorpuscular, sensory nerve terminals morphologically afferent and efferent. By immunocytochemistry, the NE cells revealed the presence of serotonin, met-enkephalin, and leu-enkephalin. A paracrine and chemoreceptor role is proposed for NEB of Ambystoma tigrinum.