Fine-structural Identification of Autonomic Nerves and their Relation to Smooth Muscle

Rosacea: I. Etiology, pathogenesis, and subtype classification

Rosacea is one of the most common conditions dermatologists treat. Rosacea is most often characterized by transient or persistent central facial erythema, visible blood vessels, and often papules and pustules. Based on patterns of physical findings, rosacea can be classified into 4 broad subtypes: erythematotelangiectatic, papulopustular, phymatous, and ocular. The cause of rosacea remains somewhat of a mystery. Several hypotheses have been documented in the literature and include potential roles for vascular abnormalities, dermal matrix degeneration, environmental factors, and microorganisms such as Demodex folliculorum and Helicobacter pylori. This article reviews the current literature on rosacea with emphasis placed on the new classification system and the main pathogenic theories. Learning objective At the conclusion of this learning activity, participants should be acquainted with rosacea's defining characteristics, the new subtype classification system, and the main theories on pathogenesis.

All-or-none augmentation of Ca2+ sensitivity in alpha-toxin-permeabilized single smooth muscle cells from guinea-pig taenia caecum

1. Isolated smooth muscle cells from guinea-pig taenia caecum were permeabilized by use of Staphylococcus aureus alpha-toxin, and the sarcoplasmic reticulum Ca2+ store was depleted by exposure to 0.1 microM A23187. 2. Shortening of alpha-toxin-permeabilized single smooth muscle cells was induced by increasing free Ca2+ but was not induced by 0.2 microM free Ca2+. 3. Shortening of the permeabilized cells was caused by application of acetylcholine (ACh) with free Ca2+ concentration held at 0.2 microM. Permeabilized smooth muscle cells responded to 0.3 microM or 1 microM ACh with 0.2 microM Ca2+ with maximal shortening. The concentration-response relationship to ACh had a very steep slope and the cell shortening appeared to be an all-or-none response rather than a graded response, as was the shortening of intact cells to ACh. 4. The shortening of permeabilized cells was also induced by application of guanosine 5'-triphosphate (GTP) with 0.2 microM free Ca2+, showing an all-or-none response. The threshold concentration of GTP that induced an all-or-none response was between 10 microM and 30 microM. 5. These results suggest that Ca2+ sensitivity is augmented by stimulation of the muscarinic receptor or GTP-binding protein(s) in an all-or-none manner. It seems probable that this contributes to the all-or-none response to ACh in intact smooth muscle cells.

All-or-none shortening of isolated single smooth muscle cells from different organs to acetylcholine

1. Single smooth muscle cells from the guinea-pig taenia caecum and the fundus of guinea-pig stomach were prepared by collagenase digestion under different, mild conditions. 2. Most of the cells either from taenia caecum or from the fundus of stomach responded repeatedly, showing an all-or-none response to acetylcholine (ACh). 3. The threshold concentrations of ACh were different for the cells of the two tissues. Although individual cells showed an all-or-none response to ACh, the average responses of all the cells were graded, like that of whole tissues. 4. Thus, isolated single smooth muscle cells from different tissues and under different conditions responded to ACh in an all-or-none manner such as the twitch observed in skeletal muscle. 5. These results suggest that the isolation of cells reveals the fundamental characteristics of smooth muscle cells as excitable.

Electron microscopic structure and innervation of the carotid baroreceptor region in the rock hyrax (Procavia capensis)

Semi-thin plastic sections reveal that the carotid baroreceptor region in the rock hyrax comprising the origin of the internal carotid artery has a preponderantly elastic structure and a thick tunica adventitia. In contrast, the common carotid artery has a musculoelastic structure, whereas the cranial segment of the internal carotid artery (immediately distal to the baroreceptor areas) shows the features of a muscular artery. Electron microscopy discloses the presence of sensory nerve endings within the parts of the tunica adventitia adjoining the preponderantly elastic zone of the internal carotid artery. These nerve endings are characterized by varicose regions containing a large quantity of mitochondria. Bundles of collagen fibers in the tunica adventitia form convolutions or whorls around the nerve terminals and often terminate on the surface of the elastic fibers or into the basement membranes of the neuronal profiles. The large content of elastic tissue in the tunica media of the baroreceptor region may render the vessel wall highly distensible to intraluminal pressure changes. This, in turn, would facilitate the transmission of the stimulus intensity to the sensory nerve terminals located in the tunica adventitia. It is suggested that the stretching of elastic fibers may form the main mechanical event leading to the distortion of the associated nerve terminals. However, a change in the geometrical configuration of the bundles of collagen under the influence of the elastic fibers may provide a better insight into the mechanisms of distortion of the baroreceptors related to and/or in contact with collagen fibers.

Innervation of the guinea pig spleen studied by electron microscopy

The innervation of the guinea pig spleen was investigated by electron microscopy. Unmyelinated nerve fibers in the capsulotrabecular and arterial systems were found to contain large and small granular and small agranular synaptic vesicles in their terminals and are thought to be sympathetic adrenergic in nature. They influence the contraction of the smooth muscle cells by diffusion innervation in these systems. These nerve terminals were also scattered in both the red and the white pulp. Pulp nerves wrapped by Schwann cells were further enclosed by myofibroblastic reticular cells. This condition revealed that the pulp nerves pass through the connective-tissue spaces of the reticular fibers, which contain elastic fibers, collagenous fibrils, and lamina densa-like materials of the usual basement laminae. One of the target cells for the pulp nerves is considered to be the myofibroblastic reticular cell in the reticular meshwork. Neurotransmitter substances released from the naked adrenergic nerve terminals travel through the reticular fibers and may play a role, by both close association innervation and diffusion innervation, in the contraction of reticular cells to expose the reticular fibers. At the exposed sides, connective-tissue elements of the reticular fibers are bathed with blood plasma, and the included naked nerve terminals, devoid of Schwann cells but with basement laminae of these cells, face free cells at some distance or are in close association with free cells, especially lymphocytes, macrophages, and plasma cells. The close ultrastructural relationship between the naked adrenergic nerve terminals and immunocytes strongly suggests that there is an intimate relationship between the immune system and the sympathetic nervous system through both close association innervation and diffusion innervation. Thus splenic adrenergic nerves of the guinea pig may play a triple role in 1) contraction of smooth muscle cells to regulate blood flow in the organ, 2) induction of the exposure of reticular fibers by contraction of the reticular cells in order to form a close relationship of the nerve terminals with the immunocytes, and 3) subsequent neuroimmunomodulation of the immunocytes.

The role of adenosine triphosphate in migraine

Classical migraine is associated with two distinct phases; an initial vasoconstriction followed by vasodilatation. The "purinergic" hypothesis for migraine was originally put forward in 1981 as a basis for the reactive hyperaemia and pain during the headache phase. It was suggested that adenosine 5'-triphosphate (ATP) and its breakdown products adenosine 5'-monophosphate and adenosine were strong contenders for mediating the vasodilatation following the initial vasospasm and subsequent hypoxia. ATP was also implicated in the pathogenesis of pain during migraine via stimulation of primary afferent nerve terminals located in the cerebral vasculature. Recent studies have shown that the ATP-induced cerebral vasodilation is endothelium-dependent via activation of P2Y-purinoceptors on the endothelial cell surface and subsequent release of endothelium-derived relaxing factor (EDRF); and that the endothelial cells are the main local source of the ATP involved, although adenosine 5'-diphosphate and ATP released from aggregating platelets may also contribute to this vasodilatation. These findings have extended the "purinergic" hypothesis for migraine in two ways. Firstly, they have clarified the mechanism of purinergic vasodilatation during the headache phase of migraine. Secondly, they suggest that a purinergic mechanism may also be involved in the initial local vasospasm, via P2X-purinoceptors on smooth muscle cells occupied by ATP released either as a cotransmitter with noradrenaline from perivascular sympathetic nerves or from damaged endothelial cells.

Morphology of synapses in the autonomic nervous system

The ultrastructure of synapses in the autonomic nervous system is reviewed. The synaptic organization of the parasympathetic ganglia is relatively simple. Preganglionic axons form synapses either on the soma or on short perikaryal processes of the ganglionic neurons. The presynaptic terminals have a cholinergic morphology and contain mainly small clear vesicles with a few large dense cored vesicles. A few neuropeptides have been localized to the large dense cored vesicles of these terminals. The postganglionic parasympathetic axons ramify within their target tissues where they form close associations, but not true synaptic contacts. Sites of release of transmitter are recognized morphologically as varicosities along the length of the axon that contain clusters of small clear vesicles with a few large dense cored vesicles. The organization of the sympathetic nervous system is somewhat more complex. In addition to acetylcholine, enkephalin also exists in these terminals, probably in the large dense cored vesicles. There are at least three types of ganglion cell neurons in the paravertebral portion of the sympathetic nervous system: those that contain norepinephrine alone, those that contain norepinephrine along with neuropeptide Y, and those that contain acetylcholine and vasoactive intestinal polypeptide. The first type provides innervation to the parenchyma of the target tissues, while the second mainly innervates blood vessels. The third type innervates the sweat glands. In the prevertebral ganglia, a fourth type of neuron exists that contains norepinephrine and somatostatin. This neuron probably innervates the gut. Preganglionic terminals of the cholinergic type form synaptic connections mainly with the dendrites of the sympathetic ganglion neurons. In addition to the types of synapses described for the paravertebral ganglia, neurons in the prevertebral ganglia receive synaptic connections from dorsal root ganglia and from the enteric nervous system. The sympathetic ganglia also contain interneurons that receive preganglionic synapses and form efferent synapses with some of the principal ganglion cells. The interneurons have been shown to contain a variety of transmitters, including norepinephrine, epinephrine, dopamine, serotonin, and a number of neuropeptides. The postganglionic sympathetic axons have a similar morphology to the parasympathetic axons. They form networks in their targets, and the axons display varicosities with concentrations of both small and large vesicles. After appropriate fixation, these vesicles are seen to possess dense cores.(ABSTRACT TRUNCATED AT 400 WORDS)

Why is flushing limited to a mostly facial cutaneous distribution?

Despite the systemic nature of many agents that provoke flushing reactions, the erythema is most prominent in the "blush area." To elucidate the physiologic basis for such a limited distribution, two types of flushing challenges were studied in normal volunteers. Nicotinic acid provokes flushing through a direct action of vasodilator prostaglandins on vascular smooth muscle. The flushing reaction provoked by oral thermal challenge is mediated via neural mechanisms. Both agents led to increases in cutaneous blood flow at both malar and forearm sites. Both absolute and proportional increases were consistent with the view that the greater vascular capacitance in the visible, superficial cutaneous vasculature in the blush area accounts for the limited distribution of flushing in response to a systemic stimulus.

Muscarinic receptor binding and Ca2+ influx in the all-or-none response to acetylcholine of isolated smooth muscle cells

Isolated smooth muscle cells from guinea pig taenia caecum were prepared by collagenase digestion. Isolated single smooth muscle cells showed an all-or-none response to acetylcholine (ACh) under our experimental conditions. A Scatchard plot of the specific binding of [3H]quinuclidinyl benzilate (QNB) to the cells gave a straight line, and the KD and Bmax values were calculated as 0.18 +/- 0.03 nM and 1.11 +/- 0.10 pmol/mg protein, respectively. ACh competitively inhibited the specific binding of [3H]QNB in a concentration-dependent manner. Thus, although the cells showed an all-or-none response, ACh bound to the receptor concentration dependently. The contraction of the cells in response to ACh was inhibited in a concentration-dependent manner, by nicardipine suggesting that the contraction of smooth muscle cells in response to ACh depended on the influx of extracellular Ca2+. The ACh-stimulated increase of the Ca2+ influx was very rapid and correlated well with the contraction of the cells; it decreased after reaching a maximum. The all-or-none response of the cells could be due to a rapid influx of Ca2+. These results suggest that ACh binds to its receptor in a concentration-dependent manner, and that when the binding reaches a certain threshold, a rapid influx of Ca2+ occurs and the cells show an all-or-none response, followed by an efflux of Ca2+.

Lymph heart musculature in birds

Development and innervation of the lymph heart musculature of chicken, emu, rhea, and duck was studied by electron microscopy at post-hatch ages from 3 days to adulthood. Development of innervation was monitored by acetylcholinesterase staining. Horseradish peroxidase was used to determine the extent of the transverse tubule network. Chickens were unusual among these birds in that lymph heart myocytes had already undergone a definitive differentiation and degeneration by 3 days. In ducks and ratite birds, lymph heart myocytes more slowly but progressively differentiate a cytomorphology that does not conform in all characteristics to cardiac or skeletal muscle and even resembles in some aspects, smooth muscle. Myofibrils become the dominant cytoplasmic structure, transverse tubules form "internal couplings" with agranular reticulum cisternae, and "external couplings" are formed between myocytes at myomyal junctions. The myomyal junctions also contain AChE-positive reaction product and some subplasmalemmal vesicles that lack a dense core. The lymph heart myocardium of ducks of 2 weeks demonstrated mitotic figures. In adult ducks the myosatellite cell numbers diminish and a characteristic pattern of myocyte degeneration appears. In juvenile ducks and ratites some myocytes differentiate to conductile cells, much as the conductile myocytes and myofibers of the blood heart. The lymph heart innervation is described, and the role of nerve in differentiation and maintenance of myocyte morphology in the lymph heart is discussed.

The innervation of the myometrium of the cynomolgus monkey (Macaca fascicularis). A quantitative electron-microscopic study

The autonomic innervation of the myometrium of Macaca fascicularis consists of bundles of unmyelinated nerve fibres running between the smooth muscle cells, and is therefore considered to be of the "fascicular (= unitary) type". Close contacts between nerve fibres and smooth muscle fibres were not found. Modification of the chromaffin method according to Tranzer and Richards made it possible to visualize the heterogeneity of the nerve fibres in a single bundle. The following fibre types were found to coexist: (1) noradrenergic fibres containing "synaptic" vesicles with a dense granule, (2) cholinergic fibres containing empty "synaptic vesicles", and (3) non-adrenergic non-cholinergic (NANC) fibres containing only or predominantly large dense-cored vesicles, which do not react with this method. Noradrenergic fibres are the most numerous (around 60%), followed by NANC fibres (30%) and cholinergic elements (around 10%). The distribution of these three types is similar in the cervix, the isthmus and the body of the uterus in pregnant and non-pregnant females.

Fine structure of the photosensitive iris of the toad, Bufo marinus

The iris of the toad Bufo marinus is directly photosensitive and will constrict in response to light striking only the iris. This is true even when the iris is isolated from the rest of the eye, and therefore from reflex neuronal influences initiated in the retina. This autonomous response is probably mediated by the sphincter pupillae muscle, since no specialized photoreceptors are present in the iris, nor does the sphincter exhibit any specializations likely to subserve a purely photoreceptive function. The photosensitive sphincter appears typical of smooth muscle and, like mammalian sphincters, possesses many intercellular junctions. The iris possesses a well-developed neuronal plexus with fibers projecting into the sphincter muscle layer. Nerve terminals contain small, agranular (30-70nm) and large, dense-cored (80-120nm) vesicles. No consistent postsynaptic specializations are seen on any cells of the iris, including the cells of the sphincter muscle. The anterior pigment epithelial cells of the iris appear specialized and resemble the myoepithelial dilator muscle described by Kelly and Arnold ('72) for the iris of rats.

A simultaneous demonstration of particular enteric neuronal cell types with the NADH:nitro BT-dehydrogenase reaction and of nerve fibres containing enkephalin-like immunoreactivity in the myenteric plexus of the porcine small intestine

The myenteric plexus of the porcine small intestine is studied using a combined method for the simultaneous visualization of enteric intramural neuronal cell bodies and peptidergic nerve fibers. As earlier reported, the histochemical method for demonstration of the NADH-dependent dehydrogenase reaction allows the identification of the three neuron types of Dogiel but, in addition, the afore mentioned staining method creates fair conditions in the tissue for the subsequent indirect immunocytochemical visualization of neuropeptides, as demonstrated in this work by means of the indirect immunofluorescence method for enkephalin-like immunoreactivity. Intense fluorescent varicosities of enkephalin-like nerve fibres were found to ramify around dark-blue stained ganglionic cells of type I, type II and type III in a manner suggestive of innervation.

Adrenergic innervation of the tunica media in the saphenous artery of the fetal and newborn guinea-pig

Previous studies have demonstrated that adrenergic nerves are located in the medial-adventitial border of the muscular arteries. Observations made in this study have revealed that adrenergic nerves penetrate into the outer medial layer of the saphenous artery in fetal and newborn guinea-pigs, while in the adult these nerves are located in the medial-adventitial border. It is proposed that the adrenergic nerves located in the tunica media may have a trophic effect on the medial smooth muscle. It is further suggested that the final refinement of the dual control system of arterial walls, by nerves and circulating catecholamines, involves exclusion of adrenergic nerves from the tunica media.

Ultrastructure and innervation of the swimbladder of Tetractenos glaber (Tetraodontidae)

The general structure, ultrastructure and innervation of the swimbladder of the smooth toadfish, Tetractenos glaber, were examined with light-microscopic, fluorescence-histochemical, and transmission electron-microscopic techniques. The structure of the swimbladder is similar to that of other euphysoclists. Fluorescence histochemistry showed adrenergic fibres in both the secretory and resorptive areas of the swimbladder. Transmission electron microscopy revealed two morphologically distinct axon profiles: type-I profiles containing many small, flattened vesicles; type-II profiles containing both large, granular vesicles and rounded, small clear vesicles in varying proportions. The gas-gland cells and surrounding muscularis mucosae are innervated by both type-I and type-II fibres. Type-I fibres also innervate pre-rete arteries. The rete- and gas-gland capillaries do not appear to be innervated. Arteries running to the resorptive area are innervated by type-I fibres. Both type-I and type-II profiles make contact with the muscularis mucosae in the resorptive area. Only type-I fibres innervate the radial dilator muscle in the oval sphincter region, whereas only type II fibres innervate the circular muscle of the oval sphincter. Type-I fibres took up alpha-methyl-noradrenaline, and could not be found after pre-treatment with 6-hydroxydopamine. They are, therefore, assumed to be adrenergic. Type-II fibres were tentatively identified, by exclusion, as cholinergic.

Evidence for vasoactive intestinal polypeptide as a neurotransmitter in smooth muscle of the urogenital tract

The localization of vasoactive intestinal polypeptide (VIP) in the anococcygeus muscle of the rat, rabbit and cat was investigated by radioimmunoassay and immunohistochemistry. High concentrations of VIP-like immunoreactivity were found in the anococcygeus muscle of all 3 species. VIP-like immunoreactivity was observed in a network of nerve fibres branching throughout the muscle which were unaffected by treatment with 6-hydroxydopamine. VIP, when applied exogenously to isolated preparations of the anococcygeus, produced dose-related relaxations of tone in all 3 species with a time course and maximum response similar to non-adrenergic, non-cholinergic inhibitory nerve stimulation. These observations provide further evidence in support of VIP as a suitable candidate for the non-adrenergic, non-cholinergic inhibitory neurotransmitter in the anococcygeus muscle.

Neural coordination of excitation of ferret trachealis muscle

The distribution of junction potentials and synaptic potentials to muscle cells and ganglion cells in the ferret trachealis muscle-nerve plexus preparation was studied with local electrical stimulation of branches of the laryngeal nerve or the interganglionic nerve trunk. Stimulations evoked excitatory junction potentials in muscle cells and fast excitatory postsynaptic potentials in ganglion (AH) cells located throughout the preparation, regardless of the location of the stimulating electrode. Evoked excitatory junction potentials were nearly simultaneous in widely separated muscle cells, suggesting that excitation of different muscle cells is coordinated. The apparent conduction velocity to muscle cells after a local nerve stimulation was 0.1-0.2 m/s. Dissemination of input to ganglion cells and muscle cells was dependent on the integrity of the interganglionic nerve trunk. There was evidence based on analysis of conduction velocities that coupling of electrical activity in different AH ganglion cells and muscle cells was related to the following: 1) an interlacing arrangement of myelinated preganglionic neurons that enter the plexus from multiple branches of the laryngeal nerve, and 2) interlacing neural circuits characterized by synapses between neurons whose cell bodies lie in different ganglia.

Ultrastructure of vesicourethral innervation. II. Postganglionic axoaxonal synapses in intrinsic innervation of the vesicourethral lissosphincter: a new structural and functional concept in micturition

The interrelationships of postganglionic axons in intrinsic neuroplexuses of the vesicourethral lissosphincter ('internal sphincter') were studied ultrastructurally in the cat and rat of both sexes. Direct axoaxonal contracts between cholinergic and adrenergic axons were common in preterminal axon bundles and at neuroeffector junctions. Similar contacts between 2 cholinergic or 2 adrenergic axons were less frequent. Most contacts were ultrastructurally simple, but some had focal areas of very close axolemmal apposition, and some were focally specialized as bona fide chemical synaptic complexes. The axoaxonal contacts are introduced as a complex interaxonal synaptic system that chemically, and possibly also electrically, modulates neurotransmission in postganglionic axons innervating the lissosphincter, presynaptically (prejunctionally) at the infraganglionic level, especially by reciprocal cholinergic/adrenergic axonal interaction. This synaptic system is introduced as a potential, hitherto unrecognized, site of action of autonomic drugs, and as a key factor in the neural mechanism controlling continent closure of the lissosphincter during bladder filling, its opening to initiate and maintain voiding, and its closure to terminate the micturition cycle.

Ultrastructure of vesicourethral innervation. I. Neuroeffector and cell junctions in the male internal sphincter

The ultrastructure of neuroeffector and cell junctions in smooth muscle of the internal sphincter was studied in the male cat and rat. Muscle cells of the sphincter have the same features of smooth muscle elsewhere, with frequent adherens-type junctions. Neuroeffector junctions are established with sphincter muscle cells by cholinergic and/or adrenergic axons, which probably are not distributed on a 1:1 nerve:muscle basis. The neuroeffector junctions are classified according to their cleft width, their overall morphology, the functional class of their axonal component, and the number of axonal and muscle cell elements involved. These observations unequivocally confirm the principle of dual cholinergic-adrenergic control of the male internal sphincter, and indicate that its mechanism of neuromuscular transmission is both direct via neuroeffector and indirect via muscle cell junctions.

Ultrastructural features of the innervation and smooth muscle of the rabbit facial vein, and their relationship to function

The purpose of this study was to determine to what extent the ultrastructure of the intramedial plexus of autonomic nerves and the smooth muscle of the rabbit facial vein could be correlated with the functional properties of this vessel. The mean observed widths of neuromuscular clefts were 250 nm in untreated control vessels, 260 in the dilated vein, and 390 in the contracted vein. Variation in the plane of section and in cell surface contours may lead to overestimation of cleft width, particularly in contracted vessels; the conclusion was reached, therefore, that the actual mean cleft width in this vessel, which may be closer to 200 nm, is relatively narrow in comparison with other blood vessels. There is probably little significant variation in cleft width with changes in vessel diameter. This narrow cleft correlates with the pronounced neurogenic response of this vessel. The smooth muscle cells of the facial vein appear to contain a relatively small amount of sarcoplasmic reticulum, which may be related to the dependence of maintained tone on extracellular calcium. Areas of close apposition of cell surfaces, with gaps of approximately 15 nm, may be related to propagation of electrical activity from one smooth muscle cell to another.

Nerve endings in human sympathetic ganglia

Forty-eight human sympathetic ganglia from 22 sympathectomies were examined ultrastructurally after one of three different fixations: (1) glutaraldehyde + osmium tetroxide, (2) glutaraldehyde + potassium dichromate + osmium tetroxide, or (3) potassium permanganate. Three different kinds of synapsing nerve ending could be identified after all fixation schedules. Type 1: "Cholinergic," containing small, agranular vesicles 40-60 nm in diameter (75% of all vesicles) and some large granular vesicles (100 nm in diameter). The number of type 1 profiles decreased with increasing age. Type 2: "Adrenergic," containing small granular vesicles 40-70 nm in diameter (over 90% of the vesicles). Type 3: "Nonadrenergic, noncholinergic," characterized by large opaque vesicles 80 -160 nm in diameter (over 50% of all vesicles). The frequencies of the types were counted after potassium permanganate fixation: type 1 - 71%, type 2 - 23%, and type 3 - 6%. In addition, at least two types of nerve profiles were observed which did not form synapses: (1) profiles entirely filled with mitochondria (mitochondrial accumulation), and (2) large nerve profiles full of different kinds of vesicles, myelin figures, and mitochondria (axonal dilatation). It is concluded that the sympathetic ganglion cells receive cholinergic and adrenergic innervation and also a third type of innervation, the possible peptidergic nature of which is discussed.

Autonomic innervation of receptors and muscle fibres in cat skeletal muscle

Cat hindlimb muscles, deprived of their somatic innervation, have been examined with fluorescence and electron microscopy and in teased, silver preparations; normal diaphragm muscles have been examined with electron microscopy only. An autonomic innervation was found to be supplied to both intra- and extrafusal muscle fibres. It is not present in all muscle spindles and is not supplied at all to tendon organs. Fluorescence microscopy revealed a noradrenergic innervation distributed to extrafusal muscle fibres and some spindles. On the basis of the vesicle content of varicosities the extrafusal innervation was identified as noradrenergic (32 axons traced), and the spindle innervation as involving noradrenergic, cholinergic and non-adrenergic axons (14 traced). Some of the noradrenergic axons that innervate spindles and extrafusal muscle fibres are branches of axons that also innervate blood vessels. We cannot say whether there are any noradrenergic axons that are exclusively distributed to intra- or extrafusal muscle fibres. The varicosities themselves may be in neuroeffective association with striated muscle fibres only, or with both striated fibres and the smooth muscle cells in the walls of blood vessels. The functional implications of this direct autonomic innervation of muscle spindles and skeletal muscle fibres are discussed and past work on the subject is evaluated.

Pathophysiology of migraine: a new hypothesis

Cerebral blood flow is thought to decrease during the preheadache phase of migraine and increase during the headache phase. Most investigations of the pathophysiology of migraine have been concerned with the factors that trigger the preheadache phase. The present hypothesis proposes that, regardless of the triggering factors associated with vasospasm, this will be followed by a common event--namely, reactive hyperaemia due to hypoxia. It is suggested that adenosine triphosphate (ATP), perhaps released from "purinergic" nerves, and its breakdown products adenosine monophosphate (AMP) and adenosine are strong contenders for agents mediating this vasodilatation. ATP is a potent dilator of cerebral vessels and its breakdown products are also dilators. High concentrations of AMP and adenosine have been collected in cerebrospinal fluid during vasodilatation following ischaemia or hypoxia. The presence of ATP and its breakdown products could also explain pain in migraine. These substances stimulate primary afferent nerve terminals in the skin and produce pain in human skin blisters; and nerve profiles that resemble afferent terminals in their ultrastructure have been described in the adventitia of cerebral arteries and in the subarachnoid meshwork. The asymmetrical nature of migraine headaches, the changes in platelet aggregation, and the responses to several therapeutic procedures are consistent with this hypothesis. Some analogues of ATP might have beneficial effects on migraine headache.

Effects of ovarian steroids and pregnancy on adrenergic nerves of uterus and oviduct

This review concerns the influence of ovarian steroids and of pregnancy on norepinephrine (NE) metabolism in the adrenergic neurons of the female reproductive tract and speculates on the physiological consequences of this influence. Estrogen and progesterone affect not only the NE content of these nerves but also the turnover of NE, the activity of its synthetic enzyme, and releases of NE from nerve terminals. During pregnancy additional factors including stretch-induced hypertrophy come into play and cause degeneration of the nerves in the uterine corpus. This degeneration makes the muscle supersensitive to NE and may also induce morphological changes in the muscle cell membrane. As a result there may be a withdrawal of neural inhibitory influences on the corpus, allowing spontaneous myogenic contractions to intensify. Although the physiological significance of the steroid-transmitter interactions are still unclear, these nerves per se are of interest because they represent a model system for the study of neuroendocrine regulation in the peripheral nervous system.

Alteration of electrophysiological properties of airway smooth muscle from sensitized guinea-pigs

Glass microelectrodes were used to study electrophysiological properties of guinea-pig airway smooth muscle (m. trachealis transversus). The resting membrane potential (Em) of airway smooth muscle was found to be -40.4 +/- 0.5 mV (307 cells, 28 preparations). Twenty-seven percent of all cells successfully impaled showed regular spontaneous electrical activity (amplitude of 2-20 mV, with maximum rate of depolarization 15.0 +/- 2.2 mV . sec-1). Forty-four percent of cells showed irregular fluctuations in Em and the remaining cells showed no electrical activity. All three groups of cells had a similar distribution of individual Em values. The sensitization of animals (14 days incubation period) caused a slight but significant increase (P less than 0.001) in Em to -43.1 +/- 0.9 mV. Repeated daily exposure of sensitized animals to aerosolized albumin for two weeks caused a significant reduction of Em to -27.8 +/- 0.8 mV (P less than 0.001). Five weeks repeated exposure caused a further reduction in Em of airway smooth muscle cells to -22.6 +/- 0.7 mV (P less than 0.001). The responses to both histamine (10(-4) M) and isoprenaline (5 x 10(-6) M), as gauged by changes in Em, were altered in the trachea of chronically exposed guinea-pigs. The changes in airway smooth muscle electrical properties were related to the number of times the animals were exposed to inhaled antigen. Even after two weeks of daily exposure, the changes were marked. Airway smooth muscle alteration may be important in the pathogenesis of bronchial asthma.

Nerve endings in the human prostate

The ultrastructure of nerve endings in the human prostate was studied using glutaraldehyde-OsO4 and KMnO4 fixation. The nerve endings were classified into three categories according to the size of the vesicles and the contents of the synaptic profiles. In addition to the conventional adrenergic and cholinergic axons, a third type of axon profile containing a predominance of large granular vesicles was constantly found. Synaptic contacts were found only on smooth muscle cells. No epithelial innervation could be demonstrated. The functions and possible transmitters of the various types of axon terminals are discussed.

Reinnervation following guanethidine-induced sympathectomy of adult rats

The reinnervation of various tissues by autonomic neurons has been studied in adult rats which had been sympathectomized by chronic guanethidine treatment (30 or 60 mg/kg/day for 8--15 weeks). In the heart, iris, ileum, mesentery, vas deferens and epididymis, fluorescence histochemistry reveals an almost complete disappearance of adrenergic fibres which is very longlasting. Even after 63 weeks few fluorescent fibres can be seen in these tissues and the density of innervation is not increased by incubation in alpha-methylnoradrenaline. The superior cervical ganglion represents an exception; large numbers of fluorescent fibres but few fluorescent ganglion cells were apparent during recovery. Axon counts carried out by electron microscopy on the vas deferens showed that after recovery for one year the number of axons was similar to that of controls; however, the pattern of innervation was abnormal, small granular vesicles were rarely seen and there was little uptake of 5-hydroxydopamine. On the basis of this evidence and of some pharmacological data it is suggested that there is a limited reinnervation by adrenergic axons accompanied by a great increase in the number of non-adrenergic, possibly cholinergic, axons.

Types of nerve terminals in fetal and neonatal rabbit myocardium

With the use of electron microscopy 4 types of axonal profiles were observed in the developing myocardium of rabbits: 1) adrenergic axons which contained mainly small dense-core vesicles and which presumably can store 5-hydroxy-dopamine; 2) cholinergic axons which contained small clear synaptic vesicles and which were acetylcholinesterase-positive; 3) axons which contained large vesicles filled with moderately electron-dense material and which resembled purinergic axons; and 4) profiles filled with mitochondria, vesicles of various sizes, lysosome-like bodies, and microtubules and which resembled sensory terminals.

Autonomic neuroeffector junctions--reflex vasodilatation of the skin

A general model of the autonomic neuroeffector junction is proposed. In this model, emphasis is placed on the muscle effector bundle with electrotonic coupling between individual cells via gap junctions (or nexuses) and en passage release of transmitter from autonomic nerve varicosities. This release results in transmission to effector cells across junctional clefts ranging from about 20 nm in the vas deferens and iris to as much as 2000 nm in some large arteries. The ultrastructural identification of different autonomic nerve types is described. Current theories on the synthesis, storage, release, and inactivation of transmitter during cholinergic, adrenergic, and purinergic transmission are summarized. Some speculations are made about the possible involvement of purinergic nerves in the innervation of vessels and mast cells in the skin, and whether this involvement results in a functional link between ATP, histamine, bradykinin, and prostaglandin in cutaneous vasodilatation. Another possibility considered as the basis for this reflex is the release of substance P from sensory (pain) nerve collaterals in the skin.

Electron microscopy of adrenergic, cholinergic, and "p-type" nerves in the myometrium and a special kind of synaptic contacts with smooth muscle cells

In the cat uterus, three types of axons have been indentified by electron microscopy on the basis of the appearance of the synaptic vesicles in the axon varicosities following treatment with 5-hydroxydopamine: (1) most axons were adrenergic, with numerous small osmiophilic vesicles of a diameter of approximately 50 nm. together with large (100 to 150 nm. in diameter) granules, (2) some axons contained only empty small granules together with the large granules; these are probably cholinergic, and (3) a small number of the axon varicosities had only large-sized vesicles with a moderately electron-dense content. They are interpreted as a polypeptide type of nerves ("p-terminals"). Close appositions at a distance of 25 nm. were sometimes found between the varicosities. A specialized neuromuscular connection was found: the muscle cells at "the end" of muscle bundles extended small stout processes, containing numerous myofilaments, onto a small nerve bundle, the distance being 20 to 25 nm.

Anatomical studies of simple invertebrate synapses utilizing stage rotation election microscopy and densitometry

The radial nerve cords of starfish and the central ganglia of a gastropod mollusc were examined for the presence of chemical synapses. No structures with the degree of specialization of synapses in the vertebrate CNS were observed. Presumed chemical synapses, which possessed slight but variable paramembrane densities, were examined with a tilting stage. This showed that such densities were frequently due to overlap of vesicle and axon membrane within the section, which were resolved at the correct angle of tilt. Many structures resembled demonosomes. The necessity for care in interpreting the structure of chemical synapses in vertebrates is emphasized.

Fluorescence histochemical and electron-microscopical observations on the innervation of the atrial myocardium of the adult human heart

The existence of both adrenergic and cholinergic innervation of the atrial myocardium of the adult human heart was demonstrated by means of fluorescence induced by formaldehyde or glyoxylic acid and by electron microscopy. The adrenergic fluorescing axons (1) followed the course of blood vessels as typical perivascular nerve plexuses, and (2) formed a three-dimensional fairly dense nerve net obviously not related to the blood vessels. The varicosities frequently came into close apposition on myocardial cells. Several types of nerve terminals were differentiated at electron microscopy: (1) an "adrenergic" type containing small (diameter 450-700 A) dense-cored vesicles and usually (in various proportions) small "empty" and/or large (900-1500 A) dense-cored vesicles, (2) a "cholinergic" type containing small (ca. 500 A) "empty" vesicles and occasionally also some large (mean diameter ca. 1200 A) dense-cored vesicles, (3) a "pale" type containing only a few or no vesicles, (4) a "disintegrated" type containing degenerated mitochondria, autophagic vacuoles, and occasional normal-looking mitochondria, (5) nerve terminals containing a large number of mitochondria in addition to varying vesicle populations, and (6) a (possibly baroreceptive type of) nerve terminal containing myelinlike lamellated structures. The "disintegrated" and the "pale" types of nerve terminals possibly represent different stages of axonal degeneration, or may correspond to diminution in the transmitter substance concentration under certain pathophysiologic conditions, respectively. Nerve terminals crowded with mitochondria may be sensory and involved in mechano-or chemoreceptive functions. In preliminary experiments convincing evidence was obtained that the glyoxylic acid-induced fluorescence histochemical method will be suitable for comparative studies on (human) clinical specimens, e.g., for analyzing the degree of the functional activity of the intrinsic adrenergic innervation of the myocardium under various pathophysiologic conditions. The modification which appeared most appropriate for such studies is described in detail, and is proposed for use as a standard method in other similar or related studies on human clinical series. The essential criteria for analyzing the specimens at fluorescence microscopy are suggested as well.

The altrastructure of Auerbach's plexus in the guinea-pig. I. Neuronal elements

The ultrastructural features of nerve cell bodies and axon profiles within Auerbach's plexus in the stomach, ileum, caecum and colon of the guinea-pig have been examined. Nerve cell bodies have been tentatively classified into nine different types according to their size, distribution of organelles, location and relationship to satellite cells. Except for cell size, no attempt has been made to correlate ultrastructual with light microscopical observations. On the basis of vesicular size, shape and content, eight morphologically distinct types of axon profile have been identified as well as two profile types which are thought to reflect different physiological conditions. The axons contained various populations of small, mostly granular vesicles; small, round agranular vesicles; small, flattened vesicles; large flattened or elongated vesicles; and three types of large vesicle with granular contents distinguished by size. Some correlation between types of axon profile and two types of nerve cell body was recognized. However, more than one type of axon profile usually formed synapses with one type of cell body, and a precise correlation was not determined.

Comparative studies of purinergic nerves

Purinergic nerves supply the gastrointestinal tract of vertebrates, including fish, amphibians, reptiles and birds, as well as mammals. Their cell bodies are located in Auerbach's plexus and their axons extend in an anal direction before innervating mainly the circular muscle coat. In the stomach they are controlled by preganglionic cholinergic fibres of parasympathetic origin. They are involved in "receptive relaxation" of the stomach, "descending inhibition" in peristalsis and reflex relaxation of oesophageal and internal anal sphincters. The terminal varicosities of purinergic nerves are characterised by a predominance of "large opaque vesicles," which can be distinguished from the "large granular vesicles" found in small numbers in both adrenergic and cholinergic nerves. Stimulation of purinergic nerves with single pulses produces hyperpolarisations of up to 25 mV (inhibitory junction potentials) in smooth muscle cells. These potentials are unaffected by atropine, adrenergic neuron blocking agents or sympathetic denervation, but are abolished by tetrodotoxin. The "rebound contraction" which characteristically follows cessation of purinergic nerve stimulation is probably due to prostaglandin. Evidence that ATP is the transmitter released from purinergic nerves includes: (1) synthesis and storage of ATP in nerves; (2) release of ATP from the nerves when they are stimulated; (3) exogenously applied ATP mimicking the action of nerve-released transmitter, both producing a specific increase in K+ conductance; (4) the presence of Mg-activated ATPase, 5'-nucleotidase and adenosine deaminase, enzymes which inactivate ATP; (5) drugs (including quinidine, some 2-substituted imidazolines, 2-2'pyridylisatogen and dipyridamole) which produce similar blocking or potentiating effects on the response to exogenously applied ATP and nerve stimulation. Speculations are made about the evolution and development of the nervous system, including the possibility that purinergic nerves are a primitive nerve type.

Reciprocal synapses between cholinergic axons and small granule-containing cells in the rat cardiac ganglion

Electron microscopy of the rat cardiac ganglion shows occurrence of small granule-containing cells that form reciprocal synaptic junctions with cholinergic terminals. At the synaptic junctions which are from axon to granule-containing cell, the intraaxonal vesicles are clustered against the junctional axolemma, but dense-cored vesicles in the postsynaptic cell do not cluster towards the membrane densities in these synapses. By contrast, the synaptic zone polarized in the opposite direction shows an absence of axonal vesicles in close proximity to the postsynaptic axolemma, but there is a marked aggregation of dense-cored vesicles towards the presynaptic specializations of granule-containing cells. The synaptic zones are multifocal rather than bifocal, and the minimal distance separating each synaptic zone is about 0.3 mu. These findings may indicate that cholinergic excitation of some or all granule-containing cells causes a reciprocal inhibition of one or more cholinergic terminals.