Differential distribution of nerve terminals immunoreactive for substance P and cholecystokinin in the sympathetic preganglionic cell column of the filefish Stephanolepis cirrhifer

Confocal imaging of autonomic preganglionic neurons in the spinal cord of the caecilian Typhlonectes natans (Amphibia: Gymnophiona)

Little is known about the spinal sympathetic organization in the caecilian amphibians. We examined for the first time the location of sympathetic preganglionic neurons (SPNs) in the spinal cord using a panel of specific markers expressed in SPNs. The SPNs of anuran amphibians form two cell columns segregated mainly in the lateral and medial marginal areas of the central gray matter. In the caecilian Typhlonectes natans immunoreactivity for galanin and ChAT is found in most laterally arranged neurons lying in spinal segments 2-7. They are encircled by TH- and nNOS-immunoreactive nerve fibers. These neurons might project specifically to a population of adrenergic sympathetic postganglionic neurons in paravertebral ganglia and/or non-adrenergic sympathetic postganglionic neurons in the celiac ganglia. However the segmental restriction and target specificity of the neurons of the species studied are not known. As mucous and granular glands in the dermis may represent one of the peripheral targets of the adrenergic ganglion cells and reflect the prominent preganglionic cell columns, an immunohistochemical study was done also on these glands. Retrograde-tracing studies are, however, needed to study the segmental localization of the preganglionic neurons and their projections to the postganglionic neurons in sympathetic ganglia.

Complex innervation patterns of the conus arteriosus in the heart of the longnose gar, Lepisosteus osseus

Anatomical and functional studies of the autonomic innervation in the conus arteriosus of the garfishes are lacking. This study reveals that the conus arteriosus of the longnose gar is primarily myocardial in nature, but additionally, large numbers of smooth muscle cells are present in the subendocardium. A well-developed system of adrenergic, cholinergic, substance P (SP) and neuronal nitric oxide synthase (nNOS) positive nerve terminals are found in the wall of the conus arteriosus. Coronary blood vessels running in the adventitia receive a rich supply of nNOS positive nerve fibers, thus suggesting their importance in the nitrergic control of blood flow in the conus arteriosus. The present data show that the patterns of autonomic innervation of the garfish conus arteriosus are more complex than previously appreciated.

Nervous control of photophores in luminescent fishes

Functional studies of the autonomic innervation in the photophores of luminescent fishes are scarce. The majority of studies have involved either the stimulation of isolated photophores or the modulatory effects of adrenaline-induced light emission. The fish skin is a highly complex organ that performs a wide variety of physiological processes and receives extensive nervous innervations. The latter includes autonomic nerve fibers of spinal sympathetic origin having a secretomotor function. More recent evidence indicates that neuropeptide-containing nerve fibers, such as those that express tachykinin and its NK1 receptor, neuropeptide Y, or nitric oxide, may also play an important role in the nervous control of photophores. There is no anatomical evidence that shows that nNOS positive (nitrergic) neurons form a population distinct from the secretomotor neurons with perikarya in the sympathetic ganglia. The distribution and function of the nitrergic nerves in the luminous cells, however, is less clear. It is likely that the chemical properties of the sympathetic postganglionic neurons in the ganglia of luminescent fishes are target-specific, such as observed in mammals.

Postganglionic nerve cell bodies and neurotransmitter localization in the teleost heart

A study was undertaken to determine the distribution of specific types of autonomic nerves and the presence of various transmitter substances in the heart of two teleost species: the mullet (Mugil cephalus) and the Nile catfish (Synodontis nigriventris). Large nerve trunks in the sinus venosus were shown to contain tyrosine hydroxylase immunoreactivity and indicate the location of adrenergic nerve fibers, which are also associated with a coronary circulation to the ventricular myocardium in the mullet heart. Fluorescence immunolabelling methods revealed that the atrium and the outer and inner compact muscle of the ventricle have nerves in which substance P and galanin (GA) are localized. It seems likely that the cell bodies (perikarya) of the substance P and GA-immunopositive axons are located at sites outside the heart. The GA-immunopositive nerve fibers may represent a population of axons of intramural postganglionic nerve cell bodies. Most intracardiac nerve cell bodies are located in the sinus venosus and in the sinoatrial junction and reveal immunoreactivity to substance P, GA, neuronal nitric oxide synthase (nNOS), vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP). Furthermore, substance P immunoreactivity is present in the cardiac cells intermingled with the substance P-immunopositive nerve fibers. A nerve plexus consisting of a well-developed network of nerve fibers and nerve cell bodies may possibly correspond to a cardiac pacemaker, but its function in fish cardiac regulation is unknown and remains to be elucidated.

Distribution and neurotransmitter localization in the heart of the ray-finned fish, bichir (Polypterus bichir bichir Geoffroy St. Hilaire, 1802)

Anatomical and physiological studies of cardiovascular control are lacking in the ray-finned fish, the bichirs. The present immunohistochemical studies on the bichir (Polypterus bichir bichir) demonstrated the occurrence of intracardiac neurons and nerve fibers in the heart. Immunoreactivity to tyrosine hydroxylase (TH) and acetylcholinesterase (AchE) and various neuropeptides (substance P, galanin, vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP)), including neuronal nitric oxide synthase (nNOS), was found in the nerve cell bodies lying close to the Sinus venosus and the sino-atrial region. The main intracardiac localization of the nervous tissue is a network of nerve fibers, presumably corresponding to the postganglionic outflow giving rise to nerve terminals and the nerve cell bodies. In addition, the heart is innervated by extrinsic monoamine-containing nerve fibers supplying the Conus arteriosus and Sinus venosus, and substance P and galanin immunopositive fibers probably originating from cranial and spinal ganglia. The adrenergic innervation of the heart of the bichir is similar to that of the teleosts, but further studies are required on nervous control of the heart.

Innervation of lung and heart in the ray-finned fish, bichirs

Anatomical and functional studies of the autonomic innervation in the lung and the heart of the bichirs are lacking. The present review paper describes the presence of nerve fibers located in the muscle layers of the lung and its submucosa, the collection of unipolar neurons found in the submucosal and muscle layers of the glottis in a bichir species (Polypterus bichir bichir). Putative oxygen chemoreceptive, neuroepithelial cells (NECs) in the lung mucosa are also included. The latter share many immunohistochemical characteristics similar to those observed in the carotid body and neuroepithelial bodies of mammals. A packed collection of paraganglion cells is located within the trunk of the pulmonary vagus nerves. The paper also examines the occurrence of intracardiac neurons and nerve fibers in the heart of the above species. These studies show that various neurotransmitters may indicate different patterns of innervation in the lung and the heart of the bichirs. However, there is still much to be discovered about the lung and cardiovascular nervous control of these primitive fishes.

The Sympathetic Nervous System of Anamniotes

The sympathetic nervous system develops as an evolutionary trait with gnathostomes (jawed vertebrates), but not with agnathan fishes (i.e., hagfishes and lampreys). Organization of the sympathetic preganglionic neuronal columns is different in teleosts and anurans. In the teleosts so far examined, the majority of sympathetic preganglionic neurons (SPNs) are located in the dorsal part of the spinal central gray matter. In Tetraodontiformes, the cell column occupies only two rostral spinal segments, which are distinct in their cytoarchitecture and projections. On the other hand, the SPNs of anurans form two cell columns segregated mediolaterally. The lateral and medial columns are also distinct in their cytoarchitecture and projections. The neuroactive substances expressed in the SPNs both in teleosts and anurans are coded to the projections. In anurans, the SPNs containing gonadotrophin-releasing hormone and those containing calcitonin gene-related peptide are involved in the regulation of blood vessels and cutaneous glands, respectively. In the filefish, the SPNs containing galanin project specifically to non-adrenergic non-cholinergic postganglionic neurons in the cranial sympathetic ganglia. Therefore, both anuran and teleost systems have different morphological and chemical-coded patterns for functional variation, although the anuran sympathetic nervous system has more organizational similarity with that of amniotes.

Partial cloning and expression of mRNA coding choline acetyltransferase in the spinal cord of the goldfish, Carassius auratus

Choline acetyltransferase (ChAT, EC 2.3.1.6) synthesizes a neurotransmitter, acetylcholine in cholinergic neurons. ChAT is considered to be the most specific marker for cholinergic neurons. To obtain a better marker of the neurons, as the first step, we isolated a partial ChAT cDNA from the goldfish (Carassius auratus) brain by RT-PCR methods. The partial cDNA of the goldfish ChAT was composed of 718 nucleotides. The amino acid sequence of the goldfish ChAT is approximately 70% identical to those of mammalian and chicken ChAT. Northern blot analysis demonstrated that ChAT mRNA was expressed in the brain and the spinal cord of the goldfish, and much abundant in the spinal cord. In the spinal cord of the goldfish, ChAT-positive neurons were detected mainly in the ventral horn by in situ hybridization. In addition, fluorescence in situ hybridization combined with a retrograde labeling by using True Blue demonstrated ChAT mRNA positive neurons were exactly motoneurons. In the cord, putative presynaptic sympathetic neurons were also labeled.

Neuropeptides and the control of food intake in fish

The brain, particularly the hypothalamus, integrates input from factors that stimulate (orexigenic) and inhibit (anorexigenic) food intake. In fish, the identification of appetite regulators has been achieved by the use of both peptide injections followed by measurements of food intake, and by molecular cloning combined with gene expression studies. Neuropeptide Y (NPY) is the most potent orexigenic factor in fish. Other orexigenic peptides, orexin A and B and galanin, have been found to interact with NPY in the control of food intake in an interdependent and coordinated manner. On the other hand cholecystokinin (CCK), cocaine and amphetamine-regulated transcript (CART), and corticotropin-releasing factor (CRF) are potent anorexigenic factors in fish, the latter being involved in stress-related anorexia. CCK and CART have synergistic effects on food intake and modulate the actions of NPY and orexins. Although leptin has not yet been identified in fish, administration of mammalian leptin inhibits food intake in goldfish. Moreover, leptin induces CCK gene expression in the hypothalamus and its actions are mediated at least in part by CCK. Other orexigenic factors have been identified in teleost fish, including the agouti-related protein (AgRP) and ghrelin. Additional anorexigenic factors include bombesin (or gastrin-releasing peptide), alpha-melanocyte-stimulating hormone (alpha-MSH), tachykinins, and urotensin I. In goldfish, nutritional status can modify the expression of mRNAs encoding a number of these peptides, which provides further evidence for their roles as appetite regulators: (1) brain mRNA expression of CCK, CART, tachykinins, galanin, ghrelin, and NPY undergo peri-prandial variations; and (2) fasting increases the brain mRNA expression of NPY, AgRP, and ghrelin as well as serum ghrelin levels, and decreases the brain mRNA expression of tachykinins, CART, and CCK. This review will provide an overview of recent findings in this field.

Monoaminergic and peptidergic axonal projections to the vagal motor cell column of a teleost, the filefish Stephanolepis cirrhifer

In an immunohistochemical study, the vagal motor nucleus of a teleost, the filefish Stephanolepis cirrhifer, could be divided into a rostral part and a caudal part, and the former into a dorsolateral group and a ventromedial group. The dorsolateral group consisted of neurons immunoreactive for calcitonin gene-related peptide, whereas the ventrolateral-caudal group was negative for calcitonin gene-related peptide. The latter group was retrogradely labeled after dextran amine injection to the visceral ramus of the vagus nerve, suggesting that it is a general visceral efferent column, made up of parasympathetic preganglionic neurons, whereas the dorsolateral rostral group is a special visceral efferent column. In the general visceral efferent column, a dense concentration of nerve fibers immunoreactive for serotonin, tyrosine hydroxylase, cholecystokinin-8, and substance P, and a small number of fibers immunoreactive for neuropeptide Y was observed. Perikarya in contact with varicose terminals immunoreactive for these substances were frequently seen. In contrast, in the special visceral efferent column, only a moderate concentration of neuropeptide Y-immunoreactive nerve fibers and a sparse distribution of fibers immunoreactive for tyrosine hydroxylase were observed. Perikarya in contact with varicose terminals immunoreactive for these substances were rare. These results suggest that the vagal parasympathetic preganglionic neurons might receive multiple inputs of monoaminergic and peptidergic fibers involved in the regulation of the visceral organs. On the other hand, monoaminergic and peptidergic afferent fibers might be of much less significance in the activity of the special visceral efferent component of the vagus nerve.

Catecholaminergic innervation of the sympathetic preganglionic cell column of the filefish Stephanolepis cirrhifer

Nerve fibers immunoreactive for enzymes synthesizing catecholamines were examined in the central autonomic nucleus, a column of sympathetic preganglionic neurons, in the filefish Stephanolepis cirrhifer. Varicose nerve fibers immunoreactive for tyrosine hydroxylase were densely distributed in the rostral part, sometimes in contact with perikarya but were sparse in the caudal part of this nucleus. Fluorescent double labeling distinguished noradrenergic nerve fibers immunoreactive for both tyrosine hydroxylase and dopamine beta hydroxylase, and dopaminergic fibers immunoreactive only for tyrosine hydroxylase. In the brainstem, catecholaminergic neurons were observed in the locus coeruleus, the caudal dorsomedial reticular zone of the medulla, and the area postrema. Double labeling of tyrosine hydroxylase and dopamine beta hydroxylase showed that the neurons in the locus coeruleus were all noradrenergic, and those in the caudal dorsomedial medulla were mostly noradrenergic, whereas the area postrema contained both noradrenergic and dopaminergic neurons. No catecholaminergic neurons were found in the ventral region of the brainstem. After application of DiI to the central autonomic nucleus, retrogradely labeled neurons were seen in the caudal dorsomedial medulla but not in the locus coeruleus or the area postrema. These findings suggest that the sympathetic preganglionic neurons of the filefish may receive noradrenergic axonal projections from neurons in the caudal dorsomedial medulla. In the light of previous studies, inputs of these catecholaminergic fibers to the central autonomic nucleus may be involved in regulation of sympathetic activity of peripheral organs, together with serotoninergic and peptidergic inputs to this nucleus.

Selective projections of cholecystokinin-8 immunoreactive fibers to galanin immunoreactive sympathetic preganglionic neurons in a teleost, Stephanolepis cirrhifer

In the cellular column of sympathetic preganglionic neurons (SPNs) of the filefish Stephanolepis cirrhifer, neurons containing galanin (GAL) form a distinct population projecting specifically to non-adrenergic postganglionic neurons in the celiac and cranial sympathetic ganglia. The present study showed that virtually all of the GAL-immunopositive SPNs made contact with many nerve terminals immunopositive for cholecystokinin octapeptide (CCK-8). GAL-negative preganglionic neurons made contact with only 26% of this type of nerve terminal; CCK-8-immunopositive nerve fibers appeared to project selectively to GAL-immunopositive SPNs with projections to specific targets. The CCK-8-positive nerve fibers might be of primary sensory origin, and participate in the visceral reflexes.

Up-regulation of TNF-producing T cells in the bone marrow: a key mechanism by which estrogen deficiency induces bone loss in vivo

In vivo studies have shown T cells to be central to the mechanism by which estrogen deficiency induces bone loss, but the mechanism involved remains, in part, undefined. In vitro, T cells from ovariectomized mice produce increased amounts of tumor necrosis factor (TNF), which augments receptor activator of NF-kappa B ligand (RANKL)-induced osteoclastogenesis. However, both the mechanism and the relevance of this phenomenon in vivo remain to be established. In this study, we found that ovariectomy increased the number of bone marrow T cell-producing TNF without altering production of TNF per T cell. Attesting to the essential contribution of TNF, ovariectomy induced rapid bone loss in wild type (wt) mice but failed to do so in TNF-deficient (TNF(-/-)) mice. Furthermore, ovariectomy induced bone loss, which was absent in T cell-deficient nude mice, was restored by adoptive transfer of wt T cells, but not by reconstitution with T cells from TNF(-/-) mice. These findings demonstrate the key causal role of T cell-produced TNF in the bone loss after estrogen withdrawal. Finally, ovariectomy caused bone loss in wt mice and in mice lacking p75 TNF receptor but failed to do so in mice lacking the p55 TNF receptor. These findings demonstrate that enhanced T cell production of TNF resulting from increased bone marrow T cell number is a key mechanism by which estrogen deficiency induces bone loss in vivo. The data also demonstrate that the bone-wasting effect of TNF in vivo is mediated by the p55 TNF receptor.