Axonal transport of adrenaline, noradrenaline and phenylethanolamine-N-methyl transferase (PNMT) in sympathetic neurons of the cod, Gadus morhua

Immunolocalization of neurotransmitter-synthesizing enzymes and neuropeptides with associated receptors in the photophores of the hatchetfish, Argyropelecus hemigymnus Cocco, 1829

Anatomical and functional studies of the autonomic innervation of the photophores of luminescent fishes are scarce. The present immunohistochemical study demonstrated the presence of nerve fibers in the luminous epithelium and lens epithelium of the photophores of the hatchet fish, Argyropelecus hemigymnus and identified the immunoreactive elements of this innervation. Phenylethanolanine N-methyltransferase (PNMT) and catecholamine (CA)-synthesizing enzymes were detected in nerve varicosities inside the two epithelia. Neuropeptides were localized in neuropeptide Y (NPY) and substance P (SP)- and its NK11 receptor-immunopositive nerves in the lens epithelium. Neuropeptides were also localized in non-neural cell types such as the lens cells, which displayed immunoreactivities for pituitary adenylate cyclase activating peptide (PACAP) and their receptors R-12 and 93093-3. This reflects the ability of the neuropeptide-containing nerves and lens cells to turn on and off the expression of selected messengers. It appears that the neuropeptide-containing nerves demonstrated in this study may be sensory. Furthermore, neuronal nitric oxide synthase-immunopositive axons associated with photocytes in the luminous epithelium have previously been described in this species. Whereas it is clear that the photophores receive efferent (motor) fibers of spinal sympathetic origin, the origin of the neuropeptide sensory innervation remains to be determined. The functional roles of the above neuropeptides or their effects on the bioluminescence or the chemical nature of the terminals, either sensory or postganglionic neurons innervating the photophores, are still not known.

The autonomic nervous system and chromaffin tissue: neuroendocrine regulation of catecholamine secretion in non-mammalian vertebrates

If severe enough, periods of acute stress in animals may be associated with the release of catecholamine hormones (noradrenaline and adrenaline) into the circulation; a response termed the acute humoral adrenergic stress response. The release of catecholamines from the sites of storage, the chromaffin cells, is under neuroendocrine control, the complexity of which appears to increase through phylogeny. In the agnathans, the earliest branching vertebrates, the chromaffin cells which are localized predominantly within the heart, lack neuronal innervation and thus catecholamine secretion in these animals is initiated solely by humoral mechanisms. In the more advanced teleost fish, the chromaffin cells are largely confined to the walls of the posterior cardinal vein at the level of the head kidney where they are intermingled with the steroidogenic interrenal cells. Catecholamine secretion from teleost chromaffin cells is regulated by a host of cholinergic and non-cholinergic pathways that ensure sufficient redundancy and flexibility in the secretion process to permit synchronized responses to a myriad of stressors. The complexity of catecholamine secretion control mechanisms continues through the amphibians, reptiles and birds although neural (cholinergic) regulation may become increasingly important in birds. Discrete adrenal glands are present in the non-mammalian tetrapods but unlike in mammals, there is no clear division of a steroidogenic cortex and a chromaffin cell enriched medulla. However, in all groups, there is an obvious intermingling of chromaffin and steroiodogenic cells. The association of the two cell types may be particularly important in the amphibians and birds because like in mammals, the enzyme catalysing the methylation of noradrenaline to adrenaline, PNMT, is under the control of the steroid cortisol.

Cold-stable and cold-adapted microtubules

Most mammalian microtubules disassemble at low temperature, but some are cold stable. This probably has little to do with a need for cold-stable microtubules, but reflects that certain populations of microtubules must be stabilized for specific functions. There are several routes by which to achieve cold stability. Factors that interact with microtubules, such as microtubule-associated proteins, STOPs (stable tubule only polypeptides), histones, and possibly capping factors, are involved. Specific tubulin isotypes and posttranslational modifications might also be of importance. More permanent stable microtubules can be achieved by bundling factors, associations to membranes, as well as by assembly of microtubule doublets and triplets. This is, however, not the explanation for cold adaptation of microtubules from poikilothermic animals, that is, animals that must have all their microtubules adapted to low temperatures. All evidence so far suggests that cold adaptation is intrinsic to the tubulins, but it is unknown whether it depends on different amino acid sequences or posttranslational modifications.

Galanin-like immunoreactivity in extrinsic and intrinsic nerves to the gut of the Atlantic cod, Gadus morhua, and the effect of galanin on the smooth muscle of the gut

The presence of galanin-like immunoreactivity in nerves to the stomach of the Atlantic cod has been investigated by immunohistochemistry. The distribution of ganglion cells showing galanin-like immunoreactivity was compared with the total distribution in nerves and ganglia. Projection studies were made to determine the origin of the galanin neurons. The effect of galanin was studied in smooth muscle strip preparations of the gut wall and arteries. Galanin-like immunoreactive ganglion cells frequently occurred along the vagal branches to the stomach. Most of them projected cranially. Immunoreactive nerve fibers were present in all layers of the gut and around arterial branches on the surface of the stomach. Ligations of the vagus and splanchnic nerves produced accumulations of immunoreactive material on both sides of the ligature. Galanin produced weak contractile effects unaffected by tetrodotoxin on the gut wall and on gut arteries. It is concluded that a population of the ganglion cells along the vagus nerve in the Atlantic cod contains a galanin-like peptide. Some of these cells may be parts of autonomic parasympathetic pathways innervating the gut of the Atlantic cod, having direct excitatory effects on the smooth muscles of the gut wall and gut arteries.

Uptake and release of [3H]-serotonin in photophores of the midshipman fish, Porichthys notatus

A kinetic analysis of [3H]-5-HT uptake in the photocytes of the photophores of Porichthys notatus revealed a high affinity (Km: 1.71 X 10(-7] and low affinity component (Km: 1.10 X 10(-5) M). The high affinity uptake was sodium- and potassium-dependent but largely insensitive to temperatures between 0 and 20 C. Ouabain (5 X 10(-3) M) and dinitrophenol (10(-3) M) reduced uptake significantly. DMI, imipramine and fluoxetine, in that order of potency, greatly inhibited [3H]-5-HT uptake. Noradrenaline and adrenaline reduced uptake in a non-competitive manner, while dopamine, tryptophan, 5-hydroxytryptophan and Cypridina luciferin had little or not effect on uptake. Non-facilitated luminescent responses to electrical stimulation were accompanied by release of [3H]-5-HT accumulated in the photocytes. Facilitatory luminescence excitation consistently failed to induce the release of [3H]-5-HT. Electrical and adrenaline (10(-5) M) stimulation of photophores after [3H]-5-HT release has occurred, failed to elicit any additional luminescent response. The photophores were responsive to KCN (10(-3) M) under these conditions. The results indicate that a specific carrier-mediated transport system is responsible for photocytic [3H]-5-HT uptake, and that release of photocytic [3H]-5-HT is stringently regulated and followed by inhibition of luminescence excitability.

Activity of tyrosine hydroxylase (EC 1.14.16.2) from chromaffin and nervous tissue of the Atlantic cod, Gadus morhua

1. The activity of tyrosine hydroxylase (TH; EC 1.14.16.2) was estimated in vitro in crude tissue homogenates from the posterior cardinal veins (chromaffin tissue) and the coeliac ganglion (adrenergic neurons) of the Atlantic cod, Gadus morhua. 2. TH from the chromaffin tissue showed its highest activity at pH = 6.0 and a temperature of 30-35 degrees C, and was stimulated by low concentrations of catalase (20 micrograms/ml). 3. Estimations of the absolute TH activity in vitro showed values of 110 +/- 30 nmol/g X hr for the chromaffin tissue and 1120 +/- 280 nmol/g X hr for the coeliac ganglion.

Neuropharmacology of adrenergic neurons in teleost fish

Although this brief review is based on relatively few types of experiments in few species of teleosts, it is possible to summarize some points of interest regarding the similarities and differences in the mechanisms of adrenergic neurotransmission in fish compared to the higher vertebrates. 1. There is a substantial mixing of cranial autonomic ("parasympathetic") and spinal autonomic ("sympathetic") pathways in the cranial nerves. This close relationship between the two systems and the differences in the nature of the neurons of cranial origin (cholinergic, and non-adrenergic, non-cholinergic) and spinal origin (adrenergic, cholinergic and mixed "polynergic") gives a basis in fish also for a complex pattern of innervation of the various organs. 2. Adrenaline is the major transmitter substance in the adrenergic neurons of most teleosts studied, but there are exceptions within the same species. For instance, in the swimbladder mucosa of the cod, noradrenaline dominates, while adrenaline is the major catecholamine in most other organs innervated by adrenergic neurons. The reasons for the regional differences are not known and further studies of the rate of catecholamine turn-over in the adrenergic neurons of fish are clearly indicated. 3. Adrenoceptors of both the alpha- and the beta-type show great similarities with those of mammals. Some differences in the potencies of certain compounds (e.g., clonidine and methoxamine) exist and receptor binding studies should add valuable information about the adrenoceptors of teleosts. The existence of a subtype of beta-adrenoceptor (beta 2) has been proposed and further work is needed to confirm or deny the applicability of the beta 1/beta 2 adrenoceptor terminology in fish. 4. There appears to be some differences in the mode of action of the so called "indirectly acting amines", such as tyramine, between teleosts and mammals. While the uptake of tyramine into the nerve terminals in mammals appears to take place via the cocaine-sensitive neuronal uptake system which is also responsible for catecholamine uptake (uptake 1), tyramine uptake in cod neurons appears to be via a separate pathway. 5. Presynaptic supersensitivity of the type seen in mammals has also been demonstrated in teleost adrenergic neurons. Both denervation (chemical or surgical) and blockade of the neuronal uptake mechanism by cocaine or desipramine produce this type of supersensitivity, while post-synaptic supersensitivity has so far not been described in teleosts. The effects of removal of the uptake system shows that the uptake process may be as important in teleosts as in mammals in the removal of adrenergic transmitter from the synaptic cleft. 6. In the total picture of adrenergic functions in fish, the circulating catecholamines take a special role...

Axonal transport and subcellular distribution of dopamine-beta-hydroxylase in the cod, Gadus morhua

The axonal transport of dopamine-beta-hydroxylase (DBH; E.C. 1.14.17.1) was studied in the splanchnic nerve of the cod in vivo, and the subcellular localization of the same enzyme was studied in the chromaffin tissue from the cod head kidney. The mean rate of axonal transport for cod DBH was 18.6 mm/24 h at 10 degrees C. The mobile fraction was estimated to 22%, giving an absolute rate of transport of 85 mm/24 h at 10 degrees C. Evidence for a retrograde transport of DBH was also obtained, with an accumulation distal to a ligature of 12% of the accumulation proximal to the ligature at 3 days. DBH from the chromaffin tissue appeared to be strongly bound to the adrenergic granules, with only a small amount (ca 4%) recovered in the soluble phase.

Activity of dopamine-beta-hydroxylase (DBH) and phenylethanolamine-N-methyl transferase (PNMT) in heart, lung and chromaffin tissue from the Florida spotted gar Lepisosteus platyrhincus (Holostei)

The activities of dopamine-beta-hydroxylase (DBH; E.C. 1.14.17.1) and phenylethanolamine-N-methyl transferase (PNMT; E.C. 2.1.1.10) were estimated in homogenates from the heart, the lung and the posterior cardinal veins from Lepisosteus platyrhincus. Both enzymes could be detected in all three tissues, the activity being highest in the chromaffin tissue of the posterior cardinal veins. The activity of DBH estimated in the present in vitro experiments was about 100-fold higher than the PNMT activity. Preliminary experiments with substrate specificity for the PNMT shows a low (heart) or undetectable (lung and cardinal veins) methylation of phenylethylamine, and the specific PNMT inhibitor SK&F 64139 (1 micro M) lowered the PNMT activity in all three tissues by 55-75%. The presence of PNMT in the adrenergically innervated tissues puts Lepisosteus with the teleosts and the amphibians among vertebrates with capacity for truly adrenergic, as opposed to noradrenergic, transmission.

Reflex adrenergic inhibition of gastric motility by nociceptive intestinal stimulation and peritoneal irritation in the cat

The effects on gastric motility of nociceptive stimulation to jejunum and colon were studied in vagotomized anesthetized cats. Mechanical nociceptive stimulation and diathermy of the jejunum and proximal colon elicited reflex gastric inhibition that was significantly more pronounced than that obtained by stimulation of distal colon. Similarly differentiated reflex responses were induced by electric afferent stimulation of nerves from the respective intestinal segments. Strong nociceptive stimuli from the abdominal cavity, induced by peritonitis, completely blocked vagal excitatory influences on gastric motility, as did multiple nerve stimulation. The gastric inhibitory response to abdominal irritation persisted after adrenalectomy but was eliminated during spinal anesthesia or adrenergic blockade. During gastric suppression in animals with abdominal peritonitis cholinergic potentiation with synstigmin administration could only modestly increase gastric tone. It is concluded that intestinal nociceptive stimulation causes gastric inhibition via sympathetic reflex arches that are segmentally differentiated. These adrenergically mediated inhibitory reflexes are powerful enough to block completely myenteric cholinergic neurons. The results suggest that adrenergic blockade or spinal anesthesia is the logical procedure for treating postoperative adrenergic gastric inhibition. The presently studied sympatho-sympathetic adrenergic reflexes seem to work in synergism with sympatho-vagal nonadrenergic reflexes in suppressing gastric motility during paralytic ileus.

Spino-vagal nonadrenergic inhibition of gastric motility elicited by abdominal nociceptive stimulation in the cat

Reflex inhibition of gastric motility in response to intestinal nociception and afferent nerve stimulation was studied in anesthetized cats. Mechanical stimulation of the small and large intestines elicited marked gastric inhibition, which was imitated by direct electrical stimulation of mesenteric or splanchnic afferents. The reflex response was resistant to atropine, guanethidine, and adrenalectomy. Spinal cord transection at the cervical level or spinal anesthesia completely blocked the reflex, as did vagotomy or vagal cold blockade. Chemical peritoneal stimulation by hydrochloric acid induced long-lasting gastric inhibition, which was not blocked by antiadrenergic or anticholinergic drugs. This response was reduced, but not completely blocked by spinal anesthesia or spinal cord transection. It is concluded that various nociceptive intestinal stimuli suppress gastric motility via a spino-vagal reflex mechanism composed of spinal afferents in the sympathetic nerves, spinobulbar ascending pathways, and vagal nonadrenergic inhibitory fibers to the stomach. In addition, vago-vagal reflexes evidently contribute to the gastric suppression induced by diffuse peritoneal irritation. These two reflex mechanisms are suggested to be mainly responsible for postoperative gastric inhibition, together with sympatho-adrenergic reflexes.

Catecholamine synthesis in the chromaffin tissue of the African lungfish, Protopterus aethiopicus

The activities of dopamine-beta-hydroxylase (DBH, E.C. 1.14.17.1) and phenylethanol-N-methyl transferase (PNMT, E.C.1.1.1.10) were determined in tissue homogenates from the chromaffin tissue containing atrium and intercostal arteries from the African lungfish. Clearly measurable activities of DBH were found in both kinds of tissues, while PNMT activity was ascertained only in the intercostal arteries. The activity of DBH in the atrium indicates a possibility for local synthesis of the large amounts of catecholamines, especially noradrenaline, found in this tissue. Catecholamines synthetized in and released from the chromaffin tissues of Protopterus, may be of great importance for the adrenergic control in this animal in the absence of a well developed sympathetic nervous system.