Changes in enzyme patterns produced by high potassium concentration and dibutyryl cyclic AMP in organ cultures of sympathetic ganglia

Electroacupuncture Stimulation Regulates Adipose Lipolysis via Catecholamine Signaling Mediated by NLRP3 Suppression in Obese Rats

Chronic low-grade inflammation of visceral adipose tissue can cause obesity-associated insulin resistance, leading to metabolic syndrome. However, anti-inflammatory drugs and those for obesity management can lead to serious side effects such as abnormal heart rate and blood pressure. Consequently, this study aimed to explore the therapeutic potential of electroacupuncture stimulation (ES) for obesity and associated chronic inflammation. Sprague-Dawley male rats were fed a high-fat diet (HFD) for ten weeks to build an obesity model, and half of the diet-induced obesity (DIO) rats were received ES. The levels of inflammatory factors were detected by ELISA and qPCR analysis. The nerve-associated macrophages were marked with immunofluorescence staining. The molecular mechanism of NLRP3 inflammasome in ES was determined by the NLRP3 inflammasome activation model. Compared to HDF rats, ES showed decreased body weight and chronic inflammatory damage. Specifically, this occurred via a decrease in monoamine oxidase-A (MAOA) expression, which suppressed noradrenaline degradation. MAOA is expressed in nerve-associated macrophages (NAMs), and ES attenuated NAMs by suppressing the NLRP3 inflammasome. The NLRP3 agonist blocked the noradrenaline degradation-reducing effect of ES, and an increase in lipolysis via the inhibition of the NLRP3 inflammasome attenuated NAMs. Thus, our findings suggest that ES induced lipolysis via activation of the NLRP3 inflammasome in nerve-associated macrophages (NAMs), independently of sympathetic nervous system activity.

The cholinergic stimulating effects of ciliary neurotrophic factor and leukemia inhibitory factor are mediated by protein kinase C

The intracellular mechanisms through which two trophic factors, ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF), regulate cholinergic development were examined in sympathetic neuron cultures. Treatment with CNTF or LIF increased levels of choline acetyltransferase (ChAT) activity by 375 and 350%, respectively. However, in neuronal cultures depleted of protein kinase C (PKC) activity by chronic phorbol ester treatment, neither CNTF nor LIF elevated ChAT activity. Further, the stimulation of ChAT due to increased cell density was not observed in PKC-depleted sympathetic neurons. The inhibition of CNTF-stimulated ChAT by phorbol ester occurred in a dose-dependent manner and chronic phorbol ester treatments did not alter the levels of the catecholamine biosynthetic enzyme tyrosine hydroxylase. Moreover, increased levels of diacylglycerol, an endogenous activator of PKC, were observed in sympathetic neurons treated with CNTF. However, neither CNTF nor LIF stimulated the hydrolysis of phosphatidylinositol 4,5-bisphosphate. These observations suggest that a common PKC-dependent pathway, which is independent of phosphatidylinositol 4,5-bisphosphate hydrolysis, mediates the cholinergic stimulating effects of CNTF, LIF, and cell-cell contact in cultured sympathetic neurons.

Retrograde factors in peripheral nerves

The relationship between the neuron and its target is explored and the possible mechanisms for achieving correct connections are analysed. The most plausible mechanism is the presence of a retrograde intra-axonal message from the target to the neuronal cell body. The molecular form of the message and the mechanisms to achieve this signal transduction are discussed and it is proposed that there are two types of neurotrophic factors. One has a short-acting second messenger, itself incapable of surviving for the time required for transport to the cell body and thus requiring the transport of the message-generating complex to the cell body. The other has a long-lasting second messenger complex which is well able to survive the transport to the cell body so that there is no need for the transport of the neurotrophic factor itself. Thus all neurotrophic factors do not themselves require retrograde axonal transport and such non-transportable factors may generate intricate messages due to associations of signal transduction molecules via binding sites such as phosphorylated tyrosines and the src homology domain 2.

Regulation of neurotransmitter expression by a membrane-derived factor

Cell-cell contact appears to play a critical role in the expression of transmitter traits in developing neurons. We have previously shown that cell membrane contact induces the de novo appearance of choline acetyltransferase (CAT) in virtually pure cultures of dissociated sympathetic neurons. A membrane-associated CAT-inducing factor has been extracted and purified 5000-fold. This factor exerts differential effects on transmitter traits in cultured sympathetic neurons. After 3 days in vitro, neurons exposed to the factor contained 40-fold higher levels of the neuropeptide substance P than controls. Somatostatin exhibited a similar dramatic elevation. In contrast, the factor had no effect on leucine-enkephalin. Further, the specific activity of tyrosine hydroxylase was reduced to 5% of control activity in treated cultures. These effects occurred in the absence of any increases in cell number. Thus, it appears that cell contact via membrane-associated factors may exert differential effects on phenotypic expression.

Biochemistry and genetics of monoamine oxidase

This chapter reviews the two mitochondrial flavin containing isozymes of monoamine oxidase. Section 1, "Biochemistry" discusses assays, substrates and inhibitors, phylogenic and tissue distribution, interactions with lipids, nutritional studies, protein structure, kinetic and chemical mechanistic proposals, and biosynthesis. Section 2, "Inheritance" discusses possible genes involved in expression, genetic studies of platelet MAO-B and fibroblast MAO-A, and chromosomal location. Section 3, "Molecular Genetics" reviews the cloning of their cDNAs, their intra- and interspecies homology and structural inferences made from deduced amino acid sequences. Section 4, "Regulation" gives an overview of levels in development and aging, and effect of drugs. The final section 5, "Role in Human Disease" discusses physiological function and effects of altered levels in humans and animal models including complete absence due to a submicroscopic chromosomal deletion in several human patients.

The cAMP cascade in the nervous system: molecular sites of action and possible relevance to neuronal plasticity

Many intercellular messages regulate the activity of their target cells by altering the intracellular level of cAMP and, as a consequence, the phosphorylation state of proteins which serve as substrates for cAMP-dependent protein kinase. Such regulation plays a crucial role in neuronal development, neuronal function, and neuronal plasticity (e.g., elementary learning mechanisms). Ample information has been accumulated in recent years on the enzymes that regulate the level of cAMP or respond to it, on the regulation of cAMP synthesis by neurohormones, neurotransmitters, ions, and toxins, on neuronal-specific substrate proteins that are phosphorylated by the cAMP-dependent kinase, and on the interaction of the cAMP-cascade with other second-messenger systems within neurons. Such data, obtained by a combination of molecular-biological, biochemical, and cellular approaches, shed light on the detailed mechanisms by which modulation of a ubiquitous molecular cascade leads to a great variety of short-term as well as long-term specific neuronal responses and alterations.

Depolarizing stimuli increase tyrosine hydroxylase in the mouse locus coeruleus in culture

The influence of membrane depolarization on the development and regulation of brain noradrenergic neurons was studied in explant cultures of the mouse locus coeruleus (l.c.). Exposure to the depolarizing agents veratridine or elevated K+ significantly increased the catalytic activity of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis. The effects of veratridine were prevented by tetrodotoxin, suggesting that transmembrane Na+ influx was necessary for the rise in TH. Morphometric analysis indicated that the rise in TH activity was not accompanied by altered TH-positive cell number or cell diameter. Rather, TH fluorescence intensity increased in each neuron, suggesting that depolarization increased TH per neuron. Immunoblot and densitometric analysis indicated that depolarization did, indeed, increase TH immunoreactive protein. Moreover, depolarization elevated enzyme activity in cultured neurons expressing the normal developmental increase in TH, as well as those in which plateau levels had already been attained. We conclude that depolarization and/or Na+ influx regulates a critical transmitter macromolecule in brain neurons, as in the periphery, by altering enzyme molecule number.

Differential regulation of peptide and catecholamine characters in cultured sympathetic neurons

Mechanisms regulating peptidergic, noradrenergic and cholinergic development were compared in dissociated cell cultures of neonatal rat sympathetic ganglia. The majority of cultured neurons contained at least two neurotransmitters and many neurons contained three or more. These studies were undertaken to determine whether co-existing transmitters were co-ordinately regulated by the environment. Co-culture of sympathetic neurons with ganglion non-neuronal cells increased substance P and choline acetyltransferase activity but decreased somatostatin and tyrosine hydroxylase activity. Conversely, elimination of non-neuronal cells virtually abolished neuronal expression of substance P and choline acetyltransferase and increased somatostatin and tyrosine hydroxylase. Consequently, under these conditions, somatostatin and tyrosine hydroxylase were similarly regulated, whereas substance P was associated with choline acetyltransferase. By contrast, stimulation of adenylate cyclase or treatment with membrane-permeable adenosine 3',5'-phosphate analogs increased tyrosine hydroxylase and decreased choline acetyltransferase, but had no effect on substance P or somatostatin levels. Moreover, potassium- or veratridine-induced membrane depolarization increased tyrosine hydroxylase but decreased substance P, somatostatin and norepinephrine levels. However, inhibition of neurotransmitter release with magnesium or calcium-free medium prevented the decrease in norepinephrine levels but not the decrease in substance P and somatostatin. Consequently, the effects of membrane depolarization on peptide levels cannot be ascribed to release and subsequent depletion of substance P and somatostatin and must result from decreased net synthesis (synthesis minus catabolism) of the transmitters. Nerve growth-factor treatment also differentially regulated transmitter metabolism; nerve growth factor increased protein-specific activities of tyrosine hydroxylase and choline acetyltransferase but did not increase the protein-specific content of substance P and somatostatin. Quantitative transmitter expression was also influenced by neuron density; increasing density elevated substance P and choline acetyltransferase activity but decreased somatostatin and tyrosine hydroxylase activity per neuron. Finally, culture of sympathetic neurons in a defined (serum-free) medium also altered some but not all traits, decreasing substance P, somatostatin and choline acetyltransferase without any change in tyrosine hydroxylase.(ABSTRACT TRUNCATED AT 400 WORDS)

Determination of synaptic phenotype: insulin and cAMP independently initiate development of electrotonic coupling between cultured sympathetic neurons

Electrotonic coupling between pairs of sympathetic neurons dissociated from superior cervical ganglia of neonatal rats is rare when cells are cultured for 2 weeks in a nutrient medium plus serum and is common when cells are cultured for the same period in serum-free defined medium. This defined medium is the same nutrient medium with five added factors (progesterone, transferrin, putrescine, insulin, and selenium). When added singly to serum-containing medium, insulin and, to a lesser extent, selenium promote the development of electrotonic and dye coupling. The insulin effect is obtained with doses as low as 0.01 microgram/ml and is maximal after exposures from 3 to 5 days. The incidence of electrotonic coupling is also enhanced by exposure of cells to dibutyryl cAMP. This effect is obtained with doses as low as 0.1 mM, is faster (being maximal at approximately equal to 12 hr exposure), and is prolonged in the presence of the phosphodiesterase inhibitor caffeine. Butyrate itself promotes coupling to a small extent, but cAMP involvement is confirmed by similar effects of other membrane permeant analogues. Endogenous levels of cAMP are significantly elevated in cultures grown in the defined medium but not in those in serum-containing medium to which insulin or selenium are added. We conclude that the promotion of coupling by cAMP and by insulin or selenium are independent. The development of coupling in the defined medium thus seems to be a consequence of the addition of promoting substances (insulin, selenium) and the removal of an inhibitory effect of serum on cAMP levels.

Morphological and biochemical studies on the development of cholinergic properties in cultured sympathetic neurons. I. Correlative changes in choline acetyltransferase and synaptic vesicle cytochemistry

Under certain culture conditions, neonatal rat superior cervical ganglion neurons display not only a number of expected adrenergic characteristics but, paradoxically, also certain cholinergic functions such as the development of hexamethonium-sensitive synaptic contacts and accumulation of choline acetyltransferase (ChAc). The purpose of this study was to determine whether the entire population of cultured neurons was aquiring cholinergic capabilities, or whether this phenomenon was restricted to a subpopulation. After 1--6 and 8 wk in culture, neurons were fixed in KMnO4 after incubation in norepinephrine and prepared for electron microscopy analysis of synaptic vesicle content to determine whether vesicles were dense cored or clear. ChAc, acetylcholinesterase (AChE), and DOPA-decarboxylase (DDC) activities were assayed in sister cultures. In the period from 1 to 8 wk in culture, the average ChAc activity per neuron increased 1,100-fold, and the DDC and AChE activities increased 20- and 30-fold, respectively. After 1 wk in culture, 48 of 50 synaptic boutons contained predominantly dense-cored vesicles, but by 8 wk the synaptic vesicle population was predominantly of the clear type. At intermediate times, the vesicle population in many boutons was mixed. The morphology of the synaptic contacts on neuronal surfaces was that characteristic of autonomic systems, with no definite clustering of the vesicles adjacent to the area of contact. Increased vesicle size correlated with increasing age in culture and the presence of a dense core. Considering these data along with available physiological studies, we conclude that these cultures contain one population of neurons that is initially adrenergic. Over time, under conditions of this culture system, this population develops cholinergic mechanisms. That a neuron may, at a given time, express both cholinergic and adrenergic mechanisms is suggested by the approximately equal numbers of clear and dense-cored vesicles in the boutons found at the intermediate times.

Modulatory role of catecholamines on tyrosine hydroxylase induction

The possible modulatory role of cytoplasmic catecholamines on tyrosine hydroxylase induction was studied. Rat superior cervical ganglia were kept in organ culture and after 48 h tyrosine hydroxylase activity was determined. Exposure to 10(-4) M carbachol during 4 h almost doubled the control activity. Incubation with 10(-5) M noradrenaline or 10(-5) M dopamine impaired the carbachol-mediated induction of the enzyme. This effect was not blocked by 10(-7) M propranolol, 2.4 X 10(-6) M haloperidol or 3.1 X 10(-6) M phentolamine. Inhibition of monoamine oxidase activity by 5.1 X 10(-4) M pargyline inhibited the effect of carbachol. When the pool of endogenous catecholamines was decreased by alpha-methyl-p-tyrosine, carbachol induced tyrosine hydroxylase to the same extent as in non-depleted ganglia. It is suggested that the long-term regulation of tyrosine hydroxylase is modulated by a strategic cytoplasmic pool of catecholamines.

Selective induction of tyrosine hydroxylase and dopamine beta-hydroxylase by nerve growth factor: comparison between adrenal medulla and sympathetic ganglia of adult and newborn rats

Administration of NGF to newborn and adult rats elicits a selective increase in TH and DBH both in sympathetic ganglia and adrenal medulla. This effect does not depend on intact preganglionic cholinergic fibers. The augmented enzyme activity results from enhanced enzyme synthesis since it can be abolished by cycloheximide and NGF has been shown to enhance the incorporation of [3H]leucine into DBH molecules. The responsiveness of the adrenal medulla to NGF is also supported by light and electron microscopic autoradiograms which show that intravenously injected 125I-NGF is accumulated with high selectivity in adrenal chromaffin as compared to adjacent adrenal cortical cells. In spite of the many similarities between the response of the adrenergic neurons and adrenal chromaffin cells to NGF, there are also two distinct differences. (a) In newborn rats the ratio between the TH increase effected by a single and 10 subsequent daily injections of NGF is 1:2 in the adrenal medulla and 1:7 in the superior cervical ganglia. (b) If adrenal medullae are transferred to organ culture after intravenous injection of NGF, maximal TH response is initiated 60-90 min after NGF administration. In superior cervical ganglia only a half-maximal response is initiated at that time. After a stationary phase a second increase starts after about 6 h to reach the maximum after 12 h. The biphasic time course of the initiation of TH induction by NGF in sympathetic ganglia is in agreement with the time course of 125I-NGF accumulation after intravenous injection27 reflecting the moiety of NGF reaching the cell bodies of the adrenergic neurons directly by the blood stream (initial accumulation) and by retrograde axonal transport (second phase).

Effects of db cAMP on tyrosine hydroxylase activity of ganglia and nerve endings

Preincubation of intact superior cervical ganglia or nictitating membrane for 2 h with dibutyryl cyclic AMP (db cAMP) increased the hydroxylation of tyrosine. This effect was not blocked by the protein synthesis inhibitor, cycloheximide. The Km of tyrosine hydroxylase for the substrate, tyrosine, and for the cofactor, reduced pteridine, were decreased by db cAMP. There were no changes in the Vmax of the enzyme. The inhibitory potency of noradrenaline on the hydroxylation of tyrosine was also decreased. Thus an inductive effect may be ruled out. The activation of the enzyme was only observed when the tissues were preincubated with the db cAMP and not when the cyclic nucleotide was added to the isolated enzyme. Preincubation of cervical ganglia for 4 h with db cAMP increased activity of decarboxylase and monoamine oxidase in tissue homogenates without changing the tyrosine hydroxylase activity.

Differences in sensitivity to nerve growth factor of axon formation and tyrosine hydroxylase induction in cultured sympathetic neurons

Superior cervical ganglia from 2-day-old and 3-week-old rats were maintained in vitro for up to 2 weeks in the presence of a range of concentrations of nerve growth factor up to 100 micrograms/ml. Nerve fibre length and density were measured and tyrosine hydroxylase activity of these cultures assayed after various times. Ganglia were also examined for catecholamines and neuronal numbers using fluorescence histochemistry and histology respectively. In cultures maintained without nerve growth factor, or in those containing low concentrations of nerve growth factor (3 ng/ml), tyrosine hydroxylase decreased to 5-10% of the initial levels by 14 days in vitro. The presence of the high concentration of 1 microgram/ml nerve growth factor in the culture medium or the addition of such a concentration during the culture period did not prevent an initial decrease in tyrosine hydroxylase but subsequently increased the enzyme activity. The maximal effect of nerve growth factor on nerve fibre density was at low concentrations whereas its maximal effect on neuronal survival, tyrosine hydroxylase activity or nerve fibre elongation was at high concentrations. After 2 days in culture, maximum neurite production occurred in cultures containing 10 ng/ml, while maximum nerve fibre elongation and tyrosine hydroxylase activity occurred in cultures containing 100 micrograms/ml nerve growth factor. We conclude that low concentrations of nerve growth factor, as occur in plasma, cause maximum axon formation while high concentrations of nerve growth factor, as occur in effector organs, induce maximum tyrosine hydroxylase activity and cell survival. The former process may be mediated via cell surface receptors and the latter via retrograde axonal transport of nerve growth factor to the cell body, following uptake by the terminal regions of the axons.

Effects of axotomy on the trans-synaptic regulation of enzyme activity in adult rat superior cervical ganglia

The effects of surgical transection of the postganglionic nerve trunk of the superior cervical ganglion on the total protein content and levels of the enzymes tyrosine hydroxylase, DOPA decarboxylase and choline acetyltransferase have been studied in the adult rat. There is a minor decrease in the total activities of these 3 enzymes accompanied by a large increase in the total protein content of the ganglion. The trans-synaptic induction of the enzyme tyrosine hydroxylase by reserpine is not affected by postganglionic axotomy. Increased activity mediated by reserpine caused no change in the total activities of either DOPA decarboxylase or choline acetyltransferase. Previously observed effects of postganglionic axotomy on preventing transmission through the ganglion are compared with these results and the possible mechanisms by which trans-synaptic induction may occur are discussed.

Effects of dbcAMP and theophylline on rat adrenal medulla grown in tissue culture

Explants of rat adrenal medulla were grown in tissue culture. The effects of various doses of dbcAMP ranging from 0.001 mM up to 1 mM and equimolar amounts of theophylline were recorded by phase contrast optics and catecholamine histochemistry (glyoxylic acid method) over six days. There was a dose-dependent inhibition of the normally occurring outgrowth of Schwann cells, "chromaffin" cells and axons from the explants. Maintenance of glyoxylic acid-induced fluorescence in "chromaffin" cells was dose-dependent, too. Since theophylline is known to enhance intracellular levels of cAMP only, these effects are probably due to the action of cAMP. cAMP obviously maintains the degree of differentiation of chromaffin cells. Thus it could be argued that a certain degree of dedifferentiation is a prerequisite for the formation of axons from these cells.

Mechanisms of tyrosine hydroxylase and dopamine beta-hydroxylase induction in organ cultures of rat sympathetic ganglia by potassium depolarization and cholinomimetics

It was the aim of the present study to elucidate the mechanisms involved in specific tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) induction by potassium depolarization and cholinomimetics in rat superior cervical ganglia kept in organ culture. The effect of high (54 mM) potassium concentration on intact ganglia seems to result in a dual action: a) a specific induction of TH and DBH via release of acetylcholine from preganglionic cholinergic nerve terminals. b) a non-specific effect on terminal adrenergic neurons resulting in a general increase of protein synthesis as indicated by the increase in DOPA decarboxylase (DDC) and monoamine oxidase (MAO) activities. In decentralized superior cervical ganglia potassium depolarization failed to produce the specific TH and DBH induction although a small increase in DDC activity persisted. Carbamylcholine, acetylcholine and nicotine at concentrations of 10(-4) M elicited a selective induction of TH and DBH both in intact and decentralized ganglia via nicotinic receptor stimulation. Bethanechol, predominantly stimulating muscarinic receptors had no significant effect on TH activity. A 4 h pulse of 10(-4) M carbamylcholine produced optimal induction of DBH and TH 24 h and 48 h later respectively. Longer exposure to carbamylcholine resulted in a significantly smaller rise in TH activity.