Regulatory Interactions Among Axon Terminals Affecting the Release of Different Transmitters from Rat Striatal Slices Under Hypoxic and Hypoglycemic Conditions

An in vitro model of ischemia was utilized to study the effects of both oxygen and glucose depletion on transmitter release from rat striatal slices. The spontaneous and stimulation-evoked releases of tritiated dopamine, gamma-aminobutyric acid, glutamate, and acetylcholine were measured. Hypoxia increased the evoked release of glutamate and dopamine without effect on the resting release. In contrast, hypoglycemia itself increased the resting release of dopamine. Hypoxia in combination with hypoglycemia provoked a massive release of glutamate, dopamine, and gamma-aminobutyric acid. The effect on acetylcholine release was less pronounced. Ca2+ withdrawal partly reduced the effect of hypoxia combined with hypoglycemia on dopamine release and application of tetrodotoxin (1 microM) abolished it. MK-801 (3 microM), an N-methyl-D-aspartate receptor antagonist, attenuated the effect of hypoxia and hypoglycemia on [3H]dopamine release. omega-Conotoxin (0.1 microM) had a similar effect on stimulation-evoked release under a hypoxic condition. The D2 receptor antagonist sulpiride (100 microM) failed to enhance the release of [3H]acetylcholine in hypoxia combined with hypoglycemia. It was suggested that in response to hypoxia combined with hypoglycemia there is a massive release of glutamate due to the increased firing rate which in turn releases dopamine from the axon terminals through stimulation of presynaptic N-methyl-D-aspartate receptors. Dopaminergic inhibitory control on ACh release seems not to be operative under conditions of hypoxia combined with hypoglycemia.     

The effects of some putative transmitters and biogenic amines on uropod abductor muscle in the crayfish Procambarus clarkii and Cambaroides japonicus

The effects of some putative transmitters and biogenic amines were examined on the uropod ventral abductor exopodite (AbdExV) muscle in two crayfish species Procambarus clarkii and Cambaroides japonicus. Bath application of L-glutamate to the AbdExV muscle caused sustained contract while gamma-aminobutyric acid (GABA) depressed the nerve-evoked contraction of the muscle. Acetylcholine (ACh) had no effect on both the resting tension and the nerve-evoked contraction. Iontophoresis of L-glutamate and GABA onto the surface of the muscle fiber further confirmed that glutamate and GABA are the possible excitatory and inhibitory transmitters respectively at the neuromuscular junction of AbdExV muscle. Bath application of 5-hydroxytryptamine (5-HT) and octopamine (Oct) caused enhancement of the nerve-evoked contraction but dopamine (DA) had no effect on both the resting tension and the nerve-evoked contraction.     

The mechanism of block of glutamate synapses by dipicolinic acid

The effect of dipicolinic acid (2,6-pyridine dicarboxylic acid) on the mealworm neuromuscular junction was studied using conventional microelectrode recording techniques. Dipicolinic acid (10^?5-10^?3 M) added to the bathing solution reversibly blocked neuromuscular transmission. The depolarization in response to iontophoretically applied L-glutamate (glutamate potential) was not affected by dipicolinic acid even when the neurally evoked excitatory postsynaptic potential (EPSP) was totally abolished. Focal extracellular recordings from single synaptic sites revealed that in the presence of 1 x 10^?4 M dipicolinic acid the presynaptic spike was unchanged, but the quantal content for evoked transmitter release was reduced. The calcium-dependent action potential elicited by direct stimulation of the muscle fiber was not impaired by dipicolinic acid. These results suggest that dipicolinic acid interferes with the transmitter-releasing mechanism from the presynaptic terminal.     

Chemical sensitivity of the hyperneural nerve-muscle preparation of the American cockroach

The hyperneural muscle of Periplaneta americana responded with sustained contracture to applications of l-glutamic acid at near 10^?4 M. d-glutamic acid was much less active. The responses of a particular preparation to glutamate were usually extremely consistent and highly reproducible; however, some preparations showed no response to l-glutamic acid even at 10^?2 M whereas neurally evoked responses were normal. High magnesium, low calcium perfused onto the preparations blocked neurally evoked contractions. The glutamate response was blocked reversibly in low calcium solutions. suggesting that the glutamate effect, when present, was presynaptic.Dopamine, acetylcholine, 5-hydroxytryptamine, synephrine, Rogitine^®, strychnine, strychnine, pentobarbital, and picrotoxin, all suspected to varying degrees of some action on insect central or peripheral synaptic transmission, had no effect on the patterns of neurally evoked contracture of the hyperneural muscle. A new transducer is described for use with low force insect muscle contractions.     

Some pharmacological properties of neuromuscular transmission in the oviduct of the locust,Locusta migratoria

The effects of various pharmacological agents on neurally evoked contractions of the visceral muscles of the oviduct of Locusta migratoria have been examined. The pentapeptide, proctolin, at low concentrations (10^?11 M?10^?10 M), induced an increase in the amplitude of neurally evoked contractions and basal tonus, and induced the appearance and increased the frequency of myogenic contractions. Glutamate, at 10^?4 M, produced a small transient contraction which in some preparations was accompanied by a reduction in amplitude of neurally evoked contractions. Octopamine, at 10^?6 M, reduced the amplitude of neurally evoked contractions and also resulted in a relaxation of the muscles. The octopaminergic effects were inhibited by the α-aminergic antagonist phentolamine. Neurally evoked contractions were unaffected by dopamine, 5-HT or the acetylcholine receptor antagonists atropine and hexamethonium. Acetylcholine increased the amplitude of neurally evoked contractions, but only at the high concentration of 10^?3 M. The possible role of proctolin and glutamate as excitatory neuro-transmitters and the inhibitory action of octopamine is discussed.     

Effects of biogenic amines and hormones on butterfly Malpighian tubules: Dopamine stimulates fluid secretion

Isolated Malpighian tubules of Papilio demodocus, the citrus swallowtail butterfly, were stimulated by biogenic amines as well as by cyclic AMP and the naturally occuring diuretic hormone. The greatest secretory response was obtained with 5-hydroxytryptamine, and smaller responses with dopamine and noradrenaline, but none of these amines could induce the maximal secretion rates obtained with cyclic AMP and diuretic hormone. Various other biogenic amines, hormones and pharmacological agents, including adrenaline, had no effect on Papilio tubules. The blocking agents cyproheptadine, phentolamine and propranolol did not alter the tubule response to biogenic amines.     

The aminergic control of cockroach salivary glands

The acinar salivary glands of cockroaches receive a dual innervation from the subesophageal ganglion and the stomatogastric nervous system. Acinar cells are surrounded by a plexus of dopaminergic and serotonergic varicose fibers. In addition, serotonergic terminals lie deep in the extracellular spaces between acinar cells. Excitation-secretion coupling in cockroach salivary glands is stimulated by both dopamine and serotonin. These monoamines cause increases in the intracellular concentrations of cAMP and Ca(2+). Stimulation of the glands by serotonin results in the production of a protein-rich saliva, whereas stimulation by dopamine results in saliva that is protein-free. Thus, two elementary secretory processes, namely electrolyte/water secretion and protein secretion, are triggered by different aminergic transmitters. Because of its simplicity and experimental accessibility, cockroach salivary glands have been used extensively as a model system to study the cellular actions of biogenic amines and to examine the pharmacological properties of biogenic amine receptors. In this review, we summarize current knowledge concerning the aminergic control of cockroach salivary glands and discuss our efforts to characterize Periplaneta biogenic amine receptors molecularly.     

Cellular and molecular mechanisms controlling melatonin release by mammalian pineal glands

1. The pineal gland is regulated primarily by photoperiodic information attaining the organ through a multisynaptic pathway initiated in the retina and the retinohypothalamic tract. 2. Norepinephrine (NE) released from superior cervical ganglion (SCG) neurons that provide sympathetic innervation to the pineal acts through alpha1- and beta 1- adrenoceptors to stimulate melatonin synthesis and release. 3. The increase in cyclic AMP mediated by beta 1-adrenergic activation is potentiated by the increase in Ca2+ flux, inositol phospholipid turnover, and prostaglandin and leukotriene synthesis produced by alpha 1-adrenergic activation. 4. Central pinealopetal connections may also participate in pineal control mechanisms; transmitters and modulators in these pathways include several neuropeptides, amino acids such as gamma-aminobutyric acid (GABA) and glutamate, and biogenic amines such as serotonin, acetylcholine, and dopamine. 5. Secondary regulatory signals for pineal secretory activity are several hormones that act on receptors sites on pineal cells or at any stage of the neuronal pinealopetal pathway.     

Reverse-phase high-performance liquid chromatographic separation and electrochemical detection of norepinephrine,dopamine, serotonin,and related major metabolites

A convenient method for the determination of biogenic amines and their metabolites in small samples of brain tissue weighing from 0.5 to 5 mg, based on reverse-phase chromatography, is described. The biogenic amines, norepinephrine, dopamine, and serotonin, and the metabolites normetanephrine and 3-methoxytyramine were separated by ion-pair chromatography on a μBondapak phenyl column with an aqueous eluant, while the metabolites 3,4-dihydroxyphenylacetic acid, homovanillic acid, 3-methoxy-4-hydroxyphenylglycol, and 5-hydroxyindoleacetic acid were separated on a μBondapak C18 column with a methanol aqueous mobile phase. The sensitivity of the method is in the picogram range, from 20 to 100 pg, depending on the substances analyzed.     

Detection of transmitter release with carbon fiber electrodes

The use of constant voltage amperometry is described as an analytical technique for the detection of biogenic amines. This technique can be used to measure the amount of transmitter released from individual organelles and to determine the kinetic properties of transmitter discharge from the organelle providing unique insight into properties of signal transmission from secretory cells.     

EFFECTS OF AMINES ON THE LEVEL OF N-ACETYL-ASPARTATE AND N-ACETYL- ASPARTYL-GLUTAMATE IN MOUSE BRAIN TISSUE SLICES

The effect of some biogenic amines and amino acids on the level of N-acetyl-asparticacid and N-acetyl-aspartyl-glutamic acid has been investigated in mouse brain tissue slices. The amines all caused a significant decrease in the levels of N-acetyl-aspartic acid and N-acetytl-aspartyl-glutamic acid within 5 min of incubation, while the amino acids, in spite of being possible transmitter candidates, had no such effect.     

Glutamate regulation of non-quantal release of acetylcholine in the rat neuromuscular junction

Glutamate, previously demonstrated to participate in regulation of the resting membrane potential in skeletal muscles, also regulates non-quantal acetylcholine (ACh) secretion from rat motor nerve endings. Non-quantal ACh secretion was estimated by the amplitude of endplate hyperpolarization (H-effect) following blockade of skeletal muscle post-synaptic nicotinic receptors by (+)-tubocurarine and cholinesterase by armin (diethoxy-p-nitrophenyl phosphate). Glutamate was shown to inhibit non-quantal release but not spontaneous and evoked quantal secretion of ACh. Glutamate-induced decrease of the H-effect was enhanced by glycine. Glycine alone also lowered the H-effect, probably due to potentiation of the effect of endogenous glutamate present in the synaptic cleft. Inhibition of N-methyl-d-aspartate (NMDA) receptors with (+)-5-methyl-10,11-dihydro-5H-dibenzocyclohepten-5,10-imine (MK801), dl-2-amino-5-phosphopentanoic acid (AP5) and 7-chlorokynurenic acid or the elimination of Ca2+ from the bathing solution prevented the glutamate-induced decrease of the H-effect with or without glycine. Inhibition of muscle nitric oxide synthase by NG-nitro-l-arginine methyl ester (l-NAME), soluble guanylyl cyclase by 1H[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) and binding and inactivation of extracellular nitric oxide (NO) by haemoglobin removed the action of glutamate and glycine on the H-effect. The results suggest that glutamate, acting on post-synaptic NMDA receptors to induce sarcoplasmic synthesis and release of NO, selectively inhibits non-quantal secretion of ACh from motor nerve terminals. Non-quantal ACh is known to modulate the resting membrane potential of muscle membrane via control of activity of chloride transport and a decrease in secretion of non-quantal transmitter following muscle denervation triggers the early post-denervation depolarization of muscle fibres.     

Biogenic amines and GABA in the larval and adult forms of the nematode Nippostrongylus brasiliensis.

1. Simultaneous detection (HPLC and electrochemical detection) of biological extracts of larval and adult stages of Nippostrongylus brasiliensis was performed in order to assay biogenic amines. 2. Gamma-amino-butyric acid was assayed in the same samples. 3. Tryptophan, 5-hydroxyindoleacetic acid were at the same level in adults and larvae. 4. 5-Hydroxytryptophan, serotonin, dihydroxyphenylalanine and dopamine were significantly higher in larvae in which gamma-amino-butyric acid was not detected.     

Presynaptic effects of octopamine, serotonin, and cocktails of the two modulators on neuromuscular transmission in crustaceans

The effect of the biogenic amines octopamine and serotonin, and of both amines combined (cocktails) on transmitter release at neuromuscular junctions of two crustaceans was studied. octopamine (10(-8) mol l(-1) to 10(-6) mol l(-1)) either enhanced or decreased evoked transmitter release through presynaptic effects. The results were identical for the slow and the fast excitor in the closer muscle of the crab, and for the excitor in the opener muscle of the crayfish. Application of serotonin always resulted in a strong increase of release. However, this potentiating effect of serotonin was reduced in strength by subsequent application of cocktails consisting of serotonin and octopamine. In all experiments, a cocktail of serotonin and octopamine was less effective than serotonin alone. The decrease in the mean quantal content m by octopamine was due to a reduction of the probability of release p. Since both amines are synthesized in the central nervous system and are released from neurohaemal organs into the haemolymph bathing the neuromuscular junctions, the results suggest that the two amines, when present together, modulate transmitter release in an antagonistic way, and that the level of the two determines synaptic efficacy.     

Glutamate excitatory effects on ampullar receptors of the frog

Summary The action of glutamate on frog ampullar receptors was investigated to assess the potential role of this excitatory amino acid as an afferent transmitter in the hair cell system. Intracellular recordings from single afferent units in the isolated labyrinth revealed that glutamate and the glutamate receptor agonists, N-methyl-D-aspartic acid, quisqualic acid and kainic acid increase dose-dependently the frequency of the resting afferent discharge of EPSPs and spikes and produce long lasting depolarizations. After blocking synaptic transmission by using 5 mM Co²⁺, the same compounds elicited only depolarizations of amplitude comparable to those observed in normal saline. Quisqualic acid and kainic acid were much more potent than N-methyl-D-aspartic acid in increasing the frequency of afferent discharge and in causing axonal depolarizations. The depolarization caused by glutamate was reduced dose-dependently by the competitive non-NMDA receptor antagonist 6-cyano-7-nitroquinaxoline-2,3 dione and disappeared almost completely in Na⁺-free Ringer solution. These results are consistent with the hypothesis that glutamate is the afferent transmitter in vestibular organs and indicate that receptors mainly of the non-NMDA type are present not only at postsynaptic level but also in hair cells. Presynaptic glutamate receptors may function as autoreceptors controlling by a positive feed-back mechanism the release of the afferent transmitter.     

Biogenic amines and gaba in the larval and adult forms of the nematode Nippostrongylus brasiliensis

1. Simultaneous detection (HPLC and electrochemical detection) of biological extracts of larval and adult stages of Nippostrongylus brasiliensis was performed in order to assay biogenic amines.2. Gamma-amino-butyric acid was assayed in the same samples.3. Tryptophan, 5-hydroxyindoleacetic acid were at the same level in adults and larvae.4. 5-Hydroxytryptophan, serotonin, dihydroxyphenylalanine and dopamine were significantly higher in larvae in which gamma-amino-butyric acid was not detected.     

Neuromuscular block in locust skeletal muscle caused by a venom preparation made from the digger wasp Philanthus triangulum F. from Egypt.

A preparation from P. triangulum F., made by extracting abdomens and purified by Sephadex filtration, does not affect potassium ion-induced contractions of the retractor unguis muscle of S. gregaria, but the reduction of the glutamate contractions is at least as pronounced as the effect on the neurally-evoked twitch. Glutamate potentials are affected at a lower venom dose than are the neurally evoked excitatory postsynaptic potentials (EPSPs). The half-decay-time of the glutamate potentials starts to decrease just before the decrease in amplitude is initiated.In the retractor unguis muscle the resting plasma membrane is slightly depolarized at high venom concentrations, but this effect cannot explain the effects on neuromuscular transmission. It is concluded that the venom preparation of P. triangulum affects the glutamate or transmitter-induced transient permeability change, possibly by blocking the open ion-channels.     

Effect of methylcobalamine on the processes of posttraumatic regeneration of the salivary glands

Experiments on rats were made to study membrane potentials (MP) of secretory cells of the salivary glands, the content of biogenic amines and lactate dehydrogenase (LDH) isozymes of the salivary gland tissue in trauma after pretreatment with methylcobalamine. Twenty-four hours after trauma the salivary gland showed a decrease in the content of LDH aerobic fractions, the lowering of noradrenaline concentration with no changes in the MP of glandular cells outside the zone of injury. Administration of cobalamine did not cause any changes in the parameters under study. There was an increase in the polarization level of acinar and duct cells, normalization of noradrenaline content, and a rise of adrenalin concentration with persistent reduction in aerobic fractions of LDH in salivary gland trauma after pretreatment with methylcobalamine. It is concluded that methylcobalamine administration may have a therapeutic effect in salivary gland trauma.     

Glutamate inhibitors in the crayfish neuromuscular junction

1. The effects of chlorisondamine and TI-233 on the crayfish neuromuscular junction were investigated in order to compare the action of glutamate with that of the excitatory transmitter. 2. The glutamate-induced synaptic current was inhibited by both of these two drugs. Excitatory junctional potentials were significantly reduced by chlorisondamine, whereas they were increased by TI-233. 3. It is suggested that chlorisondamine and TI-233 are powerful non-competitive antagonists for glutamate. 4. A quantum analysis of extracellular EJPs demonstrated that chlorisondamine did not possess presynaptic action in the crayfish neuromuscular junction. Chlorisondamine shortened the decay phase of extracellular EJPs, and the decay was frequently fitted by a double exponential in relatively low concentrations. 5. Semilogarithmic plots of the decay phase of the glutamate current evoked by a short glutamate pulse were nearly linear, but they shifted from linearity to some extent in the presence of chlorisondamine, showing prolongation of the glutamate current tails. 6. When TI-233 was added to the bathing solution at a concentration of 0.1 mM, the quantum content of extracellular EJPs was increased by about two times, but the average unit size was not changed. 7. There was no change in the rise time and the decay phase of the glutamate potential in the presence of TI-233. 8. Pharmacological difference between glutamate responses and EJPs was revealed in the presence of chlorisondamine and TI-233. Unless this difference can be explicated with a reasonable explanation on the glutamate transmitter hypothesis, it is difficult to confirm that glutamic acid is an excitatory transmitter at the crayfish neuromuscular junction.     

Amino Acids and Biogenic Amines in Cerebrospinal Fluid of Patients with Parkinson's Disease

To study changes in amino acid metabolism and biogenic amines in Parkinson's disease, we set up a prospective study and measured biogenic amines, their main metabolites, and 22 different amino acids, in cerebrospinal fluid of Parkinson's disease patients (n = 24) and age-matched controls (n = 30). A trend toward higher dopamine levels in Parkinson's disease patients was interpreted as an effect of treatment with levodopa and/or selegiline. Significantly lower concentrations of the dopamine metabolite 3,4-dihydroxyphenylacetic acid in the Parkinson's disease group might reflect dopaminergic cell loss. Our results revealed decreased serotonin catabolism that was interpreted as an effect of treatment with selegiline. Whereas all amino acid levels were unchanged, taurine was significantly lower in Parkinson's disease patients. Studies showed that taurine exerts a trophic action on the central nervous system. In this view, decreased taurine in a neurodegenerative disorder as Parkinson's disease deserves attention.