Biomedical subjects

E S Vizi

Publications and source records attributed to E S Vizi.

At least 19 recordsLinked to original sources

PubMed1999

Presynaptically located CB1 cannabinoid receptors regulate GABA release from axon terminals of specific hippocampal interneurons.

To understand the functional significance and mechanisms of action in the CNS of endogenous and exogenous cannabinoids, it is crucial to identify the neural elements that serve as the structural substrate of these actions. We used a recently developed antibody against the CB1 cannabinoid receptor to study this question in hippocampal networks. Interneurons with features typical of basket cells showed a selective, intense staining for CB1 in all hippocampal subfields and layers. Most of them (85.6%) contained cholecystokinin (CCK), which corresponded to 96.9% of all CCK-positive interneurons, whereas only 4.6% of the parvalbumin (PV)-containing basket cells expressed CB1. Accordingly, electron microscopy revealed that CB1-immunoreactive axon terminals of CCK-containing basket cells surrounded the somata and proximal dendrites of pyramidal neurons, whereas PV-positive basket cell terminals in similar locations were negative for CB1. The synthetic cannabinoid agonist WIN 55,212-2 (0.01-3 microM) reduced dose-dependently the electrical field stimulation-induced [3H]GABA release from superfused hippocampal slices, with an EC50 value of 0. 041 microM. Inhibition of GABA release by WIN 55,212-2 was not mediated by inhibition of glutamatergic transmission because the WIN 55,212-2 effect was not reduced by the glutamate blockers AP5 and CNQX. In contrast, the CB1 cannabinoid receptor antagonist SR 141716A (1 microM) prevented this effect, whereas by itself it did not change the outflow of [3H]GABA. These results suggest that cannabinoid-mediated modulation of hippocampal interneuron networks operate largely via presynaptic receptors on CCK-immunoreactive basket cell terminals. Reduction of GABA release from these terminals is the likely mechanism by which both endogenous and exogenous CB1 ligands interfere with hippocampal network oscillations and associated cognitive functions.

Animals↗

PubMed1999

Involvement of P2 purinoceptors and the nitric oxide pathway in [3H]purine outflow evoked by short-term hypoxia and hypoglycemia in rat hippocampal slices.

The objective of this study was to study how the outflow of [3H]purines is altered during a brief period of ischemic-like conditions in superfused hippocampal slices and to show whether it is regulated by P2 purinoceptors and the nitric oxide (NO) pathway. The outflow of [3H]purines increased in response to 5 min of combined hypoxia/hypoglycemia. High performance liquid chromatography analysis verified the efflux of [3H]adenosine-triphosphate, [3H]adenosine-diphosphate, [3H]adenosine-monophosphate, [3H]adenosine, [3H]inosine, and [3H]hypoxanthine in response to ischemic-like conditions. The P2 receptor antagonists suramin and pyridoxal-phosphate-6-azophenyl-2'-4'-disulphonic-acid-tetrasodium (PPADS) reduced significantly the [3H]purine efflux evoked by ischemic-like conditions, showing that P2 purinoceptors are involved in the initiation of purine outflow. The NO synthase inhibitor N-nitro-l-arginine-methyl-ester (l-NAME) attenuated significantly the [3H]purine outflow, evoked by ischemic-like conditions, while 7-nitroindazole (7-NI) caused only a mild decrease in the outflow. The NO donor sodium nitroprusside increased significantly the basal efflux of [3H]purines. In summary, a brief period of combined hypoxia/hypoglycemia induced the efflux of ATP in addition to the outflow of other purines. Since P2 receptor antagonists decreased the [3H]purine outflow evoked by ischemic-like conditions we propose that ATP, acting on P2 purinoceptors, is responsible for further efflux of purines after ischemic-like period. It seems likely that NO is also involved in the regulation of purine outflow, since inhibition of NO production attenuated the [3H]purine outflow, evoked by ischemic-like conditions, while exogenous NO facilitated the basal outflow.

Adenosine Triphosphate↗

PubMed1999

Excessive release of [3H]noradrenaline and glutamate in response to simulation of ischemic conditions in rat spinal cord slice preparation: effect of NMDA and AMPA receptor antagonists.

In the present study we investigated the effects of NMDA and non-NMDA glutamate receptor antagonists on the ischemia-evoked release of [3H]noradrenaline from rat spinal cord slices. An in vitro ischemia model (oxygen and glucose deprivation) was used to simulate the ischemic conditions known to cause neuronal injury. Spinal cord slices were loaded with [3H]noradrenaline and superfused with Krebs solution in a micro-organ bath. Both axonal stimulation and ischemia increased the release of [3H]noradrenaline, but the release in response to glucose and oxygen deprivation was [Ca2+]o independent. Dizocilpine (MK-801), an NMDA receptor antagonist, suppressed the release of [3H]noradrenaline produced by ischemia, while it enhanced the release of [3H]noradrenaline evoked by electrical field stimulation. In contrast, LY300168 (GYKI-53655) [(+/-)-3-N-methylcarbamyde-1-(4-aminophenyl)-4-methyl-1.8-methylen e-dioxy-5H-2.3-benzodiazepine] and its (-)isomer LY303070 (GYKI-53784) [(-)-3-N-methylcarbamyde-1-(4-aminophenyl)-4-methyl-1.8-methylene- dioxy-5H-2.3-benzodiazepine] AMPA receptor antagonists, had no effect on the release of [3H]noradrenaline evoked by either electrical stimulation or ischemia. Desipramine, a noradrenaline uptake inhibitor, potentiated the release of [3H]noradrenaline evoked by ischemia, while in the absence of [Ca2+]o but under conditions when [3H]noradrenaline release was further increased, it reduced the release. Dizocilpine also decreased glutamate and aspartate release, measured by high performance liquid chromatography, during ischemia. It is concluded that glutamate release and NMDA receptors, but not AMPA receptors, are involved in the acute effect of oxygen and glucose deprivation on the excessive release of noradrenaline and that this release is not related to physiological axonal conduction.

Animals↗

PubMed1999

Effect of neostigmine on the hippocampal noradrenaline release: role of cholinergic receptors.

The effect of the cholinesterase inhibitor neostigmine on hippocampal noradrenaline (NA) release was studied using in vivo microdialysis. Local application of neostigmine significantly increased the release of NA. The effect was potentiated by coperfusion of the nicotinic antagonist mecamylamine but was completely blocked by the muscarinic antagonist atropine. The neostigmine-evoked NA release was not affected by the M2-selective muscarinic antagonist gallamine but was completely blocked by the M1-selective muscarinic antagonist pirenzepine. While muscarinic antagonists had no effect on the resting release of NA, mecamylamine increased it. Our data indicate that acetylcholine can stimulate the hippocampal NA release via M1 muscarinic receptors and that a population of nicotinic receptors mediate inhibitory tone on hippocampal NA release. The fact that neostigmine is able to enhance both cholinergic and noradrenergic neurotransmission may help to understand the beneficial effect of cholinesterase inhibitors in Alzheimer's disease.

Acetylcholine↗

PubMed1999

Neurochemical evidence of dopamine release by lateral olivocochlear efferents and its presynaptic modulation in guinea-pig cochlea.

In this study, using an in vitro superfusion technique for the first time, we provide direct neurochemical evidence of the transmitter role of dopamine at the level of lateral olivocochlear efferent fibres of the guinea-pig cochlea. Our results revealed that nerve terminals are able to take up and release dopamine upon axonal stimulation. Since dopamine is thought to protect the afferent nerve fibres from damage due to acoustic trauma or ischaemia, enhancement of the release of dopamine, a potential therapeutic site of these injuries, was investigated. Positive modulation of dopamine release has been shown by a D1 dopamine receptor agonist, an antagonist and piribedil. Furthermore, negative feedback on the stimulation-evoked release of dopamine via D2 dopamine receptors has been excluded. Electrical stimulation of the cochlear tissue produced a significant and reproducible release of [3H]dopamine, which could be blocked by tetrodotoxin (1 microM) and cadmium (100 microM), proving that axonal activity releases dopamine and its dependence on Ca2+ influx verifies its neuronal origin. Nomifensine, a high-affinity dopamine uptake blocker, prevented the tissue from taking up [3H]dopamine from the bathing solution, also indicating the neural origin of dopamine released in response to stimulation. SKF-38393 (a selective D1 agonist) increased both the resting and electrically evoked release of dopamine. Piribedil (a D3/D2/D1 agonist), a drug under investigation, known to prevent acoustic trauma or ischaemia-induced hearing loss, had a similar and concentration-dependent increasing effect on both resting and evoked release of dopamine. The effect of both drugs on stimulation-evoked release could be prevented by SKF-83566 (a selective D1 antagonist). However, SKF-83566 alone enhanced the resting and axonal conduction-associated release of dopamine. D2 agonists and antagonists failed to modulate the release of dopamine, indicating the lack of negative feedback modulation of dopamine release. Our results suggest that the release of dopamine was subjected to modulation by a D1 receptor agonist and an antagonist. In addition, it is concluded that D2 receptors are not involved in the modulation of dopamine release. This observation may have clinical relevance in the prevention or therapy of particular types of hearing loss, because enhanced dopaminergic input into the primary auditory neuron may inhibit the (over)excitation of this neuron by glutamatergic input from inner hair cells.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1999

Local regulation of vasopressin and oxytocin secretion by extracellular ATP in the isolated posterior lobe of the rat hypophysis.

It is now widely accepted that ATP functions as a signalling substance in the nervous system. The presence of P2 receptors mediating the action of extracellular ATP in brain regions involved in hormonal regulation raises the possibility that a similar role for ATP might also exist in the neuroendocrine system. In this study, the release from the rat isolated neurohypophysis preparation of endogenous ATP, oxytocin and vasopressin (AVP) were measured simultaneously using luciferin-luciferase and RIA techniques. After 70 min preperfusion, electrical field stimulation caused a rapid increase in the amount of ATP in the effluent and the release of AVP and oxytocin also increased stimulation-dependently. Inhibition of voltage-dependent Na+ channels by tetrodotoxin (1 microM) reduced the stimulation-evoked release of AVP and oxytocin; however, the evoked release of ATP remained unaffected. The effect of endogenous ATP on the hormone secretion was tested by suramin (300 microM), the P2 receptor antagonist. Suramin significantly increased the release of AVP, and the release of oxytocin was also enhanced. ATP, when applied to the superfusing medium, decreased the release of AVP, but not that of oxytocin, and its effect was prevented by suramin. ATP (60 nmol), added to the tissues, was readily decomposed to ADP, AMP and adenosine measured by HPLC combined with ultraviolet light detection, and the kinetic parameters of the enzymes responsible for inactivation of ATP (ectoATPase and ecto5'-nucleotidase) were also determined (Km=264+/-2.7 and 334+/-165 microM and vmax=6.7+/-1.1 and 2.54+/-0.24 nmol/min per preparation (n=3) for ectoATPase and ecto5'-nucleotidase respectively). Taken together, our data demonstrate the stimulation-dependent release, P2 receptor-mediated action and extracellular metabolism of endogenous ATP in the posterior lobe of the hypophysis and indicate its role, as a paracrine regulator, in the local control of hormone secretion.

Adenosine Triphosphate↗

PubMed1998

Lobeline inhibits Ca2+ current in cultured neurones from rat sympathetic ganglia.

The effect of lobeline was studied on the voltage-activated Ca2+ current in sympathetic neurones from the rat superior cervical ganglia using the whole-cell variant of the patch-clamp technique. Lobeline (10-300 microM) inhibited the Ca2+ current evoked by voltage steps from -80 mV (holding potential) to 0 mV (test potential) in a dose dependent manner. The inhibitory effects of noradrenaline (10 microM) and lobeline (100 microM) were compared using a prepulse protocol with high (+80 mV) depolarization. Within the same cell depolarizing prepulses decreased the inhibitory effect of noradrenaline but did not change the extent of lobeline inhibition. Addition of GTPgammaS (300 microM) to the pipette solution did not prevent the inhibitory effect of lobeline (100 microM) but greatly reduced that of noradrenaline (100 microM). Our experiments suggest, that the weak nicotinic agonist lobeline exerts a direct blocking effect on Ca2+ channels at concentrations commonly used to release transmitters.

Animals↗

PubMed1998

An agonist of adenosine A3 receptors decreases interleukin-12 and interferon-gamma production and prevents lethality in endotoxemic mice.

We have recently observed that the selective adenosine A3 receptor agonist N6-(3-iodobenzyl)-adenosine-5'-N-methyluronamide (IB-MECA) augments interleukin-10 and inhibits tumor necrosis factor-alpha production in endotoxemic mice. In the present study, we extended our investigations into the effect of this compound on the bacterial lipopolysaccharide (endotoxin)-induced inflammatory response in the BALB/c, as well as in the C57BL/6 interleukin-10+/+ and the interleukin-10 deficient C57BL/6 interleukin-10(0)/0 mice strains. In the BALB/c mice, i.p. pre-treatment with IB-MECA (0.2 and 0.5 mg/kg) decreased lipopolysaccharide (60 mg/kg i.p.)-induced plasma levels of interleukin-12 (p40 and p70), interferon-gamma, and nitrite/nitrate (breakdown products of nitric oxide (NO)). On the other hand, pre-treatment with this compound failed to influence lipopolysaccharide-induced plasma interleukin-1 alpha, interleukin-6, and corticosterone concentrations. Similar to its effect in BALB/c mice, IB-MECA enhanced the release of interleukin-10 in the C57BL/6 interleukin-10+/+ mice. Furthermore, IB-MECA inhibited the production of interleukin-12, interferon-gamma, and NO in both the C57BL/6 interleukin-10+/+ and C57BL/6 interleukin-10(0)/0 mice, suggesting that the inhibition of pro-inflammatory cytokine production by this compound is independent of the increased release of interleukin-10. Finally, pre-treatment with this compound protected mice against lipopolysaccharide (60 mg/kg i.p.)-induced lethality. These results indicate that stimulation of adenosine A3 receptors has potent anti-inflammatory effects and may represent a potential strategy in the treatment of septic shock and other inflammatory diseases.

Adenosine↗

PubMed1998

Stimulation of beta-adrenoceptors inhibits endotoxin-induced IL-12 production in normal and IL-10 deficient mice.

Stimulation of beta-adrenoceptors has been shown to regulate the production of various inflammatory mediators. In the present study, we investigated in mice whether ligation of beta-adrenoceptors, modulates lipopolysaccharide (LPS)-induced plasma levels of interleukin (IL)-12, interferon-gamma (IFN-gamma), and IL-10. In BALB/c mice, isoproterenol (1-10 mg kg(-1) , i.p.), a selective agonist of beta-adrenoceptors and also dexamethasone (10 mg kg(-1), i.p.) pretreatment 30 min before the administration of LPS suppressed plasma IL-12 (p40 and p70) concentrations as determined at various time points after the LPS challenge. The inhibition of IL-12 release by isoproterenol was prevented by the beta-adrenoceptor antagonist propranolol confirming the involvement of beta-adrenoceptors in the effect of isoproterenol. Furthermore, pretreatment of the animals with propranolol alone enhanced LPS-induced plasma IL-12, suggesting that endogenous catecholamines inhibit IL-12 production via the beta-adrenoceptors. In IL-10 deficient C57BL/6 IL-10(-/-) mice, plasma levels of IL-12 and IFN-gamma were significantly higher than in their counterparts, with more than 70-fold increase in IL-12. Furthermore, while augmenting the IL-10 response in C57BL/6 IL-10(+/+), isoproterenol inhibited the production of IL-12 in both the C57BL/6 IL-10(+/+) and C57BL/6 IL-10(-/-) mice, suggesting that the inhibition of IL-12 production by this compound is independent of the increased release of IL-10. Our results demonstrate, for the first time, that stimulation of beta-adrenoceptors by isoproterenol or endogenous catecholamines suppresses IL-12 production in vivo.

Adrenergic beta-Agonists↗

PubMed1998

Receptor-mediated local fine-tuning by noradrenergic innervation of neuroendocrine and immune systems.

Immune responses can be modulated by noradrenergic input at (1) hypothalamic (CRF and ACTH release), (2) immune cell (cytokine production), and (3) adrenal cortex (glucocorticoid production) level. Elucitating the basic mechanisms responsible for immunological responses and diseases may be helpful in developing therapeutic approaches for many disorders, such as autoimmune diseases.

Adrenal Cortex↗

PubMed1998

Na+ channel block prevents the ischemia-induced release of norepinephrine from spinal cord slices.

The principal finding of the present study with rat spinal cord slices was the novel demonstration of the [Ca2+]o-independent effect of ischemia on norepinephrine release and its antagonism by tetrodotoxin and low temperature (10 degrees C). Our finding that tetrodotoxin antagonized the effects of glucose deprivation on norepinephrine release in a [Ca2+]o-independent way suggests that Na+ channel block alone, i.e., the prevention of Na+ accumulation, may account for the protective action. Low temperature completely prevented the effect of ischemia on norepinephrine release but did not change the release associated with axonal activity. This finding is in good agreement with the observation that small changes in brain temperature critically determine the extent of neuronal injury from ischemia and suggests that both [Ca2+]o-independent release and cell injury are associated with the norepinephrine membrane carrier. It is suggested, therefore, that drugs able to attenuate the increase in [Na+]i during ischemia may be useful agents to protect against ischemic damage if given before the insult.

4-Aminopyridine↗

PubMed1998

Neurochemistry and pharmacology of the major hippocampal transmitter systems: synaptic and nonsynaptic interactions.

Hippocampus plays a crucial role in important brain functions (e.g. memory, learning) thus in the past two decades this brain region became a major objective of neuroscience research. During this period large number of anatomical, neurochemical and electrophysiological data have been accumulated. While excellent reviews have been published on the anatomy and electrophysiology of hippocampal formation, the neurochemistry of this area has not been thoroughly surveyed. Therefore the aim of this review is to summarize the neurochemical and pharmacological data on the release of the major neurotransmitters found in the hippocampal region: glutamate (GLU), gamma-amino butyric acid (GABA), acetylcholine (ACh), noradrenaline (NA) and serotonin (5-HT). In addition, this review analyzes the synaptic and nonsynaptic interactions between hippocampal neuronal elements and overviews how auto- and heteroreceptors are involved in the presynaptic modulation of transmitter release. The presented data clearly show that transmitters released from axon terminals without synaptic contact play an important role in the fine tuning of communication between neurons within a neuronal circuit.

Animals↗

PubMed1998

Suppression of IL-12 production by phosphodiesterase inhibition in murine endotoxemia is IL-10 independent.

Phosphodiesterase (PDE) inhibitors are potent regulators of various immune processes. Immune cells contain type IV and type III PDE. Here we studied in mice the effects of rolipram, a selective PDE IV inhibitor, and amrinone, a selective PDE III blocker, on plasma levels of IL-12 (p70), IFN-gamma, IL-1, TNF-alpha, and nitric oxide (NO) induced by intraperitoneal injection of Escherichia coli lipopolysaccharide (LPS) (80 mg/kg). Pretreatment of BALB/c mice with both rolipram (1-25 mg/kg) and amrinone (10-100 mg/kg) decreased plasma IL-12 levels in a dose-dependent manner. Similarly, LPS-elicited plasma IFN-gamma concentrations were suppressed by both rolipram and amrinone. However, LPS-induced plasma IL-1alpha levels were not affected by either of these compounds. In addition, rolipram inhibited IL-12, IFN-gamma, TNF-alpha and nitrite/nitrate (breakdown products of NO) production in C57BL/6 IL-10(+/+) mice as well as in their IL-10-deficient counterparts (C57BL/6 IL-10(-/-)). Our results suggest that rolipram and amrinone decrease the immune activation in endotoxemia through inhibition of the production of pro-inflammatory mediators IL-12, IFN-gamma, TNF-alpha and NO. These effects are not the consequences of the increase in IL-10 production by PDE inhibition.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1998

Role of different bombesin receptor subtypes mediating contractile activity in cat upper gastrointestinal tract.

Mammalian bombesin-like peptides, gastrin-releasing peptide (GRP) and neuromedin B (NMB) are known to increase the motility of different segments in the gut. The present study was carried out to identify the bombesin receptor subtypes mediating the contractions induced by exogenous bombesin-like peptides in muscle strips isolated from cat esophagus, fundus, and duodenum. Both GRP-10 and NMB evoked concentration-dependent contractions in circular strips of esophagus and fundus and in longitudinal strips of the duodenum. These contractions were tetrodotoxin- and atropine-resistant. The potency of NMB in esophageal strips was 33 times higher than that of GRP-10. The NMB-preferring receptor antagonists D-Nal-Cys-Tyr-D-Trp-Lys-Val-Cys-Nal-NH2 (SSocta) and D-Nal-cyclo[Cys-Tyr-D-Trp-Orn-Val-Cys]-Nal-NH2 (BIM-23127) shifted the NMB and GRP concentration-response curves to the right, while the GRP-preferring receptor antagonist [D-Phe6]Bombesin(6-13)-methyl-ester (BME) did not affect the response to the peptides. Isolated muscle strips from the cat fundus and duodenum showed a higher sensitivity to GRP-10 than to NMB. In both segments, BME shifted the GRP-10 and NMB concentration-response curves to the right, while SSocta had no effect. The antagonism of BME was competitive on duodenal but not competitive on fundic muscle. We conclude that the direct myogenic action of GRP-10 and NMB in the esophagus is mediated mainly via NMB-preferring receptors, while GRP-preferring receptors are responsible for the contractile responses to bombesin-like peptides in feline fundus and duodenum. Our data suggest that the GRP receptor population located on fundic muscle might be nonhomogeneous.

Animals↗

PubMed1998

ATP released by LPS increases nitric oxide production in raw 264.7 macrophage cell line via P2Z/P2X7 receptors.

P2Z/P2X7 receptor is a particular type of purinoceptor, which is selectively expressed on the surface of immune cells in neuronal and non-neuronal tissues. Despite intensive research on its involvement in the immune response, the exact mechanism whereby it affects intercellular signaling is far from clear yet. In this study, the effect of activation P2Z/P2X7 receptor was investigated on the bacterial lipopolysaccharide induced nitric oxide production in RAW 264.7 macrophage call line using the nitrite/nitrate assay. The P2Z/P2X7 receptor agonist 3'-O-(4-benzoylbenzoyl)-adenosine 5'triphosphate increased concentration-dependency the lipoplysaccharide (10 microg/ml) induced nitric oxide production between 10 microM and 250 microM. ATP also increased nitric oxide production in response to lipopolysaccharide, while ADP, 2-methylo-thio-adenosine 5'-triphosphate and adenosine 5'triphosphate-gamma-S was without effect. Pretreatment with oxidized adenosine triphosphate, the selective P2Z/P2X7 receptor antagonise (300 microM-1 microM) strongly decreased lipopolysaccaride induced nitric oxide production. Furthermore, on macrophages, pretreated with oxidized adenosine 5'-triphosphate (300 microM-1 mM), 3'-O-(4-benzoylbenzoyl)-adenosine 5'-triphosphate and ATP did not affect lipopolysaccharide induced nitric oxide production. 15 min lipopolysaccharide treatment induced a transient and reversible release of endogenous ATP from RAW 264.7 cells, measured by the luciferin-luciferase assay. The effect of lipopolysaccharide to promote ATP release was concentration-dependent between 1-10 microg/ml. In summary, our results show that P2Z/P2X7 receptor activation results in an increase in nitric oxide production in response to lipopolysaccharide challenge. Since the P2Z/P2X7 receptor antagonist oxidized adenosine triphosphate decreased lipopolysaccharide induced nitric oxide production, and lipopolysaccharide was able to promote ATP release from macrophage cells, it seems likely that endogenous ATP is involved in nitric oxide formation during endotoxin challenge.

Adenosine Triphosphate↗

PubMed1998

Different temperature dependence of carrier-mediated (cytoplasmic) and stimulus-evoked (exocytotic) release of transmitter: a simple method to separate the two types of release.

The temperature dependence of transmitter release associated with axonal conduction, evoked by ligand-gated mechanism and by reversed operation of plasma membrane transporter was studied in superfused slice preparation. When the temperature was reduced from 37-17 degrees C the release of [3H]noradrenaline ([3H]NA) and [3H]dopamine ([3H]DA) in response to field stimulation was significantly enhanced in slice preparations of the hippocampus and main olfactory bulbs. The release of [3H]dopamine evoked by a ligand-gated mechanism (nicotine receptor stimulation) was potentiated at low temperature (12 degrees C). In contrast, when transmitter release was evoked by ouabain, a drug inhibiting Na+/K+-activated ATPase and thereby increasing [Na+]i the release of [3H]GABA was enhanced. This release was very sensitive to cooling (Q10=3.5 between 37 degrees C and 27 degrees C), indicating that the release was induced by a reversed operation of the transporter. The excessive release of [3H]NA from the hippocampal slice in response to oxygen and glucose deprivation (simulation of ischemia) was also inhibited in a temperature-dependent manner. Because at low temperatures (17-12 degrees C) only one type of release mechanism (exocytosis) is operational and carrier-mediated uptake and release is inhibited, this temperature condition provides a method to study the mode of action of different drugs (e.g. amphetamine) and the effect(s) of certain conditions (e.g. ischemia) on the mechanisms of transmitter release, specifically whether they exert their transmitter releasing effect through an exocytotic process or through the reversed operation of plasma membrane transporter. This finding also suggests that it would be important to re-examine mechanistic conclusions based on results from electrophysiological, neurochemical and pharmacological studies that have been carried out at room temperature (approximately 20 degrees C). In particular because transmitter release associated with the action potential, diffusion, receptor kinetics, active transport in both directions (uptake and release) and the probability of transmitter release are all temperature dependent, it would seem important to carry out experiments involving these processes at physiological temperature (37 degrees C).

Animals↗

PubMed1998

Co-release of endogenous ATP and [3H]noradrenaline from rat hypothalamic slices: origin and modulation by alpha2-adrenoceptors.

The release of endogenous ATP, measured by the luciferin-luciferase assay, and of [3H]noradrenaline from the in vitro superfused rat hypothalamic slices were studied. ATP and [3H]noradrenaline were released simultaneously during resting conditions and in response to low and high frequency field electrical stimulation; the release of both substances were frequency dependent between 2 Hz and 16 Hz. The stimulation-induced release of ATP and [3H]noradrenaline was diminished by more than 80% under Ca2+-free conditions. Tetrodotoxin inhibited the majority of the evoked release of both ATP and [3H]noradrenaline, however, it was less effective in reducing the release of [3H]noradrenaline, than that of ATP. Bilateral stereotaxic injection of 6-hydroxydopamine (4 microg/side) to the ventral part of the ventral noradrenergic bundle, originating from the A1 cell group in the brainstem, resulted in a 55% reduction of endogenous noradrenaline content of the hypothalamic slices, and the tritium uptake and the stimulation-evoked release of [3H]noradrenaline was also markedly reduced. While the basal release of ATP was not affected, the evoked release was diminished by 72% by this treatment. Perfusion of the slices with noradrenaline (100 microM) initiated rapid and continuous tritium release; on the other hand, it did not release any ATP. In contrast, 6 min perfusion of (-)nicotine and 1,1-dimethyl-4-phenyl-piperazinium iodide evoked parallel release of ATP and [3H]noradrenaline which was inhibited by the nicotinic receptor antagonist mecamylamine; 6-hydroxydopamine lesion of the ventral part of the ventral noradrenergic bundle did not affect the nicotine-evoked ATP and [3H]noradrenaline release. While CH 38083, a non subtype-selective alpha2-antagonist and BRL44408, the subtype-selective alpha2AD antagonist augmented the evoked release of [3H]noradrenaline, ARC239, a selective alpha2BC antagonist was without effect. In contrast, neither of the alpha2-antagonists significantly affected the evoked-release of ATP. In summary, we report here that endogenous ATP and [3H]noradrenaline are co-released stimulation-dependently from superfused rat hypothalamic slices. A significant part of the release of both compounds is derived from the nerve terminals, originating from the A1 catecholaminergic cell group of brainstem nuclei. Unlike that from the peripheral sympathetic transmission, noradrenaline and alpha1-adrenoceptor agonists were unable to promote the release of ATP. Conversely, parallel ATP and noradrenaline release could be induced by nicotine receptor activation, but this release does not originate from the same nerve endings. The evoked-release of [3H]noradrenaline is inhibited by endogenous noradrenaline via alpha2AD subtype of adrenoreceptors, while the release of ATP is not subject to this autoinhibitory modulation. In conclusion, our results support the view that ATP is involved in the neurotransmission in the hypothalamus, but the sources of the released ATP and noradrenaline seem to be not identical under different stimulatory and modulatory conditions.

Adenosine Diphosphate↗

PubMed1998

The triangular septal nucleus as the major source of ATP release in the rat habenula: a combined neurochemical and morphological study.

The role of ATP as a fast neurotransmitter is emerging from several lines of physiological and pharmacological studies. The bulk of experimental data on release properties and purinergic receptor-mediated postsynaptic potentials derives from studies in the habenula, but the source of the stimulation-evoked ATP release in this region is still unknown. In the present study, retrograde and anterograde tracing techniques were used to establish that both calretinin-containing and calretinin-negative neurons in the triangular septal and septofimbrial nuclei send a massive projection to the medial habenula, where they form asymmetrical synapses with their target neurons. The cells of origin, their axon terminals, as well as their synaptic targets remained unstained in sections immunostained for GABA. Electrolytic lesions of this anatomically circumscribed pathway resulted in an over 80% decrease in ATP release from habenula slices evoked by electric field stimulation. The possibility of transneuronal effects and release from local collaterals of habenular projection neurons accounting for the decreased ATP release has been excluded, since (i) there were no signs of neuronal degeneration, chromatolysis or atrophy in the habenula, (ii) the projection neurons have extremely sparse local collaterals and (iii) there are apparently no interneurons in the habenula. We conclude that the projection from the triangular septal and septofimbrial nucleus to the habenula uses ATP as a fast neurotransmitter, and its co-transmitter, if any, is likely to be glutamate.

Adenosine Triphosphate↗