Nerve Terminals In Rats Research Articles

KCNQ Channels Enable Reliable Presynaptic Spiking and Synaptic Transmission at High Frequency.

The presynaptic action potential (AP) is required to drive calcium influx into nerve terminals, resulting in neurotransmitter release. Accordingly, the AP waveform is crucial in determining the timing and strength of synaptic transmission. The calyx of Held nerve terminals of rats of either sex showed minimum changes in AP waveform during high-frequency AP firing. We found that the stability of the calyceal AP waveform requires KCNQ (KV7) K+ channel activation during high-frequency spiking activity. High-frequency presynaptic spikes gradually led to accumulation of KCNQ channels in open states which kept interspike membrane potential sufficiently negative to maintain Na+ channel availability. Blocking KCNQ channels during stimulus trains led to inactivation of presynaptic Na+, and to a lesser extent KV1 channels, thereby reducing the AP amplitude and broadening AP duration. Moreover, blocking KCNQ channels disrupted the stable calcium influx and glutamate release required for reliable synaptic transmission at high frequency. Thus, while KCNQ channels are generally thought to prevent hyperactivity of neurons, we find that in axon terminals these channels function to facilitate reliable high-frequency synaptic signaling needed for sensory information processing.SIGNIFICANCE STATEMENT The presynaptic spike results in calcium influx required for neurotransmitter release. For this reason, the spike waveform is crucial in determining the timing and strength of synaptic transmission. Auditory information is encoded by spikes phase locked to sound frequency at high rates. The calyx of Held nerve terminals in the auditory brainstem show minimum changes in spike waveform during high-frequency spike firing. We found that activation of KCNQ K+ channel builds up during high-frequency firing and its activation helps to maintain a stable spike waveform and reliable synaptic transmission. While KCNQ channels are generally thought to prevent hyperexcitability of neurons, we find that in axon terminals these channels function to facilitate high-frequency synaptic signaling during auditory information processing.

N-Glycosylation in isolated rat nerve terminals.

N-linked glycosylation is a ubiquitous protein modification that is capable of modulating protein structure, function and interactions. Many proteins in the brain associated with the synapse and important for synaptic transmission are highly glycosylated and their glycosylation could be important for learning and memory related molecular processes and synaptic plasticity. In the present study, we extend the knowledge of the synaptic glycome and glycoproteome by performing glycan- and intact glycopeptide-focused analyses of isolated rat nerve terminals (synaptosomes) by LC-MS/MS. Overall, glycomics identified a total of 41 N-glycans in isolated synaptosomes. Sialylated N-glycans represented only 7% of the total abundance of the rat synaptosome N-glycome with oligomannose, neutral hybrid and complex type N-glycans being the most abundant structures. Using detergent extraction of the active zone proteins from the synaptosomes revealed a change in the active zone glycan abundance in comparison with the rest of the synaptosome glycan content. Characterization of intact sialylated N-linked glycopeptides enriched by titanium dioxide chromatography revealed more than 85% selectivity of sialylated species and the presence of NeuGc on active zone proteins. In addition, both disialic and trisialic acid modified glycans were present on synaptic glycoproteins, although oxonium ion profiling revealed that trisialic units were only present on glycoproteins in the detergent soluble fraction. However, correct identification of intact sialylated N-linked glycopeptides using the Byonic program failed, most likely due to the lack of peptide backbone fragmentation during tandem mass spectrometry.

Depolarization-dependent Induction of Site-specific Changes in Sialylation on N-linked Glycoproteins in Rat Nerve Terminals

Synaptic transmission leading to release of neurotransmitters in the nervous system is a fast and highly dynamic process. Previously, protein interaction and phosphorylation have been thought to be the main regulators of synaptic transmission. Here we show that sialylation of N-linked glycosylation is a novel potential modulator of neurotransmitter release mechanisms by investigating depolarization-dependent changes of formerly sialylated N-linked glycopeptides. We suggest that negatively charged sialic acids can be modulated, similarly to phosphorylation, by the action of sialyltransferases and sialidases thereby changing local structure and function of membrane glycoproteins. We characterized site-specific alteration in sialylation on N-linked glycoproteins in isolated rat nerve terminals after brief depolarization using quantitative sialiomics. We identified 1965 formerly sialylated N-linked glycosites in synaptic proteins and found that the abundances of 430 glycosites changed after 5 s depolarization. We observed changes on essential synaptic proteins such as synaptic vesicle proteins, ion channels and transporters, neurotransmitter receptors and cell adhesion molecules. This study is to our knowledge the first to describe ultra-fast site-specific modulation of the sialiome after brief stimulation of a biological system.

Consequences of perinatal hypoxia in developing brain: Changes in GABA transporter functioning in cortical, hippocampal and thalamic rat nerve terminals

Perinatal hypoxia leads to behavioral abnormalities, cognitive disabilities, and epilepsy resulting from alterations in neurodevelopment, maturation and construction of the network. Considering a particular role of γ-aminobutyric acid (GABA) for an immature brain, we analysed transporter-mediated [3H]GABA uptake in the cortical, hippocampal and thalamic nerve terminals isolated from rats of different age in the control and after perinatal hypoxia. The state of hypoxia was induced by exposure of rats at the age of 10 postnatal days (pd) (that corresponds approximately to the time of birth in humans) to a respiratory medium with low O2 content (4% O2 and 96%N2) for 12min (up to the initiation of clonico-tonic seizures). Here, we found that the initial rate of [3Н]GABA uptake was higher in the young rats (pd 17–19) as compared to the older ones (pd 24–26, 38–40 and 66–73) in both control and hypoxia groups. It decreased abruptly by 50% in the thalamus and by 25% in the cortex for the period from pd 17–19 to pd 66–73. In the hippocampus, a decrease in the rate during the same time interval was 25%. Exposure to hypoxia had no effect on the intensity of [3Н]GABA uptake by the cortical and thalamic nerve terminals, but caused a significant age-dependent attenuation (by 35%) of the uptake intensity in the hippocampal ones. Significant age-dependent hypoxia-independent decrease in [3Н]GABA uptake with step-like dynamics of changes was shown in the thalamus and cortex. Gradual age-dependent hypoxia-dependent decrease in [3Н]GABA uptake was revealed in the hippocampus, and so a particular vulnerability of the latest structure to hypoxia as compared to the cortex and thalamus was revealed.

New effects of GABAB receptor allosteric modulator rac-BHFF on ambient GABA, uptake/release, Em and synaptic vesicle acidification in nerve terminals.

Positive allosteric modulators of GABAB receptors have great therapeutic potential for medications of anxiety, depression, etc. The effects of recently discovered modulator rac-BHFF on the key characteristics of GABAergic neurotransmission were investigated in cortical and hippocampal presynaptic nerve terminals of rats (synaptosomes). The ambient level of [(3)H]GABA that is a balance between release and uptake of the neurotransmitter increased significantly in the presence of rac-BHFF (at concentrations 10-30μM). The initial velocity of synaptosomal [(3)H]GABA uptake was suppressed by the modulator. In the presence of GABA transporter blocker NO-711, it was shown that rac-BHFF increased tonic release of [(3)H]GABA from synaptosomes (at concentrations 3-30μM). Rac-BHFF within the concentration range of 0.3-30μM did not enhance inhibiting effect of (±)-baclofen on depolarization-induced exocytotic release of [(3)H]GABA. Rac-BHFF (0.3-30μM) caused dose-dependent depolarization of the plasma membrane and dissipation of the proton gradient of synaptic vesicles in synaptosomes that was shown in the absence/presence of GABAB receptor antagonist saclofen using fluorescent dyes rhodamine 6G and acridine orange, respectively, and so, the above effects of rac-BHFF were not associated with the modulation of presynaptic GABAB receptors. Therefore, drug development strategy of positive allosteric modulation of GABAB receptors is to eliminate the above side effects of rac-BHFF in presynapse, and vice versa, these new properties of rac-BHFF may be exploited appropriately.

Coenzyme Q10 Inhibits the Release of Glutamate in Rat Cerebrocortical Nerve Terminals by Suppression of Voltage-Dependent Calcium Influx and Mitogen-Activated Protein Kinase Signaling Pathway

This study investigates the effects and possible mechanism of coenzyme Q10 (CoQ10) on endogenous glutamate release in the cerebral cortex nerve terminals of rats. CoQ10 inhibited the release of glutamate evoked by the K+ channel blocker 4-aminopyridine (4-AP). CoQ10 reduced the depolarization-induced increase in cytosolic [Ca2+]c but did not alter the 4-AP-mediated depolarization. The effect of CoQ10 on evoked glutamate release was abolished by blocking the Cav2.2 (N-type) and Cav2.1 (P/Q-type) Ca2+ channels and mitogen-activated protein kinase kinase (MEK). In addition, CoQ10 decreased the 4-AP-induced phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) and synaptic vesicle-associated protein synapsin I, a major presynaptic substrate for ERK. Moreover, the inhibition of glutamate release by CoQ10 was strongly attenuated in mice without synapsin I. These results suggest that CoQ10 inhibits glutamate release from cortical synaptosomes in rats through the suppression of the presynaptic voltage-dependent Ca2+ entry and ERK/synapsin I signaling pathway.

Changes in the levels of CAM kinase II and synapsin I caused by oxidative stress in the rat brain, and its prevention by vitamin E

To define whether oxidative stress and aging induce abnormal dissociation of neurotransmitter-enclosing synaptic vesicles in rat brain nerve terminals, we assessed the activation of Ca+/calmodulin dependent protein kinase II (CAM kinase II) and changes in the levels of synapsin I, which is a synaptic vesicle-associated protein involved in the modulation of neurotransmitter release. Assessment of young rats subjected to hyperoxia-induced oxidative stress and normal aged rats revealed that synaptic CAM kinase II in the rat brain was markedly activated through oxidative stress and aging. In accordance with the activation of CAM kinase II, the levels of phosphorylated synapsin I increased significantly in nerve terminals. Furthermore, it was found that vitamin E prevents these oxidative stress-induced abnormal processes in rat nerve terminals. These results suggest that oxidative stress and aging facilitate the mobilization of neurotransmitter-enclosing synaptic vesicles from the reserve pool in the nerve terminal, thereby inducing abnormal accumulation of synaptic vesicles in the synapse, and that vitamin E inhibits this process in the brain through its antioxidative action.

Developmental shift to a mechanism of synaptic vesicle endocytosis requiring nanodomain Ca2+

Ca(2+) is thought to be essential for the exocytosis and endocytosis of synaptic vesicles. However, the manner in which Ca(2+) coordinates these processes remains unclear, particularly at mature synapses. Using membrane capacitance measurements from calyx of Held nerve terminals in rats, we found that vesicle endocytosis is initiated primarily in Ca(2+) nanodomains around Ca(2+) channels, where exocytosis is triggered. Bulk Ca(2+) outside of the domain could also be involved in endocytosis at immature synapses, although only after extensive exocytosis at more mature synapses. This bulk Ca(2+)-dependent endocytosis required calmodulin and calcineurin activation at immature synapses, but not at more mature synapses. Similarly, GTP-independent endocytosis, which occurred after extensive exocytosis at immature synapses, became negligible after maturation. We propose that nanodomain Ca(2+) simultaneously triggers exocytosis and endocytosis of synaptic vesicles and that the molecular mechanisms underlying Ca(2+)-dependent endocytosis undergo major developmental changes at this fast central synapse.

Presynaptic BK type Ca 2+-activated K + channels are involved in prostanoid TP receptor-mediated inhibition of noradrenaline release from the rat gastric sympathetic nerves

Previously, we reported that prostanoid TP receptor mediates the inhibition of electrically evoked noradrenaline release from gastric sympathetic nerves in rats. Prostanoid TP receptor has been shown to activate phospholipase C (PLC), which catalyzes the hydrolysis of phosphatidylinositol 4,5-bisphosphate to inositol 1,4,5-triphosphate (IP 3) and diacylglycerol; IP 3 triggers the release of Ca 2+ from intracellular stores and diacylglycerol activates protein kinase C. In the present study, therefore, we examined whether these PLC-mediated mechanisms are involved in the TP receptor-mediated inhibition of gastric noradrenaline release using an isolated, vascularly perfused rat stomach. U-46619 (9,11-dideoxy-9α,11α-methanoepoxy PGF 2α) (a prostanoid TP receptor agonist)-induced inhibition of noradrenaline release from the stomach was reduced by U-73122 [1-[6-[[(17β)-3-methoxyestra-1,3,5(10)-trien-17-yl]-amino]hexyl]-1 H-pyrrole-2,5-dine] (a PLC inhibitor) and ET-18-OCH 3 (1- O-octadecyl-2- O-methyl- sn-glycero-3-phosphorylcholine) (a phosphatidylinositol-specific PLC inhibitor), respectively. 2-APB (2-aminoethyldiphenyl borate) (a putative IP 3 receptor antagonist) also abolished the U-46619-induced inhibition of noradrenaline release, but Ro 31-8220 [2-{1-[3-(amidinothio)propyl]-1 H-indol-3-yl}-3-(1-methylindol-3-yl)-maleimide] (a protein kinase C inhibitor) had no effect. Furthermore, a small dose of tetraethylammonium and charybdotoxin [blockers of BK type Ca 2+-activated K + channel] abolished the U-46619-induced inhibition, but apamin (a blocker of SK-type Ca 2+-activated K + channel) had no effect. These results suggest that BK type Ca 2+-activated K + channels are involved in prostanoid TP receptor-mediated inhibition of electrically evoked noradrenaline release from the gastric sympathetic nerve terminals in rats.

Small voltage changes at nerve terminals travel up axons to affect action potential initiation

Nerve terminals are generally considered the destination points for electrical signals, which propagate unidirectionally from the soma to nerve terminals. Here, we demonstrate that small hyperpolarizations or depolarizations (~10 mV), generated under physiological conditions in rat nerve terminals, backpropagate up the axon (~400 – 800 µm), and change the threshold for initiating action potentials and thus firing patterns. These results suggest a novel mechanism for information processing in neurons and neuronal circuits.

Brain-derived neurotrophic factor inhibits GABA uptake by the rat hippocampal nerve terminals

The lifespan of the predominant inhibitory neurotransmitter in the central nervous system, γ-aminobutyric acid (GABA), is determined by its uptake into neurons and glia, through high-affinity Na +/Cl − dependent transporters (GATs). We now evaluated how the uptake of GABA by nerve endings, which is mostly mediated by the GAT-1 subtype, is modulated by brain-derived neurotrophic factor (BDNF). BDNF (10–200 ng/ml) decreased GAT-1-mediated GABA uptake by isolated hippocampal rat nerve terminals (synaptosomes), an effect that occurred within 1 min of incubation with BDNF and blocked by the tyrosine kinase inhibitor K252a (100 nM) as well as by the PLC inhibitor, U73122 (3 μM). Maximum inhibition was attained with 100 ng/ml BDNF. In contrast with what has been observed for other synaptic actions of BDNF, the inhibition of GABA transport by BDNF does not require tonic activation of adenosine A 2A receptors since it was not blocked by the A 2A receptor antagonist SCH 58261 (50 nM). However, in synaptosomes previously depleted of extracellular endogenous adenosine by incubation with adenosine deaminase (1 U/ml), activation of A 2A receptors with the A 2A receptor agonist, CGS 21680 (30 nM), enhanced the inhibitory effect of BDNF upon GABA transport, an action prevented by the A 2A receptor antagonist, SCH 58261 (50 nM). It is concluded that BDNF, through TrkB and PLCγ signalling inhibits GAT-1-mediated GABA transport by nerve endings and that this action is not dependent on, but can be enhanced by, TrkB/A 2A receptor cross talk.

Theoretical and electrophysiological evidence for axial loading about aortic baroreceptor nerve terminals in rats

Arterial baroreceptors are essential for neurocirculatory control, providing rapid hemodynamic feedback to the central nervous system. The pressure-dependent discharge of carotid and aortic baroreceptor afferents has been extensively studied. A common assumption has been that circumferential deformation of the arterial wall is the predominant mechanical force affecting baroreceptor discharge. However, in vivo the arterial tree is under significant longitudinal tension, leading to the hypothesis that axially directed forces may contribute to baroreceptor function. To test this hypothesis, we utilized a combination of finite element modeling methods and an in vitro rat aortic arch preparation. Model formulation utilized traditional analytic constructs available in the literature followed by refinement of model material parameters through direct comparison of computationally and experimentally generated pressure-diameter curves. The numerical simulations strongly indicated a functional role for axial loading within the region of the baroreceptive nerve terminal. This prediction was confirmed through single-fiber recording of baroreceptor nerve discharge under conditions with and without longitudinal tension in the vessel preparation. The recordings (n = 5) demonstrated that longitudinal tension significantly (P < 0.02) lowered both the pressure threshold (P(th), mmHg) for baroreceptor discharge and sensitivity (S(th), Hz/mmHg). The effect was nearly instantaneous and sustained; i.e., under longitudinal tension average P(th) was 84 +/- 3 mmHg and S(th) was 0.71 +/- 0.15 Hz/mmHg, which immediately increased to a P(th) of 94 +/- 4 mmHg and a S(th) of 1.20 +/- 0.32 Hz/mmHg with loss of axial tension. Possible explanations of how an abrupt change in axial loading could result in a synchronized increase in afferent drive of the baroreceptor reflex, and the potentiating effect this could have on neurogenically mediated orthostatic intolerance are discussed.

Attenuation of phospholipid signaling provides a novel mechanism for the action of valproic acid.

Valproic acid (VPA) is used to treat epilepsy and bipolar disorder and to prevent migraine. It is also undergoing trials for cancer therapy. However, the biochemical and molecular biological actions of VPA are poorly understood. Using the social amoeba Dictyostelium discoideum, we show that an acute effect of VPA is the inhibition of chemotactic cell movement, a process partially dependent upon phospholipid signaling. Analysis of this process shows that VPA attenuates the signal-induced translocation of PH(Crac)-green fluorescent protein from cytosol to membrane, suggesting the inhibition of phosphatidylinositol-(3,4,5)-trisphosphate (PIP(3)) production. Direct labeling of lipids in vivo also shows a reduction in PIP and PIP(2) phosphorylation following VPA treatment. We further show that VPA acutely reduces endocytosis and exocytosis-processes previously shown to be dependent upon PIP(3) production. These results suggest that in Dictyostelium, VPA rapidly attenuates phospholipid signaling to reduce endocytic trafficking. To examine this effect in a mammalian model, we also tested depolarization-dependent neurotransmitter release in rat nerve terminals, and we show that this process is also suppressed upon application of VPA and an inhibitor of phosphatidylinositol 3-kinase. Although a more comprehensive analysis of the effect of VPA on lipid signaling will be necessary in mammalian systems, these results suggest that VPA may function to reduce phospholipid signaling processes and thus may provide a novel therapeutic effect for this drug.

Persistence of tolerance to methamphetamine-induced monoamine deficits

Methamphetamine is a highly addictive and potent stimulant, the use of which has increased significantly in recent years. In addition to the severe behavioral and societal consequences associated with methamphetamine abuse, methamphetamine can cause persistent damage to monoaminergic nerve terminals in rats, as measured by either monoamine concentrations or activity of the rate limiting synthetic enzymes, tyrosine hydroxylase and tryptophan hydroxylase. Repeated, sub-neurotoxic doses of methamphetamine, however, can cause rats to become resistant to the neurotoxic effects of multiple high-dose administrations of methamphetamine; a phenomenon known as tolerance. This study investigates the persistence of tolerance evoked by pretreatment with escalating-dose administrations of methamphetamine. Rats were pretreated over several days with low, escalating doses of methamphetamine, followed by high-dose methamphetamine challenge after variable recovery periods. Results revealed that tolerance to monoaminergic deficits persisted for at least one week, but was completely eliminated by 31 days. There were no differences in the distribution of methamphetamine or its major metabolite, amphetamine, between methamphetamine-pretreated animals and saline-pretreated animals 2 h after the final methamphetamine challenge injection, and there were no regional differences in methamphetamine concentrations between the frontal cortex, hippocampus or striatum. We also observed that while methamphetamine pretreatment attenuated the hyperthermia caused by the high-dose methamphetamine challenge, significant reductions in methamphetamine-induced hyperthermia were not required for the development of tolerance with this regimen.

Increase of acetylcholine release by Panax ginseng root enhances insulin secretion in Wistar rats

The present study was designed to ascertain the effect of Panax ginseng root on plasma glucose and investigate the possible mechanisms for the effect. Ninety minutes after the oral administration of P. ginseng root to fasting Wistar rats, plasma glucose decreased in a dose-dependent manner. Simultaneous with the reduction in plasma glucose, an increase in the plasma level of insulin and C-peptide was also observed. Moreover, disruption of the available synaptic acetylcholine (ACh), using the inhibitor for choline uptake (hemicholinium-3), or the inhibitor for vesicular choline transport (vesamicol), abolished the metabolic actions of P. ginseng root. Conversely, physostigmine, at a concentration sufficient to inhibit acetylcholinesterase, enhanced the metabolic effect of P. ginseng root. It is possible that P. ginseng root mediates the release of ACh from nerve terminals to enhance insulin secretion. Blockade of the actions of P. ginseng root by 4-diphenylacetoxy- N-methylpiperdine methiodide (4-DAMP) suggested that the site of action is the muscarinic M 3 receptor. Taken together, the results suggest that P. ginseng root has the ability to increase the release of ACh from nerve terminals in rats so as to stimulate muscarinic M 3 receptors activity located in the pancreatic cells for the secretion of insulin, which in turn lower plasma glucose.

Neurophysiological and immunohistochemical studies on Guillain-Barré syndrome with IgG anti-GalNAc-GD1a antibodies—effects on neuromuscular transmission

We investigated the epitopes and functional role of IgG anti-GalNAc-GD1a antibodies appearing in serum from a patient with Guillain-Barré syndrome (GBS) and IgG anti-GalNAc-GD1a antibody that was produced by immunization of a rabbit with GalNAc-GD1a. Both sera blocked neuromuscular transmission in muscle–spinal cord co-culture cells. The acetylcholine-induced potential did not reduce by adding sera, suggesting that the blockade is presynaptic. The effect was complement-independent and purified IgG from serum of the patient or the rabbit had the same effects. The epitope with both anti-GalNAc-GD1a antibodies was observed in the soma of large neurons in the anterior horns of the adult rat spinal cord and their motor axons of rat ventral roots. Both anti-GalNAc GD1a antibodies reacted strongly with the motor nerve terminals in rats. The anti-GalNAc-GD1a antibodies may block neuromuscular transmission by attacking on presynaptic motor axon, probably affecting the ion channels in the presynaptic motor axon.

The Human Immunodeficiency Virus-1 Protein Tat and Its Discrete Fragments Evoke Selective Release of Acetylcholine from Human and Rat Cerebrocortical Terminals through Species-Specific Mechanisms

The effect of the human immunodeficiency virus-1 protein Tat was investigated on neurotransmitter release from human and rat cortical nerve endings. Tat failed to affect the release of several neurotransmitters, such as glutamate, GABA, norepinephrine, and others, but it evoked the release of [3H]ACh via increase of cytosolic [Ca2+]. In human nerve terminals, the Tat effect partly depends on Ca2+ entry through voltage-sensitive Ca2+ channels, because Cd2+ halved the Tat-evoked release. Activation of group I metabotropic glutamate receptors (mGluR) and mobilization of Ca2+ from IP3-sensitive intraterminal stores are also involved, because the Tat effect was prevented by mGluR antagonists 2-methyl-6-(phenylethynyl)pyridine hydrochloride and 7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxylate ethyl ester and by the IP3 receptor antagonists heparin and xestospongin C. Furthermore, the group I selective mGlu agonist (RS)-3,5-dihydroxyphenylglycine enhanced [3H]ACh release. In rat nerve terminals, the Tat-evoked release neither depends on external Ca2+ ions entry nor on IP3-mediated mechanisms. Tat seems to cause mobilization of Ca2+ from ryanodine-sensitive internal stores because its effect was prevented by both 8-bromo-cyclic adenosine diphosphate-ribose and dantrolene. The Tat-evoked release from human synaptosomes was mimicked by the peptide sequences Tat 32-62, Tat 49-86, and Tat 41-60. In contrast, the Tat 49-86 and Tat 61-80 fragments, but not the Tat 32-62 fragment, were active in rat synaptosomes. In conclusion, Tat elicits Ca2+-dependent [3H]ACh release by species-specific intraterminal mechanisms by binding via discrete amino acid sequences to different receptive sites on human and rat cholinergic terminals.

Is frequent dosing with ecstasy a risky business for dopamine-containing neurons?

Over the past 20 years 3,4-methylenedioxymethamphetamine (MDMA; also known as ‘ecstasy’) has become a widely used recreational drug of abuse. However, studies have indicated that it is neurotoxic to serotonergic nerve terminals in rats and non-human primates and dopaminergic nerve terminals in mice. Recently, this tenet has been questioned following a study suggesting that MDMA can cause toxicity to dopamine-containing neurons in monkeys. In this article, the factors contributing to this change in neurotoxic profile are discussed.

Effects of 8- iso-prostaglandin E 2 and 8- iso-prostaglandin F 2α on the release of noradrenaline from the isolated rat stomach

In the present experiment, we examined the effect of 8- iso-prostaglandin E 2 and 8- iso-prostaglandin F 2α on the release of noradrenaline from the isolated rat stomach. The postganglionic sympathetic nerves were electrically stimulated twice at 1 Hz for 1 min and test reagents were added during the second stimulation. 8-Iso-prostaglandin E 2 (10 −8–10 −6 M) and 8- iso-prostaglandin F 2α (10 −7–10 −5 M) dose-dependently reduced the evoked noradrenaline release, and these inhibitory potencies were as follows: 8- iso-prostaglandin E 2>8- iso-prostaglandin F 2α. The inhibitory effect of 8- iso-prostaglandin F 2α, but not 8- iso-prostaglandin E 2, was abolished by 10 −6 M SQ-29548 ([1 S-[1α,2α( Z),3α,4α]]-7-[3-[[2-[(phenylamino)carbonyl]hydrazino] methyl]-7-oxabicyclo[2,2,1]hept-2-yl]-5-heptenoic acid) (a prostanoid TP receptor antagonist). On the other hand, the inhibitory effect of 8- iso-prostaglandin E 2 was abolished by 10 −5 M AH-6809 (6-isopropoxy-9-oxoxanthene-2-carboxylic acid) (a prostanoid EP receptor antagonist), which also attenuated the inhibitory effects of ONO-AE-248 (16 S-9-deoxy-9β-chloro-15-deoxy-16-hyfroxy-17,17-trimethylene 19, 20-didehydro prostaglandin F 2) (a selective EP 3 receptor agonist) on the evoked release of noradrenaline. The inhibitory effect of 8- iso-prostaglandin F 2α, but not 8- iso-prostaglandin E 2, was abolished by pertussis toxin. These results suggest that 8- iso-prostaglandin F 2α inhibits noradrenaline release through TP receptors, whereas 8- iso-prostaglandin E 2 seems to inhibit noradrenaline release through EP 3 receptors, located on the gastric sympathetic nerve terminals in rats.

Depletion of radiosensitive leukocytes exacerbates the heart sympathetic denervation and parasitism in experimental Chagas' disease in rats

The acute phase of the Trypanosoma cruzi infection induces damage of the heart sympathetic nerve terminals in rats. The participation of the radiosensitive leukocytes in this process was assessed in young rats submitted to gamma irradiation 1 day before infection with T. cruzi, Y strain. Gamma irradiation increased the heart noradrenergic denervation evaluated at day 12 of infection by histochemical and electron-microscopic methods. The presence of numerous macrophages with ultrastructural features of activation and a significant rise in the myocardial parasitism suggest the involvement of radioresistant macrophages or parasite factors, or both, on the damage of the nerve terminals.