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At least 73 records · Page 4Linked to original sources
PubMed1982

The use of low concentrations of divalent cations to demonstrate a role for N-methyl-D-aspartate receptors in synaptic transmission in amphibian spinal cord.

1 Synaptic potentials and the responses of frog spinal cord to various acidic amino acids were examined by means of the sucrose gap recording technique. 2 Divalent cations (50-250 microM) specifically antagonized responses evoked at N-methyl-D-aspartate (NMDA) receptors by N-methyl D,L aspartic acid (NMDLA). The rank order of potency was Ni2+ greater than Co2+ greater than Mg2+ greater than Mn2+. Responses to glutamate and aspartate were relatively insensitive to these concentrations of divalent cations. 3 The rank order of potency for divalent ions (1 mM) for antagonism of synaptic transmission in bullfrog sympathetic ganglia was Mn2+ greater than Co2+ greater than Ni2+ greater than Mg2+. Thus synaptic transmission in ganglia was especially sensitive to Mn2+ whereas NMDLA responses were especially sensitive to Co2+ and Mg2+. 4 It was possible to depress selectively the dorsal root-dorsal root potential (DR-DRP) and dorsal root-ventral root potential (DR-VRP) of frog spinal cord using low doses of Co2+ or Mg2+ which did not affect VR-DRP (ventral root-dorsal root potential). It was not possible to produce this selective depression of DR-DRP and DR-VRP with Mn2+, as this cation non-selectively depressed all responses. 5 These results suggest that: (i) divalent cations do not antagonize NMDLA responses by blocking Ca2+ channels which may mediate the response; (ii) postsynaptic NMDA receptors are activated by a neurotransmitter involved in the DR-DRP and DR-VRP pathways but not by any neurotransmitters involved in the VR-DRP pathway; (iii) the neurotransmitter activating NMDA receptors in amphibian spinal cord may be an aspartate-like substance rather than aspartate itself or glutamate.

Animals↗
PubMedDate not supplied

Synaptic transmission in ammonia intoxication.

Ammonia intoxication allegedly plays a significant role in the pathophysiology of hepatic encephalopathy. In order to understand the pathogenesis of this encephalopathy it is necessary to know the effects of ammonia on the mechanisms by which neurons communicate, i.e., excitatory and inhibitory synaptic transmissions. NH4+ decreases excitatory synaptic transmission mediated by glutamate. Possibly, this effect is related to a depletion of glutamate in presynaptic terminals. NH4+ decreases inhibitory synaptic transmission mediated by hyperpolarizing Cl(-)-dependent inhibitory postsynaptic potentials. This effect is related to the inactivation of the extrusion of Cl- from neurons by NH4+. By the very same action, NH4+ also decreases the hyperpolarizing action of Ca2+- and voltage-dependent Cl- currents. These currents may modify the efficacy of the synaptic input to neurons and increase neuronal excitability. Estimates derived from experimental observations suggest that an increase of CNS tissue NH4+ to 0.5 mumol/g is sufficient to disturb excitatory and inhibitory synaptic transmission and to initiate the encephalopathy related to acute ammonia intoxication. Chronic portasystemic shunting of blood, as in hepatic encephalopathy, significantly changes the relation between CNS NH4+ and function of synaptic transmission. A portacaval shunt increases the tissue NH4+ necessary to disturb synaptic transmission. However, after a portasystemic shunt, synaptic transmission becomes extremely sensitive to any acute increase of NH4+ in the CNS.

Ammonia↗
PubMed2000

Glycolysis prevents anoxia-induced synaptic transmission damage in rat hippocampal slices.

Prolonged anoxia can cause permanent damage to synaptic transmission in the mammalian CNS. We tested the hypothesis that lack of glucose is the major cause of irreversible anoxic transmission damage, and that anoxic synaptic transmission damage could be prevented by glycolysis in rat hippocampal slices. The evoked population spike (PS) was extracellularly recorded in the CA1 pyramidal cell layer after stimulation of the Schaffer collaterals. When the slice was superfused with artificial cerebrospinal fluid (ACSF) containing 4 mM glucose, following 10 min anoxia, the evoked PS did not recover at all after 60 min reoxygenation. When superfusion ACSF contained 10 mM glucose with or without 0.5 mM alpha-cyano-4-hydroxycinnate (4-CIN), after 60 min reoxygenation the evoked PS completely recovered following 10 min anoxia. When superfusion ACSF contained 20 mM glucose with or without 1 mM sodium cyanide (NaCN), after 60 min reoxygenation the evoked PS completely recovered even following 120 min anoxia. In contrast, when superfusion ACSF contained 4 mM glucose, following 10 min 1 mM NaCN chemical anoxia alone, without anoxic anoxia, the evoked PS displayed no recovery after 60 min reoxygenation. Moreover, when 16 mM mannitol and 16 sodium L-lactate were added into 4 mM glucose ACSF, following 10 min anoxia the evoked PS failed to recover at all after 60 min reoxygenation. The results indicate that elevated glucose concentration powerfully protected the synaptic transmission against anoxic damage, and the powerful protection is due to anaerobic metabolism of glucose and not a result of the higher osmolality in higher glucose ACSF. We conclude that lack of glucose is the major cause of anoxia-induced synaptic transmission damage, and that if sufficient glucose is supplied, glycolysis could prevent this damage in vitro.

Animals↗
PubMed2006

Deficits in synaptic transmission and learning in amyloid precursor protein (APP) transgenic mice require C-terminal cleavage of APP.

Synaptic dysfunction has been shown to be one of the earliest correlates of disease progression in animal models of Alzheimer's disease. Amyloid-beta protein (Abeta) is thought to play an important role in disease-related synaptic dysfunction, but the mechanism by which Abeta leads to synaptic dysfunction is not understood. Here we describe evidence that cleavage of APP in the C terminus may be necessary for the deficits present in APP transgenic mice. In APP transgenic mice with a mutated cleavage site at amino acid 664, normal synaptic transmission, synaptic plasticity, and learning were maintained despite the presence of elevated levels of APP, Abeta42, and even plaque accumulation. These results indicate that cleavage of APP may play a critical role in the development of synaptic and behavioral dysfunction in APP transgenic mice.

Alzheimer Disease↗
PubMed1987

The probabilistic nature of synaptic transmission at a mammalian excitatory central synapse.

The synaptic connection between single group I afferents and dorsal spinocerebellar tract (DSCT) neurons in the cat spinal cord has been studied in an attempt to gain insight into the mechanisms of excitatory synaptic transmission in the mammalian CNS. Fluctuations in the amplitude of single group I fiber EPSPs in DSCT neurons were examined using a numerical deconvolution procedure to reduce the effects of contaminating noise. In general, it was found that single fiber EPSPs fluctuate in peak amplitude between discrete levels separated by equal or quantal increments. Many previous studies have proposed simple binomial statistics as a general model of quantal synaptic transmission. In the present study we show that simple binomial statistics do not describe the fluctuations in amplitude of single group I fiber EPSPs in DSCT neurons. It is suggested that nonuniformities in the probability of transmitter release from release site to release site explain the failure of the binomial model to describe the EPSP fluctuation pattern at this synapse. Nonuniform quantal transmission is proposed as a more adequate description of excitatory synaptic transmission in the mammalian CNS.

Animals↗
PubMed1997

Orphanin FQ inhibits synaptic transmission and long-term potentiation in rat hippocampus.

It is known that opioid peptides acting on opioid receptors can modulate hippocampal synaptic functions. Although a novel member of the opioid receptor family, ORL1 receptors, that displays high-sequence homology with classical opioid receptors is abundant in the hippocampus, little is known regarding its role in synaptic function. The present study was designed to investigate whether activation of the ORL1 receptor by its natural ligand, orphanin FQ, could modulate synaptic transmission and synaptic plasticity in the hippocampus. The actions of orphanin FQ in the CA1 and dentate gyrus were examined by field potential recordings in response to stimulation of Schaffer collaterals and perforant path, respectively. Our results showed that orphanin FQ, but not the inactive analog des-Phe1-orphanin FQ, reduced both the slope of the excitatory postsynaptic potentials and population spike amplitude. The inhibitory effect of orphanin FQ is dose dependent and probably involves a presynaptic mechanism, as suggested by the significantly increased paired-pulse facilitation evoked in the presence of orphanin FQ. In addition, orphanin FQ was found to inhibit the induction of long-term potentiation at the Schaffer collateral-CA1 synapse. These results demonstrate that orphanin FQ can function as an inhibitory modulator regulating synaptic transmission and synaptic plasticity in the hippocampus, suggesting that activation of ORL1 receptors may play an important role in synaptic plasticity involved in learning and memory.

Amino Acid Sequence↗
PubMed1992

Characteristics of synaptic transmission in reinnervating rat skeletal muscle.

Synaptic transmission, and its sensitivity to the effects of 3,4-diaminopyridine (3,4-DAP) and the phosphatase 2,3-butanedione monoxime (BDM), was examined for "crushed fiber" preparations of rat extensor digitorum longus muscle undergoing reinnervation after nerve crush. While mean quantal content (m) of endplate potentials (EPPs) was low early during reinnervation (10-24 days after nerve crush), elevation of temperature or extracellular calcium concentration restored m toward normal. However, m achieved control values for reinnervating preparations exposed to 3,4-DAP. 3,4-DAP also activated quiescent motor nerve terminals: after exposure to this drug, synaptic transmission was detected as early as 8 days after nerve crush. BDM too activated quiescent regenerating motor nerve terminals and increased m to normal. It also prolonged EPP and endplate current decay, suggesting a pre-synaptic effect on the synchrony of transmitter release and/or a post-synaptic effect on the open time of acetylcholine-gated endplate channels. While the effects of temperature, extracellular calcium, 3,4-DAP, and BDM suggest that regenerating nerve terminals can mobilise a reserve of quanta, this reserve is abnormally low, since hemicholinium-3 caused rapid rundown of EPP amplitude at repetitively stimulated regenerating endplates.

4-Aminopyridine↗
PubMed1999

Ecto-ATPase activity in cerebellum: implication to the function of synaptic transmission.

The involvement of ATP in synaptic transmission was examined in synapses on granule cells of the rat cerebellum using ecto-ATPase activity. Reaction product was found in a majority but not all synapses between axodendritic, axoaxonic, and dendrodendritic appositions of granule cells and was associated with extracellular surface of both pre- and postsynaptic membranes. Specificity of the detection was justified by using diethyl pyrocarbonate, specific inhibitor of ecto-ATPase activity. These observations provide direct morphological evidence in support of the view that ATP participates in synaptic transmission and indicate functional heterogeneity of synapses in cerebellum.

Adenosine Triphosphatases↗
PubMed2005

SNAP-29-mediated modulation of synaptic transmission in cultured hippocampal neurons.

Identifying the molecules that regulate both the recycling of synaptic vesicles and the SNARE components required for fusion is critical for elucidating the molecular mechanisms underlying synaptic plasticity. SNAP-29 was initially isolated as a syntaxin-binding and ubiquitously expressed protein. Previous studies have suggested that SNAP-29 inhibits SNARE complex disassembly, thereby reducing synaptic transmission in cultured superior cervical ganglion neurons in an activity-dependent manner. However, the role of SNAP-29 in regulating synaptic vesicle recycling and short-term plasticity in the central nervous system remains unclear. In the present study, we examined the effect of SNAP-29 on synaptic transmission in cultured hippocampal neurons by dual patch clamp whole-cell recording, FM dye imaging, and immunocytochemistry. Our results demonstrated that exogenous expression of SNAP-29 in presynaptic neurons significantly decreased the efficiency of synaptic transmission after repetitive firing within a few minutes under low and moderate frequency stimulations (0.1 and 1 Hz). In contrast, SNAP-29 did not affect the density of synapses and basal synaptic transmission. Whereas neurotransmitter release was unaffected during intensive stimulation, recovery after synaptic depression was impaired by SNAP-29. Furthermore, knockdown of SNAP-29 expression in neurons by small interfering RNA increased the efficiency of synaptic transmission during repetitive firing. These findings suggest that SNAP-29 acts as a negative modulator for neurotransmitter release, probably by slowing recycling of the SNARE-based fusion machinery and synaptic vesicle turnover.

Action Potentials↗
PubMed1990

Aminergic modulation of graded synaptic transmission in the lobster stomatogastric ganglion.

Graded chemical synaptic transmission is important for establishing the motor patterns produced by the pyloric central pattern generator (CPG) circuit of the lobster stomatogastric ganglion (Raper, 1979; Anderson and Barker, 1981; Graubard et al., 1983). We examined the modulatory effects of the amines dopamine (DA), serotonin (5-HT), and octopamine (Oct) on graded synaptic transmission at all the central chemical synapses made by the pyloric dilator (PD) neuron onto its follower cells, using synaptic input-output curves measured from cell somata. DA strongly reduced the graded synaptic strength at all the PD synapses. DA reduction of chemical synaptic strength from PD onto the inferior cardiac (IC) neuron could change the sign of synaptic interaction between these 2 cells from inhibitory to excitatory by uncovering a weak electrical connection. 5-HT had weaker and more variable effects, reducing graded synaptic strength from the PD onto the lateral pyloric and pyloric neurons and enhancing the weak synapse from the PD to the IC cell. Oct strongly enhanced the graded synaptic strength at all the PD central synapses. Oct enhancement of graded synaptic strength between the PD and IC cells could also change the sign of the interaction: weak, excitatory electrical coupling, which was sometimes dominant before Oct, was masked by the enhanced chemical inhibitory interaction during Oct application. Measurements of electrical coupling between 2 PD cells and between 2 postsynaptic cells suggest that Oct does not change the input resistance of these cells and may act directly at the PD synapses. The effects of DA and 5-HT are most easily explained by their general reductions in pre- and postsynaptic input resistance. DA, 5-HT, and Oct each produce a distinct pyloric motor pattern (Flamm and Harris-Warrick, 1986a). These amine-induced motor patterns may be explained by the unique actions of each amine on the intrinsic membrane properties of different pyloric CPG neurons (Flamm and Harris-Warrick, 1986b) and by modulation of graded synaptic transmission between the pyloric neurons.

Action Potentials↗
PubMed2001

Mutations in the second C2 domain of synaptotagmin disrupt synaptic transmission at Drosophila neuromuscular junctions.

The synaptic vesicle protein, synaptotagmin, has been hypothesized to mediate several functions in neurotransmitter release including calcium sensing, vesicle recycling, and synaptic vesicle docking. These hypotheses are based on evidence from in vitro binding assays, peptide and antibody injection experiments, and genetic knockout studies. Synaptotagmin contains two domains that are homologous to the calcium ion (Ca(2+))-binding C2 domain of protein kinase C. The two C2 domains of synaptotagmin have broadly differing ligand-binding properties. We have focused on the second C2 domain (C2B) of synaptotagmin I, in particular, on a series of conserved lysine residues on beta-strand 4 of C2B. This polylysine motif binds clathrin-adapter protein AP-2, neuronal calcium channels, and inositol high polyphosphates. It also mediates Ca(2+)-dependent oligomerization. To investigate the importance of these lysine residues in synaptic transmission, we have introduced synaptotagmin I (syt) transgenes harboring specific polylysine motif mutations into flies otherwise lacking the synaptotagmin I protein (syt(null)). Electrophysiological analyses of these mutants revealed that evoked transmitter release is decreased by approximately 36% and that spontaneous release is increased approximately twofold relative to syt(null) flies that express a wild type syt transgene. Synaptotagmin expression in both the mutant and the wild type transgenic lines was equivalent, as measured by semiquantitative Western blot analysis. Thus, the alteration in synaptic transmission was due to the mutation and not to the level of synaptotagmin expression. We conclude that synaptotagmin interactions mediated by the C2 B polylysine motif are required to attain full synaptotagmin function in vivo.

Amino Acid Motifs↗
PubMed1976

Calcium dependency of excitatory chemical synaptic transmission in the frog cerebellum in vitro.

Chemical synaptic transmission was studied with microelectrode techniques in isolated frog cerebella maintained in vitro. Purkinje cell (PC) EPSPs, elicited by selective monosynaptic electrical stimulation of both the parallel fiber (PF) and climbing fiber (CF) inputs, could be inverted by depolarizing (outward) current injections. Evoked synaptic transmission at both junctions was reduced by lowering the extracellular concentration of calcium ions ([Ca2+]) below 2 mM. Raising [Ca2+] above 2 mM to 8 mM did not further increase synaptic transmission. Mg2+, Sr2+, and Ba2+ did not substitute for Ca2+ in the transmission process.

Animals↗
PubMed2005

Nicotinic modulation of glutamatergic synaptic transmission in region CA3 of the hippocampus.

Cholinergic modulation of synaptic transmission in the hippocampus appears to be involved in learning, memory and attentional processes. In brain slice preparations of hippocampal region CA3, we have explored the effect of nicotine on the afferent connections of stratum lacunosum moleculare (SLM) vs. the intrinsic connections of stratum radiatum (SR). Nicotine application had a lamina-selective effect, causing changes in synaptic transmission only in SLM. The nicotinic effect in SLM was characterized by a transient decrease in synaptic potential size followed by a longer period of enhancement of synaptic transmission. The effect was blocked by gamma-aminobutyric acid (GABA)ergic antagonists, indicating the role of GABAergic interneurons in the observed nicotinic effect. The biphasic nature of the nicotinic effect could be due to a difference in receptor subtypes, as supported by the effects of the nicotinic antagonists mecamylamine and methyllycaconitine. Nicotinic modulation of glutamatergic synaptic transmission could complement muscarinic suppression of intrinsic connections, amplifying incoming information and providing a physiological mechanism for the memory-enhancing effect of nicotine.

Aconitine↗
PubMed2005

Fear learning induces persistent facilitation of amygdala synaptic transmission.

In the maintenance phase of fear memory, synaptic transmission is potentiated and the stimulus requirements and signalling mechanisms are altered for long-term potentiation (LTP) in the cortico-lateral amygdala (LA) pathway. These findings link amygdala synaptic plasticity to the coding of fear memories. Behavioural experiments suggest that the amygdala serves to store long-term fear memories. Here we provide electrophysiological evidence showing that synaptic alterations in rats induced by fear conditioning are evident in vitro 10 days after fear conditioning. We show that synaptic transmission was facilitated and that high-frequency stimulation dependent LTP (HFS-LTP) of the cortico-lateral amygdala pathway remained attenuated 10 days following fear conditioning. Additionally, we found that the low-frequency stimulation dependent LTP (LFS-LTP) measured 24 h after fear conditioning was absent 10 days post-training. The persistent facilitation of synaptic transmission and occlusion of HFS-LTP suggests that, unlike hippocampal coding of contextual fear memory, the cortico-lateral amygdala synapse is involved in the storage of long-term fear memories. However, the absence of LFS-LTP 10 days following fear conditioning suggests that amygdala physiology 1 day following fear learning may reflect a dynamic state during memory stabilization that is inactive during the long-term storage of fear memory. Results from these experiments have significant implications regarding the locus of storage for maladaptive fear memories and the synaptic alterations induced by these memories.

Amygdala↗
PubMed2000

Modification of adenosine modulation of synaptic transmission in the hippocampus of aged rats.

We compared the modulation of synaptic transmission by adenosine A(1) receptors in the hippocampus of aged (24 months) and young adult rats (6 weeks). The adenosine A(1) receptor agonist, N(6)-cyclopentyladenosine, was less potent (P:<0.05) to inhibit synaptic transmission in aged (EC(50)=53 nM) than young adult (EC(50)=14 nM) hippocampal slices, these effects being prevented by the A(1) receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX). In contrast with the lower effect of the A(1) receptor agonist, it was observed that blockade of A(1) receptors with DPCPX (50 nM), or removal of endogenous extracellular adenosine with adenosine deaminase (2 u ml(-1)), caused a more pronounced disinhibition of synaptic transmission in aged rats. Also consistent with a more intense A(1) receptor-mediated inhibitory tonus by endogenous adenosine in aged rats was the finding that to fully prevent the depression of synaptic transmission induced by 3 min hypoxia, a higher concentration of DPCPX was required in slices from aged (100 nM) than from young (50 nM) rats. It is concluded that in hippocampal slices of aged rats the efficiency of A(1) receptors to modulate synaptic transmission is reduced, but this may be compensated by an enhanced inhibitory tonus by endogenous adenosine.

Adenosine↗
PubMed2002

Adenosine A(2A) receptor facilitation of hippocampal synaptic transmission is dependent on tonic A(1) receptor inhibition.

Adenosine tonically inhibits synaptic transmission through actions at A(1) receptors. It also facilitates synaptic transmission, but it is unclear if this facilitation results from pre- and/or postsynaptic A(2A) receptor activation or from indirect control of inhibitory GABAergic transmission. The A(2A) receptor agonist, CGS 21680 (10 nM), facilitated synaptic transmission in the CA1 area of rat hippocampal slices (by 14%), independent of whether or not GABAergic transmission was blocked by the GABA(A) and GABA(B) receptor antagonists, picrotoxin (50 microM) and CGP 55845 (1 microM), respectively. CGS 21680 (10 nM) also inhibited paired-pulse facilitation by 12%, an effect prevented by the A(2A) receptor antagonist, ZM 241385 (20 nM). These effects of CGS 21680 (10 nM) were occluded by adenosine deaminase (2 U/ml) and were made to reappear upon direct activation of A(1) receptors with N(6)-cyclopentyladenosine (CPA, 6 nM). CGS 21680 (10 nM) only facilitated (by 17%) the K(+)-evoked release of glutamate from superfused hippocampal synaptosomes in the presence of 100 nM CPA. This effect of CGS 21680 (10 nM), in contrast to the isoproterenol (30 microM) facilitation of glutamate release, was prevented by the protein kinase C inhibitors, chelerythrine (6 microM) and bisindolylmaleimide (1 microM), but not by the protein kinase A inhibitor, H-89 (1 microM). Isoproterenol (30 microM), but not CGS 21680 (10-300 nM), enhanced synaptosomal cAMP levels, indicating that the CGS 21680-induced facilitation of glutamate release involves a cAMP-independent protein kinase C activation. To discard any direct effect of CGS 21680 on adenosine A(1) receptor, we also show that in autoradiography experiments CGS 21680 only displaced the adenosine A(1) receptor antagonist, 1,3-dipropyl-8-cyclopentyladenosine ([(3)H]DPCPX, 0.5 nM) with an EC(50) of 1 microM in all brain areas studied and CGS 21680 (30 nM) failed to change the ability of CPA to displace DPCPX (1 nM) binding to CHO cells stably transfected with A(1) receptors. Our results suggest that A(2A) receptor agonists facilitate hippocampal synaptic transmission by attenuating the tonic effect of inhibitory presynaptic A(1) receptors located in glutamatergic nerve terminals. This might be a fine-tuning role for adenosine A(2A) receptors to allow frequency-dependent plasticity phenomena without compromising the A(1) receptor-mediated neuroprotective role of adenosine.

Adenosine↗
PubMed1994

Activity-dependent enhancement of synaptic transmission in hippocampal slices treated with the phosphatase inhibitor calyculin A.

The role of protein phosphatases in regulating synaptic transmission in the CA1 region of the hippocampus was examined using slices pretreated with calyculin A, a specific inhibitor of protein phosphatases 1 and 2A. Stimulation of afferents at 1 Hz (but not 0.1 Hz) for periods of 5-10 min caused a long-lasting enhancement of synaptic transmission. The increase in synaptic responses was not due to a change in fiber excitability, as there was a shift to the left in the input-output curve following the synaptic enhancement. The enhancement was observed only in the input that received the 1 Hz stimulation and not in an independent control pathway, indicating that the increase in synaptic strength is input specific and limited to repetitively activated synapses. Applying 1 Hz stimulation when synaptic transmission was blocked by replacing extracellular Ca2+ with Mg2+ prevented or significantly reduced any change in synaptic efficacy after reperfusion with normal Ca(2+)-containing medium. In contrast, 1 Hz stimulation given when synaptic transmission was blocked by non-NMDA and NMDA glutamate receptor antagonists still caused a synaptic enhancement following washout of the antagonists. The enhancement of synaptic transmission also was not blocked by loading CA1 cells with the calcium chelator BAPTA. Thus, influx of Ca2+ into presynaptic elements is required for the synaptic enhancement elicited by 1 Hz stimulation in calyculin A-treated hippocampal slices. Consistent with the activation of processes that cause an increase in transmitter release, the magnitude of paired-pulse facilitation decreased following the synaptic enhancement, and the NMDA receptor-mediated component of the synaptic response was increased by 1 Hz stimulation. These results suggest that when protein phosphatases are inhibited by calyculin A, prolonged periods of 1 Hz stimulation lead to activation of presynaptic Ca(2+)-dependent protein kinases, resulting in a persistent increase in evoked transmitter release. They also indicate that the activity of presynaptic protein phosphatases is critically important for limiting increases in synaptic strength following repetitive afferent activity.

2-Amino-5-phosphonovalerate↗
PubMed1983

Nicotinamide adenine dinucleotide depresses synaptic transmission in the hippocampus and has specific binding sites on the synaptic membranes.

The electrical activity of transverse slices of hippocampus was used as a bioassay in which extracts of fresh brain tissue were screened for biological activity. A factor that depressed synaptic transmission was identified as nicotinamide adenine dinucleotide (NAD). This depressant action of NAD could be observed at concentrations in the range 1-10 microM and the degree of depression was monotonically related to the concentration of NAD in the bathing medium. NAD did not affect the antidromic invasion of the granule cells nor did it alter the relationship between the electrically evoked excitatory postsynaptic field potential (e.p.s.p.) and the population discharge of the granule cells (population spike). These results suggest that NAD did not affect the electrical excitability of the neuronal membranes. NAD had little effect on the sensitivity of granule cells to iontophoretically applied L-glutamate, the putative excitatory transmitter for the perforant path-granule cell pathway. Pure synaptosomal membranes, free of mitochondria, had two binding sites for NAD: a high affinity site with a Kd of 1 microM and a low affinity site with a Kd of 17 microM. These sites were similar in affinity to those of mitochondria, although the density of the high affinity sites was 5 X greater in the synaptosomal membranes. Adenosine had a relatively weak affinity for the NAD binding sites. It was concluded that NAD probably depressed synaptic transmission in the dentate gyrus by binding to sites on the presynaptic nerve terminal and reducing the amount of transmitter released by a nerve impulse. The physiological significance of this view is discussed.

Animals↗