Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0011570 (depression)
 172,036 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the brain, most fast excitatory synaptic transmission is mediated through L-glutamate acting on postsynaptic ionotropic glutamate receptors. These receptors are of two kinds--the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)/kainate (non-NMDA) and the N-methyl-D-aspartate (NMDA) receptors, which are thought to be colocalized onto the same postsynaptic elements. This excitatory transmission can be modulated both upward and downward, long-term potentiation (LTP) and long-term depression (LTD), respectively. Whether the expression of LTP/LTD is pre-or postsynaptically located (or both) remains an enigma. This article will focus on what postsynaptic modifications of the ionotropic glutamate receptors may possibly underly long-term potentiation/depression. It will discuss the character of LTP/ LTD with respect to the temporal characteristics and to the type of changes that appears in the non-NMDA and NMDA receptor-mediated synaptic currents, and what constraints these findings put on the possible expression mechanism(s) for LTP/LTD. It will be submitted that if a modification of the glutamate receptors does underly LTP/LTD, an increase/ decrease in the number of functional receptors is the most plausible alternative. This change in receptor number will have to include a coordinated change of both the non-NMDA and the NMDA receptors.
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PMID:Ionotropic glutamate receptors. Their possible role in the expression of hippocampal synaptic plasticity. 873 37

The delta 2 subunit of ionotropic glutamate receptors is expressed only in the cerebellar Purkinje cell. In mutant mice deficient in the delta 2 protein, cerebellar long-term depression and motor coordination are impaired. We examined behavioural plasticity in these mutant mice after unilateral vestibular destruction. After intratympanic injection of sodium arsanilate, the mice showed roll head tilt and their righting response under a rotation load was impaired. These symptoms improved with time. However, compensation of the righting response was retarded in the mutant mice. These results suggest that motor learning of the delta 2 mutant mice is disturbed, and that the static and dynamic components of vestibular compensation may be controlled by different neuronal mechanisms.
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PMID:Retarded vestibular compensation in mutant mice deficient in delta 2 glutamate receptor subunit. 874 48

1. This report examines alterations in presynaptic and postsynaptic processes mediated by gamma-aminobutyric acid-B (GABAB) receptors within hippocampal region CA1 in a model of chronic temporal lobe epilepsy (TLE). Intracellular recordings were obtained in pyramidal cells from combined hippocampal/parahippocampal control slices and slices obtained > or = 1 mo after a period of self-sustaining limbic status epilepticus (SSLSE) induced by continuous hippocampal stimulation. 2. Monosynaptic inhibitory postsynaptic potentials (IPSPs) were evoked by placement of the stimulating electrode in stratum pyramidale within 500 microns of the recording electrode in the presence of the ionotropic glutamate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione and D(-)-2-amino-5-phosphonovaleric acid. Control IPSPs exhibited early (GABAA-receptor-mediated) and late (GABAB-receptor-mediated) components. In contrast, post-SSLSE IPSPs displayed only a GABAA-receptor-mediated IPSP. Post-SSLSE IPSPs were completely eliminated by antagonists of the GABAA receptor (bicuculline methiodide and picrotoxin). In control tissue, GABAB receptor antagonists P-(3-aminopropyl)-P-diethoxymethyl-phosphinic acid (CGP 55845A), 3-N[1-(S)-(3,4-dichlorophenyl) ethyl]amino-2-(S)- hydroxypropyl-P-benzyl-phosphinic acid (CGP 35348), and 2-hydroxysaclofen eliminated the late component of the biphasic IPSP but had no discernible effect on IPSPs evoked in post-SSLSE CA1 pyramidal cells. 3. A paired pulse paradigm was employed to investigate the integrity of presynaptic GABAB-receptor-mediated inhibition of GABA release. To isolate pure GABAA-receptor-mediated responses, and thus facilitate comparison with post-SSLSE tissue, control neurons were penetrated with intracellular electrodes containing Cs2SO4/lidocaine, N-ethyl bromide (QX-314), and IPSPs were evoked employing the monosynaptic IPSP protocol. In controls, paired pulses [interpulse intervals (IPIs) of 70-1,500 ms] resulted in a diminution of the second early, GABAA-receptor-mediated chloride IPSP (IPSPA) relative to the first; maximum paired pulse depression (PPD) occurred at an IPI of 100 ms. GABAB receptor antagonists reduced PPD without affecting the amplitude of IPSPAs; the GABAB receptor agonist baclofen reduced the amplitude of both the first and second IPSPA and largely alleviated PPD. In contrast, no PPD was evident at any IPI in post-SSLSE neurons. Neither antagonists nor agonists of GABAB-receptor-mediated processes had an effect on either the degree of PPD or the amplitude of IPSPs. 4. To better approximate the pattern of CA1 pyramidal cell activation occurring during epileptiform activity. IPSPAs were evoked by trains of stimuli. In controls, mean monosynaptic IPSPA amplitude decreased by approximately 60% during a 3-Hz, 5-s train, with more than half the decline coming between the first and second IPSPs. In post-SSLSE, no significant IPSPA depression resulted from delivery of stimulus trains. Baclofen reduced the amplitude of control IPSPAs evoked during stimulus trains; both agonist and antagonists significantly lessened the degree of IPSP depression. These same agents altered neither IPSP amplitude nor the degree of use-dependent IPSP depression produced in post-SSLSE tissue during stimulus trains. 5. We conclude that a dysfunction of both presynaptic and postsynaptic GABAB-receptor-mediated processes occurs in hippocampal area CA1 in the post-SSLSE model of TLE. GABAB receptor agonists and antagonists had no effect on post-SSLSE CA1 pyramidal cell synaptic responses, whereas antagonists of the GABAA receptor completely eliminated IPSPs. Repetitive activation produced no use-dependent synaptic depression. The implications of these findings for the epileptogenic potential of post-SSLSE CA1 and the "dormant basket cell" hypothesis are discussed.
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PMID:Profound disturbances of pre- and postsynaptic GABAB-receptor-mediated processes in region CA1 in a chronic model of temporal lobe epilepsy. 887 Dec 36

The neostriatum is the entryway into the basal ganglia and is the site of many of the neurological defects involving basal ganglia function. Thus, it is important to understand the regulation of synaptic transmission at afferent synapses innervating the neostriatum. Cortical glutamatergic and nigral dopaminergic afferent input impinge on neurons in the neostriatum, providing the most significant afferent inputs to this structure. Our understanding of the mechanisms involved in transmission and modulation of transmission at these synapses has greatly increased. It is now apparent that the corticostriatal glutamatergic inputs produce rapid depolarization of striatal neurons via activation of ionotropic AMPA-type glutamate receptors. In addition, transmission is modulated by a number of presynaptic, G-protein-coupled receptors but, surprisingly, relatively little evidence of postsynaptic modulation has been observed. Corticostriatal synapses also express certain forms of plasticity, most notably short- and long- term synaptic depression (STI) and LTD, respectively). It appears that LTD may involve convergent actions of glutamate and dopamine. Striatal LTD may have important roles in information storage and motor set selection in the striatum. However, some aspects of synaptic transmission in the striatum remain unclear. In particular, the exact physiological roles of dopaminergic nigrostriatal input and the role of NMDA-type glutamate receptors are not well understood. In addition, intrastriatal synaptic connections have received relatively little attention as compared with extrinsic input to the neostriatum. Future studies will need to focus on elucidating these aspects of neostriatal function.
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PMID:Synaptic transmission and modulation in the neostriatum. 889 45

Intracellular recordings were obtained from neocortical brain slices of adult rats maintained in vitro. The effect of metabotropic glutamate receptor activation on spike frequency adaptation in regular spiking layer II and III neurons was determined. Putative metabotropic glutamate receptor agonists and antagonists, as well as inhibitors of intracellular signaling systems, were tested. Activation of metabotropic glutamate receptors by bath applied (1S,3R)-1-aminocyclopentane-1,3-dicarboxylate (1S,3R-ACPD; 50-200 microM) reduced the first interspike interval and increased action potential frequency at all current intensities. This effect was not blocked by ionotropic glutamate receptor antagonists. Under these recording conditions, quisqualate (1-10 microM) similarly reduced spike frequency adaptation. Neither 1R,3S-ACPD, L-2-carboxycyclopropylglycine-I nor the putative presynaptic metabotropic glutamate receptor agonist, L-2-amino-4-phosphonobutyrate, mimicked the effects of 1S,3R-ACPD or quisqualate. Bath application of the putative metabotropic glutamate receptor antagonist, alpha-methyl-4-carboxyphenylglycine, competitively antagonized the excitatory actions of 1S,3R-ACPD. Another putative antagonist, L-2-amino-3-phosphonopropionate, failed to antagonize the reduction in spike frequency adaptation. Intracellular injection of guanosine-5'-O-(2-thiodiphosphate), a non-hydrolysable analog of GTP, inhibited the postsynaptic metabotropic glutamate receptor-mediated effects. However, the depression of synaptic transmission by 1S,3R-ACPD was not antagonized by this compound. The decrease in spike frequency adaptation by 1S,3R-ACPD was not prevented by prior exposure to the non-specific protein kinase inhibitors H-7 or H-8 (10 microM), the protein kinase A inhibitor H-89 (0.25 microM) or the protein kinase C inhibitor staurosporine (0.10 microM). These data suggest that the metabotropic glutamate receptor-mediated reduction in spike adaptation requires the activation of specific G-protein-coupled metabotropic glutamate receptor subtypes located on postsynaptic sites. The increase in neuronal excitability observed in the adult neocortex may be mediated either by an unidentified G-protein-coupled second messenger or via a membrane-delimited G-protein action.
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PMID:G-protein activation by metabotropic glutamate receptors reduces spike frequency adaptation in neocortical neurons. 892 28

The delta 2 glutamate receptors are prominently expressed in Purkinje cells and are thought to play a key role in the induction of cerebellar long-term depression. The synaptic and subsynaptic localization of delta receptors in rat cerebellar cortex was investigated with sensitive and high-resolution immunogold procedures. After postembedding incubation with an antibody raised to a C-terminal peptide of delta 2, high gold particle densities occurred in all parallel fiber synapses with Purkinje cell dendritic spines, whereas other synapses were consistently devoid of labeling. Among the types of immunonegative synapse were climbing fiber synapses with spines and parallel fiber synapses with dendritic stems of interneurons. At the parallel fiber-spine synapse, gold particles signaling delta receptors were restricted to the postsynaptic specialization. By the use of double labeling with two different gold particle sizes, it was shown that delta and AMPA GluR2/3 receptors were colocalized along the entire extent of the postsynaptic specialization without forming separate domains. The distribution of gold particles representing delta receptors was consistent with a cytoplasmic localization of the C terminus and an absence of a significant presynaptic pool of receptor molecules. The present data suggest that the delta 2 receptors are targeted selectively to a subset of Purkinje cell spines and that they are coexpressed with ionotropic receptors in the postsynaptic specialization. This arrangement could allow for a direct interaction between the two classes of receptor.
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PMID:Differential localization of delta glutamate receptors in the rat cerebellum: coexpression with AMPA receptors in parallel fiber-spine synapses and absence from climbing fiber-spine synapses. 898 4

The classical view of fast chemical synaptic transmission is that released neurotransmitter acts locally on postsynaptic receptors and is cleared from the synaptic cleft within a few milliseconds by diffusion and by specific reuptake mechanisms. This rapid clearance restricts the spread of neurotransmitter and, combined with the low affinities of many ionotropic receptors, ensures that synaptic transmission occurs in a point-to-point fashion. We now show, however, that when transmitter release is enhanced at hippocampal mossy fibre synapses, the concentration of glutamate increases and its clearance is delayed; this allows it to spread away from the synapse and to activate presynaptic inhibitory metabotropic glutamate receptors (mGluRs). At normal levels of glutamate release during low-frequency activity, these presynaptic receptors are not activated. When glutamate concentration is increased by higher-frequency activity or by blocking glutamate uptake, however, these receptors become activated, leading to a rapid inhibition of transmitter release. This effect may be related to the long-term depression of mossy fibre synaptic responses that has recently been shown after prolonged activation of presynaptic mGluRs (refs 2, 3). The use-dependent activation of presynaptic mGluRs that we describe here thus represents a negative feedback mechanism for controlling the strength of synaptic transmission.
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PMID:Use-dependent increases in glutamate concentration activate presynaptic metabotropic glutamate receptors. 902 60

This review is a critical appraisal of the widespread assumption that high extracellular glutamate, resulting from enhanced pre-synaptic release superimposed on deficient uptake and/or cytosolic efflux, is the key to excessive glutamate-mediated excitation in neurological disorders. Indeed, high extracellular glutamate levels do not consistently correlate with, nor necessarily produce, neuronal dysfunction and death in vivo. Furthermore, we exemplify with spreading depression that the sensitivity of an experimental or pathological event to glutamate receptor antagonists does not imply involvement of high extracellular glutamate levels in the genesis of this event. We propose an extension to the current, oversimplified concept of excitotoxicity associated with neurological disorders, to include alternative abnormalities of glutamatergic transmission which may contribute to the pathology, and lead to excitotoxic injury. These may include the following: (i) increased density of glutamate receptors; (ii) altered ionic selectivity of ionotropic glutamate receptors; (iii) abnormalities in their sensitivity and modulation; (iv) enhancement of glutamate-mediated synaptic efficacy (i.e. a pathological form of long-term potentiation); (v) phenomena such as spreading depression which require activation of glutamate receptors and can be detrimental to the survival of neurons. Such an extension would take into account the diversity of glutamate-receptor-mediated processes, match the complexity of neurological disorders pathogenesis and pathophysiology, and ultimately provide a more elaborate scientific basis for the development of innovative treatments.
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PMID:Altered glutamatergic transmission in neurological disorders: from high extracellular glutamate to excessive synaptic efficacy. 904 28

In this report we describe the actions of two novel compounds, (RS)-alpha-cyclopropyl-4-phosphonophenylglycine (CPPG) and (S)-alpha-ethylglutamate (EGLU), which are potent antagonists at two types of presynaptic metabotropic glutamate (mGlu) receptors in the neonatal rat spinal cord. Selective activation of these receptors by L-2-amino-4-phosphonobutyrate (L-AP4) or (1S,3S)-1-aminocyclopentane-1,3-dicarboxylic acid ((1S,3S)-ACPD) results in the depression of the monosynaptic component of the dorsal root-evoked ventral root potential (DR-VRP). CPPG produces rightward parallel shifts of the dose-response curves for both L-AP4- and (1S,3S)-ACPD, with Schild slope in each case close to unity, consistent with a competitive mechanism of antagonism. CPPG is the most potent antagonist yet described for both L-AP4- and (1S,3S)-ACPD-sensitive presynaptic mGlu receptors but displays a 30-fold selectivity for the L-AP4-sensitive receptor over the (1S,3S)-ACPD-sensitive receptor (KD values 1.7 microM and 53 microM, respectively). EGLU, on the other hand, is selective for the (1S,3S)-ACPD-sensitive receptor, displaying little or no activity at the L-AP4-sensitive site. EGLU produces a rightward parallel shift of the dose-response curve to (1S,3S)-ACPD, with Schild slope close to unity, again indicative of a competitive mode of antagonism (KD 66 microM). Both CPPG and EGLU displayed only weak or no antagonist activity at postsynaptic metabotropic and ionotropic glutamate receptors.
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PMID:Potent antagonists at the L-AP4- and (1S,3S)-ACPD-sensitive presynaptic metabotropic glutamate receptors in the neonatal rat spinal cord. 912 5

The prelimbic region of medial frontal cortex in the rat receives a direct input from the hippocampus and this functional connection is essential for aspects of spatial memory. Activity-dependent changes in the effectiveness of synaptic transmission in the medial frontal cortex, namely long-term potentiation (LTP) and long-term depression (LTD) can persist for tens of minutes or hours and may be the basis of learning and memory storage. Glutamatergic activation of ionotropic receptors is required to induce both LTP and LTD. We now present evidence of the involvement of metabotropic glutamate receptors in LTP in isolated slices of frontal cortex. Repetitive bursts of stimulation at theta frequencies (TBS) were applied to layer II, and monosynaptic EPSPs were monitored in layer V neurons of the prelimbic area. TBS was found to be more effective at inducing LTP than tetanic stimulation at 100 Hz and produced LTP that lasted >30 min in 8 out of 14 neurons. Tetanic stimulation at 100 Hz in the presence of the N-methyl--aspartate (NMDA)-antagonist 2-amino-5-phosphonopentanoate (AP5) was reported to be a reliable method of inducing LTD in prelimbic cortex (). However we found that this protocol did not facilitate the induction of LTD. The role of metabotropic glutamate receptors (mGluR) in LTP was assessed by using the selective, broad-spectrum antagonist (R, S)-alpha-methyl-4- carboxyphenylglycine (MCPG). This drug significantly reduced the incidence of LTP after TBS to only 1 of 14 neurons (P < 0.02, chi2 test). The pooled responses to TBS in MCPG showed significantly reduced potentiation [(P < 0.02, analysis of variance (ANOVA)]. The broad-spectrum mGluR agonist (1S, 3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) and the selective group I agonist S-3 hydroxyphenylglycine(S-3HPG) both produced membrane depolarization, an increase in number of spikes evoked by depolarizing current pulses, and a reduction in the afterhyperpolarization. Similar effects were produced by these agonists even when synaptic transmission was blocked by use of the gamma-aminobutyric acid-B (GABAB) receptor agonist, 200 microM baclofen, which suggests that group I mGluRs are present on layer V neurons. We conclude that mGluRs participate in the production of LTP in prelimbic cortex, and that this excitatory effect could be mediated by the postsynaptic group I mGluRs.
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PMID:Metabotropic glutamate receptors are involved in long-term potentiation in isolated slices of rat medial frontal cortex. 940 23


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