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Activation of Group I and Group II Metabotropic Glutamate Receptors Causes LTD and LTP of Electrical Synapses in the Rat Thalamic Reticular Nucleus. J Neurosci 2015; 35:7616-25. [PMID: 25972185 DOI: 10.1523/jneurosci.3688-14.2015] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Compared with the extensive characterization of chemical synaptic plasticity, electrical synaptic plasticity remains poorly understood. Electrical synapses are strong and prevalent among the GABAergic neurons of the rodent thalamic reticular nucleus. Using paired whole-cell recordings, we show that activation of Group I metabotropic glutamate receptors (mGluRs) induces long-term depression of electrical synapses. Conversely, activation of the Group II mGluR, mGluR3, induces long-term potentiation of electrical synapses. By testing downstream targets, we show that modifications induced by both mGluR groups converge on the same signaling cascade--adenylyl cyclase to cAMP to protein kinase A--but with opposing effects. Furthermore, the magnitude of modification is inversely correlated to baseline coupling strength. Thus, electrical synapses, like their chemical counterparts, undergo both strengthening and weakening forms of plasticity, which should play a significant role in thalamocortical function.
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Bergeron R, Imamura Y, Frangioni JV, Greene RW, Coyle JT. Endogenous N-acetylaspartylglutamate reduced NMDA receptor-dependent current neurotransmission in the CA1 area of the hippocampus. J Neurochem 2007; 100:346-57. [PMID: 17241157 DOI: 10.1111/j.1471-4159.2006.04253.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
N-Acetylaspartylglutamate (NAAG) is a neuropeptide found in high concentrations in the brain. Using whole-cell recordings of CA1 pyramidal neurons in acute hippocampal slices, we found that either (i) the application of exogenous NAAG or (ii) an increase of endogenous extracellular NAAG, caused by the inhibition of its catabolic enzyme glutamate carboxypeptidase II (GCP II), resulted in a significant reduction in the amplitude of the isolated NMDA receptor (NMDAR) component of the evoked excitatory postsynaptic current (EPSC). Conversely, reduction of endogenous extracellular NAAG caused by either (i) perfusion with a soluble form of pure human GCP II or (ii) affinity purified antibodies against NAAG, enhanced the amplitude of the isolated NMDAR current. Bath application of GCP II inhibitor induced a progressive loss of spontaneous NMDAR miniatures. Furthermore, NAAG blocked the induction of long-term potentiation at Schaffer collateral axons-CA1 pyramidal neuron synapses. All together, these results suggest that NAAG acts as an endogenous modulator of NMDARs in the CA1 area of the hippocampus.
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Affiliation(s)
- Richard Bergeron
- Ottawa Health Research Institute, Department of Psychiatry, Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada.
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Alexander GM, Godwin DW. Unique presynaptic and postsynaptic roles of Group II metabotropic glutamate receptors in the modulation of thalamic network activity. Neuroscience 2006; 141:501-13. [PMID: 16690217 DOI: 10.1016/j.neuroscience.2006.03.060] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2005] [Revised: 03/03/2006] [Accepted: 03/18/2006] [Indexed: 11/27/2022]
Abstract
The thalamic reticular nucleus (TRN) is a sheet of GABAergic neurons that project to other TRN neurons and to associated thalamocortical relay nuclei. The TRN receives glutamatergic synaptic inputs from cortex as well as reciprocal inputs from the collaterals of thalamocortical neurons. In addition to ionotropic glutamate receptors, metabotropic glutamate receptors (mGluRs) are present in the TRN circuitry. Using whole cell voltage clamp recordings, we pharmacologically characterized unique pre- and postsynaptic functions for Group II mGluRs (mGluR 2 and mGluR 3) within the TRN circuitry in ferrets. mGluR 2 was found on presynaptic cortical axon terminals in the TRN, where it reduced glutamate release, while mGluR 3 acted postsynaptically on TRN cells to increase membrane conductance. Using miniature inhibitory postsynaptic current analysis, we also found that picrotoxin-sensitive intra-TRN GABA-mediated neurotransmission was not affected by administration of a Group II mGluR agonist, indicating that neither mGluR 2 nor 3 acts on presynaptic GABA-containing terminals within the TRN. Because strong corticothalamic activation is implicated in abnormal thalamic rhythms, we used extracellular recordings in the lateral geniculate nucleus to study the effect of Group II mGluR agonists upon these slow oscillations. We induced approximately 3 Hz spike-and-wave discharge activity through corticothalamic stimulation, and found that such activity was reduced in the presence of the Group II mGluR agonist, (-)-2-oxa-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate (LY379268). These data indicate that Group II mGluR reduce the impact of corticothalamic excitation, and that they may be a useful target in the reduction of absence-like rhythms.
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Affiliation(s)
- G M Alexander
- Neuroscience Program, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157, USA
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Turner JP, Salt TE. Group II and III metabotropic glutamate receptors and the control of the nucleus reticularis thalami input to rat thalamocortical neurones in vitro. Neuroscience 2004; 122:459-69. [PMID: 14614910 DOI: 10.1016/j.neuroscience.2003.08.014] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Intracellular recordings were made from neurones in the thalamic reticular nucleus (TRN) and ventro-basal (VB) thalamus in slices of rat midbrain in vitro. Electrical stimulation of the medial lemniscus or TRN resulted in the generation of complex synaptic potentials containing disynaptic inhibitory post-synaptic potentials (IPSPs) in VB thalamocortical neurones. Analysis of the excitatory synaptic responses in TRN neurones indicates they can produce burst output response irrespective of the level of sub-threshold membrane potential. This suggests that network-evoked IPSPs in VB thalamocortical neurones occur following a burst of TRN action potentials. Using ionotropic glutamate receptor antagonists, the activation of these disynaptic events was blocked, and the monosynaptic IPSPs that resulted from the direct activation of the TRN could be isolated. The selective Group II agonists LY354740 (1-10 microM) and N-acetyl-aspartyl-glutamate (NAAG; 100-500 microM) both caused a reversible depression of these monosynaptic TRN IPSPs without any effect on membrane potential or input resistance. Likewise, the specific Group III agonist L-2-amino-4-phosphonobutanoate (10-500 microM), but not (RS)-4-phosphonophenylglycine (1 and 30 microM) also caused a reversible depression of these IPSPs, again without any effect on membrane potential or input resistance.Thus, the IPSPs recorded in VB thalamocortical neurones, evoked by TRN activation, can be depressed by the activation of either Group II or III metabotropic glutamate receptors. This is consistent with the location of these receptor types on the presynaptic terminals of TRN axons in the VB thalamus. This raises the possibility that, during periods of intense excitatory activity, glutamate release could influence the release of GABA from TRN axon terminals in the thalamus. In addition, as NAAG is located in the axons and terminals arising from the TRN, there is the possibility that this dipeptide is also released by these terminals to control the release of GABA during periods of high activity in the TRN.
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Affiliation(s)
- J P Turner
- Department of Visual Science, Institute of Ophthalmology, University College London, 11-43 Bath Street, London EC1V 9EL, UK.
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Moffett JR. Reductions in N-acetylaspartylglutamate and the 67 kDa form of glutamic acid decarboxylase immunoreactivities in the visual system of albino and pigmented rats after optic nerve transections. J Comp Neurol 2003; 458:221-39. [PMID: 12619078 DOI: 10.1002/cne.10570] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
This study compares the immunohistochemical distributions of N-acetylaspartylglutamate (NAAG) and the large isoform of the gamma-aminobutyric acid (GABA)-synthesizing enzyme glutamic acid decarboxylase (GAD(67)) in the visual system of albino and pigmented rats. Most retinal ganglion cells and their axons were strongly immunoreactive for NAAG, whereas GAD(67) immunoreactivity was very sparse in these cells and projections. In retinorecipient zones, NAAG and GAD(67) immunoreactivities occurred in distinct populations of neurons and in dense networks of strongly immunoreactive fibers and synapses. Dual-labeling immunohistochemistry indicated that principal neurons were stained for NAAG, whereas local interneurons were stained for GAD(67). In contrast to the distribution observed in retinorecipient zones, most or all neurons were doubly stained for NAAG and GAD(67) in the thalamic reticular nucleus. Ten days after unilateral optic nerve transection, NAAG-immunoreactive fibers and synapses were substantially reduced in all contralateral retinal terminal zones. The posttransection pattern of NAAG-immunoreactive synaptic loss demarcated the contralateral and ipsilateral divisions of the retinal projections. In addition, an apparent transynaptic reduction in GAD(67) immunoreactivity was observed in some deafferented areas, such as the lateral geniculate. These findings suggest a complicated picture in which NAAG and GABA are segregated in distinct neuronal populations in primary visual targets, yet they are colocalized in neurons of the thalamic reticular nucleus. This is consistent with NAAG acting as a neurotransmitter release modulator that is coreleased with a variety of classical transmitters in specific neural pathways.
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Affiliation(s)
- John R Moffett
- Department of Biology, Georgetown University, Washington, DC 20057-1229, USA.
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Williamson LC, Eagles DA, Brady MJ, Moffett JR, Namboodiri MAA, Neale JH. Localization and Synaptic Release of N-acetylaspartylglutamate in the Chick Retina and Optic Tectum. Eur J Neurosci 2002; 3:441-451. [PMID: 12106183 DOI: 10.1111/j.1460-9568.1991.tb00831.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The neuropeptide, N-acetylaspartylglutamate (NAAG), was identified in the chick retina (1.4 nmol/retina) by HPLC, radioimmunoassay and immunohistochemistry. This acidic dipeptide was found within retinal ganglion cell bodies and their neurites in the optic fibre layer of the retina. Substantial, but less intense, immunoreactivity was detected in many amacrine-like cells in the inner nuclear layer and in multiple bands within the inner plexiform layer. In addition, NAAG immunoreactivity was observed in the optic fibre layer and in the neuropil of the superficial layers of the optic tectum, as well as in many cell bodies in the tectum. Using a newly developed, specific and highly sensitive (3 fmol/50 microl) radioimmunoassay for NAAG, peptide release was detected in isolated retinas upon depolarization with 55 mM extracellular potassium. This assay also permitted detection of peptide release from the optic tectum following stimulation of action potentials in retinal ganglion cell axons of the optic tract. Both of these release processes required the presence of extracellular calcium. Electrically stimulated release from the tectum was reversibly blocked by extracellular cadmium. These findings suggest that NAAG serves an extracellular function following depolarization-induced release from retinal amacrine neurons and from ganglion cell axon endings in the chick optic tectum. These data support the hypothesis that NAAG functions in synaptic communication between neurons in the visual system.
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Affiliation(s)
- Lura C. Williamson
- Department of Biology, Georgetown University, Washington D.C., USA 20057
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Gafurov B, Urazaev AK, Grossfeld RM, Lieberman EM. N-acetylaspartylglutamate (NAAG) is the probable mediator of axon-to-glia signaling in the crayfish medial giant nerve fiber. Neuroscience 2002; 106:227-35. [PMID: 11564432 DOI: 10.1016/s0306-4522(01)00271-8] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Glial cell hyperpolarization previously has been reported to be induced by high frequency stimulation or glutamate. We now report that it also is produced by the glutamate-containing dipeptide N-acetylaspartylglutamate (NAAG), by its non-hydrolyzable analog beta-NAAG, and by NAAG in the presence of 2-(phosphonomethyl)-pentanedioic acid (2-PMPA), a potent inhibitor of the NAAG degradative enzyme glutamate carboxypeptidase II. The results indicate that NAAG mimics the effect of nerve fiber stimulation on the glia. Although glutamate has a similar effect, the other presumed product of NAAG hydrolysis, N-acetylaspartate, is without effect on glial cell membrane potential, as is aspartylglutamate (in the presence of 2-PMPA). The hyperpolarization induced by stimulation, glutamate, NAAG, beta-NAAG, or NAAG plus 2-PMPA is completely blocked by the Group II metabotropic glutamate receptor antagonist (S)-alpha-ethylglutamate but is not altered by antagonists of Group I or III metabotropic glutamate receptors. The N-methyl-D-aspartate receptor antagonist MK801 reduces but does not eliminate the hyperpolarization generated by glutamate, NAAG or stimulation. These results, in combination with those of the preceding paper, are consistent with the premise that NAAG could be the primary axon-to-glia signaling agent. When the unstimulated nerve fiber is treated with cysteate, a glutamate reuptake blocker, there is a small hyperpolarization of the glial cell that can be substantially reduced by pretreatment with 2-PMPA before addition of cysteate. A similar effect of cysteate is seen during a 50 Hz/5 s stimulation. From these results we suggest that glutamate derived from NAAG hydrolysis appears in the periaxonal space under the conditions of these experiments and may contribute to the glial hyperpolarization.
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Affiliation(s)
- B Gafurov
- Department of Physiology, The Brody School of Medicine of East Carolina University, Greenville, NC 27858, USA
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Abstract
N-Acetylaspartylglutamate (NAAG) is a neuropeptide found in millimolar concentrations in brain that is localized to subpopulations of glutamatergic, cholinergic, GABAergic, and noradrenergic neuronal systems. NAAG is released upon depolarization by a Ca(2+)-dependent process and is an agonist at mGluR3 receptors and an antagonist at NMDA receptors. NAAG is catabolized to N-acetylaspartate and glutamate primarily by glutamate carboxypeptidase II, which is expressed on the extracellular surface of astrocytes. The levels of NAAG and the activity of carboxypeptidase II are altered in a regionally specific fashion in several neuropsychiatric disorders.
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Affiliation(s)
- J T Coyle
- Department of Psychiatry, Harvard Medical School, Belmont, Massachusetts 02178, USA.
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Repérant J, Rio JP, Ward R, Wasowicz M, Miceli D, Medina M, Pierre J. Enrichment of glutamate-like immunoreactivity in the retinotectal terminals of the viper Vipera aspis: an electron microscope quantitative immunogold study. J Chem Neuroanat 1997; 12:267-80. [PMID: 9243346 DOI: 10.1016/s0891-0618(97)00018-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
A post-embedding immunogold study was carried out to estimate the immunoreactivity to glutamate in retinal terminals, P axon terminals and dendrites containing synaptic vesicles in the superficial layers of the optic tectum of Vipera. Retinal terminals, identified following either intraocular injection of tritiated proline, horseradish peroxidase (HRP) or short-term survivals after retinal ablation, were observed to be highly glutamate-immunoreactive. A detailed quantitative analysis showed that about 50% of glutamate immunoreactivity was localized over the synaptic vesicles, 35.8% over mitochondria and 14.2% over the axoplasmic matrix. The close association of immunoreactivity with the synaptic vesicles could indicate that Vipera retino-tectal terminals may use glutamate as their neurotransmitter. P axon terminals and dendrites containing synaptic vesicles, strongly gamma-aminobutyric (GABA)-immunoreactive, were shown to be also moderately glutamate-immunoreactive, but two to three times less than retinal terminals. Moreover, in P axon terminals, the glutamate immunoreactivity was denser over mitochondria than over synaptic vesicles, possibly reflecting the 'metabolic' pool of glutamate, which serves as a precursor in the formation of GABA.
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Affiliation(s)
- J Repérant
- INSERM U-106, Laboratoire de Neuromorphologie, Paris, France
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Abstract
The acidic dipeptide N-acetylaspartylglutamate (NAAG), which satisfies many of the criteria for a neurotransmitter, was identified immunohistochemically within two human retinae. We observed NAAG immunoreactivity in retinal ganglion cells, their dendrites in the inner plexiform layer, and their axons in the optic nerve fiber layer. The vast majority of ganglion cells were stained, including displaced ganglion cells, ganglion cells of different sizes, and those whose dendrites arborized in the inner and outer sublaminae of the inner plexiform layer, that is, presumed On- and Off- cells. The sizes of labeled and unlabeled cells in the ganglion cell layer, as measured in counterstained material, suggest that the unlabeled cells consist primarily or only of displaced amacrine cells. We also saw immunoreactivity in small cells along the inner margin of the inner nuclear layer, presumably amacrine cells, and in small cells with little cytoplasm in the inner plexiform and ganglion cell layers, presumably displaced amacrine cells. These results are consistent with a role for NAAG in the transmission of visual information from the retina to the rest of the brain. Further, they are similar to those reported previously in rat, cat and monkey, thus demonstrating the relevance of previous studies to humans.
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Affiliation(s)
- S B Tieman
- Department of Biological Sciences, State University of New York, Albany 12222, USA.
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Carter RE, Feldman AR, Coyle JT. Prostate-specific membrane antigen is a hydrolase with substrate and pharmacologic characteristics of a neuropeptidase. Proc Natl Acad Sci U S A 1996; 93:749-53. [PMID: 8570628 PMCID: PMC40126 DOI: 10.1073/pnas.93.2.749] [Citation(s) in RCA: 251] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
This report demonstrates that the investigational prostatic carcinoma marker known as the prostate-specific membrane antigen (PSM) possesses hydrolytic activity with the substrate and pharmacologic properties of the N-acetylated alpha-linked acidic dipeptidase (NAALADase). NAALADase is a membrane hydrolase that has been characterized in the mammalian nervous system on the basis of its catabolism of the neuropeptide N-acetylaspartylglutamate (NAAG) to yield glutamate and N-acetylaspartate and that has been hypothesized to influence glutamatergic signaling processes. The immunoscreening of a rat brain cDNA expression library with anti-NAALADase antisera identified a 1428-base partial cDNA that shares 86% sequence identity with 1428 bases of the human PSM cDNA [Israeli, R. S., Powell, C. T., Fair, W. R. & Heston, W.D.W. (1993) Cancer Res. 53, 227-230]. A cDNA containing the entire PSM open reading frame was subsequently isolated by reverse transcription-PCR from the PSM-positive prostate carcinoma cell line LNCaP. Transient transfection of this cDNA into two NAALADase-negative cell lines conferred NAAG-hydrolyzing activity that was inhibited by the NAALADase inhibitors quisqualic acid and beta-NAAG. Thus we demonstrate a PSM-encoded function and identify a NAALADase-encoding cDNA. Northern analyses identify at least six transcripts that are variably expressed in NAALADase-positive but not in NAALADase-negative rat tissues and human cell lines; therefore, PSM and/or related molecular species appear to account for NAAG hydrolysis in the nervous system. These results also raise questions about the role of PSM in both normal and pathologic prostate epithelial-cell function.
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Affiliation(s)
- R E Carter
- Department of Psychiatry, Massachusetts General Hospital-East, Charlestown 02129, USA
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Salt TE, Eaton SA. Functions of ionotropic and metabotropic glutamate receptors in sensory transmission in the mammalian thalamus. Prog Neurobiol 1996; 48:55-72. [PMID: 8830348 DOI: 10.1016/0301-0082(95)00047-x] [Citation(s) in RCA: 133] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The thalamic relay nuclei play a pivotal role in gating and processing sensory information en route to the cerebral cortex. The major ascending sensory afferents and the descending cortico-fugal afferents to the thalamus almost certainly use the excitatory amino acid L-glutamate as their transmitter. This paper reviews the nature of this transmission in terms of the receptor types which may be used (NMDA, AMPA, kainate and metabotropic glutamate receptors), their electrophysiological and pharmacological properties, and their differential location in the thalamus on neurones, terminals and glial elements. Whilst AMPA receptors, probably of more than one variety, are likely to mediate fast transmission in the thalamus, the contributions of NMDA receptors and metabotropic glutamate receptors to sensory responses under different stimulus conditions may be more varied. This is discussed in the context of the possible functional significance of the interplay of L-glutamate-gated currents with intrinsic membrane currents of thalamic neurones. The interaction of L-glutamate transmission with other modulators (acetylcholine, noradrenaline, serotonin, glycine, D-serine, nitric oxide, arginine, redox agents) is considered.
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Affiliation(s)
- T E Salt
- Department of Visual Science, University College London, U.K
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Moffett JR, Namboodiri MA. Differential distribution of N-acetylaspartylglutamate and N-acetylaspartate immunoreactivities in rat forebrain. JOURNAL OF NEUROCYTOLOGY 1995; 24:409-33. [PMID: 7595659 DOI: 10.1007/bf01181604] [Citation(s) in RCA: 103] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Contradictory immunohistochemical data have been reported on the localization of N-acetylaspartylglutamate in the rat forebrain, using different carbodiimide fixation protocols and antibody purification methods. In one case, N-acetylaspartylglutamate immunoreactivity was observed in apparent interneurons throughout all allocortical and isocortical regions, suggesting possible colocalization with GABA. In another case, strong immunoreactivity was observed in numerous pyramidal cells in neocortex and hippocampus, suggesting colocalization with glutamate or aspartate. Reconciling these disparate findings is crucial to understanding the role of N-acetylaspartylglutamate in nervous system function. Antibodies to N-acetylaspartylglutamate and a structurally related molecule, N-acetylaspartate, were purified in stages, and their cross-reactivities with protein conjugates of N-acetylaspartylglutamate and N-acetylaspartate were monitored at each stage by solid-phase immunoassay. Reduction of the cross-reactivity of the anti-N-acetylaspartylglutamate antibodies of N-acetylaspartate-protein conjugates to about 1% eliminated significant staining of most pyramidal neurons in the rat forebrain. Utilizing highly purified antibodies, the distributions of N-acetylaspartylglutamate and N-acetylaspartate were examined in several major telencephalic and diencephalic regions of the rat, and were found to be distinct. N-acetylaspartylglutamate-immunoreactivity was observed in specific neuronal populations, including many groups thought to use GABA as a neurotransmitter. Among these were the globus pallidus, ventral pallidum, entopeducular nucleus, thalamic reticular nucleus, and scattered non-pyramidal neurons in all layers of isocortex and allocortex. N-acetylaspartate-immunoreactivity was more broadly distributed than N-acetylaspartylglutamate-immunoreactivity in the rat forebrain, appearing strongest in many pyramidal neurons. Although N-acetylaspartate-immunoreactivity was found in most neurons, it exhibited a great range of intensities between different neuronal types.
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Affiliation(s)
- J R Moffett
- Department of Biology, Georgetown University, Washington, DC 20057-1028, USA
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De Biasi S, Amadeo A, Spreafico R, Rustioni A. Enrichment of glutamate immunoreactivity in lemniscal terminals in the ventropostero lateral thalamic nucleus of the rat: an immunogold and WGA-HRP study. Anat Rec (Hoboken) 1994; 240:131-40. [PMID: 7810910 DOI: 10.1002/ar.1092400114] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
BACKGROUND The ventropostero lateral nucleus (VPL) is a thalamic somatosensory center receiving inputs from limbs and trunk; some of this input is via terminals of the dorsal column medial lemniscal pathway. These fibers convey non-noxious somesthesic information. METHODS In this study the neurochemical content of lemniscal afferents in VPL of rats was investigated at the electron microscopic level by combining anterograde transport of horseradish peroxidase conjugated to wheat germ agglutinin, injected in the dorsal dorsal column nuclei, with postembedding immunogold labeling for glutamate (Glu). RESULTS Anterograde labeling in VPL was detected only in myelinated axons and in large terminals containing round synaptic vesicles, interpreted as lemniscal afferents. Quantitative evaluation of gold particle density showed enrichment of Glu immunolabeling in the identified lemniscal terminals with respect to other neuronal profiles. Observation of serial sections immunoreacted for Glu demonstrated consistency of labeling, whereas in alternate sections immunoreacted for Glu and for the inhibitory amino acid GABA these two antigens were always present in distinct types of terminals. CONCLUSIONS These findings are in agreement with several lines of evidence, obtained with different experimental approaches, supporting the hypothesis that Glu plays a major role in conveying sensory stimuli to the thalamus from second order neurons in the dorsal column nuclei.
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Affiliation(s)
- S De Biasi
- Dipartimento di Fisiologia e Biochimica generali, Sezione di Isotologia e Anatomia umana, Milano, Italy
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Montero VM. Quantitative immunogold evidence for enrichment of glutamate but not aspartate in synaptic terminals of retino-geniculate, geniculo-cortical, and cortico-geniculate axons in the cat. Vis Neurosci 1994; 11:675-81. [PMID: 7918218 DOI: 10.1017/s0952523800002984] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
A postembedding immunogold procedure was used on thin sections of the dorsal lateral geniculate nucleus (LGN) and perigeniculate nucleus (PGN) of the cat to estimate qualitatively and quantitatively, at the electron-microscopic (EM) level, the intensity of glutamate or aspartate immunoreactivities on identifiable synaptic terminals and other profiles of the neuropil. On sections incubated with a glutamate antibody, terminals of retinal and cortical axons in the LGN, and of collaterals of geniculo-cortical axons in the PGN, contain significantly higher density of immunogold particles than GABAergic terminals, glial cells, dendrites, and cytoplasm of geniculate cells. By contrast, in sections incubated with an aspartate antibody, terminals of retino-geniculate, cortico-geniculate, and geniculo-cortical axons did not show a selective enrichment of immunoreactivity, but instead the density of immunogold particles was generally low in the different profiles of the neuropil, with the exception of nucleoli. These results suggest that glutamate, but not aspartate, is a neurotransmitter candidate in the retino-geniculo-cortical pathways.
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Affiliation(s)
- V M Montero
- Department of Neurophysiology, University of Wisconsin, Madison
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Broman J. Neurotransmitters in subcortical somatosensory pathways. ANATOMY AND EMBRYOLOGY 1994; 189:181-214. [PMID: 7913798 DOI: 10.1007/bf00239008] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Investigations during recent years indicate that many different neuroactive substances are involved in the transmission and modulation of somesthetic information in the central nervous system. This review surveys recent developments within the field of somatosensory neurotransmission, emphasizing immunocytochemical findings. Increasing evidence indicates a widespread role for glutamate as a fast-acting excitatory neurotransmitter at different levels in somatosensory pathways. Several studies have substantiated a role for glutamate as a neurotransmitter in primary afferent neurons and in corticofugal projections, and also indicate a neurotransmitter role for glutamate in ascending somatosensory pathways. Other substances likely to be involved in somatosensory neurotransmission include the neuropeptides. Many different peptides have been detected in primary afferent neurons with unmyelinated or thinly myelinated axons, and are thus likely to be directly involved in primary afferent neurotransmission. Some neurons giving rise to ascending somatosensory pathways, primarily those with cell bodies in the dorsal horn, are also immunoreactive for peptides. Recent investigations have shown that the expression of neuropeptides, both in primary afferent and ascending tract neurons, may change as a result of various kinds of peripheral manipulation. The occurrence of neurotransmitters in intrinsic neurons and neurons providing modulating inputs to somatosensory relay nuclei (the dorsal horn, the lateral cervical nucleus, the dorsal column nuclei and the ventrobasal thalamus) is also reviewed. Neurotransmitters and modulators in such neurons include acetylcholine, monoamines, GABA, glycine, glutamate, and various neuropeptides.
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Affiliation(s)
- J Broman
- Department of Cell Biology, Faculty of Health Sciences, University of Linköping, Sweden
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Wroblewska B, Wroblewski JT, Saab OH, Neale JH. N-acetylaspartylglutamate inhibits forskolin-stimulated cyclic AMP levels via a metabotropic glutamate receptor in cultured cerebellar granule cells. J Neurochem 1993; 61:943-8. [PMID: 7689644 DOI: 10.1111/j.1471-4159.1993.tb03606.x] [Citation(s) in RCA: 93] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The neuronal dipeptide N-acetylaspartylglutamate (NAAG) fulfills several of the criteria for classification as a neurotransmitter including localization in synaptic vesicles, calcium-dependent release after neuronal depolarization, and low potency activation of N-methyl-D-aspartate receptors. In the present study, the influence of NAAG on metabotropic receptor activation in cerebellar granule cells was examined in cell culture. Stimulation of granule cell adenylate cyclase with forskolin increased cyclic AMP (cAMP) several hundredfold above basal levels within 10 min in a concentration-dependent manner. Although glutamate, NAAG, and the metabotropic receptor agonist trans-1-amino-1,3-cyclopentanedicarboxylic acid did not alter the low basal cAMP levels, the application of 300 microM glutamate or NAAG or trans-1-amino-1,3-cyclopentanedicarboxylic acid reduced forskolin-stimulated cAMP in granule cells by 30-50% in the absence or presence of inhibitors of ionotropic acidic amino acid receptors, as well as 2-amino-4-phosphonobutyrate. No additivity in the inhibition of cAMP was found when 300 microM NAAG and trans-1-amino-1,3-cyclopentanedicarboxylic acid were coapplied. The beta-analogue of NAAG failed to reduce cAMP levels. Similar effects of NAAG and glutamate were obtained under conditions of inhibition of phosphodiesterase activity and were prevented by pretreatment of the cells with pertussis toxin. These data are consistent with the activation by NAAG of a metabotropic acidic amino acid receptor coupled to an inhibitory G protein. In contrast, the metabotropic acidic amino acid receptor coupled to phosphoinositol turnover in these cells was not activated by NAAG.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- B Wroblewska
- Department of Biology, Georgetown University, Washington, D.C. 20057-1028
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Tsai G, Slusher BS, Sim L, Coyle JT. Immunocytochemical distribution of N-acetylaspartylglutamate in the rat forebrain and glutamatergic pathways. J Chem Neuroanat 1993; 6:277-92. [PMID: 7903856 DOI: 10.1016/0891-0618(93)90033-z] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
N-acetylaspartylglutamate (NAAG) is an acidic dipeptide found in high concentration throughout the rat central nervous system. NAAG has been proposed as a neurotransmitter/modulator in some excitatory glutamatergic pathways where it is released by a Ca(2+)-dependent process with neuronal activity. Previous immunocytochemical studies have revealed few neurons exhibiting NAAG-like immunoreactivity (LI) in the forebrain, especially in putative glutamatergic neurons. In this study, we present a detailed map of NAAG-LI in rat forebrain utilizing a modified fixation technique that markedly enhances sensitivity. NAAG-LI is located in most of the putative glutamatergic pathways in the forebrain including pyramidal neurons in motor and sensory cortices and the hippocampal formation. Co-localization of NAAG-LI to cholinergic systems of the forebrain was quite extensive with the exception of the striatal local circuit neurons. A noteworthy feature of NAAG-LI-positive neuronal groups is that they were often configured in hierarchical relationships. For example, the pyramidal neurons of the motor cortex and the motor neurons of the brainstem and and spinal cord expressed NAAG-LI; also, several inter-related components of the limbic system stained for NAAG-LI. Taken together, these findings indicate that NAAG is a neuropeptide localized to subpopulations of neurons throughout forebrain as well as in brainstem and spinal cord.
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Affiliation(s)
- G Tsai
- Department of Neuroscience, Harvard Medical School, Belmont, MA 02178
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19
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Cassidy M, Neale JH. Localization and transport of N-acetylaspartylglutamate in cells of whole murine brain in primary culture. J Neurochem 1993; 60:1631-8. [PMID: 8097231 DOI: 10.1111/j.1471-4159.1993.tb13385.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
N-Acetylaspartylglutamate (NAAG) is the most abundant neuropeptide in the mammalian nervous system. Considerable data support the hypothesis that NAAG is synaptically released in a manner consistent with neurotransmission. Primary murine brain cultures containing neurons and glia expressed 1.2-3.5 nmol of NAAG/mg of protein. In contrast to conclusions drawn from immunohistochemistry, pure glial cultures also expressed high levels of NAAG (0.6-2.11 nmol/mg of protein). These data suggest that although a subpopulation of neurons contains very high NAAG levels, micromolar concentrations of the peptide also are present in glia. Both culture types demonstrated robust extracellular peptidase activity when incubated with NAAG, as well as peptide transport. Uptake of [3H]NAAG was both temperature and sodium dependent, yet relatively insensitive to the presence of extracellular glutamate. These results indicate that synaptically released NAAG, as well as that which may be released from glia, is removed from the extracellular space by direct uptake as well as the robust enzymatic degradation of the peptide. A kinetic analysis of this NAAG transport (estimated Km = 1.8 microM) suggests a high-affinity NAAG transport system. The balance of the two processes of direct peptide uptake and peptide hydrolysis would markedly influence the sequence of receptor-mediated events that follow NAAG release.
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Affiliation(s)
- M Cassidy
- Department of Biology, Georgetown University, Washington D.C
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20
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Ray JP, Russchen FT, Fuller TA, Price JL. Sources of presumptive glutamatergic/aspartatergic afferents to the mediodorsal nucleus of the thalamus in the rat. J Comp Neurol 1992; 320:435-56. [PMID: 1378457 DOI: 10.1002/cne.903200403] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The distribution of presumptive glutamatergic and/or aspartatergic neurons retrogradely labeled following injections of 3HD-aspartate into the mediodorsal nucleus of the thalamus (MD) in the rat was compared to the distribution of neurons labeled by comparable injections of the nonspecific retrograde tracer wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP). Cells retrogradely labeled by WGA-HRP were found in the prefrontal and agranular insular cortices; in forebrain structures such as the amygdaloid complex, the piriform cortex, the ventral pallidum and the reticular nucleus of the thalamus; and in several different parts of the brainstem, such as the superior colliculus, central grey, and substantia nigra, pars reticulata. Some, but not all, of these projections are presumably glutamatergic and/or aspartatergic. The projections to MD from the prefrontal and agranular insular cortices are well labeled with 3H-D-aspartate, as are projections from the anterior cortical amygdaloid nucleus. Projections from the superior colliculus to the lateral portion of MD also label with this tracer. However, other forebrain and brainstem projections to MD are not labeled with 3H-D-aspartate, and apparently do not use glutamate or aspartate as a neurotransmitter. These include the projections from the basal and accessory basal amygdaloid nuclei, as well as possibly GABAergic projections from the ventral pallidum and the substantia nigra, pars reticulata. A small fraction of the cells in the piriform cortex that project to MD label with 3H-D-aspartate, suggesting that this projection may be heterogeneous. In other experiments, presumptive GABAergic projections to MD were studied by using 3H-GABA as a retrograde tracer. Although in these cases the thalamic reticular nucleus is well labeled, the ventral pallidum and the substantia nigra, pars reticulata are only poorly labeled. Pallidal projections to the ventromedial thalamic nucleus (VM), which are likely to be GABAergic, were also studied with this technique. After injections of 3H-GABA into VM, only a few cells in the substantia nigra, pars reticulata, or entopeduncular nucleus were labeled. This result suggests 3H-GABA has limited usefulness as a transmitter-specific retrograde tracer.
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Affiliation(s)
- J P Ray
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110
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21
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Williamson LC, Neale JH. Uptake, Metabolism, and Release of N-[3H]-Acetylaspartylglutamate by the Avian Retina. J Neurochem 1992; 58:2191-9. [PMID: 1349345 DOI: 10.1111/j.1471-4159.1992.tb10963.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
N-Acetylaspartylglutamate (NAAG) is a nervous system-specific dipeptide that is released from retinal neurons on depolarization. In the present study, extracellular metabolism, uptake, and release of [3H]NAAG were examined in the chick retina. After in vitro incubation with NAAG radiolabeled in the glutamate moiety, [3H]glutamate and [3H]NAAG increased in retinal cells through time- and temperature-dependent processes, which were reduced in the absence of extracellular sodium. Coincubation of cells with [3H]NAAG and aspartylglutamate or phosphate resulted in the decreased extracellular appearance of [3H]glutamate, produced by hydrolysis of radiolabeled NAAG, and a consequent increased availability of [3H]NAAG for transport into the retinal cells. When this tissue was incubated with radiolabeled NAAG, glutamate, glutamine, or aspartate under similar conditions, only [3H]NAAG served as a significant source for the appearance of intracellular [3H]NAAG. These data support the conclusion that [3H]NAAG can be transported into retinal cells, whereas [3H]glutamate transport is the predominant process after release of this amino acid from NAAG by extracellular peptidase activities. After uptake, [3H]NAAG entered a cellular pool, from which the peptide was secreted under depolarizing conditions and in a calcium-dependent manner.
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Affiliation(s)
- L C Williamson
- Department of Biology, Georgetown University, Washington, DC 20057
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Slusher BS, Tsai G, Yoo G, Coyle JT. Immunocytochemical localization of the N-acetyl-aspartyl-glutamate (NAAG) hydrolyzing enzyme N-acetylated alpha-linked acidic dipeptidase (NAALADase). J Comp Neurol 1992; 315:217-29. [PMID: 1545010 DOI: 10.1002/cne.903150208] [Citation(s) in RCA: 80] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
N-acetylated alpha-linked acidic dipeptidase (NAALADase) is a membrane bound enzyme that cleaves glutamate from the endogenous neuropeptide N-acetyl-aspartyl-glutamate (NAAG). We report the immunocytochemical localization of NAALADase in rat brain and kidney by using specific anti-NAALADase antiserum. NAALADase-immunoreactivity (NAALADase-IR) was widely distributed, abundant in neuropil, absent from neuronal cytoplasm, and displayed regional heterogeneity. Staining was selectively enriched in several structures previously reported to contain NAAG-immunoreactivity (NAAG-IR) including the amygdala, caudate-putamen, central gray, dorsal raphe, globus pallidus, hippocampus, hypothalamus, locus coerulus, medial and lateral geniculate, olfactory bulb, periaqueductal gray, solitary nucleus, spinal trigeminal nucleus, substantia nigra, superior colliculus, and thalamus. Staining within these structures was enriched in neuropil; no intracellular staining was detected, even after colchicine treatment. In addition, NAALADase-IR was observed in some NAAG-containing fiber tracts including the corpus callosum, fornix, habenular commissure, solitary tract, stria medularis, and stria terminalis. The co-localization of NAALADase-IR and NAAG-IR support the hypothesis that NAALADase is responsible for the catabolism of NAAG in vivo. NAALADase-IR was also detected in brain regions that, to date, have not revealed NAAG-IR, including the bed nucleus of the stria terminalis and the median eminence. In addition, NAALADase-IR was detected in the rat kidney cortex, specifically in the brush border of the proximal convoluted tubules. The observation that NAALADase-IR was more widespread than NAAG-IR suggests that NAALADase may also be involved in the catabolism of other structurally related neural and renal peptides.
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Affiliation(s)
- B S Slusher
- Department of Neuroscience, John Hopkins School of Medicine, Baltimore, Maryland 21205
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Moffett JR, Williamson LC, Neale JH, Palkovits M, Namboodiri MA. Effect of optic nerve transection on N-acetylaspartylglutamate immunoreactivity in the primary and accessory optic projection systems in the rat. Brain Res 1991; 538:86-94. [PMID: 2018935 DOI: 10.1016/0006-8993(91)90380-e] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Evidence has been presented in recent years that support the hypothesis that N-acetylaspartylglutamate (NAAG) may be involved in synaptic transmission in the optic tract of mammals. Using a modified fixation protocol, we have determined the detailed distribution of NAAG immunoreactivity (NAAG-IR) in retinal ganglion cells and optic projections of the rat. Following optic nerve transection, dramatic losses of NAAG-IR were observed in the neuropil of all retinal target zones including the lateral geniculate nucleus, superior colliculus, nucleus of the optic tract, the dorsal and medial terminal nuclei and suprachiasmatic nucleus. Brain regions were microdissected and NAAG levels measured by a radioimmunoassay (RIA) (IC50: NAAG = 2.5 nM, NAA = 100 microM; smallest detectable amount = 1-2 pg/assay). Large decreases (50-60%) in NAAG levels were detected in the lateral geniculate, superior colliculus and suprachiasmatic nucleus. Moderate losses (25-45%) were noted in the pretectal nucleus and the nucleus of the optic tract. Smaller changes (15-20%) were detected in the paraventricular nucleus and the pretectal area. These results are consistent with a synaptic communication role for NAAG in the visual system.
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Affiliation(s)
- J R Moffett
- Department of Biology, Georgetown University, Washington, DC 20057
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Williamson LC, Neale JH. Calcium-dependent release of N-acetylaspartylglutamate from retinal neurons upon depolarization. Brain Res 1988; 475:151-5. [PMID: 2905618 DOI: 10.1016/0006-8993(88)90209-0] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
N-Acetylaspartylglutamate (NAAG) is present in high concentrations specifically in the nervous system. Its neuronal distribution, presence in synaptic vesicles and its excitatory actions support the hypothesis that this dipeptide participates in communication between neurons. Following the incorporation of [3H]glutamate by frog retinal cells in vivo, the release of radiolabeled glutamate, GABA and NAAG was studied during acute incubation of the retina in vitro. Release of the radiolabeled amino acids and dipeptide was stimulated by elevated extracellular potassium. The release required the presence of extracellular calcium. These data are the first which demonstrate the release of NAAG following biosynthesis from a radiolabeled precursor and are consistent with synaptic release of this dipeptide.
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Affiliation(s)
- L C Williamson
- Department of Biology, Georgetown University, Washington, D.C. 20057
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