RESUMO
NMDA receptors are composed of proteins from two families: NMDAR1 and NMDAR2. We used quantitative double-label in situ hybridization to examine in rat brain the expression of NMDAR1, NMDAR2A, NMDAR2B, and NMDAR2C mRNA in six neurochemically defined populations of striatal neurons: preproenkephalin (ENK) and preprotachykinin (SP) expressing projection neurons, and somatostatin (SOM), glutamic acid decarboxylase 67 (GAD67), parvalbumin (PARV), and choline acetyltransferase (ChAT) expressing interneurons. NMDAR1 was expressed by all striatal neurons: strongly in ENK, SP, PARV and ChAT neurons, and less intensely in SOM and GAD67 positive cells. NMDAR2A mRNA was present at moderate levels in all striatal neurons except those containing ChAT. Labeling for NMDAR2B was strong in projection neurons and ChAT interneurons, and only moderate in SOM, GAD67 and PARV interneurons. NMDAR2C was scarce in striatal neurons, but a low level signal was detected in GAD67 positive cells. NMDAR2C expression was also observed in small cells not labeled by any of the markers, most likely glia. These data suggest that all striatal neurons have NMDA receptors, but different populations have different subunit compositions which may affect function as well as selective vulnerability.
Assuntos
Interneurônios/química , Neostriado/química , Neostriado/citologia , Receptores de N-Metil-D-Aspartato/genética , Animais , Biomarcadores , Colina O-Acetiltransferase/genética , Fibras Colinérgicas/química , Fibras Colinérgicas/enzimologia , Primers do DNA , Encefalinas/genética , Regulação Enzimológica da Expressão Gênica , Glutamato Descarboxilase/genética , Hipocampo/química , Hipocampo/citologia , Hipocampo/enzimologia , Hibridização In Situ , Interneurônios/enzimologia , Interneurônios/ultraestrutura , Neocórtex/química , Neocórtex/citologia , Neocórtex/enzimologia , Neostriado/enzimologia , Parvalbuminas/genética , Precursores de Proteínas/genética , RNA Mensageiro/análise , Ratos , Somatostatina/genética , Taquicininas/genética , Transcrição Gênica/fisiologiaRESUMO
The corticostriatal pathway is among the largest glutamatergic pathways in the brain, and of particular interest to the study of glutamatergic transmission. The metabotropic glutamate receptors (mGluRs) couple the actions of glutamate to intracellular second messenger systems through G-proteins. The most prominent of the mGluRs present in the target of this pathway, the striatum, is mGluR5. The identity of the G-proteins mediating the actions of mGluR5 are unknown, but the receptor is linked to stimulation of phosphoinositide (PI) turnover and largely resistant to the effects of pertussis toxin, which inhibits some G-proteins. We used in situ hybridization to examine the expression and regulation of three pertussis toxin insensitive G-protein alpha sub-units: Gq, G11, and Gz. We found that these mRNAs are differentially distributed in the rat brain, but all three are expressed by striatal neurons. After glutamatergic deafferentation of the striatum by decortication, there is a modest upregulation of G11 mRNA, while expression of Gq and Gz are unchanged. Following dopaminergic deafferentation, expression of Gq, G11, and Gz are not altered, although expression of the pertussis-sensitive sub-unit Go is increased. Our data suggests that Gz, Gq, and G11 are each expressed by striatal neurons, and therefore may be involved in mediating the actions of mGluR5 in these cells. After decortication G11 is upregulated, but the magnitude of this effect is small, and alone seems insufficient to account for the marked biochemical supersensitivity of glutamate-stimulated PI turnover which is observed.
Assuntos
Corpo Estriado/metabolismo , Proteínas de Ligação ao GTP/genética , Fragmentos de Peptídeos/genética , Toxina Pertussis , RNA Mensageiro/análise , Fatores de Virulência de Bordetella/farmacologia , Vias Aferentes/fisiologia , Animais , Descorticação Cerebral , Proteínas de Ligação ao GTP/química , Hibridização In Situ , Masculino , Oxidopamina , RNA Mensageiro/biossíntese , Ratos , Ratos Sprague-DawleyRESUMO
Early-onset torsion dystonia, an autosomal dominant disease associated with the DYT1 locus on 9q34, is the most frequent genetic form of dystonia. Recent work has revealed that the causative mutation in most cases is deletion of a glutamate residue from the carboxy terminal of torsinA, a 332 amino acid protein encoded by the DYT1 gene. To gain insight into how deletion of a single amino acid can produce such a profound movement disorder, we have mapped the expression of the DYT1 gene in normal human postmortem brain. DYT1 mRNA is highly enriched in the dopamine neurons of the substantia nigra pars compacta. Intense expression was also found in the cerebellum and hippocampal subfields. The prominent expression of the DYT1 gene within the substantia nigra pars compacta, which provides dopaminergic innervation to the basal ganglia, implicates a disturbance of dopaminergic function in the pathophysiology of early-onset torsion dystonia.
Assuntos
Química Encefálica/genética , Proteínas de Transporte/genética , Distonia Muscular Deformante/genética , Chaperonas Moleculares , Idade de Início , Idoso , Gânglios da Base/química , Feminino , Expressão Gênica/fisiologia , Hipocampo/química , Humanos , Hibridização In Situ , Masculino , Pessoa de Meia-Idade , Sondas RNA , RNA Mensageiro/análise , Substância Negra/química , Transcrição Gênica/fisiologiaRESUMO
Metabotropic glutamate receptors (mGluRs), which couple glutamate to second messengers, have important roles in the regulation of movement by the basal ganglia. We used two polyclonal antisera to mGluR1a and mGluR2/3 and confocal laser microscopy to investigate the localization of these receptors in the basal ganglia of the rat. The mGluRs were visualized in combination with an antibody to tyrosine hydroxylase (TH), an antibody to microtubule-associated protein 2 (MAP2, a dendritic marker), or SV2 (an antibody to a protein associated with presynaptic terminals). In the neostriatum, punctate mGluR1a immunoreactivity (ir) was present in the neuropil. This staining did not colocalize with MAP2-ir or SV2-ir and was not altered by decortication or unilateral 6-hydroxydopamine (6-OHDA) lesions. In the globus pallidus and substantia nigra pars reticulata, however, mGluR1a-ir was tightly clustered along large MAP2-ir dendrites. In contrast to the variations in mGluR1a-ir staining, similar punctate neuropil mGluR2/3-ir staining was observed within all basal ganglia structures. In the neostriatum, these puncta were abundant; unlike mGluR1a, many mGluR2/3-ir puncta colocalized with SV2-ir, and striatal mGluR2/3-ir puncta were markedly reduced in number after decortication. Neither mGluR1a-ir nor mGluR2/3-ir could be detected in TH-ir soma within substantia nigra pars compacta, or in TH-ir striatal terminals. Overall, our observations suggest that mGluR1a and mGluR2/3 receptors have distinct cellular localizations in different components of the basal ganglia circuitry and are likely to subserve distinct functions. Our data support the presence of mGluR2/3 on the terminals of corticostriatal afferents, where they may regulate glutamate release. In contrast, mGluR1a appears to be a postsynaptic receptor of neurons in the neostriatum, globus pallidus, and substantia nigra pars reticulata.
