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1.
The present study describes the effects of gamma-aminobutyric acid (GABA) and its antagonists, bicuculline and 2-hydroxysaclofen,
on visual responses of neurons in the pigeon nucleus lentiformis mesencephali (nLM). The results indicate that GABA significantly
reduces both spontaneous activity and visual responsiveness, and GABA A antagonist bicuculline but not GABA B antagonist 2-hydroxysaclofen enhances visual responses of nLM cells examined. Furthermore, inhibition produced by motion
in the null-direction of pretectal neurons is diminished by bicuculline but not by 2-hydroxysaclofen. It is therefore concluded
that the null-direction inhibition of directional cells in the pigeon nLM is predominantly mediated by GABA and GABA A receptors. This inhibition may at least in part underlie directional asymmetry of optokinetic responses. 相似文献
2.
The effects of γ-aminobutyric acid (GABA) and its antagonists bicuculline and 2-hydroxysaclofen on neuronal firings in the
nucleus of basal optic root (nBOR) in pigeons were studied by using extracellular recording and microiontophoretic techniques.
The results suggest that GABA may be an inhibitory neurotransmitter or modulator within nBOR, functioning by means of main
mediation of GABA A receptors and of minor mediation of GABA B receptors. Furthermore, GABA and its GABA A receptors are involved in the modulation of directional selectivity in part of nBOR neurons.
Project supported by the National Natural Science Foundation of China and Amherst College. 相似文献
3.
The responses of inhibitory neurons/synapses to motoneuron injury in the cranial nervous system remain to be elucidated. In this study, we analyzed GABA A receptor (GABA AR) and GABAergic neurons at the protein level in the transected rat facial nucleus. Immunoblotting revealed that the GABA ARα1 protein levels in the axotomized facial nucleus decreased significantly 5–14 days post-insult, and these levels remained low for 5 weeks. Immunohistochemical analysis indicated that the GABA ARα1-expressing cells were motoneurons. We next examined the specific components of GABAergic neurons, including glutamate decarboxylase (GAD), vesicular GABA transporter (VGAT) and GABA transporter-1 (GAT-1). Immunoblotting indicated that the protein levels of GAD, VGAT and GAT-1 decreased transiently in the transected facial nucleus from 5 to 14 days post-insult, but returned to the control levels at 5 weeks post-insult. Although GABA ARα1 protein levels in the transected nucleus did not return to their control levels for 5 weeks post-insult, the administration of glial cell line—derived neurotrophic factor at the cut site significantly ameliorated the reductions. Through these findings, we verified that the injured facial motoneurons suppressed the levels of GABA ARα1 protein over the 5 weeks post-insult, presumably due to the deprivation of neurotrophic factor. On the other hand, the levels of the GAD, VGAT and GAT-1 proteins in GABAergic neurons were transiently reduced in the axotomized facial nucleus at 5–14 days post-insult, but recovered at 4–5 weeks post-insult. 相似文献
4.
We have investigated the role of N-methyl- d-aspartate receptors (NMDARs) and γ-aminobutyric acid receptors type A (GABA ARs) at an early stage of P19 neuronal differentiation. The subunit expression was profiled in 24-hour intervals with RT-PCR and functionality of the receptors was verified via fluo-3 imaging of Ca 2+ dynamics in the immature P19 neurons showing that both NMDA and GABA excite neuronal bodies, but only polyamine-site sensitive NMDAR stimulation leads to enhanced Ca 2+ signaling in the growth cones. Inhibition of NR1/NR2B NMDARs by 1 μM ifenprodil severely impaired P19 neurite extension and fasciculation, and this negative effect was fully reversible by polyamine addition. In contrast, GABA AR antagonism by a high dose of 200 μM bicuculline had no observable effect on P19 neuronal differentiation and fasciculation. Except for the differential NMDAR and GABA AR profiles of Ca 2+ signaling within the immature P19 neurons, we have also shown that inhibition of NR1/NR2B NMDARs strongly decreased mRNA level of NCAM-180, which has been previously implicated as a regulator of neuronal growth cone protrusion and neurite extension. Our data thus suggest a critical role of NR1/NR2B NMDARs during the process of neuritogenesis and fasciculation of P19 neurons via differential control of local growth cone Ca 2+ surges and NCAM-180 signaling. 相似文献
5.
Abstract: The GABA A receptor is a heterooligomeric protein complex composed of multiple receptor subunits. Developmental changes in the pattern of expression of 11 GABA A receptor subunits in individual rat embryonic hippocampal neurons on days 1–21 in culture and acutely dissociated hippocampal neurons from postnatal day (PND) 5 rat pups were investigated using the technique of single-cell mRNA amplification. We demonstrate that multiple GABA A receptor subunits are expressed within individual hippocampal neurons, with most cells simultaneously expressing α1, α2, α5, β1, and γ2 mRNAs. Further, relative expression of several GABA A receptor subunit mRNAs changes significantly in embryonic hippocampal neurons during in vitro development, with the relative abundance (compared with β-actin) of α1, α5, and γ2 mRNAs increasing 2.3-, 2.7-, and 3.8-fold, respectively, from days 1 to 14, and β1 increasing 5-fold from days 1 to 21. In situ hybridization with antisense digoxigenin-labeled α1, β1, and γ2 RNA probes demonstrates a similar increase in expression of subunit mRNAs as embryonic hippocampal neurons mature in vitro. Relative abundances of α1, β1, and γ2 subunit mRNAs in acutely dissociated PND 5 hippocampal neurons are also significantly greater than in embryonic day 17 neurons on day 1 in vitro and exceed the peak values seen in cultured neurons on days 14–21, suggesting that GABA A receptor subunit mRNA expression within individual hippocampal neurons follows a similar, if somewhat delayed, developmental pattern in vitro compared with in vivo. These findings suggest that embryonic hippocampal neuronal culture provides a useful model in which to study the developmental regulation of GABA A receptor expression and that developmental changes in GABA A receptor subunit expression may underlie some of the differences in functional properties of GABA A receptors in neonatal and mature hippocampal neurons. 相似文献
6.
The neurotransmitter gamma-aminobutyric acid (GABA) and subtypes of GABA receptors were recently identified in adult testes. Since adult Leydig cells possess both the GABA biosynthetic enzyme glutamate decarboxylase (GAD), as well as GABA A and GABA B receptors, it is possible that GABA may act as auto-/paracrine molecule to regulate Leydig cell function. The present study was aimed to examine effects of GABA, which may include trophic action. This assumption is based on reports pinpointing GABA as regulator of proliferation and differentiation of developing neurons via GABA A receptors. Assuming such a role for the developing testis, we studied whether GABA synthesis and GABA receptors are already present in the postnatal testis, where fetal Leydig cells and, to a much greater extend, cells of the adult Leydig cell lineage proliferate. Immunohistochemistry, RT-PCR, Western blotting and a radioactive enzymatic GAD assay evidenced that fetal Leydig cells of five-six days old rats possess active GAD protein, and that both fetal Leydig cells and cells of the adult Leydig cell lineage possess GABA A receptor subunits. TM3 cells, a proliferating mouse Leydig cell line, which we showed to possess GABA A receptor subunits by RT-PCR, served to study effects of GABA on proliferation. Using a colorimetric proliferation assay and Western Blotting for proliferating cell nuclear antigen (PCNA) we demonstrated that GABA or the GABA A agonist isoguvacine significantly increased TM3 cell number and PCNA content in TM3 cells. These effects were blocked by the GABA A antagonist bicuculline, implying a role for GABA A receptors. In conclusion, GABA increases proliferation of TM3 Leydig cells via GABA A receptor activation and proliferating Leydig cells in the postnatal rodent testis bear a GABAergic system. Thus testicular GABA may play an as yet unrecognized role in the development of Leydig cells during the differentiation of the testicular interstitial compartment. 相似文献
7.
Motor neurones of the crayfish walking system display inhibitory responses evoked either by γ-amino butyric acid (GABA) or
glutamate, possibly involving the same receptor (Pearlstein et al. 1994). In order to test if this sensibility to both GABA
and glutamate was a specific property of crayfish GABA receptors, pharmacological characteristics of GABA-evoked responses
in both sensory terminals from CB chordotonal organ and motor neurones of the walking system have been compared. Both receptors
are GABA-gated Cl − channels activated by specific GABA A (muscimol, isoguvacine), GABA B (3-aminopropyl phosphinic acid), and GABA C ( cis-4-amino crotonic acid) agonists, and blocked by competitive (β-guanidino propionic acid) and non-competitive (picrotoxin)
antagonists. They were insensitive to specific GABA A (bicuculline, SR-95531) and GABA B (phaclofen) antagonists. Furthermore, in both cases, nipecotic acid and the modulatory drug diazepam had no effect. However,
our results demonstrate that GABA receptors of sensory terminals are different from those of motor neurones. GABA-induced
desensitisation only occurred in sensory terminals. Moreover, glutamate was shown to activate GABA-gated Cl − channels in motor neurones, but not in sensory terminals. Therefore, GABA is likely to be the endogenous neurotransmitter
of presynaptic inhibition in sensory terminals, whereas inhibition between antagonistic motor neurones would be achieved by
glutamate.
Accepted: 10 July 1996 相似文献
8.
In the sensory ganglia, neurons are devoid of synaptic contacts, and ganglion neurons surrounded by one of glial cells, satellite
cells. Recent studies suggest that neurons and satellite cells interact through neurotransmitters. In the present study, intracellular
Ca 2+ ([Ca 2+] i) dynamics of neurons and satellite cells from one of viscerosensory ganglia, nodose ganglion (NG), were investigated by stimulation
with glutamate and its agonist and/or the antagonist of the GABA A receptor bicuculline. In the specimens containing neurons with satellite cells, glutamate and a metabotropic glutamate receptor
(mGluR) agonist t-ACPD evoked [Ca 2+] i increases in both neurons and surrounding satellite cells. Moreover, bicuculline also induced [Ca 2+] i increases in neurons and satellite cells. However, in the isolated neurons, bicuculline did not cause an increase in [Ca 2+] i, suggesting that satellite cells are equipped with the ability to release GABA. In the neurons associated with satellite
cells, the delay time until the onset of a response was shorter in the case of glutamate stimulation with bicuculline than
that without bicuculline (107.3 ± 93.4 vs. 231.8 ± 97.0 s, p < 0.01). Furthermore, immunoreactivities for glutamate transporter, GLAST, and GABA transporter, GAT-3, were observed in
both neurons and satellite cells of NG. In conclusion, the levels of [Ca 2+] i of NG neurons and surrounding satellite cells are increased by glutamate through at least mGluRs, and endogenous GABA modulates
these responses; GABA inhibition is dependent on a close association between neurons and satellite cells. Such neuron–glia
interaction in the nodose ganglion may regulate sensory information from visceral organs. 相似文献
9.
Effects of neurotransmitters on dendritic morphology were analyzed in cocultures of neurons and astrocytes from the neonatal rat olfactory bulb by means of immunocytochemical staining and morphometry. About 70% of the neurons were γ-aminobutyric acid (GABA)-immunoreactive on day 7 of the coculture. Morphometric analysis of neurons having no contact with other neurons revealed that incubation of the coculture with either a sodium channel blocker, tetrodotoxin, or GABA A receptor antagonists such as bicuculline or picrotoxin resulted in a decreased number of dendritic branch points as compared to neurons in control cultures, while the same treatment did not affect radial dendritic outgrowth or the number of primary dendrites. Application of a GABA B receptor antagonist, phaclofen, or an AMPA-type glutamate receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione, had no detectable effect on dendritic morphology. Incubation of the coculture with a GABA A receptor agonist, muscimol, enhanced branching and reversed the inhibitory effect of tetrodotoxin. Branching was also enhanced by increasing extracellular K +. The inhibitory effect of tetrodotoxin or bicuculline and the stimulatory effect of muscimol or elevated K + were abolished when neurons were grown on a monolayer of dead astrocytes, indicating that the morphoregulatory action of GABA requires living astrocytes to operate. Astrocytes pretreated with muscimol before the addition of neurons supported branching better than those without pretreatment. These results suggest that various aspects of dendritic growth are regulated by distinct mechanisms, and that neuron-to-astrocyte signaling mediated by GABA promotes dendritic branching. © 1998 John Wiley & Sons, Inc. J Neurobiol 37: 251–264, 1998 相似文献
10.
We cultured a P19 mouse teratocarcinoma cell line and induced its neuronal differentiation to study the function of ionotropic glutamate receptors (GluRs) in early neuronal development. Immunocytochemical studies showed 85% neuronal population at 5 days in vitro (DIV) with microtubule-associated protein 2-positive staining. Thirty percent and 50% of the cells expressed the alpha-amino-3-hydroxy-5-methyl-4-isopropinonate (AMPA) receptor subunit, GluR2/3, and the kainate (kainic acid; KA) receptor subunit, GluR5/6/7, respectively. In Western blot analysis, the temporal expression of GluR2/3 began to appear at 3 DIV, whereas GluR5/6/7 was already expressed in the undifferentiated cells. P19-derived neurons began to respond to glutamate, AMPA and KA, but not to the metabotropic GluR agonist trans-1-aminocyclopentane-1,3-decarboxylic acid, by 5 DIV in terms of increases in intracellular calcium and phospholipase C-mediated poly-phosphoinositide turnover. Furthermore, KA reduced cell death of P19-derived neurons in both atmospheric and hypobaric conditions in a phospholipase C-dependent manner. The common AMPA/KA receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione, but not the AMPA receptor antagonist, 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide disodium, profoundly increased hypobaric insult-induced neurotoxicity. In a flow cytometry study, the nerve growth factor-mediated antiapoptotic effect was facilitated by AMPA, with an induction of TrkA, but not p75(NTR) expression. Therefore, AMPA and KA receptors might mediate neurotrophic functions to facilitate neurotrophic factor signaling to protect neurons against hypoxic insult in early neuronal development. 相似文献
11.
Astrocytes are the major glial cells in brain tissue and are involved, among many functions, ionic and metabolic homeostasis maintenance of synapses. These cells express receptors and transporters for neurotransmitters, including GABA. GABA signaling is reportedly able to affect astroglial response to injury, as evaluated by specific astrocyte markers such as glial fibrillary acid protein and the calcium-binding protein, S100B. Herein, we investigated the modulatory effects of the GABAA receptor on astrocyte S100B secretion in acute hippocampal slices and astrocyte cultures, using the agonist, muscimol, and the antagonists pentylenetetrazol (PTZ) and bicuculline. These effects were analyzed in the presence of tetrodotoxin (TTX), fluorocitrate (FLC), cobalt and barium. PTZ positively modify S100B secretion in hippocampal slices and astrocyte cultures; in contrast, bicuculline inhibited S100B secretion only in hippocampal slices. Muscimol, per se, did not change S100B secretion, but prevented the effects of PTZ and bicuculline. Moreover, PTZ-induced S100B secretion was prevented by TTX, FLC, cobalt and barium indicating a complex GABAA communication between astrocytes and neurons. The effects of two putative agonists of GABAA, β-hydroxybutyrate and methylglyoxal, on S100B secretion were also evaluated. In view of the neurotrophic role of extracellular S100B under conditions of injury, our data reinforce the idea that GABAA receptors act directly on astrocytes, and indirectly on neurons, to modulate astroglial response. 相似文献
13.
The region that becomes the ventromedial nucleus of the hypothalamus (VMH) is surrounded by cells and fibers containing immunoreactive gamma‐aminobutyric acid (GABA) by embryonic day 13 (E13), several days before the nucleus emerges in Nissl stains. As GABA plays many roles during neural development, we hypothesized that it influences VMH development, perhaps by providing boundary information for migrating neurons. To test this hypothesis we examined the VMH in embryonic mice in which the β3 subunit of the GABA A‐receptor, a receptor subunit that is normally highly expressed in this nucleus, was disrupted by gene targeting. In β3 ?/? embryos the VMH was significantly larger, and the distribution of cells containing immunoreactive estrogen receptor‐α was expanded compared to controls. Using in vitro brain slices from wild‐type C57BL/6J mice killed at E15 we found that treatment with the GABA A antagonist bicuculline increased the number of cells migrating per video field analyzed in the VMH. In addition, treatment with either bicuculline or the GABA A agonist muscimol altered the orientation of cell migration in particular regions of this nucleus. These data suggest that GABA is important for the organization of cells during VMH formation. © 2001 John Wiley & Sons, Inc. J Neurobiol 49: 264–276, 2001 相似文献
14.
GABA receptor binding to mammalian neuronal membranes has been classified into at least 2 subtypes—GABA A and GABA B binding sites. In catfish brain GABA A receptor sites have previously been demonstrated. Evidence is now presented that under appropriate conditions which rule out GABA A receptor binding, [ 3H]GABA binds to membranes prepared from catfish brain. This binding is bicuculline-insensitive but differs enough from mammalian GABA B binding to cast some doubt on the idea that GABA B receptors exist in catfish brain. Specific binding was detected that was saturable and exhibited a dissociation constant of 4μM. (±)Baclofen, a potent inhibitor in rat brain, was a weak inhibitor, producing a maximum of 43% inhibition. This inhibitory effect could be enhanced, however, in the presence of 320 μM isoguvacine. [ 3H]GABA binding was unaffected by bicuculline. Thus bicuculline-insensitive GABA binding sites exist in catfish brain but they differ in a number of ways from the GABA B receptor site found in mammals. Furthermore, a third [ 3H]GABA binding site appears to exist that is both baclofen- and bicuculline-insensitive, yet is inhibited by high concentrations of isoguvacine, a known GABA A agonist. 相似文献
15.
A developmental “switch” in chloride transporters occurs in most neurons resulting in GABA A mediated hyperpolarization in the adult. However, several neuronal cell subtypes maintain primarily depolarizing responses to GABA A receptor activation. Among this group are gonadotropin-releasing hormone-1 (GnRH) neurons, which control puberty and reproduction. NKCC1 is the primary chloride accumulator in neurons, expressed at high levels early in development and contributes to depolarization after GABA A receptor activation. In contrast, KCC2 is the primary chloride extruder in neurons, expressed at high levels in the adult and contributes to hyperpolarization after GABA A receptor activation. Anion exchangers (AEs) are also potential modulators of responses to GABA A activation since they accumulate chloride and extrude bicarbonate. To evaluate the mechanism(s) underlying GABA A mediated depolarization, GnRH neurons were analyzed for 1) expression of chloride transporters and AEs in embryonic, pre-pubertal, and adult mice 2) responses to GABA A receptor activation in NKCC1 -/- mice and 3) function of AEs in these responses. At all ages, GnRH neurons were immunopositive for NKCC1 and AE2 but not KCC2 or AE3. Using explants, calcium imaging and gramicidin perforated patch clamp techniques we found that GnRH neurons from NKCC1 -/- mice retained relatively normal responses to the GABA A agonist muscimol. However, acute pharmacological inhibition of NKCC1 with bumetanide eliminated the depolarization/calcium response to muscimol in 40% of GnRH neurons from WT mice. In the remaining GnRH neurons, HCO 3
- mediated mechanisms accounted for the remaining calcium responses to muscimol. Collectively these data reveal mechanisms responsible for maintaining depolarizing GABA A mediated transmission in GnRH neurons. 相似文献
16.
Primary lens epithelial cell (LEC) cultures derived from newborn (P0) and one-month-old (P30) mouse lenses were used to study GABA (gamma-aminobutyric acid) signaling expression and its effect on the intracellular Ca 2+ ([Ca 2+] i) level. We have found that these cultures express specific cellular markers for lens epithelial and fiber cells, all components of the functional GABA signaling pathway and GABA, thus recapitulating the developmental program of the ocular lens. Activation of both GABA-A and GABA-B receptors (GABA AR and GABA BR) with the specific agonists muscimol and baclofen, respectively induces [Ca 2+] i transients that could be blocked by the specific antagonists bicuculline and CGP55845 and were dependent on extracellular Ca 2+. Bicuculline did not change the GABA-evoked Ca 2+ responses in Ca 2-containing buffers, but suppressed them significantly in Ca 2+-free buffers suggesting the two receptors couple to convergent Ca 2+ mobilization mechanisms with different extracellular Ca 2+ sensitivity. Prolonged activation of GABA BR induced wave propagation of the Ca 2+ signal and persistent oscillations. The number of cells reacting to GABA or GABA + bicuculline in P30 mouse LEC cultures expressing predominantly the synaptic type GABA AR did not differ significantly from the number of reacting cells in P0 mouse LEC cultures. The GABA-induced Ca 2+ transients in P30 (but not P0) mouse LEC could be entirely suppressed by co-application of bicuculline and CGP55845. The GABA-mediated Ca 2+ signaling may be involved in a variety of Ca 2+-dependent cellular processes during lens growth and epithelial cell differentiation. 相似文献
18.
We have previously shown that short-lasting reduction of cerebral blood flow by bilateral clamping of carotid arteries (BCCA) results in long-lasting increase in regional GABA concentration and decrease in seizure susceptibility in rats. In the present experiments, the effect of BCCA on GABA turnover and the enzymes involved in GABA synthesis and degradation were studied in rats. Regional GABA turnover was measured by means of GABA accumulation induced by the GABA-transaminase (GABA-T) inhibitor aminooxyacetic acid (AOAA). Fourteen days after BCCA, GABA turnover was significantly increased in hippocampus, substantia nigra and cortex, but not different from sham-operated controls in several other brain regions, including striatum, hypothalamus and cerebellum. The activity of glutamate decarboxylase (GAD) measured ex vivo did not show any changes in investigated structures, while the activity of GABA-T was slightly increased in hippocampus. The increased GABA turnover in some brain regions may explain our previous findings of increased GABA content in these brain regions and decreased sensitivity of BCCA treated animals to the GABA A-receptor antagonist bicuculline. 相似文献
19.
This study was designed to examine the effects of intracerebroventricular (ICV) injection of bicuculline (GABA A receptor antagonist) and muscimol (GABA A receptor agonist) on glutamate-induced eating response in 24-h food-deprived (FD24) broiler cockerels. At first, guide cannula
was surgically implanted in the right lateral ventricle of chickens. In experiment 1, birds were ICV injected with different
doses of glutamate. In experiment 2, birds were administered with effective dose of glutamate after bicuculline. In experiment
3, chickens received muscimol prior to the injection of glutamate, and cumulative food intake was determined at 3-h postinjection.
The results of this study showed that glutamate decreases food consumption in FD24 broiler cockerels ( P ≤ 0.05), and this reduction occurs in a dose-dependent manner. Moreover, the inhibitory effect of glutamate on food intake
was significantly increased with bicuculline pretreatment, and this effect was attenuated with muscimol ( P ≤ 0.05). These results suggest that there is an interaction between glutamatergic and GABAergic systems (through GABA A receptor) on food intake in broiler cockerels. 相似文献
20.
GABA A channels were activated by GABA in outside-out patches from rat cultured hippocampal neurons. They were blocked by bicuculline
and potentiated by diazepam. In 109 of 190 outside-out patches, no channels were active before exposure to GABA (silent patches).
The other 81 patches showed spontaneous channel activity. In patches containing spontaneous channel activity, rapid application
of GABA rapidly activated channels. In 93 of the silent patches, channels could be activated by GABA but only after a delay
that was sometimes as long as 10 minutes. The maximum channel conductance of the channels activated after a delay increased
with GABA concentration from less than 10 pS (0.5 μ m GABA) to more than 100 pS (10 m m GABA). Fitting the data with a Hill-type equation gave an EC
50 value of 33 μ m and a Hill coefficient of 0.6. The channels showed outward rectification and were chloride selective. In the presence of
1 μ m diazepam, the GABA EC
50 decreased to 0.2 μ m but the maximum conductance was unchanged. Diazepam decreased the average latency for channel opening. Bicuculline, a GABA
antagonist, caused a concentration-dependent decrease in channel conductance. In channels activated with 100 μ m GABA the bicuculline IC
50 was 19 μ m. The effect of GABA on channel conductance shows that the role of the ligand in GABA A receptor channel function is more complex than previously thought.
Received: 23 October 2000/Revised: 27 February 2001 相似文献
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