Properties of the GABAA receptor of rat posterior pituitary nerve terminals

1995 ◽  
Vol 73 (3) ◽  
pp. 1135-1144 ◽  
Author(s):  
S. J. Zhang ◽  
M. B. Jackson
Keyword(s):  
Gabaa Receptor ◽  
Nerve Terminal ◽  
Gabaa Receptors ◽  
Gabab Receptor ◽  
Gabab Receptors ◽  
Receptor Protein ◽  
Nerve Terminals ◽  
Posterior Pituitary ◽  
Pipette Solution ◽  
Long Duration

1. We investigated gamma-aminobutyric acid (GABA) receptors using thin slice patch-clamp techniques in the swellings along axons of posterior pituitary nerve terminals. 2. Activation of the nerve terminal GABAA receptor induced a mean conductance change of 1.5 nS. Normalizing to area gave a mean conductance density of 0.38 mS/cm2. 3. Whereas GABAA receptor-mediated responses could be seen in 91% of the nerve terminals tested, GABAB receptor-mediated responses could not be detected. The GABAB receptor agonist baclofen had no effect on holding current or on voltage-activated K+ and Ca2+ channels. It is unlikely that nerve terminals of the posterior pituitary contain GABAB receptors. 4. The channel gated by the nerve terminal GABAA receptor exhibited only a single open conductance level. Only fully open and fully closed states were observed. Subconductance states typical of other GABAA receptor channels were not seen in the GABA-gated channels of posterior pituitary nerve terminals. 5. Both open time and closed time distributions were biexponential, indicating at least two open and two closed conformations of the channel. At a higher GABA concentration, long-duration openings predominated, suggesting that long-duration openings were distinguished from short-duration openings by the occupation of a greater number of agonist binding sites. 6. Sustained application of GABA desensitized the receptor with simple exponential kinetics. The time constant for desensitization was approximately 9 s for both GABA and muscimol. 7. Zinc ions at concentrations of 100 microM reduced GABA responses by only 22%. This weak sensitivity to zinc, together with a previous observation of benzodiazepine sensitivity, suggested that the nerve terminal GABAA receptor possesses a gamma-subunit. 8. Responses mediated by the GABAA receptor persist in whole terminal recordings without Mg-ATP in the pipette solution. Thus, in contrast to many other GABAA receptors, this receptor showed no rundown in the absence of ATP. 9. The GABAA receptor channel of posterior pituitary nerve terminals has many properties in common with GABAA receptors of other preparations. A number of subtle differences between the nerve terminal receptor described here and cell body receptors described elsewhere may reflect the presence of receptor protein subunits unique to nerve terminals.

scholarly journals Neonatal Clonazepam Administration Induced Long-Lasting Changes in GABAA and GABAB Receptors

2020 ◽  
Vol 21 (9) ◽  
pp. 3184
Author(s):  
Hana Kubová ◽  
Zdeňka Bendová ◽  
Simona Moravcová ◽  
Dominika Pačesová ◽  
Luisa Rocha ◽  
...  
Keyword(s):  
Gabaa Receptor ◽  
Receptor Binding ◽  
Brain Structure ◽  
Gabab Receptor ◽  
Brain Structures ◽  
Emotional Behavior ◽  
Gabab Receptors ◽  
Behavioral Impairment ◽  
Almost All ◽  
The Brain

Benzodiazepines (BZDs) are widely used in patients of all ages. Unlike adults, neonatal animals treated with BZDs exhibit a variety of behavioral deficits later in life; however, the mechanisms underlying these deficits are poorly understood. This study aims to examine whether administration of clonazepam (CZP; 1 mg/kg/day) in 7–11-day-old rats affects Gama aminobutyric acid (GABA)ergic receptors in both the short and long terms. Using RT-PCR and quantitative autoradiography, we examined the expression of the selected GABAA receptor subunits (α1, α2, α4, γ2, and δ) and the GABAB B2 subunit, and GABAA, benzodiazepine, and GABAB receptor binding 48 h, 1 week, and 2 months after treatment discontinuation. Within one week after CZP cessation, the expression of the α2 subunit was upregulated, whereas that of the δ subunit was downregulated in both the hippocampus and cortex. In the hippocampus, the α4 subunit was downregulated after the 2-month interval. Changes in receptor binding were highly dependent on the receptor type, the interval after treatment cessation, and the brain structure. GABAA receptor binding was increased in almost all of the brain structures after the 48-h interval. BZD-binding was decreased in many brain structures involved in the neuronal networks associated with emotional behavior, anxiety, and cognitive functions after the 2-month interval. Binding of the GABAB receptors changed depending on the interval and brain structure. Overall, the described changes may affect both synaptic development and functioning and may potentially cause behavioral impairment.

scholarly journals Quantitative studies on the localization of the cholinergic receptor protein in the normal and denervated electroplaque from Electrophorus electricus.

1978 ◽  
Vol 79 (1) ◽  
pp. 200-216 ◽  
Author(s):  
J P Bourgeois ◽  
J L Popot ◽  
A Ryter ◽  
J P Changeux
Keyword(s):  
Nerve Terminal ◽  
Cholinergic Receptor ◽  
Receptor Protein ◽  
Nerve Terminals ◽  
Alpha Toxin ◽  
Surface Binding ◽  
Electrophorus Electricus ◽  
Electric Organs ◽  
Grain Distribution ◽  
Silver Grains

Electroplaques dissected from the electric organ of Electrophorus electricus are labeled by tritiated alpha1-isotoxin from Naja nigricollis, a highly selective reagent of the cholinergic (nicotinic) receptor site. Preincubation of the cell with an excess of unlabeled alpha-toxin and with a covalent affinity reagent or labeling in the presence of 10(-4) M decamethonium reduces the binding of [3H]alpha-toxin by at least 75%. Absolute surface densities of alpha-toxin sites are estimated by high-resolution autoradiography on the basis of silver grain distribution and taking into account the complex geopmetry of the cell surface. Binding of [3H]alpha-toxin on the noninnervated face does not differ from background. Labeled sites are observed on the innervated membrane both between the synapses and under the nerve terminals but the density of sites is approx. 100 times higher at the level of the synapses than in between. Analysis of the distance of silver grains from the innervated membrane shows a symmetrical distribution centered on the postsynaptic plasma membrane under the nerve terminal. In extrasynaptic areas, the barycenter of the distribution lies approximately 0.5 micrometer inside the cell, indicating that alpha-toxin sites are present on the membrane of microinvaginations, or caveolae, abundant in the extrajunctional areas. An absolute density of 49,600 +/- 16,000 sites/micrometer2 of postsynaptic membrane is calculated; it is in the range of that found at the crest of the folds at the neuromuscular junction and expected from a close packing of receptor molecules. Electric organs were denervated for periods up to 142 days. Nerve transmission fails after 2 days, and within a week all the nerve terminals disappear and are subsequently replaced by Schwann cell processes, whereas the morphology of the electroplaque remains unaffected. The denervated electroplaque develops some of the electrophysiological changes found with denervated muscles (increases of membrane resting resistance, decrease of electrical excitability) but does not become hypersensitive to cholinergic agonists. Autoradiography of electroplaques dissected from denervated electric organs reveals, after labeling with [3H]alpha-toxin, patches of silver grains with a surface density close to that found in the normal electroplaque. The density of alpha-toxin binding sites in extrasynaptic areas remains close to that observed on innervated cells, confirming that denervation does not cause an increase in the number of cholinergic receptor sites. The patches have the same distribution, shape,and dimensions as in subneural areas of the normal electroplaque, and remnants of nerve terminal or Schwann cells are often found at the level of the patches. They most likely correspond to subsynaptic areas which persist with the same density of [3H]alpha-toxin sites up to 52 days after denervation. In the adult synapse, therefore, the receptor protein exhibits little if any tendency for lateral diffusion.

Discrimination of post- and presynaptic GABAB receptor-mediated responses by tetrahydroaminoacridine in area CA3 of the rat hippocampus

1993 ◽  
Vol 69 (2) ◽  
pp. 630-635 ◽  
Author(s):  
N. A. Lambert ◽  
W. A. Wilson
Keyword(s):  
Gabaa Receptor ◽  
Gabab Receptor ◽  
Hippocampal Slices ◽  
Outward Current ◽  
Gabab Receptors ◽  
Rat Hippocampus ◽  
Stratum Radiatum ◽  
Paired Pulse ◽  
Paired Pulse Depression ◽  
Area Ca3

1. The effects of the K+ channel blocker 9-amino-1,2,3,4-tetrahydroacridine (THA) on the actions of baclofen and gamma-aminobutyric acid (GABA) at post- and presynaptic GABAB receptors were studied with whole-cell voltage-clamp recording in area CA3 of rat hippocampal slices. 2. The effect of THA on postsynaptic GABAB receptor-mediated responses was studied in neurons perfused internally with potassium gluconate and guanosine triphosphate (GTP). At a holding potential of -70 mV, the GABAB receptor agonist (+/-)-baclofen (30 microM) induced an outward current and increased membrane conductance. In the presence of the excitatory amino acid receptor antagonists 6,7-dinitroquinoxaline-2,3-dione (DNQX) and (+/-)-2-amino-5-phosphonovalerate (APV), stimulation in stratum pyramidale or proximal stratum radiatum evoked GABAA receptor-mediated, fast monosynaptic inhibitory postsynaptic currents (IPSCs) and GABAB receptor-mediated, late monosynaptic IPSCs. THA (0.3 mM) blocked the baclofen-induced current and conductance increase and GABAB receptor-mediated IPSCs. 3. The effect of THA on presynaptic GABAB receptor-mediated responses was studied in neurons perfused internally with Cs+ and lidocaine N-ethyl bromide (QX-314), which blocked post-synaptic GABAB receptor-mediated responses. Stimulation in the presence of DNQX and APV evoked GABAA receptor-mediated IPSCs; when pairs of stimuli were delivered 200 ms apart the second IPSC was depressed. Baclofen reversibly depressed IPSCs, and partially occluded paired-pulse depression of IPSCs. The GABAB receptor antagonist CGP 35348 (0.5-1.0 mM) reversed baclofen-induced depression of IPSCs and partially blocked paired-pulse depression. Baclofen-induced and paired-pulse depression of IPSCs were not by affected by THA (0.3 mM). 4. Baclofen reversibly decreased the amplitude and frequency of spontaneous monosynaptic IPSCs (sIPSCs). Depression of sIPSCs by baclofen was unchanged by THA. 5. These results indicate that THA blocks the actions of baclofen and GABA at post- but not presynaptic GABAB receptors. We conclude that post- and presynaptic GABAB receptors in area CA3 of the rat hippocampus couple to different effector mechanisms; postsynaptic GABAB receptors activate THA-sensitive K+ channels, and presynaptic GABAB receptors decrease neurotransmitter release through a THA-insensitive mechanism.

scholarly journals Natural Product Isoliquiritigenin Activates GABAB Receptors to Decrease Voltage-Gate Ca2+ Channels and Glutamate Release in Rat Cerebrocortical Nerve Terminals

Biomolecules ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1537
Author(s):  
Tzu-Yu Lin ◽  
Cheng-Wei Lu ◽  
Pei-Wen Hsieh ◽  
Kuan-Ming Chiu ◽  
Ming-Yi Lee ◽  
...  
Keyword(s):  
Gabab Receptor ◽  
Glutamate Release ◽  
Receptor Activation ◽  
Gabab Receptors ◽  
Nerve Terminals ◽  
Type B ◽  
Kinase C ◽  
Acid Type ◽  
Dependent Inhibition ◽  
Ca2 Channels

Reduction in glutamate release is a key mechanism for neuroprotection and we investigated the effect of isoliquiritigenin (ISL), an active ingredient of Glycyrrhiza with neuroprotective activities, on glutamate release in rat cerebrocortical nerve terminals (synaptosomes). ISL produced a concentration-dependent inhibition of glutamate release and reduced the intraterminal [Ca2+] increase. The inhibition of glutamate release by ISL was prevented after removing extracellular Ca2+ or blocking P/Q-type Ca2+ channels. This inhibition was mediated through the γ-aminobutyric acid type B (GABAB) receptors because ISL was unable to inhibit glutamate release in the presence of baclofen (an GABAB agonist) or CGP3548 (an GABAB antagonist) and docking data revealed that ISL interacted with GABAB receptors. Furthermore, the ISL inhibition of glutamate release was abolished through the inhibition of Gi/o-mediated responses or Gβγ subunits, but not by 8-bromoadenosine 3′, 5′-cyclic monophosphate or adenylate cyclase inhibition. The ISL inhibition of glutamate release was also abolished through the inhibition of protein kinase C (PKC), and ISL decreased the phosphorylation of PKC. Thus, we inferred that ISL, through GABAB receptor activation and Gβγ-coupled inhibition of P/Q-type Ca2+ channels, suppressed the PKC phosphorylation to cause a decrease in evoked glutamate release at rat cerebrocortical nerve terminals.

scholarly journals GABA receptors in the olfactory epithelium of the gilthead seabream (Sparus aurata)

2022 ◽  
Author(s):  
Rita A. Costa ◽  
Zélia Velez ◽  
Peter C. Hubbard
Keyword(s):  
Gabaa Receptor ◽  
Olfactory Epithelium ◽  
Gabaa Receptors ◽  
Gaba Receptors ◽  
Sparus Aurata ◽  
Receptor Protein ◽  
High Pco2 ◽  
Gilthead Seabream ◽  
Exact Function ◽  
Gabaa Receptor Antagonist

Exposure to high PCO2/low pH seawater induces behavioural alterations in fish; a possible explanation for this is a reversal of Cl−/HCO3− currents through GABAA receptors (the GABAA receptor theory). However, the main evidence for this is that gabazine, a GABAA receptor antagonist, reverses these effects when applied to the water, assuming that exposure to systems other than the CNS would be without effect. Here, we show the expression of both metabotropic and ionotropic GABA receptors, and the presence of GABAA receptor protein, in the olfactory epithelium (OE) of gilthead seabream. Furthermore, exposure of the OE to muscimol (a specific GABAA receptor agonist) increases or decreases the apparent olfactory sensitivity to some odorants. Thus, although the exact function of GABAA receptors in the OE is not yet clear, this may complicate the interpretation of studies wherein water-borne gabazine is used to reverse the effects of high CO2 levels on olfactory-driven behaviour in fish.

scholarly journals Effect of GABAB Receptor Agonist SKF97541 on Cortical and Hippocampal Epileptic Afterdischarges

2014 ◽  
pp. 529-534 ◽  
Author(s):  
P. FÁBERA ◽  
P. MAREŠ
Keyword(s):  
Gabaa Receptors ◽  
Receptor Agonist ◽  
Gabab Receptor ◽  
Dorsal Hippocampus ◽  
Brain Structures ◽  
Gabab Receptors ◽  
Adult Rats ◽  
Inhibitory Postsynaptic Potentials ◽  
Male Wistar Rats ◽  
Epileptic Afterdischarges

Activation of GABAB receptors leads to longer inhibitory postsynaptic potentials than activation of GABAA receptors. Therefore GABAB receptors may be a target for anticonvulsant therapy. The present study examined possible effects of GABAB receptor agonist SKF97541 on cortical and hippocampal epileptic afterdischarges (ADs). Epileptic ADs elicited by electrical stimulation of sensorimotor cortex or dorsal hippocampus were studied in adult male Wistar rats. Stimulation series were applied 6 times with 10- or 20-min interval. Either interval was efficient for reliable elicitation of cortical ADs but stimulation at 10-min intervals did not reliably elicit hippocampal ADs, many stimulations were without effect. SKF97541 in dose 1 mg/kg significantly prolonged cortical ADs. Duration of hippocampal ADs was not significantly changed by either dose of SKF97541 in spite of a marked myorelaxant effect of the higher dose. Our present data demonstrated that neither cortical nor hippocampal ADs in adult rats were suppressed by GABAB receptor agonist SKF97541. Proconvulsant effect on cortical ADs indicates a different role in these two brain structures. In addition, duration of refractory period for electrically-induced ADs in these two structures in adult rats is different.

Parathyroid Ca2+-conducting currents are modulated by muscarinic receptor agonists and antagonists

1997 ◽  
Vol 273 (5) ◽  
pp. E880-E890 ◽  
Author(s):  
Wenhan Chang ◽  
Tsui-Hua Chen ◽  
Stacy A. Pratt ◽  
Benedict Yen ◽  
Michael Fu ◽  
...  
Keyword(s):  
Muscarinic Receptors ◽  
Inositol Phosphate ◽  
Receptor Protein ◽  
Dependent Manner ◽  
Rt Pcr ◽  
Pipette Solution ◽  
Pcr Products ◽  
Inositol Phosphate Accumulation ◽  
Receptor Cdna ◽  
Dose Dependent

Parathyroid cells express Ca2+-conducting cation currents, which are activated by raising the extracellular Ca2+ concentration ([Ca2+]o) and blocked by dihydropyridines. We found that acetylcholine (ACh) inhibited these currents in a reversible, dose-dependent manner (50% inhibitory concentration ≈10−8 M). The inhibitory effects could be mimicked by the agonist (+)-muscarine. The effects of ACh were blunted by the antagonist atropine and reversed by removing ATP from the pipette solution. (+)-Muscarine enhanced the adenosine 3′,5′-cyclic monophosphate (cAMP) production by 30% but had no effect on inositol phosphate accumulation in parathyroid cells. Oligonucleotide primers, based on sequences of known muscarinic receptors (M1-M5), were used in reverse transcriptase-polymerase chain reaction (RT-PCR) to amplify receptor cDNA from parathyroid poly (A)+ RNA. RT-PCR products displayed >90% nucleotide sequence identity to human M2- and M4-receptor cDNAs. Expression of M2-receptor protein was further confirmed by immunoblotting and immunocytochemistry. Thus parathyroid cells express muscarinic receptors of M2 and possibly M4 subtypes. These receptors may couple to dihydropyridine-sensitive, cation-selective currents through the activation of adenylate cyclase and ATP-dependent pathways in these cells.

The spinal GABA system modulates burst frequency and intersegmental coordination in the lamprey: differential effects of GABAA and GABAB receptors

1993 ◽  
Vol 69 (3) ◽  
pp. 647-657 ◽  
Author(s):  
J. Tegner ◽  
T. Matsushima ◽  
A. el Manira ◽  
S. Grillner
Keyword(s):  
Spinal Cord ◽  
Locomotor Activity ◽  
Gabaa Receptor ◽  
Gabab Receptor ◽  
Gaba Uptake ◽  
Phase Lag ◽  
Fictive Locomotion ◽  
Burst Frequency ◽  
Intersegmental Coordination ◽  
Burst Pattern

1. The effect of spinal GABAergic neurons on the segmental neuronal network generating locomotion has been analyzed in the lamprey spinal cord in vitro. It is shown that gamma-aminobutyric acid (GABA)A- and GABAB-mediated effects influence the burst frequency and the intersegmental coordination and that the GABA system is active during normal locomotor activity. 2. Fictive locomotor activity was induced by superfusing the spinal cord with a Ringer solution containing N-methyl-D-aspartate (NMDA, 150 microM). The efferent locomotor activity was recorded by suction electrodes from the ventral roots or intracellularly from interneurons or motoneurons. If a GABA uptake blocker was added to the perfusate, the burst rate decreased. This effect was counteracted by GABAB receptor blockade by phaclofen or 2-(OH)-saclofen. If instead a GABAB receptor agonist (baclofen) was added during fictive locomotion, a depression of the burst rate occurred. It was concluded that a GABAB receptor activation due to an endogenous release of GABA caused a depression of the burst activity with a maintained well-coordinated locomotor activity. 3. If a GABAA receptor antagonist (bicuculline) is applied during fictive locomotion elicited by NMDA, a certain increase of the burst rate occurred. Conversely, if a selective GABAA agonist (muscimol) was administered, the burst rate decreased. Similarly, if the GABAA receptor activity was potentiated by activation of a benzodiazepine site by diazepam, the burst rate was reduced. If, however the GABAergic effect was first enhanced by an uptake blocker (nipecotic acid), an administration of a GABAA antagonist (bicuculline) increased the burst rate, but in addition, the burst pattern became less regular with recurrent shorter periods without clear reciprocal burst activity. The GABAA receptor activity appears important for the rate control and for permitting a regular burst pattern. 4. The intersegmental coordination in the lamprey is characterized by a rostrocaudal constant phase lag of approximately 1% of the cycle duration between the activation of consecutive segments during forward swimming. This rostrocaudal phase lag can be reversed during backward swimming, which can be induced also experimentally in the isolated spinal cord by providing a higher excitability to the caudal segments. In a split-bath configuration, a GABA uptake blocker or a GABAB agonist was administered to the rostral part of the spinal cord, which caused a reversal of the phase lag as during backward swimming. If GABAA receptors were blocked under similar conditions, the intersegmental coordination became irregular. It is concluded that an increased GABA activity in a spinal cord region can modify the intersegmental coordination.(ABSTRACT TRUNCATED AT 400 WORDS)

In vitro and in vivo GABAA Receptor Interaction of the Propanidid Metabolite 4-(2-[Diethylamino]-2-Oxoethoxy)-3-Methoxy-Benzeneacetic Acid

Pharmacology ◽  
2018 ◽  
Vol 103 (1-2) ◽  
pp. 10-16 ◽  
Author(s):  
Alessia Cenani ◽  
Robert J. Brosnan ◽  
Heather K. Knych
Keyword(s):  
Gabaa Receptor ◽  
Gabaa Receptors ◽  
Water Solubility ◽  
Plasma Concentrations ◽  
Receptor Activation ◽  
Receptor Interaction ◽  
Dependent Manner ◽  
Benzeneacetic Acid

Background: Propanidid is a γ-aminobutyric acid type A (GABAA) receptor agonist general anesthetic and its primary metabolite is 4-(2-[diethylamino]-2-oxoethoxy)-3-methoxy-benzeneacetic acid (DOMBA). Despite having a high water solubility at physiologic pH that might predict low-affinity GABAA receptor interactions, DOMBA is reported to have no effect on GABAA receptor currents, possibly because the DOMBA concentrations studied were simply insufficient to modulate GABAA receptors. Our objectives were to measure the propanidid and DOMBA concentration responses on ­GABAA receptors and to measure the behavioral responses of DOMBA in mice at concentrations that affect GABAA receptor currents in vitro. Methods: GABAA receptors were expressed in oocytes using clones for the human GABAA α1, β2 and γ2s subunits. The effects of DOMBA (0.2–10 mmol/L) and propanidid (0.001–1 mmol/L) on oocyte GABAA currents were studied using standard 2-electrode voltage clamp techniques. Based on in vitro results, 6 mice received ­DOMBA 32 mg intraperitoneal and were observed for occurrence of neurologic effects and DOMBA plasma concentration was measured by liquid chromatography tandem mass spectrometry. Results: DOMBA both directly activates GABAA receptors and antagonizes its GABA-mediated opening in a concentration-dependent manner at concentrations between 5–10 and 0.5–10 mmol/L respectively. In vivo, DOMBA produced rapid onset sedation at plasma concentrations that correlate with direct GABAA receptor activation. Conclusion: DOMBA modulation of GABAA receptors is associated with sedation in mice. Metabolites of propanidid analogues currently in development may similarly modulate GABAA, and impaired elimination of these metabolites could produce clinically relevant neurophysiologic effects.

Sign in / Sign up

Export Citation Format

Share Document