Rate Of GABA Release Research Articles

Fentanyl and naloxone effects on glutamate and GABA release rates from anterior hypothalamus in freely moving rats

Fentanyl, a μ-opioid receptor agonist, has been studied for its neuro/psycho-pharmacological effects since its first clinical use; however, its effect on the release rate of the Central Nervous System (CNS) neurotransmitters has not been yet elucidated. In the present study the influence of fentanyl on the release rates of glutamate and GABA is investigated. Specifically, we examined the effects of intravenous (10 μg/kg) as well as intrahypothalamic (0.1nmol/min) fentanyl administration on the release rates of GABA and glutamate in the superfusate of anterior hypothalamus, under tail pinch manipulation. The release rate of the neurotransmitters was monitored by the push–pull superfusion technique. To investigate the role of fentanyl the opioid antagonist, naloxone 0.1 mg/kg was administered intravenously, or 50nmol/min intrahypothalamicaly. The amino acids were determined by High Performance Liquid Chromatography (HPLC) and fluorimetric detection after NBD-Cl derivatisation. After intravenous fentanyl administration a significant decrease of glutamate and increase of GABA release rates were observed. However during the pain manipulations, the release rate of glutamate was increased. Intravenous naloxone did not affect significantly the release rates of both amino acids, while intrahypothalamic antagonist administration reversed the alterations in both neurotransmitters release rates. Our results demonstrate that there is an opioid-glutamatergic transmission pathway, located in hypothalamus and that opioids can activate NMDA receptors, thus reducing the nociceptive threshold and the opioid analgesic effect.

Sinoaortic denervation abolishes blood pressure-induced GABA release in the locus coeruleus of conscious rats

Male Sprague–Dawley rats underwent sinoaortic denervation (SAD) or sham operation. We examined changes in the release rates of GABA, glutamate and arginine in the locus coeruleus (LC) elicited by experimental blood pressure increases (i.v. noradrenaline infusion for 3 min, 4 μg kg −1 min −1) or decreases (i.v. sodium nitroprusside infusion for 3 min, 150 μg kg −1 min −1). The release of the neurotransmitters was monitored by the push–pull superfusion technique. Mean blood pressure did not differ between sham-operated and SAD rats but blood pressure lability was greatly enhanced in SAD rats and accompanied by increased basal release of glutamate in the LC. GABA release was not affected. A rise in blood pressure induced by noradrenaline enhanced GABA release in the LC of sham-operated rats. This effect was abolished by SAD. Glutamate release did not respond to hypertension either in SAD or in sham-operated rats. Nitroprusside led to a fall in blood pressure which was more pronounced and lasted longer in SAD than in sham-operated rats. In SAD rats, glutamate release was enhanced by nitroprusside. The depressor response had no effect on glutamate release in sham-operated rats. GABA release did not respond to this stimulus in either SAD or sham-operated rats. SAD and blood pressure changes did not influence the release rate of arginine. In conclusion, experimental hypertension increases GABAergic activity in the LC by stimulating peripheral baroreceptors. In SAD rats, augmented blood pressure lability seems to be at least partly due to elevated glutamate outflow within the LC.

Release of glutamate and GABA in the amygdala of conscious rats by acute stress and baroreceptor activation: differences between SHR and WKY rats

To reveal the functional importance of amino acid neurotransmission in the amygdala (AMY) of conscious spontaneously hypertensive rats (SHR) and Wistar–Kyoto (WKY) rats, the in vivo release of glutamate (GLU) and GABA in this brain structure was studied using the push–pull superfusion technique. Basal GLU and GABA release rates in the AMY were comparable in SHR and WKY rats, although arterial blood pressure (BP) in SHR (152±6 mmHg) was higher than in WKY rats (102±4 mmHg). Neuronal depolarization by superfusion with veratridine enhanced the release of GLU and GABA to a similar extent in both rat strains. On the other hand, exposure to noise stress (95 dB) for 3 min led to a tetrodotoxin-sensitive increase in GLU release in the AMY of SHR, but not WKY rats. The concurrent pressor response to noise was enhanced in SHR as compared to WKY rats. A rise in BP induced by intravenous infusion of phenylephrine for 9 min had no effect on amino acid release in the AMY of both strains. The data suggest an exaggerated stress response of glutamatergic neurons in the AMY of SHR as compared with WKY rats, which might be of significance for the strain differences in the cardiovascular and behavioural responses to stress. The results also show that, in both rat strains, glutamatergic and GABAergic neurons in the AMY are not modulated by baroreceptor activation. Moreover, hypertension in adult SHR does not seem to be linked to a disturbed synaptic regulation of glutamatergic or GABAergic transmission in the AMY.

Activation of Gene Expression of the γ-Aminobutyric Acid Rather than the Glutamatergic System in the Preoptic Area during the Preovulatory Gonadotropin Surge of the Rat

There is increasing evidence that in the rat prior to and during the preovulatory LH surge, release rates of GABA in the preoptic area (POA) are decreased while no such changes occurred in the mediobasal hypothalamus (MBH). In addition, GnRH release appears to be facilitated by an increased preoptic excitation of glutamate (GLU). To investigate whether such changes of secretory activity of intrahypothalamic GABA or GLU neurons are associated with altered gene expression of biosynthetic enzymes or transporter proteins characteristic for either neuronal system, we determined mRNA levels of the two forms of the GABA-synthesizing enzyme glutamate decarboxylase (GAD65 and GAD67), the glutamate-synthesizing enzyme glutaminase (GLS), the GABA transporter type 1 (GAT-1) and the glutamate-aspartate transporter type 1 (GLAST). Competitive RT-PCRs using mutant cRNAs as internal standards were conducted with mRNA extracted from microdissected tissue of POA and MBH from diestrous, proestrous, and estrous rats. Proestrous animals were subgrouped according to their endocrine status as follows: ‘prior to’, on the ‘ascending’ or on the ‘descending’ limb of the LH peak, and ‘after the LH surge (post)’. During the preovulatory LH surge, mRNA concentrations of GAD67 and GAT-1 in the POA were significantly increased compared to those observed on diestrous (2.8-fold for GAD67 and 2.5-fold for GAT-1, p < 0.01), while in the MBH the amount of both mRNAs remained constant. The expression levels of GAD65, GLS and GLAST were without any changes in the POA as well as in the MBH. These findings support the hypothesis that in rats induction of the preovulatory LH surge is controlled at the level of GnRH perikarya, and suggest that altered activities of intrapreoptic GABA neurons at both transcriptional and secretory levels are pivotal for the preovulatory activation of GnRH neurons.

The release of inhibitory amino acids in the hypothalamus is tonically modified by impulses from aortic baroreceptors as a consequence of blood pressure fluctuations.

We investigated in conscious, freely moving rats whether the release of GABA, taurine and arginine in the hypothalamus is influenced by impulses originating from peripheral baroreceptors. The posterior hypothalamic nucleus was superfused with artificial cerebrospinal fluid through a push-push cannula and the release of amino acids was determined in the hypothalamic superfusate of control rats, as well as of rats after bilateral aortic denervation (AD). AD led to hypertension and increased the lability of arterial pressure. In sham-operated rats, intravenous infusion of phenylephrine increased blood pressure and the hypothalamic release of GABA and taurine. AD almost abolished the phenylephrine-induced release of the inhibitory amino acids. Similarly, the pressor response to hypervolaemia, elicited by blood injection, enhanced the release rates of GABA and taurine only in sham-operated rats. Baroreceptor unloading evoked either by intravenous infusion of nitroprusside, or by haemorrhage, decreased the release rates of GABA and taurine in sham-operated rats but not in AD rats. Electrical stimulation of the afferent aortic depressor nerve enhanced extracellular GABA and taurine in the posterior hypothalamic nucleus. The release rate of arginine was not influenced by alterations in baroreceptor activity either in sham-operated or in AD rats. The findings support the idea that, in the hypothalamus, GABA and taurine are involved in central blood pressure regulation. The release of these two amino acids seems to be driven tonically by baroreceptor impulses. Moreover, the findings indicate that the baroreceptors of the aortic arch play a crucial role in the mediation of changes in hypothalamic GABA and taurine outflow so as to counteract blood pressure fluctuations.

In vivo release patterns and cardiovascular properties of inhibitory and excitatory amino acids in the hypothalamus

The posterior hypothalamus of conscious, freely moving rats was superfused with artificial cerebrospinal fluid through a push-pull cannula and the release of amino acids was determined in the superfusate. Under basal conditions, the release rates of taurine, GABA and glutamate fluctuated according to ultradian rhythms with different frequencies. Hypothalamic superfusion with veratridine or high concentrations of potassium choride enhanced the release rates of taurine, GABA and glutamate in a concentration-dependent way. Tetrodotoxin decreased the basal release rates of the three amino acids. The release of arginine was not influenced significantly by these compounds. A fall of blood pressure elicited by intravenous infusion of nitroprusside decreased the release rates of GABA and taurine and enhanced the release of glutamate. Infusion of noradrenaline increased blood pressure and release rates of GABA and taurine, while the release of glutamate was not influenced. Neither the pressor, nor the depressor responses to drugs influenced the release of arginine in the hypothalamus. It is concluded that the inhibitory amino acids taurine and GABA released from hypothalamic neurons possess a tonic hypotensive function. The excitatory amino acid glutamate, released from glutamatergic neurons of the hypothalamus, seems to possess a hypertensive function in counteracting a fall of blood pressure.

Monoclonal antibodies can uncouple the main α-latrotoxin effects: Toxin-induced ca 2+ influx and stimulated neurotransmitter release

A panel of monoclonal antibodies has been produced against α-latrotoxin using black widow spider venom. Five of them were characterized relative to their affinity for α-latrotoxin and ability to modify the main toxin effects—to increase calcium permeability of synaptosomes, to stimulate the neurotransmitter release and to form the ion channels in artificial lipid membrane. The results reported here show that: (i) the monoclonal antibodies do not alter the α-latrotoxin affinity for the membrane acceptor; (ii) two monoclonal antibodies, A6 and A24, can simultaneously inhibit the α-latrotoxin induced Ca 2+ uptake and GABA release; (iii) monoclonal antibodies A4 completely block the toxin-induced Ca 2+ uptake, but decrease partially the rate of GABA release; (iv) monoclonal antibodies A15 that do not modify the α-latrotoxin ability to stimulate Ca 2+ uptake and GABA release are able to alter the properties of channels formed by the toxin in the artificial lipid bilayer. From these data we hypothesize that the α-latrotoxin molecule has separate functional sites which provide a high-affinity binding to the membrane acceptor, the toxin-induced Ca 2+ uptake and toxinstimulated neurotransmitter release. A separate part of α-latrotoxin molecule is responsible for the formation of cationic channels in the artificial lipid bilayer.

Further evidence that preoptic anterior hypothalamic GABAergic neurons are part of the GnRH pulse and surge generator.

The in vivo release rates of GABA from the preoptic/anterior hypothalamic area (PO/AH) of ovariectomized rats were assessed by means of a focal perfusion cannula system. Seven days after surgery all animals received a sc silastic capsule implant containing either estradiol-17 beta (E2) or corn oil, and they were perfused 3 days later. Perfusate fractions were sampled at 5-min intervals and blood was collected every 10 min over a period of 5 h. In ovariectomized animals PO/AH GABA release was pulsatile without any diurnal rhythm. Prior to frequency analysis by means of the pulsar-programme, LH and GABA values were z-transformed. Significant LH peaks of all examined ovariectomized rats were superimposed and GABA data were arranged accordingly. It became evident that LH episodes are preceded by a significant reduction of preoptic anterior hypothalamic GABA release. The secretion patterns of GABA and LH were profoundly affected by E2 replacement. During early noon when LH levels were low, constantly elevated hypothalamic GABA release rates were observed in E2-substituted rats in comparison to ovariectomized rats. GABA release rates fell significantly during the E2-induced LH surge. Our previous demonstration of the existence of a large number of estrogen-respective GABAergic neurons in the PO/AH is suggestive of these neurons changing their activity in response to estrogen treatment. We conclude that these estrogen-respective GABAergic neurons are involved in the generation of GnRH pulses as well as in the generation of the so-called positive feedback effect of E2 on LH release.(ABSTRACT TRUNCATED AT 250 WORDS)

Rates of release of GABA and catecholamines in the mediobasal hypothalamus of ovariectomized and ovariectomized estrogen-treated rats: correlation with blood prolactin levels.

Push-pull cannulae were implanted into the mediobasal hypothalamus of ovariectomized (ovx) rats. After recovery animals were treated with estradiolbenzoate (E2B) or oil and they were perfused 3 days later. Only the E2B-treated animals which exhibited prolactin surges in the afternoon without concomitant LH surges were used in this study. In ovx animals hypothalamic GABA release, measured in 5-min intervals, was pulsatile, with pulses occurring every 37 min. This pattern was profoundly affected by E2B treatment: the pulse frequency was significantly reduced to 1 pulse every 117 min in steroid-treated rats. No differences in overall mean GABA release rates and pulse amplitudes were observed in ovx vs. E2B-treated rats. Our earlier demonstration of the existence of a large number of estrogen-receptive, GABAergic neurons in the MBH of rats is suggestive that these neurons change their secretory pattern in response to estrogen treatment. Estrogen-induced prolactin surges were accompanied by increased hypothalamic NE release. Concomitant changes in DA or E release rates were not demonstrable since catecholamine concentrations were too low to be reliable. However, the daily overall release rates of these two catecholamines were lower in E2B-treated rats compared to ovx animals. It is concluded that the positive feedback action of estradiol on prolactin release involves a stimulatory noradrenergic mechanism and may also involve estrogen-receptive, GABAergic neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopaminergic regulation of GABA release from the intact goldfish retina

The rate of release of [ 3H]GABA from intact goldfish retinas was studied using a modified superfusion technique. Small, significant increases in the rate of GABA release were observed when the retinas were exposed to dopamine (DA) (100–1000 μM); however, when free Ca 2+ was removed from the medium, the basal rate of GABA release was increased and DA became inhibitory. Forskolin, a non-specific stimulator of adenylate cyclase in intact cells, also inhibited GABA release in the absence of Ca 2+. There was no significant effect of forskolin in the presence of Ca 2+; however, (+)-butaclamol, a dopamine antagonist, increased basal GABA release under these conditios. l-glutamic acid ( l-Glu) (1–10 mM) causes up to a 10-fold increase in GABA release. In the presence of Ca 2+, DA did not significantly alter the effects of l-Glu; however, in the absence of Ca 2+ a significant inhibition of the effects of l-Glu by DA was observed. Forskolin, on the other hand, inhibited the effects of l-Glu both in the presence and absence of Ca 2+. Finally, EGTA (0.3–1 mM) produced a large release of GABA: this release was inhibited by DA, forskolin, theophylline and 8-bromo cyclic AMP. These results suggest a model wherein DA stimulates Ca 2+-dependent GABA release from one site and inhibits Ca 2+-independent GABA release from another site via cyclic AMP-mediated event.

Blood prolactin levels and in vivo hypothalamic catecholamine and GABA release rates

Journal Article Blood prolactin levels and in vivo hypothalamic catecholamine and GABA release rates Get access H Jarry, H Jarry Abt. für Reproduktionsbiologie, Deutsches PrimatenzentrumAbt. für klin. Exp. Endokrinologie, Universität Göttingen Search for other works by this author on: Oxford Academic Google Scholar M Sprenger, M Sprenger Abt. für Reproduktionsbiologie, Deutsches PrimatenzentrumAbt. für klin. Exp. Endokrinologie, Universität Göttingen Search for other works by this author on: Oxford Academic Google Scholar W Wuttke W Wuttke Abt. für Reproduktionsbiologie, Deutsches PrimatenzentrumAbt. für klin. Exp. Endokrinologie, Universität Göttingen Search for other works by this author on: Oxford Academic Google Scholar Acta Endocrinologica (Norway), Volume 110, Issue 1_Supplement_a, Apr 1979, Pages S1–S2, https://doi.org/10.1530/acta.0.109S001-a Published: 01 April 1985

3-Mercaptopropionic acid inhibits GABA release from rat brain slices in vitro

3-Mercaptopropionic acid (3MP) (1 mM) inhibited the potassium-evoked release of endogenous GABA from slices of rat hippocampus and cerebral cortex in vitro. This did not appear to be due to an inhibition of GABA biosynthesis, since 3MP failed to affect the basal rate of GABA release or to accelerate the decline in the GABA content of tissue slices during prolonged exposure to 3MP (up to 120 min). 3MP, furthermore, inhibited the potassium-evoked release of [ 3H]GABA from preloaded brain slices, suggesting a direct inhibitory effect on GABA release. The threshold concentration was approximately 0.1 mM. 3MP at 1 mM failed to inhibit the potassium-evoked release of [ 3H]5-hydroxytryptamine, [ 3H]noradrenaline or somatostatin under similar conditions. The ability of 3MP to inhibit GABA release may contribute to the convulsant properties of this substance in vivo.

In vivo release of endogenous gamma-aminobutyric acid from rat striatum: effects of muscimol, oxotremorine, and morphine.

Abstract: A push‐pull cannula technique was used to study the in vivo release of endogenous GABA from the striaturn of chloral hydrate anaesthesized rats. The GABA in the perfusate was isolated with hplc and fluorimetrically detected (detection limit 0.6 pmol, signalhoke = 3). The mean resting release of GABA under steady state conditions was 1.62 ± 0.09 pmo/min (n = 180, ± s.E.M.). GABA release was increased after addition of depolarizing amounts of potassium to the perfusion medium. Inhibition of GABA synthesis with 3‐mercaptopropionic acid (MPA, 0.5 mM) or blockade of the neuronal activity with tetrodotoxin (TTX, 0.2 μM) diminished the spontaneous release of GABA. MPA, but not TTX, reduced the potassium‐induced increase in GABA release. Striatal GABA release was decreased by local application of muscimol (l0 μM) but enhanced by picrotoxin (100 μM); the latter counteracted the effect of muscimol. Intrastriatally applied serotonin (100 μM) did not affect the rate of endogenous GABA release. Oxotremorine (25 μM) added to the perfusion medium slightly increased the striatal GABA release. This effect was blocked both by locally applied atropine (100 μM) and haloperidol (5 μM). The latter two drugs did not themselves affect the rate of GABA release. Perfusion with morphine (100 μM) inhibited striatal GABA release. This effect was not influenced by haloperidol, but was no longer observed in the presence of nalorphine (10 μM) which itself did not alter GABA release. These results indicate that GABA released from the striatum is, at least in part, of neuronal origin and that the spontaneous GABA release can be affected by various neuromodulators (including GABA, enkephalins, and acetylcholine).

Biphasic and opposite effects of dopamine and apomorphine on endogenous GABA release in the rat substantia nigra.

Abstract: A push‐pull cannula technique was used to study the in vivo release of endogenous GABA in the rat substantia nigra. Intranigral application of both dopamine (DA) and apomorphine produced biphasic changes in the rate of endogenous GABA release. The presence of 10 μM‐DA in the perfusion medium increased GABA release (140%). At 25 μM‐DA, both stimulation and inhibition of the nigral GABA release were observed. Higher concentrations of DA produced a decrease of the GABA release (50%). A small amount of apomorphine (10 μM in the perfusion medium) resulted in a decrease in GABA release (75%). Application of 25 μM‐apomorphine produces opposite effects, similar to those observed after addition of 25 μM‐DA. We observed an enhanced GABA release from the substantia nigra at 100 μM‐apomorphine in the perfusion medium (360%). The presence of 5 μM‐haloperidol produced a small decrease in the rate of GABA release (80%). Both the inhibitory effect of 25 μM‐DA and the excitatory effect of 100 μM‐apomorphine could be blocked by haloperidol added to the perfusion medium. Dibutyryl cyclic AMP (1.5 mM) and 2‐amino‐6, 7‐dihydroxyl(1, 2, 3, 4) tetrahydronapthalene (ADTN) (50 μM) added to the perfusion medium produced an inhibition of nigral GABA release (55% and 35% respectively) similar to that observed after addition of 50 μM‐DA. The amounts of lysine and ethanolamine (measured with GABA concurrently) released into the perfusion medium did not change in most of the experiments. The changes in the rates of release of these compounds that were observed in some experiments were either in the same or in the opposite direction of the change in GABA release. These results suggest that dopaminergic processes within the substantia nigra affect GABA‐ergic neurotransmission and that DA and apomorphine have different effects on GABA release.