Extracellular K+ concentration during electrical stimulation of rat isolated sympathetic ganglia,vagus and optic nerves

Recordings of extracellular potassium concentration ([K⁺]_e) were made in rat isolated sympathetic ganglia, vagus and optic nerves using ion sensitive microelectrodes. Repetitive orthodromic stimulation of ganglia resulted in [K⁺]_e increases of up to 7 mmol/1 above resting level (6 mmol/1), which were followed by post-stimulus undershoots. Activation of vagal A and B fibres did not significantly alter [K⁺]_e but C-fibre activity induced rises of up to 5 mmol/1. Repetitive stimulation of the predominantly mylinated optic nerve resulted in [K⁺]_e rises of up to 2.5 mmol/1. In the ganglion and vagus nerve, application of ouabain (30–1000 μmol/1) led to a raised baseline [K⁺]_e concentration, an increase in the peak achieved during stimulation and a reduced undershoot amplitude. The amplitude of the undershoot in normal solution was shown to be dependent on the duration of the preceding stimulation period as well as the amplitude of the preceding [K⁺]_e rise. In ganglia and vagus nerves, bath application of γ-aminobutyric acid (10–100μmol/1) and carbachol (10–1000 μmol/1) also elevated [K⁺]_e.It is concluded that repetitive activity in rat peripheral and central nerve fibres leads to significant changes in extracellular K⁺ ion-concentration and that the restoration of these levels is strongly dependent on the intact activity of the membrane Na^+/K⁺ pump.     

gamma-Aminobutyric acid decreases levels of messenger ribonucleic acid encoding prolactin in the rat pituitary

The effect of gamma-aminobutyric acid (GABA) on levels of messenger ribonucleic acid (mRNA) encoding prolactin (PRL) was studied in cultured anterior pituitary cells, in vitro and in intact rats, in vivo. As quantitated by hybridization to a 32P-labeled rat PRL complementary deoxyribonucleic acid (cDNA) probe, levels of PRL mRNA in cultured pituitary cells were decreased by about 50% following 3 days exposure to 10(-5) M GABA. This effect was mimicked by muscimol (10(-6) M) and antagonized by bicuculline (10(-5) M). An increase of endogenous GABA levels in vivo effected by injection of GABA transaminase blockers (aminooxyacetic acid, 20 mg/kg, twice daily; vinyl GABA, 800 mg/kg) into rats resulted in a similar decrease in rat PRL mRNA levels in the adenohypophysis 3-4 days following commencement of the drug treatment. These findings suggest that GABA might inhibit PRL gene expression by a direct action on lactotrophs of the adenohypophysis.     

帕金森病大鼠模型纹状体中谷氨酸、γ-氨基丁酸与多巴胺之间的关系

目的:了解帕金森病大鼠模型纹状体内谷氨酸(glutamate,Glu)、γ-氨基丁酸(gama-aminobutyric acid,GABA)和多巴胺(dopamine,DA)之间的关系,从而进一步探讨帕金森病的发病机制。方法:动物分为溶剂对照组、假手术组和帕金森模型组。大脑右侧黑质致密部和前脑内侧束两点注射6-羟基多巴胺(6-hydroxydopamine,6-OHDA)建立帕金森病大鼠模型,溶剂对照组注入生理盐水,假手术组不注射任何药物,采用脑微透析术于建模后第3,4,5,6周连续动态透析大鼠毁损侧纹状体,结合高效液相色谱(HPLC)动态监测各组谷氨酸、GABA和多巴胺的变化。结果:(1)PD组纹状体内多巴胺含量到第5周仅为溶剂对照组和假手术组的1/5;(2)谷氨酸含量随建模时间逐渐升高,到第6周PD组是溶剂对照组和假手术组的1倍以上;(3)GABA含量呈下降趋势,到第6周约降至溶剂对照组、假手术组的1/2。结论:帕金森病大鼠模型纹状体内谷氨酸的变化与多巴胺分泌可能存在某种联系;GABA含量随建模时间的增加而下降。     

gamma-Aminobutyric acidA (GABAA) receptors modulate [3H]GABA release from isolated neuronal growth cones in the rat

Potassium-induced release of gamma-[3H]aminobutyric acid [( 3H]GABA) from a growth cone-enriched fraction isolated from neonatal rat forebrain was inhibited by the GABA mimetic muscimol in a dose-dependent manner (IC50 15 nM). The GABA antagonist bicuculline completely reversed the effect of muscimol. Bicuculline alone slightly potentiated the K+-induced release of [3H]GABA. Baclofen, a proposed selective agonist for a bicuculline-insensitive GABAB receptor, was found to cause only a slight reduction in the K+-induced release of [3H]GABA. These results are compatible with the presence of a negative feedback mechanism mediated by GABAA receptors for controlling [3H]GABA release from growth cones of the developing rat forebrain.     

Differential effect of kainic acid on somatostatin, GABAergic and cholinergic neurons in the rat striatum

Kainic acid was injected into the rat striatum and its effects on presumptive striatal cholinergic, GABAergic and somatostatin-containing neurons were examined with three histochemical staining methods. Presumptive cholinergic and GABAergic neurons are damaged to a similar extent, but somatostatin neurons are more sensitive to the neurotoxic effect of kainic acid and are more severely affected.     

High affinity uptake and Ca2+-dependent release of glutamic acid in the developing cerebellum

This study was undertaken in order to evaluate the postulated role of glutamic acid as the neurotransmitter for the parallel fibers of the cerebellar cortex. We studied the Ca2+-dependent release and the high affinity uptake of glutamic acid in the developing cerebellum. The Ca2+-dependent release of glutamic acid from cerebellar molecular layer during development closely follows the time course of parallel fibers synaptogenesis. Little glutamic acid release was observed at 15 days, then it increased to the adult values at the 21st postnatal day. In the rat the bulk of synapses of the parallel fibers appear between the 15th and the 21st postnatal days, the time at which the nerve terminals of the climbing fibers, the other excitatory input to the Purkinje cells, are already developed. An enhanced Na+-dependent, high affinity uptake of glutamic acid was observed in the developing cerebellum relative to the adult rat. That this higher accumulation of glutamic acid is not related to a releasable pool is suggested by the fact that an enhanced glutamic acid, Ca2+-dependent release relative to the adult was not observed. These results support the view that glutamic acid is the transmitter for the cerebellar parallel fibers.     

Absence of modifications in gamma-aminobutyric acid metabolism after repeated generalized seizures in amygdala-kindled rats

Alterations in gamma-aminobutyric acid (GABA) metabolism have been investigated in the kindling model of epilepsy. Numerous generalized seizures were induced by amygdala-kindling stimulations in rats. One week after the last stimulation, there were no changes in GABA levels nor in the activity of enzymes responsible for the synthesis (glutamic acid decarboxylase) and catabolism (GABA transaminase and succinyl semialdehyde dehydrogenase). These results do not exclude other changes in GABA function as modifications of transport or receptors.     

ECL cell histamine mobilization and parietal cell stimulation in the rat stomach studied by microdialysis and electron microscopy

Aim: Gastrin stimulates acid secretion by mobilizing histamine from enterochromaffin‐like (ECL) cells that occur predominantly at the base of the gastric glands. The parietal cells occur higher up in the glands nearer to the gastric lumen. The present study was performed to assess whether histamine is transported from the ECL cell via the microcirculation (endocrine route) or local diffusion (paracrine route). Methods: Totally isolated, vascularly perfused, rat stomachs were examined both in basal and gastrin‐stimulated state. Histamine concentrations, determined by radioimmunoassay in venous effluent and microdialysate from an indwelling probe in the submucosa, were monitored over a period of 240 min. Gastrin‐17 was infused through an arterial catheter for 120 min. The parietal cells were examined by electron microscopy, and the percentage of actively secreting parietal cells (displaying secretory canaliculi) in four regions along the glands (basal to surface, zones I–IV) was determined. Results: Gastrin stimulated acid secretion and histamine release as well as parietal cell activation. Upon gastrin stimulation, histamine concentration in the microdialysate was 2.5‐fold higher than in the venous effluent (P = 0.008). The parietal cells in the upper part of the gland (zone III) were found to be activated the most. Conclusion: As the histamine concentrations were higher in the tissue (microdialysate) than in blood, histamine seems to reach the parietal cells via the paracrine route. The fraction of active parietal cells seems to depend more on the age of the parietal cells than on the distance from the ECL cell.     

The effect of some putative neurotransmitters on the release of 5-hydroxytryptamine and gamma-aminobutyric acid from slices of the rat midbrain raphe area.

The effect of various putative transmitters has been studied on the efflux of [³H]5-hydroxytryptamine and [³H]γ-aminobutyric acid from small superfused slices of the midbrain raphe area of the rat. The slices apparently contained functionally intact terminals for these transmitters since a depolarizing stimulus (50 mM KCl) stimulated the rate of efflux of [³H]5-hydroxytryptamine and [³H]γ-aminobutyric acid in a calcium-dependent fashion. Furthermore, slices accumulated radioactivity with apparent high affinity mechanisms. γ-Aminobutyric acid (50 and 100 μ m) and substance P (100 and 500μ m) stimulated the efflux of [³H]5-hydroxytryptamine. The effect of γ-aminobutyrate was blocked by picrotoxin (50 μ m) but not by strychnine (1 μ m). Other inhibitory amino acids (β-alanine, taurine and glycine) were without effect on the release of [³H]5-hydroxytryptamine. l-Noradrenaline (0.2–1 mM) stimulated the efflux of [³H]γ-aminobutyric acid but not that of [3H]5-hydroxytryptamine. Phentolamine (10μ m) but not (±)-propranolol (10 μ m) abolished the effect of 1 mM noradrenaline. Neither dopamine nor 5-hydroxytryptamine influenced the efflux of [3H]γ-aminobutyric acid.It is possible that interactions in the midbrain raphe area proposed from other studies can be mediated through presynaptic influences on transmitter release.     

The effects of hyperthermia on polyribosomes and amino acid levels in infant rat brain

Brain polyribosomes prepared from infant rats exposed to elevated ambient temperatures (39.5°C for 45 min) are highly disaggregated. Disaggregation is evident 15 min after the animals have entered the hot environment and is nearly maximal after 25 min. Substantial recovery of polyribosomes is seen 20 min after the hyperthermic rats are transferred from 39.5 to 33°C ambient temperature, indicating that heat-induced disaggregation is quickly reversible. During hyperthermia the levels of certain amino acids in the brain, particularly essential amino acids, rise markedly. The increases in amino acid levels are reversed within 1 h after the rats are transferred from the hot environment to 33°C ambient temperature. The levels of amino acids in blood plasma also rise during hyperthermia; however, the increases are relatively smaller and less selective than in the brain but are also reversed by returning the animals to 33°C ambient temperature.Injection of phenylalanine into infant rats causes hyperphenylalaninemia, elevated brain phenylalanine levels, and brain polyribosome disaggregation (Aoki & Siegel, 1970). The present observations show that elevated brain amino acid levels and polyribosome disaggregation are also linked in hyperthermic infant rats, but it is not yet clear if the two phenomena are causally related. Although the mechanisms of the increases of blood and brain amino acid levels remain to be elucidated, they may have a significant bearing on the functional status of the protein synthetic machinery of the brain, on the levels of neurotransmitter substances in the brain which are derived from amino acid precursors, and on the intermediary metabolism of the brain.     

A comparison of the effects of acute and one year's continuous neuroleptic treatment on the release of [3H]glutamate and [3H]acetylcholine from rat striatal slices

The effect of neuroleptic drugs administered acutely or continuously for 1 year on the release of [³H]glutamate and [³H]acetylcholine from striatal slices in vitro has been compared.Acute in vivo administration of haloperidol, trifluoperazine and clozapine increased the potassium-evoked release of [³H]acetylcholine from striatal slices in a dose-dependent fashion, whereas sulpiride was without effect. None of the neuroleptics given acutely had any effect on the potassium-evoked striatal release of [³H]glutamate.Potassium-evoked striatal release of [³H]acetylcholine in animals receiving 1 year's continuous administration of haloperidol, trifluoperazine or sulpiride was no different from that in age-matched control animals, but was less than controls in animals receiving clozapine for 1 year. All drugs caused a decrease in potassium-evoked striatal [³H]glutamate release following drug administration for 1 year compared to age-matched controls.The reversal of the acute action of neuroleptic drugs on striatal [³H]acetylcholine and [³H]glutamate release is consistent with a functional increase in striatal dopamine transmission following long-term neuroleptic treatment.     

Intrinsic gamma-aminobutyric acid neurons in the nucleus of the solitary tract and the rostral ventrolateral medulla of the rat: an immunocytochemical and biochemical study

Sympathoexcitatory neurons in the C1 adrenergic area of the rostral ventrolateral medulla (RVL) are tonically inhibited by gamma-aminobutyric acid (GABA). To identify the source of this GABAergic input, the distribution of neurons containing glutamate decarboxylase (GAD) was determined immunocytochemically in rats treated with colchicine. Numerous GAD-stained neurons were located in the nucleus of the solitary tract (NTS) and in RVL. Unilateral lesions in NTS did not alter GABA content or GAD activity in RVL, indicating that the afferent projection from NTS to RVL is not GABAergic. Intrinsic GABAergic neurons in RVL may provide tonic inhibition of vasomotor neurons in the C1 area.     

gamma-Aminobutyric acid partly mediates the pentobarbitone depression of synaptic excitation in the guinea-pig olfactory cortex in vitro

Pentobarbitone depresses synaptic excitation in the guinea-pig olfactory cortex slice in vitro. A study has been made to elucidate the possible role of gamma-aminobutyric acid (GABA) in this depression by testing pentobarbitone in the presence of high concentrations of the GABA blockers, i.e. picrotoxin or bicuculline. These blockers reduced the action of pentobarbitone; the dose-depression curve for pentobarbitone was shifted to the right by a factor of 2.3. It is concluded that pentobarbitone has a bimodal action, one action via GABA and another unrelated to GABA or Cl- conductances.     

Production of extracellular quinolinic acid in the striatum studied by microdialysis in unanesthetized rats

Striatal microdialysis was performed in awake rats in an attempt to produce extracellular quinolinic acid (QUIN) from its putative bioprecursors L-tryptophan, L-kynurenine and 3-hydroxyanthranilic acid (3HANA). Test compounds were included in the microperfusion solution. QUIN concentrations in the dialysate remained below the assay sensitivity (i.e. less than 20 nM) under baseline conditions or after extensive perfusion with 1 mM L-tryptophan or L-kynurenine. 3HANA (10-300 microM) caused dose-dependent increases in extracellular QUIN, which attained steady-state concentrations after 4 h. The initial rate of QUIN production was significantly increased in the ibotenate-lesioned striatum, suggesting a pivotal role of astroglia in the deposition of brain QUIN.     

Free amino acids and the uptake and binding of taurine in the central nervous system of rats treated with guanidinoethanesulphonate

The content of free amino acids in the central nervous system, the uptake of taurine by slices and synaptosomes and taurine binding to synaptic membranes have been studied on adult male Wistar rats after a prolonged administration of 2-guanidinoethanesulphonate with or without a taurine-free diet. The 2-guanidinoethanesulphonate administration both alone and together with a taurine-free diet considerably reduced taurine levels in all regions studied, viz. cerebrum, cerebellum, brain stem and spinal cord, but the contents of methionine and γ-aminobutyric acid were increased. On the normal diet the maximal taurine loss occurred after a 3-week 2-guanidinoethanesulphonate administration, when also the 2-guanidinoethanesulphonate accumulation in the cerebrum was largest. On the taurine-free diet the taurine levels were still low after the 4-week 2-guanidinoethanesulphonate administration when the taurine content in cerebral synaptosomes was also reduced to almost one half.2-Guanidinoethanesulphonate treatment modified the uptake and binding processes ot taurine in the synaptosomal preparations. The maximal high-affinity taurine uptake was reduced, whereas the affnity of the specific sodium-independent binding sites for taurine increased. The results suggest that the neuromodulator properties of taurine could be affected by the reduced taurine levels and or by the accumulated 2-guanidinoethanesulphonate.     

Immunocytochemical visualization of taurine: Neuronal localization in the rat cerebellum

A novel technique for immunocytochemical demonstration of taurine (Tau) is presented. Antisera raised against Tau conjugated to protein by glutaraldehyde (GA) react selectively with similar conjugates in model systems and in tissue fixed with GA. In rat cerebellum, Tau-like immunoreactivity is high in the Purkinje cells but low in other cell types, including the stellate cells for which Tau has been proposed as transmitter.     

Antagonistic effect of delta-aminovaleric acid on bicuculline-insensitive gamma-aminobutyric acid B (GABA B) sites in the rat's brain

The effect of delta-aminovaleric acid (delta-AV) on bicuculline-insensitive gamma-aminobutyric acid B (GABA B) sites in the central nervous system (CNS) was investigated by binding studies and experiments on slices in vitro. delta-AV inhibited [3H]GABA (10 nM) binding to GABA B sites in a rat brain membrane preparation with an IC50 value of 10(-4) M. It also inhibited [3H]baclofen (20 nM) binding with an IC50 value of 10(-4) M. In preparations of hippocampal slices, (-)-baclofen (5 microM) reduced the population spikes evoked by stimulating the Schaffer collaterals in CA1 pyramidal cells in the presence of 100 microM bicuculline. delta-AV (1 mM) antagonized this inhibitory action of baclofen. Since baclofen is an agonist of GABAB sites, our results indicate that delta-AV has an antagonistic effect on GABAB sites in the CNS.     

Immunohistochemical identification of gamma-aminobutyric acid-containing neurons in the rat basolateral amygdala

The peroxidase-antiperoxidase immunohistochemical technique was used together with an antiserum to gamma-aminobutyric acid (GABA) to identify GABA-containing structures in the rat basolateral amygdala (ABL). Morphological characteristics of GABA-positive neurons in ABL indicate that they correspond to class II, and perhaps class III, local circuit neurons observed in previous Golgi studies. GABA-positive punctate structures resembling axon terminals were observed both in the neuropil and forming peri-cellular baskets around large unlabeled perikarya in ABL. These results suggest that the strong intrinsic inhibition noted in electrophysiological studies of ABL is due primarily to synapses of GABAergic class II neurons with class I projection neurons.     

Retarded learning induced by intracerebral administration of amino acids in the neonatal chick

In newly hatched chicks retarded learning develops following intracerebral injections of cycloheximide and is manifest at times well after the drug is no longer acting. Intracerebral administration of amino acid mixtures containing the putative central transmitters glutamate, aspartate and γ-aminobutyric acid and taurine is also effective in producing birds showing retarded learning. The critical period for the effectiveness of these amino acids in producing retardation is the same as for cycloheximide. Intracerebral cycloheximide was shown to result in increased brain concentrations of glutamate and aspartate but not of γ-aminobutyrate or taurine.It is suggested that the accumulation of the two putative excitatory transmitters (glutamate and aspartate) in the developing chick brain prior to the establishment of the blood brain barrier may underlie the retarded learning produced by cycloheximide.