Biomedical subjects

R Tapia

Publications and source records attributed to R Tapia.

At least 73 records · Page 4Linked to original sources

PubMed1990

Seizures and wet-dog shakes induced by 4-aminopyridine, and their potentiation by nifedipine.

The behavioral and electrographic effects of 4-aminopyridine (4-AP) administered i.p. or microinjected into the hippocampal CA1 region (i.h.) were studied in rats. The modification of such effects by the systemic administration of the Ca2+ antagonist dihydropyridine, nifedipine, was also studied. 4-AP i.p. (5 mg/kg) induced generalized tonic convulsions in 74% of the animals and death in 13%. Convulsions were characterized by electrical discharges of relatively short duration in all structures studied (frontal cortex, amygdala, dorsal hippocampus and dorsal raphe). Limbic seizures and frequent wet-dog shakes were observed when 4-AP was administered i.h. (2-4 nmol) and this behavior was correlated with hippocampal discharges, which rapidly propagated to the other structures. Pretreatment with nifedipine (7.5-50 mg/kg s.c.) markedly potentiated the effects of 4-AP. The percentage of rats that died during generalized convulsion after i.p. 4-AP increased to 56-87% and the frequency of wet-dog shakes increased after i.h. microinjection of 4-AP. Moreover, nifedipine-treated rats showed long-lasting (greater than 60 min) continuous discharges in all structures studied (status epilepticus). These results are discussed in the light of the possible participation of Ca2+ channels in the convulsant effect of 4-AP and its potentiation by nifedipine.

4-Aminopyridine↗

PubMed1990

Transmitter release in hippocampal slices from rats with limbic seizures produced by systemic administration of kainic acid.

The systemic injection of kainic acid (KA) has been shown to destroy neurons in the hippocampus and to induce limbic-type seizure activity. However, little is known on the neurochemical events that are associated with this convulsant effect. In the present work we studied the spontaneous and the K(+)-stimulated release of labeled tau-aminobutyric acid (GABA), glutamate, serotonin and dopamine, in hippocampal slices of KA-treated rats, at the moment of clinical seizures (2 h) and 72 h later. At the onset of convulsions we found a 40-45% decrease in the K(+)-stimulated release of GABA. The release of the other neurotransmitters was not significantly affected by KA treatment. After 72 h GABA release was still reduced by 30-40%. It is concluded that the epileptogenic effect of KA in the hippocampus is probably related to a diminished inhibitory GABAergic neurotransmission.

Animals↗

PubMed1990

Circling behavior induced by intranigral administration of ruthenium red and 4-aminopyridine in the rat.

We have studied the effects of the unilateral intranigral microinjection of Ruthenium Red and 4-aminopyridine in the rat, as compared with that of muscimol. The three drugs produced contralateral turning when injected into the central nigra reticulata. Muscimol was the most effective but its effect disappeared in 3-4 h, whereas that of Ruthenium Red lasted for up to 3 days. When injected into the caudoventromedial nigra, Ruthenium Red produced intense ipsiversive turning, 4-aminopyridine weak ipsiversive turning and muscimol intense contraversive turning. Pretreatment with haloperidol (i.p.) abolished the effect of Ruthenium Red after injection into the caudoventromedial nigra but only partially reduced it after administration into the central nigra. The effect of muscimol, when injected into either of the nigral regions studied, was only slightly diminished by haloperidol. The release of [3H]GABA in slices of the Ruthenium Red-injected substantia nigra was not altered. Histological examination showed that the microinjected Ruthenium Red was located mainly inside the soma of nigral neurons. It is concluded that alterations of transmitter release are probably responsible for the circling behavior induced by 4-aminopyridine, but the effects of Ruthenium Red seem to be secondary to its penetration into the neuronal somas. Dopaminergic neurons seem to play an important role in the ipsilateral turning induced by Ruthenium Red when injected into the caudoventromedial nigra.

4-Aminopyridine↗

PubMed1990

[Thallium poisoning: Prussian blue treatment in 4 cases].

Four patients with thallium toxicity were treated with Prussian blue, 125 mg/kg/day. The diagnosis was made on clinical grounds and confirmed by detection of thallium in the urine. Electromyographic, evoked potentials and electroencephalographic studies confirmed quick clinical and electrophysiologic improvement of the patients.

Adult↗

PubMed1989

Functional changes of brain mitochondria during experimental hepatic encephalopathy.

Several functional parameters were studied in a non-synaptic population of brain mitochondria from rats made cirrhotic by chronic treatment with carbon tetrachloride, with and without coma produced by a single injection of ammonium acetate. The following changes were observed in mitochondria from cirrhotic rats, independently of the presence of coma: (a) a large decrease in oxygen consumption with pyruvate-malate as substrate, but not with succinate, in both states 3 and 4; (b) a modified volume oscillation pattern, characterized by a notable diminution in the amplitude of the oscillation; (c) an altered pattern of acyl groups, with a decrease in the proportion of unsaturated with respect to saturated fatty acids. The following parameters were also measured in brain mitochondria from the cirrhotic rats and were found unchanged: (a) malate dehydrogenase and ATPase activities; (b) content of cytochromes; (c) phospholipid composition; (d) total fatty acid content. The possible significance of the changes observed is discussed in terms of the membranal and biochemical alterations that may be involved in the mechanism of hepatic encephalopathy.

Adenosine Triphosphatases↗

PubMed1989

Chelation of endogenous membrane calcium inhibits gamma-aminobutyric acid uptake in synaptosomes.

In a previous work, we have demonstrated that calcium chelators induce the release of gamma-aminobutyric acid (GABA) from synaptosomes in a Na+ -dependent manner and that this release is blocked by cations such as Mg2+, La3+, and ruthenium red. In the present study, we show that treatment of synaptosomes with 0.1 mM EGTA in the absence of both Ca2+ and Mg2+ inhibits the sodium-dependent high-affinity uptake of [3H]GABA by about 50%. This inhibition increased to about 65% with 1.5 mM EGTA, and it was completely prevented by an excess of Ca2+ or by 1.2 mM Mg2+. In contrast, when EDTA was used as a chelator, Mg2+ was unable to reverse the inhibition. The inhibitory effect of 0.1 mM EGTA was also prevented by 250 microM La3+ or by 20 microM ruthenium red. In the absence of chelators and the presence of Ca2+ and Mg2+, 50 microM and 200 microM La3+ inhibited GABA uptake by about 20 and 50%, respectively, whereas 20 microM ruthenium red produced a nonsignificant 25% inhibition and nifedipine was without effect. It is concluded that the membrane-surface negative charges, probably those of the sialic acid molecules that have been implicated in the functioning of the GABA carrier, must be neutralized by endogenous Ca2+ or by another cation in order to permit the adequate function of the transporter. The inhibition by La3+ in the absence of the chelators could be explained by a binding of this cation to the Na+ sites on the GABA carrier.

Animals↗

PubMed1989

Brain regional thallium distribution in rats acutely intoxicated with Tl2SO4.

The content of thallium in seven body organs and eight brain regions of rats acutely exposed to Tl2SO4 was compared. Rats received a single i.p. injection of Tl2SO4 at three doses: 16, 32 and 48 mg/kg. At 24 h after treatment, thallium content in kidney was higher than in all other organs studied and whole brain had the lowest thallium concentration. A thallium differential distribution was found among brain regions. The highest thallium concentration was found in the hypothalamus and the lowest in the cortex. This distribution pattern was similar with the three doses used. Time course of thallium accumulation in brain was found to be considerably more rapid in the hypothalamus than in other regions, particularly the cortex, suggesting differences in thallium entry into brain parenchyma. Thallium brain regional differential distribution might be related to some of the symptoms of thallium central neurotoxicity.

Animals↗

PubMed1988

Glutamate decarboxylase inhibition and vitamin B6 metabolism in brain of cirrhotic rats chronically treated with carbon tetrachloride.

In a previous work we found that the activity of glutamate decarboxylase (GAD), the enzyme responsible for the synthesis of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA), is decreased in comatose cirrhotic rats after chronic treatment with CCl4. In the present report we studied the participation of pyridoxal phosphate in the inhibition of GAD, as well as the concentration of this coenzyme and the activity of its synthesizing enzyme, pyridoxal kinase, in the brain of the cirrhotic rats. Furthermore, cirrhotic animals were treated with three inhibitors of GAD, and the effects of such treatment were compared to those of ammonium. Liver failure resulted in a 25% inhibition of GAD activity when measured in the absence of added pyridoxal phosphate. Treatment with the GAD inhibitors thiosemicarbazide or 3-mercaptopropionic acid enhanced this inhibition and produced convulsions at a dose that had no behavioral effects in control rats. Treatment with ammonia resulted in a comatose state and in a 25-40% inhibition of GAD. Both pyridoxal kinase activity and pyridoxal phosphate levels were found to be decreased by 15-20% in the brain of the cirrhotic rats. We concluded that chronic liver failure results in a decreased pyridoxal phosphate and GABA synthesis in brain, with a consequent diminished efficiency of GABAergic neurotransmission; these effects are probably related to the manifestations of neuronal hyperexcitability that are frequently seen in human hepatic encephalopathy.

Acetates↗

PubMed1988

Regional brain GABA metabolism and release during hepatic coma produced in rats chronically treated with carbon tetrachloride.

Hepatic coma was induced in rats chronically treated with CCl4, by means of a single injection of ammonium acetate. The activities of glutamate decarboxylase (GAD) and GABA transaminase (GABA-T), as well as the synaptosomal uptake and release of [3H]GABA, were measured in the following brain areas of the comatose rats: cortex, striatum, hypothalamus, hippocampus, midbrain and cerebellum. Hepatic coma was associated with a general decrease of GAD activity, whereas GABA-T activity was diminished only in the hypothalamus, striatum and midbrain. During hepatic coma, the K+-stimulated [3H]GABA release was notably diminished in the striatum and cerebellum, whereas a significant increase was observed in the hippocampus. [3H]GABA uptake increased in most regions after CCl4 treatment, independently of the presence of coma. The results indicate that GABAergic transmission seems to be decreased in most cerebral regions during hepatic coma.

4-Aminobutyrate Transaminase↗

PubMed1988

Relationship of dihydropyridine binding sites with calcium-dependent neurotransmitter release in synaptosomes.

In the present work, we have studied the effect of ruthenium red (RuR), La3+ and 4-aminopyridine (4-AP) on the specific binding of (+)-[3H]PN200-110 to synaptosomes, as well as the effect of nitrendipine, nifedipine, and BAY K 8644 on gamma-[3H]aminobutyric acid [( 3H]GABA) release induced by potassium depolarization and by 4-AP in synaptosomes. Scatchard plots indicated that neither RuR nor 4-AP modifies the KD and Bmax of [3H]PN200-110 specific binding, whereas La3+ decreased the Bmax by about 25%; when the effect of the drugs on the total binding of PN200-110 was studied, a similar inhibition by La3+ was found. The calcium antagonists, nitrendipine and nifedipine, did not affect at all the potassium-stimulated release of [3H]GABA nor its release induced by 4-AP. The calcium agonist BAY K 8644 failed to affect both the spontaneous and the potassium-stimulated GABA release. Our results suggest that the binding sites of dihydropyridines in presynaptic membranes are not related to the calcium channels involved in neurotransmitter release with which RuR, La3+, and 4-AP interact.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1987

Neurotransmitters of the cerebellar glomeruli: uptake and release of labeled gamma-aminobutyric acid, glycine, serotonin and choline in a purified glomerulus fraction and in granular layer slices.

We have studied some properties of the uptake and release of labeled gamma-aminobutyric acid (GABA), glycine, serotonin and choline in a purified fraction of glomeruli and in slices of the granular layer of the rat cerebellum. The uptake of both GABA and glycine into the glomerulus particles was dependent on the presence of Na+ in the medium. In contrast, the uptake of both serotonin and choline was Na+-independent. In slices of the granular layer also a slight Na+-dependence was observed for both serotonin and choline uptake; imipramine and hemicholinium partially inhibited the uptake of serotonin and choline, respectively. Choline uptake into the glomerulus particles showed two components, with apparent Km values of 16.8 and 102 microM. GABA release was stimulated by K+-depolarization about 100% (peak stimulation) and this value was reduced to 50% when Ca2+ was omitted. The release of glycine was stimulated more rapidly and notably than GABA (200%) and this stimulation was completely abolished in the absence of Ca2+. Serotonin release from the glomerulus particles was only slightly stimulated by depolarization, but this stimulation was strictly Ca2+-dependent. In slices of the granular layer, this stimulation was considerably larger (about 40%) and it was also almost totally dependent on Ca2+. In contrast, after loading with labeled choline the release of radioactivity from both the glomerulus particles and the cerebellar slices was not stimulated at all by K+-depolarization, either in the presence or in the absence of Ca2+. Most of the radioactivity released spontaneously corresponded to choline, and only a small proportion (8-14%) to acetylcholine. From the results of the release experiments and taking into account the pertinent data from the literature, it is concluded that GABA and glycine are probably the transmitters of different populations of Golgi axon terminals, whereas serotonin might be the transmitter of at least a certain population of the mossy fiber giant terminals, in the rat cerebellar glomeruli. In contrast, acetylcholine does not seem to have any transmitter role in the synaptic structures of the glomeruli.

Animals↗

PubMed1987

Changes in lipid peroxidation induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and 1-methyl-4-phenylpyridinium in mouse brain homogenates.

We studied the effect of the Parkinson-inducing drug 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and of its metabolite 1-methyl-4-phenylpyridinium (MPP+) on lipid peroxidation in mouse brain homogenates in vitro. MPTP (0.35-1.4 mM) inhibited both spontaneous and Fe2+-induced peroxidation in a dose-dependent manner. MPP+, on the other hand, produced a slight enhancement of lipid peroxidation at 1.4 and 2.1 mM concentrations. These results are discussed in terms of the possible mechanisms of MPTP and MPP+ neurotoxicity.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed1986

Differential calcium dependence of gamma-aminobutyric acid and acetylcholine release in mouse brain synaptosomes.

The dependence of gamma-aminobutyric acid (GABA) and acetylcholine (ACh) release on Ca2+ was comparatively studied in synaptosomes from mouse brain, by correlating the influx of 45Ca2+ with the release of the transmitters. It was observed that exposure of synaptosomes to a Na+-free medium notably increases Ca2+ entry, and this condition was used, in addition to K+ depolarization and the Ca2+ ionophore A23187, to stimulate the influx of Ca2+ and the release of labeled GABA and ACh. The effect of ruthenium red (RuR) on these parameters was also investigated. Of the three experimental conditions used, the absence of Na+ in the medium proved to be the most efficient in increasing Ca2+ entry. RuR inhibited by 60-70% the influx of Ca2+ stimulated by K+ depolarization but did not affect its basal influx or its influx stimulated by the absence of Na+ or by A23187. The release of ACh was stimulated by K+ depolarization, absence of Na+ in the medium, and A23187 in a strictly Ca2+-dependent manner, whereas the release of GABA was only partially dependent on the presence of Ca2+ in the medium. The extent of stimulation of ACh release was related to the extent of Ca2+ entry, whereas no such correlation was observed for GABA. In the presence of Na+, RuR did not affect the release of the transmitters induced by A23187. In the absence of Na+, paradoxically RuR notably enhanced the release of both ACh and GABA induced by A23187, in a Ca2+-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1986

Gonadotropin-secreting pituitary adenoma with concomitant hypersecretion of testosterone and elevated sperm count. Treatment with LRH agonist.

Hypersecretion of both FSH and LH was demonstrated in a man with pituitary macroadenoma, who also presented elevated levels of blood testosterone and an increased sperm count. The patient underwent transsphenoidal surgery followed immediately by cranial irradiation. Immunocytochemical analysis of the tumour revealed the presence of FSH, LH, TSH and the alpha-subunit. Gel chromatography of the serum on Sephadex G-100 revealed immunoactive FSH, LH and the alpha-subunit which coeluted with the labelled standards of corresponding hormones. Blood levels of both gonadotropins and testosterone remained persistently elevated up to one year following surgical decompression of the tumour and radiotherapy. It was decided to treat this patient with sc administration of 100 micrograms D-Trp6-LRH biweekly. After 20 weeks, LRH-analogue treatment resulted in the reduction of serum FSH and LH levels and a diminishing in tumour size as assessed by computed tomography scan of the pituitary. This report shows that in a patient with clinically and biochemically documented gonadotropin-secreting adenoma, inducing a state of persistent gonadal hyperfunction, pituitary surgery and cranial irradiation failed to normalize the biochemical abnormality; however, therapy with D-Trp6-LRH agonist induced clinical, biochemical and radiologic improvement.

Adenoma↗

PubMed1985

Mechanism of the calcium-dependent stimulation of transmitter release by 4-aminopyridine in synaptosomes.

The mechanism of the Ca2+-dependent stimulation of neurotransmitter release by 4-aminopyridine in synaptosomes was studied. The stimulation of gamma-[3H]aminobutyric acid and [3H]acetylcholine release by 4-aminopyridine was not significantly affected either by tetrodotoxin or by the absence of Na+ in the medium, whereas the toxin notably inhibited the release of both transmitters induced by veratridine. On the other hand, the release of labeled gamma-aminobutyric acid induced by 4-aminopyridine was inhibited by both La3+ and ruthenium red, two blockers of Ca2+ transport in synaptosomes. In other experiments, 4-aminopyridine had only a slight stimulatory effect, if any, on the influx of 45Ca2+ into synaptosomes, under both resting and K+-depolarizing conditions. Ruthenium red inhibited the stimulation by K+ of the 45Ca2+ uptake, and 4-aminopyridine did not antagonize this inhibition. We conclude that the transmitter-releasing action of 4-aminopyridine in synaptosomes does not involve an excitatory effect on the membrane which may result in the opening of voltage-sensitive Na+ channels. 4-Aminopyridine does not seem to act either by enhancing Ca2+ entry into the synaptosomes. It is proposed that 4-aminopyridine facilitates the coupling between Ca2+ binding and transmitter secretion at the presynaptic membrane.

4-Aminopyridine↗

PubMed1985

Effects of drugs on neurotransmitter release: experiments in vivo and in vitro.

Calcium ions play a fundamental role in the release of transmitters in the nervous system. Therefore, drugs capable of modifying Ca2+ transport are useful tools for studying the mechanisms of such release in vivo and in vitro. In this article the action of some of these drugs on motor behavior, as well as on Ca2+ uptake and neurotransmitter release in synaptosomes, is reviewed. Ruthenium red (RuR) inhibits Ca2+ uptake and transmitter release in synaptosomes, and produces flaccid paralysis when injected intraperitoneally (IP) and convulsions after intracranial administration. Drugs which stimulate the Ca2+-dependent transmitter release in synaptosomes, such as 4-aminopyridine, antagonize the paralysis produced by RuR. Lanthanum ions also inhibit Ca2+ uptake and neurotransmitter release in synaptosomes, but no paralysis was observed after La2+ IP injection. However, this cation blocks the binding of RuR to the presynaptic membrane, and prevents the RuR-induced paralysis. Veratridine and the Ca2+ chelator EGTA were used to demonstrate in synaptosomes that besides the Ca2+-dependent mechanism of release of the central inhibitory transmitter gamma-aminobutyric acid (GABA), there seems to be a strictly Na+-dependent process which is not shared by other transmitters such as acetylcholine or dopamine.

4-Aminopyridine↗

PubMed1985

Binding of lanthanum ions and ruthenium red to synaptosomes and its effects on neurotransmitter release.

A technique for studying the binding of La3+ to synaptosomes in a double-beam spectrophotometer, using murexide as indicator, is described. The binding of La3+ was very rapid and Scatchard plots revealed two components, with KD values of 0.6 and 27 microM in a Na+-free medium (sucrose medium) and 2.3 and 63 microM in an ionic medium containing 135 mM Na+. The binding of the cationic dye ruthenium red (RuR) showed only one site, with a KD of 3.7 microM. La3+ binding was partially inhibited by RuR and vice versa, and La3+ was also capable of partially displacing RuR previously bound to the synaptosomes, particularly in the sucrose medium. The release of labeled gamma-aminobutyric acid (GABA) stimulated by K+ depolarization was inhibited by La3+ concentrations at or above 1 microM, in the ionic medium, whereas in the sucrose medium 2.5 microM or higher La3+ concentrations notably stimulated the spontaneous release of both GABA and glutamic acid. It is concluded that La3+ and RuR share at least one type of binding site, which is probably the high-affinity La3+ site. Since both La3+ and RuR at low concentrations have been shown to block the depolarization-induced Ca2+ entry in synaptosomes, this site might be related to the voltage-dependent Ca2+ entry involved in neurotransmitter release.

Animals↗

PubMed1984

Stimulation of [3H]gamma-aminobutyric acid release by calcium chelators in synaptosomes.

The effect of EGTA on the release of labeled gamma-aminobutyric acid (GABA), glutamate, acetylcholine, and dopamine was studied in superfused synaptosomes from mouse brain. In the absence of both Ca2+ and Mg2+, EGTA and also EDTA at 50 microM or higher concentrations induced a 2.5-5-fold stimulation of [3H]GABA release, similar to that produced by potassium depolarization, whereas only a slight effect, or no effect at all, was observed on the release of the other transmitters studied. The GABA-releasing action of EGTA was practically abolished in the presence of Mg2+. In contrast, the effect of EDTA was also observed when the medium contained Mg2+. Studies on the ionic dependence showed that the stimulation of GABA release by EGTA was abolished in a Na+-free medium. Li+ did not substitute Na+ for the EGTA effect, which was also independent of chloride. This Na+ dependence does not seem to involve voltage-sensitive channels, since tetrodotoxin did not affect the GABA-releasing action of EGTA, whereas in parallel superfusion chambers it blocked over 80% the stimulation of GABA release by veratridine. In contrast, two calcium channel blockers in synaptosomes, La3+ and the cationic dye ruthenium red, greatly inhibited the GABA-releasing effect of EGTA. L-2,4-Diaminobutyric acid, an inhibitor of the Na+-dependent GABA carrier, did not affect the releasing action of EGTA, whereas in a parallel experiment this drug inhibited by more than 90% the exchange of labeled GABA with unlabeled GABA.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗