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Biomedical subjects

R Tapia

Publications and source records attributed to R Tapia.

At least 109 records · Page 6Linked to original sources
PubMed1976

Convulsions or flaccid paralysis induced by ruthenium red depending on route of administration.

Ruthenium red was administered to mice and cats intracranially or intraperitoneally. In mice, intracisternal administration produced status epilepticus and tonic convulsions. In contrast, intraperitoneal administration induced total flaccid paralysis lasting several hours. These effects of Ruthenium red were partially blocked by the simultaneous administration of CaCl2. EDTA, at doses much greater than those of Ruthenium red, produced effects similar to those of the dye, which were also blocked by CaCl2 administration. In cats, intraventricular or intrahippocampal administration of Ruthenium red through a permanently implanted cannula produced after a few minutes subclinical paroxysmal activity in all brain regions recorded. After several hours the animals developed typical grand mal seizures. Intraperitoneal injection of Ruthenium red to cats did not affect the EEG but markedly depressed muscular activity. Administration of carbachol to the latter animals produced myoclonic responses. These results are discussed in relation to the inhibitory effect of Ruthenium red on Ca2+ transport and binding to membranes, and to the role of this cation on neurotransmitter release.

Animals↗
PubMed1976

Properties of soluble and particulate cysteine sulfinate decarboxylase of the adult and the developing rat brain.

Some properties of cysteine sulfinate decarboxylase (CSD) activity were studied in the pellet and supernatant of a 18,000 X g centrifugation of isotonic sucrose rat brain homogenates. About 50% of the enzyme activity was found associated to the particulate fraction and 16% of the activity remained particle bound after hypo-osmotic shock of the 18,000 X g pellet. The activity of the 18,000 X g supernatant showed a lower dependence on exogenous pyridoxal phosphate (PLP) than the activity in the particulate fraction. The CSD activity of these fractions also differed in optimal pH and in apparent kinetic constants. The enzyme associated to particles showed the highest Vmax and the lowest Km. The activity and kinetic characteristics of CSD were studied during brain postnatal development. In the newborn brain only a small amount of the enzyme activity was found associated to the 18,000 X g pellet. CSD in brain homogenates of immature rats was less dependent on free PLP and showed a higher Km and a lower Vmax as compared with the enzyme in the adult brain. Between birth and adulthood the enzyme activity increased more than 10-fold in the particulate fraction and 2-fold in the soluble fraction. It is concluded that the differences observed in CSD activity between newborn and adult brain are due to an increase of the particulate form of the enzyme during postnatal development.

Animals↗
PubMed1975

GABA metabolism and cerebral protein synthesis.

Glutamate decarboxylase (GAD) activity and [14C)leucine incorporation into brain protein in vivo were measured in mice injected with L-glutamic acid-gamma-hydrazide and 60 min later with pyridoxal-5'-phosphate; this combined treatment produces a decrease in GAD activity and an increase in GABA levels. Under such conditions, protein synthesis was inhibited to the same extent as GAD activity. A parellelism between the decrease in GAD activity and that in protein synthesis was also observed in brain cortex slices treated with GAD inhibitors. This treatment did not affect leucine incorporation into protein in liver slices. The results support the previously suggested hypothesis that a certain pool of GABA may have a role in the regulation of protein synthesis in brain, and further suggest that the synthesis of GABA may be more important in this respect than its total concentration.

Aminobutyrates↗
PubMed1975

Subcellular fractionation of rat cerebellum: an electron microscopic and biochemical investigation. III. Isolation of large fragments of the cerebellar glomeruli.

By a combination of differential and sucrose density gradient (both discontinuous and linear) centrifugation, large fragments of the cerebellar glomeruli were isolated in high purity from hand homogenised tissue. The final preparation contained only about 1% of the tissue protein, but over 90% of its volume was accounted for by the glomerulus particles. The ultrastructure of the glomerulus particles was well preserved. The enzyme profile was characteristic: the glomerulus particles were enriched in glutamate decarboxylase (GAD) activity (relative specific activity (RSA), 2.54), but the RSA of choline acetyltransferase (ChAc) was only 1.05. These findings are consistent with the view that GAD activity is very high in the inhibitory Golgi terminals, which occupy only a small fraction of the total volume of the particles, and acetylcholine may be a transmitter only in a relatively small fraction of the mossy fibre terminals. The glomerulus particles also contained a high concentration of succinate dehydrogenase (SDH) activity (RSA, 1.91), whereas the RSA of glutamate dehydrogenase (GDH) was only 1.15. The great asset of this preparation for future investigations is that it is composed almost exclusively from pre- and postsynaptic neuronal structures. Fractions containing neuropil fragments of non-glomerular origin were also obtained, but the profile of the estimated enzymes did not indicate unique characteristics.

Acetyltransferases↗
PubMed1975

Seizure susceptibility in the developing mouse and its relationship to glutamate decarboxylase and pyridoxal phosphate in brain.

The relationship between the susceptibility to convulsions, the content of pyridoxal 5'-phosphate and the activity of pyridoxal kinase (EC 2.7.1.35) and glutamate decarboxylase (EC 4.1.1.15) in brain, was studied in the developing mouse. Seizures were induced by pyridoxal phosphate-gamma-glutamyl hydrazone (PLPGH), a drug previously reported to reduce the levels of pyridoxal 5'-phosphate and as a consequence to inhibit the activity of glutamate decarboxylase in brain of adult mice. It was found that the seizure pattern, as well as the time of appearance of convulsions, differed between 2- and 5-day old mice and 10-day old or older mice, indicating a progressive increase in seizure susceptibility during development. In brain, pyridoxal kinase activity and pyridoxal 5'-phosphate levels were decreased by the administration of PLPGH at all ages studied, whereas glutamate decarboxylase activity was inhibited less than 25% in 2- and 5-day old mice, and about 50% thereafter. Parallelly, the activation of glutamate decarboxylase by pyridoxal 5'-phosphate added in vitro to control homogenates was less in 2- and 5-day old mice than in older animals. It is concluded that the increase in the susceptibility to seizures induced by PLPGH during development is probably related to the increase observed in the sensitivity of glutamate decarboxylase in vivo to a decrease of pyridoxal 5'-phosphate levels. The correlation between pyridoxal 5'-phosphate, glutamate decarboxylase, and seizure susceptibility seems to be established at about 10 days of age.

Animals↗
PubMed1975

Differences in some properties of newborn and adult brain glutamate decarboxylase.

Some properties of glutamate decarboxylase (EC 4.1.1.15) activity in brain of newborn and adult mouse were studied comparatively. It was found that glutamate decarboxylase of the newborn brain was strongly inactivated by homogenization in hypotonic medium, centrifugation of isotonic sucrose homogenates, preincubation at 37 degrees C or the addition of Triton-X-100, whereas the adult brain enzyme was practically unaffected by any of these conditions. It was also found that the newborn glutamate decarboxylase was less activated by pyridoxal 5'-phosphate and less inhibited by pyridoxal 5'-phosphate oxime-O-acetic acid, than the adult enzyme. These differences do not exist for brain dihydroxyphenylalanine decarboxylase (EC 4.1.1.26) and are not due to the release of inhibitors from the newborn brain. On the basis of the results obtained it is postulated that two forms of glutamate decarboxylase exist in brain: a newborn form, which is unstable and has high affinity for pyridoxal 5'-phosphate, and an adult form, which is much more stable and has low affinity for pyridoxal 5'-phosphate. The possible implications of these findings in the establishment of the gamma-aminobutyric acid dependent synaptic inhibitory mechanisms during development are discussed.

Age Factors↗