Carlos J. Gómez

Hormonal regulation of brain development I. The effect of neonatal thyroidectomy upon nucleic acids, protein and two enzymes in developing cerebral cortex and cerebellum of the rat

Abstract The changes in protein, nucleic acids, aspartate amino transferase, and aspartate transcarbamoylase during postnatal development of the cerebral cortex and cerebellum of the rat have been studied. With the exception of nucleic acids, the patterns of change are similar in both tissues. Neonatal thyroidectomy produced a significant increase in the DNA content of the cerebral cortex, but only slightly affected that of the cerebellum. This condition led to a substantial decrease of RNA and protein in both tissues. The lack of thyroid function from birth produced a marked depression of mitochondrial aspartate amino transferase, but did not affect the level of the soluble enzyme. This condition also led to a slight increase of cerebellar aspartate transcarbamoylase, but did not affect its level in the cerebral cortex.

Hormonal regulation of brain development II. Effect of neonatal thyroidectomy on succinate dehydrogenase and other enzymes in developing cerebral cortex and cerebellum of the rat

The changes of succinate dehydrogenase, glutamate decarboxylase, GABA transaminase, Mg-adenosine triphosphatase and Na+-K+-adenosine triphosphatase were studied throughout the postnatal development of the cerebral cortex and cerebellum of the cat. Results expressed as a function of wet tissue were compared with those related to DNA. The latter way of expression appears to be a better indication of the biochemical and morphological changes related to maturation. During normal morphogenesis of the cerebral cortex and cerebellum the activity of all the enzymes increases sharply from the 10th postnatal day onward, the greatest rates occurring between the 10th and the 30th postnatal days. The patterns of change are similar in both the cerebral cortex and cerebellum. Thyroid deprivation from birth leads to a significant decrease in all the enzymes of the cerebral cortex studied. It also produces a substantial depression of GABA transaminase and Na+-K+-adenosine triphosphatase in the cerebellum. In this tissue, succinate dehydrogenase and glutamate decarboxylase are only temporarily affected, whereas Mg-adenosine triphosphatase is unaffected.

Hormonal regulation of brain development. III. Effects of triiodothyronine and growth hormone on the biochemical changes in the cerebral cortex and cerebellum of neonatally thyroidectomized rats

Abstract The effects of l -triiodothyronine and bovine growth hormone, administered to neonatally thyroidectomized rats, have been studied in connection with the changes in nucleic acid content and enzymic activities of the cerebral cortex and cerebellum. When administered from the 10th day of age, both triiodothyronine and bovine growth hormone were effective in correcting the alterations produced by neonatal thyroidectomy. On the contrary, when the beginning of treatments were delayed until the 15th day of age, triiodothyronine and/or bovine growth hormone showed no restoring effect. The finding that bovine growth hormone was as effective as triiodothyronine raises the question of whether the effects of early thyroid dysfunction on cerebral development reflect a direct action of thyroid hormone on this process or whether they are indirectly mediated.

Rapid purification of proteolipids from rat brain subcellular fractions by chromatography on a lipophilic dextran gel

Proteolipids from adult rat brain subcellular fractions were purified by a one-step procedure involving chromatography through Sephadex LH-60 eluted with an acidified chloroform-methanol mixture. The protein peak was eluted with the void volume and was free of adventitious lipids. The degree of purification was similar to that attained with the neutral-acidified chloroform-methanol dialysis method with the advantage that this new procedure can be carried out in only 3 h, with a recovery of proteins of 95-100%. Samples containing different lipid/protein ratios passed through the gel gave similar elution profiles. When labeled amino acids or palmitic acid were added to myelin total lipid extracts, no radioactivity was eluted with the protein, indicating that the proteolipid apoproteins purified by this method do not adsorb hydrophobic low-molecular-weight compounds.

Hormonal regulation of brain development. IV. Effect of neonatal thyroidectomy upon incorporationin vivo ofl-[3H]phenylalanine into proteins of developing rat cerebral tissues and pituitary gland

Abstract After the subcutaneous administration of l -[3H]phenylalanine, the pattern of changes in the entry of the amino acid into tissues and its incorporation into proteins has been studied comparatively in the cerebral cortex, cerebellum, hypothalamus and pituitary gland from developing rats. During normal development, the changes in the uptake of the amino acid and its rate of disappearance in cerebral tissues markedly contrasted with those occuring in the pituitary gland. Whereas in the former, such processes increased progressively with age, in the pituitary gland they remained unchanged throughout the entire experimental period. Striking differences were also observed in relation to the protein-synthetic ability, which decreased markedly with age in the cerebral tissues, and increased up to 15 days without further changes in the pituitary gland. Neonatal thyroidectomy produced a significant increase in the entry of the amino acid into all the tissues studied; this condition also led to a decreased rate of disappearance in the cerebral tissues, but did not affect such process in the pituitary gland. The RSA of proteins in cerebral tissues was significantly decreased in hypothyroid rats, suggesting an impairment of protein synthesis. The observation that protein synthesis was also depressed in the pituitary gland by neonatal thyroidectomy, suggests that thyroid hormone might play a critical role in pituitary metabolism during early postnatal life.

INFLUENCE OF NEONATAL HYPOTHYROIDISM ON AMINO ACIDS IN DEVELOPING RAT BRAIN

CONCOMITANTLY with post-natal development of the neuropil and with the appearance of myelin, a progressive increase in the concentration of several free amino acids has been found in normal developing brain of rats, cats, and rabbits (SCHADE and BAXTER, 1960; VERNADAKIS and WOODBURY, 1962; BERL and PURPURA, 1963 ; MIHAILOVIC and KOZALIC, 1964). Neonatal thyroidectomy in rats produces several morphological alterations in the brain (BARNETT, 1943; EAYRS, I961a; LEGRAND, KRIEGEL and JOST, 1961) coincident with changes in the spontaneous electrical activity (BRADLEY, EAYRS and SCHMALBACH, 1960) and a decrease in the activity of certain enzymes (HAMBURGH and FLEXNER, 1957) and in the oxidative metabolism of glucose in cerebral cortex (GHITTONI and GOMEZ, 1964). The present work was undertaken to find out the influence of neonatal thyroid deprivation upon the changes occurring in free amino acids of brain during post-natal development. The results indicate that thyroid deficiency at birth leads to a transitory depression of the concentration of glutamic acid, glutamine, and GABA, and to permanent changes in the levels of aspartic acid and taurine in the brain.

BINDING OF d‐[DIMETHYL14C]TUBOCURARINE, ACETYLCHOLINESTERASE AND PROTEOLIPIDS IN SUBCELLULAR MEMBRANES OF CEREBRAL CORTEX OF THE DEVELOPING RAT1

Abstract— The cerebral cortex of rats at postnatal ages of 5,15,30 and 50 days was homogenized and fractionated to separate the crude mitochondrial fraction. This fraction was osmotically shocked and the Mi fraction and subfractions were separated. The variations with age in the morphological composition of subfractions M1 0·8, Mi 1·3 and M1p were studied under the electron microscope. Because of the changes observed in the various fractions the need for such type of control is stressed.

Hormonal regulation of brain development. V. Effect of neonatal thyroidectomy on lipid changes in cerebral cortex and cerebellum of developing rats

Summary The changes of cerebrosides, gangliosides, phospholipids, cholesterol, and proteolipid protein were studied throughout early postnatal maturation of the cerebral cortex and cerebellum of the rat. Results expressed per unit of wet tissue were compared with those based on DNA content. The latter way of expression presents a better relation with chemical and histological events taking place through maturation. Neonatal thyroidectomy produced a significant decrease in almost all lipids of the cerebral cortex studied, and a transient depression of phosphatidylcholine and phosphatidyl ethanolamine. It also produced a substantial decrease of cerebrosides, gangliosides, sphingomyelin and phosphoinositosides in the cerebellum. In this tissue, phosphatidyl ehtanolamine is only temporally affected, whereas phosphatidylcholine, proteolipids and cholesterol are unaffected.

Hormonal regulation of brain development. VI. Kinetic studies of the incorporation in vivo of [3H]orotic acid into RNA of brain subcellular fractions of 10-day-old normal and hypothyroid rats

Abstract The time course incorporation of the precursor into RNA from brain subcellular fractions has been studied after the intra-arachnoidal injection of [5-3H]orotic acid in 10-day-old normal and neonatally radio-thyroidectomized rats. Neonatal thyroidectomy produced a significant depression of the formation of nuclear ‘rapidly labelled’ RNA, and a decreased rate of incorporation into microsomal RNA. Neither the labelling of the acid-soluble pool of precursors nor the incorporation into RNA from mitochondrial and soluble fractions was affected by this condition. Kinetic studies of the labelling of different nuclear and microsomal RNA species, separated by linear sucrose gradients, confirm that neonatal thyroidectomy reduced the transcriptional activity of nuclei, and suggest that it may also be responsible for alterations in post-transcriptional regulatory mechanisms.

Amino acid changes in the mouse brain during audiogenic seizures and recovery.

Abstract Presensitized mice of the A2G strain were subjected to the sound provided by the sustained ringing of a 100 db electric doorbell. The animal responded with a phase of running behavior beginning 10 sec after the onset of the auditory stimulus and lasting about 40–50 sec; this phase was followed by generalized tonic-clonic convulsions, catatonic state and recovery. The brain concentration of glutamate and glutamine decreased significantly during the running behavior phase and dropped further at the moment of maximal convulsions, whereas that of aspartate and GABA remained unchanged during running behavior and decreased during seizures. During the phase of recovery the normal levels were rapidly restored; glutamine showed the highest rate of accumulation, in contrast to GABA, showing the slower one. Subcutaneous administration of GABA led to a significant increase in the brain concentration of GABA and glutamate, which was roughly proportional to the administered dose. Maximal increases were observed 30 min after administration and returned to normal in 150 min. Systemically administered GABA afforded a protection against sound-induced seizures, decreasing the percentage of the number of animals convulsing. In spite of this protection, the concentration of amino acids in brain from pretreated mice, regardless if they convulsed or not, was essentially the same as that found in the brain of nonexposed control mice; however, a marked decrease was observed in GABA and, to a much lesser degree, in glutamate when compared with pretreated non-exposed controls. The results led to the conclusion that the brain concentration of GABA was not a determining factor in the production of sound-induced seizures.