BRAIN ENERGETICS IN OXYGEN-INDUCED CONVULSIONS

Mice were exposed to 6 ATA of 100% oxygen. The effect of high oxygen pressure (OHP), disulphiram and both disulphiram and oxygen as a function of the length of oxygen exposure on cerebral cortical ATP, phosphocreatine, lactate, pyruvate and glucose was determined. Neither OHP nor disulphiram altered ATP prior to the onset of convulsions. The combination of OHP and disulphiram appeared to elevate cerebral ATP, particularly during the early exposure period. OHP had no effect on phosphocreatine, however, disulphiram, both alone and in combination with OHP increased cerebral cortical phosphocreatine. ATP and phosphocreatine were unchanged in mice sacrificed either at the onset or 9 s after the onset of oxygen convulsions. Lactate and pyruvate increased as the length of time the mice were exposed to OHP increased although neither lactate nor pyruvate levels differed significantly from control levels at either the onset or 9 s after the onset of convulsions. Disulphiram by itself lowered cerebral lactate, and prevented the increase in lactate and pyruvate in mice exposed to OHP. OHP and disulphiram increased cerebral glucose with the combination of both OHP and disulphiram appearing to have an additive effect. Glucose also remained elevated at the onset or 9 s after the onset of oxygen convulsions.     

Correlation between decreases in brain gamma-aminobutyric acid levels and susceptibility to convulsions induced by hyperbaric oxygen

Abstract— The susceptibility of mice to seizures at hyperbaric pressures of oxygen (OHP) was placed on a quantitative basis and compared with the corresponding rate of decrease in brain GABA concentration. The influence of small amounts of carbon dioxide in the breathing mixture on these effects of OHP was also determined. A correlation between the rate of decrease in GABA and susceptibility to seizures was shown to exist not only over the varying oxygen pressures and varying concentrations of carbon dioxide used in the present experiments out also over varying animal species (a previous study). The critical oxygen pressure for decreases in brain GABA to occur was shown to be 30 p.s.i.g. This value agreed closely with the well documented critical pressure necessary to produce seizures in both animals and man. The probability that lowered brain GABA levels play a major role in the etiology of OHP convulsions was discussed.     

Tissue Distribution, Metabolism, Anticonvulsant Efficacy, and Effect on Brain Amino Acid Levels of the Glia-Selective γ-Aminobutyric Acid Transport Inhibitor 4,5,6,7-Tetrahydroisoxazolo[4,5-c]pyridin-3-ol in Mice and Chicks

Using tritium-labelled 4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridin-3-ol (THPO) its tissue distribution and metabolism were investigated in adult mice and 4-day-old chicks after systemic administration of the drug. It was found not to be significantly metabolized in the brain since metabolites of THPO corresponding to only approximately 8% of the parent compound could be detected 30 min after administration of the drug intramuscularly in mice. In the liver, however, THPO was found to be metabolized to a considerable extent. In chicks THPO metabolites were found in the brain but they accounted for less than 35% of the radioactivity. The brain concentration of THPO in mice and chicks corresponded to respectively 10 and 50% of the dose injected intramuscularly and the tissue level was essentially constant for at least 3 h after injection. Following systemic administration of THPO to mice and chicks the contents of aspartate, glutamate, glutamine, and gamma-aminobutyric acid (GABA) in whole brain and in synaptosomes was determined. It was found that only GABA contents were affected being increased in synaptosomes from mice and decreased in whole brain in chicks. Doses of THPO, which in chicks but not in mice led to brain levels that were sufficient to inhibit glial GABA uptake, were found to protect chicks but not mice against isonicotinic acid hydrazide-induced seizures. The findings are compatible with the notion that THPO exerts its anticonvulsant activity by inhibition of astrocytic GABA uptake.     

Reserpine effects on neurotransmitters in chick heart during growth

Effects of tranquilizing agents on neurotransmitters in the heart have not been widely studied. Thus, the effect of intraperitoneal injection of reserpine, (2.5 mg/kg bw) on the concentrations of excitatory (glutamic acid, glutamine, aspartic acid, asparagine), inhibitory (GABA, glycine, alanine, taurine), neurotransmitters as well as the enzymes (GOT and GPT) and total protein were measured in both heart and serum of chicks at different ages (1, 7, 30, 90 and 180 days). Reserpine induced a decrease in the excitatory amino acids and an increase in GABA in both heart and serum in most ages. Glycine and alanine increased in the heart and decreased in serum. Taurine increased in the heart of young ages (1 and 7 days) and decreased in older ones (90 and 180 days), however, it decreased in serum of most ages. Both GOT and GPT increased in heart but, in serum, GOT increased and GPT decreased in most ages. Total protein increased in the heart of young chicks and decreased in the 90- and 180-day-old chicks. In conclusion, reserpine induced a parallel decrease in the ratio glutamate, glutamine, aspartate/GABA in both myocardial tissue and serum of the different age groups. Changes observed in neurotransmitters of the heart suggest that these amino acids may play a similar role in the myocardial tissue, as is described in the central nervous system.     

THE COMPARATIVE EFFECTS OF VARIOUS HYDRA-ZIDES ON γ-AMINOBUTYRIC ACID AND ITS METABOLISM

Abstract— The administration of different hydrazides to chicks (20-23 days post-hatching) in amounts giving similar latent periods before the onset of seizures produced (i) similar rates of decrease in content of cerebral GABA, (ii) considerable but dissimilar inhibitions of cerebral GAD activity, (iii) slight inhibitions of cerebral GABA-T activity. The results support the view that low GABA levels were involved in. the etiology of the seizures but seemed to rule out the possibility that a reduced turnover of GABA was responsible for the occurrence of the convulsions.     

Regulation of parental investment in the Antarctic petrel Thalassoica antarctica: an exchange experiment

An experiment was conducted on the Antarctic petrel to test whether the parents were able to respond to changes in food demand of their offspring. Two experimental groups were formed by replacing eight 20-day-old chicks with 10-day-old chicks, and vice versa. The growth rate of chicks in the experimental groups was compared with that in two control groups with chicks of known age. The growth rate of 10-day-old chicks in the nests of parents which initially had 20-day-old chicks did not differ significantly from that in their respective control groups. This indicates that those parents were able to raise a new young nestling, despite having already raised another chick from hatching to 20 days. However, the 20-day-old chicks placed in nests with 10-day-old chicks had a significantly lower growth rate than their control group. Feeding rate per day and nest did not differ significantly among any of the groups. This suggests that the observed difference in growth rate between 20-day-old chicks is related to a lower amount of food delivered per visit to experimental chicks. Thus, in the Antarctic petrel, the feeding rate apparently is not regulated by the status of the chick, but by the parents' ability to gather food or willingness to provide food for the chicks.Publication no. 137 from the Norwegian Antarctic Research Expedition (NARE) 1989/90     

POSTNATAL CHANGES IN THE HIGH AFFINITY UPTAKE OF GLYCINE and GABA IN THE RAT CENTRAL NERVOUS SYSTEM

Abstract— High affinity uptake systems for GABA into slices of cerebral cortex and for glycine into slices of spinal cord have been demonstrated in rats of 1 and 10 days postnatal age and compared with the systems in tissue slices from adult rats. For both systems there was an increase in the maximal rate of uptake of the substrate with development. For glycine uptake there was no significant change in apparent K_m during development, whereas there was a four-fold increase in the apparent K_m for GABA uptake. There were some changes with development in the apparent substrate specificity of the two systems suggesting increased specificity with maturation. Bicuculline and strychnine, antagonists of the postsynaptic inhibitory actions of GABA and glycine, produced convulsions in 1-, 2- and 10-day-old rats following intraperitoneal injection of doses somewhat lower than those required to convulse adult rats. These findings are consistent with other evidence that glycine and GABA are functioning as inhibitory transmitters at least as soon as 1 day after birth.     

Alterations in Uptake and Release Rates for GABA, Glutamate, and Glutamine During Biochemical Maturation of Highly Purified Cultures of Cerebral Cortical Neurons, a GABAergic Preparation

This study demonstrates that virtually homogenous cultures of mouse cerebral neurons, obtained from 15-day-old embryos, differentiate at least as well as cultures which in addition contain astrocytes. This was indicated by glutamate decarboxylase activity which within 2 weeks rose from a negligible value to twice the level in the adult mouse cerebral cortex, and by a gamma-aminobutyric acid (GABA) uptake rate which quadrupled during the second week in culture and reached higher values than in brain slices. Within the same period, the GABA content increased four to five times to 75 nmol/mg protein, and a potassium-induced increase in [14C]GABA efflux became apparent. Although the development was faster than in vivo, optimum differentiation required maintenance of the cultures beyond the age of 1 week. Uptake and release rates for glutamate and glutamine underwent much less developmental alteration. At no time was there any potassium-induced release of radioactivity after exposure to [14C]glutamate, and the glutamate uptake was only slightly increased during the period of GABAergic development. This indicates that exogenous glutamate is not an important GABA precursor. Similarly, glutamine uptake was unaltered between days 7 and 14, although a small potassium-induced release of radioactivity after loading with glutamine suggests a partial conversion to GABA.     

HYDRAZIDE-INDUCED SEIZURES AND CEREBRAL OF LEVELS γ-AMINOBUTYRIC ACID: A RE-EVALUATION

Data have been presented indicating that in chicks the time lag in the onset of seizures after the administration of hydrazides was not caused by a slow penetration of the convulsant agents into the brain. A correlation was evident between the rate of decrease in concentration of cerebral GABA and the susceptibility of chicks to hydrazide-induced seizures. Earlier studies precluding a role for GABA in hydrazide-induced convulsions were re-examined.     

The composition of liver chromatin proteins from embryos, chicks and adult chickens

The chemical composition of chromatin from the livers of 12-, 15- and 19-day-old embryos, of 1-day-old chicks and of adult chickens was analysed. The process of embryonic development is accompanied by an increase in non-histone chromatin proteins and chromatin RNA, as well as in the phosphorus content of chromatin phosphoproteins. The amount of these components decreases in the livers of 1-day-old chicks and adults. Two-dimensional polyacrylamide gel electrophoresis of acid-soluble chromatin proteins showed an increase in the amount of the H1 histone in 19-day-old embryos and adult chickens. Non-histone proteins of embryo liver chromatin showed a high content of the fraction of Mr of about 40 000; this was not the case for adult chickens. The non-histone protein fraction of Mr of about 120 000, characteristic of adult chicken liver proteins, was not found in the livers of 12- and 15-day-old embryos. Non-histone chromatin proteins isolated from the livers of animals of different age exhibited also quantitative differences.     

Release of Endogenous Taurine and γ-Aminobutyric Acid from Brain Slices from the Adult and Developing Mouse

The spontaneous and potassium-stimulated release of endogenous taurine and gamma-aminobutyric acid (GABA) from cerebral cortex and cerebellum slices from adult and developing mice was studied in a superfusion system. The spontaneous release of GABA was of the same magnitude in slices from adult and developing mice, but the spontaneous release of taurine was considerably greater in the adults. The potassium-stimulated release of GABA from cerebral cortex slices was about five times greater in adult than in 3-day-old mice, but the potassium-stimulated release of taurine was more than six times greater in 3-day-old than in adult mice. In cerebellar slices from 7-day-old mice, potassium stimulation also evoked a massive release of taurine, whereas the evoked release from slices from adult mice was rather negligible. Also in cerebellar slices the potassium-stimulated release of GABA exhibited the opposite quantitative pattern. The stimulated release of both GABA and taurine was partially calcium dependent. The results suggest that taurine may be an important regulator of excitability in the developing brain.     

Developmental study of digestive motor response to dietary pattern in young broilers

1. Gastrointestinal (GI) morphometry and motility were measured in young broilers (3, 8 and 15 days old) when they were submitted to three dietary patterns (ad libitum food, acute 48-hr fast and cumulative semi-starvation). 2. All GI regions were hypertrophied when acute or intermittent starvation were applied; lightly when acute starvation was applied and strongly with intermittent starvation. 3. All the 3-, 8- and 15-day-old acutely and intermittently starved chickens increased GI motility at the shortest times (0.5 and 1 hr) after the marker administration, but decreased GI motility at the longest times (2 and 4 hr). 4. The GI motor response of intermittently starved chicks was faster than the observed one in acutely starved chicks. The GI tract of intermittent starved chicks increased its motor response proportionally to the broilers age, while acutely starved chicks decreased their GI motility when the broilers age was increased. 5. A relationship between morphometrical and motor GI responses to dietary pattern has been inferred. From the gizzard and small bowel hypertrophy caused by intermittent starvation, an increased reflex GI motor response can be expected. Acute starvation only caused a light increase of GI motility, because it only increased the gizzard morphometry. 6. We concluded that young chicks respond to acute starvation by means of a short-term mechanism (an increase of GI motor reflexes) and responds to intermittent starvation by means of a medium- and long-term mechanism (a hypertrophy of GI tract and its subsequent increase of GI motor reflexes).     

Effect of hyperbaric oxygen on 2-deoxy-d-glucose andl-glutamate transport in rat cortical synaptosomes

Initial velocities of uptake ofl-glutamic acid and 2-deoxy-d-glucose (2-Dg) have been measured in cortical synaptosomes from rats which had been exposed to oxygen at high pressure (OHP) and compared to similar measurements in normobaric controls. Exposure to OHP had no significant effect on glutamate uptake at any combination of sodium and glutamate used. In contrast, OHP reduced 2-Dg uptake by an average of 17.5%. Although Kt was little affected, OHP exposure reduced apparent maximal transport capacity by 15%. Since hyperbaria with normal pO₂ had no significant effect on uptake, the effect of OHP is an oxygen effect, rather than a pressure effect. The effects of OHP on uptake do not parallel the effects of age; glutamate transport capacity was reduced in aged animals, while 2-Dg transport was unaffected.     

Hematocrit is related to age but not to nutritional condition in greater flamingo chicks

We measured the hematocrit from greater flamingo chicks Phoenicopterus roseus over 4 years to test whether this blood parameter was related to the nutritional condition of chicks, as there are controversial results on whether hematocrit may be used as an index of body condition. We also tested whether hematocrit increased with chick age, as there would be an age-related increase of oxygen demand due to exercising. We found no evidences that hematocrit was related neither to the nutritional nor to the body condition of chicks. Hematocrit increased with chick age, which may be related to the increased requirements of chicks for oxygen delivery during development.     

Kinetics of tert-[35S]Butylbicyclophosphorothionate Binding in the Cerebral Cortex of Newborn and Adult Rats: Effects of GABA and Receptor Desensitization

Abstract: The effects of GABA on the kinetics of tert -[³⁵S]butylbicyclophosphorothionate ([³⁵S]TBPS) binding to the convulsant site of GABA_A receptors were studied in membrane suspensions from the cerebral cortex of newborn (1-day-old) and adult (90-day-old) rats. TBPS dissociation was biphasic in neonates and adults, indicating that more than one interconvertible state of [³⁵S]TBPS binding sites may be present in the cerebral cortex. In the absence of GABA, the fast ( t _1/2, 11 min) and slow ( t _1/2, 77 min) components of TBPS dissociation in newborn rats were approximately fourfold slower than in adults. The acceleration of the dissociation rates caused by 2 µ M GABA, however, was more robust in neonates than in adults (six- to ninefold vs. twofold increase, respectively). Moreover, the dissociation rates of TBPS in membranes preincubated with 2 µ M GABA (dissociation started by adding 40 µ M picrotoxin) were two- to fourfold slower than in membranes preincubated without GABA (dissociation started by adding 40 µ M picrotoxin plus 2 µ M GABA). Taken together, these results suggest that (1) the closed state of GABA_A receptors is associated with a more effective steric barrier for the binding of TBPS in neonates compared with adults, (2) GABA produces a larger acceleration of the binding kinetics of TBPS in neonates than in adults, and (3) long incubations with GABA may cause receptor desensitization, which in turn slows down the dissociation rates of TBPS.     

Cecal Propionic Acid as a Biological Indicator of the Early Establishment of a Microbial Ecosystem Inhibitory toSalmonellain Chicks

Experiments were conducted to evaluate the effects of different competitive exclusion (CE) cultures on the concentration of cecal propionic acid in 3-day-old broiler chicks, and the correlation between cecal propionic acid concentration and protection againstSalmonellacolonization. CE cultures that significantly (P < 0.05) increased cecal propionic acid in 3-day-old chicks decreased (P < 0.05) cecalSalmonellacolonization in 10-day-old chicks compared with the untreated controls. CE cultures that failed to significantly (P > 0.05) increase cecal propionic acid concentrations in 3-day-old chicks failed to protect (P > 0.05) against cecalSalmonellacolonization in 10-day-old chicks compared with untreated controls. A significant (P < .05) correlation (−.88) was found between cecal propionic acid concentration in 3-day-old chicks and cecalSalmonellacolonization in 10-day-old chicks.     

GABA对小鼠大脑皮质中GABA受体胚胎发育的调节

本文用ＧＡＢＡ及其受体激动剂和拮抗剂处理培养的胚胎小鼠大脑皮层神经细胞以及精确计时的妊娠小鼠,用放射配体结合法检测ＧＡＢＡＡ及ＧＡＢＡＢ的结合位点数目,研究了ＧＡＢＡ对小鼠大脑皮层ＧＡＢＡ受体胚胎发育的调节作用,结果表明：①ＧＡＢＡ可使培养１５—１７天妊龄的胚胎小鼠大脑皮层神经细胞及出生第１天的仔鼠大脑皮层中的ＧＡＢＡＡ及ＧＡＢＡＢ受体数目增加,这种作用可被蝇蕈醇（Ｍｕｓ）及巴氯芬（Ｂａｃ）分别模拟,对ＧＡＢＡＡ受体的作用可为荷包牡丹碱（Ｂｉｃ）所阻断;②用ＧＡＢＡ处理妊娠７—１３天的小鼠,仔鼠出生第１天其大脑皮层的ＧＡＢＡＡ及ＧＡＢＡＢ受体数目均无变化;③用ＧＡＢＡ处理妊娠１４—１９天的小鼠,仔鼠出生的第１天其大脑皮层中的ＧＡＢＡＡ受体数目增加而ＧＡＢＡＢ受体数目不变;④用ＧＡＢＡ处理妊娠７－１９天的小鼠,仔鼠出生第１天其大脑皮层中ＧＡＢＡＡ及ＧＡＢＡＢ受体数目增加。这说明在胚胎发育的特定时期内,ＧＡＢＡ可诱导其受体数目的增加,这个作用是由ＧＡＢＡ受体调节的。     

Light and dark adaptation influences GABA receptor sites in the chick retina

The aim of the present study was to investigate the effect of environmental conditions such as light-and-dark-adaptation on the plasticity of GABA receptor sites in the chick retina. In chicks exposed to light for 5 hr (light-adapted), specific [³H]GABA binding was increased by 35% in comparison to the binding found in chicks maintained in darkness (dark-adapted). Conversely, in the retina of chicks exposed to darkness for 5 hr, specific [³H]GABA binding was decreased by 28% with respect to that found in chicks kept in the light. Scatchard analysis of the binding data revealed that the affinity of GABA for its receptor binding site was higher in the retinas of light-adapted chicks than in those of dark-adapted chicks (K _d values of 19.20±1.23 and 27.20±1.47 nM, respectively). On the contrary, the maximal number of binding sites (B_max) remained unchanged in light- and dark-adapted chicks (5.2±0.10 and 5.3±0.15 pmol/mg protein, respectively). These results suggest the involvement of GABA receptors in the regulation of visual function.Special Issue dedicated to Prof. Eduardo DeRobertis     

Effect of 6-hydroxydopamine on brain and blood catecholamine, ammonia, and amino acid metabolism in rats subjected to high pressure oxygen induced convulsions

Effects of 6-hydroxydopamine (6-OHDA) on rat brain and blood adrenaline (A), noradrenaline (NA), ammonia (NH3), gamma-aminobutyric acid (GABA), and amino acid metabolism prior to and after high pressure oxygen (OHP) induced convulsions have been studied. 6-OHDA reduces GABA and glutamate (Glu) rior to OHP exposure in rat brain so that the concentration is even equal to that seen in nondrugged animals after convulsion. Concomitantly, 6-OHDA reduces the latency of OHP-induced convulsion significantly, and increases brain NH3, glutamine, and asparagine significantly. Although 6-OHDA, in increasing dosage, elevates blood A concentration, convulsion produces a significant further increase in A. Blood NA was not significantly changed in drugged, convulsed animals and was much less than blood NA concentrations in nondrugged convulsed animals. Increasing doses of 6-OHDA also increase NH3 in the blood significantly and convulsion increases its concentration further. Latency of convulsion seems to be related to certain monoamine levels since in some drugged animals where A and total catecholamines are still reduced 96 h after the first of two doses of 6-OHDA, NA concentrations are recovered to relatively normal and the convulsion latency time is also increased although it remains significantly abbreviated from undrugged animals' convulsion time. Low brain GABA levels seem to be a prime effector of convulsive activity.     

Oxygen consumption rates of adults and chicks during brooding in king quail (Coturnix chinensis)

Oxygen consumption rates were measured in chicks (0–7 days of age), and in non-brooding and brooding adults. Brooded chicks maintained a constant oxygen consumption rate at a chamber ambient temperature of 10–35°C (0–5 days of age: 2.95ml O₂·g^-1·h^-1 and 6–17 days of age: 5.80 ml O₂·g^-1·h^-1) while unbrooded chicks increased oxygen consumption rate at ambient temperature below 30°C to double the brooded oxygen consumption rate at 25 and 15°C for chicks < 5 days of age and>5 days of age, respectively. The massspecific oxygen consumption rate of breeding male and females (non-brooding) were significantly elevated within the thermoneutral zone thermal neutral zone (28–35°C) in comparison to non-breeding adults. Below the thermal neutral zone, oxygen consumption rate was not significantly different. The elevation in oxygen consumption rate of breeding quail was not correlated with the presence of broodpatches, which developed only in females, but is a seasonal adjustment in metabolism. Male and females that actively brooded one to five chicks had significantly higher oxygen consumption rate than non-brooding quail at ambient temperature below 30°C. Brooding oxygen consumption rate was constant during day and night, indicating a temporary suppression of the circadian rhythm of metabolism. Brooding oxygen consumption rate increased significantly with brood number, but neither adult body mass nor adult sex were significant factors in the relationship between brooding oxygen consumption rate and ambient temperature. The proportion of daylight hours that chicks were brooded by parents was negatively correlated with ambient temperature. After chicks were 5 days old brooding time was reduced but brooding oxygen consumption rate was unchanged. Heat from the brooding parent appeared to originate mainly from the apteria under the wings and legs rather than the broodpatch. The parental heat contribution to chick temperature regulation below the chicks' thermal neutral zone is achieved by increasing parental thermal conductance by a feedback control similar to that suggested for the control of egg temperature via the brood-patch. It is concluded that the brooding period is an energetic burden to parent quail, and the magnitude of the cost increases directly with brood number and inversely with ambient temperature during this period. The oxygen consumption rate of brooding parents was 5.80–6.90 ml O₂·g^-1·h^-1 (ambient temperature 10–15°C) at night and up to 5.10 ml O₂·g^-1·h^-1 (ambient temperature 18°C) during the day, which are 100 and 40% higher than non-brooding birds, respectively.Abbreviations bm body mass - SMR standard metabolic rate - T _a ambient temperature - T _b body temperature - I/O₂ oxygen consumption rate - C _wet wet thermal conductance - TNZ thermal neutral zone - ANOVA analysis of variance - ANCOVA analysis of covariance