Dopaminergic Properties of Cultured Rat Carotid Body Chemoreceptors Grown in Normoxic and Hypoxic Environments

Abstract: Using dissociated carotid body (CB) cultures prepared from neonatal (postnatal days 5–7; P7) or juvenile (postnatal day 19–20; P20) rats, we compared catecholaminergic properties and mechanisms of O₂ sensing in glomus cells grown in normoxic (Nox; 20% O₂) and chronically hypoxic (CHox; 6% O₂) environments for up to 2 weeks. In Nox cultures, basal dopamine (DA) release, determined by HPLC and normalized to the number of tyrosine hydroxylase-positive glomus cells present, was similar for P7 and P20 cultures (∼0.3 pmol/1,000 cells/15 min) and was unaffected by culture duration (2 vs. 12 days). Acute hypoxia (5 and 10% O₂) caused a dose-dependent stimulation (6× and 3× basal, respectively) in DA release, that was inhibited by nifedipine (10 µ M ). DA release was also stimulated by high extracellular K⁺ (30 m M ) and iberiotoxin (200 n M ), a selective blocker of P o ₂-regulated, Ca-dependent K⁺ channel in glomus cells. The stimulatory effect of iberiotoxin was similar to 5% O₂ in P20 cultures, but substantially less (about one-half) in P7 cultures. In contrast, in CHox cultures, basal DA release was substantially elevated, ∼8× Nox levels, although this did not correlate with significant differences in stores. Further, whereas acute hypoxia (5% O₂) and high K⁺ also stimulated DA release in CHox cultures (∼2× and ∼3× basal), iberiotoxin (200 n M ) did not. Thus, after chronic hypoxia in vitro, there is an enhanced basal catecholamine release and an apparent down-regulation of functional Ca-dependent K⁺ channels in CB chemoreceptors. These cellular adaptations may relate to changes in CB chemosensitivity during chronic hypoxemia.     

Bcl-2 Protects Neural Cells from Cyanide/Aglycemia-Induced Lipid Oxidation, Mitochondrial Injury, and Loss of Viability

Abstract: The protooncogene bcl-2 rescues cells from a wide variety of insults. Recent evidence suggests that the mechanism of action of Bcl-2 involves antioxidant activity. The involvement of free radicals in ischemia/reperfusion injury to neural cells has led us to investigate the effect of Bcl-2 in a model of delayed neural cell death. We have examined the survival of control and bcl-2 transfectants of a hypothalamic tumor cell line, GT1-7, exposed to potassium cyanide in the absence of glucose (chemical hypoxia/aglycemia). After 30 min of treatment, no loss of viability was evident in control or bcl-2 transfectants; however, Bcl-2-expressing cells were protected from delayed cell death measured following 24–72 h of reoxygenation. Under these conditions, the rate and extent of ATP depletion in response to treatment with cyanide in the absence of glucose and the rate of recovery of ATP during reenergization were similar in control and Bcl-2-expressing cells. Bcl-2-expressing cells were protected from oxidative damage resulting from this treatment, as indicated by significantly lower levels of oxidized lipids. Mitochondrial respiration in control but not Bcl-2-expressing cells was compromised immediately following hypoxic treatment. These results indicate that Bcl-2 can protect neural cells from delayed death resulting from chemical hypoxia and reenergization, and may do so by an antioxidant mechanism. The results thereby provide evidence that Bcl-2 or a Bcl-2 mimetic has potential therapeutic application in the treatment of neuropathologies involving oxidative stress, including focal and global cerebral ischemia.     

Translational arrest in hypoxic potato tubers is correlated with the aberrant association of elongation factor EF-1α with polysomes

Translation elongation factor EF-1 became stably associated with potato tuber polysomes at the onset of hypoxia, coincident with a sharp rise in lactate and decrease in tissue pH. This aberrant association of EF-1 with polysomes also occurred when aerobic tuber extracts were acidified in vitro. Upon resumption of protein synthesis, an increase in the steady-state levels of EF-1, and expression of an EF-1/GUS transgene was observed. These results indicate that translational arrest results from to the failure of EF-1 to dissociate from ribosomes during the elongation cycle, and that restoration of protein synthesis is coordinated with expression of EF-1.     

Ventilatory responses to ambient oxygen in stressed and fully settled shore crabs Carcinus maenas (L.)

Scaphognathite activity and ventilatory responses to changes of ambient oxygen have been studied in stressed and fully settled crabs, Carcinus maenas (L.). Compared with resting, fully settled animals, resting stressed crabs exhibited very high values of scaphognathite beat frequency, negative hydrostatic pressure in the gill chamber and amount of time spent ventilating, suggesting a much elevated ventilatory flow rate. Unlike fully settled animals, stressed crabs did not show significant ventilatory responses to changes of ambient oxygenation.     

Effects of root hypoxia and a low P supply on relative growth, carbon dioxide exchange rates and carbon partitioning in Pinus serotina seedlings

The present study was conducted to determine how 10 weeks of root hypoxia and a low P supply altered relative growth, and carbon acquisition and partitioning in a moderately flood tolerant pine. Pond pine (Pinus serotina Michx.) seedlings were grown in continuously flowing solution culture at 5 or 100 μM P, under aerobic or hypoxic solution conditions. Staggered harvests were used to ascertain changes in biomass allocation and relative growth over time. Carbon dioxide exchange rates (CER) were determined by infrared gas analysis, and needles were analyzed for inorganic P (Pi), sucrose, reducing sugars and starch. Although aeration treatment had no significant effect on shoot dry weight or shoot ontogeny, root dry weight of hypoxic seedlings was significantly lower than that of aerobic seedliings after 8 weeks, regardless of the P treatment. Mean relative growth rates (RGR) of roots in the high P treatment initially decreased under hypoxia, but recovered by the sixth week with the production of adventitious roots. Two weeks of hypoxic growth conditions decreased CER and stomatal conductances of seedlings in the high P treatment by more than 30% relative to their aerobic counterparts. Stomatal closure was not accompanied by a decrease in intracellular CO₂, but was accompanied by an increase in starch accumulation. Recoveries of CER, stomatal conductance and carbohydrate metabolism coincided with the recovery of root growth. Low P growth conditions did not significantly affect shoot or root dry weight until the sixth week of treatment. However, differences in seedling RGR, particularly needle RGR, were discernable during the first 2 weeks. Low P treatment effects on CER paralleled changes in needle RGR, with needle RGR more affected than CER. After 6 weeks, CER of aerobically grown seedlings in the low P treatment were only 15% lower than CER of seedlings in the high P treatment, despite a 31% and 75% reduction in needle RGR and Pi concentrations, respectively. Increased starch concentrations of recently expanded needles at this time were probably a result of diminished growth. The inhibitory effect of a low P supply on shoot growth, more specifically on needle expansion and emergence of new fascicular needles, probably limited net carbon fixed per plant more than any direct effect of low P on CER per se.     

Lethal oxygen levels at different temperatures and the preferred temperature during hypoxia of the Atlantic cod, Gadus morhua L.

The behavioural thermoregulation of Atlantic cod Gadus morhua L. was investigated in a shuttlebox at normoxia and at three levels of hypoxia: 30, 20 and 15% oxygen saturation.
The preferred temperatures at normoxia, 30, 20 and 15% oxygen saturation were 13·9, 13·1. 10·0 and 8·8° C, respectively.
A decrease in metabolism and an increased blood oxygen affinity are among the physiological advantages of selecting a lower temperature during hypoxia. Furthermore the chances of surviving low oxygen saturations are better at low temperatures.
In natural environments, this behaviour may result in habitat shifts of fish living in heterothermal environments with changing oxygen saturations, especially in coastal areas with eutrophication, as for example the Baltic Sea.     

Effect of N-Methyl-D-Aspartate Receptor Blockade on the Control of Cerebral O2 Supply/Consumption Balance During Hypoxia in Newborn Pigs

Using dizocilpine (MK-801), we tested the hypothesis that N-methyl-D-aspartate (NMDA) receptors are important controllers of cerebral O₂ supply/consumption balance in newborn piglets both during normoxia and hypoxia. Twenty-five 2 to 7-day-old piglets were anesthetized and divided into four groups: (1) Normoxia (n = 6), (2) Normoxia + MK-801 (n = 6), (3) Hypoxia (n = 6), and (4) Hypoxia + MK-801 (n = 7). Regional cerebral blood flow (rCBF) in ml/min/100 g was measured using ¹⁴C-iodoantipyrine, and we determined arterial and venous O₂ saturations by microspectrophotometry, calculating cerebral O₂ consumption (VO₂) in ml O₂/min/100 g in the cortex, hypothalamus and pons. MK-801 did not significantly affect regional VO₂ or rCBF in normoxic piglets. Hypoxia resulted in an increase in local rCBF compared to controls: from 41 ± 6 to 103 ± 18 in the cortex; 34 ± 7 to 101 ± 20 in the hypothalamus; and 45 ± 10 to 95 ± 11 in the pons. Pretreatment with MK-801 abolished this hypoxic flow effect in the cortex (51 ± 2) and hypothalamus (49 ± 5), but not in the pons (91 ± 17). Similar results were observed for VO₂ with control values of 1.9 ± 0.3, 1.6 ± 0.2 and 2.1 ± 0.3 for the cortex, hypothalamus and pons respectively. Hypoxia resulted in an increase in the VO₂ to 3.9 ± 0.4 (cortex), 3.8 ± 0.6 (hypothalamus) and 3.9 ± 0.8 (pons). Pretreatment with MK-801 prior to hypoxia abolished these effects in the cortex (2.1 ± 0.2) and hypothalamus (2.1 ± 0.2), but not in the pons (2.9 ± 0.2). These findings suggest that NMDA receptors may play a role in the control of cerebral metabolism during hypoxia in this immature porcine model.     

Protection Against Developmental Deficiencies by a Lipophilic VIP Analogue

Stearyl-Nle-VIP (SNV) is a novel agonist of vasoactive intestinal peptide (VIP) exhibiting a 100-fold greater potency than the parent molecule and specificity for a receptor associated with neuronal survival. Here, the developmental and protective effects of SNV were investigated in vivo using two models of developmental retardation, hypoxia and cholinergic blockade. In both cases chronic administration of SNV during development provided protective effects. Water maze experiments on the weaned animals have demonstrated a prophylactic action for SNV and enhancement of spatial memory in animals exposed to a cholinotoxin. SNV may act by providing neuroprotection, thereby improving cognitive functions. This work is dedicated to Prof. R.J. Wurtman whose inspiration and leadership in the field of neuroscience and cognition is beyond comparison.     

一氧化氮在缺氧耐受形成中的作用

分别给小鼠腹腔注射Ｌ－精氨酸（５０ｍｇ／ｋｇ）、Ｌ－精氨酸类似物Ｎω－ＮＩＴＲＯ－Ｌ－ＡＲＧＩＮＩＮＥ（５０ｍｇ／ｋｇ）,３０ｍｉｎ后进行急性缺氧重复实验。结果发现,Ｌ－精氨酸、Ｌ－精氨酸类似物组第一次缺氧耐受性时间平均为１１ｍｉｎ、１６ｍｉｎ,分别近似于、高于盐水对照组小鼠的第一次平均耐受时间（１２ｍｉｎ）。Ｌ－精氨酸组、Ｌ－精氨酸类似物组第二、三、四次重复缺氧的耐受时间分别为其各自第一次缺氧耐受时间的２．０、２．７、３．１;２．６、３．７、４．９倍,分别略低于、明显高于对照组（对照组第二、三、四次重复缺氧的耐受时间分别为其第一次缺氧耐受时间的２．２、３．１、３．６倍）。用荧光方法测定正常对照组第一、二、三、四次缺氧组脑内一氧化氮的含量,结果发现,一次缺氧组一氧化氮含量明显高于正常对照组,二、三、四次缺氧组,一氧化氮含量比一次缺氧组明显回降,结果提示,脑内一氧化氮减少可能有助于缺氧耐受性的形成。     

急性缺氧暴露不同时间家兔血浆心钠素、抗利尿激素、醛固酮的变化

本实验观察了８０只家兔在急性缺氧６、１２、２４、３６、４８、６０、７１ｈ后肺指数、血浆心钠素（ＡＮＰ）、抗利尿激素（ＡＶＰ）、醛固酮（ＡＬＤ）及尿量的变化。结果表明：在缺氧２４－７２ｈ,肺指数明显升高,尿量减少;缺氧１６ｈ,血浆ＡＮＰ明显升高;而缺氧４８和６０ｈ无ＡＮＰ升高现象。缺氧７２ｈ,血浆ＡＮＦ又明显高于缺氧前水平;血浆ＡＶＰ只在缺氧２４ｈ明显升高;血浆ＡＬＤ未见显著性变化。这些结果提示：在缺氧状态下,ＡＮＰ、ＡＶＰ的释放均与缺氧暴露的时间有关。这些激素的平衡失调可能与急性缺氧性肺水肿的发生有关。