Effect of alpha adrenergic blockade on brain blood flow and ventilation during hypoxia in newborn piglets.

The influence of cardiovascular changes on ventilation has been demonstrated in adult animals and humans (Jones, French, Weissman & Wasserman, 1981; Wasserman, Whipp & Castagna 1974). It has been suggested that neonatal hypoxic ventilatory depression may be related to some of the hemodynamic changes that occur during hypoxia (Brown & Lawson, 1988; Darnall, 1985; Suguihara, Bancalari, Bancalari, Hehre & Gerhardt, 1986). To test the possible relationship between the cardiovascular and ventilatory response to hypoxia in the newborn, eleven sedated spontaneously breathing piglets (age: 5.9 +/- 1.6 days; weight: 1795 +/- 317 g; SD) were studied before and after alpha adrenergic blockade with phenoxybenzamine. Minute ventilation (VE) was measured with a pneumotachograph, cardiac output (CO) by thermodilution and total and regional brain blood flow (BBF) with radiolabeled microspheres. Measurements were performed while the animals were breathing room air and after 10 min of hypoxia induced by breathing 10% O2. Hypoxia was again induced one hour after infusion of phenoxybenzamine (6 mg/kg over 30 min). After 10 min of hypoxia, in the absence of phenoxybenzamine, the animals responded with marked increases in VE (P less than 0.001), CO (P less than 0.001), BBF, and brain stem blood flow (BSBF) (P less than 0.02). However, the normal hemodynamic response to hypoxia was eliminated after alpha adrenergic blockade. There were significant decreases in systemic arterial blood pressure, CO, and BBF during hypoxia after phenoxybenzamine infusion; nevertheless, VE increased significantly (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Correlation of plasma and CSF prolactin with CSF GABA during neuroleptic treatment

We measured serum and CSF prolactin and CSF 5HIAA, HVA and GABA at two time points separated by an average period of 21 days during the beginning of neuroleptic treatment in 26 psychotic patients. Prolactin levels were higher in females at both time points, and there was little evidence of tolerance during the measurement period. The prolactin values showed considerable intercorrelation. CSF GABA tended to be negatively correlated with prolactin values, particularly in male subjects. There were few significant correlations between the prolactin measures and CSF metabolites or clinical ratings.     

Modulation of respiration during brain hypoxia

This review is a summary of the effects of brain hypoxia on respiration with a particular emphasis on those studies relevant to understanding the cellular basis of these effects. Special attention is given to mechanisms that may be responsible for the respiratory depression that appears to be the primary sequela of brain hypoxia in animal models. Although a variety of potential mechanisms for hypoxic respiratory depression are considered, emphasis is placed on changes in the neuromodulator constituency of the respiratory neuron microenvironment during hypoxia as the primary cause of this phenomenon. Hypoxia is accompanied by a net increase in neuronal inhibition due to both decreased excitatory and increased inhibitory neuromodulator levels. A survey of hypoxia-tolerant cellular systems and organisms suggests that hypoxic respiratory depression may be a manifestation of the depression of cellular metabolism, which appears to be a major adaptation to limited oxygen availability in these systems.     

Intravenous nanosomes of quercetin improve brain function and hemodynamic instability after severe hypoxia in newborn piglets

Perinatal asphyxia is a major cause of death and neurological morbidity in newborns and oxidative stress is one of the critical mechanisms leading to permanent brain lesions in this pathology. In this context we have chosen quercetin, a natural antioxidant, known also by its brain protective effects to study its potential as a therapy for brain pathology provoked by severe hypoxia in the brain. To overcame the difficulties of quercetin to access the brain, we have developed lecithin/cholesterol/cyclodextrin nanosomes as a safe and protective vehicle.We have applied the nanosomal preparation intravenously to newborn piglets submitted to a severe hypoxic or ischemic/hypoxic episode and followed them for 8 or 72 h, respectively. Either towards the end of 8 h after hypoxia or up to 72 h after, electroencephalographic amplitude records in animals that received the nanosomes improved significantly. Animals receiving quercetin also stabilized blood pressure and recovered spontaneous breathing. In this experimental group mechanical ventilation assistance was withdrawn in the first 24 h while the hypoxic and vehicle groups required more than 24 h of mechanical ventilation. Three days after the hypoxia the suckling and walking capacity in the group that received quercetin recovered significantly compared with the hypoxic groups. Pathological studies did not show significant differences in the brain of newborn piglets treated with nanosomes compared with hypoxic groups. The beneficial effects of quercetin nanosomal preparation after experimental perinatal asphyxia show it as a promising putative treatment for the damaged brain in development.     

Endogenous opioids and ventilatory adaptation to prolonged hypoxia in goats

To investigate whether endogenous opioid peptides mediate time-dependent changes in ventilatory control during prolonged hypoxia, we studied four adult goats at rest during 14 days at simulated high altitude in a hypobaric chamber (PB approximately 450 Torr). Arterial PCO2 fell during the first several hours of hypoxia, remained stable over the next 7 days, and then rose slightly (but without statistical significance) by day 14. Ventilatory responsiveness to CO2 increased during the first week of hypoxia. By day 14, while still greater than control, the ventilatory response to CO2 was less than that observed on day 7. Immunoactive beta-endorphin levels in plasma and CSF did not change during the 14-day period. Administration of naloxone on day 14 did not restore the ventilatory response to CO2 to the level observed during the first week of acclimatization. We conclude that in adult goats, time-dependent changes in ventilatory response to CO2 during acclimatization to prolonged hypoxia are not primarily attributable to alterations in endogenous opioid peptide activity.     

Neurohypophyseal peptide levels in CSF and plasma during passive avoidance behavior in rats

Levels of vasopressin (AVP), oxytocin (OXT), and neurophysin (NP) in CSF and plasma of rats were determined during acquisition and retention of passive avoidance behavior. None of the levels of neurohypophyseal peptides in CSF were changed either during the adaptation period, or during acquisition or the retention of this behavior. Moreover, no differences were found in hormone levels in CSF of the various groups of rats subjected to different shock intensities during the acquisition trial. The marked differences in individual latencies of nonavoiding rats, and the differences in latencies due to a different shock intensity applied during the learning trial were not reflected by changes in CSF hormone levels. Neither AVP nor NP levels in plasma were affected by the different shock intensities applied, when measured at 20 min after the learning trial. In contrast, a decrease in plasma OXT levels was observed after application of a shock intensity of 0.25 mA during the learning trial. During retention of the passive avoidance response plasma levels of AVP, OXT and NP were not different from the levels found in the nonshocked groups. It is suggested that under the conditions used in this study the CSF is apparently not involved in the distribution of neurohypophyseal peptides to their possible sites of behavioral action in the brain.     

Proopiomelanocortin (POMC)-related peptides in the brain of the rainbow trout, Salmo gairdneri

We have investigated the presence of ACTH, -MSH and β-endorphin, three peptides which derive from the multifunctional precursor protein proopiomelanocortin (POMC) in the brain of the rainbow trout Salmo gairdneri. Using both the indirect immunofluorescence and peroxidase-antiperoxidase techniques, a discrete group of positive cells was identified in the hypothalamus, within the anterior part of the nucleus lateralis tuberis. -MSH-containing neurons represented the most abundant immunoreactive subpopulation. Coexistence of -MSH, ACTH and β-endorphin was observed in the lateral part of the nucleus. ACTH- and β-endorphin-containing cells were mainly distributed in the rostral and caudal regions of the nucleus. In the medial portion of the nucleus lateralis tuberis, numerous cells were only stained for -MSH. Moderate to dense plexuses of immunoreactive fibers were observed in the ventral thalamus and the floor of the hypothalamus. Some of these fibers projected towards the pituitary. The concentrations of ACTH, -MSH and β-endorphin-like immunoreactivities were measured in microdissected brain regions by means of specific radioimmunoassays. Diencephalon, mesencephalon and medulla oblongata extracts gave dilution curves which were parallel to standard curves. The highest concentrations of POMC-derived peptides were found in the diencephalon (-MSH: 4.28±0.43 ng/mg prot.; ACTH: 1.08±0.09 ng/mg prot.; β-endorphin: 1.02±0.1 ng/mg prot.), while lower concentrations were detected in the mesencephalon, medulla oblongata and telencephalon. The present results demonstrate that various peptides derived from POMC coexist within the same cell bodies of the fish hypothalamus. Taken together, these data suggest that expression and processing of POMC in the fish brain is similar to that occurring in pituitary melanotrophs.     

Depression of ventilatory responses after daily, cyclic hypercapnic hypoxia in piglets.

Ventilatory responses (VRs) were measured via a sealed face mask and pneumotachograph in 30 unsedated, mixed-breed miniature piglets at 12.6 +/- 2.3 days of age (day 1) and then repeated after seven daily 24-min exposures to 10% O(2)-6% CO(2) [hypercapnic hypoxia (HH)]. Arterial blood was sampled at baseline, after 10 min of exposure, and after 10 min of recovery. VRs included hypoxia (10% O(2) in N(2)), hypercapnia (6% CO(2) in air), and HH (10% O(2)-6% CO(2)-balance N(2)). Treatment groups (n = 10 each) were exposed to 24 min of HH from day 2 to 8 as sustained HH (24 min of HH and then 24 min of air) or cyclic HH (4 min of HH alternating with 4 min of air). Day 1 and 9 data were compared in treatment and control groups. After cyclic HH, respiratory responses to CO(2) were reduced during hypercapnia and during HH (P < 0.001 vs. control for minute ventilation in both). In both treatment groups, time to peak minute ventilation was delayed in hypoxia (P = 0.02, ANOVA), and response amplitude was increased (P < 0.001 and P = 0.003, sustained and cyclic HH, respectively, vs. control). Respiratory pattern was also altered during the VRs and among treatment groups. Stimulus presentation characteristics exert effects on VRs that are independent of those elicited by daily HH.     

Oxidative phosphorylation system during steady-state hypoxia in the dog brain

The relationship between biochemical and physiological responses and tissue O2 during hypoxia was investigated in vivo in the dog brain by 31P nuclear magnetic resonance (NMR) spectroscopy. Our findings demonstrate how ATP synthesis in the brain can be maintained during hypoxia because of compensatory changes in NADH, ADP, and Pi. Eleven beagle dogs were anesthetized and mechanically ventilated, and a steady-state graded hypoxia was induced by decreasing the fraction of inspired O2 (FIO2) stepwise at 20-min intervals. Biochemical metabolites were measured using 31P-NMR and fluorescence spectroscopy. When sagittal sinus O2 partial pressure (PVO2) had decreased to 15 Torr, NADH increased by 30%, Pi increased by 50%, and phosphocreatine (PCr) decreased by 20%. In contrast, ATP remained constant. There was a 10% increase in ADP in dogs that maintained a steady temperature, but ADP decreased by as much as 30% in dogs in which body temperature decreased with the falling PVO2. PCr/Pi was logarithmically related to the phosphorylation potential during steady-state hypoxia. Compensation for the O2 lack is attributed to increases in ADP, Pi, and NADH as a result of the reciprocal relationship of the Michaelis-Menten equation. If the Michaelis-Menten constants (Km) of ADP, Pi, and O2 are the same as determined in vitro in mitochondria, the minimum brain cytosolic O2 capable of maintaining a steady-state ATP is near its Km (0.1 Torr) at a PVO2 of 7.5 Torr. At this critical O2 level, PCr/Pi is 0.9, intracellular pH is 6.75, phosphorylation potential is 38.5 mM-1, and the calculated maximum velocity of ATP formation by oxidative phosphorylation is 55% of normal.     

Measurement of rat plasma adenosine levels during normoxia and hypoxia.

A stop solution containing EDTA, EGTA, dipyridamole, erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) and d,l-alpha-glycerophosphate has been used to prevent adenosine formation and loss from rat femoral arterial blood samples prepared for measurement of plasma adenosine levels. The femoral arterial plasma adenosine concentration in normoxic rats was 79.2 +/- 12.7 nM. During a 5 min period of hypoxia (8% oxygen) plasma adenosine increased to 190.2 +/- 32.2 nM. A resting plasma adenosine level of circa 80 nM, which is 10X lower than most previous estimates, approximates the threshold levels of adenosine required for arterial dilation.     

NMDA receptor modification in the fetal guinea pig brain during hypoxia

The effect of maternal hypoxia on the modification of the fetal brain cell membrane N-methyl-d-aspartate (NMDA) receptor and its modulatory sites was investigated. Experiments were conducted in pregnant guinea pigs of 60 days of gestation. Guinea pig fetuses were exposed to maternai hypoxia (FiO₂=7%) for 60 minutes. Tissue hypoxia in the fetal brain was documented biochemically by decreased levels of ATP and phosphocreatine (91.3% and 88.6% lower than normoxia, respectively). MK-801 binding characteristics (Bmax = number of receptors, Kd = affinity of receptor) were used as an index of NMDA receptor modification. P2 membrane fraction was prepared from the cortex of normoxic and hypoxic fetal brain and washed thoroughly before carrying out the binding assay. In hypoxic brains, Bmax decreased from the normoxic control level 0.79±0.03 pmol/mg protein to 0.58±0.03 pmol/mg protein (P<0.005) and Kd value decreased (increased affinity) from 8.54±0.27 nM to 4.01±0.23 nM (P<0.005) respectively. The MK-801 binding in the absence of added glutamate and glycine in hypoxic brain was 100% higher as compared to controls, indicating an increased sensitivity of the NMDA receptor to activation. The spermine dependent maximum activation of the NMDA receptor increased to 44% in the hypoxic animals as compared to 25% in controls. The Mg²⁺ response of the NMDA receptor was not affected by hypoxia. The increased affinity and increased basal activation (tone) of the NMDA receptor during hypoxia, as well as its increased activation by spermine, would hyperstimulate the NMDA receptor-ion channel complex function which could increase the susceptibility of the fetal brain to hypoxia. The results of this study indicate that hypoxia causes differential and selective modification of specific sites (recognition, co-activator, and modulatory) of the NMDA receptor ion channel complex. The hypoxia-induced modification of the NMDA receptor modulatory sites appears to be the potential mechanism of neuroexcitotoxicity.     

Extracellular potassium homeostasis in the cat medulla during progressive brain hypoxia

Brain extracellular potassium [( K+]ec) in the ventral respiratory group of the medulla and the phrenic neurogram were recorded in anesthetized vagotomized peripherally chemodenervated ventilated cats during progressive isocapnic carbon monoxide (CO) hypoxia. During hypoxia, the phrenic neurogram was progressively depressed and became silent when arterial O2 content (CaO2) was reduced by 62 +/- 3% (SE). Gasping was seen in the phrenic neurogram when CaO2 was reduced by 78 +/- 1%. Medullary [K+]ec, an indicator of energy production failure due to O2 insufficiency, was 3.2 +/- 0.4 mM before hypoxia and was statistically unchanged at the onset of phrenic apnea during CO hypoxia (4 +/- 0.7 mM). By the onset of gasping, [K+]ec had increased to 6.1 +/- 1 mM, a value that tended to be different from control (P less than 0.1). After initiation of gasping, the rate of rise of [K+]ec increased, and [K+]ec reached a maximum value of 14.3 +/- 2.7 mM before hypoxia was terminated. With reoxygenation, [K+]ec returned to control levels within 20 min. On the basis of these results, we have drawn two major conclusions. 1) Hypoxic depression to the point of phrenic apnea does not appear to be caused by medullary energy insufficiency as measured by loss of [K+]ec homeostasis. 2) The rapid rise in [K+]ec in the medulla that characterizes severe hypoxia is closely associated with the onset of gasping in the phrenic neurogram, suggesting that gasping may serve as a marker for loss of medullary ionic homeostasis and thus onset of medullary energy insufficiency during hypoxia.     

Kainate receptor modification in the fetal guinea pig brain during hypoxia

The present study tests the hypothesis that hypoxia alters the high-affinity kainate receptors in fetal guinea pig brain. Experiments were conducted in normoxic and hypoxic guinea pig fetus at preterm (45 days of gestation) and term (60 days of gestation). Hypoxia in the guinea pig fetus was induced by exposure to maternal hypoxia (FiO₂=7%) for 60 min. Brain tissue hypoxia in the fetus was documented biochemically by decreased levels of ATP and phosphorreatine. [³H]-Kainate binding characteristics (Bmax=number of receptors, Kd=dissociation constant) were used as indices of kainate receptor modification. P₂ membrane fractions were prepared from the cortex of normoxic and hypoxic fetuses and were washed six times prior to performing the binding assays. [³H]kainate binding was performed at 0°C for 30 min in a 500 l medium containing 50 mM Tris-HCl buffer, 0.1 mM EDTA (pH 7.4), 300 g protein and varying concentrations of radiolabelled kainate ranging from 1 to 200 nM. Non-specific binding was determined in the presence of 1.0 mM glutamate. During brain development from 45 to 60 days gestation, Bmax value increased from 330±16 to 417±10 fmoles/mg protein; however, the Kd was unchanged (8.2±0.4 vs 8.8±0.5 nM, respectively). During hypoxia at 60 days, the Kd value significantly increased as compared to normoxic control (15.5±0.7 vs 8.8±0.5 nM, respectively), whereas the Bmax was not affected (435±12 vs 417±10 fmol/mg protein, respectively). At 45 days, hypoxia also increased the Kd (11.9±0.6 vs 8.2±0.4 nM) without affecting the Bmax (290±15 vs 330±16 fmol/mg protein, respectively). The results show that the number of kainate receptors increase during gestation without change in affinity and demonstrate that hypoxia modifies the high-affinity kainate receptor sites at both ages; however the effect is much stronger at 60 days (term). The decreased affinity of the site could decrease the kainate receptor-mediated fast kinetics of desensitization and provide a longer period for increased Na⁺-influx, leading to increased accumulation of intracellular Ca²⁺ by reversal of the Na⁺–Ca²⁺ exchange mechanism. In addition, Kd values for kainate-type glutamate receptor sites are 30–40 fold lower (i.e. higher affinity) than those for NMDA-displaceable glutamate sites. The higher affinity suggests that the activation of the kainate-type glutamate receptor during hypoxia could precede initiation of NMDA receptormediated excitotoxic mechanisms. We propose that hypoxia-induced modification of the high affinity kainate receptor in the fetus is a potential mechanism of neuroexcitotoxicity.     

A mathematical model of the impact of novel treatments on the A beta burden in the Alzheimer's brain,CSF and plasma

With the advent of novel therapies for Alzheimer’s disease, there is a pressing need for biomarkers that are easy to monitor, such as the amyloid-beta (Aβ) levels in the cerebrospinal fluid (CSF) and plasma. To gain a better understanding of the explanatory power of these biomarkers, we formulate and analyze a compartmental mathematical model for the Aβ accumulation in the brain, CSF and plasma, throughout the course of Alzheimer’s treatment. Our analysis reveals that the total Aβ burden in the brain is dictated by a unitless quantity called the polymerization ratio, which is the product of the production and elongation rates divided by the product of the fragmentation and loss rates. In this ratio, the production rate and loss rate include a source and sink term, respectively, related to the intercompartmental transport. Our results suggest that production inhibitors are likely to reduce the Aβ levels in all three compartments. In contrast, agents that ingest monomers off of polymers, or that increase fragmentation or block elongation, may also reduce Aβ burden in the brain, but may produce little change in—or even transiently increase—CSF and plasma Aβ levels. Hence, great care must be taken when interpreting these biomarkers.