Regional changes in monoamine synthesis in the developing rat brain during hypoxia

Fischer's oligopeptide ratio in ischemic hypoxia: prophylactic amendment of sophoretin and melatonin supplementation

Aim: The fundamental pathophysiology of ischemic-hypoxia is oxygen depletion. Fischer's ratio is essential for monitoring hypoxia intensity. Methods: the current study highlighted the prophylactic role of sophoretin (QRC) and/or melatonin (MLN) versus sodium nitrite (SN) brain hypoxia. Results: Prophylactic treatment with sophoretin and MLN, was preceded with hypoxia-induction via sodium nitrite (60 mg/kg, S.C.). SN decreased hemoglobin (Hb), elevated HIF-α, HSP-70, IL-6 and TNF-α. Sophoretin and/or MLN restored the ameliorated inflammatory biomarkers, modulated norepinephrine, dopamine, serotonin and gamma-aminobutyric acid (GABA). Similarly, single-cell gel electrophoresis (SCGE or COMET) DNA damage assay confirmed this finding. Conclusion: Treatment via sophoretin and MLN was the most effective therapy for improving sodium nitrite-induced brain injury.

Carnosine and L-arginine attenuate the downregulation of brain monoamines and gamma aminobutyric acid; reverse apoptosis and upregulate the expression of angiogenic factors in a model of hemic hypoxia in rats

PURPOSE

The purpose of the present study was to investigate the preventive effect of L-arginine (ARG) and carnosine (CAR) on hypoxia-induced neurotoxicity in rats. The impact on neuro-inflammation, apoptosis, angiogenesis, and the brain levels of monoamines and GABA were investigated.

METHODS

Rats were divided into the following: normal control, hypoxia model induced by sodium nitrite (75 mg/kg s.c), and hypoxic rats pre-treated with CAR (250 mg/kg), ARG (200 mg/kg), and their combination.

RESULTS

Data revealed that hypoxia induced significant elevation of hypoxia inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF), and its receptor reflecting the stimulation of angiogenesis. Hypoxia also resulted in increased inflammatory mediators-including nuclear factor kappa B (NF-κB), tumor necrosis factor-alpha (TNF-α), and interleukin-6 (IL-6). In addition, hypoxia initiates cerebral apoptosis as revealed by increased caspase-3 and BAX with reduced Bcl-2. These changes were associated with reduced brain levels of GABA and monoamines including noradrenaline (NADR), dopamine (DOP), and serotonin (SER). Pre-treatment with ARG and/or CAR significantly mitigated the neural changes induced by hypoxia and attenuated the elevated levels of NF-κB, TNF-α, IL-6, caspase-3, and BAX, while ameliorated the reduced levels of Bcl-2, NADR, DOP, SER, and GABA, with the best improvement observed with the combination. Further elevation of the angiogenic markers was observed indicating their role in boosting oxygen delivery to brain.

CONCLUSION

CAR, ARG, and, importantly, their combination could effectively protect against hypoxia-induced neurotoxicity, via their angiogenic, anti-inflammatory, and anti-apoptotic properties in addition to reversing the effect on GABA and monoamines.

Restoration of tryptophan hydroxylase functions and serotonin content in the Atlantic croaker hypothalamus by antioxidant treatment during hypoxic stress

Antioxidants are prototypical scavengers of oxygen-free radicals and have been shown to prevent neuroendocrine dysfunction in vertebrates during oxidative stress. In the present study, we investigated whether antioxidant treatment can reverse hypoxia-induced down-regulation of hypothalamic tryptophan hydroxylase (TPH) and serotonergic functions in Atlantic croaker. Hypothalamic neuronal contents of TPH-1 and TPH-2 proteins, serotonin (5-hydroxytryptamine, 5-HT) and its precursor, 5-hydroxytryptophan (5-HTP) as well as hypothalamic TPH-1 and TPH-2 mRNA expression and TPH activity were measured in croaker after exposure to hypoxia and treatment with pharmacological agents. Multiple injections of N-ethylmaleimide, a sulfhydryl alkylating agent, caused comparable decreases in hypothalamic TPHs functions and 5-HT contents to that induced by hypoxia exposure (dissolved oxygen: 1.7 mg/L for 4 weeks) which were partially restored by repeated injections with a nitric oxide synthase (NOS)-inhibitor and/or vitamin E. Double-labeled immunohistochemical results showed that TPHs and 5-HT neurons were co-expressed with neuronal NOS (nNOS, a neuroenzyme) that catalyzes the production of nitric oxide, a free radical, in hypothalamic neurons. These results suggest that hypoxia-induced impairment of TPH and serotonergic functions are mediated by nNOS and involve the generation of free radicals and a decrease in the antioxidant status. This study provides, to our knowledge, the first evidence of a protective role for an antioxidant in maintaining neural TPHs functions and 5-HT regulation in an aquatic vertebrate during hypoxic stress.

Hypoxia. 3. Hypoxia and neurotransmitter synthesis

Central and peripheral neurons as well as neuroendocrine cells express a variety of neurotransmitters/modulators that play critical roles in regulation of physiological systems. The synthesis of several neurotransmitters/modulators is regulated by O(2)-requiring rate-limiting enzymes. Consequently, hypoxia resulting from perturbations in O(2) homeostasis can affect neuronal functions by altering neurotransmitter synthesis. Two broad categories of hypoxia are frequently encountered: continuous hypoxia (CH) and intermittent hypoxia (IH). CH is often seen during high altitude sojourns, whereas IH is experienced in sleep-disordered breathing with recurrent apneas (i.e., brief, repetitive cessations of breathing). This article presents what is currently known on the effects of both forms of hypoxia on neurotransmitter levels and neurotransmitter synthesizing enzymes in the central and peripheral nervous systems.

Tryptophan hydroxylase: a target for neuroendocrine disruption

Tryptophan hydroxylase (TPH), the rate-limiting enzyme in serotonin (5-HT) synthesis, performs an essential role in the maintenance of serotonergic functions in the central nervous system (CNS), including regulation of the neuroendocrine system controlling reproduction. The results of recent studies in a teleost model of neuroendocrine disruption, Atlantic croaker, indicated that hypothalamic TPH is a major site of interference of hypothalamic-pituitary-gonadal function by environmental stressors. The effects of exposure to two different types of environmental stressors, low dissolved oxygen (hypoxia) and a polychlorinated biphenyl mixture (Aroclor 1254), on the stimulatory brain serotonergic system controlling reproductive neuroendocrine function in Atlantic croaker are reviewed. Exposure to both stressors produced decreases in TPH activity, which were accompanied by a fall in hypothalamic 5-HT and gonadotropin-releasing hormone (GnRH I) content in the preoptic-anterior hypothalamic area and were associated with reduction in luteinizing hormone (LH) secretion and gonadal development. Pharmacological restoration of hypothalamic 5-HT levels after exposure to both stressors also restored neuroendocrine and reproductive functions, indicating that the serotonergic system is an important site for hypoxia- and Aroclor 1254-induced inhibition of reproductive neuroendocrine functions. The mechanisms underlying downregulation of TPH activity by these stressors remain unclear but may involve alterations in hypothalamic antioxidant status. In support of this hypothesis, treatment with an antioxidant, vitamin E, was found to reverse the inhibitory effects of Aroclor 1254 on TPH activity. The results suggest that TPH is a major target for neuroendocrine disruption by diverse environmental stressors.

Changes in blood glucose and insulin secretion in patients with senile dementia of Alzheimer type

A retrospective study of 839 hospital records with various dementia diagnoses showed that 63 cases had a diagnosis of diabetes mellitus as well. None of these were found in the group of patients with senile dementia of Alzheimer type (SDAT). Oral glucose tolerance tests (OGTT) were performed in patients with SDAT, multiinfarct dementia (MID), cerebrovascular disease (CVD), hospitalized control patients (Chosp) and healthy elderly persons (Celd). Fasting blood sugar was significantly lower and the areas under the OGTT curves were significantly smaller in the SDAT group than in the CVD and the Chosp group. SDAT patients had higher insulin levels than Celd during the OGTT and on a statistically significant level 90 min after ingestion of sugar. Our findings suggest that SDAT and diabetes mellitus may not co-exist and that patients with SDAT have decreased blood sugar concentrations and elevated serum insulin levels. It is discussed whether this is an effect of the transmitter deficiencies in SDAT or may serve to explain these deficiencies.

Molecular cloning, characterization and expression of two tryptophan hydroxylase (TPH-1 and TPH-2) genes in the hypothalamus of Atlantic croaker: down-regulation after chronic exposure to hypoxia

Recently we discovered that hypoxia causes marked impairment of reproductive neuroendocrine function in Atlantic croaker, a marine teleost, which is due to a decline in hypothalamic serotonergic activity. As a first step in understanding the molecular responses of the hypothalamic serotonergic system to hypoxia, we cloned and characterized the genes for the enzymes regulating the rate-limiting step in serotonin biosynthesis, tryptophan hydroxylase (TPH-1 and TPH-2) in the croaker brain. The full-length croaker TPH-1 and TPH-2 cDNAs contain open reading frames encoding proteins with 479 and 487 amino acids, respectively, which are highly homologous to the TPH-1 (76-93%) and TPH-2 (64-92%) proteins of other vertebrates. Croaker TPH-1 and TPH-2 mRNA expression was detected throughout the brain but was greatest in the hypothalamic region. Both Northern blot analysis and real-time PCR showed that TPH-1 (transcript size approximately 2.1 kb) and TPH-2 ( approximately 1.9 kb) mRNA levels were significantly decreased in the hypothalami of croaker exposed for 2 weeks to hypoxic conditions compared with those in fish exposed to normoxic conditions. Immunohistochemistry of hypothalamic neurons with TPH antibodies showed reduced expression of TPHs in hypoxia-exposed fish compared with normoxic fish. Western blot analysis confirmed that hypoxia caused a marked decline in hypothalamic TPH protein levels, which was associated with decreases in hypothalamic TPH enzyme activity and 5-hydroxytryptophan levels. These results suggest that TPH is a major site of hypoxia-induced down-regulation of serotonergic function in croaker brains. Moreover, they provide the first evidence that hypoxia decreases the expression of TPH transcripts in vertebrate brains.

Influence of acute progressive hypoxia on cardiovascular variability in conscious spontaneously hypertensive rats

The purpose of this study is to examine the influence of acute progressive hypoxia on cardiovascular variability and striatal dopamine (DA) levels in conscious, spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY). After preparation for measurement, the inspired oxygen concentration of rats was decreased to 10% within 5 min (descent stage), maintained at 10% for 10 min (fixed stage), and then elevated back to 20% over 5 min (recovery stage). The systolic blood pressure (SBP) and heart rate (HR) variability at each stage was calculated to evaluate the autonomic nervous system response using the wavelet method. Striatal DA during each stage was measured using in vivo microdialysis. We found that SHR showed a more profound hemodynamic response to progressive hypoxia as compared to WKY. Cardiac parasympathetic activity in SHR was significantly inhibited by acute progressive hypoxia during all stages, as shown by the decrease in the high frequency band of HR variability (HR-HF), along with transient increase in sympathetic activity during the early hypoxic phase. This decrease in the HR-HF continued even when SBP was elevated. Striatal DA levels showed the transient similar elevation in both groups. These findings suggest that acute progressive hypoxic stress in SHR inhibits cardiac parasympathetic activity through reduction of baroreceptor reflex sensitivity, with potentially severe deleterious effects on circulation, in particular on HR and circulatory control. Furthermore, it is thought that the influence of acute progressive hypoxia on striatal DA levels is similar in SHR and WKY.

Brainstem monoamine pathology of neonatal hypoxic-ischemic brain damage: a model of acute stage of neonatal asphyxia

Neonatal hypoxic-ischemic encephalopathy (HIE) is one of the most severe perinatal diseases and leads to high mortality and sometimes severe neurological sequelae. At the acute stage of HIE, it is thought to be the damage of catecholaminergic system in the brainstem. And then, HIE reflects mental development throughout the norepinephrine and serotonin systems, which mainly originates in the brainstem. Therefore, we studied both systems in the brainstem of neonatal HIE model rats with tyrosine hydroxylase (TH) and tryptophan hydroxylase (TpH) immunohistochemistry and a high-performance liquid column (HPLC) to measure norepinephrine and serotonin and their metabolism. As a result, the TH-positive and TpH-positive cell numbers significantly decreased 2 days after hypoxic-ischemic (HI) insult (n=10). However, 7 days after insult (n=10), the TH-positive and TpH-positive cell numbers had recovered in most regions. HPLC demonstrated a significant difference in the norepinephrine concentration 2 days after HI insult, but not in the other monoamines.

The relationship between neuronal plasticity and serotonergic neurons in the brainstem of SIDS victims

BACKGROUND

The sudden infant death syndrome (SIDS) is still the main cause of postneonatal infant death and its cause is still unknown. Recently, the medullary serotonergic network deficiency theory has been proposed and an association between SIDS and neuronal plasticity has also been suggested. The growth-associated phosphoprotein 43 (GAP43) is a marker of synaptic plasticity and is critical for normal development of the serotonergic innervation. Therefore, the characteristics of GAP43-positive elements and their association with serotonergic neurons were here investigated in the brainstem of SIDS victims.

MATERIALS AND METHODS

The materials of this study included 26 cases of SIDS and 12 control cases. The brainstem material was collected and the immunohistochemistry of GAP43 and tryptophan hydroxylase (TrypH) carried out. The density of GAP43-positive neurons and dendrites and of TrypH-positive neurons were measured quantitatively. Nonparametric analyses of GAP43 between SIDS and non-SIDS and correlation analyses between GAP43 and TrypH were performed.

RESULTS

No significant difference in GAP43-associated findings was found between SIDS and non-SIDS nor any significant correlation between GAP43-associated findings and TrypH-positive neurons.

CONCLUSIONS

The results of this study were not in agreement with the association of GAP43 with SIDS and with serotonergic innervation in SIDS.

The correlation between serotonergic neurons in the brainstem and sleep apnea in SIDS victims

BACKGROUND

In the Sudden Infant Death Syndrome (SIDS), a medullary serotonergic network deficiency theory has been proposed, amongst many other hypotheses. The correlation between serotonergic neurons or dendritic spines in the brainstem of SIDS and sleep apnea was investigated here.

MATERIALS AND METHODS

Twenty-seven thousand infants were studied prospectively to characterize their sleep-wake behavior. Of these, 38 infants died under 6 months of age, including 26 cases of SIDS. The frequency and duration of sleep apnea were analyzed. Brainstem material was collected and immunohistochemistry for tryptophan hydroxylase (TrypH) carried out. The density of TrypH-positive neurons was measured quantitatively. Correlation analyses were carried out between the TrypH-associated pathological data and the physiological data of sleep apnea.

RESULTS

One significant positive correlation between the density of TrypH-positive neurons in the dorsal raphe nucleus of the midbrain and the duration of central apnea (p=0.027) was found in SIDS victims.

CONCLUSIONS

Some of serotonergic facts could be involved in the pathophysiology of SIDS.

Effect of hypoxia/hypercapnia on metabolism of 6-[(18)F]fluoro-L-DOPA in newborn piglets

There is evidence that the dopaminergic system is sensitive to altered p(O(2)) in the immature brain. However, the respective enzyme activities have not been measured in the living neonatal brain together with brain oxidative metabolism. Therefore 18F-labelled 6-fluoro-L-3,4-dihydroxyphenylalanine (FDOPA) together with positron emission tomography (PET) was used to estimate the activity of the aromatic amino acid decarboxylase (AADC) in the brain of fifteen newborn piglets (2-5 days old). Two PET scans were performed in each piglet. Eleven animals underwent a period of normoxia and moderate hypoxia/hypercapnia (H/H). The remaining four animals were used as an untreated control group. Simultaneously, the brain tissue p(O(2)) was recorded, the regional cerebral blood flow (CBF) was measured with colored microspheres and the cerebral metabolic rate of oxygen (CMRO(2)) was determined. In addition, in four untreated and six H/H treated piglets the relative amounts of fluorodopamine and the respective metabolites were determined in brain tissue samples using HPLC analysis. H/H conditions were induced by lowering the inspired fraction of oxygen from 0.35 to 0.10 and adding CO(2) to the inspired gas resulting in an arterial p(CO(2)) between 74 and 79 mmHg. H/H elicited a more than 3-fold increase of the CBF (P<0.05) so that the CMRO(2) remained unchanged throughout the H/H period. Despite this, the brain tissue p(O(2)) was reduced from 19+/-4 to 6+/-3 mmHg (P<0.05). The permeability-surface area product of FDOPA (PS(FDOPA)) was unchanged. However, the transfer rate of FDOPA (k(3)(FDOPA)) of the nigrostriatal dopaminergic system and the relative amounts of fluorodopamine and the respective metabolites were significantly increased (P<0.05). It is suggested that H/H induces an increase of AADC activity. However, an H/H-induced CBF increase maintains bulk O(2) delivery and preserves CMRO(2).

Anoxic and hypoxic immature rat model for measurement of monoamine using in vivo microdialysis

The immature brain is considered relatively resistant to anoxia and ischemia. Although hypoxia without ischemia has not been considered to produce brain damage in immature rats as well as in adult rats (S. Levine, Anoxic-ischemic encephalopathy in rats, Am. J. Pathol., 36 (1960) 1-17 [8]; D.E. Levy, J.B. Brieley, D.G. Silverman, F. Plum, Brief hypoxia-ischemia initially damages cerebral neurons, Arch. Neurol., 32 (1975) 450-456 [9]; J.E. Rice, R.C. Vannucci, J.B., Brieriey, The influence of immaturity on hypoxic-ischemic brain damage in rat, Ann. Neurol., 9 (1981) 131-141 [14]), hypoxia in postnatal period is possible to cause a functional brain damage (T. Hender, P. Lundborg, Regional changes in monoamine synthesis in the developing rat brain during hypoxia, Acta. Physiol. Scand., 106 (1979) 139-143 [3]; W. Ihle, J. Gross, R. Moller, Effect on chronic postnatal hypoxia on dopamine uptake by synaptosomes from striatum of adult rats, Biomed. Biochem. Acta., 44 (1985) 433-437 [7]; A. Lun, J. Gross, M. Beyer, H.D. Fischer, C. Wustmann, J. Schmidt, K. Hecht, The vulnerable period of perinatal hypoxia with regard to dopamine release and behavior in adult rats, Biomed. Biochem. Acta., 45 (1986) 619-627 [10]). Using microdialysis, we studied the anoxic or hypoxic effect on catecholamine metabolism in immature rat brain by measuring extracellular concentrations of norepinephrine (NE), dopamine (DA), and its metabolites and also 5-hydroxyindole-3-acetic acid (5-HIAA), the serotonin metabolite. DA is a well established excitatory neurotransmitter (R.C. Vannucci, Experimental biology of cerebral hypoxia-ischemia: relation to perinatal brain damage, Pediatr. Res., 27 (1990) 317-326 [16]), and in the previous report using hypoxic 7-day-old rat pups increase of DA was not detected without additional stimulations (K. Gordon, D. Johnston, M.V. Robinson, T.E. Statman, J.B. Becker, F. Silverstein, Transient hypoxia alters striatal catecholamine metabolism in immature brain: An in vivo microdialysis study, J. Neurochem., 54 (1990) 605-611 [2]). Whereas recently in newborn piglets, hypoxic hypoxia produced increase of extracellular DA (C.-C. Huang, N.S. Lajevardi, O. Tammela, A. Pastuszko, Relationship of extracellular dopamine in striatum of newborn piglets to cortical oxygen pressure, Neurochem. Res., 19 (1994) 649-655 [6]; Olano, M., Song, D., Murphy, S., Wilson, D. F. and Pastuszko, A., Relationships of dopamine, cortical oxygen pressure, and hydroxyl radicals in brain of newborn piglets during hypoxia and posthypoxic recovery, J. Neurochem., 65 (1995) 1205-1212 [13]). We consider that hypoxic ischemic brain damage of human newborns that we can treat is a damage, which does not show overt neuropathological changes. We therefore tried to show that transient anoxia and hypoxia caused biochemical alteration if the exposure did not produce marked morphological changes. This rodent model is adequate to study perinatal asphyxia and alteration of monoamine level could be useful for evaluation of brain damage, even if it is not detected histologically.

Effect of anoxia on striatal monoamine metabolism in immature rat brain compared with that of hypoxia: an in vivo microdialysis study

We examined in 5-day-old rats the effects of either anoxia or 8% hypoxia on extracellular monoamines such as dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), norepinephrine (NE), 5-hydroxytryptamine (5-HT), and 5-hydroxyindole-3-acetic acid (5-HIAA) using in vivo microdialysis and subsequent HPLC. After stabilization 64 animals were exposed to 100% nitrogen for 16 min and 40 animals to 8% oxygen for 128 min. Both anoxia and hypoxia produced acute increase in the striatal extracellular DA (anoxia: P < 0.001, hypoxia: P < 0.01). Especially in anoxia, DA levels increased transiently to 2000-times the basal levels and 6-times higher than those in hypoxia. NE also increased in both anoxia and hypoxia. DOPAC and HVA decreased during hypoxia (P < 0.01 and P < 0.001, respectively), while those in anoxia were unchanged. In anoxia, decrease tendency of their levels were in short duration and that of 5-HIAA was followed by gradual increase (P < 0.001). These data demonstrated that brief exposure to anoxia or hypoxia had significant influence on striatal monoamine metabolism in immature brain and the pattern of change of monoamine in anoxia was different from that in hypoxia.

Effects of graded levels of tissue oxygen pressure on dopamine metabolism in the striatum of newborn piglets

The effect of graded levels of tissue hypoxia on the extracellular levels of dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxyindoleacetic acid has been monitored in vivo by microdialysis. Reproducible levels of decreased oxygen in the brain were obtained by increasing the rate of ventilation from the control value of 25/min to as high as 95/min. With increasing ventilatory rate, the oxygen pressure in the cortex decreased from approximately 40 torr to 16 torr. As the oxygen pressure decreased stepwise from 40 to 27, 22, and 16 torr, the dopamine levels in the extracellular medium rose by 70, 90, and 150%, respectively, returning to baseline within a few minutes of return to control ventilation rates. Levels of the catabolic products 3,4-dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxyindoleacetic acid decreased with decreasing tissue oxygen. Unlike the dopamine levels, these catabolite levels continued to decrease through 30 min of recovery (to 50% of control), returning to baseline only after recovery periods of 1-2 h. These data suggest that hypoxia induces long-term alterations in the neurotransmitter turnover. The marked effects of mild tissue hypoxia (decrease of oxygen from 40 torr to 26 torr) on both the extracellular dopamine concentration and dopamine metabolism indicate that the metabolic consequences of decreased tissue oxygen pressure extend to higher values than generally appreciated.

Asphyctic lesion: proliferation of tyrosine hydroxylase-immunoreactive nerve cell bodies in the rat substantia nigra and functional changes in dopamine neurotransmission

Asphyxia was induced in male rat pups by performing a delayed cesarean section on pregnant Sprague-Dawley rats. Oxygen saturation and heart rate were recorded during induction of asphyxia. Animals were sacrificed at 3 weeks of age. Brain sections were stained for tyrosine-hydroxylase (TH), dopamine-and-cyclic-AMP-regulated-phosphoprotein-32 (DARPP-32) immunoreactivity (IR) and thionein. Increasing time of asphyxia caused a reduction in the number of nerve cell bodies in the CA1 and CA3 regions of the hippocampus reflecting neuronal death. Furthermore, asphyxia resulted in an increased number of TH-IR nerve cell bodies indicative of a proliferation of dopaminergic neurons in the zona compacta of the substantia nigra. Finally, a significant decrease in rearing was observed in asphyctic animals during the habituation phase, as well as following apomorphine-induced (1 mg/kg s.c.) postsynaptic dopamine receptor stimulation. On the other hand, the apomorphine-induced increase in locomotion was enhanced in asphyctic animals. The implications of these findings for hyperkinesia and attention deficits in disorders resulting from asphyxia are discussed.

Transient hypoxia alters striatal catecholamine metabolism in immature brain: an in vivo microdialysis study

Microdialysis probes were inserted bilaterally into the striatum of 7-day-old rat pups (n = 30) to examine extracellular fluid levels of dopamine, its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA). The dialysis samples were assayed by HPLC with electrochemical detection. Baseline levels, measured after a 2-h stabilization period, were as follows: dopamine, not detected; DOPAC, 617 +/- 33 fmol/min; HVA, 974 +/- 42 fmol/min; and 5-HIAA, 276 +/- 15 fmol/min. After a 40-min baseline sampling period, 12 animals were exposed to 8% oxygen for 120 min. Hypoxia produced marked reductions in the striatal extracellular fluid levels of both dopamine metabolites (p less than 0.001 by analysis of variance) and a more gradual and less prominent reduction in 5-HIAA levels (p less than 0.02 by analysis of variance), compared with controls (n = 12) sampled in room air. In the first hour after hypoxia, DOPAC and HVA levels rose quickly, whereas 5-HIAA levels remained suppressed. The magnitude of depolarization-evoked release of dopamine (elicited by infusion of potassium or veratrine through the microdialysis probes for 20 min) was evaluated in control and hypoxic animals. Depolarization-evoked dopamine efflux was considerably higher in hypoxic pups than in controls: hypoxic (n = 7), 257 +/- 32 fmol/min; control (n = 12), 75 +/- 14 fmol/min (p less than 0.001 by analysis of variance). These data demonstrate that a brief exposure to moderate hypoxia markedly disrupts striatal catecholamine metabolism in the immature rodent brain.

Changes in cerebrospinal fluid homovanillic acid in children with Ondine's curse

The cerebrospinal fluid (CSF) concentrations of three acid monoamine metabolites, two purines, and a group of amino acids were determined in two children with chronic central alveolar hypoventilation (Ondine's curse). The levels of all assayed neuroactive substances, metabolites, and amino acids, with one exception, were normal compared to an age-matched group of neurologically healthy children. The levels of the dopamine metabolite homovanillic acid in the children with Ondine's curse were approximately 2.4 times higher than expected for age range. The present findings may indicate a link between central nervous system dopamine activity and chronic central alveolar hypoventilation. Among other possible explanations, the changes seen might represent a primary alteration in dopamine activity or may reflect a change in dopamine turnover resulting from the chronic hypoventilation.

Monoamine neurotransmitter metabolism and locomotor activity during chemical hypoxia

The effects of hypoxia on metabolism of 5-hydroxytryptamine (5-HT or serotonin) and 3,4-dihydroxyphenylethylamine (DA or dopamine) were compared with those on open-field activity in male CD-1 mice. Chemical hypoxia was induced with NaNO2. Hypoxia did not alter striatal concentrations of DA, 5HT, Trp, Tyr, 5-hydroxyindoleacetic acid, or homovanillic acid. However, NaNO2 (75 mg/kg) reduced the rates of conversion of [3H]Tyr to [3H]DA (-41%) and [3H]Trp to [3H]5-HT (-39%). Hypoxia also reduced dihydroxyphenylacetic acid (DOPAC) levels (-27%) and DOPAC/DA ratios (-20%). Open-field behavior, as measured in an automated activity monitor, decreased in a dose-dependent fashion with 75-150 mg/kg of NaNO2 (-35 to -90%). Comparison with previous studies suggests that the syntheses of dopamine, serotonin, and the amino acids are equally vulnerable to hypoxic insults but may be less sensitive than the synthesis of acetylcholine.

Turnover and synthesis of biogenic amines in discrete brainstem nuclei of the rabbit

By use of a microtechnique and sensitive enzymatic isotopic assays norepinephrine (NE), dopamine (DA) and serotonin (5-HT) turnover rates were measured in 6 discrete brainstem regions. The results from young (3 days) and adult (1 year) rabbits were compared. In the dorsal raphe nucleus (dr) of the younger animals the slopes of disappearance of NE and 5-HT were significantly higher than in the adults. Whereas, in the dr the slope of the decline of DA was found to be significantly lower in younger animals. In the dr turnover rates of NE and 5-HT were higher in the young animals. However, higher turnover rates for DA were seen only in the LC-A6 region. The young animals had significantly lower turnover times for NE and 5-HT in the dr. The nts was the only nuclear group to reach significance for DA, and the young animals had longer turnover times when compared to adults. These results are indicative of the different roles the neurotransmitter systems play in maintaining homeostasis. The delicate balances in these systems in the brains of younger animals may contribute to their increased susceptibility to perturbations.

Monoamine synthesis and concentration in neonatal rat brain during hypercapnia and recovery

One-day-old rats were exposed to a gas mixture of 15% CO2-21% O2-64% N2 for a 30-min period. Monoamine synthesis in whole brain was measured during, and at various intervals after, hypercapnia by estimating the accumulation of dihydroxyphenylalanine (DOPA) and 5-hydroxytryptophan (5-HTP) after inhibition of aromatic L-amino-acid decarboxylase with NSD 1015. Endogenous concentrations of tyrosine, dopamine (DA), noradrenaline (NA), tryptophan, 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were measured at the same intervals. Exposure to CO2 induced an increased synthesis of catecholamines and 5-HT. Further, an increase in DA concentration was seen during hypercapnia, while NA and 5-HT were unchanged. After the CO2 exposure the increased in vivo synthesis rates of catecholamines and 5-HT were rapidly normalized, as was the endogenous DA concentration. A slight increase in 5-HT and 5-HIAA concentrations was seen immediately after CO2 exposure. These results indicate that in neonatal animals, hypercapnia induces changes in central monoamine neurons, primarily an increased synthesis. These alterations may be relevant to some physiological changes seen during CO2 exposure, such as the alteration in central respiratory performance.

Comparative study of monoamine levels in discrete brain areas of five rodent species

1. Dopamine, norepinephrine, serotonin and 5-hydroxyindol-acetic acid levels were studied in discrete brain areas of four wild rodent species and compared with those of laboratory mouse. 2. Monoamine levels showed significant differences in all the species studied. 3. Although it is not possible to exclude the changes induced by the captivity's stress, the results suggest that the natural hypoxic environment (high altitude) and/or the natural diet play an important role on the activity of the monoaminergic neurons. 4. Species which showed a better behavioral pattern of adaptation also showed significant differences in brain monoamine levels.

Changes in brain 5-hydroxytryptamine metabolism induced by hypobaric hypoxia

1. 5-hydroxytryptamine (5-HT) level was measured in hypothalamus, striatum and the rest of the brain of rats exposed to 1800, 5200 and 7000 m simulated altitudes. 2. Moderate hypobaric hypoxia failed to modify 5-HT level, whereas severe hypoxia reduced the amine level by about 30%. 3. Treatment with a synthesis blocking agent (PCPA) revealed a dual effect of hypoxia on the 5-HT elimination. Increased elimination observed at 1800 m was attributed to the hypoxia-induced stress and the decrease (at 5200 and 7000 m) indicated the predominance of enzymatic inhibition. 4. It was assumed that tryptophan hydroxylase was more sensitive than monoamine oxidase to a high hypobaric hypoxia.

Alteration of acetylcholine synthesis in mouse brain cortex in mild hypoxic hypoxia

Acetylcholine synthesis in four brain regions (cerebral neocortex, hippocampus, septum and striatum) of the mouse during mild hypoxic hypoxia was measured by using [U-14C]glucose and [2H4]choline. At the same time, concentrations of norepinephrine and dopamine in four brain regions (cerebral neocortex, hippocampus, striatum and hypothalamus) were also estimated. During 12% O2 hypoxia, concentrations of acetylcholine in the striatum were significantly decreased (P less than 0.05), whereas [2H4]acetylcholine, lactate and glucose did not alter in any regions studied. During 12% O2 hypoxia, concentrations of choline and [2H4]choline were significantly increased in all regions examined (P less than 0.05), except the [2H4]choline inthe striatum. Radioactivity (dpm/100 mg protein) and specific activity (dpm/nmol) of acetylcholine were significantly decreased in the cerebral neocortex, hippocampus and septum (P less than 0.01) during 12% O2 hypoxia. A particularly marked decrease was found in the hippocampus, strongly suggesting that cholinergic terminals are particularly sensitive to hypoxia. In addition, these data also suggest that the acetylcholine synthesis from glucose might be more sensitive to hypoxia than that from choline. During 12% O2 hypoxia, concentrations of catecholamine did not alter in any regions examined, whereas during 9% O2 hypoxia dopamine was significantly decreased in the cerebral neocortex and hippocampus (P less than 0.05).