Y. Dalmaz

Increased catecholamines and heart rate in children with low birth weight: perinatal contributions to sympathoadrenal overactivity

Background.  Low birth weight is associated with cardiovascular disease. The underlying mechanisms are unknown. We hypothesized that perinatal stress alters autonomic regulation of the cardiovascular system. In this study, catecholamines, heart rate (HR) and blood pressure (BP) were measured in healthy children with low birth weight.

Gestational Hypoxia Induces White Matter Damage in Neonatal Rats: A New Model of Periventricular Leukomalacia

In the premature infant, periventricular leukomalacia, usually related to hypoxic‐ischemic white matter damage, is the main cause of neurological impairment. We hypothesized that protracted prenatal hypoxia might induce white matter damage during the perinatal period. Pregnant Sparague‐Dawley rats were placed in a chamber supplied with hypoxic gas (10% O2 ‐90% N2) from embryonic day 5(E5) to E20. Neonatal rat brains were investigated by histology, immunocytochemistry, western blotting, in situ hybridization, DNA fragmentation analysis, and in vivo magnetic resonance imaging (MRI).

Prenatal hypoxia impairs the postnatal development of neural and functional chemoafferent pathway in rat

1 To define the effects of prenatal hypoxia on the postnatal development of the chemoafferent pathway, ventilation and metabolism, pregnant rats were exposed to normobaric hypoxia (10 % oxygen) from embryonic day 5 to embryonic day 20. Offspring were studied at 1, 3 and 9 weeks of age in three separate protocols. 2 Prenatal hypoxia decreased the dopamine content in the carotid bodies at all ages, and decreased the utilisation rate of noradrenaline in the caudal part of the A2 (A2c), A1 and A5 noradrenergic brainstem cell groups at 3 weeks after birth. At 9 weeks of age, the level of dopamine in the carotid bodies was still reduced but the utilisation rate of noradrenaline was enhanced in A1. 3 Rats from dams subjected to hypoxia during pregnancy hyperventilated until 3 weeks after birth. In these rats, the biphasic hypoxic ventilatory response was absent at 1 week and the increase in minute ventilation was amplified at 3 weeks. 4 Prenatal hypoxia disturbed the metabolism of offspring until 3 weeks after birth. A weak or absent hypometabolism in response to hypoxia was observed in these rats in contrast to control animals. 5 Prenatal hypoxia impairs the postnatal development of the chemoafferent pathway, as well as the ventilatory and metabolic responses to hypoxia. These alterations were mostly evident until 3 weeks after birth.

Effects of gestational hypoxia on mRNA levels of Glut3 and Glut4 transporters, hypoxia inducible factor-1 and thyroid hormone receptors in developing rat brain.

Alterations of brain development result from noxious intrauterine signals, as oxygen deprivation, which decrease glucose energetic yield. To verify the hypothesis that a defect of brain energetic adaptation is responsible for these alterations, we have studied the effects of gestational hypoxia (10% oxygen during the last 2 weeks of fetal life) on cerebral ontogenesis of glucose transporters which control the limiting step of glucose utilization by neurons. This study is realised in rats by quantification of whole brain Glut3 and Glut4 mRNA in 14- and 19-day-old embryos (E14, E19), newborn (P0) and 7 postnatal-day-old rats (P7) by using reverse transcription-polymerase chain reaction (RT-PCR) method. We have associated our study with the analysis of a transcriptional factor, the hypoxia inducible factor-1alpha (HIF-1alpha), known to control the expression of glucose transporter, and with a family of transcriptional factors, the thyroid hormone receptors (TR), regulating specific genes involved in brain development. The data show (1) for the first time the Glut4 and HIF-1alpha gene expression in fetal rat brain which are detected as soon as E14, (2) that gestational hypoxia induces an increase of mRNA transcript levels of Glut3, Glut4, TRalpha2, TRbeta1 and HIF-1alpha genes mainly or exclusively at E14, and (3) that the absence of response of Glut3 and HIF-1alpha at E19 in hypoxic vs. normoxic group could indicate an insufficient energetic adaptation at this period of development which could lead to the neural alterations observed postnatally.

Dopamine and norepinephrine dynamics in rat carotid body during long-term hypoxia

The contents of dopamine (DA), norepinephrine (NE) and 3,4-dihydroxyphenylacetic acid (DOPAC), and the utilization rates (secretion plus breakdown) of DA and NE were measured in carotid bodies of rats exposed, to normobaric hypoxia (10% O2 + 90% N2) for 0, 2, 7, 14 or 28 days. Long-term hypoxia elicited gradual increase in DA, NE and DOPAC contents, which after 28 days were increased 27, 51 and 4.6 fold, respectively. The DA utilization rate estimated after blockade of biosynthesis by alpha-methyl-p-tyrosine gradually increased from two days to the end of hypoxic exposure. The utilization rate of NE was unaltered within the first 7 days but was greatly increased after 14 and 28 days. It was concluded that the utilization rates of both DA and NE were increased by long-term hypoxia but these increases had different time courses. Dopamine, whose utilization increased in the early stage of hypoxia, might exert neurochemical effects on the chemoreceptors throughout the exposure, whereas NE, whose utilization was stimulated after two weeks of hypoxia, might play a significant role only after a delay.

Ventilatory and central neurochemical reorganisation of O2 chemoreflex after carotid sinus nerve transection in rat

The first step of this study was to determine the early time course and pattern of hypoxic ventilatory response (HVR) recovery following irreversible bilateral carotid sinus nerve transection (CSNT). The second step was to find out if HVR recovery was associated with changes in the neurochemical activity of the medullary catecholaminergic cell groups involved in the O2 chemoreflex pathway. The breathing response to acute hypoxia (10% O2) was measured in awake rats 2, 6, 10, 45 and 90 days after CSNT. In a control group of sham‐operated rats, the ventilatory response to hypoxia was principally due to increased respiratory frequency. There was a large reduction in HVR in the CSNT compared to the sham‐operated rats (−65%, 2 days after surgery). Within the weeks following denervation, the CSNT rats progressively recovered a HVR level similar to the sham‐operated rats (‐37% at 6 days, −27% at 10 days, and no difference at 45 or 90 days). After recovery, the CSNT rats exhibited a higher tidal volume (+38%) than the sham‐operated rats in response to hypoxia, but not a complete recovery of respiratory frequency. Fifteen days after CSNT, in vivo tyrosine hydroxylase (TH) activity had decreased in caudal A2C2 (−35%) and A6 cells (−35%). After 90 days, the CSNT rats displayed higher TH activity than the sham‐operated animals in caudal A1C1 (+51%), caudal A2C2 (+129%), A5 (+216%) and A6 cells (+79%). It is concluded that HVR following CSNT is associated with a profound functional reorganisation of the central O2 chemoreflex pathway, including changes in ventilatory pattern and medullary catecholaminergic activity.

Biochemical evidence for norepinephrine stores outside the sympathetic nerves in rat carotid body

Adult rats were submitted to pharmacological or surgical sympathectomy. The chronic administration of guanethidine caused tremendous reductions in the norepinephrine stores in heart and superior cervical ganglion due to the destruction of the sympathetic nerve fibers and cell bodies. Guanethidine-sympathectomy resulted in a 70% loss of norepinephrine in the carotid body, whereas the dopamine and DOPAC contents were unaltered. The surgical sympathectomy induced by removing the superior cervical ganglion led to similar results. The present data indicate that a considerable part of norepinephrine in the rat carotid body is stored in the sympathetic nerves. In addition, a significant part of norepinephrine resides outside the sympathetic nerves, probably within the glomus cells.

Activity of tryptophan hydroxylase and content of indolamines in discrete brain regions after a long-term hypoxic exposure in the rat

The influence of long-term hypoxia (10% O2, 14 days) on in vivo activity of tryptophan hydroxylase and on 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) concentration in discrete brain regions of rats was assessed. The activity of tryptophan hydroxylase was determined through 5-hydroxytryptophan accumulation (5-HTPacc) following the administration of NSD 1015. The 5-HTPacc was significantly decreased in the dorsal and median raphe (56 and 42%, respectively) and in the striatum (62%). Both 5-HTPacc and the ratio of the concentrations of 5-HIAA to 5-HT were decreased in the nucleus raphe magnus (46 and 27%, respectively), the dorsomedian medulla oblongata (52 and 51%), the locus coeruleus (62 and 40%) and the anterior hypothalamic nucleus (30 and 50%). In contrast, 5-HTPacc was increased in the ventrolateral medulla oblongata (55%) and the preoptic area (83%), but the 5-HIAA/5-HT ratio was lower in these two regions. Finally, 5-HIAA/5-HT ratio was also decreased in the periventricular nucleus and in the frontal cortex. Since various patterns of variations in 5-HTPacc and in 5-HIAA/5-HT ratio were observed, the factors affecting serotonin metabolism in hypoxic rats can be different among brain regions. These results show that, in the rat, long-term hypoxia induces changes in in vivo activity of tryptophan hydroxylase and in 5-HT and 5-HIAA content of some brain structures; some of these biochemical changes may be linked to adaptative mechanisms.

Long-term exposure to ozone alters peripheral and central catecholamine activity in rats

Abstract In addition to its noxious influence on lung airways, ozone inhalation can induce extrapulmonary neural dysfunctions the mechanisms of which are poorly understood. This study was intended to characterize the effects of long-term exposure to ozone (0.5 ppm, 5 days) on catecholamine activity in rat sympathetic efferents and brain areas of prime importance to adaptation to environmental stressors. Catecholamine activity was assessed by estimating the turnover rate of catecholamines and in vivo tyrosine hydroxylase activity in peripheral and central structures, i.e., heart, lungs, superior cervical ganglia, cerebral cortex, hypothalamus and striatum, A2 cell group within the nucleus tractus solitarius (NTS), and locus ceruleus (A6). Ozone inhibited norepinephrine turnover in heart (–48% of the control level) but not in lungs. Ozone failed to modify the tyrosine hydroxylase activity in superior cervical ganglia, and the catecholamine content in the adrenal glands. In the central nervous system, ozone inhibited tyrosine hydroxylase activity in noradrenergic brainstem cell groups, including the locus ceruleus (–62%) and the caudal A2 subset (–57%). Catecholamine turnover was decreased by ozone in the cortex (–49%) and striatum (–18%) but not in the hypothalamus. The data show that ozone can produce marked neural disturbances in structures involved in the integration of chemosensory inputs, arousal, and motor control.

Long-term prenatal hypoxia alters maturation of adrenal medulla in rat.

Catecholamine release from the adrenal medulla glands plays a vital role in postnatal adaptation. A number of pathologic situations are characterized by oxygen deficiency. The objective of the present study was to determine the influence of long-term prenatal hypoxia on maturation of the adrenal medulla. Pregnant rats were subjected to hypoxia (10% O2) from the fifth to the 20th d of gestation. The offspring were examined on the 19th d of gestation (E19), the day of birth (P0), and at postnatal (P) day of life P3, P7, P14, P21, and P68. The catecholamine content and activity of tyrosine hydroxylase (TH) in vivo were assayed by HPLC with electrochemical detection. Cellular expression of TH and phenylethanolamine N-methyl transferase was evaluated by protein immunohistochemistry and in situ hybridization of the corresponding mRNA species. Exposure to prenatal hypoxia reduced the epinephrine content of the adrenal medulla on E19, P0, P3, and P7 while increasing the norepinephrine content on E19, P0, and P14. Furthermore, the peak epinephrine to norepinephrine ratio appearing between P7 and P10 in the normoxic offspring was absent in the hypoxic offspring. The in vivo TH activity was increased on P3 and P14 and decreased on P68. The percentage of chromaffin cells in the medulla expressing TH and phenylethanolamine N-methyl transferase was lowered on E19, P0, and P7. TH and phenylethanolamine N-methyl transferase mRNA levels were reduced on P7. Clearly prenatal hypoxia results in major changes in adrenal catecholamine stores and synthesis during the perinatal period, which persist into adulthood. The capacity to cope with postnatal stress might be disturbed as a consequence of prenatal hypoxia.