Influence of long-term hypoxia on tyrosine hydroxylase in the rat carotid body and adrenal gland

Characterization of Group I Metabotropic Glutamate Receptors in Rat and Human Adrenal Glands

Glutamate and its receptors have been demonstrated to promote both basal and nicotine-evoked catecholamine release in bovine chromaffin cells. Multiple glutamate receptors, including metabotropic glutamate receptors (mGluRs), are found in the adrenal glands of several species, as well as in chromaffin cells. However, there is limited information available regarding the expression of glutamate metabotropic receptor (GRM)1-8 mRNAs and the detailed localization of group I mGluRs (mGluR1 and mGluR5) in the rat and human adrenal cortex and medulla. Therefore, we examined mRNA expression of GRM1-8 subunits using reverse transcription-polymerase chain reaction (RT-PCR) and the distribution of mGluR1 and mGluR5 by immunostaining. The results showed that the GRM1-8 mRNAs were expressed in both the cortex and medulla of rat and human adrenal glands with the exception of GRM1, which was not detectable in the rat adrenal cortex. Immunostaining of mGluR1 revealed that it was localized only in the adrenal medulla of rats but was present in both the adrenal cortex and medulla in humans. In the adrenal medulla, the central part of the adrenal glands, mGluR1 was detected in chromaffin cells but not in nerve fibers and ganglion cells. Immunoactivity of mGluR5 was visible in the capillary wall throughout the adrenal cortex and medulla in rat and human samples. Its immunoactivity was also observed in ganglion cells in the rat adrenal medulla. There was no mGluR5 immunoactivity detected in chromaffin cells and nerve fibers in the rat and human adrenal medulla. Using dissected rat adrenal medulla as a model, we found that treatment with a mGluR1 agonist activated extracellular signal-regulated kinase (ERK) 1/2 and increased the expression of tyrosine hydroxylase (TH), the rate-limiting enzyme of catecholamine synthesis. Moreover, these results showed that mGluR1 signaling was involved in hypoxia-induced upregulation of TH in the rat adrenal medulla. This study shows the expression of GRM1-8 mRNAs in rat and human adrenal glands and indicates that glutamate, through the activation of mGluRs, may play various physiological roles in the adrenal gland. Furthermore, mGluR1 may be involved in catecholamine biosynthesis by regulating TH, and mGluR5 may affect cortical and medullar hormone levels by regulating microvascular function.

Role of hypoxia and HIF2α in development of the sympathoadrenal cell lineage and chromaffin cell tumors with distinct catecholamine phenotypic features

Hypoxia has wide-ranging impact in normal physiology and disease processes. This stimulus evokes changes in gene expression mediated by transcription factors termed hypoxia-inducible factors (HIFs) that affect numerous processes: angiogenesis, cell survival, cellular metabolism, stem cell self-renewal and multipotency, migration, invasiveness, and metastatic progression in tumor cells. Over the past decade, increasing numbers of reports have emerged documenting differential roles of HIF1α and HIF2α in these processes. In cells of the sympathoadrenal lineage, both HIFs differentially mediate influences of hypoxia on catecholamine synthesis and secretion, but HIF2α signaling has particularly prominent functions in regulating developmental processes of growth and differentiation. This chapter discusses the role of HIF2α and HIF1α in the context of the development, phenotypic features, and functions of chromaffin cells. Moreover, current knowledge about tumor formation in cells of the sympathoadrenal lineage, leading to catecholamine-producing pheochromocytomas and paragangliomas, is analyzed in the light of the HIF2α signaling network.

Hypoxia inducible factor (HIF)-2 alpha is required for the development of the catecholaminergic phenotype of sympathoadrenal cells

The basic helix-loop-helix transcription factor, hypoxia inducible factor (HIF)-2alpha has been implicated in the development of the catecholaminergic phenotype in cells of the sympathoadrenal (SA) lineage; however, the underlying mechanisms and HIF-2alpha targets remain unclear. Using an immortalized rat adrenomedullary chromaffin cell line (MAH cells) derived from a fetal SA progenitor, we examined the role of HIF-2alpha in catecholamine biosynthesis. Chronic hypoxia (2% O(2), 24 h) induced HIF-2alpha in MAH cells but expression of the rate-limiting enzyme, tyrosine hydroxylase (TH) and catecholamine levels were unaltered. Interestingly, HIF-2alpha depleted MAH cells showed dramatically lower (5-12 times) levels of dopamine and noradrenaline compared with wild-type and scrambled controls, even in normoxia (21% O(2)). This was correlated with a marked reduction in the expression of DOPA decarboxylase (DDC) and dopamine beta hydroxylase (DbetaH) but not TH. Chromatin immunoprecipitation assays revealed that HIF-2alpha was bound to the DDC gene promoter which contains two putative hypoxia response elements. These data suggest that a basal level of HIF-2alpha function is required for the normal developmental expression of DDC and DbetaH in SA progenitor cells, and that loss of this function leads to impaired catecholamine biosynthesis.

Intermittent hypoxia activates peptidylglycine alpha-amidating monooxygenase in rat brain stem via reactive oxygen species-mediated proteolytic processing

Intermittent hypoxia (IH) associated with sleep apneas leads to cardiorespiratory abnormalities that may involve altered neuropeptide signaling. The effects of IH on neuropeptide synthesis have not been investigated. Peptidylglycine alpha-amidating monooxygenase (PAM; EC 1.14.17.3) catalyzes the alpha-amidation of neuropeptides, which confers biological activity to a large number of neuropeptides. PAM consists of O(2)-sensitive peptidylglycine alpha-hydroxylating monooxygenase (PHM) and peptidyl-alpha-hydroxyglycine alpha-amidating lyase (PAL) activities. Here, we examined whether IH alters neuropeptide synthesis by affecting PAM activity and, if so, by what mechanisms. Experiments were performed on the brain stem of adult male rats exposed to IH (5% O(2) for 15 s followed by 21% O(2) for 5 min; 8 h/day for up to 10 days) or continuous hypoxia (0.4 atm for 10 days). Analysis of brain stem extracts showed that IH, but not continuous hypoxia, increased PHM, but not PAL, activity of PAM and that the increase of PHM activity was associated with a concomitant elevation in the levels of alpha-amidated forms of substance P and neuropeptide Y. IH increased the relative abundance of 42- and 35-kDa forms of PHM ( approximately 1.6- and 2.7-fold, respectively), suggesting enhanced proteolytic processing of PHM, which appears to be mediated by an IH-induced increase of endoprotease activity. Kinetic analysis showed that IH increases V(max) but has no effect on K(m). IH increased generation of reactive oxygen species in the brain stem, and systemic administration of antioxidant prevented IH-evoked increases of PHM activity, proteolytic processing of PHM, endoprotease activity, and elevations in substance P and neuropeptide Y amide levels. Taken together, these results demonstrate that IH activates PHM in rat brain stem via reactive oxygen species-dependent posttranslational proteolytic processing and further suggest that PAM activation may contribute to IH-mediated peptidergic neurotransmission in rat brain stem.

Interrelationships Among Hypoxia-Inducible Factor Biology and Acid-Base Equilibrium

In this article, we try to summarize the most important novel biological information on the complex interrelationships between acid-base alterations and hypoxia-inducible factor (HIF) signaling. Extracellular and intracellular acid-base alterations affect HIF signaling in part independently of hypoxia, and involve, among others, effects on cytoprotection and apoptosis. Conversely, HIF signaling may affect systemic and local acid production rates and has been implicated in the mechanism of the acute hyperventilatory response (ie, respiratory alkalosis) in response to hypoxia as well as for hypoxia-induced pulmonary artery hypertension (PAH), although the latter data are quite preliminary and can be explained by alternative mechanisms. Thus, this review calls attention to these relationships for renal physiologists and nephrologists to stimulate focused clinical observations and specific investigative efforts as proposed in this overview.

Differential regulation of short and long dopamine D2 receptor mRNA levels by hypoxia in the adrenals of 1-day-old and adult rabbits

We tested the hypothesis that hypoxic exposure exerts distinct modulation on the mRNA level of the short and long isoform of the D2 dopamine (DA) receptor (D(2)r) and on tyrosine hydroxylase (TH) in the adrenals and superior cervical ganglion (SCG) of 1-day-old and adult rabbits. One-day-old and adult rabbits have been exposed to moderate (FiO(2): 0.15) or severe (FiO(2): 0.08) hypoxia for 0 (control), 6 or 24 h. At the end of the hypoxic exposure, the adrenals and SCG were rapidly dissected and kept frozen. Standard procedure for Northern blot and RT-PCR for evaluation of the short (D(2S)) or long (D(2L)) isoform of D(2)r and TH have been used. In the adrenals of adult rabbits, moderate and severe hypoxia decreased the D(2S) and D(2L) mRNA with a more prominent effect on the short isoform and increased TH mRNA. In 1-day-old rabbits, changes of D(2)r and TH mRNA levels were observed only after 24 h of severe or moderate hypoxic exposure and only the D(2S) receptor mRNA was significantly reduced. In the SCG, the expression level of both TH and D(2)r mRNA were not affected by hypoxic exposure in adult and newborn rabbits. Hence, sustained hypoxic exposure exerts distinct changes on mRNA level of D(2)r isoform and TH in an age- and tissue-dependent pattern.

Regulation of catecholamines by sustained and intermittent hypoxia in neuroendocrine cells and sympathetic neurons

Chronic intermittent hypoxia, a characteristic feature of sleep-disordered breathing, induces hypertension through augmented sympathetic nerve activity and requires the presence of functional carotid body arterial chemoreceptors. In contrast, chronic sustained hypoxia does not alter blood pressure. We therefore analyzed the biosynthetic pathways of catecholamines in peripheral nervous system structures involved in the pathogenesis of intermittent hypoxia-induced hypertension, namely, carotid bodies, superior cervical ganglia, and adrenal glands. Rats were exposed to either intermittent hypoxia (90 seconds of room air alternating with 90 seconds of 10% O2) or to sustained hypoxia (10% O2) for 1 to 30 days. Dopamine, norepinephrine, epinephrine, dihydroxyphenylacetic acid, and 5-hydroxytyptamine contents were measured by high-performance liquid chromatography. Expression of tyrosine hydroxylase and its phosphorylated forms, dopamine beta-hydroxylase, phenylethanolamine N-methyltransferase, and GTP cyclohydrolase-1 were determined by Western blot analyses. Both sustained and intermittent hypoxia significantly increased dopamine and norepinephrine content in carotid bodies but not in sympathetic ganglia or adrenal glands. In carotid bodies, both types of hypoxia augmented total levels of tyrosine hydroxylase protein and its phosphorylation on serines 19, 31, 40, as well as levels of GTP cyclohydrolase-1. However, the effects of intermittent hypoxia on catecholaminergic pathways were significantly smaller and delayed than those induced by sustained hypoxia. Thus, attenuated induction of catecholaminergic phenotype by intermittent hypoxia in carotid body may play a role in development of hypertension associated with sleep-disordered breathing. The effects of both types of hypoxia on expression of catecholaminergic enzymes in superior cervical neurons and adrenal glands were transient and small.

Age-related modulation of dopamine d1 receptor mRNA level by hypoxia in rabbit adrenal gland

In the perinatal period, the fetus and the neonate may be exposed to hypoxic conditions. The adrenal gland responds to systemic hypoxia by releasing catecholamines. Dopamine and dopamine D1 receptor are present in the adrenal medulla and are liable to be affected by exposure to hypoxia. We used a rabbit model to determine whether hypoxia modulates the dopamine D1 receptor (DA D1-R) mRNA expression in adrenal glands during development. Rabbits were investigated according to four different hypoxic conditions: 15% O2 for 6 h, 15% O2 for 24 h, 8% O2 for 6 h, and 8% O2 for 24 h. Control groups were maintained in normoxic conditions (21% O2). For each O2 condition, animals were studied at three different ages: 1-day old newborns, 25-day-old pups, and 6-month-old adults. We compared the hypoxic groups to their respective age normoxic group. We have shown that hypoxia decreases DA D1-R mRNA expression level, evaluated using Northern blot analysis, in newborn rabbits, whatever the duration and severity of hypoxia. This downmodulation was not observed in 25-day-old and in adult rabbits. This age-related modulation of adrenal DA D1-R mRNA could be linked to the age-related transition from the non-neurogenic to the neurogenic regulation of the adrenal function.

Activation of tyrosine hydroxylase by intermittent hypoxia: involvement of serine phosphorylation

Regulation of tyrosine hydroxylase (TH) by intermittent hypoxia (IH) was investigated in rat pheochromocytoma 12 (PC-12) cells by exposing them to alternating cycles of hypoxia (1% O2, 15 s) and normoxia (21% O2, 3 min) for up to 60 cycles; controls were exposed to normoxia for a similar duration. IH exposure increased dopamine content and TH activity by approximately 42 and approximately 56%, respectively. Immunoblot analysis revealed that comparable levels of TH protein were expressed in normoxic and IH cells. Removal of TH-bound catecholamines and in vitro phosphorylation of TH in cell-free extracts by the catalytic subunit of protein kinase A (PKA) increased TH activity in normoxic but not in IH cells, suggesting possible induction of TH phosphorylation and removal of endogenous inhibition of TH by IH. To assess the role of serine phosphorylation in IH-induced TH activation, TH immunoprecipitates and extracts derived from normoxic and IH cells were probed with anti-phosphoserine and anti-phospho-TH (Ser-40) antibody, respectively. Compared with normoxic cells, total serine and Ser-40-specific phosphorylation of TH were increased in IH cells. IH-induced activation of TH and the increase in total serine and Ser-40-specific phosphorylation of TH were inhibited by Ca2+/calmodulin-dependent protein kinase (CaMK) and PKA-specific inhibitors but not by inhibitors of the extracellular signal-regulated protein kinase pathway, suggesting that IH activates TH in PC-12 cells via phosphorylation of serine residues including Ser-40, in part, by CaMK and PKA. Our results also suggest that IH-induced phosphorylation of TH facilitates the removal of endogenous inhibition of TH, leading to increased synthesis of dopamine.

Human autonomic activity and its response to acute oxygen supplement after high altitude acclimatization

It is well established that after acclimatization at high altitude, many sympathetic pathways are hyperactive yet heart rate (HR) remains unchanged. In this study, we attempted to determine if this unchanged heart rate is due to compensatory mechanisms such as changes in parasympathetic activity or levels of receptors for autonomic neurotransmitters. We also examined the role played by hypoxia in these autonomic adaptations to high altitude. Three experiments were carried out on five healthy lowlanders both at sea level (SL) and after 2 weeks of acclimatization at 3800 m (Post-Ac) with: (a) placebo (control); (b) acute beta-adrenergic receptor blockade by propranolol (PRO), or (c) acute parasympathetic receptor blockade by glycopyrrolate (GLY). Compared with SL control values, post-Ac venous norepinephrine (NE) and dopamine increased by 96% (p < 0.001) and 55% (p < 0.05), but epinephrine and HR did not change. PRO resulted in a smaller decrease in HR (bpm) Post-Ac than at SL (15 +/- 6 vs. 21 +/- 6, p < 0.05), while GLY caused a greater increase in HR Post-Ac than at SL (59 +/- 8 vs. 45 +/- 6, p < 0.05). Breathing oxygen at SL concentration while at altitude did not decrease NE, or alter the effect of PRO on HR, but reduced the chronotropic effect of GLY by 14% (p < 0.05). These results suggest that after acclimatization to altitude, increased parasympathetic neurotransmitter release and decreased beta-adenoreceptor activity account for the unchanged HR despite enhanced sympathetic activity. Acute oxygen replacement rapidly counteracted the parasympathetic, but not sympathetic hyperactivity that occurs at high altitude.

Increased expression of tyrosine hydroxylase immunoreactivity in paraventricular and supraoptic neurons in illnesses with prolonged osmotic or nonosmotic stimulation of vasopressin release

Our previous studies indicated that in the human paraventricular (PVN) and supraoptic (SON) nuclei, tyrosine hydroxylase (TH)--the first and rate-limiting enzyme in catecholamine synthesis--is localized mainly in magnocellular neurons and that antemortem factors regulate its expression. The purpose of the present study was to investigate the distribution of TH-immunoreactive (TH-IR) perikarya of the hypothalami of a large sample of well-documented adult subjects without neurological, psychiatric or endocrinological disease in order to identify factors that could regulate the expression of TH in the human neurosecretory neurons. Our material consisted of the hypothalami of 38 subjects studied immunohistochemically for TH using the peroxidase-antiperoxidase method. Striking individual differences were observed among the subjects studied concerning the number and distribution of TH-IR perikarya within the PVN and SON. These differences were evident throughout the entire rostrocaudal length of the hypothalamus and appeared to be related neither to the age or sex of the subjects nor to the postmortem interval or staining procedures. In the sample studied, a large number of TH-IR perikarya were observed specifically in all subjects that had suffered from right-sided heart failure due to pulmonary hypertension, liver cirrhosis or dehydration. In all the above illnesses, increased production and secretion of vasopressin (VP) are reported to occur due to a decrease in 'effective' blood volume or to osmotic stimulation. We conclude that somatic illnesses leading to prolonged osmotic or nonosmotic stimulation of VP release may induce increased expression of TH immunoreactivity in the human neurosecretory neurons related to neuronal activation.

Geriatric men at altitude: hypoxic ventilatory sensitivity and blood dopamine changes

BACKGROUND

Short-term exposure to high-altitude hypoxia increases hypoxic ventilatory sensitivity (HVS) in healthy humans. Dopamine (DA) is the implicated neurotransmitter in carotid body (CB) chemoreceptor response, and the microenvironmental conditions in CB tissue are comparable to blood. Continuous DA infusion affected ventilation in animals and humans. Age-related oscillations in blood DA levels may influence peripheral chemoreflexes.

OBJECTIVE

Hypoxic ventilatory responses (HVR) relative to blood DA concentration and its precursor, dihydroxyphenylalanine (DOPA) was measured in young and elderly men during short-term altitude adaptation.

METHODS

Nine elderly climbers (group 1:61+/-1.4 years) and 7 young healthy subjects (group 2: 23+/-2 years) were tested at sea level on day 0, on day 3 after passive transport to 2,200 m, and on day 14 after climbing to 4,200 and 5,642 m.

RESULTS

Sea level HVR in group 1 was 47% lower than in group 2, accompanied by higher blood DOPA (300%) and DA (37%) content. Initial DA and DOPA concentrations showed a negative correlation with initial HVR but a positive correlation with age. Passive transport to middle altitude (2,200 m) increased HVS, doubling HVR slopes in groups 1 and 2 and producing increased maximum expired minute ventilation during isocapnic rebreathing (29 and 28%, respectively). Day 3 2,200-meter blood DOPA content decreased by 22% in group 1 and increased by 300% in group 2. DA increased in both groups.

CONCLUSION

The relationship between HVR and the reciprocal DA and DOPA values seen in both groups is associated with age, producing decreased DA receptor sensitivity and enhanced DA reuptake during adaptation to high altitude.

Peripheral chemosensitivity and central integration: neuroplasticity of catecholaminergic cells under hypoxia

The plasticity of catecholaminergic cells within the carotid body, brainstem and sympatho-adrenal system was analyzed in rats subjected to normobaric hypoxia (10% O2) lasting up to 3 weeks. Long-term hypoxia elicited structural, neurochemical and phenotypic changes in carotid body and sympathetic ganglia (SIF cells), and stimulated the norepinephrine turnover in A2 neurons located caudal to the obex, the area where the chemosensory nerve fibers end. Chemodenervation abolished central alterations. Adaptive mechanisms for increasing norepinephrine biosynthesis in hypoxia involved changes in activity of pre-existing tyrosine hydroxylase, the rate-limiting enzyme of catecholamine biosynthesis, and induction of new tyrosine hydroxylase protein. These neurochemical changes occurred after sustained hypoxia only, suggesting that noradrenergic neurons are involved in the central chemoreceptor pathway during sustained hypoxia but are not essential for regulatory responses to acute hypoxia. Acute hypoxia elicited the expression of c-Fos protein in neurons located in nucleus tractus solitarius that were not catecholaminergic. Noradrenaline released under long-term hypoxia could play a neuromodulatory role in ventilatory acclimatization. Cardiovascular responses to hypoxia are mediated by changes in sympatho-adrenal outflow, different according to the target organ. Cardiac sympathetic output and adrenal secretion were stimulated independently of carotid body chemoafferents. Early postnatal hypoxia induced long-term neurochemical changes in carotid body, brainstem and sympathetic efferents that may reveal alterations in development of neurons involved in the chemoreceptor pathway.

Post-transcriptional regulation of tyrosine hydroxylase gene expression by oxygen in PC12 cells

Reduced oxygen tension (hypoxia) leads to increased stability of mRNA for tyrosine hydroxylase (TH), the rate limiting enzyme in biosynthesis of catecholamine neurotransmitters. Hypoxia increases the half life of TH mRNA from 10 to 30 hours. The increased stability of TH mRNA during hypoxia results from fast enhanced binding of a cytoplasmic protein (hypoxia inducible protein, HIP) to a pyrimidine-rich sequence within the 3' untranslated region (3'UTR) of TH mRNA. This novel cis-element is referred to as hypoxia-inducible protein binding site (HIPBS) and is located between bases 1551 and 1578 of the 3' UTR of TH mRNA. We identified that the (U/C)(C/U)CCCU motif within the HIPBS represents the optimum protein-binding site. Mutations within this region that abolish protein binding prevent also regulation of TH mRNA stability during hypoxia. UV-crosslinking and SDS-PAGE analysis of the HIPBS-protein complexes showed the presence of a major 50 kDa complex. The formation of the complex was augmented when protein extracts were obtained from PC12 cells exposed to 5% O2. Importantly, formation of the 50 kDa complex was also increased when protein extracts were obtained from carotid bodies or superior cervical ganglia from rats exposed to 10% hypoxia for twenty-four hours.

Effects of long-term hypoxia on tyrosine hydroxylase protein content in catecholaminergic rat brainstem areas: a quantitative autoradiographic study

The nucleus tractus solitarius (NTS), the ventrolateral medulla (VLM), the dorsal motor vagus nucleus (DMnX) and the locus coeruleus (LC) are catecholaminergic brainstem areas involved in ventilatory and cardiovascular responses to hypoxia and tyrosine hydroxylation is the rate limiting step of cathecholamine biosynthesis in the central nervous system. The aim of this study was to evaluate the effects of long-term hypoxia on tyrosine hydroxylase (TH) content in these different areas using a quantitative autoradiographic technique. Two experimental groups of rats were studied: Group I (9 males, 8 females) was submitted to normobaric hypoxia (10% O2-90% N2) for 21 days and compared to 12 (6 males, 6 females) normoxic control rats (Group II). Coronal tissue sections from fresh-frozen rat brains, obtained along the caudo-rostral axis, were incubated in the presence of a TH monoclonal antibody, and the reaction was revealed by a 35S-labelled secondary antibody. TH levels were quantified in the NTS, VLM, DMnX and LC by measuring optical density on autoradiographic films using an automatic image analyser system. Regional antigen quantification was assessed by computer-assisted image analysis. Chronic hypoxia led to body weight decrease until day 5, haematocrit increase (65 +/- 2% vs. 44 +/- 2%, P < 0.01) and right ventricle hypertrophy (35 +/- 0.5% vs. 23 +/- 0.1% of the weight of the two ventricles, P < 0.01). TH protein contents expressed as percentage of controls were as follows. In males, in the rostral part of the NTS 132 +/- 9% (P < 0.02), in the caudal part of the NTS, 117 +/- 5% (P < 0.04). In female rats, the TH quantity reached a value of 124 +/- 4% (P < 0.01) in the rostral part and 126 +/- 6% (P < 0.01) in the caudal part of the NTS. In females, TH content was significantly increased in the VLM, 124 +/- 6%, P = 0.01, whereas in males there was only a non-significant trend to increase, 122 +/- 11%. In females, there was a significant increase in the DMnX, 127 +/- 9%, P = 0.05, whereas in males there was only a trend to increase, 120 +/- 5%. This study shows that long-term hypoxia induces a persistent increase in TH protein content both in the caudal and rostral part of the NTS, which are known to receive respectively chemo- and barosensory inputs, and in other catecholaminergic areas involved in baroreflex activity. Our data clearly demonstrate the implication of neurochemical mechanisms in the central relationship between chemo- and baroreflex which are responsible for changes in systemic arterial pressure and oxygen partial pressure as required for maintaining an adequate oxygen supply to the tissues.

Colocalization of tyrosine hydroxylase with oxytocin or vasopressin in neurons of the human paraventricular and supraoptic nucleus

In the developing and adult human paraventricular (PVN) and supraoptic (SON) nucleus, a large proportion of neurons contains the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH). In the present study we investigated the possible colocalization of TH with oxytocin (OXT) or vasopressin (VP) in the adult and neonatal PVN and SON. Adjacent paraffin sections were incubated simultaneously with two antibodies: a polyclonal against TH and a monoclonal against OXT or VP and stained with a double peroxidase-antiperoxidase/alkaline phosphatase method. We observed that TH-immunoreactive(IR) perikarya in the human PVN and SON were also positive for OXT or VP. A clear difference between the neonates and adult cases of our sample was observed in the proportion of TH-IR neurons that colocalize OXT or VP. In the neonates the majority of the TH-IR perikarya was also stained for VP, while only few TH-IR neurons were also positive for OXT. The opposite was observed in the adults, where the majority of the double-stained TH-IR neurons colocalizes OXT while only few TH-IR perikarya appear to contain VP. Our study establishes the colocalization of TH with OXT or VP in the adult and neonatal PVN and SON and indicates that antemortem factors such as perinatal hypoxia might increase TH-immunoreactivity of the VP neurons in man.

Regional specificity of the long-term regulation of tyrosine hydroxylase in some catecholaminergic rat brainstem areas. I. Influence of long-term hypoxia

The present study was carried out to investigate the influence of long-term hypoxia on tyrosine hydroxylase (TH) protein quantity in some catecholaminergic rat brainstem areas such as the dorsomedial medulla (DMM), the ventrolateral medulla (VLM) and the locus coeruleus (LC). TH protein quantity was also measured in a dopaminergic structure, the substantia nigra (SN). Male Sprague-Dawley rats were exposed to normobaric hypoxia (10% O2/90% N2) for 3, 7, 14 or 22 days. Controls were kept in normoxia for the same period. This study demonstrates that: (1) 3 days of hypoxia produced a 50% and a 26% increase in the quantity of TH protein in the rostral and caudal LC, respectively; (2) 14 days of hypoxia produced a 44% increase of TH protein content exclusively in the caudal part of DMM and a 31% increase in the VLM area; and (3) the stimulus failed to alter the TH protein quantity in the SN. After 14 and 22 days of hypoxia respectively, the TH protein content in the LC and DMM returned to the level of controls. To determine whether the increase in TH protein quantity could be related to a change in norepinephrine (NE) content, the rate constant of disappearance (k) of NE was measured in the catecholaminergic areas of intact or chemodenervated rats submitted to long-term hypoxia. Our results show that hypoxia causes an increase of TH protein quantity within the subpopulations of catecholaminergic areas additionally with an elevation in the NE content. These data suggest a selective response of the TH regulation to long-term hypoxia within the caudal DMM catecholaminergic area which receives chemosensory inputs.