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

Bile duct ligation increased dopamine levels in the cerebral cortex of rats partly due to induction of tyrosine hydroxylase

BACKGROUND AND PURPOSE

Liver failure is associated with psychiatric alterations, partly resulting from the increased brain dopamine levels. We investigated the relationship between increased dopamine levels and mental abnormalities using bile duct ligation (BDL) rats and the mechanism by which liver failure increased dopamine levels in SH-SY5Y cells. Behavioural tests were carried out on day 13 and 27 following BDL, along with measurements of dopamine and metabolites, expressions of enzymes and transporters related to dopamine metabolism, and its transport into the cortex and the hippocampus. SH-SY5Y cells were used to investigate whether NH₄ Cl, bile acids and bilirubin affected expression of tyrosine hydroxylase or not. Tyrosine hydroxylase (TH) expression in SH-SY5Y cells co-incubated with bilirubin and signal pathway inhibitors was measured.

KEY RESULTS

Open-field test results demonstrated BDL rats showed anxiety-like behaviour, accompanied by increased dopamine levels and expression of TH protein in the cortex. Membrane bound long form (MB)-COMT, slightly but significantly decreased. SH-SY5Y cells indicated that increased bilirubin levels was a factor in inducing TH expression. Both inhibitor of NF-κB pathway BAY 11-7082 and silencing NF-κB p65 reversed bilirubin-induced upregulation of TH protein. NF-κB activator TNF-α increased expression of TH protein. Roles of bilirubin in increases of TH protein expressions and dopamine levels were measured using hyperbilirubinemia rats. Anxiety-like behaviour, was associated with increased dopamine levels and TH protein expressions in hyperbilirubinemia rats.

CONCLUSION AND IMPLICATIONS

BDL significantly increased dopamine levels in rat cortex partly due to bilirubin-mediated TH induction. Increased bilirubin induced TH expression via activating NF-κB signalling pathway.

Matching of the postmortem hypothalamus from patients and controls

The quality of postmortem hypothalamus research depends strongly on a thorough clinical investigation and documentation of the patient's disorder and therapies. In addition, a systematic and professional neuropathological investigation of the entire brain of both the cases and the controls is absolutely crucial. In the experience of the Netherlands Brain Bank (NBB), about 20% of the clinical neurological diagnoses, despite being made in first rate clinics, have to be revised or require extra diagnoses after a complete and thorough neuropathologic review by the NBB. The neuropathology examination may reveal for instance that the elderly "controls" already have preclinical neurodegenerative alterations. In postmortem studies, the patient and control groups must be matched for as many as possible of the known confounding factors. This is necessary to make the groups as similar as possible, except for the topic being investigated. Confounding factors are present (i) before, (ii) during, and (iii) after death. They are, respectively: (i) genetic background, systemic diseases, duration and gravity of illness, medicines and addictive compounds used, age, sex, gender identity, sexual orientation, clock- and seasonal time of death, and lateralization; (ii) agonal state, stress of dying; and (iii) postmortem delay, freezing procedures, fixation, and storage time. Agonal state is generally estimated by measuring the pH of the brain. However, there are disorders in which pH is lower as a part of the disease process. Because of the large number of potentially confounding factors that differ according to, for instance, brain area and disease, a brain bank should have a large number of controls at its disposal for appropriate matching. If matching fails for some confounders, the influence of the confounders may be determined by statistical methods, such as analysis of variance or the regression models.

Distribution of tyrosine-hydroxylase-immunoreactive neurons in the hypothalamus of tree shrews

The tree shrew (Tupaia belangeri chinensis) is the closest living relative of primates. Yet, little is known about the anatomical distribution of tyrosine hydroxylase (TH)-immunoreactive (ir) structures in the hypothalamus of the tree shrew. Here, we provide the first detailed description of the distribution of TH-ir neurons in the hypothalamus of tree shrews via immunohistochemical techniques. TH-ir neurons were widely distributed throughout the hypothalamus of tree shrew. The majority of hypothalamic TH-ir neurons were found in the paraventricular hypothalamic nucleus (PVN) and supraoptic nucleus (SON), as was also observed in the human hypothalamus. In contrast, rare TH-ir neurons were localized in the PVN and SON of rats. Vasopressin (AVP) colocalized with TH-ir neurons in the PVN and SON in a large number of neurons, but oxytocin and corticotropin-releasing hormone did not colocalize with TH. In addition, colocalization of TH with AVP was also observed in the other hypothalamic regions. Moreover, TH-ir neurons in the PVN and SON of tree shrews expressed other dopaminergic markers (aromatic l-amino acid decarboxylase and vesicular monoamine transporter, Type 2), further supporting that TH-ir neurons in the PVN and SON were catecholaminergic. These findings provide a detailed description of TH-ir neurons in the hypothalamus of tree shrews and demonstrate species differences in the distribution of this enzyme, providing a neurobiological basis for the participation of TH-ir neurons in the regulation of various hypothalamic functions.

The art of matching brain tissue from patients and controls for postmortem research

The quality of postmortem research depends strongly on a thorough clinical investigation and documentation of the patient's disorder and therapies. In addition, a systematic and professional neuropathologic investigation of both cases and controls is absolutely crucial. In the experience of the Netherlands Brain Bank (NBB), about 20% of clinical neurologic diagnoses, despite being made in first-rate clinics, have to be revised or require an extra diagnosis after a complete and thorough review by the NBB. The neuropathology examination may reveal for instance that the "controls" already have preclinical neurodegenerative alterations. In postmortem studies the patient and control groups must be matched for as many of the known confounding factors as possible. This is necessary to make the groups as similar as possible, except for the topic being investigated. Confounding factors are present before, during, and after death. They are respectively: (1) genetic background, systemic diseases, duration and gravity of illness, medicines and addictive compounds used, age, sex, gender identity, sexual orientation, circadian and seasonal fluctuations, lateralization; (2) agonal state, stress of dying; and (3) postmortem delay, freezing procedures, fixation and storage time. Consequently, a brain bank should have a large number of controls at its disposal for appropriate matching. If matching fails for some confounders, then their influence may be determined by statistical methods such as analysis of variance or regression models.

Hematopoietic stem/progenitor involvement in retinal microvascular repair during diabetes: Implications for bone marrow rejuvenation

The widespread nature of diabetes affects all organ systems of an individual including the bone marrow. Long-term damage to the cellular and extracellular components of the bone marrow leads to a rapid decline in the bone marrow-hematopoietic stem/progenitor cells (HS/PCs) compartment. This review will highlight the importance of bone marrow microenvironment in maintaining bone marrow HS/PC populations and the contribution of these key populations in microvascular repair during the natural history of diabetes. The autonomic nervous system can initiate and propagate bone marrow dysfunction in diabetes. Systemic pharmacological strategies designed to protect the bone marrow-HS/PC population from diabetes induced-oxidative stress and advanced glycation end product accumulation represent a new approach to target diabetic retinopathy progression. Protecting HS/PCs ensures their participation in vascular repair and reduces the risk of vasogdegeneration occurring in the retina.

The human neurosecretory neurones under perinatal hypoxia: a quantitative immunohistochemical study of the supraoptic nucleus in autopsy material

In the rat, experimental manipulations that cause activation of the magnocellular neurosecretory neurones result in the synthesis, in addition to vasopressin (AVP) and oxytocin (OXY), of other neurotransmitters or peptides, including tyrosine hydroxylase (TH), the first and rate limiting enzyme for catecholamine biosynthesis. In the human neonate, our previous study showed that TH was selectively increased in AVP neurones of subjects that died from prolonged perinatal hypoxia. The purpose of the present study was to quantitatively investigate the expression of TH, AVP, OXY and neurophysin in magnocellular neurones of the human neonate in relation to the severity/duration of perinatal hypoxia, as estimated by neuropathological criteria. Autopsy was performed after obtaining parental written consent for diagnostic and research purposes. The intensity of the immunohistochemical reactions and the cellular/nuclear size were measured in the dorsolateral supraoptic nucleus using a computerised image analysis system. We showed that prolonged perinatal hypoxia resulted in the activation of the magnocellular neuroendocrine neurones of the human neonate, as indicated by their increased neuronal and nuclear size. OXY neurones appeared larger than the AVP ones at birth, possibly indicating an active role of foetal OXY during labour or even earlier. The gradual increase in the duration of the insult resulted in the reduction of intracellular AVP content, in parallel with a dramatic increase in the expression of TH, indicating a functional interaction of these peptides under neuronal activation. Ιsolated evidence in our series, obtained from an infant of a diabetic mother, raises the probability that in the case of hyperglycaemia the above pathogenetic mechanisms are diversified.

Reduced immunoreactivity of tyrosine hydroxylase in the hypothalamic paraventricular nucleus of the seizure sensitive gerbil

We compared the immunoreactivity and numbers of tyrosine hydroxylase (TH) immunoreactive neurons and neuropil in the paraventricular nucleus (PVN) of the hypothalamus between the seizure sensitive (SS) and seizure resistant (SR) gerbils. The distributional pattern of TH immunoreactivity was similar in both groups: TH immunoreactivity was seen mainly in magnocellular neurons of the PVN. However, total TH immunoreactivity in the neurons and neuropil in the SS gerbils was significantly lower than that in the SR gerbils. In addition, the number of TH immunoreactive neurons in the SS gerbils was also much lower than those in the SR gerbils. These results indicate that SS gerbils have a low TH immunoreactivity in the hypothalamic PVN compared with that in SR gerbils.

Morphological substrate of the catecholaminergic input of the vasopressin neuronal system in humans

It has been postulated that the stress response is associated with water balance via regulating vasopressin release. Nausea, surgical stress and insulin-induced hypoglycaemia were shown to stimulate vasopressin secretion in humans. Increased vasopressin release in turn induces water resorption through the kidneys. Although the mechanism of the stress-mediated vasopressin release is not entirely understood, it is generally accepted that catecholamines play a crucial role in influencing water balance by modulating the secretion of vasopressin. However, the morphological substrate of this modulation has not yet been established. The present study utilised double-label immunohistochemistry to reveal putative juxtapositions between tyrosine hydroxylase (TH)-immunoreactive (IR) catecholaminergic system and the vasopressin systems in the human hypothalamus. In the paraventricular and supraoptic nuclei, numerous vasopressin-IR neurones received TH-IR axon varicosities. Analysis of these juxtapositions with high magnification combined with oil immersion did not reveal any gaps between the contacted elements. In conclusion, the intimate associations between the TH-IR and vasopressin-IR elements may be functional synapses and may represent the morphological basis of vasopressin release modulated by stressors. Because certain vasopressin-IR perikarya receive no detectable TH innervations, it is possible that additional mechanisms may participate in the stress-influenced vasopressin release.

Co-expression of tyrosine hydroxylase and GTP cyclohydrolase I in arginine vasopressin-synthesizing neurons of the human supraoptic nucleus demonstrated by laser microdissection and real-time PCR

Tyrosine hydroxylase (TH), the first and limiting enzyme for catecholamine synthesis, has been identified immunohistochemically (IHC) in human neurosecretory neurons where it is found to colocalize with vasopressin (AVP) or oxytocin. TH expression shows striking interindividual variability and appears to depend on neuronal activation. Since GTP cyclohydrolase I (GCHI), the first enzyme for tetrahydrobiopterin synthesis, the essential cofactor of TH, and aromatic L-amino acid decarboxylase (AADC) have so far not been detected in neurosecretory neurons, the functional role of TH in catecholamine synthesis is still questionable. Our purpose was to investigate in postmortem hypothalamus whether GCHI and AADC mRNAs are co-expressed with TH in human AVP-synthesizing neurons. Total RNA was extracted from laser microdissected TH-IHC-identified neurons as well as from dissected parts of the dorsolateral supraoptic nucleus (dl-SON) of 12 control subjects, i.e. without known neurological, psychiatric or endocrinological illness. GCHI, AADC and TH mRNA expression was determined by real-time PCR. Our results showed that GCHI mRNA is co-expressed with TH in almost all cases that had a considerable number of TH-immunoreactive (TH-IR) neurosecretory neurons. A positive correlation was found between TH-immunohistochemical intensity and the presence of GCHI mRNA. AADC mRNA expression was detected only in microdissected areas of dl-SON in 2 cases that showed an increased number of TH-IR neurons. The co-expression of GCHI with TH indicates that TH is indeed active in human neurosecretory neurons. The apparent limited expression of AADC indicates that dopamine might be produced in human neurosecretory neurons under activation of the hypothalamoneurohypophyseal system, although the possibility that L-dopa is the final product cannot be excluded.

Absence of a difference in the neurosecretory activity of supraoptic nucleus vasopressin neurons of neuroleptic-treated schizophrenic patients

Dysfunction in water intake and metabolism has frequently been reported in schizophrenia. The general population of schizophrenics under neuroleptic treatment secretes lower amounts of vasopressin than controls at comparable values of plasma osmolality. The purpose of the present study was to investigate the synthetic activity of vasopressin neurons of the dorsolateral supraoptic nucleus in schizophrenia on postmortem material using a battery of histochemical activity markers. Our material consisted of formalin-fixed and paraffin-embedded hypothalami from 5 schizophrenic patients under neuroleptic treatment and from 5 matched controls, obtained from The Netherlands' Brain Bank. DSM-III or DSM-IV criteria were used for the clinical diagnosis. The histochemical markers used to study the neuronal activity of the magnocellular vasopressin-synthesizing neurons were: cell size, size of the Golgi apparatus, and expression of vasopressin and tyrosine hydroxylase mRNA by in situ hybridization. Morphometric evaluation and statistical analysis (Mann-Whitney U test) were performed. Our results showed no statistically significant differences in any of the neuronal activity markers between schizophrenic patients and controls. Therefore, the neurosecretory activity of vasopressin neurons of the dorsolateral part of the supraoptic nucleus does not appear to be changed in schizophrenic patients under medication. Since our sample did not include patients with reported polydipsia or hyponatremia, prospective investigation is needed to evaluate the above-mentioned neuronal activity markers in such a particular subgroup of schizophrenic patients.

Individual differences in the expression of tyrosine hydroxylase mRNA in neurosecretory neurons of the human paraventricular and supraoptic nuclei: positive correlation with vasopressin mRNA

Previous studies indicated that in the human paraventricular nucleus (PVN) and in the supraoptic nucleus (SON) tyrosine hydroxylase (TH) - the first and rate-limiting enzyme in catecholamine synthesis - is localized mainly in magnocellular neurosecretory neurons. Individual differences were observed among control subjects in number and distribution of TH-immunoreactive (IR) perikarya, indicating that antemortem factors may regulate TH expression. Since a large number of TH-IR perikarya were observed in subjects who suffered from somatic illnesses leading to prolonged osmotic or nonosmotic stimulation of vasopressin (VP) release, we suggested that TH expression is related to the activation of VP neurons. The purpose of our study was to apply (1) in situ hybridization for TH mRNA on human PVN and SON to investigate how the previously reported individual differences in TH protein expression are depicted at the transcriptional level and (2) quantitative TH immunohistochemistry and in situ hybridization for VP mRNA throughout the dorsolateral part of the SON (dl-SON) in order to elucidate whether indeed expression of TH in neurosecretory nuclei depends on activation of VP neurons. Postmortem formalin-fixed, paraffin-embedded hypothalamic sections of 16 control subjects were studied for TH protein and TH and VP mRNAs. For 6 of the above cases, the number of TH-IR neurons and the total VP mRNA levels were estimated throughout the entire dl-SON using an image analysis system. Individual variation was observed in TH mRNA expression which appears to parallel the expression of TH-protein. Using Spearman's bivariate test, a positive correlation was found between the number of TH-IR- and TH-mRNA-expressing neurons in both PVN and SON (p < 0.01) as well as between the number of TH-IR neurons and the total VP mRNA in the dl-SON (p < 0.05). Our results show (1) that the individual variability in the number of TH-IR neurons within the neurosecretory nuclei might be due to differential expression and/or stability of TH mRNA and (2) that expression of TH-immunoreactivity in human PVN and SON depends on the activation of VP neurons.

Discrete expression of TRPV2 within the hypothalamo-neurohypophysial system: Implications for regulatory activity within the hypothalamic-pituitary-adrenal axis

Transient receptor potential channel proteins (TRPs) constitute a steadily growing family of ion channels with a range of purported functions. It has been demonstrated that TRPV2 is activated by moderate thermal stimuli and, in the rat, is expressed in medium to large diameter dorsal root ganglion neurons. In this study, antisera specific for the human TRPV2 homologue were raised and characterized for immunohistochemical use. Subsequently, thorough investigation was made of the localization of this cation channel in the macaque primate brain. TRPV2-immunoreactive material was highly restrictively localized to hypothalamic paraventricular, suprachiasmatic, and supraoptic nuclei. Confocal double- and triple-labeling studies demonstrated that TRPV2 immunoreactivity is preferentially localized to oxytocinergic and vasopressinergic neurons. Few, if any, cells in these regions expressed TRPV2 immunoreactivity in the absence of oxytocin immunoreactivity or vasopressin immunoreactivity. Expression in the paraventricular and supraoptic nuclei suggests that TRPV2 is likely to play a fundamental role in mediating cation transport in neurohypophysial neurons. TRPV2 has been shown to be translocated upon cell activation and neurons expressing TRPV2 immunoreactivity in vivo are among those known to engage in sporadic, intense activity. Taken together, these data suggest that this channel may play a vital role in mediating physiological activities associated with oxytocin and vasopressin release such as parturition, lactation, and diuresis. These data may also implicate the involvement of TRPV2 in disorders of the hypothalamic-pituitary-adrenal axis, including anxiety, depression, hypertension, and preterm labor.