Stress has been reported to activate the locus coeruleus (LC)-noradrenergic system. However, the molecular link between chronic stress and noradrenergic neurons remains to be elucidated. In the present study adult Fischer 344 rats were subjected to a regimen of chronic social defeat (CSD) for 4 weeks. Measurements by in situ hybridization and Western blotting showed that CSD significantly increased mRNA and protein levels of the norepinephrine transporter (NET) in the LC region and NET protein levels in the hippocampus, frontal cortex and amygdala. CSD-induced increases in NET expression were abolished by adrenalectomy or treatment with corticosteroid receptor antagonists, suggesting the involvement of corticosterone and corticosteroid receptors in this upregulation. Furthermore, protein levels of protein kinase A (PKA), protein kinase C (PKC), and phosphorylated cAMP-response element binding (pCREB) protein were significantly reduced in the LC and its terminal regions by the CSD paradigm. Similarly, these reduced protein levels caused by CSD were prevented by adrenalectomy. However, effects of corticosteroid receptor antagonists on CSD-induced down-regulation of PKA, PKC, and pCREB proteins were not consistent. While mifeprestone and spironolactone, either alone or in combination, totally abrogate CSD effects on these protein levels of PKA, PKC and pCREB in the LC and those in the hippocampus, frontal cortex and amygdala, their effects on PKA and PKC in the hippocampus, frontal cortex and amygdala were region-dependent. The present findings indicate a correlation between chronic stress and activation of the noradrenergic system. This correlation and CSD-induced alteration in signal transduction molecules may account for their critical effects on the development of symptoms of major depression.

The present study investigated the effects of forced overexpression of Phox2a/2b, two transcription factors, in the locus coeruleus (LC) of aged rats on noradrenergic and dopaminergic phenotypes in brains. Results showed that a significant increase in Phox2a/2b mRNA levels in the LC region was paralleled by marked enhancement in expression of DBH and TH per se. Furthermore, similar increases in TH protein levels were observed in the substantial nigra and striatum, as well as in the hippocampus and frontal cortex. Overexpression of Phox2 genes also significantly increased BrdU-positive cells in the hippocampal dentate gyrus and NE levels in the striatum. Moreover, this manipulation significantly improved the cognition behavior. The in vitro experiments revealed that norepinephrine treatments may increase the transcription of TH gene through the epigenetic action on the TH promoter. The results indicate that Phox2 genes may play an important role in improving the function of the noradrenergic and dopaminergic neurons in aged animals, and regulation of Phox2 gene expression may have therapeutic utility in aging or disorders involving degeneration of noradrenergic neurons.

No description available.

Although insult of the developing noradrenergic neuronal system in the brain has been associated with redistribution of noradrenergic fiber input to various target brain regions, few studies have investigated the effects of such insults on locus coeruleus cell survival. In the present study the dorsal noradrenergic bundle was transected by means of a midbrain knife cut in rats 3 days after birth, and the effects of this lesion were determined approximately 8-10 weeks later. Bymeans of an immunofluorescent histochemical procedure. it was shown that tyrosine hydroxylase-containing fibers and dopamine β-hydroxylase-containing fibers were markedly reduced in number in the neocortex and hippocampus - regions anterograde to the site of axonal transection. It was further demonstrated that the number of fluorescent fibers coursing through the dorsal bundle was similarly reduced. Sprouting of noradrenergic fibers in the brainstem and cerebellum accompanied the above alterations. When locus coeruleus cell number was determined by counting Cresyl violet-stained nucleoli in serial sections it was found that dorsal bundle transection produced a loss of 17% of the cells of the coeruleus. By dividing the counts for each nucleus into fifths, it was additionally found that approximately 20-25% of those cells comprising the midportion of the nucleus, along a rostrocaudal axis, were the ones destroyed by axonal transection. These findings indicate that a neonatal lesion of the dorsal bundle produces a loss of cells in the midportion of the nucleus locus coeruleus, and that this effect is associated with noradrenergic neuronal hyperinnervation of the brainstem and cerebellum.

No description available.

Major depressive disorder (MDD) and suicide have been associated with elevated indices of oxidative damage in the brain, as well as white matter pathology including reduced myelination by oligodendrocytes. Oligodendrocytes highly populate white matter and are inherently susceptible to oxidative damage. Pathology of white matter oligodendrocytes has been reported to occur in brain regions that process behaviors that are disrupted in MDD and that may contribute to suicidal behavior. The present study was designed to determine whether oligodendrocyte pathology related to oxidative damage extends to brain areas outside of those that are traditionally considered to contribute to the psychopathology of MDD and suicide. Relative telomere lengths and the gene expression of five antioxidant-related genes, SOD1, SOD2, GPX1, CAT, and AGPS were measured in oligodendrocytes laser captured from two non-limbic brain areas: occipital cortical white matter and the brainstem locus coeruleus. Postmortem brain tissues were obtained from brain donors that died by suicide and had an active MDD at the time of death, and from psychiatrically normal control donors. Relative telomere lengths were significantly reduced in oligodendrocytes of both brain regions in MDD donors as compared to control donors. Three antioxidant-related genes (SOD1, SOD2, GPX1) were significantly reduced and one was significantly elevated (AGPS) in oligodendrocytes from both brain regions in MDD as compared to control donors. These findings suggest that oligodendrocyte pathology in MDD and suicide is widespread in the brain and not restricted to brain areas commonly associated with depression psychopathology.

Rett Syndrome (RTT) is a neurodevelopmental disorder affecting 1 out of 10,000 females worldwide. Mutations of the X-linked MECP2 gene encoding methyl CpG binding protein 2 (MeCP2) accounts for >90% of RTT cases. People with RTT and mice with Mecp2 disruption show autonomic dysfunction, especially life-threatening breathing disorders, which involves defects in brainstem neurons for breathing controls, including neurons in the locus coeruleus (LC). Accumulating evidence obtained from Mecp2−/Y mice suggests that imbalanced excitation/inhibition or the impaired synaptic communications in central neurons plays a major role. LC neurons in Mecp2−/Ymice are hyperexcited, attributable to the deficiency in GABA synaptic inhibition. Several previous studies indicate that augmenting synaptic GABA receptors (GABARs) leads to a relief of RTT-like symptoms in mice. The extrasynaptic GABARs located outside synaptic cleft, which have the capability to produce sustained inhibition, and may be a potential therapeutic target for the rebalance of excitation/inhibition in RTT. In contrast to the rich information of the synaptic GABARs in RTT research, however, whether Mecp2 gene disruption affects the extrasynaptic GABARs remains unclear. In this study, we show evidence that the extrasynaptic GABAR mediated tonic inhibition of LC neurons was enhanced in Mecp2−/Ymice, which seems attributable to the augmented δ subunit expression. Low-dose THIP exposure, an agonist specific to δ subunit containing extrasynaptic GABARs, extended the lifespan, alleviated breathing abnormalities, enhanced motor function, and improved social behaviors of Mecp2−/Ymice. Such beneficial effects were associated with stabilization of brainstem neuronal hyperexcitability, including neurons in the LC and the mesencephalic trigeminal V nucleus (Me5), and improvement of norepinephrine (NE) biosynthesis. Such phenomena were found in symptomatic Mecp2+/− (sMecp2+/−) female mice model as well, in which the THIP exposure alleviated the hyperexcitability of both LC and Me5 neurons to a similar level as their counterparts in Mecp2−/Y mice, and improved breathing function. In identified LC neurons of sMecp2+/− mice, the hyperexcitability appeared to be determined by both MeCP2 expression and their environmental cues. In conclusion, intervention to extrasynaptic GABAAR by chronic treatment with THIP might be a therapeutic approach to RTT-like symptoms in both Mecp2−/Y and Mecp2+/− mice models and perhaps in people with RTT as well.

Patients with Rett Syndrome (RTT) show severe breathing disorders in addition to other neuropathological features, contributing to the high incidence of sudden unexplained death and abnormal brain development. However, the molecular and cellular mechanisms underlying the breathing disorders are still unknown. Recent studies indicate that the dysfunction of brainstem norepinephrine (NE) systems are closely associated with breathing disorders in RTT patients as well as its mice model, the Mecp2-null (Mecp2─/Y) mice. This as well as the fact the major group of NE-ergic neurons in the locus coeruleus (LC) is CO2 chemosensitive suggests that the breathing disorders in RTT may be related these LC neurons. To test this hypothesis, we took a multidisciplinary approach and systematically studied these neurons using molecular biology, in-vitro brain slices, acutely dissociated neurons, immunocytochemistry, and whole-body plethysmograph. To facilitate the electrophysiological studies, we developed a new strain of transgenic mice with GFP expression selectively in the LC neurons of both WT and Mecp2─/Y mice. Breathing activity of the Mecp2─/Y mice showed selective disruptions in responses to mild hypercapnia. The defect was alleviated with the NE uptake blocker desipramine, suggesting the involvement of NE in central CO2 chemosensitivity. In the LC region, the expressions of tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) at both protein and mRNA levels reduced by ~50% in Mecp2─/Y mice. No evidence was found for selective deficiency in TH- or DBH-containing neurons in Mecp2─/Y mice, and no major loss of NE-ergic LC cells were found, indicating that the NE defect is likely to result from deficient expression of biosynthetic enzymes rather than a loss of neurons in the LC. Several intrinsic membrane properties were abnormal in Mecp2─/Y LC neurons in comparison to wild type cells, including stronger inward rectification, shorter time constant, extended action potential duration, smaller amplitude of medium afterhyperpolarization (AHP) and over-expression of fast AHP. These abnormalities seem to be associated with the altered K+ and Na+ currents. Most importantly, Mecp2─/Y LC neurons displayed defective CO2 chemosensitivity in agreement of in vivo CO2 response, likely due to excessive expression of the homomeric Kir4.1 channel. Thus, it seems that the global effect of MeCP2 on the A6 NE system contributes to the impaired systemic CO2 response as well as the breathing irregularities in Mecp2─/Y mice. Such an alteration allowed CO2 to be detected only when hypercapnia became severe, leading to periodical hyper- and hypoventilation. These findings not only provide a novel etiology for the breathing disturbances of Mecp2─/Y mice but also show direct evidence for the first time on a molecular mechanism for the central CO2 chemosensitivity.

The correct development and function of CNS is critical for brain health of the organism. Early or chronic stress causes prominent alterations in brain function, and affects the expression of neurotrophic factors in limbic brain regions involved in the regulation of mood and cognition. Recent evidences have opened the idea that in complex organisms, an altered expression of certain neurotrophins by stress could be involved in the onset and pathophysiology of most psychiatric disorders, such as depression, squizophrenia or anxiety disorders. It is hypothesized that altered levels of neurotrophic factors could contribute to the atrophy and cell death of these regions, including the hippocampus and prefrontal cortex, which would produce a malfunction in limbic-related areas, and as a consequence, a precipitation or worsening of psychiatric illnesses. We were interested in panic disorder pathophysiology, which is a stress-related disorder and is characterized by an altered cognitive processing of emotional information. Although little evidence has been found supporting a neurotrophic role in PD, recent data has revealed that NT-3/TrkC signaling might play a key role in limbic system morphology and function. Therefore, we suggest that NT-3/TrkC system is involved in PD pathogenesis. The main objective in the work of this doctoral thesis lie to determine the role of NTRK3 gene, that codifies for TrKC, in emotional cognition and stress response processes that underlies PD. To this end, we used a genetically modified mouse model of NTRK3 overexpression, which was validated as a model of PD. Here, it is characterized the effects produced by the increase of NTRK3 expression in the CNS, focusing in neural alterations that might influence changes in cognitive processes involved in coping strategies. Moreover, it is studied the mechanisms that underlie in these processes by different approaches, 1/physiologically, measuring the HPA axis response, 2/brain activation, analyzing the activation pattern to a stress stimulus, 3/cellular and gene expression profiling, characterizing key brain regions in cognitive processes, and 4/pharmacologically, studying neurotransmitters function.

Alzheimer’s disease (AD) is a degenerative disorder where the distribution of pathology throughout the brain is not random but follows a predictive pattern used for pathological staging. While the involvement of defined functional systems is fairly well established for more advanced stages, the initial sites of degeneration are still ill defined. The prevailing concept suggests an origin within the transentorhinal and entorhinal cortex (EC) from where pathology spreads to other areas. Still, this concept has been challenged recently suggesting a potential origin of degeneration in nonthalamic subcortical nuclei giving rise to cortical innervation such as locus coeruleus (LC) and nucleus basalis of Meynert (NbM). To contribute to the identification of the early site of degeneration, here, we address the question whether cortical or subcortical degeneration occurs more early and develops more quickly during progression of AD. To this end, we stereologically assesses neurone counts in the NbM, LC and EC layer-II in the same AD patients ranging from preclinical stages to severe dementia. In all three areas, neurone loss becomes detectable already at preclinical stages and is clearly manifest at prodromal AD/MCI. At more advanced AD, cell loss is most pronounced in the NbM > LC > layer-II EC. During early AD, however, the extent of cell loss is fairly balanced between all three areas without clear indications for a preference of one area. We can thus not rule out that there is more than one way of spreading from its site of origin or that degeneration even occurs independently at several sites in parallel.