Corticosterone Upregulates Gene and Protein Expression of Catecholamine Markers in Organotypic Brainstem Cultures

Molecular, Pathophysiological, and Clinical Aspects of Corticosteroid-Induced Neuropsychiatric Effects: From Bench to Bedside

Corticosteroids are frequently prescribed across medical disciplines, yet they are associated with various adverse effects, including neuropsychiatric symptoms, documented since their introduction over 60 years ago. The cellular mechanisms underlying neuropsychiatric symptoms are complex and somewhat obscure, involving multiple pathways. Notably, they include changes in excitability, cellular death of hippocampal and striatal neurons, and increased inflammation and oxidative stress. Clinical presentation varies, encompassing affective disorders (anxiety, euphoria, depression), psychotic episodes, and cognitive deficits. It is crucial to note that these manifestations often go unnoticed by treating physicians, leading to delayed detection of severe symptoms, complications, and underreporting. Discontinuation of corticosteroids constitutes the cornerstone of treatment, resolving symptoms in up to 80% of cases. Although the literature on this topic is scant, isolated cases and limited studies have explored the efficacy of psychotropic medications for symptomatic control and prophylaxis. Pharmacological intervention may be warranted in situations where corticosteroid reduction or withdrawal is not feasible or beneficial for the patient.

Molecular Mechanisms of Synaptic Plasticity: Dynamic Changes in Neuron Functions

The human brain has hundreds of billions of neurons and at least 7 million dendrites have been hypothesized to exist for each neuron, with over 100 trillion neuron-neuron, neuron-muscle, and neuron-endocrine cell synapses [...].

Changes of Dopamine and Tyrosine Hydroxylase Levels in the Brain of Germ-free Mice

Background

Dopamine (DA) is one of the most important catecholamine neurotransmitters in the central nervous system. The degeneration and deletion of dopaminergic neurons are closely linked to Parkinson's disease (PD) and other psychiatric or neurological diseases. Several studies have been suggesting that intestinal microorganisms are associated with the occurrence of central nervous diseases, including diseases that are closely related to dopaminergic neurons. However, the intestinal microorganism's regulation of dopaminergic neurons in the brain is largely unknown.

Objectives

This study aimed to investigate the hypothetical differences of DA and its synthase tyrosine hydroxylase (TH) expression in different parts of the brain of germ free (GF) mice.

Materials and Methods

Several studies in recent years have shown that commensal intestinal microbiota promotes changes in DA receptor expression, DA levels, and affects this monoamine turnover. Germ free (GF) and specific pathogen free (SPF) C57b/L male mice were used to analyze TH mRNA and expression levels, and DA levels in the frontal cortex, hippocampus, striatum, and cerebellum, using real time PCR, western blotting, and ELISA tools.

Results

Compared with SPF mice, the TH mRNA levels were decreased in the cerebellum of GF mice, while the TH protein expression was tended to increase in the hippocampus, and conversely showed significant decrease in the striatum. The average optical density (AOD) of TH immunoreactive nerve fibers and the number of axons in striatum of mice in GF group were significantly lower than that in SPF group. Compared with SPF mice, the DA concentration in the hippocampus, striatum and frontal cortex of GF mice was decreased in GF mice.

Conclusion

The changes of DA and its synthase TH in the brain of GF mice showed that the absence of conventional intestinal microbiota had certain regulatory effects on central dopaminergic nervous system, which is considered helpful for studying the effect of commensal intestinal flora on diseases related to impaired dopaminergic nerve system.

Chronic treatment with corticosterone increases the number of tyrosine hydroxylase-expressing cells within specific nuclei of the brainstem reticular formation

Cushing's syndrome is due to increased glucocorticoid levels in the body, and it is characterized by several clinical alterations which concern both vegetative and behavioral functions. The anatomical correlates of these effects remain largely unknown. Apart from peripheral effects induced by corticosteroids as counter-insular hormones, only a few reports are available concerning the neurobiology of glucocorticoid-induced vegetative and behavioral alterations. In the present study, C57 Black mice were administered daily a chronic treatment with corticosterone in drinking water. This treatment produces a significant and selective increase of TH-positive neurons within two nuclei placed in the lateral column of the brainstem reticular formation. These alterations significantly correlate with selective domains of Cushing's syndrome. Specifically, the increase of TH neurons within area postrema significantly correlates with the development of glucose intolerance, which is in line with the selective control by area postrema of vagal neurons innervating the pancreas. The other nucleus corresponds to the retrorubral field, which is involved in the behavioral activity. In detail, the retrorubral field is likely to modulate anxiety and mood disorders, which frequently occur following chronic exposure to glucocorticoids. To our knowledge, this is the first study that provides the neuroanatomical basis underlying specific symptoms occurring in Cushing's syndrome.

Hamster organotypic modeling of SARS-CoV-2 lung and brainstem infection

SARS-CoV-2 has caused a global pandemic of COVID-19 since its emergence in December 2019. The infection causes a severe acute respiratory syndrome and may also spread to central nervous system leading to neurological sequelae. We have developed and characterized two new organotypic cultures from hamster brainstem and lung tissues that offer a unique opportunity to study the early steps of viral infection and screening antivirals. These models are not dedicated to investigate how the virus reaches the brain. However, they allow validating the early tropism of the virus in the lungs and demonstrating that SARS-CoV-2 could infect the brainstem and the cerebellum, mainly by targeting granular neurons. Viral infection induces specific interferon and innate immune responses with patterns specific to each organ, along with cell death by apoptosis, necroptosis, and pyroptosis. Overall, our data illustrate the potential of rapid modeling of complex tissue-level interactions during infection by a newly emerged virus.

HIF1α is a direct regulator of steroidogenesis in the adrenal gland

Endogenous steroid hormones, especially glucocorticoids and mineralocorticoids, derive from the adrenal cortex, and drastic or sustained changes in their circulatory levels affect multiple organ systems. Although hypoxia signaling in steroidogenesis has been suggested, knowledge on the true impact of the HIFs (Hypoxia-Inducible Factors) in the adrenocortical cells of vertebrates is scant. By creating a unique set of transgenic mouse lines, we reveal a prominent role for HIF1α in the synthesis of virtually all steroids in vivo. Specifically, mice deficient in HIF1α in adrenocortical cells displayed enhanced levels of enzymes responsible for steroidogenesis and a cognate increase in circulatory steroid levels. These changes resulted in cytokine alterations and changes in the profile of circulatory mature hematopoietic cells. Conversely, HIF1α overexpression resulted in the opposite phenotype of insufficient steroid production due to impaired transcription of necessary enzymes. Based on these results, we propose HIF1α to be a vital regulator of steroidogenesis as its modulation in adrenocortical cells dramatically impacts hormone synthesis with systemic consequences. In addition, these mice can have potential clinical significances as they may serve as essential tools to understand the pathophysiology of hormone modulations in a number of diseases associated with metabolic syndrome, auto-immunity or even cancer.

Maternal stress programs accelerated aging of the basal ganglia motor system in offspring

Early-life stress involved in the programming of stress-related illnesses can have a toxic influence on the functioning of the nigrostriatal motor system during aging. We examined the effects of perinatal stress (PRS) on the neurochemical, electrophysiological, histological, neuroimaging, and behavioral correlates of striatal motor function in adult (4 months of age) and old (21 months of age) male rats. Adult PRS offspring rats showed reduced dopamine (DA) release in the striatum associated with reductions in tyrosine hydroxylase-positive (TH⁺) cells and DA transporter (DAT) levels, with no loss of striatal dopaminergic terminals as assessed by positron emission tomography analysis with fluorine-18-l-dihydroxyphenylalanine. Striatal levels of DA and its metabolites were increased in PRS rats. In contrast, D₂ DA receptor signaling was reduced and A_2A adenosine receptor signaling was increased in the striatum of adult PRS rats. This indicated enhanced activity of the indirect pathway of the basal ganglia motor circuit. Adult PRS rats also showed poorer performance in the grip strength test and motor learning tasks. The aged PRS rats also showed a persistent reduction in striatal DA release and defective motor skills in the pasta matrix and ladder rung walking tests. In addition, the old rats showed large increases in the levels of SNAP-25 and synaptophysin, which are synaptic vesicle-related proteins in the striatum, and in the PRS group only, reductions in Syntaxin-1 and Rab3a protein levels were observed. Our findings indicated that the age-dependent threshold for motor dysfunction was lowered in PRS rats. This area of research is underdeveloped, and our study suggests that early-life stress can contribute to an increased understanding of how aging diseases are programmed in early-life.