Acute Transcriptional Effects of Dexamethasone on Mouse Adrenal Gland Transcriptome

Researchers have long known that dexamethasone causes cellular and functional changes in the adrenal gland. For example, long-term dexamethasone treatment leads to reversible adrenal cortex atrophy. In the adrenal medulla, dexamethasone treatment alters the maturation and function of the neural crest-derived chromaffin cells. Here we aim to study the acute transcriptional effect of dexamethasone on mouse adrenal gland at the transcriptome level. Our data suggested that a one-hour dexamethasone treatment had a cell type-specific effect on the adrenal transcriptome. There were 922 dexamethasone-induced genes and 853 dexamethasone-suppressed genes. GO analysis showed that the upregulated genes were primarily linked to neuronal cell function. Clustered heatmaps further showed that many genes involved in the catecholamine synthesis were upregulated by dexamethasone treatment, whereas most genes involved in the steroidogenesis pathway were downregulated. Interestingly, steroidogenic factor 1 (SF1, encoded by Nr5a1), the critical transcription factor that regulates steroidogenesis, had a >2-fold decrease under the one-hour dexamethasone treatment, suggesting a possible mechanism of the acute suppression of steroidogenic activity. Our findings indicate that the acute effects of dexamethasone stimulate catecholamine synthesis in the medulla, whereas steroidogenesis in the cortex is suppressed by dexamethasone.

MON-201 Effects of Incretins on Catecholamine Synthesis by Rat Pheochromocytoma PC12 Cells

Incretins, such as gastric inhibitory polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), are metabolic hormones secreted from the intestine to stimulate insulin secretion from the pancreatic β cells. Dipeptidyl peptidase-4 (DPP-4) inhibitors, as anti-diabetic agents, increase the bioavailability of both GIP and GLP-1. Since the receptor expressions of GIP and GLP-1 are detected in various organs, incretins have been suggested to affect many kinds of tissues and organs in addition to their insulinotropic effects. For instance, GIP and GLP-1 have been reported to regulate ovarian steroidogenesis and hypothalamic-pituitary-adrenal axis including secretions of adrenocorticotropin from the pituitary and cortisol from the adrenal cortex. However, the roles of GIP and GLP-1 in the adrenal medulla have not been recognized. Here we focused on the activity of bone morphogenetic protein (BMP)-4, which is expressed in the adrenal medulla and is functionally involved in the control of catecholamine synthesis. We earlier reported that BMP-4 treatment decreased catecholamine synthesis via smad1/5/9 phosphorylation and regulated catecholamine synthesis by cooperating with glucocorticoid and melatonin in rat pheochromocytoma PC12 cells. In the present study, roles of GIP and GLP-1 in the regulation of catecholamine production were studied using PC12 cells by focusing on interaction with BMP-4 and adrenocortical steroids. Both of GIP receptor and GLP-1 receptor expressions were detected in PC12 cells. Of note, treatments with GIP, but not with GLP-1, increased dopamine synthesis and the mRNA levels of catecholamine synthetic enzymes including tyrosine hydroxylase (TH), which is a rate-limiting enzyme for catecholamine synthesis, DOPA decarboxylase (DDC), and dopamine β-hydroxylase (DBH), by PC12 cells. Treatments with GIP enhanced glucocorticoid- and aldosterone-induced TH mRNA levels by upregulating the expressions of glucocorticoid receptor (GR) as well as mineralocorticoid receptor (MR). However, treatment with GLP-1 had no effect on corticosteroid-induced TH mRNA levels or GR/MR expression. On the other hand, treatment with GIP attenuated the inhibitory effect of BMP-4 that enables to decrease TH mRNA levels by suppressing BMP-induced Smad1/5/9 phosphorylation and Id-1 transcription. Furthermore, GIP treatment upregulated the expression of inhibitory Smad7, possibly leading to the suppression of BMP-4 signaling by PC12 cells. Collectively, it was revealed that incretins, in particular, GIP has an inducing effect on catecholamine synthesis through inhibiting BMP activities as well as enhancing corticosteroid actions in adrenomedullar cells.

Behavioural changes controlled by catecholaminergic systems explain recurrent loss of pigmentation in cavefish

Multiple cave populations of the teleost Astyanax mexicanus have repeatedly reduced or lost eye and body pigmentation during adaptation to dark caves. Albinism, the complete absence of melanin pigmentation, is controlled by loss-of-function mutations in the oca2 gene. The mutation is accompanied by an increase in the melanin synthesis precursor l -tyrosine, which is also a precursor for catecholamine synthesis. In this study, we show a relationship between pigmentation loss, enhanced catecholamine synthesis and responsiveness to anaesthesia, determined as a proxy for catecholamine-related behaviours. We demonstrate that anaesthesia resistance (AR) is enhanced in multiple depigmented and albino cavefish (CF), inversely proportional to the degree of pigmentation loss, controlled by the oca2 gene, and can be modulated by experimental manipulations of l -tyrosine or the catecholamine norepinephrine (NE). Moreover, NE is increased in the brains of multiple albino and depigmented CF relative to surface fish. The results provide new insights into the evolution of pigment modification because NE controls a suite of adaptive behaviours similar to AR that may represent a target of natural selection. Thus, understanding the relationship between loss of pigmentation and AR may provide insight into the role of natural selection in the evolution of albinism via a melanin–catecholamine trade-off.

Synthesis, Packaging, and Termination of Neurotransmitters

The synthesis, packaging, and termination of action of neurotransmitters are detailed. There are far more varieties of peptide neurotransmitters than there are of low-molecular-weight neurotransmitters. Yet low-molecular-weight neurotransmitters are the ubiquitous workhorses of the nervous system. Acetylcholine, the catecholamines norepinephrine and dopamine, serotonin, glutamate, and GABA are examined in some depth. The vesicular transporters that carry low-molecular-weight neurotransmitters from the cytoplasm into synaptic vesicles are covered. The role of monoamines in affect and mood and the psychotropic effects of monoaminergic drugs are discussed. Principles of catecholamine synthesis are applied to understand phenylketonuria. Uptake of monoamines into neurons is discussed in the context of amphetamine, cocaine, and other drugs of abuse. Stiff-person syndrome, which results from an impairment of GABA synthesis, is introduced. The modes of action for peptide and gaseous neurotransmitters are briefly covered.

The Dipeptides Ile-Tyr and Ser-Tyr Exert Distinct Effects on Catecholamine Metabolism in the Mouse Brainstem

Catecholamine synthesis and transmission in the brain are influenced by the availability of Tyr in the body. In this study, we compared the effects of oral administration of Tyr-containing dipeptides Ile-Tyr, Ser-Tyr, and Tyr-Pro with Tyr alone on catecholamine metabolism in the mouse brainstem. Among these dipeptides, Ile-Tyr administration led to increases in dopamine, the dopamine metabolites homovanillic acid, and 3,4-dihydroxyphenylacetic acid, compared to administration of Ser-Tyr, Tyr-Pro, or Tyr alone. In comparison, administration of Ser-Tyr induced significantly increasing noradrenaline turnover, while Tyr-Pro administration suppressed dopamine turnover. Therefore, oral administration of Ile-Tyr, Ser-Tyr, and Tyr-Pro differentially affected metabolism of dopamine and noradrenaline. These observations strongly suggest that Tyr-containing dipeptides exert distinct effects on catecholamine metabolism in the brainstem when ingested orally.