Modulation of paraventricular firing rate by secretin in vivo

Social boldness correlates with brain gene expression in male green anoles

Within populations, some individuals tend to exhibit a bold or shy social behavior phenotype relative to the mean. The neural underpinnings of these differing phenotypes - also described as syndromes, personalities, and coping styles - is an area of ongoing investigation. Although a social decision-making network has been described across vertebrate taxa, most studies examining activity within this network do so in relation to exhibited differences in behavioral expression. Our study instead focuses on constitutive gene expression in bold and shy individuals by isolating baseline gene expression profiles that influence social boldness predisposition, rather than those reflecting the results of social interaction and behavioral execution. We performed this study on male green anole lizards (Anolis carolinensis), an established model organism for behavioral research, which provides a crucial comparison group to investigations of birds and mammals. After identifying subjects as bold or shy through repeated reproductive and agonistic behavior testing, we used RNA sequencing to compare gene expression profiles between these groups within various forebrain, midbrain, and hindbrain regions. The ventromedial hypothalamus had the largest group differences in gene expression, with bold males having increased expression of neuroendocrine and neurotransmitter receptor and calcium channel genes compared to shy males. Conversely, shy males express more integrin alpha-10 in the majority of examined regions. There were no significant group differences in physiology or hormone levels. Our results highlight the ventromedial hypothalamus as an important center of behavioral differences across individuals and provide novel candidates for investigations into the regulation of individual variation in social behavior phenotype.

Secretin Regulates Excitatory GABAergic Neurotransmission to GnRH Neurons via Retrograde NO Signaling Pathway in Mice

In mammals, reproduction is regulated by a wide range of metabolic hormones that maintain the proper energy balance. In addition to regulating feeding and energy expenditure, these metabolic messengers also modulate the functional performance of the hypothalamic-pituitary-gonadal (HPG) axis. Secretin, a member of the secretin-glucagon-vasoactive intestinal peptide hormone family, has been shown to alter reproduction centrally, although the underlying mechanisms have not been explored yet. In order to elucidate its central action in the neuroendocrine regulation of reproduction, in vitro electrophysiological slice experiments were carried out on GnRH-GFP neurons in male mice. Bath application of secretin (100 nM) significantly increased the frequency of the spontaneous postsynaptic currents (sPSCs) to 118.0 ± 2.64% compared to the control, and that of the GABAergic miniature postsynaptic currents (mPSCs) to 147.6 ± 19.19%. Resting membrane potential became depolarized by 12.74 ± 4.539 mV after secretin treatment. Frequency of evoked action potentials (APs) also increased to 144.3 ± 10.8%. The secretin-triggered elevation of the frequency of mPSCs was prevented by using either a secretin receptor antagonist (3 μM) or intracellularly applied G-protein-coupled receptor blocker (GDP-β-S; 2 mM) supporting the involvement of secretin receptor in the process. Regarding the actions downstream to secretin receptor, intracellular blockade of protein kinase A (PKA) with KT-5720 (2 μM) or intracellular inhibition of the neuronal nitric oxide synthase (nNOS) by NPLA (1 μM) abolished the stimulatory effect of secretin on mPSCs. These data suggest that secretin acts on GnRH neurons via secretin receptors whose activation triggers the cAMP/PKA/nNOS signaling pathway resulting in nitric oxide release and in the presynaptic terminals this retrograde NO machinery regulates the GABAergic input to GnRH neurons.

Distribution and Functional Implication of Secretin in Multiple Brain Regions

Secretin is a polypeptide hormone initially identified for its gastrointestinal functions. However, emerging evidences show wide distribution of secretin and secretin receptor across various brain regions from cerebral cortex, hippocampus, hypothalamus to cerebellum. In this mini review, we will firstly describe the region-specific expression pattern of secretin and secretin receptor in the brain, followed by a summary of central physiological and neurological functions mediated by secretin. Using genetic manipulation and pharmaceutical approaches, one can elucidate the role of secretin in mediating various neurological functions from simple behaviors, such as water and food intake, to more complex functions including emotion, motor, and learning or memory. At last, current weakness and future perspectives of secretin in the central nervous system will be discussed, aiming to provide the potency of using secretin or its analog for treating various neurological disorders.

Secretin, at the hub of water-salt homeostasis

Water and salt metabolism are tightly regulated processes. Maintaining this milieu intérieur within narrow limits is critical for normal physiological processes to take place. Disturbances to this balance can result in disease and even death. Some of the better-characterized regulators of water and salt homeostasis include angiotensin II, aldosterone, arginine vasopressin, and oxytocin. Although secretin (SCT) was first described >100 years ago, little is known about the role of this classic gastrointestinal hormone in the maintenance of water-salt homeostasis. In recent years, increasing body of evidence suggested that SCT and its receptor play important roles in the central nervous system and kidney to ensure that the mammalian extracellular fluid osmolarity is kept within a healthy range. In this review, we focus on recent advances in our understanding of the molecular, cellular, and network mechanisms by which SCT and its receptor mediate the control of osmotic homeostasis. Implications of hormonal cross talk and receptor-receptor interaction are highlighted.