Increased immunoreactive vasoactive intestinal peptide in the cerebro-spinal fluid (CSF) of dogs and monkeys in hepatic failure

Co-exposure of nanoplastics and arsenic causes neurotoxicity in zebrafish (Danio rerio) through disrupting homeostasis of microbiota-intestine-brain axis

Nanoplastics (NPs) and arsenic (As) are toxic pollutants prevalent on the earth and have gained considerable attention in recent decades. Although numerous studies reported NPs and As can cause neurotoxicity there are still significant knowledge gaps in illustrating their combined toxicity and its mechanism. In this study, the co-exposure of environmentally relevant concentrations of NPs and As caused neurobehavioral toxicity in zebrafish, as evidenced by reduced swimming ability, anxiety and impaired short-term learning memory. Potentially, its toxicity mechanism is through disrupting the homeostasis of microbiota-intestine-brain axis in zebrafish. Specifically, the co-exposure reduced the 5-hydroxytryptamine (5-HT) production in intestine, which led to lower levels of 5-HT transported by the blood circulation to the brain. Ultimately, neurobehavior was adversely affected by the reduced binding of 5-HT to its receptors. Intestine, the primary source of 5-HT, its impaired health (aggravation in oxidative stress, mitochondrial damage and histopathological alterations) induced the dysregulation in the 5-HT system, which may be induced by the increased accumulation of As in the intestine by the co-exposure. Besides, the reduced 5-HT levels were correlated with decreased Firmicutes and Protecbacteria and increased Actinobacteriota and Chloroflexi in intestines. Potentially, intestinal microbiota adversely regulates the intestine-brain axis by reducing SCFAs levels. Thus, the alteration of intestinal microbiota structure may be the other reason for the dysregulation of intestine-brain axis. In summary, co-exposure of NPs and As induced neurobehavior toxicity probably through disrupting the homeostasis of microbiota-intestine-brain axis. This study provides insights into assessing the environmental health risks of the pollution of NPs and As to aquatic organisms.

Discovery and characterization of gut microbiota decarboxylases that can produce the neurotransmitter tryptamine

Several recent studies describe the influence of the gut microbiota on host brain and behavior. However, the mechanisms responsible for microbiota-nervous system interactions are largely unknown. Using a combination of genetics, biochemistry, and crystallography, we identify and characterize two phylogenetically distinct enzymes found in the human microbiome that decarboxylate tryptophan to form the β-arylamine neurotransmitter tryptamine. Although this enzymatic activity is exceedingly rare among bacteria more broadly, analysis of the Human Microbiome Project data demonstrate that at least 10% of the human population harbors at least one bacterium encoding a tryptophan decarboxylase in their gut community. Our results uncover a previously unrecognized enzymatic activity that can give rise to host-modulatory compounds and suggests a potential direct mechanism by which gut microbiota can influence host physiology, including behavior.

Physiological neuroendocrinology of peptides, steroids and other hormones in cerebrospinal fluid

Cerebrospinal fluid acts as a conduit in neuroendocrine regulation. Valid assessment of normal cerebrospinal fluid levels of peptides, steroids and other hormones requires clarification of reference concentrations in control patients and normal volunteers. Awareness of factors which may alter neuronal activity and, in turn, the relative composition of cerebrospinal fluid constituents is essential to the accurate sampling and hormonal analysis of cerebrospinal fluid.

Vasoactive intestinal peptide (VIP) in magnocellular neurons of the hypothalamo-neurohypophysial system of the mink (Mustela vision) is co-localized with vasopressin or oxytocin

The distribution of vasoactive intestinal peptide (VIP) was analysed in perikarya of the mink hypothalamus with immunohistochemistry and, surprisingly, a large population of magnocellular VIP-immunoreactive neurons was present in the paraventricular and supraoptic nuclei as well as in accessory hypothalamic nuclei. From perikarya in the paraventricular as well as supraoptic nuclei, a large number of VIP immunoreactive nerve fibers was observed to enter the hypothalamo-neurohypophysial tract. Within the median eminence, a high density of VIP-immunoreactive nerve fibers was present in the external and internal zones. Fibers in the external zone of the median eminence were endowed with varicosities and perivascular terminals, while fibers in the internal zone were smooth and without terminal specializations. From the internal zone of the median eminence, fibers coursed via the infundibular stalk to terminate in perivascularly situated terminals in the neurohypophysis. In addition, a substantial number of small VIP-immunoreactive perikarya was observed within the suprachiasmatic nucleus. These perikarya were immunoreactive to neither vasopressin nor neurophysin. To elucidate the co-existence of VIP-immunoreactivity with vasopressin, oxytocin or neurophysin, a sequential double immunoperoxidase procedure to localize antigens with diaminobenzidine and benzidine dihydrochloride as chromagens was performed. From these experiments it was evident that VIP in nearly all magnocellular hypothalamo-neurohypophysial neurons co-existed with neurophysin. Based on a semi-quantitative estimate, half the VIP-immunoreactive magnocellular perikarya co-stored vasopressin, while another half co-stored oxytoxin. The present study describes the presence of a large population of VIP-containing neurons in the hypothalamo-neurohypophysial system of the mink. These findings raise evidence that within the mink, VIP may be involved in neurohypophysial physiology.

Immunohistochemical localization of vasoactive intestinal peptide (VIP) in the circumventricular organs of the rat

The indirect peroxidase-antiperoxidase immunohistochemical technique was used to investigate the possible presence of vasoactive intestinal peptide (VIP) in the circumventricular organs of the rat. Considerable numbers of VIP-immunoreactive fibers were seen in the pineal gland. A moderate amount of VIP-immunoreactive fibers was present in the median eminence, the posterior lobe of the pituitary and the area postrema, but only few fibers were found in the organum vasculosum laminae terminalis. No immunoreactivity was observed in the subfornical organ or the subcommissural organ. The circumventricular organs investigated were completely free of VIP-immunoreactive perikarya. In the circumventricular organs, VIP-immunoreactive fibers were visible between the parenchymal cells and in the perivascular spaces. The presence of coarse VIP-immunoreactive terminals in apposition to the portal vessels in the external layer of the median eminence indicates that VIP may be secreted directly into the pituitary portal circulation, thus influencing the anterior pituitary cells. The presence of large VIP-immunoreactive boutons in the posterior lobe of the pituitary suggests a secretion of VIP directly into the systemic circulation. In the pineal gland, a dense innervation by VIP-immunoreactive fibers was found in the peripheral superficial part of organ, with fibers penetrating into its central portion where they mainly terminate near in vicinity of the capillaries. In the area postrema, VIP-immunoreactive material was mainly found at the ventral border of the organ. In addition to the secretion of VIP into the bloodstream via the circumventricular organs, this study provides evidence that VIP exerts specific influence on the cellular elements of these organs.

VIPoma syndrome

Since the description of the watery diarrhea syndrome by Verner and Morrison 29 years ago, clinical and experimental observations have elucidated the pathophysiology of this disease. Vasoactive intestinal polypeptide (VIP) is produced and released by a tumor of the pancreatic islets or by a tumor of neural crest origin such as a ganglioneuroma. Under normal conditions, current evidence suggests that VIP is a neurotransmitter in the central and peripheral nervous systems and particularly in the peptidergic nervous system. The low VIP plasma concentration observed in healthy subjects is viewed as a neuronal overflow since it has been impossible to ascertain any endocrine role for circulating VIP. Markedly elevated VIP plasma levels in the VIPoma syndrome lead to intestinal secretion with severe secretory diarrhea, resulting in hypovolemia, hypokalemia, and acidosis. These symptoms subside after successful tumor removal. Approximately 50 percent of patients have metastatic spread at the time of diagnosis. For these patients, a new and promising therapeutic modality is available in the form of a subcutaneously administered somatostatin analogue that relieves symptoms through potent inhibition of VIP release from tumor tissue.

Release of vasoactive intestinal polypeptide into the cerebrospinal fluid of the fourth ventricle of the rat: involvement of cholinergic mechanism

Vasoactive intestinal polypeptide (VIP) is found abundantly in the cerebrospinal fluid (CSF). In order to clarify its source in the brain and the control mechanism of its release, cerebral ventricles of urethane-anesthetized male rats were locally perfused with the artificial CSF at a constant rate of 120 microliters/min by means of a push-pull cannula and immunoreactive VIP was continuously measured in the effluents obtained at 10 min intervals. The perfusion with veratridine, a depolarizing agent, at a rate of 5 x 10(-4) M/min, caused a significant (P less than 0.01) increase in the effluent VIP levels when the tip of a cannula was placed in the fourth ventricle but not when it was in the third or the lateral ventricle. The release of VIP into the fourth ventricle was also significantly (P less than 0.05) enhanced by the perfusion with acetylcholine (ACh) at a dose of 3.66 x 10(-5) to 1.83 x 10(-4) M/min. A simultaneous perfusion of hexamethonium (1.9 x 10(-4) M/min) blocked ACh-induced VIP release. These results indicate that VIP is released into the CSF from the wall of the fourth ventricle by a mechanism possibly involving nicotine-sensitive cholinergic pathways.