The new muscarinic M1-receptor agonist YM796 evokes yawning and increases oxytocin secretion from the posterior pituitary gland in rats

Brain histamine improves colonic hyperpermeability through the basal forebrain cholinergic neurons, adenosine A2B receptors and vagus nerve in rats

Intestinal barrier dysfunction, leaky gut, is implicated in various diseases, including irritable bowel syndrome (IBS) and neurodegenerative conditions like Alzheimer's disease. Our recent investigation revealed that basal forebrain cholinergic neurons (BFCNs), critical for cognitive function, receive signals from butyrate and orexin, playing a role in regulating intestinal barrier function through adenosine A2B signaling and the vagus. This study explores the involvement and function of brain histamine, linked to BFCNs, in the regulation of intestinal barrier function. Colonic permeability, assessed by quantifying absorbed Evans blue in rat colonic tissue, showed that histamine did not affect increased colonic permeability induced by LPS when administered subcutaneously. However, intracisternal histamine administration improved colonic hyperpermeability. Elevating endogenous histamine levels in the brain with SKF91488, a histamine N-methyltransferase inhibitor, also improved colonic hyperpermeability. This effect was abolished by intracisternal chlorpheniramine, an histamine H1 receptor antagonist, not ranitidine, an H2 receptor antagonist. The SKF91488-induced improvement in colonic hyperpermeability was blocked by vagotomy, intracisternal pirenzepine (suppressing BFCNs activity), or alloxazine (an adenosine A2B receptor antagonist). Additionally, intracisternal chlorpheniramine injection eliminated butyrate-induced improvement in colonic hyperpermeability. These findings suggest that brain histamine, acting via the histamine H1 receptor, regulates intestinal barrier function involving BFCNs, adenosine A2B signaling, and the vagus. Brain histamine appears to centrally regulate intestinal barrier function influenced by butyrate, differentiating its actions from peripheral histamine in conditions like IBS, where mast cell-derived histamine induces leaky gut. Brain histamine emerges as a potential pharmacological target for diseases associated with leaky gut, such as dementia and IBS.

Activation of basal forebrain cholinergic neurons improves colonic hyperpermeability through the vagus nerve and adenosine A2B receptors in rats

Intestinal barrier dysfunction, a leaky gut, contributes to the pathophysiology of various diseases such as dementia and irritable bowel syndrome (IBS). We recently clarified that orexin, ghrelin, or adenosine A2B signaling in the brain improved leaky gut through the vagus nerve. The present study was performed to clarify whether basal forebrain cholinergic neurons (BFCNs) are implicated in the central regulation of intestinal barrier function. We activated BFCNs using benzyl quinolone carboxylic acid (BQCA), a positive muscarinic M1 allosteric modulator, and evaluated colonic permeability by quantifying the absorbed Evans blue in rat colonic tissue. Intracisternal (not intraperitoneal) injection of BQCA blocked the increased colonic permeability in response to lipopolysaccharide. Vagotomy blocked BQCA-induced improvement of colonic hyperpermeability. Intracisternally administered pirenzepine, a muscarinic M1 selective antagonist, prevented intestinal barrier function improvement by intravenously administered 2-deoxy-d-glucose, central vagal stimulant. Adenosine A2B receptor antagonist but not dopamine or opioid receptor antagonist prevented BQCA-induced blockade of colonic hyperpermeability. Additionally, intracisternal injection of pirenzepine blocked orexin- or butyrate-induced intestinal barrier function improvement. These results suggest that BFCNs improve leaky gut through adenosine A2B signaling and the vagal pathway. Furthermore, BFCNs mediate orexin- or butyrate-induced intestinal barrier function improvement. Since BFCNs play a role in cognitive function and a leaky gut is associated with dementia, the present finding may lead us to speculate that BFCNs are involved in the development of dementia by regulating intestinal barrier function.

Treatment with dexamethasone alters yawning behavior induced by cholinergic but not dopaminergic agonist

Because stressful manipulations have been reported to modify drug-induced yawning, the present study investigated the effects of single and repeated treatment with a synthetic glucocorticoid, dexamethasone (DEXA) on apomorphine- and pilocarpine-induced yawning in male rats. Neither single nor repeated treatment with DEXA altered apomorphine-induced yawning. Single administration of DEXA, however, resulted in an increased number of yawns induced by pilocarpine. Conversely, repeated administration of DEXA led to a decreased number of yawns induced by pilocarpine. In conclusion, the present findings show that dopaminergic and cholinergic are distinctly altered by DEXA, in terms of yawning behavior when animals received DEXA.

The neuropharmacology of yawning

Yawning is a phylogenetically old, stereotyped event that occurs alone or associated with stretching and/or penile erection in humans and in animals from reptiles to birds and mammals under different conditions. Although its physiological function is still unknown, yawning is under the control of several neurotransmitters and neuropeptides at the central level as this short overview of the literature on the neurochemistry of yawning shows. Among these substances, the best known are dopamine, excitatory amino acids, acetylcholine, serotonin, nitric oxide, adrenocorticotropic hormone-related peptides and oxytocin, that facilitate yawning and opioid peptides that inhibit this behavioral response. Some of the above compounds interact in the paraventricular nucleus of the hypothalamus to control yawning. This hypothalamic nucleus contains the cell bodies of oxytocinergic neurons projecting to extra-hypothalamic brain areas that play a key role in the expression of this behavioral event. When activated by dopamine, excitatory amino acids and oxytocin itself, these neurons facilitate yawning by releasing oxytocin at sites distant form the paraventricular nucleus, i.e. the hippocampus, the pons and/or the medulla oblongata. Conversely, activation of these neurons by dopamine, oxytocin or excitatory amino acids, is antagonized by opioid peptides, that, in turn, prevent the yawning response. The activation and inhibition, respectively of these oxytocinergic neurons is related to a concomitant increase and decrease, respectively, of paraventricular nitric oxide synthase activity. However, other neuronal systems in addition to the central paraventricular oxytocinergic neurons are involved in the control of yawning, since they do not seem to be involved in the expression of yawning induced by the stimulation of acetylcholine or serotoninergic receptors, nor by adrenocorticotropic hormone (ACTH) and related peptides. Nitric oxide is also involved in the induction of yawning by the latter compounds and neuronal links, for instance between dopamine and acetylcholine and dopamine and serotonin, seem to be involved in the yawning response. Finally, other neurotransmitters, i.e. gamma-aminobutyric acid (GABA) and noradrenaline, and neuropeptides, i.e. neurotensin and luteinizing hormone-releasing hormone (LH-RH), influence this behavioral response. In conclusion, in spite of some recent progress, little is known of, and more has to be done to identify, the neurochemical mechanisms underlying yawning at the central level.