Abstract figure legend This study introduces staircase light stimuli mimicking changes in ambient light intensities across night to day transition with the inclusion of more naturalistic, high temporal frequency modulations presented at each step. It has been used here to probe irradiance coding properties of the suprachiasmatic nucleus (SCN) at population and single cell level in anaesthetised mouse. We observed monotonic relationships between firing rate and irradiance at both population and single cell level, although individual neurons track different portions of irradiance range. Thus, we provide evidence of the existence of sparse irradiance code at the level of the SCN. Figure created with BioRender.com.

Abstract figure legend Both morphine and fentanyl profoundly suppress breathing activity. However, when doses are scaled to produce similar respiratory rhythm generation effects, fentanyl induces transient obstructions to airflow not observed with morphine. These obstructions may involve the bronchi and bronchioles, as they can be reversed with common bronchodilators like salbutamol and adrenaline.

Abstract figure legend The dorsal vagal complex (DVC) receives inputs from the substantia nigra pars compacta (SNpc) via a nigro-vagal pathway. The present study examined whether this nigro-vagal pathway extends its influence to the proximal colon. In rats, colonic-projecting neurons in the dorsal motor nucleus of the vagus (DMV) receive inputs from SNpc neurons, as demonstrated by simultaneous anterograde (SNpc) and retrograde (proximal colon) neuronal tracing. Activation of SNpc neurons via the ionotropic glutamate selective agonist, NMDA, increases proximal colonic motility and tone in a manner that was reduced by brainstem pretreatment with the dopaminergic D1-like antagonist SCH23390, but not by the D2-like antagonist L741646. These studies suggest that the nigro-vagal pathway tonically modulates the tone and motility of the proximal colon and excites vagal efferent motoneurons via activation of dopaminergic D1 receptors.

Abstract figure legend The proportional assist ventilator (PAV) increases mouth pressure/airway pressure thereby altering the pressure gradient to breathe. As such, oesophageal pressure (surrogate for intrathoracic pressure) decreases, which will reduce the energetic work of breathing (W_b) thereby attenuating the impact of the respiratory muscle pump on venous return (less blood coming back to the heart), and subsequently stroke volume and cardiac output will decrease.

Abstract figure legend Dopamine, serotonin and ghrelin regulate neuronal excitability in the rodent lumbosacral defecation centre. In vivo, agonists of dopamine D2 receptors (D2R), 5-hydroxytryptamine type 2 (5-HT2) and ghrelin receptors (GHSR) lead to increased propulsive colonic motility. We found that a subset of preganglionic neurons (PGNs) express D2R, 5-HT2 and GHSR receptors and that dopamine, serotonin and ghrelin receptor agonists each increased neuronal excitability. We discovered that a role of the ghrelin receptor is to reverse the effect of dopamine at D2R from inhibition to excitation. Created with Biorender.com.

Abstract figure legend Research using animal models has demonstrated that motoneuron intrinsic properties change with ALS disease progression. In this study, we monitored alterations in intrinsic motor neurone properties over time in humans by assessing the contribution of persistent inward current to motoneuron firing. Our study assessed muscles with preserved force values, before the onset of muscle weakness (earlier stages of the disease), and those displaying clinical signs of weakness (later stages of the disease) in individuals with ALS. Our data showed that intrinsic motoneuron excitability is augmented, becoming hyperexcitable, at earlier disease stages. Subsequently, intrinsic motoneuron excitability decreases, becoming hypoexcitable, when muscle weakness progresses (later stages of the disease).

Abstract figure legend Acute and chronic stress exert wide-ranging effects across the gut–brain axis. In the case of acute stress, the enteric nervous system may be activated and gut contractility modified. This is associated with altered serotonin metabolism in the gastrointestinal tract as well as activation of the innate immune system and suppression of the adaptive immune system. Less is known about how acute stress impacts gastrointestinal physiology and the gut microbiome. Chronic stress, depending on the type, timing and duration of exposure, impairs vagal signalling and enteric nerve function, impairs gut motility and induces visceral hypersensitivity. Both cellular and humoral immunity are suppressed, and the gut barrier exhibits reduced mucus layer thickness, increased paracellular permeability and infiltration of circulating immune cells, as well as increased mast cell degranulation. The gut microbiome exhibits reduced stability and altered composition and function. Specifically, the relative abundance of beneficial bacteria is reduced.