ATP activates damage-sensing neurons (nociceptors) and can evoke a sensation of pain. The ATP receptor P2X3 is selectively expressed by nociceptors and is one of seven ATP-gated, cation-selective ion channels. Here we demonstrate that ablation of the P2X3 gene results in the loss of rapidly desensitizing ATP-gated cation currents in dorsal root ganglion neurons, and that the responses of nodose ganglion neurons to ATP show altered kinetics and pharmacology resulting from the loss of expression of P2X(2/3) heteromultimers. Null mutants have normal sensorimotor function. Behavioural responses to noxious mechanical and thermal stimuli are also normal, although formalin-induced pain behaviour is reduced. In contrast, deletion of the P2X3 receptor causes enhanced thermal hyperalgesia in chronic inflammation. Notably, although dorsal-horn neuronal responses to mechanical and noxious heat application are normal, P2X3-null mice are unable to code the intensity of non-noxious 'warming' stimuli.

Airway hyperresponsiveness and inflammation are fundamental hallmarks of allergic asthma that are accompanied by increases in certain polycations, such as eosinophil cationic protein. Levels of these cations in body fluids correlate with asthma severity. We show that polycations and elevated extracellular calcium activate the human recombinant and native calcium-sensing receptor (CaSR), leading to intracellular calcium mobilization, cyclic adenosine monophosphate breakdown, and p38 mitogen-activated protein kinase phosphorylation in airway smooth muscle (ASM) cells. These effects can be prevented by CaSR antagonists, termed calcilytics. Moreover, asthmatic patients and allergen-sensitized mice expressed more CaSR in ASMs than did their healthy counterparts. Indeed, polycations induced hyper-reactivity in mouse bronchi, and this effect was prevented by calcilytics and absent in mice with CaSR ablation from ASM. Calcilytics also reduced airway hyperresponsiveness and inflammation in allergen-sensitized mice in vivo. These data show that a functional CaSR is up-regulated in asthmatic ASM and targeted by locally produced polycations to induce hyperresponsiveness and inflammation. Thus, calcilytics may represent effective asthma therapeutics.

cDNAs encoding three splice variants of the P2X2 receptor were isolated from rat cerebellum. The first variant has a serine/proline-rich segment deleted from the intracellularly located carboxyl-terminal domain of the P2X2 subunit. The second and third variants have the splice site in the second half of the predicted first transmembrane domain. Either a 12-amino acid insertion or a six-amino acid deletion occurs at this position. cRNAs for these isoforms of the P2X2 subunit were injected into Xenopus laevis oocytes and tested for function. ATP evoked inward currents only with the splice variant [designated P2X2(b)] having the 69-amino acid deletion. The potencies of various agonists at the homomeric P2X2(b) receptor were not significantly different from those at the P2X2(a) homomeric channel. However, the P2X2(b) receptor showed significantly lower antagonist sensitivity. In contrast to the nondesensitizing P2X2(a) receptor, prolonged application of ATP produced a more rapid desensitization of the P2X2(b) receptor. When the P2X2(a) and P2X2(b) receptor responses were recorded in transfected mammalian cells, this difference was again found. The change in desensitization may be determined by proline/serine-rich segments and/or phosphorylation motifs that are removed from the tail region in formation of the P2X2(b) subunit. In situ hybridization of the three newly isolated isoforms of the P2X2 subunit was performed at the macroscopic and cellular levels; transcripts for two of them [P2X2(b) and p2x2(c)] but not the third [p2x2(d)], which carries the 12-amino acid addition, were present in many structures in the neonatal rat brain and on sensory and sympathetic ganglia. mRNA for the p2x2(d) splice variant was present only in the nodose ganglion, at a low level.

Mid-life hypertension and cerebrovascular dysfunction are associated with increased risk of later life dementia, including Alzheimer's disease (AD). The classical renin-angiotensin system (cRAS), a physiological regulator of blood pressure, functions independently within the brain and is overactive in AD. cRAS-targeting anti-hypertensive drugs are associated with reduced incidence of AD, delayed onset of cognitive decline, and reduced levels of Aβ and tau in both animal models and human pathological studies. cRAS activity is moderated by a downstream regulatory RAS pathway (rRAS), which is underactive in AD and is strongly associated with pathological hallmarks in human AD, and cognitive decline in animal models of CNS disease. We now show that enhancement of brain ACE2 activity, a major effector of rRAS, by intraperitoneal administration of diminazene aceturate (DIZE), an established activator of ACE2, lowered hippocampal Aβ and restored cognition in mid-aged (13-14-month-old) symptomatic Tg2576 mice. We confirmed that the protective effects of DIZE were directly mediated through ACE2 and were associated with reduced hippocampal soluble Aβ 42 and IL1-β levels. DIZE restored hippocampal MasR levels in conjunction with increased NMDA NR2B and downstream ERK signalling expression in hippocampal synaptosomes from Tg2576 mice. Chronic (10 weeks) administration of DIZE to pre-symptomatic 9-10-month-old Tg2576 mice, and acute (10 days) treatment in cognitively impaired 12-13-month-old mice, prevented the development of cognitive impairment. Together these data demonstrate that ACE2 enhancement protects against and reverses amyloid-related hippocampal pathology and cognitive impairment in a preclinical model of AD.

No abstract

Adenosine 5′-triphosphate (ATP) is known to play a significant role as a neurotransmitter in smooth muscle. There is evidence to show that ATP can cause bladder contractions and may also be involved in the processing of sensory information in the urinary bladder. These effects are likely to be mediated by P2X receptors, namely P2X₁ and P2X₃, respectively. This study set out to investigate their distribution in rat and human urinary bladders. P2X₁ receptor immunoreactivity was found on detrusor muscle fibres and P2X₃ receptor immunoreactivity was found in the urothelium of both species. This is the first demonstration of a non-neuronal localisation for P2X₃ receptors. No clear evidence was found for the presence of P2X₃ receptors on calcitonin gene-related peptide-containing sensory nerves and therefore P2X₃ receptors may not have a direct role in the mediation of sensory responses to ATP in the urinary bladder.

1 Apparent species di erences in the responses of recombinant P2X 7 receptors to repeated application of 2'-and 3'-O-(4-benzoylbenzoyl)-ATP (BzATP) have been investigated. 2 Repeated application of 100 mM BzATP resulted in a progressive increase in current magnitude (current growth) at mouse and human, but not rat P2X 7 receptors. 3 Current growth was thought to re¯ect progressive dilation of the P2X 7 ion-channel to a pore permeable to large molecules (MW5900), suggesting that channel dilation was not occurring at the rat P2X 7 receptor. However, 100 mM BzATP produced a rapid in¯ux of YO-PRO-1 (MW375) in cells expressing rat or human P2X 7 receptors. 4 There were, however, species di erences in agonist potency such that 100 mM BzATP was a supra-maximal concentration at rat, but not human or mouse, P2X 7 receptors. Importantly, when sub-maximal concentrations of BzATP or ATP were examined, current growth occurred at rat P2X 7 receptors. 5 The rate of current growth and YO-PRO-1 accumulation increased with agonist concentration and appeared more rapid at rat and human, than at mouse P2X 7 receptors. 6 The potency of BzATP and ATP was 1.5 ± 10 fold lower in naõÈ ve cells than in cells repeatedly exposed to ATP. 7 This study demonstrates that current growth occurs at mouse, rat and human P2X 7 receptors but only when using sub-maximal concentrations of agonist. Previously, current growth was thought to re¯ect the progressive increase in pore diameter of the P2X 7 receptor ion channel, however, the results of this study suggest a progressive increase in agonist potency may also contribute.

Midlife obesity is a risk factor of late onset Alzheimer's disease (LOAD) but why this is the case remains unknown. As systemic inflammation is involved in both conditions, obesity-related neuroinflammation may contribute to damage in limbic structures important in LOAD. Here, we investigated the hypothesis that systemic inflammation would mediate central obesity related effects on limbic tissue microstructure in 166 asymptomatic individuals (38–71 years old). We employed MRI indices sensitive to myelin and neuroinflammation [macromolecular proton fraction (MPF) and kf] from quantitative magnetization transfer (qMT) together with indices from neurite orientation dispersion and density imaging (NODDI) to investigate the effects of central adiposity on the fornix, parahippocampal cingulum, uncinate fasciculus (compared with whole brain white matter and corticospinal tract) and the hippocampus. Central obesity was assessed with the Waist Hip Ratio (WHR) and abdominal visceral and subcutaneous fat area fractions (VFF, SFF), and systemic inflammation with blood plasma concentrations of leptin, adiponectin, C-reactive protein and interleukin 8. Men were significantly more centrally obese and had higher VFF than women. Individual differences in WHR and in VFF were negatively correlated with differences in fornix MPF and kf, but not with any differences in neurite microstructure. In women, age mediated the effects of VFF on fornix MPF and kf, whilst in men differences in the leptin and adiponectin ratio fully mediated the effect of WHR on fornix MPF. These results suggest that visceral fat related systemic inflammation may damage myelin-related properties of the fornix, a key limbic structure known to be involved in LOAD.