ObjectivesTo determine the extent and nature of changes in utilisation of healthcare services during COVID-19 pandemic.DesignSystematic review.EligibilityEligible studies compared utilisation of services during COVID-19 pandemic to at least one comparable period in prior years. Services included visits, admissions, diagnostics and therapeutics. Studies were excluded if from single centres or studied only patients with COVID-19.Data sourcesPubMed, Embase, Cochrane COVID-19 Study Register and preprints were searched, without language restrictions, until 10 August, using detailed searches with key concepts including COVID-19, health services and impact.Data analysisRisk of bias was assessed by adapting the Risk of Bias in Non-randomised Studies of Interventions tool, and a Cochrane Effective Practice and Organization of Care tool. Results were analysed using descriptive statistics, graphical figures and narrative synthesis.Outcome measuresPrimary outcome was change in service utilisation between prepandemic and pandemic periods. Secondary outcome was the change in proportions of users of healthcare services with milder or more severe illness (eg, triage scores).Results3097 unique references were identified, and 81 studies across 20 countries included, reporting on >11 million services prepandemic and 6.9 million during pandemic. For the primary outcome, there were 143 estimates of changes, with a median 37% reduction in services overall (IQR −51% to −20%), comprising median reductions for visits of 42% (−53% to −32%), admissions 28% (−40% to −17%), diagnostics 31% (−53% to −24%) and for therapeutics 30% (−57% to −19%). Among 35 studies reporting secondary outcomes, there were 60 estimates, with 27 (45%) reporting larger reductions in utilisation among people with a milder spectrum of illness, and 33 (55%) reporting no difference.ConclusionsHealthcare utilisation decreased by about a third during the pandemic, with considerable variation, and with greater reductions among people with less severe illness. While addressing unmet need remains a priority, studies of health impacts of reductions may help health systems reduce unnecessary care in the postpandemic recovery.PROSPERO registration numberCRD42020203729.

Mechanosensory channels of sensory cells mediate the sensations of hearing, touch, and some forms of pain. The TRPA1 (a member of the TRP family of ion channel proteins) channel is activated by pain-producing chemicals, and its inhibition impairs hair cell mechanotransduction. As shown here and previously, TRPA1 is expressed by hair cells as well as by most nociceptors (small neurons of dorsal root, trigeminal, and nodose ganglia) and localizes to their sensory terminals (mechanosensory stereocilia and peripheral free nerves, respectively). Thus, TRPA1 channels are proposed to mediate transduction in both hair cells and nociceptors. Accordingly, we find that heterologously expressed TRPA1 display channel behaviors expected for both auditory and nociceptive transducers. First, TRPA1 and the hair cell transducer share a unique set of pore properties not described for any other channel (block by gadolinium, amiloride, gentamicin, and ruthenium red, a ranging conductance of ϳ100 pS that is reduced to 54% by calcium, permeating calcium-induced potentiation followed by closure, and reopening by depolarization), supporting a direct role of TRPA1 as a pore-forming subunit of the hair cell transducer. Second, TRPA1 channels inactivate in hyperpolarized cells but remain open in depolarized cells. This property provides a mechanism for the lack of desensitization, coincidence detection, and allodynia that characterize pain by allowing a sensory neuron to respond constantly to sustained stimulation that is suprathreshold (i.e., noxious) and yet permitting the same cell to ignore sustained stimulation that is subthreshold (i.e., innocuous). Our results support a TRPA1 role in both nociceptor and hair cell transduction.

We describe a novel mechanism for vital fluorescent dye entry into sensory cells and neurons: permeation through ion channels. In addition to the slow conventional uptake of styryl dyes by endocytosis, small styryl dyes such as FM1-43 rapidly and specifically label hair cells in the inner ear by entering through open mechanotransduction channels. This labeling can be blocked by pharmacological or mechanical closing of the channels. This phenomenon is not limited to hair cell transduction channels, because human embryonic kidney 293T cells expressing the vanilloid receptor (TRPV1) or a purinergic receptor (P2X2) rapidly take up FM1-43 when those receptor channels are opened and not when they are pharmacologically blocked. This channel permeation mechanism can also be used to label many sensory cell types in vivo. A single subcutaneous injection of FM1-43 (3 mg/kg body weight) in mice brightly labels hair cells, Merkel cells, muscle spindles, taste buds, enteric neurons, and primary sensory neurons within the cranial and dorsal root ganglia, persisting for several weeks. The pattern of labeling is specific; nonsensory cells and neurons remain unlabeled. The labeling of the sensory neurons requires dye entry through the sensory terminal, consistent with permeation through the sensory channels. This suggests that organic cationic dyes are able to pass through a number of different sensory channels. The bright and specific labeling with styryl dyes provides a novel way to study sensory cells and neurons in vivo and in vitro, and it offers new opportunities for visually assaying sensory channel function.

Mechanical deflection of the sensory hair bundles of receptor cells in the inner ear causes ion channels located at the tips of the bundle to open, thereby initiating the perception of sound. Although some protein constituents of the transduction apparatus are known, the mechanically gated transduction channels have not been identified in higher vertebrates. Here, we investigate TRP (transient receptor potential) ion channels as candidates and find one, TRPA1 (also known as ANKTM1), that meets criteria for the transduction channel. The appearance of TRPA1 messenger RNA expression in hair cell epithelia coincides developmentally with the onset of mechanosensitivity. Antibodies to TRPA1 label hair bundles, especially at their tips, and tip labelling disappears when the transduction apparatus is chemically disrupted. Inhibition of TRPA1 protein expression in zebrafish and mouse inner ears inhibits receptor cell function, as assessed with electrical recording and with accumulation of a channel-permeant fluorescent dye. TRPA1 is probably a component of the transduction channel itself.

Growth cone motility is regulated by both fast voltage-dependent Ca2+ channels and by unknown receptor-operated Ca2+ entry mechanisms. Transient receptor potential (TRP) homomeric TRPC5 ion channels are receptor-operated, Ca2+-permeable channels predominantly expressed in the brain. Here we show that TRPC5 is expressed in growth cones of young rat hippocampal neurons. Our results indicate that TRPC5 channel subunits interact with the growth cone-enriched protein stathmin 2, are packaged into vesicles and are carried to newly forming growth cones and synapses. Once in the growth cone, TRPC5 channels regulate neurite extension and growth-cone morphology. Dominant-negative TRPC5 expression allowed significantly longer neurites and filopodia to form. We conclude that TRPC5 channels are important components of the mechanism controlling neurite extension and growth cone morphology.

Members of the BNaC/ASIC family of ion channels have been implicated in mechanotransduction and nociception mediated by dorsal root ganglion (DRG) neurons. These ion channels are also expressed in the CNS. We identified the PDZ domain protein PICK1 as an interactor of BNaC1(ASIC2) in a yeast two-hybrid screen. We show by two-hybrid assays, glutathione S-transferase pull-down assays, and coimmunoprecipitations that the BNaC1⅐PICK1 interaction is specific, and that coexpression of both proteins leads to their clustering in intracellular compartments. The interaction between BNaC1 and PICK1 requires the PDZ domain of PICK1 and the last four amino acids of BNaC1. BNaC1 is similar to two other BNaC/ASIC family members, BNaC2 (ASIC1) and ASIC4, at its extreme C terminus, and we show that PICK1 also interacts with BNaC2. We found that PICK1, like BNaC1 and BNaC2, is expressed by DRG neurons and, like the BNaC1␣ isoform, is present at their peripheral mechanosensory endings. Both PICK1 and BNaC1␣ are also coexpressed by some pyramidal neurons of the cortex, by pyramidal neurons of the CA3 region of hippocampus, and by cerebellar Purkinje neurons, localizing to their dendrites and cell bodies. Therefore, PICK1 interacts with BNaC/ASIC channels and may regulate their subcellular distribution or function in both peripheral and central neurons. BNaC1 and BNaC21 are members of the DEG/ENaC superfamily of ion channel subunits (1-4). Members of this family have two transmembrane domains separated by a large extracellular loop, with cytoplasmic amino and C termini (5-8). They form homomeric and heteromeric channels that are permeable to sodium but are not gated by voltage. DEG/ENaC channels have been implicated in several forms of mechanosensation. For example, certain members of the degenerin branch are necessary for the sensation of touch in Caenorhabditis elegans (9). Members of the ENaC branch in mammals control Na ϩ and fluid absorption in the kidney, colon, and lung (10 -12), but they have also been found at baroreceptor (13) and somatic touch receptor endings (14, 15). The Pickpocket channel of Drosophila melanogaster also localizes to putative mechanosensory nerve endings (16).The mammalian BNaC/ASIC branch of the superfamily contains four genes, encoding at least six isoforms: BNaC1␣ (also known as BNC1, MDEG, and ASIC2) (2-4) and its differentially spliced isoform, BNaC1␤ (MDEG2) (17); BNaC2␣ (ASIC␣ or ASIC1) (4, 18) and its differentially spliced isoform, BNaC2␤ (ASIC␤) (19); DRASIC (ASIC3 or TNaC) (20 -23); and ASIC4 (SPASIC) (24, 25). These genes are expressed in both central and peripheral neurons and form channels that can be activated by extracellular protons (26). Because tissue acidosis is a source of pain (27), it has been proposed that these ion channels may play a role in acid-induced nociception (26,28).In addition, recent work has demonstrated that BNaC1 is required for normal mechanosensation. Mice with a targeted deletion of the BNaC1 gene show reduced sensitivity of rapidly and slowly adapting mechanor...

Summary Intense noise damages the cochlear organ of Corti, particularly the outer hair cells (OHCs)[1], however this epithelium is not innervated by nociceptors of somatosensory ganglia, which detect damage elsewhere in the body. The only sensory neurons innervating the organ of Corti originate from the spiral ganglion, roughly 95% of which innervate exclusively inner hair cells (IHCs)[2-4]. Upon sound stimulation, IHCs release glutamate to activate AMPA-type receptors on these myelinated type-I neurons, which carry the neuronal signals to the cochlear nucleus. The remaining spiral ganglion cells (type-IIs) are unmyelinated and contact OHCs[2-4]. Their function is unknown. Using immunoreactivity to cFos, we documented neuronal activation in the brainstem of Vglut3−/− mice, in which the canonical auditory pathway (activation of type-I afferents by glutamate released from inner hair cells) is silenced[5, 6]. In these deaf mice, we found responses to noxious noise, that damages hair cells, but not to innocuous noise, in neurons of the cochlear nucleus, but not in the vestibular or trigeminal nuclei. This response originates in the cochlea and not in other areas also stimulated by intense noise (middle ear and vestibule) as it was absent in CD1 mice with selective cochlear degeneration but normal vestibular and somatosensory function. These data imply the existence of an alternative neuronal pathway from cochlea to brainstem that is activated by tissue-damaging noise and does not require glutamate release from IHCs. This detection of noise-induced tissue damage, possibly by type-II cochlear afferents, represents a novel form of sensation we term auditory nociception.

We have been studying the genes needed for the production of a set of six mechanosensory neurons in Caenorhabditis elegans as a model for cell fate determination. As with many cellular systems, the combinatorial action of both positively and negatively acting factors determines the developmental fate of these touch cells and restricts their final number to six cells (ALML/R, AVM, PLML/R, and PVM) in adults (Mitani et al. 1993).Screens for touch-insensitive (Mec) mutants (Chalfie and Sulston 1981;Chalfie and Au 1989) have identified several genes required for either touch cell development or function. The two most proximally acting genes needed for touch cell development are unc-86 and mec-3. unc-86 encodes a POU-type homeoprotein expressed in 57 neurons (Finney et al. 1988;Finney and Ruvkun 1990), including the six touch cells, that is needed not only to produce appropriate touch cell lineages, but also to initiate transcription from the mec-3 gene (Way and Chalfie 1988). mec-3 encodes a LIM-type homeodomain transcription factor. mec-3 mutations do not affect touch cell lineages, but do affect the differentiation of the 10 cells in which it is expressed: the six touch cells, which sense gentle touch to the body, the two FLP neurons, which sense touch at the very tip of the head (Kaplan and Horvitz 1993), and the two PVD neurons, which sense harsh touch to the body (Way and Chalfie 1989). The maintained expression of mec-3 and the subsequent expression of touch cell characteristics require the combined action of both UNC-86 and MEC-3, which appear to form heterodimers (Xue et al. 1992(Xue et al. , 1993Duggan et al. 1998).The targets of this regulation in the touch cells are several genes needed for the function of these cells as mechanoreceptors. These function genes include the ␤-tubulin gene mec-7 (Savage et al. 1989(Savage et al. , 1994, the channel subunit gene mec-4 (Driscoll and Chalfie 1991), and mec-18, which encodes an apparent CoA synthetase (G. Gu and M. Chalfie, unpubl.). Because wild-type animals express mec-4 and mec-18 exclusively and mec-7 strongly only in the touch cells (Mitani et al. 1993; G. Gu and M. Chalfie, unpubl.), these genes can be used as markers for the differentiation of these cells.The coexpression of unc-86 and mec-3 in the FLP and PVD cells (Way and Chalfie 1989;Finney and Ruvkun 1990) indicates that other genes restrict touch cell fate to or promote such fate in the six touch cells seen in wildtype animals. Some of these genes have been identified because mutations in them affect the expression of touch cell markers (Mitani et al. 1993). One gene, lin-14, which encodes a nucleoprotein (Ruvkun and Giusto 1989), appears to regulate touch cell differentiation positively; the continued expression of this gene or the absence of its negative regulator, lin-4, leads to a lineage change so that the lineages that usually give rise to the PVD neurons give rise to touch cell-like neurons. The FLP cells normally express lin-14 as well as unc-86 and mec-3. These cells do not express touch ce...