Microneurography studies have identified larger afferent proportions innervating the anterolateral foot sole of humans that are postulated to provide mechanosensitive feedback to maintain balance during gait as foot contact moves from the heel to the lateral arch then finally to the digits ( Strzalkowski et al., 2018). Ruffini endings however are less sensitive to skin indentation than Merkel cells, but more sensitive to skin stretch perceiving the direction of skin stretch caused by an object or surface, and the position of the digits relative to one another ( Johnson, 2001). Merkel cells can discriminate points, edges, and textures and respond to sustained indentation in proportion to the indentation depth. In contrast, SA afferents resolve spatial details well. Meissner’s corpuscles provide critical feedback for grip control, responding to slip between the skin and an object ( Johnson, 2001). RA afferents are very limited in spatial resolution but respond to dynamic skin deformation, stretch, and low (Meissner’s corpuscles) or high (Pacinian corpuscles) frequency vibration. SA afferents have a prolonged response that lasts for the duration of the stimulus whereas RA afferents respond briefly at the beginning and end of a stimulus ( Rice and Albrecht, 2008). Four classes of low-threshold mechanoreceptors have been described in glabrous skin, including the human foot sole: rapidly adapting type I (RAI) afferents terminating at Meissner’s corpuscles, slowly adapting type I (SAI) afferents terminating at Merkel cells, RAII afferents terminating at Pacinian corpuscles, and SAII afferents terminating at Ruffini endings ( Johnson, 2001). The anatomical distribution and density of afferents and mechanoreceptors influence sensory feedback, as does mechanoreceptor function. Finally, a larger density of Meissner-like corpuscles in footpads 3 and 4 in male itga1-null mice compared to wild type controls paves the way for future site-specific single fiber in vivo recordings to provide insight into the role of integrin α1β1 in tactile mechanotransduction.Īfferent neurons and their mechanoreceptor endings in the glabrous skin of the foot sole are critical to providing the sensory information that is necessary for stance and gait ( Strzalkowski et al., 2015, 2018). The increased density of Merkel cells and Meissner-like corpuscles in footpads 1 and 3 and Meissner-like corpuscles in footpad 4 suggests their role in anteroposterior balance, while Meissner-like corpuscle concentrations in digits 2 and 5 support their role in mediolateral balance. Meissner-like corpuscles were located exclusively in the glabrous skin of the footpads and digit tips, however, Merkel cells were found throughout hairy and glabrous skin. Merkel cells and Meissner-like corpuscles were present, however, Ruffini endings and Pacinian corpuscles were not observed. Footfall patterns were analyzed as a first step in correlating mechanoreceptor distribution and functionality. Intact hind paws were processed, serially sectioned, and stained to visualize mechanoreceptors. The itga1-null mouse is lacking the integrin α1 subunit, which binds exclusively to the β1 subunit, thus rendering integrin α1β1 nonfunctional while leaving the numerous other pairings of the β1 subunit undisturbed. The purpose of this study, therefore, was to determine and compare the distribution of mechanoreceptors across the hind paw skin and the footfall patterns of itga1-null and wild type mice. For example, it has been shown that integrin α1β1 is necessary for the function of TRPV4 that is highly expressed by afferent units. Also, the role of integrin α1β1 in mechanoreceptor function is unclear, though it is expressed by keratinocytes in the stratum basale where it is likely involved in a variety of mechanotransduction pathways and ion channel functionalities. Electrophysiological studies of hind paw skin reveal the different types of afferent responses and their receptive fields, however, the anatomical distribution of mechanoreceptor endings is unknown. Department of Human Health and Nutritional Sciences, College of Biological Science, University of Guelph, Guelph, ON, CanadaĪfferent neurons and their mechanoreceptors provide critical sensory feedback for gait. Valerie Wai, Lauren Roberts, Jana Michaud, Leah R.
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