Cutaneous Innervation in the Red-Eared Slider Turtle: Novel Identification and Analysis of Scale Sensilla and Sensory...

The red-eared slider turtle inhabits environments ranging from freshwater to semiterrestrial settings. Understanding the sensory adaptations of this species is crucial, particularly concerning its limb skin, which plays a key role in environmental interaction and survival. This study presents the first detailed identification of scale sensilla and sensory corpuscles in the red-eared slider's limb skin, offering insights into their innervation and distribution. We combined scanning electron microscopy (SEM), light microscopy, and immunofluorescence with ten antibodies to elucidate the sensory architecture and adaptation mechanisms of the turtle's skin. The antibodies include E-cadherin, four neural markers (Nestin, PGP9.5, neuron-specific enolase [NSE], and Synaptophysin), and five additional markers (PDGFRα, CD34, Vimentin, α-SMA, and Tom20) to analyze sensory structures and distribution patterns. SEM revealed scale sensilla resembling artichokes, with concentric layers surrounding a central dome featuring microplicae, grooves, and pores. Light microscopy showed these sensilla as dome-shaped structures elevated above the epidermal surface. Immunofluorescence with E-cadherin highlighted scale sensilla cells, central cells, and dermal papillae, while neural markers confirmed sensory nerves within the scale sensilla, underscoring their sensory role. Three types of sensory corpuscles were identified in the limb skin: Meissner's and Ruffini corpuscles in the dermis, and Pacinian corpuscles in the hypodermis. The four neural markers showed strong expression in sensory nerve fiber endings across all corpuscles, highlighting their roles in detecting pressure, vibration, and tactile stimuli. CD34 and PDGFRα were expressed in perineurial fibroblast-like cells and telocytes within the external capsules and concentric lamellae of Pacinian corpuscles, as well as in the external capsules of Meissner's and Ruffini corpuscles, with telocytes surrounding all three types. Vimentin was found in connective tissue and lamellar cells in all corpuscles, suggesting its role in structural support. α-SMA was strongly expressed in Pacinian corpuscles and minimally in Meissner's and Ruffini corpuscles, indicating its primary role in maintaining structural integrity in Pacinian corpuscles. Tom20 highlighted high mitochondrial activity in the nerve fibers and supporting cells of all corpuscles, with the highest expression in Meissner's corpuscles, reflecting the significant metabolic demands of these sensory structures. This study offers unprecedented insights into the sensory architecture of the red-eared slider turtle's skin. The novel identification and analysis of scale sensilla and sensory corpuscles, combined with 10 antibodies, enhances our understanding of the skin's innervation and its role in environmental adaptation, contributing valuable knowledge to sensory biology and herpetology.