The spinal nerves innervate putative chemosensory cells in the ventral skin of desert toads, Bufo alvarius

Abstract

Toads normally obtain water by absorption across their skin from osmotically dilute sources. When hyperosmotic salt solutions are presented as a hydration source to dehydrated desert toads, they place the ventral skin onto the source but soon afterwards escape to avoid dehydration. The escape behavior coincides with neural excitation of the spinal nerves that innervate putative chemosensory cells in the ventral skin. In the present study, fluorescent dye translocated through the spinal nerves to those receptor cells in the epidermis was photoconverted in the presence of 3, 3'-diaminobenzidine tetrahydrochloride for electron-microscopic observation of the cells and associated nerve terminals. Most of the photoconverted cells were located in the deepest layer of the epidermis, with some being in more intermediate layers. No labeled cell was seen in the outermost layer of living cells. In desert toads, flask cells and Merkel cells are occasionally seen in the epidermis. An association of nerve fibers with these epidermal cells has been reported in some species of the anurans. In the present study, however, the cytological features of the photoconverted cells are neither reminiscent of flask cells nor Merkel cells, but are similar to those of surrounding epithelial cells in each layer of the epidermis. We hypothesize a sensory function for these cells, because they have a close association with nerve fibers and participate in the transepithelial transport of salts that must pass through all cell layers of the skin.

Structural aspects of the Eberth-Katschenko layer of Bufo ictericus integument: histochemical characterization and biochemical analysis of the cutaneous calcium (Amphibian, Bufonidae)

“…The integument of anuran amphibians is basically formed by an epidermal and a dermal layer, and as amphibia occur in a wide spectrum of different habitats, the integument performs several functions such as mechanical protection (Farquhar and Palade, 1965;Fox, 1986a,b), chemical defense (Bueno et al, 1981;Delfino et al, 1995), sensory perception (Mearow and Diamond, 1988;Koyama et al, 2001), ionic transportation (Sullivan et al, 2000), water absorption (Hoffman and Katz, 1999;Sullivan et al, 2000), respiration (Duellman and Trueb, 1994), and osmoregulation (Bentley and Yorio, 1976).…”

A preliminary assessment of anuran physiological and morphological adaptation to the Caatinga, a Brazilian semi-arid environment

“…Thereafter, a number of contributions have revealed diverse traits of ventral skin morphology that differ among species and affect water uptake, such as thickness, sculpturing, presence of verruca hidrophilica (protrusions that increase surface area and characterize the ventral integument of many anuran amphibians), or increased capillary bedding [5]. Furthermore, the ventral skin of some anurans have chemosensory properties and can detect salts, helping individuals to avoid hyper-osmotic sources of water [18].…”

Sensory cutaneous papillae in the sea lamprey (Petromyzon marinus L.): I. Neuroanatomy and physiology

“…Subsequently, studies have reported putative SCCs on the barbels and nasopharynx of hagfish (Braun, , ; Braun & Northcutt, ), on the skin surface of brook lampreys ( Lampetra planeri Bloch) and river lampreys ( Lampetra fluviatilis L.), including the oral, gill pore, dorsal fin and genital regions (Baatrup & Døving, ; Fox, Lane, & Whitear, ; Whitear & Lane, ), on the skin, gills, and oropharynx of chondrichthyes and bony fish (Codina et al, ; Hansen, Ghosal, Caprio, Claus, & Sorensen, ; Kotrschal, ; Kotrschal, Krautgartner, & Hansen, ; Kotrschal, Peters, & Atema, ; Kotrschal, Whitear, & Adam, ; Kuciel et al, ; Peach, ; Peters, Kotrschal, & Krautgartner, ; Peters, Van Steenderen, & Kotrschal, ; Silver & Finger, ; Whitear & Moate, ). Other studies have described SCCs on the skin and in the oral cavity of amphibians (Koyama, Nagai, Takeuchi, & Hillyard, ; Nagai, Koyama, Von Seckendorff Hoff, & Hillyard, ; Osculati & Sbarbati, ; Whitear, ), and in the airways of reptiles and mammals (Finger et al, ; Hansen, ; Saunders, Christensen, Finger, & Tizzano, ; Sbarbati, Crescimanno, Benati, & Osculati, ; Sbarbati, Crescimanno, Bernardi, & Osculati, ; Sbarbati & Osculati, ; Tizzano et al, ; Tizzano, Merigo, & Sbarbati, ). The study of SCC innervation and physiology has been challenging because of the scarcity and widespread distribution of these cells.…”