Epidermal structure and dynamics of the toad, Bufo bufo, deprived of the pars distalis of the pituitary gland

Abstract

Structural changes and epidermal dynamics of the toad, Bufo bufo, were followed during 14 days after ablation of the pars distalis of the pituitary gland by taking skin biopsies 2, 17, 24, 40 and 65 hours, and 7 and 14 days after the operation. The rate of differentiation of new cornified layers was moderately increased during the first week, and highly increased during the second week after removal of the pars distalis. The keratinization process became gradually abnormal with regard to initial keratinization (formation of a peripheral dense band) as well as to final keratinization (laydown of an interfibrillar dense matrix). The structural manifestations of the keratinization process after pars distalis ablation are discussed in relation to those of intact toads. By counting the number of cells in the different “compartments” of the epidermis, it is shown that the total number of cells per length or square unit of stratum corneum remained constant in spite of at least five layers of stratum corneum being produced in a 14‐day period during which intact toads would have produced only one or two corneal layers. This shows that cell production can keep up with the increased rate of formation of corneal layers for at least 14 days after removal of the pars distalis, and consequently the rate of cell divisions must have increased. It was further shown that the ratio between the number of cells in the stratum germinativum and in the stratum intermedium was decreased, which is discussed in relation to epidermal dynamics. In Merkel cells, the number of granules increased, and eventually the granules became included within lysosome‐like bodies, indicating a secretory function of these cells. The findings are discussed in relation to the knowledge of mammalian Merkel cell structure and function. No significant change was observed in the flask cells. The control of amphibian epidermal proliferation, differentiation and moulting is discussed. It is concluded that these processes should be considered separately since they may not necessarily be coupled to one another and probably are differently controlled.

Host Stress Response Is Important for the Pathogenesis of the Deadly Amphibian Disease, Chytridiomycosis, in Litoria caerulea

“…In amphibians, GCs are critical regulators of blood ion homeostasis [19]–[24], appetite [25], [26], skin shedding [27]–[30], and WBC numbers and immune function [31]–[37]. A normal, adaptive, regulatory mechanism to maintain sodium homeostasis is likely a moderate, transitory elevation in CORT secretion to increase cutaneous uptake of sodium as well as digestive uptake (facilitated by increased appetite) [23], [24], [26].…”

First line of defence: the role of sloughing in the regulation of cutaneous microbes in frogs

“…Following a sloughing event, most amphibians will consume their slough ( Bendsen, 1956 ; Herman, 1992 ; Weldon et al , 1993 ). The period of time between the recurrent sloughing events is known as the intermoult interval, and this interval can vary from days to weeks depending on the species ( Bouwer et al , 1953 ; Jorgensen and Larsen, 1960 , 1961 , 1964 ; Jorgensen et al , 1965 ; Budtz, 1979 ; Jørgensen, 1988 ). The sloughing process is regulated hormonally via the thyroid, adrenal and pituitary glands ( Taylor and Ewer, 1956 ; Jorgensen and Larsen, 1960 , 1961 , 1964 ; Jorgensen, et al , 1965 ; Budtz, 1979 ; Jørgensen, 1988 ); however, sloughing frequency and the associated length of the intermoult interval can also be influenced by environmental conditions, including temperature, light and food availability ( Bendsen, 1956 ; Taylor and Ewer, 1956 ; Stefano and Donoso, 1964 ; Larsen, 1976 ; Herman, 1992 ).…”