Responsiveness and ultrastructure of slowly adapting type I cutaneous mechanoreceptors in vitamin A deficient rats.

Abstract

SUMMARY1. Single-unit recordings were made from afferent nerve fibres supplying slowly adapting type I (s.a. I) cutaneous mechanoreceptors in anaesthetized vitamin A deficient and control rats.2. Trains of thirty repetitive mechanical stimuli with 0-1 s rise time, 1-9 s plateau phase, and 0 7 s interstimulus interval were applied. A feed-back mechanism maintained the force of stimulation at 20 mN during the plateau phases and the contact force between stimuli at 0 5 mN.3. All displacement values in the group ofvitamin A deficient rats were significantly larger than the corresponding control values. Residual indentations were increased by 70-100 % while maximal indentations were only about 40 % higher. These results indicate a non-linear increase in compliance of the skin and underlying tissues.4. S.a. I receptors were found to be significantly less responsive in vitamin A deficient animals. Mean numbers of impulses were about 25 % lower in the vitamin A deficient group than in controls throughout the entire train of thirty stimuli.5. In vitamin A deficient rats, Merkel cells and adjoining nerve terminals showed signs of degeneration of a variety of cell organelles, particularly the mitochondria.6. Degenerative changes induced by vitamin A deficiency especially in the Merkel cells appeared to be a major cause ofthe reduction ofresponsiveness in s.a. I receptors.

Effect of age on the structure of Meissner corpuscles in murine digital pads

“…These findings were supported by similar age-related changes found in a study of murine Meissner corpuscles in diabetic and age-matched nondiabetic littermates (Ras and Nava, 1986). Analogous age changes were also observed in the crural Pacinian corpuscles of the mouse (Nava, 1988) and Merkel domes from vitamin A-deficient rats (Baumann et al, 1986). Structural changes found in Meissner corpuscles will assist in understanding age-associated distal axonopathy (Vlassara, 19881, and may aid intensifying efforts to understand the apparatus producing mechanoelectric transduction if subsequent electrophysiological correlation is attempted.…”

“…Mitochondria1 degeneration seen in the present study of aging mouse digital corpuscles is also described in the aging optic nerves of mice (Johnson, 1978) and Merkel domes of Vitamin A deficient rats (Baumann et al, 1986). According to the mitochondrial mutation theory of aging, during maturation of the organism an increasing number of mitochondria lose the ability to divide as a consequence of mitochondrial DNA injury, and thus become susceptible to progressive membrane damage secondary to lipid peroxidation and cross-linking (Miquel et al, 1983).…”

Mechanical properties of skin and responsiveness of slowly adapting type I mechanoreceptors in rats at different ages.

“…In contrast, conditions other than ageing that alter the viscoelastic properties of the skin may not affect all displacement parameters to the same extent. For example in vitamin A deficiency, as described in detail in the accompanying paper (Baumann et al 1986), the compliance of the skin was larger than in the (adult) control rats. The increase in residual indentation at 0 5 mN contact force was very close to the values obtained in the young rats in this study.…”

“…The 'young' population was fed normal rat chow (Purina). The 'adult' group was the control population for vitamin A deficient rats described in the accompanying paper (Baumann, Cheng-Chew, Hamann & Leung, 1986) and was fed a vitamin A deficient diet (Purina) supplemented with vitamin A. Until 3 months of age there was no significant difference in body weight between the two groups (P > 0-2).…”

Proceedings of the Physiological Society and the Societa Italiana Di Fisiologia, 11‐13 July 1985, Oxford Meeting: Communications

“…1). (Baumann, Cheng-Chew, Hamann & Leung, 1984). The present experiments were performed to look for clues initially in the ultrastructure and later the cell function for the mode of action of this phenomenon.…”