Acute effects of neomycin on slowly adapting type I and type II cutaneous mechanoreceptors in the anaesthetized cat and rat.

Baumann, Klaus I.; Hamann, Wolfgang; Leung, Mun-Fai

doi:10.1113/jphysiol.1990.sp018116

Cited by 23 publications

(9 citation statements)

References 18 publications

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“…This notion is compatible with a vast amount of previous circumstantial evidence, e.g. irregular discharge patterns of cat SA type I units suggesting release of transmitters from Merkel cells (Horch, Whitehorn & Burgess, 1974); selective decreases of mechanical responses of SA type I units by perfusion of Ca2" channel blockers (Yamashita et al 1986); correlation of decreased responses of SA type I units with reduction in Merkel cell granules in a hypoxic environment (Findlater, Cooksey, Anand, Paintal & Iggo, 1987); susceptibility of SA type I units to neomycin suggesting the presence of functional synapses from Merkel cells to nerve terminals (Baumann, Hamann & Leung, 1990). The possibility has been raised that the nerve terminal is mechanoreceptive under certain conditions, such as mechanical stimulation with high frequency components (Gottschaldt & VahleHinz, 1981).…”

Section: Discussion Discrepancy Between Present and Previous Studiesmentioning

confidence: 99%

Selective phototoxic destruction of rat Merkel cells abolishes responses of slowly adapting type I mechanoreceptor units.

Ikeda

Yamashita

Ono

et al. 1994

The Journal of Physiology

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Section: Discussion Discrepancy Between Present and Previous Studiesmentioning

confidence: 99%

Selective phototoxic destruction of rat Merkel cells abolishes responses of slowly adapting type I mechanoreceptor units.

Ikeda

Yamashita

Ono

et al. 1994

The Journal of Physiology

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“…Electrophysiological in vivo studies have suggested the involvement of chemical synaptic transmission in the transduction process of the mammalian SAI mechanoreceptor (Findlater, Cooksey, Anand, Paintal & Iggo, 1987;Pacitti & Findlater, 1988;Baumann, Hamann & Leung, 1990) and of counterparts in frogs (frog type I mechanoreceptor) (Yamashita, Ogawa & Taniguchi, 1986). The highthreshold (L-type) Ca2" channel in Merkel cells may contribute to release of the transmitter as is the case for the same channel in sensory receptor cells such as hair cells (Ohmori, 1984;Hudspeth & Lewis.…”

Section: Y Yamashita and Otihersmentioning

confidence: 99%

Voltage‐dependent currents in isolated single Merkel cells of rats.

Yamashita

Akaike

Wakamori

et al. 1992

The Journal of Physiology

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SUMMARY1. Merkel cells were dissociated enzymatically from the footpad epidermis of 10-to 20-day-old rats pretreated with fluorescent dye, quinacrine, for purposes of staining. The fluorescent Merkel cells had an elongated or elliptic shape in situ, yet the dissociated ones were round (7-12 #m in diameter).2. Electrical recordings were performed in the whole-cell configuration using a conventional patch-clamp technique. The mean resting membrane potential of fluorescent Merkel cells was -54 0 mV, the value being greater than the -2641 mV of non-fluorescent epidermal cells. No voltage-dependent channel was observed in non-fluorescent cells.3. The Merkel cells had no Na+ spike in an external standard solution, but tetrodotoxin-resistant long-lasting action potentials were evoked by depolarization with injection of constant currents in an external solution containing Ba2+.4. In Merkel cells under voltage clamp, depolarizing step pulses (800 ms) from a holding potential (VH) of -80 mV elicited predominantly outward K+ currents composed of transient and sustained components: the former was selectively inhibited by 4-aminopyridine (4-AP), while the latter was inhibited by both tetraethylammonium (TEA) and quinacrine. Quinacrine was more effective and selective than TEA in blocking the sustained K+ current but had no effect on the current at the low concentration (10-7or 3 x 10`6 M) used for staining the Merkel cells.5. The sustained outward K+ current (IKD) was activated at potentials more positive than -20 or -10 mV at a VH of -50 mV, at which potential the transient outward K+ channel was completely inactivated. The potential for half-inactivation in the steady-state inactivation curve for IKD was -33 mV.6. The transient outward K+ current (IA) was activated at potentials more positive than -50 mV at a VH of -80 mV. The potential for half-inactivation in the steady-state inactivation curve for IA was -64 mV.7. When the outward K+ currents were blocked by adding both TEA and 4-AP, only a sustained inward Ca2+ current was observed. In an external solution containing 10 mM-Ca2+, ICa was evoked by potentials more positive than -20 mV at a VH of -80 mV, and the maximum inward current appeared around +10 mV. 8. In external solution containing 25 mM-Ba2 , the potential for half-inactivation of the steady-state inactivation curve for IBa was -34 mV.9. The selectivity of the Ca2+ channel for divalent cations was in the order Ba2+ > Sr2+ > Ca2+.10. Organic and inorganic Ca2+ antagonists blocked IBa in a concentrationdependent manner, the potency of inhibition being in the order w-conotoxin > flunarizine = nicardipine > diltiazem > verapamil, and La3+ > Cd2+ > Co2+.11. It is concluded that Merkel cells have at least three distinct voltage-gated currents: a delayed K+ current (IKD), a transient A-current (IA) and a high-threshold (L-type) Ca2+ current (ICa). The electrical and pharmacological properties of these voltage-dependent channels are essentially similar to those of other excitable cells.

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“…Within the thickened epidermis of touch domes, the peripheral terminals of SAIs form expanded disc-like endings that lie in synapse-like apposition to Merkel cells in the basal epidermis (Munger, 1965;Iggo and Muir, 1969). The latter are neural crest-derived neuroendocrine cells (Szeder et al, 2003a) that appear to play an essential role in the transduction of mechanical stimuli into electrical activity of SAI afferents (Findlater et al, 1987;Iggo et al, 1988;Baumann et al, 1990;Ikeda et al, 1994;cf. Nurse and Cooper, 1988;Mills and Diamond, 1995).…”

mentioning

confidence: 99%

Central and peripheral anatomy of slowly adapting type I low‐threshold mechanoreceptors innervating trunk skin of neonatal mice

Woodbury

Koerber

2007

J of Comparative Neurology

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Despite intensive study, our understanding of the neuronal structures responsible for transducing the broad spectrum of environmental energies that impinge upon the skin has rested on inference and conjecture. This major shortcoming motivated the development of ex vivo somatosensory system preparations in neonatal mice in the hope that their small size might allow the peripheral terminals of physiologically identified sensory neurons to be labeled intracellularly for direct study. The present report describes the first such study of the peripheral terminals of four slowly adapting type I low-threshold mechanoreceptors (SAIs) that innervated the back skin of neonatal mice. In addition, this report includes information on the central anatomy of the same SAI afferents that were identified peripherally with both physiological and anatomical means, providing an essentially complete view of the central and peripheral morphology of individual SAI afferents in situ. Our findings reveal that SAIs in neonates are strikingly adult-like in all major respects. Afferents were exquisitely sensitive to mechanical stimuli and exhibited a distinctly irregular, slowly adapting discharge to stimulation of 1-4 punctate receptive fields in the skin. Their central collaterals formed transversely oriented and largely nonoverlapping arborizations limited to regions of the dorsal horn corresponding to laminae III-V. Their peripheral arborizations were restricted entirely within miniaturized touch domes, where they gave rise to expanded disc-like endings in close apposition to putative Merkel cells in basal epidermis. These findings therefore provide the first direct confirmation of the functional morphology of this physiologically unique afferent class.

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Acute effects of neomycin on slowly adapting type I and type II cutaneous mechanoreceptors in the anaesthetized cat and rat.

Cited by 23 publications

References 18 publications

Selective phototoxic destruction of rat Merkel cells abolishes responses of slowly adapting type I mechanoreceptor units.

Selective phototoxic destruction of rat Merkel cells abolishes responses of slowly adapting type I mechanoreceptor units.

Voltage‐dependent currents in isolated single Merkel cells of rats.

Central and peripheral anatomy of slowly adapting type I low‐threshold mechanoreceptors innervating trunk skin of neonatal mice

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