The Merkel cell as a possible mechanoreceptor cell

Area of Science:

• Neuroscience
• Dermatology
• Sensory Biology

Background:

• Merkel cells (MCs) form Merkel cell-neurite complexes (MCN-complexes) in vertebrate skin, crucial for slowly adapting mechanoreception (SAI/Ft-I units).
• The precise role of MCs versus nerve terminals in mechanotransduction remains debated, with some hypotheses placing mechanoreception solely at the nerve endings.

Purpose of the Study:

• To review recent findings investigating the hypothesis that Merkel cells themselves function as mechanoreceptors.
• To elucidate the distinct roles of Merkel cells and associated nerve terminals in processing mechanical stimuli.

Main Methods:

• Selective degeneration of Merkel cells using quinacrine irradiation in rat skin.
• Pharmacological blockade of synaptic transmission in MCN-complexes using Ca antagonists.
• Electrical stimulation (anodal/cathodal current) of Merkel cell-neurite complex receptive fields.

Main Results:

• Degeneration of Merkel cells selectively abolished tonic discharges in SAI units, while phasic responses persisted.
• Blocking synaptic transmission significantly reduced tonic responses but left phasic responses largely intact.
• Anodal current application induced tonic discharges, supporting Merkel cell mechanosensitivity, while stimulation thresholds differed from other sensory cells.

Conclusions:

• Findings strongly indicate Merkel cells act as mechanoreceptors mediating tonic responses.
• Nerve terminals likely transduce the phasic component of mechanical stimuli.
• Further research on MC membrane channels and neurotransmitters is needed to definitively establish MCs as mechanoreceptors.