Morphological evaluation of Merkel cells and small lamellated sensory receptors in the equine foot.

The research article investigates the existence of specific sensory receptors, more precisely Merkel cells and small lamellated Pacinian-like corpuscles (SLPCs), in the foot of a horse, providing a clearer understanding of the complex assortment of neural components in the equine foot.

Objective and Sample

• The objective of this study is to inspect the foot of a horse for signs of sensory receptors such as Merkel cells and SLPCs. The researchers obtained forefeet from seven horses that were euthanized for reasons other than foot diseases.

Procedure

• The acquired feet were disarticulated and cut into either sagittal or cross sections. These sections were then soaked in neutral-buffered 4% formalin, a solution that helps to preserve biological specimens.
• After the fixation process, samples were extracted from the middle of the dorsal side of the hoof wall and from the frog (cuneus ungulae) between the apex and central sulcus. The frog in this context refers to an area of the horse’s hoof.
• The formalin-fixed, paraffin-embedded hoof wall and frog sections were processed for peroxidase immunohistochemistry, a technique used to visually localize the presence and quantity of specific proteins in tissues. These sections were then dyed with H&E, Alcian blue, and Masson trichrome stains for histologic evaluation.

Results

• Sensory nerves and specific receptors were identified in the dermal and epidermal tissues of the equine foot, including in the hoof wall laminae, coronet, and frog.
• Merkel cells were identified by their reactivity with specific antisera to villin, cytokeratin 20, and protein gene product 9.5 in the coronet’s skin and hoof wall.
• The research discovered that these cells were dispersed among basilar keratinocytes within the frog, coronary skin, and secondary skin laminae. This provides vital information about the localization and possible function of Merkel cells in horse feet.
• SLPCs were found within the superficial dermis associated with the central ridge of the frog of the foot (known as frog stay).
• A high number of S100 protein and protein gene product 9.5 immunoreactive sensory nerves closely connected to these receptors were present in the dermal tissues within both the frog and hoof wall. This indicates that these sensory nerves appear to be associated with the sensory receptors identified.

Conclusions and Clinical Relevance

• The discovery of Merkel cells and SLPCs, known to respectively detect tactical and vibrational stimuli, further elucidated the vast diversity of neural elements within the horse’s foot.
• This research could improve the understanding of how horses perceive touch and vibration in their feet, which could have significant implications in the field of veterinary medicine and treatment of equine foot diseases.