Observations on morphology and function of cutaneous and subcutaneous sensory mechanoreceptors : an experimental study in mammals

Tactile sensory discrimination is dependent upon an intact system of peripheral mechanoreceptors, their nerve fibre afferents with cell bodies in the dorsal root ganglion and the dorsal column-medial lemniscal system which relays tactile information from the skin to the cortex. Injury to any part of the afferent pathways leads to compromised mechanoreceptive perception. The present study was initiated to extend our knowledge on the morphology and function of peripheral receptors subserving mechanoreception in mammals during normal conditions and after nerve injury.

Human Pacinian corpuscles (PC) were clustered close to digital nerves and vessels. Differences in corpuscular size did not reflect morphological variations. PCs in distal phalanges were smaller than in proximal parts of the hand. Nerve afferents of PCs, recognised in close neighbourhood to SA 11 units, were segregated in an orderly fashion in the median nerve at elbow level. PCs but non Meissner corpuscles (MC) and Merkel cells were immuno-reactive to the glucose transporter 1 (Glut-1). Immature and denervated PCs had a strong Glut-1 immuno-reaction. Perineurial cells of peripheral nerves down-regulated Glut-1 during Wallerian degeneration. TGF-ß isoforms appeared in normal and denervated mechanoreceptors. TGF-ß was maintained in sensory neurons, satellite cells of dorsal root ganglia and in peripheral nerves following injury. TGF-ß signalling seems to involve autocrine and paracrine mechanisms. Lamellar cells of the PC expressed the low affinity p75 receptor for neurotrophins and the high affinity trk B receptor in young and adult animals. The increased expression of P75 and trk B in denervated immature and adult PCs supports the notion that anterogradely transported BDNF might promote development and regeneration in PCs. Kitten PCs exhibited a growth inhibition following nerve injury.

Conclusion: The data agree with the idea of a general orderly organisation of the somatosensory system in the periphery. Mechanoreceptors differ from each other in terms of their expression of growth factors, cytokines, neurotrophins and their respective receptors. The Pacinian corpuscle can be considered to have the most resemblance to peripheral nerves.

List of scientific papers

I. Stark B, Carlstedt T, Hallin RG, Risling M (1998). Distribution of human Pacinian corpuscles in the hand. A cadaver study. J Hand Surg Br. 1998 Jun;23(3):370-2.
https://pubmed.ncbi.nlm.nih.gov/9665528

II. Wu G, Ekedahl R, Stark B, Carlstedt T, Nilsson B, Hallin RG (1999). Clustering of Pacinian corpuscle afferent fibres in the human median nerve. Exp Brain Res. 126(3):399-409.
https://pubmed.ncbi.nlm.nih.gov/10382624

III. Stark B, Carlstedt T, Cullheim S, Risling M (1999). Developmental and lesion-induced changes in the distribution of the glucose transporter Glut-1 in the central and peripheral nervous system. Exp Brain Res. 2000 Mar;131(1):74-84.
https://pubmed.ncbi.nlm.nih.gov/10759173

IV. Stark B, Carlstedt T, Risling M. Distribution of TGF-beta, the TGF-beta type I receptor and the R-II receptor in peripheral nerves and mechanoreceptors;observations on changes after traumatic injury. [Manuscript]

V. Stark B, Risling M, Carlstedt T. Distribution of the neurotrophin receptors, p75 and trkB in peripheral mechanoreceptors; observations on changes after injury. [Submitted]