Differing Neurophysiologic Mechanosensory Input From Glabrous and Hairy Skin in Juvenile Rats

Abstract

Sensory afferents in skin encode and convey thermal and mechanical conditions, including those that threaten tissue damage. A small proportion of skin, the glabrous skin of the distal extremities, is specialized to explore the environment in fine detail. Aside from increased innervation density, little is known regarding properties of mechanosensory afferents to glabrous skin in younger animals that explain the exquisite precision and high contrast in rapidly sampling physical structures, including those that threaten injury. To assess this, we obtained intact neuronal intracellular recordings in vivo from 115 mechanosensitive afferent neurons from lumbar and thoracic dorsal root ganglia in juvenile rats. Two characteristics were unique to glabrous skin: a threefold higher proportion of fast-conducting to slow-conducting afferents that were high-threshold mechanosensitive nociceptors compared with hairy skin and a twofold faster conduction velocity of fast-conducting nociceptors compared with hairy skin. Additionally differences were found in mechanical thresholds between glabrous skin and hairy skin for each fiber type. These differences reflect and help explain the rapid response of skin specialized to explore the physical environment. Additionally, these results highlight potential limitations of using passive electrical properties and conduction velocity alone to characterize primary afferents without knowledge of the skin type they innervated.

Nerve injury induced activation of fast-conducting high threshold mechanoreceptors predicts non-reflexive pain related behavior

“…A week after either pSNL or Sham surgery, cellular recordings were made under anesthesia, after a dorsal midline incision was made in trunk skin and the L4 dorsal root ganglion (DRG) and adjacent spinal cord were exposed by laminectomy as previously described (illustrated in Figure 1A) [26]. The tissue was continuously superfused with oxygenated artificial cerebrospinal fluid as described [26].…”

“…The tissue was continuously superfused with oxygenated artificial cerebrospinal fluid as described [26]. …”

“…DRG soma were impaled with borosilicate microelectrodes (80–250 MΩ) containing 1 M potassium acetate. Intracellular penetrations with a resting membrane potential of ≤−40 mV were characterized further as previously described [26–28]. Only cells capable of generating a somatic action potential (AP) (by current somatic injection, 25 and 500 ms pulses) and with impalements stable long enough to adequately explore the full extent of the skin at the L4 dermatome (>2 min) were included.…”

Mechanical sensibility of nociceptive and non-nociceptive fast-conducting afferents is modulated by skin temperature

“…As illustrated in Fig. 1, a dorsal midline incision was made in trunk skin and either L4, L5, or T11 dorsal root ganglion (DRG) and adjacent spinal cord were exposed by laminectomy as previously described (Boada et al 2010 The spinal column was secured using custom clamps and the preparation was transferred to a preheated (32-34°C) recording chamber where the superfusate was slowly raised to 37°C (MPRE8; Cell MicroControls, Norfolk, VA). Pool temperature adjacent to the DRG was monitored with a thermocouple (IT-23; Physitemp, Clifton, NJ).…”

“…We speculate that these changes in encoding capabilities could profoundly alter the function of cross-fiber inhibition at central integration sites. of incision (Boada et al 2012) or differences between mechanosensory afferents innervating glabrous and hairy skin (Boada et al 2010). When a cell was obtained meeting criteria for study in the current protocol, it was examined according to the methods below.…”