Cutaneous sensory receptors in the rat foot

Abstract

1. A total of 574 cutaneous afferent units in the sural and plantar nerves supplying the skin of the rat foot was examined: 399 A beta-units, 55 A delta-units, and 120 C-units. Their receptive-field (RF) properties were similar to those described in other mammals. However, the receptor type composition of units was different between the two nerves. 2. The sural A beta-fiber sample (n = 160) consisted of G-hair (41%), field (11%), rapidly adapting (RA; 6%), slowly adapting type I (SA-I; 7%), and type II (SA-II; 35%) mechanoreceptors. The plantar A beta-fiber sample (n = 239) was composed of G-hair (3%), RA (35%), SA-I (30%), SA-II (24%), and Pacinian corpuscle (PC; 8%) mechanoreceptors. 3. The RFs of SA-II units were located on both hairy and glabrous skin overlying the foot joints. Many of the SA-II units responded to movement of the foot joints. The RFs of both SA-I and RA units were small in size and located in high density on the toe tips and footpads. PC units were very sensitive to vibration and had extremely large RFs as in other species, although they were rare and found only in the plantar nerve. Field units were similar to SA-II units in response properties and RF distribution. 4. The sural A delta-fiber sample (n = 44) included nociceptors (68%), D-hair (27%), and cold (5%) receptors. All sampled plantar A delta-fibers (n = 11) were nociceptors. Of A delta-nociceptor units, A delta-mechanical nociceptors (73%) were dominant. 5. The sural C-fiber sample (n = 85) included nociceptors (44%), C-mechanoreceptors (33%), and cold receptors (21%). The plantar C-fiber sample (n = 35) included nociceptors (77%) and cold receptors (23%). No warm units were found among either the sural or plantar nerve fibers. Of C-nociceptors, C-mechanoheat nociceptors (80%) were dominant. 6. The results indicate that all well-known types of cutaneous receptors, except warm receptors, exist in the foot skin of the rat. On the basis of the fact that RFs of RA and SA-I units are in high density on the toe tips and footpads, it is suggested that those regions may have a spatial discriminating capacity. It is also suggested that SA-II receptors may play a role in proprioception, because they have RFs on the skin over foot joints and respond to joint movement.(ABSTRACT TRUNCATED AT 400 WORDS)

Sensory afferents regenerated into dorsal columns after spinal cord injury remain in a chronic pathophysiological state

“…When we recorded from single fibers ( figure 4C), the CV of the uninjured segment was well within this range for Aβ fibers (Feasby et al, 1981,Shin et al, 1997. The regenerated axon segments did not conduct slower than 2m/sec, the upper CV of C-fibers (Leem et al 1993) and these axon segments were able to follow reliably at stimulation frequencies of up to 10 Hz, a frequency at which C-fibers show conduction changes (Koga et al 2005). Since we stimulated regenerated fibers at spinal level T9, it is also unlikely that the fibers were displaced Ia afferents that normally terminate in Clarke's column.…”

Spinal Processing of Noxious and Innocuous Cold Information: Differential Modulation by the Periaqueductal Gray

“…EC has been used previously in behavioral studies, and similar temperature changes have been reported (Hao et al, 1996(Hao et al, , 1999Sjolund et al, 1998). These temperature changes are sufficiently cold to activate populations of nociceptive afferents (LaMotte and Thalhammer, 1982;Lynn and Carpenter, 1982;Leem et al, 1993;Kajander, 1996, 1997). However, temperatures reported to produce cold pain sensation in humans and nociceptive behaviors in animals are highly variable, likely due to the wide variety of stimuli used and responses measured, making comparison between studies difficult.…”

“…Innocuous cooling activates subsets of A␦-and C-fiber lowthreshold afferents (Bessou and Perl, 1969;Leem et al, 1993;Campero et al, 1996). More intense cold stimuli additionally activate populations of nociceptive afferents (both A␦-and C-fiber units), which display a range of activation thresholds and encode changes in stimulus intensity (LaMotte and Thalhammer, 1982;Lynn and Carpenter, 1982;Leem et al, 1993;Kajander, 1996, 1997;Cain et al, 2001).…”

“…More intense cold stimuli additionally activate populations of nociceptive afferents (both A␦-and C-fiber units), which display a range of activation thresholds and encode changes in stimulus intensity (LaMotte and Thalhammer, 1982;Lynn and Carpenter, 1982;Leem et al, 1993;Kajander, 1996, 1997;Cain et al, 2001). At the spinal level, electrophysiological studies have demonstrated that wide-dynamicrange and nociceptive-specific neurons in the dorsal horn are excited by cold stimuli and encode intensity to noxious cold over a wide range of temperatures (Christensen and Perl, 1970;Khasabov et al, 2001;Brignell et al, 2008).…”

Developmental Adaptation of Rat Nociceptive Withdrawal Reflexes after Neonatal Tendon Transfer

“…A change of movement pattern would produce a corresponding change in the sensory feedback that ensues on muscle contraction, because the feedback from most cutaneous mechanoreceptors reflects the change in load on the skin surface (Fleischer et al, 1983;Willis and Coggeshall, 1991;Leem et al, 1993). The change of receptive fields corresponded to the induced changes of the movement patterns of the manipulated muscles.…”