DRG sensory neurons were classified during intracellular in vivo electrophysiological experiments according to parameters reported previously by other laboratories to distinguish DRG neuron types, including: 1) the configuration of the AP, 2) the conduction velocity, and 3) the response properties to application of natural stimuli to peripheral receptive fields [26 (link),27 (link),61 (link)-64 (link)].
The sensory receptive properties of each DRG neuron were examined using hand-held mechanical stimulators and classified as previously described. The threshold of activation, the depth of the receptive field and the pattern of adaption were the major factors to further classify neurons into low threshold mechanoreceptor (LTM), high threshold mechanoreceptor (HTM) and unresponsive neurons. LTM neurons were further classified using soft brush, light pressure with a blunt object, light tap and vibration. Many LTM neurons are cutaneous, and include guard/field neurons (GF), rapidly adapting (RA) neurons, Pacinian afferents, slowly adapting (SA) neurons. A group of neurons with deeper receptive fields that were very sensitive to light pressure and/or leg movement and often showed ongoing activity, were classified as muscle spindle (MS) neurons. These neurons also exhibited slow adaptation to dorsal root stimulation, to intracellular injection of depolarizing current and to leg movement. HTM neurons responded to noxious stimuli including noxious pinch and application of sharp objects such as the end of a syringe needle. Neurons that did not respond to any of the innocuous or noxious mechanical stimuli listed above were classed as unresponsive [26 (link)]. Heat nociceptors and specific cooling receptors were not included in this study due to the very low numbers of such neurons.
Neurons were also classified according to dorsal root CVs: C-fiber neurons (≤ 0.8 mm/ms), Aδ-fiber neurons (1.5-6.5 mm/ms) and Aα/β-fiber neurons (> 6.5 mm/ms). This classification has been used as a means of classification of neurons in other models of peripheral neuropathy [7 (link),10 (link),13 (link),65 (link),66 (link)].
Compared to other criteria from other groups [64 (link),67 (link)], these criteria most closely matched the present study, including similar surgical procedure, recording technique and setting, etc. It should be noted that as excitability of sensory neurons can be altered in models of peripheral neuropathy, functional classification was based primarily on responses to activation of the peripheral receptive fields. However, classification was also based on AP configuration and on responses to activation.
The sensory receptive properties of each DRG neuron were examined using hand-held mechanical stimulators and classified as previously described. The threshold of activation, the depth of the receptive field and the pattern of adaption were the major factors to further classify neurons into low threshold mechanoreceptor (LTM), high threshold mechanoreceptor (HTM) and unresponsive neurons. LTM neurons were further classified using soft brush, light pressure with a blunt object, light tap and vibration. Many LTM neurons are cutaneous, and include guard/field neurons (GF), rapidly adapting (RA) neurons, Pacinian afferents, slowly adapting (SA) neurons. A group of neurons with deeper receptive fields that were very sensitive to light pressure and/or leg movement and often showed ongoing activity, were classified as muscle spindle (MS) neurons. These neurons also exhibited slow adaptation to dorsal root stimulation, to intracellular injection of depolarizing current and to leg movement. HTM neurons responded to noxious stimuli including noxious pinch and application of sharp objects such as the end of a syringe needle. Neurons that did not respond to any of the innocuous or noxious mechanical stimuli listed above were classed as unresponsive [26 (link)]. Heat nociceptors and specific cooling receptors were not included in this study due to the very low numbers of such neurons.
Neurons were also classified according to dorsal root CVs: C-fiber neurons (≤ 0.8 mm/ms), Aδ-fiber neurons (1.5-6.5 mm/ms) and Aα/β-fiber neurons (> 6.5 mm/ms). This classification has been used as a means of classification of neurons in other models of peripheral neuropathy [7 (link),10 (link),13 (link),65 (link),66 (link)].
Compared to other criteria from other groups [64 (link),67 (link)], these criteria most closely matched the present study, including similar surgical procedure, recording technique and setting, etc. It should be noted that as excitability of sensory neurons can be altered in models of peripheral neuropathy, functional classification was based primarily on responses to activation of the peripheral receptive fields. However, classification was also based on AP configuration and on responses to activation.
Free full text: Click here
