Responses of Primary Afferent Fibers to Acupuncture-Like Peripheral Stimulation at Different Frequencies: Characterization by Single-Unit Recording in Rats / 神经科学通报·英文版

The pain-relieving effect of acupuncture is known to involve primary afferent nerves (PANs) via their roles in signal transmission to the CNS. Using single-unit recording in rats, we characterized the generation and transmission of electrical signals in Aβ and Aδ fibers induced by acupuncture-like stimuli. Acupuncture-like signals were elicited in PANs using three techniques: manual acupuncture (MAc), emulated acupuncture (EAc), and electro-acupuncture (EA)-like peripheral electrical stimulation (PES). The discharges evoked by MAc and EAc were mostly in a burst pattern with average intra-burst and inter-burst firing rates of 90 Hz and 2 Hz, respectively. The frequency of discharges in PANs was correlated with the frequency of PES. The highest discharge frequency was 246 Hz in Aβ fibers and 180 Hz in Aδ fibers. Therefore, EA in a dense-disperse mode (at alternating frequency between 2 Hz and 15 Hz or between 2 Hz and 100 Hz) best mimics MAc. Frequencies of EA output >250 Hz appear to be obsolete for pain relief.

Differential Expression of Ca²⁺-buffering Protein Calretinin in Cochlear Afferent Fibers: A Possible Link to Vulnerability to Traumatic Noise

The synaptic contacts of cochlear afferent fibers (CAFs) with inner hair cells (IHCs) are spatially segregated according to their firing properties. CAFs also exhibit spatially segregated vulnerabilities to noise. The CAF fibers contacting the modiolar side of IHCs tend to be more vulnerable. Noise vulnerability is thought to be due to the absence of neuroprotective mechanisms in the modiolar side contacting CAFs. In this study, we investigated whether the expression of neuroprotective Ca²⁺-buffering proteins is spatially segregated in CAFs. The expression patterns of calretinin, parvalbumin, and calbindin were examined in rat CAFs using immunolabeling. Calretinin-rich fibers, which made up ~50% of the neurofilament (NF)-positive fibers, took the pillar side course and contacted all IHC sides. NF-positive and calretinin-poor fibers took the modiolar side pathway and contacted the modiolar side of IHCs. Both fiber categories juxtaposed the C-terminal binding protein 2 (CtBP2) puncta and were contacted by synaptophysin puncta. These results indicated that the calretinin-poor fibers, like the calretinin-rich ones, were afferent fibers and probably formed functional efferent synapses. However, the other Ca²⁺-buffering proteins did not exhibit CAF subgroup specificity. Most CAFs near IHCs were parvalbumin-positive. Only the pillar-side half of parvalbumin-positive fibers coexpressed calretinin. Calbindin was not detected in any nerve fibers near IHCs. Taken together, of the Ca²⁺-buffering proteins examined, only calretinin exhibited spatial segregation at IHC-CAF synapses. The absence of calretinin in modiolar-side CAFs might be related to the noise vulnerability of the fibers.

Distributions of purinergic P2X_3 receptor immunoreactive afferent fibers in the rat pharyngeal mucosa / 解剖学报

Objective To study the distribution of purinergic P2X_3 receptor immunoreactive afferent fibers in the rat pharyngeal mucosa and provide morphological evidence for exploring the role of ATP in the signal transduction of sensory stimuli. Methods Twelve adult Wistar rats were used and immunofluorescenthistochemical double-labeling technique combined laser confocal scanning microscope was applied in the present study. Results 1.P2X_3 immunoreactive fibers were observed on sections from all parts of pharyngeal mucosa. Two types of positive fibers were found. One was free nerve fibers covered with many varicosities. Another one ramified in mucosa and showed complex arborization endings. Nerve plexus in mucosa were formed by P2X_3 immunoreactive fiber ramifications. 2.Most calcitonin gene-related peptide (CGRP) positive fibers intermingled with P2X_3 immunoreactive fiber arborizations. A few P2X_3 immunoreactive fibers were covered with many varicosities co-localized with CGRP. 3.In petrosal ganglion, most neurons were stained with P2X_3 or CGRP immunoreactivity and small number of P2X_3 immunoreactive neurons co-stained with CGRP. Conclusion These results indicated that the different types of afferent fibers in rat pharyngeal mucosa expressed purinergic P2X_3 receptor immunoreactivity and ATP might be related to nociceptive or physiological signals transduction in rat pharyngeal mucosa.

Mechanical Hyperalgesia Induced by Blocking Calcium-activated Potassium Channels on Capsaicin-sensitive Afferent Fiber

Small and large conductance Ca2+-activated K+ (SKCa and BKCa) channels are implicated in the modulation of neuronal excitability. We investigated how changes in peripheral KCa channel activity affect mechanical sensitivity as well as the afferent fiber type responsible for KCa channel-induced mechanical sensitivity. Blockade of SKCa and BKCa channels induced a sustained decrease of mechanical threshold which was significantly attenuated by topical application of capsaicin onto afferent fiber and intraplantar injection of 1-ethyl-2-benzimidazolinone. NS1619 selectively attenuated the decrease of mechanical threshold induced by charybdotoxin, but not by apamin. Spontaneous flinching and paw thickness were not significantly different after KCa channel blockade. These results suggest that mechanical sensitivity can be modulated by KCa channels on capsaicin-sensitive afferent fibers.

DEVELOPMENTAL ORGANIZATION OF PRIMARY AFFERENT FIBERS IN THE DORSAL HORN OF THE MOUSE LUMBAR SPINAL CORD / 神经解剖学杂志

The present study was designed to examine the morphological pattern of primary afferent projections into the spinal dorsal horn by labeling the lumbar dorsal root ganglia with carbocyanine fluorescent dye DiI in mouse embryos and neonatal pups aged embryonic day 12 to postnatal day 3 (E12-P3). Primary afferent fibers projected into dorsal funiculus at E13, but did not penetrated into gray matter of dorsal horn until E15. The afferent projections became dense and entered the spinal gray matter more deeply at E16 and E17. By E18 the intensity of primary afferent in the deep part of the dorsal horn increased and their branching patterns became more complicated. Some of these primary fibers were also observed to ramify extensively in the superficial laminae. The projection pattern of primary afferent remained unchanged after birth, but the intensity of afferent terminals increased in the superficial laminae. In addition, afferent fiber collaterals that projected into the contralateral dorsal horn were also observed. They were first examined at E16 and mainly originated from the medial and deep part of the dorsal horn. Around birth, the contralateral projections were also found to originate from the lateral part of dorsal horn. Our results indicate that laminar organization of primary afferents in the spinal dorsal horn is established during the late embryonic and early postnatal stages.This organization then undergoes further refinement to match the pattern seen in the adult.

Comparative Study on the Nociceptive Responses Induced by Whole Bee Venom and Melittin

The present study was undertaken to confirm whether melittin, a major constituent of whole bee venom (WBV), had the ability to produce the same nociceptive responses as those induced by WBV. In the behavioral experiment, changes in mechanical threshold, flinching behaviors and paw thickness (edema) were measured after intraplantar (i.pl.) injection of WBV (0.1 mg & 0.3 mg/paw) and melittin (0.05 mg & 0.15 mg/paw), and intrathecal (i.t.) injection of melittin (6microgram). Also studied were the effects of i.p. (2 mg & 4 mg/kg), i.t. (0.2microgram & 0.4microgram) or i.pl. (0.3 mg) administration of morphine on melittin- induced pain responses. I.pl. injection of melittin at half the dosage of WBV strongly reduced mechanical threshold, and increased flinchings and paw thickness to a similar extent as those induced by WBV. Melittin- and WBV-induced flinchings and changes in mechanical threshold were dose- dependent and had a rapid onset. Paw thickness increased maximally about 1 hr after melittin and WBV treatment. Time-courses of nociceptive responses induced by melittin and WBV were very similar. Melittin-induced decreases in mechanical threshold and flinchings were suppressed by i.p., i.t. or i.pl. injection of morphine. I.t. administration of melittin (6microgram) reduced mechanical threshold of peripheral receptive field and induced flinching behaviors, but did not cause any increase in paw thickness. In the electrophysiological study, i.pl. injection of melittin increased discharge rates of dorsal horn neurons only with C fiber inputs from the peripheral receptive field, which were almost completely blocked by topical application of lidocaine to the sciatic nerve. These findings suggest that pain behaviors induced by WBV are mediated by melittin-induced activation of C afferent fiber, that the melittin- induced pain model is a very useful model for the study of pain, and that melittin-induced nociceptive responses are sensitive to the widely used analgesics, morphine.

EFFECTS OF MORPHINE ON THE TERMINAL OF AFFERENT FIBER OF INJURED SCIATIC NERVE IN SPINAL LAMINA Ⅱ OF RAT——A HISTOCHEMICAL STUDY OF THE FLUORIDE-RESISTANT ACID PHOSPHATASE (FRAP) / 解剖学报

Objective To explore the effects of morphine on the terminal of primary afferent fiber distributing in spinal lamina Ⅱ after the sciatic nerve crush. Methods The positive reactive areas of fluoride-resistant acid phosphatase(FRAP) at spinal lamina Ⅱ were measured by the FRAP histochemistry and microcomputer image analysis techniques, after sciatic nerve was injured 15 days and 30 days both in morphine and control groups of rats. Results The positive reactive areas of FRAP at spinal lamina Ⅱ were depleted on different degree in two groups of rat after sciatic nerve was injured. The positive reactive areas of FRAP were greater 40% on injured sciatic nerve in 30 days than in 15 days in control group. In morphine group, the positive reactive areas of FRAP were larger 22% on injured sciatic nerve in 30 days than in 15 days; simulaneously also were bigger 19% than on injured sciatic nerve 30 days of control group.Conclusion The positive reactive areas of FRAP at spinal lamina Ⅱ show recovering enlargement as the surviving time lengthens in both groups of rats injured sciatic nerve.Morphine may enhance the positive reactive area of FRAP at spinal lamina Ⅱ in rat of sciatic nerve crush.

Gender differences between visceral and baroreceptor afferent neurons of rats / 中国药理学通报

Aim To investigate the gender differences in electrophysiology and neuroanatomy of myelinated and unmyelinated visceral and baroreceptor afferent neurons(VANs and ABNs) of adult rats.Methods VANs and ABNs were isolated enzymatically and Vagus-nodose slice preparation was also applied in this study.For identification of ABNs,aortic depressor nerve(ADN) was labeled using fluorescent dye.Whole-cell patch technique was used to record action potential(AP).Electronic microscopy was selected for morphological analysis of ADN.Results(1) A-and C-type VANs were identified and significant differences of AP discharge profiles between female and male were not established;(2) except for the traditionally classified A-and C-types,myelinated Ah-type VGNs were also identified with faster conduction velocity,lower firing threshold,and higher neuronal excitability.Importantly,these Ah-types were found in female rats with a similar frequency like A-types but rarely seen in males.(3) Ah-type ABNs were also identified by fluorescence.(4) Morphological data showed that myelinated fiber in ADN was ~25% of total and this result was consistent with our electrophysiological data.(5) Firing frequency of Ah-types(20~40 Hz) was lowered than that of A-types(40~150 Hz,P

Changes in Impulse Discharge of Muscular Afferent Fiber Activated by Lactic Acid / 대한정형외과학회잡지

In anesthetized cats the effects of lactate-activated muscle spindle upon the group Ia muscular afferent fibers were studied. Laminectomy was done from L5 to Sl spinal cord level. Extracellular recording was done at dorsal root to record the impulse discharge from group Ia muscular afferent fibers. 1) Muscle spindle of Gastrocnemius-Soleus muscle were activated by lactate injection and exhibited increased impulse discharge through group Ia muscular afferent fibers. 2) There was latency of 7-12 seconds before muscle spindle is activated by lactate injection. But the whole response was not dose related. 3) The response pattern after lactate injection was divided into three groups which were excitation, inhibition and inhibition with preceding excitation. 4) Some responses were similar to those of bradykinin, sympathetic stimulation (adrenaline injection) and succinylcholine injection. 5) It was suggested that muscle spindle has characteristics of polymodal receptor which has responses to not only mechanical stimulation but also chemical stimulation.