Spontaneous activity and responses to nonnoxious and noxious stimuli then were recorded 5 min after the administration of lidocaine. Lidocaine was dissolved in 0. The air puff stimuli and pinch stimuli were applied at least three times before and after the incision and after administration of lidocaine.
Spontaneous firing rates were determined by averaging the activity over 5-min periods when there was no contact with the RF. Some of the variables are expressed as percentages of control values preincision values. P values of less than 0. An animal preparation could be maintained in a stable condition for more than 10 h, comparable with the previous experimental state.
Although stable recording was obtained from a single neuron for up to 3 h, 11 neurons were lost during incision and wound closure, and 10 neurons were lost within 30 min after the incision had been made.
As a result, stable recordings could be maintained in 18 neurons over a period of 30 min after the incision. Data obtained from these 18 neurons thus was analyzed in the current study. All neurons studied had membrane potentials more negative than —55 mV. The number of neurons, depths of cell location, membrane potentials, and input membrane resistances are shown in table 1. RFs of all neurons examined in the current study were located on the shaved skin of the hairy hindquarter lumbar and gluteal regions of the rat.
In the voltage clump mode holding voltage, —70 mV , the mean amplitude and frequency of spontaneous EPSCs were A barrage of APs was observed in all multireceptive neurons and nociceptive neurons during the incision and clipping of the skin fig.
Mean rates of APs during the incision and wound closure were 2. The incision and wound closure elicited EPSPs with a barrage of APs, but occurrence of APs disappeared immediately after the wound closure had been completed, and spontaneous APs were not seen subsequently.
B An example of multireceptive neurons in response to air-puff stimuli and pinch stimuli before Pre and after the incision had been made Incision. C An example of nociceptive neurons in response to air-puff stimuli and pinch stimuli before Pre and after the incision had been made Incision.
D Mean rates of APs in response to air-puff stimuli and pinch stimuli in multireceptive neurons upper panels and in nociceptive neurons lower panels before Pre and after the incision had been made Incision. Responses of multireceptive neurons to nonnoxious and noxious stimuli and those of nociceptive neurons to noxious stimuli greatly increased after the incision had been made fig.
In the subthreshold neurons, nonnoxious and noxious stimuli did not evoke APs before or after the incision had been made fig. B An example of subthreshold neurons in response to air-puff stimuli and pinch stimuli before Pre and after the incision had been made Incision.
C Firing rates of APs evoked by nonnoxious and noxious stimuli before and after the incision had been made. Administration of lidocaine abolished sustained spontaneous AP firing fig. A An example of the effect of systemic administration of lidocaine on spontaneously occurring action potentials APs.
In two of eight multireceptive neurons and in one of five nociceptive neurons, spontaneous APs were seen after incision and wound closure with staples S. Spontaneous pain seems to be present in an incision model, but the magnitude of spontaneous pain is not as great as that of other types of persistent pain models. The relatively low incidence of neurons with spontaneous AP firing after the incision may reflect the relatively small magnitude of spontaneous pain-related behavior in the incision model.
Incision injury may not reduce activity of the interneurons, and high-threshold neurons do not respond to nonnoxious stimuli after incision. The results suggest that nociceptive SG neurons, but not high-threshold neurons located in deep laminae, 6 may be responsible for behavioral allodynia seen in the incision model. If so, it is likely that these subthreshold SG neurons are functional when the descending inhibition is disrupted, 31 and surgical incision may not affect the inhibitory influence on SG neurons.
Although mechanisms of enhanced sensitivity to pain allodynia and hyperalgesia in postoperative pain are thought to differ from those in other types of tissue injury-induced pain, 2,11—13 systemic administration of lidocaine has been shown to relieve postoperative pain in a clinical setting.
It is thus likely that spontaneous AP firing in SG neurons originates from the injured site and that systemic administration of lidocaine exerts its reversing effect on increased responsiveness of SG neurons after incision. Previous studies demonstrated little effect of systemically administered lidocaine on normal pain thresholds but demonstrated profound effects on acute painful conditions after tissue injury induced by application of chemical irritants.
Only data obtained in the current clamp mode were analyzed in the present study. Neuronal excitability results from balance between excitatory synapse transmission and inhibitory synapse transmission. If the inhibitory inputs to SG neurons are lost, as was described in previous reports after nerve injury, 20 SG neurons will be excited in response to nonnoxious stimuli, possibly resulting in allodynia.
Thus, the in vivo patch-clamp technique is a good tool to investigate changes in balance between excitatory and inhibitory synapse transmission in SG neurons in a postoperative pain state.
Further study using in vivo patch-clamp recording thus is required to obtain insights into the mechanisms of postoperative pain, focusing on analysis of changes in EPSCs and IPSCs of SG neurons after incision injury.
The authors thank Shigekazu Sugino, M. Department of Anatomy, Sapporo Medical University School of Medicine, Sapporo, Japan , for their help in data analysis and identifying SG neurons using intracellular injection of biocytin. Sign In or Create an Account. Advanced Search. Sign In. Skip Nav Destination Article Navigation. Close mobile search navigation Article navigation. Volume , Issue 3.
Previous Article Next Article. Materials and Methods. Article Navigation. Laboratory Investigations March This Site. Google Scholar. Hidemasa Furue, Ph. Yuji Kozuka, M. Therefore we analysed the spike initiation time and its variation to rule out the possibility of involvement of the intercalated neuron. For these experiments, 9 connections were chosen with suprathreshold EPSPs and rapid spike initiation. The postsynaptic neurons had high R IN 2.
In the connection shown in Fig. In CC, the fluctuations in the quantal transmitter release caused variation of the spike initiation time. The histogram showed a broad distribution of the initiation times from 1. This histogram was binned at 1 ms which is usually considered as the largest latency variation allowed for the monosynaptic connection. The mean initiation time in all 9 connections was 8. Therefore, an existence of multiple synapses between the neurons is likely explanation for the composite EPSC.
We also tested whether composite EPSCs could be modelled by simultaneously activating synapses with different somatodendritic locations. In the simulation shown in Fig. These simulations confirmed that the composite EPSCs could be evoked by the activation of multiple synapses of one presynaptic neuron distributed along the somatodendritic domain of the postsynaptic neuron.
Points 1—6 and the g M values were: dendrite 0. A simple EPSC was simulated by activating the somatic synapse only trace, soma. B, simulation with two dendritic synapses, proximal dendrite 0.
Simultaneous activation of these synapses gave a composite EPSC seen at the soma. Finally, in two connections with composite EPSCs we have succeeded to obtain a detailed filling with biocytin of both the axon terminals of the presynaptic SG EIN and the dendritic arbores of the postsynaptic neuron. The presynaptic cell axon formed a dense network in the vicinity of the postsynaptic cell body Fig.
At higher magnification Fig. In the other labelled connection, three putative synaptic contacts have also been revealed. Although it was not possible to estimate the electrotonic distance between the synapses and their total number, or to attribute the groups of synapses to the components of a composite EPSC, the labelling experiments suggested that multiple synaptic contacts between an SG EIN and a postsynaptic neuron can form the anatomical basis for the composite EPSCs.
The postsynaptic neuron was filled with biocytin in whole-cell mode, while the presynaptic one through the cell-attached pipette [28]. B, both cell bodies were in the SG. The axon of the postsynaptic neuron red ran along the dorsal surface of the grey matter, gave a collateral in the lateral column, and turned medially to re-enter the grey matter.
The presynaptic cell axon black formed a dense network in the vicinity of the cell bodies and divided into two major branches which travelled to deeper laminae and turned towards the dorsal grey commissure. Soma and dendrites of the presynaptic neuron are shown in green. C, a number of close appositions between the varicosities of the presynaptic axon and the dendrites and soma of the postsynaptic neuron were detected in regions 1—3 blue arrows. Some of them are shown arrowheads on the photomicrograph of the region 1.
Objective; x oil-immersion , numerical aperture 1. Thus, paired recordings, computer simulation and biocytin labelling indicated that the majority of the monosynaptic EPSCs are likely to be generated by transmitter release in multiple synapses formed by the axon of an SG EIN on a postsynaptic neuron. In some connections, however, it was possible to analyse individual components of the composite EPSC and estimate the release probability of the corresponding synapses.
We analysed 10 such synapses in 5 connections. The release probability in these synapses was 0. If two such synapses were single and independent, the expected failure rate for their composite response no synapse activated would be 1—0. Indeed, the mean failure rate for the bi-component response in these connections was 0. These values suggested that the two synapses were individual and operated independently. In 10 of 36 connections with induced LTP Fig.
One of these connections first showed EPSCs with only one component corresponding to activation of more distal synapse 2 Fig. After the application of induction protocol, a new component corresponding to activation of more proximal synapse 1 appeared Fig.
These components could be seen both individually and overlapping as a composite EPSC. We plotted the amplitudes of the components corresponding to synapse 1 and synapse 2 Fig.
In the episodes with overlapping responses, the EPSC amplitude for synapse 1 was measured from the baseline to the inflection point, and for synapse 2 from the inflexion point to the peak. As one can judge from the plot, the LTP was caused by the activation of previously silent proximal synapse 1, while the distal synapse 2 did not show substantial alteration of activity.
A, LTP associated with an activation of a previously silent synapse. A1, EPSC elicited before the application of the induction protocol corresponded to activation of more distal synapse 2. A new component corresponded to activation of more proximal synapse 1.
Two plots show the amplitudes of the EPSC components corresponding to synapse 1 and synapse 2 during the experiment. The amplitudes were measured from non-averaged traces. Two plots show the EPSC components corresponding to synapse 1 and synapse 2. In the remaining 7 connections, the induced LTP was associated with an increase in the amplitude of components forming the composite EPSC.
Thus, transmission efficacy can be increased through activation of silent synapses and potentiation of already active synapses. In this study we have described several novel properties of the neuronal network in the spinal SG.
In particular, we have characterized excitatory synapses formed by glutamatergic SG interneurons on postsynaptic neurons located in laminae I-III. Implementation of independent electrodes for stimulation of and recording from one neuron allowed study of the spike initiation process.
Spikes in SG neurons consisted of two components similar to those described in motoneurons [37] — [39]. The fast one was an electrotonic projection of the spike generated in the AIS while the slow one corresponded to the antidromic spike invasion to the axon hillock and soma [42] , [43]. Similar thresholds were also obtained for synaptically evoked spikes in paired recordings. The true number of EINs forming multiple synapses may be even higher. The filter frequency 3 kHz used in our experiments did not allow to see transitions faster than 0.
Furthermore, there are silent synapses between the neurons which may become active under certain conditions. Therefore, formation of multiple synapses on a postsynaptic neuron appears to be a general property of an SG EIN. The time intervals between the components of composite EPSCs could be explained by the electrotonic distances between the synapses in a postsynaptic neuron.
In some cases, however, components with longer latency did not have apparently slower rise predicted from our simulations see Figs. Therefore, it is possible that some presynaptic factors, like different axonal conduction time for each synaptic terminal, could also contribute to different latencies of the EPSC components. For example, different spike propagation delays at the branching points of the presynaptic axon could contribute to the intervals between the EPSC components.
AMPARs are known as main transducers of fast central glutamatergic synapses [53]. The distributions of the rise times and the decay time constants were in the range predicted by the model for the fast synapses located at different electrotonic distances from the soma. Allowing 0. This time might further increase due to the spike propagation delays at the axon branching points.
However, the long latencies observed in our study were likely to be caused by the EPSC propagation in the dendrites of postsynaptic neuron. Thus, the variations in the EPSC kinetics and latencies reflected a broad somatodendritic distribution of synapses in the postsynaptic neuron. It is believed that excitatory connections between dorsal horn neurons are weak, and EPSPs of 0. However, these conclusions were based on low-R IN recording from a postsynaptic neuron, which reduced the amplitude of depolarization induced by activation of a given synaptic conductance see Fig.
Furthermore, dialysis of the presynaptic neuron could affect its capacity of transmitter release in multiple synapses. Thus, the true efficacy of excitatory transmission in those studies appeared to be underestimated. Our data show that transmission between dorsal horn neurons can be effective. First, a non-dialysed SG EIN releases transmitter in multiple synapses, thus, increasing effective conductance depolarizing the postsynaptic membrane.
Second, a high R IN preserved in postsynaptic neuron allows better conversion of the synaptic conductance into membrane depolarization. R IN in dorsal horn neurons was shown to change with temperature [54].
LTP could be induced through activation of silent synapses and through potentiation of already active synapses. One cannot exclude, however, that potentiation of the components of a composite EPSC was also caused by recruitment of silent synapses with similar electrotonic location, so that their activation did not result in generation of an apparently new component.
It is possible that the activation of silent synapses and the strengthening of already active synapses can cooperate in induction of LTP. Reports about the balance between the excitatory and inhibitory connections in the spinal dorsal horn are contradictory. Studies using in situ hybridization [8] , immunocytochemistry [9] and the high-R IN paired recordings in VC [4] and this study showed that the majority of SG neurons are excitatory, whereas inhibitory neurons form a minority.
In contrast, the low-R IN CC recordings revealed more numerous inhibitory connections, and the authors suggested that the difference in the results was caused by a better detection of weak distal inhibitory inputs in CC [49] , [50]. However, our measurements of the membrane noise have shown that the high-R IN VC has higher signal-to-noise ratio. The last factor which has not been considered so far is the driving force for the inhibitory inputs.
Thus, analyses of all factors showed that our VC recording has higher detection power. The true reason for lower frequency of excitatory connections in [2] , [3] , [49] can be a shunt of distal inputs by low-R IN recording.
Indeed, the longest latencies of IPSPs 3. A recent study using the laser scanning photostimulation technique revealed that the inhibitory receptors are confined to the narrow peri-somatic region of an SG neuron while the glutamate receptors are more widespread [5].
Therefore, shunt of weak distal inputs [2] , [3] , [49] , which are mostly excitatory [5] , led to an underestimation of the number of excitatory connections. The driving force for inhibitory inputs in [50] is unclear. Furthermore, identification of monosynaptic IPSPs demands analysis of latency variations for individual traces. Therefore, many IPSPs in [50] smallest 0.
Thus, uncontrolled voltages and consideration of IPSPs with amplitudes below the resolution limit allowing tests for monosynaptic connectivity question conclusions about the high percentage of inhibitory connections [50]. Its axon forms multiple synapses on the soma and dendrites of a postsynaptic neuron. The excitatory transmission is frequently effective and an SG EIN can elicit spike in a postsynaptic neuron.
The excitatory synapses are dynamic and can change their functional state through diverse forms of plasticity. These properties of the SG EINs are important for understanding the mechanisms of the spinal nociceptive processing. Browse Subject Areas? Click through the PLOS taxonomy to find articles in your field. Abstract Background Substantia gelatinosa SG, lamina II is a spinal cord region where most unmyelinated primary afferents terminate and the central nociceptive processing begins.
Methodology To describe the functional organization and properties of excitatory synapses formed by SG EINs, we did non-invasive recordings from pairs of monosynaptically connected neurons. Introduction The spinal SG is an important part of the nociceptive processing system. Biocytin Labelling In the labelling experiments, a postsynaptic neuron was filled by biocytin in the whole-cell mode using pipette containing in mM : KCl 3, K-gluconate Download: PPT.
Spike Initiation in an SG Neuron The estimation of firing threshold in a neuron is needed for evaluation of efficacy of synaptic transmission.
Detection of Distal Dendritic Inputs at the Soma VC is widely used as a principal mode for recording spontaneous and evoked synaptic activity in the superficial dorsal horn [4] , [14] , [45] — [48].
Figure 9. Effect of R IN on the resolution of distal inputs. Efficacy of Synaptic Transmission Transmission efficacy was studied in 22 connections. Short-Term Plasticity Short-term plasticity sub-second range was induced in 7 connections using a standard paired-pulse protocol Fig.
Figure Composite EPSCs evoked by transmitter release in multiple synapses. Discussion In this study we have described several novel properties of the neuronal network in the spinal SG. Rapid Spike Initiation in SG Neurons Implementation of independent electrodes for stimulation of and recording from one neuron allowed study of the spike initiation process. Functional Balance between the Excitatory and Inhibitory Inputs Reports about the balance between the excitatory and inhibitory connections in the spinal dorsal horn are contradictory.
References 1. Basbaum A, Jessel T The perception of pain. Principles of neural science. New York: Mc Graw Hill. J Neurosci — View Article Google Scholar 3. Lu Y, Perl ER A specific inhibitory pathway between substantia gelatinosa neurons receiving direct C-fiber input.
View Article Google Scholar 4. J Physiol — View Article Google Scholar 5. View Article Google Scholar 6. J Neurophysiol — It occurs in a subject with previous injuries such as amputation in which the dorsal roots are literally absent from the cord. Even though no sensory signals can enter the cord, the subject often feels extreme pain in the denervated parts of the body. For example, an amputee will often apparently feel pain in a part of his body that has been removed.
The phenomenon of phantom limb pain is a common experience after a limb has been amputated or its sensory roots have been destroyed in which the pain is felt in a part of the body that no longer exists. A complete break of the spinal cord also often leads to a phantom body pain below the level of the break.
The source of phantom pain is complex and not well understood. It has been suggested that there may be abnormal discharges 1 from the remaining cut ends of nerves which grow into nodules called neuromas , 2 from overactive spinal neurons, 3 from abnormal flow of signals through the somatosensory cortex, or 4 from burst-firing neurons in the thalamus.
Acute pain arises from activation of nociceptors for a limited time and is not associated with significant tissue damage e. Chronic pain is prolonged pain lasting for months or longer that arises from tissue injury, inflammation, nerve damage, tumor growth, lesion or occlusion of blood vessels.
Chronic pain, such as lower back pain, rheumatoid and osteoarthritis, and headache see "Headaches" below may result from constant inflammatory activity which activates G proteins. In some cases, the pain persists long after the injury heals, but there is no treatment that will eliminate the pain.
One possible explanation for chronic pain is a phenomenon called sensitization. Following continuation and prolong noxious stimulation, nearby silent nociceptive neurons that previously were unresponsive to stimulation, now become responsive.
In addition, some of the chemicals produced and released at the injured site also alter the physiological properties of nociceptors. The nociceptors begin to initiate pain signals spontaneously, which cause chronic pain.
In addition, weak stimuli, such as a light touch that previously had no effect on these nociceptors, will further activate the nociceptors which result in severe pain signals.
The persistent barrage of nerve impulses results in long-term changes in nerve cell activity at the level of the spinal cord and higher centers in the brain. It appears that peripheral and central sensitization persists after the injury apparently has healed. The sensitization of nociceptive neurons after injury results from the release of different chemicals from the damaged area. It is known that substance P and calcitonin gene-related peptides are released from peripheral nerve ending which stimulate most cells to release algesic substances which further potentiates the pain from the injury.
In contrast, central sensitization resulting from severe and persistent injury which cause prolonged release of glutamate on nociceptive dorsal horn cells, this constant glutamate release via G protein dependant phosphorylation cascades results in opening of postsynaptic ion channels gated by the NMDA receptors. This phenomenon is also termed "wind up.
Fibromyalgia is characterized by widespread chronic pain throughout the body, including fatigue, anxiety and depression.
It is now believed that it has a genetic component which tends to run in families. A headache is a poorly understood type of pain that can be either acute or chronic. There are about different types and causes of headaches. The following are some categories of disorders associated with headaches:. Because of the importance of warning signals of dangerous circumstances, several nociception pathways are involved to transmitting these signals and some of them are redundant.
The neospinothalamic tract conducts fast pain via A delta fibers and provides information of the exact location of the noxious stimulus, and the multisynaptic paleospinothalamic and archispinothalamic tracts conduct slow pain via C fibers , a pain which is poorly localized in nature.
Pain activates many brain areas, which link sensation, perception, emotion, memory and motor reaction. Therefore, many pain clinics target their treatments to block the perception of pain using psychosomatic means of treatments such as biofeedback, hypnosis, physical therapy, electrical stimulation, and acupuncture-multimodal treatment. John Thomas experiences visceral pain around the upper left lung.
The neospinothalamic tract carries nociceptive information from the skin only via A delta fibers, while visceral pain is carried via C fibers. A surgeon attempting to treat chronic pain from the pelvic region will suggest to make a lesion in the:. Tactile and pain sensation are lost contralaterally at different levels below the lesion.
Thermal sensation is lost in the ipsilateral side above the lesion. Kinesthetic and tectile senses are lost ipsilaterally below the lesion. Thermal and pain sensation are lost contralaterally below the lesion while kinesthetic and tactile senses remain on the ipsilateral side.
The withdrawal reflex is lost. Atrophy is developed in the muscles below the lesion. Select the best answer: Pain impulses arising within the abdominal and thoracic cavities may reach the CNS by:.
At the level of the ventral trigeminothalamic tract, pain fibers are generally crossed or uncrossed? At the ventral trigeminothalamic tract, the fibers are already crossed and ascend to the thalamus.
From the above nerve fibers, only the lateral spinothalamic tract carries pain sensation, and sections of these fibers will prevent pain information from getting to the brain.
Sensitivity and reactivity to noxious stimuli are essential to the well-being and survival of an organism. Neospinothalamic Tract The neospinothalamic tract has few synapses and constitutes the classical lateral spinothalamic tract LST Figure 7.
Content on this page requires a newer version of Adobe Flash Player. A surgeon attempting to treat chronic pain from the pelvic region will suggest to make a lesion in the: A.
Anterior lateral corodotomy interrupt the spinothalamic tract carrying the pain sensation. In Brown-Sequard syndrome: A.
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