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Biomedical subjects

Kjell Hole

Publications and source records attributed to Kjell Hole.

At least 19 recordsLinked to original sources
PubMed2005

[Molecular mechanisms in acute and chronic pain states].

BACKGROUND: Pain is a sense necessary for survival and has a complex neurobiological basis. In recent years a powerful battery of techniques has been developed to unravel the mechanisms by which painful stimuli are transduced and processed both in the acute and pathological state. MATERIAL AND ANALYSIS: We review the literature with special emphasis on recent discoveries regarding the molecular transduction mechanisms in nociceptors and novel molecular and cellular mechanisms underlying the spinal processing of painful stimuli. RESULTS AND INTERPRETATION: The mechanisms by which sensory neurons initiate hyperalgesia and touch-evoked pain (allodynia) have been addressed particularly successfully in recent studies. The rich variety of key molecular players that have emerged in physiological and pathophysiological pain states reflects the sophistication and uniqueness of this important sense. This is good news for both the pain scientist and the pain clinician since it increases the intellectual challenge and provides a plethora of targets for novel analgesics and treatments.

Acute Disease↗
PubMed2005

Long-term potentiation in spinal nociceptive systems--how acute pain may become chronic.

Chronic pain is a major problem since it is difficult to treat and the understanding of the underlying neurobiology is sparse. The mechanisms underpinning the transition of acute into chronic pain remain unclear. However, long-term potentiation (LTP) in spinal nociceptive systems may be one such mechanism. Here, we briefly review the literature regarding LTP in spinal nociceptive systems including our own data on LTP in deep convergent nociceptive neurons. Furthermore, we discuss the role of this phenomenon in understanding the neurobiology of chronic pain and the possible therapeutic implications.

Acute Disease↗
PubMed2003

Stimulation of spinal 5-HT(2A/2C) receptors potentiates the capsaicin-induced in vivo release of substance P-like immunoreactivity in the rat dorsal horn.

Stimulation of spinal serotonin (5-HT)(2A/2C) receptors has previously been reported to lead to either a pro-nociceptive or an anti-nociceptive response. Behavioral data have indicated that the pro-nociceptive effect is related to the release of substance P (SP). The aim of this in vivo microdialysis study was to investigate if stimulation of spinal 5-HT(2A/2C) receptors by the selective agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine (DOI) induces spontaneous or capsaicin-evoked increase in the release of SP-like immunoreactivity (SP-LI) in the rat dorsal horn. A dose of capsaicin (25 microM in the perfusion medium administered for 30 min), which did not lead to a significant release of SP-LI on its own, induced a significant increase of greater than 4-fold of the SP-LI level following spinal application of 50 nmol DOI. Higher (500 nmol) or lower (5 nmol) doses of DOI failed to induce a similar effect. In rats with a peripheral inflammation, induced by carrageenan, capsaicin (25 microM) induced a non-significant increase of SP-LI. A significant 8-fold increase of the SP-LI level was detected following administration of 50 nmol DOI in combination with capsaicin. The effect of DOI, which was completely prevented by co-administration of the 5-HT(2A) receptor antagonist ketanserin in control animals without peripheral inflammation, was only partly blocked in animals with carrageenan induced peripheral inflammation. In conclusion, stimulation of 5-HT(2A/2C) receptors facilitates the capsaicin-evoked release of SP-LI in the dorsal horn in both animals with and without carrageenan-induced unilateral inflammation. The observation that the highest dose of DOI failed to induce SP-LI release may be due to an inhibitory postsynaptic action at this dose.

Animals↗
PubMed2003

Spinal cord stimulation inhibits long-term potentiation of spinal wide dynamic range neurons.

It has been suggested that long-term potentiation (LTP) of dorsal horn neurons is a phenomenon that contributes to the development of chronic neuropathic pain. Spinal cord stimulation (SCS) may be an effective tool in alleviating such pain. The aim of this electrophysiological study in rats was to examine if SCS suppresses LTP of dorsal horn wide dynamic range (WDR) neurons. Increased knowledge of the mechanisms behind the effects of SCS may facilitate its further advancement and improve clinical efficacy. As previously shown, intensive, high-frequency electrical stimulation of the sciatic nerve in the rat induces an increased firing response of WDR neurons. Here we report that SCS gradually reduced this increased C-fiber response back to the baseline level. However, A-fiber responses were neither potentiated by the conditioning stimulus used nor were they affected by SCS. These data suggest that SCS affects the C-fiber component of dorsal horn central sensitization which is noteworthy since SCS, based on previous studies, is believed to primarily influence A-fiber functions.

Animals↗
PubMed2002

Spinal substance P release in vivo during the induction of long-term potentiation in dorsal horn neurons.

Long-term potentiation (LTP) in wide dynamic range (WDR) neurons in the dorsal horn has been suggested to contribute to central sensitization and the development of chronic pain. Indirect experimental evidence indicates an involvement of substance P (SP), in this respect. The aim of the present study was to monitor the extracellular level of substance P-like immunoreactivity (SP-LI) in the dorsal horn of the rat during and after induction of LTP in WDR neurons in vivo. Electrophysiological recordings of single (WDR) neurons were performed in parallel with microdialysis in the dorsal horn under urethane-anaesthesia. The amount of SP-LI in the microdialysate was determined by radioimmunoassay. As previously shown, high frequency conditioning stimulation of the sciatic nerve induced an increased firing response of WDR neurons. An increased response to C-fibre stimulation, but not A-fibre stimulation, could be determined. A significant increase of the extracellular level of SP-LI in the dorsal horn was detected during, but not after, induction of LTP. These data suggest that SP may be involved in the induction of LTP by high frequency stimulation. However, the maintenance of spinal LTP following high frequency peripheral nerve stimulation does not seem to depend on an increased release of SP.

Animals↗
PubMed2002

Cellular memory in spinal nociceptive circuitry.

Besides transmitting and processing, neurons may also store information for prolonged periods of time (e.g. by use-dependent change in synaptic strength). In 1966 long-term potentiation (LTP) of synaptic transmission was discovered in the hippocampus, an area implicated in learning and memory. Recent studies show that similar mechanisms apply to pain pathways, at least in the spinal cord, and may account for some forms of clinical problems like hyperalgesia, allodynia, and deafferentation pain states, such as phantom pain. In this review, we briefly summarize key aspects of synaptic plasticity known from the brain and in the spinal cord. Then we describe and discuss related changes in spinal nociceptive neurons based on results from our own laboratory.

Humans↗
PubMed2001

Induction of long-term potentiation of single wide dynamic range neurones in the dorsal horn is inhibited by descending pathways.

Previous studies have shown that long-term potentiation (LTP) in the dorsal horn may be induced by noxious stimuli. In this study it is investigated whether induction of LTP in the dorsal horn may be affected by the descending pathways. Extracellular recordings of wide dynamic range (WDR) neurones in the lumbar dorsal horn in intact urethane-anaesthetized Sprague--Dawley rats were performed, and the electrically evoked neuronal responses in these neurones were defined as A-fibre and C-fibre responses according to latencies. Using a short-term cold block of the thoracic spinal cord, which produced a completely reversible increase of the A-fibre and C-fibre responses, the influence of the descending inhibitory system on the induction of LTP by electrical high-frequency conditioning applied to the sciatic nerve was examined. As previously shown the A-fibre responses were almost unchanged following the conditioning. In contrast, the C-fibre responses following the same conditioning were strongly increased. Thus, a clear LTP of the nociceptive transmission in the dorsal horn was observed following electrical high-frequency conditioning. Interestingly, we found that the LTP was more powerful when the effects of the descending pathways were temporarily eliminated during conditioning. It is concluded that induction of LTP by electrical high-frequency conditioning stimulation, which may be part of the wider term central sensitization, is inhibited by descending pathways.

Animals↗
PubMed2001

Increased spinal N-methyl-D-aspartate receptor function after 20 h of carrageenan-induced inflammation.

Spinal N-methyl-D-aspartate (NMDA) receptors are thought to be important in states of central hyperexcitability induced by e.g. inflammation or painful neuropathies. The carrageenan model of inflammatory pain has been and still is widely used as is the NMDA receptor antagonist 2-amino-5-phosphonopentanoic acid (AP5) to investigate NMDA receptor function. Here we present two novel findings using electrophysiological technique: the NMDA receptor function in the spinal cord is increased following 20 h of carrageenan-induced inflammation and further that only the D-isomer of AP5 is active in the spinal cord. Exogenous NMDA (0.5 and 5 nmol) applied onto the dorsal spinal cord produced a significantly greater facilitation and D-AP5 (1.25 micromol) a significantly greater inhibition of the C-fibre evoked response of the wide dynamic range (WDR) neurones studied in carrageenan (20 h after injection) compared to control rats. The present and two recent studies suggest central changes are different and possibly greater in the later (20 h) compared to the earlier (2-6 h) phase of carrageenan-induced inflammation. In conclusion, 20 h of carrageenan-induced inflammation increases the function of spinal NMDA receptor involved in nociceptive transmission and in addition the D-isomer of AP5 should be used when NMDA receptor antagonism is wanted in the spinal cord.

2-Amino-5-phosphonovalerate↗
PubMed1999

Natural noxious stimulation can induce long-term increase of spinal nociceptive responses.

It is conceivable that plasticity in pain control systems and chronic pain may be due to mechanisms similar to learning. Long-term potentiation (LTP) in the hippocampus is often studied as a model of learning and memory. It has recently been shown that long-term excitation may be induced in single wide dynamic range (WDR) neurones in the spinal dorsal horn of rats after tetanic stimulation to the sciatic nerve. The present study shows that similar long-term changes can also be induced by a severe natural stimulus. Single unit extracellular recordings were made in urethane anaesthetized rats and the firing responses of WDR neurones evoked by a single electrical stimulus to the peripheral nerve were recorded every 4 min. After repeated crushing of tissue (including bone) corresponding to the receptive field of the WDR neurones (the conditioning stimulus) followed by a proximal total peripheral nerve block, the C-fibre evoked responses were increased (P < 0.001) for a 3 h observation period compared with baseline responses and control animals. In control animals the nerve block was applied before the conditioning stimulus. We suggest that a long-term increase of the excitability of WDR neurones may be important for the development of long lasting and chronic pain disorders after an acute but severe noxious stimulus.

Analysis of Variance↗
PubMed1999

Dorsal horn NMDA receptor function is changed after peripheral inflammation.

The N-methyl-D-aspartic acid (NMDA) receptor antagonist D, L-2-amino-5-phosphonopentanoic acid (AP5) caused a stronger inhibition of wind-up in single wide dynamic range (WDR) neurons after carrageenan inflammation compared with control neurons without inflammation in the receptive field. This indicates that even a short period (2.5 h) of inflammation induces changes in the function of NMDA receptors. The drug effect was also studied in separate control experiments with few wind-up inducing stimulus trains and little nociceptive input prior to baseline recordings. In these control experiments all evoked responses were reduced by the drug, but the wind-up was significantly increased. A wind-up increase after NMDA receptor antagonism has been reported in two previous studies. Thus, other mechanisms than NMDA receptor stimulation may be more important for the wind-up in not sensitized dorsal horn neurons. As for long-term potentiation, it seems that NMDA receptor antagonists have an increased effect after sensitization. Thus, sensitized and not sensitized dorsal horn neurons may respond differently to an NMDA receptor active drug. In rats nerve stimulation and halothane anaesthesia induced larger evoked responses to afferent stimulation than cutaneous stimulation and urethane anaesthesia, the AP5 effect was however similar.

2-Amino-5-phosphonovalerate↗
PubMed1993

The tail-flick and formalin tests in rodents: changes in skin temperature as a confounding factor.

In the tail-flick test as well as in the late phase in the formalin test skin temperature may in an important way influence the response. A reduced skin temperature may be misinterpreted as analgesia, and an increased skin temperature as hyperalgesia. These effects and the mechanisms that cause them are discussed. It is of particular importance to be aware of these confounding factors when using drugs or making lesions that influence blood flow or temperature regulation. It is important that all variables influencing the test results are kept constant throughout the experiment. This includes not only the ambient temperature, but also factors that may influence the vasomotor tone of the animals.

Animals↗
PubMed1992

The formalin test: an evaluation of the method.

The formalin test for nociception, which is predominantly used with rats and mice, involves moderate, continuous pain generated by injured tissue. In this way it differs from most traditional tests of nociception which rely upon brief stimuli of threshold intensity. In this article we describe the main features of the formalin test, including the characteristics of the stimulus and how changes in nociceptive behaviour may be measured and interpreted. The response to formalin shows an early and a late phase. The early phase seems to be caused predominantly by C-fibre activation due to the peripheral stimulus, while the late phase appears to be dependent on the combination of an inflammatory reaction in the peripheral tissue and functional changes in the dorsal horn of the spinal cord. These functional changes seem to be initiated by the C-fibre barrage during the early phase. In mice, the behavioural response in the late phase depends on the ambient temperature. We argue that the peripheral tissue temperature as well as other factors influencing the peripheral inflammation may affect the response, possibly confounding the results obtained with the test. Furthermore, we discuss the methods of recording the response and the value of observing more than one aspect of behaviour. Scoring of several behavioural variables provides a means of assessing motor or sensorimotor function as possible causes for changes in behaviour. In conclusion, the formalin test is a valuable addition to the battery of methods available to study nociception.

Animals↗
PubMed1992

Intrathecal co-administration of substance P and NMDA augments nociceptive responses in the formalin test.

The effects of intrathecal administration of substance P and N-methyl-D-aspartate (NMDA) were studied in the formalin test in mice. Both substances were administered 5 min before injection of formalin into the hind paw. Co-administration of substance P and NMDA intensified the response in both the 1st (0-10 min) and the 2nd phase (20-30 min) of the formalin test, and increased the duration of the response. The increase in the response to formalin depended on the formalin concentration and was significant with 1% and 5% concentrations of formalin but not with a 0.05% concentration. No increase in the response was observed when NMDA or substance P was given alone. These findings indicate that concurrent activation of spinal NMDA and substance P receptors induces an enhancement of spinal transmission of nociception, and that this enhancement is dependent on the intensity or the quality of the peripheral stimulus.

Animals↗
PubMed1990

The role of descending noradrenergic systems in regulation of nociception: the effects of intrathecally administered alpha-adrenoceptor antagonists and clonidine.

It has been proposed that descending noradrenergic systems exercise a tonic inhibition of nociception at the spinal level. The recent finding that changes in tail skin temperature (TT) may have a strong effect on the tail-flick latency makes a reevaluation of this hypothesis necessary. The alpha-adrenoceptor agonist clonidine injected intrathecally (i.th.) in a dose of 60 micrograms increased the response temperature in the increasing hot plate test 10 min after injection, and prolonged the tail-flick latency 30-60 min after injection. A considerable part of the change in tail-flick latency was caused by a reduction in TT. The alpha 1-antagonist prazosin (30 and 60 micrograms) tended to increase the response temperature in the increasing hot plate test after 60 min, and to prolong the latency in the tail-flick test. These effects were not statistically significant. Clonidine and prazosin induced sensorimotor impairment and a reduction in body temperature after 30-60 min. The alpha 2-antagonist yohimbine had no effect in the increasing hot plate test, but reduced the tail-flick latency 10 min after drug administration. This reduction could be explained by an increase in TT. The results suggest that the reduced latency in the tail-flick test after i.th. injection of yohimbine is caused by an increase in the tail blood flow, and does not support the hypothesis of a tonic bulbospinal noradrenergic inhibition of nociception. The time course of response latencies suggests that supraspinal mechanisms may be involved in the effects of i.th. clonidine and prazosin in the tail-flick test, while there seems to be a spinally mediated antinociceptive effect of clonidine that can be demonstrated in the increasing hot plate test.

Animals↗
PubMed1990

The formalin test in mice: effect of formalin concentration.

The effect of different formalin concentrations on the nociceptive response in the formalin test was examined in mice. Subcutaneous formalin injection induces 2 distinct periods of high licking activity: an early phase lasting the first 5 min, and a late phase lasting 20-30 min after the injection. Formalin concentrations of 0.02-0.2% induced only the early phase, while concentrations of 1% or more induced both the early phase and the late phase. The ability of the test to show the antinociceptive effect of morphine and acetylsalicylic acid was similar for high and low formalin concentrations. For both these analgesics, a lower dose was needed to induce antinociception in the late phase than in the early phase using the same formalin concentration. Indomethacin had no effect in the early phase. In the late phase indomethacin induced antinociception when 1% formalin was used, while no significant effect was observed using 5% formalin. Clear histological changes in the paw were demonstrated after formalin concentrations that induced both phases. Lower formalin concentrations induced only very small changes. Using a low formalin concentration (0.2%), repeated testing using the same paw could be performed at intervals of 1 week without any significant change in the response. It was concluded that the formalin concentration should be kept as low as possible to minimize the suffering of the animal. Formalin concentrations of 0.05-0.2% are recommended for studying the early phase. Formalin concentrations of 1% or higher have to be used when studying the nociceptive response in the late phase.

Analgesics↗
PubMed1989

The apparent antinociceptive effect of desipramine and zimelidine in the tail flick test in rats is mainly caused by changes in tail skin temperature.

Tricyclic antidepressants have shown antinociceptive properties in some, but not in all, animal studies using the tail flick test. Tail flick latency has been found to be strongly negatively correlated to tail skin temperature with its highest correlation found when the temperature is measured close to the heated spot. The selective 5-HT reuptake inhibitor zimelidine, as well as the noradrenaline reuptake inhibitor desipramine, increased tail flick latencies. However, this increase could largely be explained by a concomitant reduction in tail skin temperature. The highest dose of desipramine investigated (25 mg/kg) seemed to possess antinociceptive properties in this test also after correction for the fall in tail skin temperature. Lower doses of desipramine (5 and 15 mg/kg) and zimelidine (5, 20 and 30 mg/kg) were either inactive or their effect on tail flick latency could be explained by the fall in tail skin temperature. The apparent antinociceptive effect of zimelidine in the tail flick test thus seems to be due to an effect on tail skin temperature. Desipramine also seems to have its main effect due to a similar mechanism; however, the highest dose of desipramine used induced significant antinociception.

Analgesics↗
PubMed1988

Acute and chronic treatment with selective serotonin uptake inhibitors in mice: effects on nociceptive sensitivity and response to 5-methoxy-N,N-dimethyltryptamine.

The tail-flick and increasing temperature hot-plate tests were employed to study the effects of acute or chronic treatment with zimelidine, alaproclate or chlorimipramine on nociception and response to 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) in mice. A single dose of the serotonin (5-HT) uptake inhibitors produced antinociception in the hot-plate test but not in the tail-flick test. After chronic administration, reduced tail-flick latencies were demonstrated 24, 48, 72 and 144 h after withdrawal of zimelidine treatment, 48 h after withdrawal of alaproclate and 48 and 96 h after withdrawal of chlorimipramine treatment. The hot-plate response temperatures were slightly lowered after chronic zimelidine treatment but not after treatment with alaproclate or chlorimipramine. The response to 5-MeODMT was not altered by a single dose of the 5-HT uptake inhibitors, however, after withdrawal of chronic treatment this response was increased in the tail-flick test but not in the hot-plate test. It was concluded that acute and chronic treatment with 5-HT uptake inhibitors modulate nociception differently, and that chronic treatment induces supersensitivity of spinal postsynaptic 5-HT receptors. Different modulation of different 5-HT receptor subpopulations by these compounds may possibly contribute to the test-dependent results.

Alanine↗