Modulation Of Nociceptive Input Research Articles

Circadian functional changes of pain-processing brainstem nuclei and implications for cluster headache: A 7 Tesla imaging study.

Pain thresholds and primary headaches, including cluster headache attacks, have circadian rhythmicity. Thus, they might share a common neuronal mechanism. This study aimed to elucidate how the modulation of nociceptive input in the brainstem changes from noon to midnight. Insights into the mechanism of these fluctuations could allow for new hypotheses about the pathophysiology of cluster headache. This repeated measure observational study was conducted at the University Hospital Zurich from December 2019 to November 2022. Healthy adults between 18 and 85 years of age were eligible. All participants were examined at noon and midnight. We tested the pain threshold on both sides of the foreheads with quantitative sensory testing, assessed tiredness levels, and obtained high-field (7 Tesla) and high-resolution functional magnetic resonance imaging (MRI) at each visit. Functional connectivity was assessed at the two visits by performing a region-of-interest analysis. We defined nuclei in the brainstem implicated in processing nociceptive input as well as the thalamus and suprachiasmatic nucleus as the region-of-interest. Ten people were enrolled, and seven participants were included. First, we did not find statistically significant differences between noon and midnight of A-delta-mediated pain thresholds (median mechanical pain threshold at noon: left 9.2, right 9.2; at night: left 6.5, right 6.1). Second, after correction for a false discovery rate, we found changes in the mechanical pain sensitivity to have a statistically significant effect on changes in the functional connectivity between the left parabrachial nucleus and the suprachiasmatic nucleus (T = -40.79). The MRI data analysis suggested that brain stem nuclei and the hypothalamus modulate A-delta-mediated pain perception; however, these changes in pain perception did not lead to statistically significantly differing pain thresholds between noon and midnight. Hence, our findings shed doubt on our hypothesis that the physiologic circadian rhythmicity of pain thresholds could drive the circadian rhythmicity of cluster headache attacks.

Physiological brainstem mechanisms of trigeminal nociception: An fMRI study at 3T

The brainstem is a major site of processing and modulation of nociceptive input and plays a key role in the pathophysiology of various headache disorders. However, human imaging studies on brainstem function following trigeminal nociceptive stimulation are scarce as brainstem specific imaging approaches have to address multiple challenges such as magnetic field inhomogeneities and an enhanced level of physiological noise. In this study we used a viable protocol for brainstem fMRI of standardized trigeminal nociceptive stimulation to achieve detailed insight into physiological brainstem mechanisms of trigeminal nociception. We conducted a study of 21 healthy participants using a nociceptive ammonia stimulation of the left nasal mucosa with an optimized MR acquisition protocol for high resolution brainstem echoplanar imaging in combination with two different noise correction techniques. Significant BOLD responses to noxious ammonia stimulation were observed in areas typically involved in trigeminal nociceptive processing such as the spinal trigeminal nuclei (sTN), thalamus, secondary somatosensory cortex, insular cortex and cerebellum as well as in a pain modulating network including the periaqueductal gray area, hypothalamus (HT), locus coeruleus and cuneiform nucleus (CNF). Activations of the left CNF were positively correlated with pain intensity ratings. Employing psychophysiological interaction (PPI) analysis we found enhanced functional connectivity of the sTN with the contralateral sTN and HT following trigeminal nociception. We also observed enhanced functional connectivity of the CNF with the RVM during painful stimulation thus implying an important role of these two brainstem regions in central pain processing. The chosen approach to study trigeminal nociception with high-resolution fMRI offers new insight into human pain processing and might thus lead to a better understanding of headache pathophysiology.

Electroacupuncture at 2/100 Hz Activates Antinociceptive Spinal Mechanisms Different from Those Activated by Electroacupuncture at 2 and 100 Hz in Responder Rats

We examined the effects of intrathecal injection of desipramine and fluoxetine (selective inhibitors of norepinephrine and 5-HT uptake, resp.), thiorphan and neostigmine (inhibitors of enkephalinase and acetylcholinesterase, resp.), gabapentin (a GABA releaser), and vigabatrin (an inhibitor of GABA-transaminase) on the antinociception induced by 2 Hz, 100 Hz, or 2/100 Hz electroacupuncture (EA) applied bilaterally to the Zusanli (ST36) and Sanyinjiao (SP6) acupoints using the rat tail-flick test. We show that 2 Hz EA antinociception lasts longer after the administration of drugs that increase the spinal availability of norepinephrine, acetylcholine, or GABA; 100 Hz EA antinociception lasts longer after drug that increases the spinal availability of norepinephrine; 2/100 Hz EA antinociception lasts longer after drugs that increase the spinal availability of endogenous opioids or GABA. We conclude that the antinociceptive effect of 2/100 Hz EA is different from the synergistic effect of alternate stimulation at 2 and 100 Hz because the effect of the former is not changed by increasing the spinal availability of serotonin and lasts longer after the administration of vigabatrin. The combination of EA with drugs that increase the availability of spinal neurotransmitters involved in the modulation of nociceptive inputs may result in a synergistic antinociceptive effect in the rat tail-flick test.

Distribution of NADPH diaphorase-exhibiting primary afferent neurons in the trigeminal ganglion and mesencephalic trigeminal nucleus of the rabbit.

1. Nitric oxide (NO) is highly reactive gaseous molecule to which many physiological and pathological functions have been attributed in the central (CNS) and peripheral (PNS) nervous system. The present investigation was undertaken to map the distribution pattern of the enzyme responsible for the synthesis of NO, nitric oxide synthase (NOS), and especially its neuronal isoform (nNOS) in the population of primary afferent neurons of the trigeminal ganglion (TG) and mesencephalic trigeminal nucleus (MTN) of the rabbit. 2. In order to identify neuronal structures expressing nNOS we applied histochemistry to its specific histochemical marker nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd). 3. We found noticeable amount of NADPHd-exhibiting primary afferent neurons in TG of the rabbit under physiological conditions. The intensity of the histochemical reaction was highly variable reaching the maximum in the subpopulation of small-to-medium-sized neurons. The large-sized neurons were only weakly stained or actually did not posses any NADPHd-activity. In addition, NADPHd-positive nerve fibers were detected between clusters of the ganglionic cells and in the peripheral branches of the trigeminal nerve (TN). NADPHd-exhibiting MTN neurons were noticed in the whole rostrocaudal extent of the nucleus even though some differences were found concerning the ratio of NADPHd-positive versus NADPHd-negative cell bodies. Similarly, we observed striking diversity in the intensity of NADPHd histochemical reaction in the subpopulations of small-, medium-, and large-sized MTN neurons. 4. The predominant localization of NADPHd in the subpopulation of small-to-medium-sized TG neurons which are generally considered to be nociceptive suggests that NO probably takes part in the modulation of nociceptive inputs from the head and face. Furthermore, we tentatively assume that NADPHd-exhibiting MTN neurons probably participate in transmission and modulation of the proprioceptive impulses from muscle spindles of the masticatory muscles and mechanoreceptors of the periodontal ligaments and thus provide sensory feedback of the masticatory reflex arc.

Striatal Inhibition of Nociceptive Responses Evoked in Trigeminal Sensory Neurons by Tooth Pulp Stimulation

The noxious evoked response in trigeminal sensory neurons was studied to address the role of striatum in the control of nociceptive inputs. In urethane-anesthetized rats, the jaw opening reflex (JOR) was produced by suprathreshold stimulation of the tooth pulp and measured as electromyographic response in the digastric muscle, with simultaneous recording of noxious responses in single unit neurons of the spinal trigeminal nucleus pars caudalis (Sp5c). The microinjection of glutamate (80 etamol/0.5 microl) into striatal JOR inhibitory sites significantly decreased the A delta and C fiber-mediated-evoked response (53 +/- 4.2 and 43.6 +/- 6.4% of control value, P < 0.0001) in 92% (31/34) of nociceptive Sp5c neurons. The microinjection of the solvent was ineffective, as was microinjection of glutamate in sites out of the JOR inhibitory ones. In another series of experiments, simultaneous single unit recordings were performed in the motor trigeminal nucleus (Mo5) and the Sp5c nucleus. Microinjection of glutamate decreased the noxious-evoked response in Sp5c and Mo5 neurons in parallel with the JOR, without modifying spontaneous neuronal activity of trigeminal motoneurons (n = 8 pairs). These results indicate that the striatum could be involved in the modulation of nociceptive inputs and confirm the role of the basal ganglia in the processing of nociceptive information.

L-Arginine/nitric oxide pathway in chronic tension-type headache: relation with serotonin content and secretion and glutamate content

Previous research of our group demonstrated an increase in l-arginine/nitric oxide (NO) pathway activity in patients with chronic daily headache (CDH) with a previous history of migraine, which was associated with a reduced platelet serotonin content and increased Ca 2+ levels. In the present work, we assessed the variations in l-arginine/NO pathway activity and platelet cyclic guanosine 3′,5′-monophosphate (cGMP) levels in 25 patients affected by chronic tension-type headache (CTTH) (8 M, 17 F; age range: 34-54 years). The NO production, shown spectrophotometrically by stoichiometric transformation of oxyhemoglobin to methemoglobin due to NO synthase (NOS) activity, and inter platelet cGMP concentration, assessed with a RIA method, were determined in parallel to variations of aggregation response to 0.3 μg/ml collagen. The intracellular platelet calcium concentrations were also determined using fluorescence polarisation spectrometry. Platelet serotonin content and collagen-induced secretion as well as glutamate content were also determined with high-performance liquid chromatography (HPLC). The above parameters were compared with those of an age-matched control group. A reduction in aggregation platelet response was found. The reduction in platelet aggregation was coupled with an increased NO and cGMP production ( p<0.0002 and p<0.001, respectively). A significant increase in cytosolic Ca 2+ concentration was also detected compared to control individuals ( p<0.001). This was accompanied by a reduced platelet content and collagen-induced secretion of serotonin and increased content of glutamate ( p<0.0001, p<0.0001 and p<0.001, respectively). The above findings were more evident in patients with analgesic abuse. It can be hypothesized that the increased NOS activity shown in platelets of CTTH patients reflects an analogous central up-regulation of NOS activity in the spinal horn/trigeminal nucleus and supraspinal structures involved in the modulation of nociceptive input from myofascial cranial structures contributing to central sensitization. The increase in NOS activity seems to be associated with a hyposerotonergic status, particularly in patients with analgesic abuse, and this can contribute to central sensitization in CTTH patients. The increase in platelet glutamate content in the same patients suggests the implication of the above excitatory amino acid in spinal and supraspinal structures involved in head pain induction and maintenance.

Mice over-expressing galanin have elevated heat nociceptive threshold.

The neuropeptide galanin may have a role in modulation of nociceptive input at spinal level. Here we report that mice over-expressing galanin exhibit significant elevation of nociceptive threshold to thermal stimulation in comparison to wild-type mice as assessed by the tail flick and paw heat irradiation tests. No change in response to mechanical or cold stimulation was seen. The elevated heat nociceptive threshold in the galanin over-expressing mice was reversed by intrathecal application of the putative galanin receptor antagonist M-35, galanin-(1-12)-pro-bradykinin-(2-9). The results thus support that galanin has an inhibitory function in rodent spinal cord.

Postthoracotomy Pain Management

In modern medicine, postoperative analgesia is consid ered an integral part of the anesthetic management. Thoracotomy has been reported to be among the most intense clinical postoperative pain experiences. If pain is poorly controlled in the postoperative period, respira tory excursions, movements, and coughing may result in muscle splinting, atelectasis and postoperative pulmo nary dysfunction. This article focuses on the various analgesic modalities that are available for altering the flow of nociceptive information from the periphery to cortex: (1) the transduction of nociceptive information at the peripheral receptor (local anesthetics, nonsteroi dal anti-inflammatory drugs); (2) the transmission of nociceptive information along the afferent sensory neu ral pathways (intercostal, intrapleural, or epidural local anesthetics); and finally, (3) the modulation of nocicep tive input at the level of the dorsal horn of the spinal cord (lumbar or thoracic epidural and intrathecal opi oids) or the brain (systemic opioids). Finally, the role of preemptive analgesia in thoracic surgery is discussed.

Substance P and enkephalin immunoreactivities in axonal boutons presynaptic to physiologically identified dorsal horn neurons. An ultrastructural multiple-labelling study in the cat

A combination of intracellular electrophysiological recording and injection of horseradish peroxidase with ultrastructural immunocytochemistry was used to investigate the synaptic interplay between substance P- and enkephalin-immunoreactive axonal boutons and three types of functionally characterized dorsal horn neurons in the cat spinal cord. The dorsal horn neurons were classified as nociceptive specific, wide dynamic range and non-nociceptive based on their responses to innocuous and noxious stimuli. Most of the nociceptive neurons (either nociceptive specific or wide dynamic range) contained enkephalin immunoreactivity, but none of the non-nociceptive neurons were positive for enkephalin. Three types of immunoreactive boutons were found in contact with the functionally characterized dorsal horn neurons. These boutons were positive for either substance P, enkephalin, or substance P+enkephalin. Quantitative analysis revealed that the percentages of substance P-immunoreactive boutons apposed to the cell bodies, proximal dendrites and distal dendrites of nociceptive neurons were significantly higher than those of non-nociceptive neurons. Furthermore, the percentages of substance P+enkephalin-immunoreactive axonal boutons apposed to the distal dendrites of nociceptive neurons were significantly higher than those of non-nociceptive neurons and the percentages of enkephalin-immunoreactive boutons apposed to the cell bodies and proximal dendrites of nociceptive neurons were significantly higher than in non-nociceptive neurons. Finally, neither enkephalin-immunoreactive nor substance P+enkephalin-immunoreactive boutons were ever seen presynaptic to substance P-immunoreactive boutons. These results provide evidence of an anatomical substrate within the dorsal horn for the interaction of substance P-mediated with enkephalin-mediated mechanisms. The data support the idea that the modulation of nociceptive input in the dorsal horn by enkephalinergic neurons occurs mainly via a postsynaptic mechanism, and thus suggest that dorsal horn enkephalinergic neurons participate in a local inhibitory feedback loop in a distinct pathway from the previously postulated opioid-mediated depression of substance P release from primary afferent terminals.

Inhibitory effects of electrical stimulation of thalamic nucleus submedius area on the rat tail flick reflex

This study in lightly anesthetized rats found that unilateral electrical stimulation delivered to the ventral part of the thalamic nucleus submedius (Sm), the thalamic reuniens nucleus (Re) and the hypothalamic dorsal area (DA) markedly depressed the TF reflex, and this inhibitory effect increased following increasing stimulation intensity. Stimulation in the dorsal part of Sm did not produce any or only slight depression of the TF reflex. Furthermore, an ipsilateral electrolytic lesion of the ventrolateral orbital cortex (VLO) eliminated the unilateral Sm-evoked inhibition, but not the inhibition elicited by Re and DA and contralateral Sm stimulation. Finally, after bilateral electrolytic lesions of the ventrolateral periaqueductal gray (PAG) the DA and Re and contralateral Sm-evoked inhibitions were also eliminated. The results suggest that the Sm plays an important role in modulation of nociceptive inputs, and this role of Sm is mediated by the VLO and leads to activation of the PAG descending inhibitory system and depression of the nociceptive inputs at the spinal cord level.

1,4-Benzodiazepines Antagonize Opiate-Induced Antinociception in Mice

The influence of diazepam, midazolam, and flunitrazepam on the antinociceptive effect of morphine, fentanyl, and buprenorphine was studied using the hot-plate test and the tail-flick test in mice. Diazepam and midazolam induced a dose-dependent attenuation of the effect of all three opiates in both tests of nociception. Flunitrazepam antagonized the antinociceptive effect only in the tail-flick test. The benzodiazepine effect could not be explained by altered tail-skin temperature. The antagonism did not correlate well with the sedative or muscle-relaxing properties of the benzodiazepines, and a different mechanism may therefore be involved. It is proposed that the antagonism represents an interaction between benzodiazepines and opioid systems in the brain participating in modulation of nociceptive inputs.

Pharmacokinetic aspects of intrathecal morphine analgesia.

Fifteen patients undergoing thoracotomy were given 0.25 or 0.50 mg morphine intrathecally (L2-L3 or L3-L4) for an analgetic and pharmacokinetic study. Administration of morphine at the end of the operation resulted in a highly variable duration of analgesia ranging from 1-20.5 and 1-40 h for the 0.25 and 0.50 mg groups, respectively. Calculation of cumulative consumption pattern of additional analgesics given im indicated a dose-related analgesia lasting around 12 h. Morphine concentrations in the CSF were high and dose dependent. Thus, at 1 h, CSF concentrations (means +/- SEM) were 4,228 +/- 361 ng/ml and 10,447 +/- 1,538 ng/ml for the 0.25 and 0.50-mg groups, respectively. The plasma concentrations generally were very low, i.e., under 1 ng/ml. For the 0.50 and 0.25 mg groups, the terminal elimination half-life in CSF was 175 +/- 9 min and 196 +/- 13 min, respectively: the volume of CSF distribution was 0.88 +/- 0.16 ml X kg-1 and 1.06 +/- 0.17 ml X kg-1, respectively: and the clearance from CSF was 2.81 +/- 0.41 microliter X kg-1 X min-1 and 3.41 +/- 0.55 microliter X kg-1 X min-1, respectively (means +/- SEM). The study indicates that the significant pharmacokinetic parameter related to the long duration of analgesia after intrathecal morphine administration probably is the high CSF concentrations found, since the rate of elimination from CSF is similar to what is reported for morphine in plasma. Furthermore, modulation of nociceptive input in the thoracic region also may be achieved by lumbar administration, but a slower onset should be anticipated.

The Neurology of Spinal Pain

The neuroanatomical and physiological aspects of pain derived from the spine are reviewed. An explanation is presented of the influence of passive movement as it relates to the interaction of the mechanoreceptor afferent nerves' modulation of nociceptive input.