We identified major ion channels influencing the resting membrane potential of nociceptive sensory neurons and demonstrated that changes of somatic/perisomatic membrane potential of these neurons can ...strongly influence peripheral nociceptive transmission.
Peripheral sensory ganglia contain somata of afferent fibres conveying somatosensory inputs to the central nervous system. Growing evidence suggests that the somatic/perisomatic region of sensory neurons can influence peripheral sensory transmission. Control of resting membrane potential (Erest) is an important mechanism regulating excitability, but surprisingly little is known about how Erest is regulated in sensory neuron somata or how changes in somatic/perisomatic Erest affect peripheral sensory transmission. We first evaluated the influence of several major ion channels on Erest in cultured small-diameter, mostly capsaicin-sensitive (presumed nociceptive) dorsal root ganglion (DRG) neurons. The strongest and most prevalent effect on Erest was achieved by modulating M channels, K2P and 4-aminopiridine-sensitive KV channels, while hyperpolarization-activated cyclic nucleotide-gated, voltage-gated Na+, and T-type Ca2+ channels to a lesser extent also contributed to Erest. Second, we investigated how varying somatic/perisomatic membrane potential, by manipulating ion channels of sensory neurons within the DRG, affected peripheral nociceptive transmission in vivo. Acute focal application of M or KATP channel enhancers or a hyperpolarization-activated cyclic nucleotide-gated channel blocker to L5 DRG in vivo significantly alleviated pain induced by hind paw injection of bradykinin. Finally, we show with computational modelling how somatic/perisomatic hyperpolarization, in concert with the low-pass filtering properties of the t-junction within the DRG, can interfere with action potential propagation. Our study deciphers a complement of ion channels that sets the somatic Erest of nociceptive neurons and provides strong evidence for a robust filtering role of the somatic and perisomatic compartments of peripheral nociceptive neuron.
Analgesics targeting the δ-opioid receptor (DOR) may lead to fewer side effects than conventional opioid drugs, which mainly act on μ-opioid receptors (MOR), because of the less abundant expression ...of DOR in the CNS compared with MOR. Analgesic potential of DOR agonists increases after inflammation, an effect that may be mediated by DOR expressed in the peripheral sensory fibers. However, the expression of functional DOR at the plasma membrane of sensory neurons is controversial. Here we have used patch-clamp recordings and total internal reflection fluorescence microscopy to study the functional expression of DOR in sensory neurons from rat trigeminal (TG) and dorsal root ganglia (DRG). Real-time total internal reflection fluorescence microscopy revealed that treatment of TG and DRG cultures with the inflammatory mediator bradykinin (BK) caused robust trafficking of heterologously expressed GFP-tagged DOR to the plasma membrane. By contrast, treatment of neurons with the DOR agonist d-Ala(2), d-Leu(5)-enkephalin (DADLE) caused a decrease in the membrane abundance of DOR, suggesting internalization of the receptor after agonist binding. Patch-clamp experiments revealed that DADLE inhibited voltage-gated Ca(2+) channels (VGCCs) in 23% of small-diameter TG neurons. Pretreatment with BK resulted in more than twice as many DADLE responsive neurons (54%) but did not affect the efficacy of VGCC inhibition by DADLE. Our data suggest that inflammatory mediator-induced membrane insertion of DOR into the plasma membrane of peripheral sensory neurons may underlie increased DOR analgesia in inflamed tissue. Furthermore, the majority of BK-responsive TG neurons may have a potential to become responsive to DOR ligands in inflammatory conditions.
Metastatic pancreatic cancer (mPC) still harbors a dismal prognosis. Our previous trial (PRODIGE 4-ACCORD 11) demonstrated the superiority of 6-month chemotherapy with fluorouracil, leucovorin, ...irinotecan, and oxaliplatin (FOLFIRINOX) over gemcitabine for overall survival. The high limiting oxaliplatin-related neurotoxicity supports the evaluation of an oxaliplatin stop-and-go strategy and a sequential strategy in mPC.
In this phase II study, patients were randomly assigned to receive either 6 months of FOLFIRINOX (arm A), 4 months of FOLFIRINOX followed by leucovorin plus fluorouracil maintenance treatment for controlled patients (arm B), or a sequential treatment alternating gemcitabine and fluorouracil, leucovorin, and irinotecan every 2 months (arm C). The primary end point was progression-free survival at 6 months.
Between January 2015 and November 2016, 276 patients (mean age: 63 years; range: 40-76 years) were enrolled (A: 91, B: 92, and C: 90). Grade 3 or 4 neurotoxicity occurred in 10.2% of patients in arm A and 19.8% in arm B. The median ratio of received dose/targeted dose of oxaliplatin was 83% in arm A and 92% in arm B. The 6-month progression-free survival was 47.1% in A, 42.9% in B, and 34.1% in C. The median overall survival was 10.1 months in arm A, 11.2 in arm B, and 7.3 in arm C. Median survival without deterioration in quality-of-life scores was higher in the maintenance arm (11.4 months) than in arms A and C (7.2 and 7.5 months, respectively).
Maintenance with leucovorin plus fluorouracil appears to be feasible and effective in patients with mPC controlled after 4 months of induction chemotherapy with FOLFIRINOX. Severe neurotoxicity was higher in the maintenance therapy arm, probably because of the higher cumulative dose of oxaliplatin.
Neurons which discharge selectively during waking (waking selective) have been found in the tuberomamillary nucleus (TM) and adjacent areas of the posterior hypothalamus. Although they share some ...electrophysiological properties with aminergic neurons, there is no direct evidence that they are histaminergic. We have recorded from posterior hypothalamic neurons during the sleep–wake cycle in freely moving cats, and investigated the effects on waking selective neurons of specific ligands of histaminergic H3-receptors, which autoregulate the activity of histaminergic neurons. Two types of neurons were seen. Waking selective neurons, termed “waking-on (W-on),” were located exclusively within the TM and adjacent areas, and discharged at a low regular rate during waking (1.71–2.97
Hz), decreased firing during light slow wave sleep (SWS), became silent during deep SWS and paradoxical sleep (PS) and resumed their activity on, or a few seconds before, awakening. “Waking-related” neurons, located in an area dorsal to the TM, displayed a similar, although less regular, low rate of firing (1.74–5.41
Hz) and a similar discharge profile during the sleep–wake cycle; however, unlike “W-on” neurons, they did not completely stop firing during deep SWS and PS. Intramuscular (i.m.) injection of ciproxifan (an H3-receptor antagonist, 1
mg/kg), significantly increased the discharge rate of W-on neurons and induced
c-fos expression in histamine-immunoreactive neurons, whereas i.m. injection of imetit (an H3-receptor agonist, 1
mg/kg) or microinjection of α-methylhistamine (another H3-receptor agonist, 0.025–0.1
μg/0.2
μl) in the vicinity of these cells significantly decreased their discharge rate. Moreover, the effect of the antagonist was reversed by the agonists and vice versa. In contrast, “waking-related” neurons were unaffected by these H3-receptor ligands. These data provide evidence for the histaminergic nature of “W-on” neurons and their role in cortical desynchronization during waking, and highlight the heterogeneity of posterior hypothalamic neuronal populations, which might serve different functions during the wakefulness.
•Osteoarthritis (OA) patients are in need of new, disease-modifying drugs.•Disease-modifying OA drugs could target cartilage repair or degradation pathways.•Development of intra-articular OA drugs is ...associated with unique challenges.•OA drug candidate dosing strategy is defined regardless of administration route.
Osteoarthritis (OA) is a common disease worldwide with large unmet medical needs. To bring innovative treatments to OA patients, we at Merck have implemented a comprehensive strategy for drug candidate evaluation. We have a clear framework for decision-making in our preclinical pipeline, to design our clinical proof-of-concept trials for OA patients. We have qualified our strategy to define and refine dose and dosing regimen, for treatments administered either systemically or intra-articularly (IA). We do this through preclinical in vitro and in vivo studies, and by back-translating results from clinical studies in OA patients.
Intense training is the most clinically successful treatment modality following incomplete spinal cord injuries (SCIs). With the advent of plasticity enhancing treatments, understanding how ...treatments might interact when delivered in combination becomes critical. Here, we investigated a rational approach to sequentially combine treadmill locomotor training with antibody mediated suppression of the fiber growth inhibitory protein Nogo-A. Following a large but incomplete thoracic lesion, rats were immediately treated with either anti-Nogo-A or control antibody (2weeks) and then either left untrained or step-trained starting 3weeks after injury for 8weeks. It was found that sequentially combined therapy improved step consistency and reduced toe dragging and climbing errors, as seen with training and anti-Nogo-A individually. Animals with sequential therapy also adopted a more parallel paw position during bipedal walking and showed greater overall quadrupedal locomotor recovery than individual treatments. Histologically, sequential therapy induced the greatest corticospinal tract sprouting caudally into the lumbar region and increased the number of serotonergic synapses onto lumbar motoneurons. Increased primary afferent sprouting and synapse formation onto lumbar motoneurons observed with anti-Nogo-A antibody were reduced by training. Animals with sequential therapy also showed the highest reduction of lumbar interneuronal activity associated with walking (c-fos expression). No treatment effects for thermal nociception, mechanical allodynia, or lesion volume were observed. The results demonstrate that sequential administration of anti-Nogo-A antibody followed in time with intensive locomotor training leads to superior recovery of lost locomotor functions, which is probably mediated by changes in the interaction between descending sprouting and local segmental networks after SCI.
•Sequential combination of anti-Nogo-A antibody and locomotor training enhanced recovery after incomplete spinal cord injury.•Only the combination group showed sprouting of corticospinal tract fibers into lumbar segments.•Locomotor training significantly reduced sprouting of Ia afferents into spinal cord compared to anti-Nogo-A antibody group.•No changes in mechanical allodynia or thermal nociception were detected in any group.
Cholinergic transmission plays a pivotal role in learning, memory and cognition, and disturbances of cholinergic transmission have been implicated in neurological disorders including Alzheimer’s ...disease, epilepsy and schizophrenia. Pharmacological alleviation of these diseases by drugs including
N
-desmethylclozapine (NDMC), promising in animal models, often fails in patients. We therefore compared the effects of NDMC on glutamatergic and GABAergic transmission in slices from rat and human neocortex. We used carbachol (CCh; an established agonist at metabotropic muscarinic acetylcholine (ACh) receptors (mAChRs)) as a reference. Standard electrophysiological methods including intracellular and field potential recordings were used. In the rat neocortex, NDMC prevented the CCh-induced decrease of GABA
A
and GABA
B
receptor-mediated responses but not the CCh-induced increase of the paired-pulse depression. NDMC reduced neither the amplitude of the excitatory postsynaptic potentials (EPSP) nor antagonized the CCh-induced depression of EPSP. In the human neocortex, however, NDMC failed to prevent CCh-induced decrease of the GABA
B
responses and directly reduced the amplitude of EPSP. These data suggest distinct effects of NDMC in rat and human at M
2
and M
4
mAChRs underlying presynaptic modulation of GABA and glutamate release, respectively. In particular, NDMC might be a M
2
mAChR antagonist in the rat but has no activity at this receptor in human neocortex. However, NDMC has an agonistic effect at M
4
mAChR in the human but no such effect in the rat neocortex. The present study confirms that pharmacology at mAChRs can differ between species and emphasizes the need of studies in human tissue.
Matrix Gla protein (MGP) is a 14-kD extracellular matrix protein of the mineral-binding Gla protein family. Studies of MGP-deficient mice suggest that MGP is an inhibitor of extracellular matrix ...calcification in arteries and the epiphyseal growth plate. In the mammalian growth plate, MGP is expressed by proliferative and late hypertrophic chondrocytes, but not by the intervening chondrocytes. To investigate the functional significance of this biphasic expression pattern, we used the ATDC5 mouse chondrogenic cell line. We found that after induction of the cell line with insulin, the differentiating chondrocytes express MGP in a stage-specific biphasic manner as in vivo. Treatment of the ATDC5 cultures with MGP antiserum during the proliferative phase leads to their apoptosis before maturation, whereas treatment during the hypertrophic phase has no effect on chondrocyte viability or mineralization. After stable transfection of ATDC5 cells with inducible sense or antisense MGP cDNA constructs, we found that overexpression of MGP in maturing chondrocytes and underexpression of MGP in proliferative and hypertrophic chondrocytes induced apoptosis. However, overexpression of MGP during the hypertrophic phase has no effect on chondrocyte viability, but it does reduce mineralization. This work suggests that coordinated levels of MGP are required for chondrocyte differentiation and matrix mineralization.
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