Dexamethasone-sparing on days 2-4 with combined palonosetron, neurokinin-1 receptor antagonist, and olanzapine in cisplatin: a randomized phase III trial (SPARED Trial).

BACKGROUND: This study evaluated the non-inferiority of dexamethasone (DEX) on day 1, with sparing on days 2-4 in cisplatin-based chemotherapy. METHODS: Patients with malignant solid tumors who were treated with cisplatin (≥50 mg/m²) were randomly assigned (1:1) to receive either DEX on days 1-4 (Arm D4) or DEX on day 1 (Arm D1) plus palonosetron, NK-1 RA, and olanzapine (5 mg). The primary endpoint was complete response (CR) during the delayed (24-120 h) phase. The non-inferiority margin was set at -15%. RESULTS: A total of 281 patients were enrolled, 278 of whom were randomly assigned to Arm D4 (n = 139) or Arm D1 (n = 139). In 274 patients were included in the efficacy analysis, the rates of delayed CR in Arms D4 and D1 were 79.7% and 75.0%, respectively (risk difference -4.1%; 95% CI -14.1%-6.0%, P = 0.023). However, patients in Arm D1 had significantly lower total control rates during the delayed and overall phases, and more frequent nausea and appetite loss. There were no significant between-arm differences in the quality of life. CONCLUSION: DEX-sparing is an alternative option for patients receiving cisplatin; however, this revised administration schedule should be applied on an individual basis after a comprehensive evaluation. CLINICAL TRIALS REGISTRY NUMBER: UMIN000032269.

SLFN11 promotes stalled fork degradation that underlies the phenotype in Fanconi anemia cells.

Fanconi anemia (FA) is a hereditary disorder caused by mutations in any 1 of 22 FA genes. The disease is characterized by hypersensitivity to interstrand crosslink (ICL) inducers such as mitomycin C (MMC). In addition to promoting ICL repair, FA proteins such as RAD51, BRCA2, or FANCD2 protect stalled replication forks from nucleolytic degradation during replication stress, which may have a profound impact on FA pathophysiology. Recent studies showed that expression of the putative DNA/RNA helicase SLFN11 in cancer cells correlates with cell death on chemotherapeutic treatment. However, the underlying mechanisms of SLFN11-mediated DNA damage sensitivity remain unclear. Because SLFN11 expression is high in hematopoietic stem cells, we hypothesized that SLFN11 depletion might ameliorate the phenotypes of FA cells. Here we report that SLFN11 knockdown in the FA patient-derived FANCD2-deficient PD20 cell line improved cell survival on treatment with ICL inducers. FANCD2-/-SLFN11-/- HAP1 cells also displayed phenotypic rescue, including reduced levels of MMC-induced chromosome breakage compared with FANCD2-/- cells. Importantly, we found that SLFN11 promotes extensive fork degradation in FANCD2-/- cells. The degradation process is mediated by the nucleases MRE11 or DNA2 and depends on the SLFN11 ATPase activity. This observation was accompanied by an increased RAD51 binding at stalled forks, consistent with the role of RAD51 antagonizing nuclease recruitment and subsequent fork degradation. Suppression of SLFN11 protects nascent DNA tracts even in wild-type cells. We conclude that SLFN11 destabilizes stalled replication forks, and this function may contribute to the attrition of hematopoietic stem cells in FA.

5-HT2A receptor activation enhances NMDA receptor-mediated glutamate responses through Src kinase in the dendrites of rat jaw-closing motoneurons.

KEY POINTS: 5-HT increases the excitability of brainstem and spinal motoneurons, including the jaw-closing motoneurons, by depolarizing the membrane potential and decreasing the medium-duration afterhyperpolarization. In this study, we focused on how 5-HT enhances postsynaptic glutamatergic responses in the dendrites of the jaw-closing motoneurons. We demonstrate that 5-HT augments glutamatergic signalling by enhancing the function of the GluN2A-containing NMDA receptor (NMDAR) through the activation of 5-HT2A receptors (5-HT2A Rs) and Src kinase. To enhance glutamatergic responses, activation of the 5-HT2A Rs must occur within ∼60 µm of the location of the glutamate responses. 5-HT inputs to the jaw-closing motoneurons can significantly vary their input-output relationship, which may contribute to wide-range regulation of contractile forces of the jaw-closing muscles. ABSTRACT: Various motor behaviours are modulated by 5-HT. Although the masseter (jaw-closing) motoneurons receive both glutamatergic and serotonergic inputs, it remains unclear how 5-HT affects the glutamatergic inputs to the motoneuronal dendrites. We examined the effects of 5-HT on postsynaptic responses evoked by single- or two-photon uncaging of caged glutamate (glutamate responses) to the dendrites of masseter motoneurons in postnatal day 2-5 rats of either sex. Application of 5-HT induced membrane depolarization and enhanced the glutamate-response amplitude. This enhancement was mimicked by the 5-HT2A receptor (5-HT2A R) agonist and was blocked by the 5-HT2A/2C R antagonist. However, neither the 5-HT2B R nor the 5-HT2C R agonists altered glutamate responses. Blockade of the NMDA receptors (NMDARs), but not AMPA receptors, abolished the 5-HT-induced enhancement. Furthermore, the selective antagonist for the GluN2A subunit abolished the 5-HT-induced enhancement. 5-HT increased GluN2A phosphorylation, while the Src kinase inhibitor reduced the 5-HT-induced enhancement and GluN2A phosphorylation. When exposure to the 5-HT2A R agonist was targeted to the dendrites, the enhancement of glutamate responses was restricted to the loci of the dendrites near the puff loci. Electron microscopic immunohistochemistry revealed that both the NMDARs and the 5-HT2A Rs were close to each other in the same dendrite. These results suggest that activation of dendritic 5-HT2A Rs enhances the function of local GluN2A-containing NMDARs through Src kinase. Such enhancement of the glutamate responses by 5-HT may contribute to wide-range regulation of contractile forces of the jaw-closing muscles.

Involvement of histaminergic inputs in the jaw-closing reflex arc.

Histamine receptors are densely expressed in the mesencephalic trigeminal nucleus (MesV) and trigeminal motor nucleus. However, little is known about the functional roles of neuronal histamine in controlling oral-motor activity. Thus, using the whole-cell recording technique in brainstem slice preparations from Wistar rats aged between postnatal days 7 and 13, we investigated the effects of histamine on the MesV neurons innervating the masseter muscle spindles and masseter motoneurons (MMNs) that form a reflex arc for the jaw-closing reflex. Bath application of histamine (100 µM) induced membrane depolarization in both MesV neurons and MMNs in the presence of tetrodotoxin, whereas histamine decreased and increased the input resistance in MesV neurons and MMNs, respectively. The effects of histamine on MesV neurons and MMNs were mimicked by an H1 receptor agonist, 2-pyridylethylamine (100 µM). The effects of an H2 receptor agonist, dimaprit (100 µM), on MesV neurons were inconsistent, whereas MMNs were depolarized without changes in the input resistance. An H3 receptor agonist, immethridine (100 µM), also depolarized both MesV neurons and MMNs without changing the input resistance. Histamine reduced the peak amplitude of postsynaptic currents (PSCs) in MMNs evoked by stimulation of the trigeminal motor nerve (5N), which was mimicked by 2-pyridylethylamine but not by dimaprit or immethridine. Moreover, 2-pyridylethylamine increased the failure rate of PSCs evoked by minimal stimulation and the paired-pulse ratio. These results suggest that histaminergic inputs to MesV neurons through H1 receptors are involved in the suppression of the jaw-closing reflex although histamine depolarizes MesV neurons and/or MMNs.

Bropirimine inhibits osteoclast differentiation through production of interferon-ß.

Bropirimine is a synthetic agonist for toll-like receptor 7 (TLR7). In this study, we investigated the effects of bropirimine on differentiation and bone-resorbing activity of osteoclasts in vitro. Bropirimine inhibited osteoclast differentiation of mouse bone marrow-derived macrophages (BMMs) induced by receptor activator of nuclear factor κB ligand (RANKL) in a concentration-dependent manner. Furthermore, it suppressed the mRNA expression of nuclear factor of activated T-cells, cytoplasmic, calcineurin-dependent 1 (NFATc1), a master transcription factor for osteoclast differentiation, without affecting BMM viability. Bropirimine also inhibited osteoclast differentiation induced in co-cultures of mouse bone marrow cells (BMCs) and mouse osteoblastic UAMS-32 cells in the presence of activated vitamin D3. Bropirimine partially suppressed the expression of RANKL mRNA in UAMS-32 cells induced by activated vitamin D3. Finally, the anti-interferon-ß (IFN-ß) antibody restored RANKL-dependent differentiation of BMMs into osteoclasts suppressed by bropirimine. These results suggest that bropirimine inhibits differentiation of osteoclast precursor cells into osteoclasts via TLR7-mediated production of IFN-ß.

Electrophysiological and morphological properties of rat supratrigeminal premotor neurons targeting the trigeminal motor nucleus.

The electrophysiological and morphological characteristics of premotor neurons in the supratrigeminal region (SupV) targeting the trigeminal motor nucleus (MoV) were examined in neonatal rat brain stem slice preparations with Ca(2+) imaging, whole cell recordings, and intracellular biocytin labeling. First, we screened SupV neurons that showed a rapid rise in intracellular free Ca(2+) concentration ([Ca(2+)]i) after single-pulse electrical stimulation of the ipsilateral MoV. Subsequent whole cell recordings were generated from the screened SupV neurons, and their antidromic responses to MoV stimulation were confirmed. We divided the antidromically activated premotor neurons into two groups according to their discharge patterns during the steady state in response to 1-s depolarizing current pulses: those firing at a frequency higher (HF neurons, n = 19) or lower (LF neurons, n = 17) than 33 Hz. In addition, HF neurons had a narrower action potential and a larger afterhyperpolarization than LF neurons. Intracellular labeling revealed that the axons of all HF neurons (6/6) and half of the LF neurons (4/9) entered the MoV from its dorsomedial aspect, whereas the axons of the remaining LF neurons (5/9) entered the MoV from its dorsolateral aspect. Furthermore, the dendrites of three HF neurons penetrated into the principal sensory trigeminal nucleus (Vp), whereas the dendrites of all LF neurons were confined within the SupV. These results suggest that the types of SupV premotor neurons targeting the MoV with different firing properties have different dendritic and axonal morphologies, and these SupV neuron classes may play unique roles in diverse oral motor behaviors, such as suckling and mastication.

Tudor domain containing 7 (Tdrd7) is essential for dynamic ribonucleoprotein (RNP) remodeling of chromatoid bodies during spermatogenesis.

In the male germline in mammals, chromatoid bodies, a specialized assembly of cytoplasmic ribonucleoprotein (RNP), are structurally evident during meiosis and haploidgenesis, but their developmental origin and regulation remain elusive. The tudor domain containing proteins constitute a conserved class of chromatoid body components. We show that tudor domain containing 7 (Tdrd7), the deficiency of which causes male sterility and age-related cataract (as well as glaucoma), is essential for haploid spermatid development and defines, in concert with Tdrd6, key biogenesis processes of chromatoid bodies. Single and double knockouts of Tdrd7 and Tdrd6 demonstrated that these spermiogenic tudor genes orchestrate developmental programs for ordered remodeling of chromatoid bodies, including the initial establishment, subsequent RNP fusion with ubiquitous processing bodies/GW bodies and later structural maintenance. Tdrd7 suppresses LINE1 retrotransposons independently of piwi-interacting RNA (piRNA) biogenesis wherein Tdrd1 and Tdrd9 operate, indicating that distinct Tdrd pathways act against retrotransposons in the male germline. Tdrd6, in contrast, does not affect retrotransposons but functions at a later stage of spermiogenesis when chromatoid bodies exhibit aggresome-like properties. Our results delineate that chromatoid bodies assemble as an integrated compartment incorporating both germline and ubiquitous features as spermatogenesis proceeds and that the conserved tudor family genes act as master regulators of this unique RNP remodeling, which is genetically linked to the male germline integrity in mammals.

Optical imaging of neurons related to fictive swallowing using GCaMP6f in an arterially perfused rat preparation.

OBJECTIVE: It is difficult to comprehensively study the activity patterns and distribution of neurons in the brainstem that control the act of swallowing, as they are located deep in the brain. In this study, we aimed to evaluate the usefulness of calcium imaging using GCaMP6f in arterially perfused preparations to study the activity of swallowing-related neurons in the brainstem. METHODS: Arterially perfused rat preparations were prepared 3-4 weeks after the injection of a neuron-specific virus expressing GCaMP6f. Fictive swallowing was induced by repetitive electrical stimulation of the superior laryngeal nerve (SLN). Simultaneously, the activity of GCaMP6f-expressing neurons in the dorsal brainstem, between 0.1 and 4.8 mm rostral to the obex, was assessed by changes in the intracellular calcium concentration using confocal laser microscopy. RESULTS: Neurons responding to stimulation of the SLN included swallowing-related neurons (48%), which showed an increase in fluorescence intensity at the time of swallowing bursts in the cervical vagus nerve, and stimulation-related neurons (52%), which showed an increase in fluorescence intensity through stimulation, regardless of the swallowing bursts. Despite a broad search area, swallowing-related neurons were localized exclusively in and around the solitary nucleus. In contrast, most stimulation-related neurons were located in the brainstem reticular formation, which is more rostral than the solitary nucleus. CONCLUSIONS: Calcium imaging using GCaMP in arterially perfused rat preparations is useful for an efficient search of the activity pattern and distribution of neurons located in a wide area of the brainstem.

Involvement of ghrelin in the regulation of swallowing motor activity in an arterially perfused rat preparation.

Ghrelin, a peripheral peptide produced in the stomach, is involved in the neural networks that control food intake. Alterations in motor components, such as swallowing, are believed to be significant in the regulation food intake by orexigenic signals. However, there has been no detailed investigation of the relationship between ghrelin and swallowing activities induced in motor nerves innervating the pharyngeal and laryngeal muscles. In this study, we examined the effects of ghrelin administration on swallowing motor activity in arterially perfused rats. Injection of distilled water (0.5 ml) into the oral cavity or electrical stimulation of the superior laryngeal nerve evoked swallowing motor activity in the cervical vagus nerve. Administration of ghrelin (6 nM), but not des-acylated ghrelin (6 nM), into the perfusate increased the peak burst amplitude and burst duration, and shortened the first burst interval of water injection-induced swallowing. These ghrelin-induced changes in swallowing motor activity were blocked by the administration of JMV2959 (6 µM), a growth hormone secretagogue receptor antagonist. In preparations in which the hypothalamus was removed, ghrelin had no effect on swallowing motor activity. Furthermore, ghrelin-induced changes were counteracted by the administration of BIBO3304 (1 µM) or L-152,804 (1 µM), antagonists of neuropeptide Y Y1 and Y5 receptors, respectively, which are essential for ghrelin-induced enhancement of food intake. Ghrelin also increased the peak burst amplitude and burst duration of the swallowing motor activity evoked by electrical stimulation of the superior laryngeal nerve, although the effects of ghrelin on the number of swallowing bursts and burst intervals varied with stimulus intensity. These results suggest that ghrelin enhances the magnitude and frequency of bursts of swallowing motor activity by acting via the hypothalamic neural network, and that neuropeptide Y Y1 and Y5 receptors are involved in this enhancement.

Mouse Slfn8 and Slfn9 genes complement human cells lacking SLFN11 during the replication stress response.

The Schlafen (SLFN)11 gene has been implicated in various biological processes such as suppression of HIV replication, replication stress response, and sensitization of cancer cells to chemotherapy. Due to the rapid diversification of the SLFN family members, it remains uncertain whether a direct ortholog of human SLFN11 exists in mice. Here we show that mSLFN8/9 and hSLFN11 were rapidly recruited to microlaser-irradiated DNA damage tracks. Furthermore, Slfn8/9 expression could complement SLFN11 loss in human SLFN11-/- cells, and as a result, reduced the growth rate to wild-type levels and partially restored sensitivity to DNA-damaging agents. In addition, both Slfn8/9 and SLFN11 expression accelerated stalled fork degradation and decreased RPA and RAD51 foci numbers after DNA damage. Based on these results, we propose that mouse Slfn8 and Slfn9 genes may share an orthologous function with human SLFN11. This notion may facilitate understanding of SLFN11's biological role through in vivo studies via mouse modeling.

Shared GABA transmission pathology in dopamine agonist- and antagonist-induced dyskinesia.

Dyskinesia is involuntary movement caused by long-term medication with dopamine-related agents: the dopamine agonist 3,4-dihydroxy-L-phenylalanine (L-DOPA) to treat Parkinson's disease (L-DOPA-induced dyskinesia [LID]) or dopamine antagonists to treat schizophrenia (tardive dyskinesia [TD]). However, it remains unknown why distinct types of medications for distinct neuropsychiatric disorders induce similar involuntary movements. Here, we search for a shared structural footprint using magnetic resonance imaging-based macroscopic screening and super-resolution microscopy-based microscopic identification. We identify the enlarged axon terminals of striatal medium spiny neurons in LID and TD model mice. Striatal overexpression of the vesicular gamma-aminobutyric acid transporter (VGAT) is necessary and sufficient for modeling these structural changes; VGAT levels gate the functional and behavioral alterations in dyskinesia models. Our findings indicate that lowered type 2 dopamine receptor signaling with repetitive dopamine fluctuations is a common cause of VGAT overexpression and late-onset dyskinesia formation and that reducing dopamine fluctuation rescues dyskinesia pathology via VGAT downregulation.

Developmental changes in GABAergic and glycinergic synaptic transmission to rat motoneurons innervating jaw-closing and jaw-opening muscles.

Trigeminal motoneurons (MNs) innervating the jaw-closing and jaw-opening muscles receive numerous inhibitory synaptic inputs from GABAergic and glycinergic neurons, which are essential for oromotor functions, such as the orofacial reflex, suckling, and mastication. The properties of the GABAergic and glycinergic inputs of these MNs undergo developmental alterations during the period in which their feeding behavior proceeds from suckling to mastication; however, the detailed characteristics of the developmental patterns of GABAergic and glycinergic transmission in these neurons remain to be elucidated. This study was conducted to investigate developmental changes in miniature inhibitory postsynaptic currents (mIPSCs) in masseter (jaw-closing) and digastric (jaw-opening) MNs using brainstem slice preparations obtained from Wistar rats on postnatal day (P)2-5, P9-12, and P14-17. The frequency and amplitude of glycinergic mIPSCs substantially increased with age in both the masseter and digastric MNs. The rise time and decay time of glycinergic mIPSCs in both MNs decreased during development. In contrast, the frequency of GABAergic components in masseter MNs was higher at P2-5 than at P14-17, whereas that in the digastric MNs remained unchanged throughout the postnatal period. The proportion of currents mediated by GABA-glycine co-transmission was higher at P2-5, and then it decreased with age in both MNs. These results suggest that characteristics related to the development of inhibitory synaptic inputs differ between jaw-closing and jaw-opening MNs and between GABAergic and glycinergic currents. These distinct developmental characteristics may contribute to the development of feeding behaviors.

Postnatal Maturation of Glutamatergic Inputs onto Rat Jaw-closing and Jaw-opening Motoneurons.

Motoneurons that innervate the jaw-closing and jaw-opening muscles play a critical role in oro-facial behaviors, including mastication, suckling, and swallowing. These motoneurons can alter their physiological properties through the postnatal period during which feeding behavior shifts from suckling to mastication; however, the functional synaptic properties of developmental changes in these neurons remain unknown. Thus, we explored the postnatal changes in glutamatergic synaptic transmission onto the motoneurons that innervate the jaw-closing and jaw-opening musculatures during early postnatal development in rats. We measured miniature excitatory postsynaptic currents (mEPSCs) mediated by non-NMDA receptors (non-NMDA mEPSCs) and NMDA receptors in the masseter and digastric motoneurons. The amplitude, frequency, and rise time of non-NMDA mEPSCs remained unchanged among postnatal day (P)2-5, P9-12, and P14-17 age groups in masseter motoneurons, whereas the decay time dramatically decreased with age. The properties of the NMDA mEPSCs were more predominant at P2-5 masseter motoneurons, followed by reduction as neurons matured. The decay time of NMDA mEPSCs of masseter motoneurons also shortened remarkably across development. Furthermore, the proportion of NMDA/non-NMDA EPSCs induced in response to the electrical stimulation of the supratrigeminal region was quite high in P2-5 masseter motoneurons, and then decreased toward P14-17. In contrast to masseter motoneurons, digastric motoneurons showed unchanged properties in non-NMDA and NMDA EPSCs throughout postnatal development. Our results suggest that the developmental patterns of non-NMDA and NMDA receptor-mediated inputs vary among jaw-closing and jaw-opening motoneurons, possibly related to distinct roles of respective motoneurons in postnatal development of feeding behavior.

Intrinsic properties and synaptic connectivity of Phox2b-expressing neurons in rat rostral parvocellular reticular formation.

The paired-like homeobox 2b gene (Phox2b) is critical for the development of the autonomic nervous system. We have previously demonstrated the distinct characteristics of Phox2b-expressing (Phox2b+) neurons in the reticular formation dorsal to the trigeminal motor nucleus (RdV), which are likely related to jaw movement regulation. In this study, we focused on Phox2b+ neurons in the rostral parvocellular reticular formation (rPCRt), a critical region for controlling orofacial functions, using 2-11-day-old Phox2b-EYFP rats. Most Phox2b+ rPCRt neurons were glutamatergic, but not GABAergic or glycinergic. Approximately 65 % of Phox2b+ rPCRt neurons fired at a low frequency, and approximately 24 % of Phox2b+ rPCRt neurons fired spontaneously, as opposed to Phox2b+ RdV neurons. Stimulation of the RdV evoked inward postsynaptic currents in more than 50 % of Phox2b+ rPCRt neurons, while only one Phox2b+ rPCRt neuron responded to stimulation of the nucleus of the solitary tract. Five of the 10 Phox2b+ neurons sent their axons that ramified within the trigeminal motor nucleus (MoV). Of these, the axons of the two neurons terminated within both the MoV and rPCRt. Our findings suggest that Phox2b+ rPCRt neurons have distinct electrophysiological and synaptic properties that may be involved in the motor control of feeding behavior.

Bone morphogenetic protein 2 enhances mouse osteoclast differentiation via increased levels of receptor activator of NF-κB ligand expression in osteoblasts.

1α,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] induces osteoclast formation via induction of receptor activator of NF-κB ligand (RANKL, also called TNF-related activation-induced cytokine: TRANCE) in osteoblasts. In cocultures of mouse bone marrow cells and osteoblasts, 1,25(OH)(2)D(3) induced osteoclast formation in a dose-dependent manner, with maximum osteoclast formation observed at concentrations greater than 10(-9) M of 1,25(OH)(2)D(3). In the presence of bone morphogenetic protein 2 (BMP-2), the maximum formation of osteoclasts was seen with lower concentrations of 1,25(OH)(2)D(3) (greater than 10(-11) M), suggesting that BMP-2 enhances osteoclast formation induced by 1,25(OH)(2)D(3). In addition, the expressions of RANKL mRNA and proteins were induced by 1,25(OH)(2)D(3) in osteoblasts, and further upregulated by BMP-2. In mouse bone marrow cell cultures without 1,25(OH)(2)D(3), BMP-2 did not enhance osteoclast differentiation induced by recombinant RANKL and macrophage colony-stimulating factor (M-CSF), indicating that BMP-2 does not target osteoclast precursors. Furthermore, BMP-2 up-regulated the expression level of vitamin D receptor (VDR) in osteoblasts. These results suggest that BMP-2 regulates mouse osteoclast differentiation via upregulation of RANKL in osteoblasts induced by 1,25(OH)(2)D(3).

Case of polyhydramnios complicated by Opitz G/BBB syndrome.

Opitz G/BBB syndrome is a congenital disorder characterized by midline defects, such as hypertelorism, cleft lip and/or palate, hypospadias, and by dysphagia often caused by laryngo-tracheo-esophageal abnormalities. We experienced a case of polyhydramnios in a male dichorionic diamniotic (DD) twin, who was diagnosed with Opitz G/BBB syndrome after birth. It is suggested that severe dysphagia was causatively associated with the development of polyhydramnios. In cases of Opitz G/BBB syndrome, boys are usually more heavily affected than girls, who generally manifest only hypertelorism. In the differential diagnosis of polyhydramnios of unidentified cause in male fetuses, it may be helpful to consider maternal facial characteristics, especially hypertelorism.

Responses evoked by electrical stimulation of the brainstem reticular formation in the jaw-opening and hypoglossal motor nerves of an arterially perfused rat preparation.

The interneuronal system in the brainstem reticular formation plays an important role in elaborate muscle coordination during various orofacial motor behaviors. In this study, we examined the distribution in the brainstem reticular formation of the sites that induce monosynaptic motor activity in the mylohyoid (jaw-opening) and hypoglossal nerves using an arterially perfused rat preparation. Electrical stimulation applied to 286 and 247 of the 309 sites in the brainstem evoked neural activity in the mylohyoid and hypoglossal nerves, respectively. The mean latency of the first component in the mylohyoid nerve response was significantly shorter than that in the hypoglossal nerve response. Moreover, the latency histogram of the first component in the hypoglossal nerve responses was bimodal, which was separated by 4.0 ms. The sites that induced short-latency (<4.0 ms) motor activity in the mylohyoid nerve and the hypoglossal nerve were frequently distributed in the rostral portion and the caudal portion of the brainstem reticular formation, respectively. Such difference in distributions of short-latency sites for mylohyoid and hypoglossal nerve responses likely corresponds to the distribution of excitatory premotor neurons targeting mylohyoid and hypoglossal motoneurons.

Enhancement of swallowing motor activity by the ACE inhibitor imidapril in an arterially perfused rat preparation.

Pharmacological agents that elevate dopamine and substance P concentrations have been suggested to prevent aspiration pneumonia and improve impaired swallowing processes. However, little is known about the effects of such agents on swallowing activities induced in motor nerves innervating the pharyngeal and laryngeal muscles. In this study, we examined the effects of imidapril, cilostazol, and amantadine, which are often prescribed for swallowing disorders, on swallowing motor activity. We recorded the efferent activities of the cervical vagal nerve, hypoglossal nerve, and phrenic nerve using arterially perfused rats aged between 21-35 postnatal days. The vagal nerve activity was used for evaluation of swallowing motor activity. When 1.25 ml of distilled water was injected into the oral cavity, or the superior laryngeal nerve was electrically stimulated, synchronized swallowing bursts were evoked in the vagal and hypoglossal nerves, while inspiratory discharges were inhibited in all the recorded nerves. Administration of imidapril (60 ng/ml) but not cilostazol (2.5 µg/ml) and amantadine (200 ng/ml) to the perfusate increased the mean peak amplitude of orally evoked swallowing bursts in the vagal nerve. Such increase in the peak amplitude by imidapril was antagonized by the administration of the NK1 receptor antagonist aprepitant (5 µg/ml) or the D1 receptor antagonist LE300 (2.5 µg/ml). In contrast, neither imidapril nor cilostazol caused a significant increase in swallowing bursts evoked by electrical stimulation of the superior laryngeal nerve. These results suggest that imidapril treatment may improve impaired swallowing by enhancing pharyngeal muscle activities via an increase in substance P and dopamine concentrations.

Serotonin1B receptor-mediated presynaptic inhibition of proprioceptive sensory inputs to jaw-closing motoneurons.

The proprioceptive sensory inputs from neurons in the mesencephalic trigeminal nucleus (MesV) to masseter motoneurons (MMNs) play an important role in regulating masseter muscle activity during mastication. Several histological studies have shown that serotonin (5-HT) fibers densely innervate both the MesV and the trigeminal motor nucleus. However, the functional roles of 5-HT in the regulation of the excitatory synaptic inputs from MesV afferents to MMNs remain to be clarified. Thus, using the whole-cell recording technique in brainstem slice preparations from juvenile Wistar rats aged between postnatal days 8 and 12, we examined the effects of 5-HT on the excitatory synaptic inputs from MesV afferents to MMNs. Bath application of 5-HT reduced the peak amplitude of excitatory postsynaptic potentials evoked in MMNs by electrical stimulation of the MesV afferents (eEPSPs), and this inhibitory effect of 5-HT on eEPSPs was replicated with the 5-HT1B receptor agonist CP-93129 but not by the 5-HT1A receptor agonist 8-OH-DPAT. Moreover, the 5-HT1B receptor antagonist SB-224289 but not the 5-HT1A receptor antagonist WAY-100635 antagonized the inhibitory effect of 5-HT on eEPSPs. CP-93129 increased the paired-pulse ratio and decreased the frequency of miniature excitatory postsynaptic currents (mEPSCs), while it did not alter the mEPSC amplitude. These results suggest that presynaptic 5-HT1B receptors are involved in the inhibition of the excitatory synaptic inputs from MesV afferents to MMNs. Such inhibition may regulate MesV afferent activity during mastication.

Nanomechanical characterization of time-dependent deformation/recovery on human dentin caused by radiation-induced glycation.

An increase in non-enzymatic collagen matrix cross-links, such as advanced glycation end-products (AGEs), is known to be a major complication in human mineralized tissues, often causing abnormal fractures. However, degradation of mechanical properties in relation to AGEs has not been fully elucidated at the material level. Here, we report nanoscale time-dependent deformation and dimensional recovery of human tooth dentin that has undergone glycation induced by x-ray irradiation. The reduction in enzymatic collagen cross-linking and the increased level of AGEs with concomitant growth of disordered collagen matrix diminished creep deformation recovery in the lower mineralized target region. However, the elevated AGEs level alone did not cause a reduction in time-dependent deformation and its recovery in the higher mineralized target region. In addition to the elevated AGEs level, the degradation of the mechanical properties of mineralized tissues should be assessed with care in respect to multiple parameters in the collagen matrix at the molecular level.