The Effects of Mutual Interaction of Orexin-A and Glucagon-Like Peptide-1 on Reflex Swallowing Induced by SLN Afferents in Rats

(1) Background: Our previous studies revealed that orexin-A, an appetite-increasing peptide, suppressed reflex swallowing via the commissural part of the nucleus tractus solitarius (cNTS), and that glucagon-like peptide-1 (GLP-1), an appetite-reducing peptide, also suppressed reflex swallowing via the medial nucleus of the NTS (mNTS). In this study, we examined the mutual interaction between orexin-A and GLP-1 in reflex swallowing. (2) Methods: Sprague–Dawley rats under urethane–chloralose anesthesia were used. Swallowing was induced by electrical stimulation of the superior laryngeal nerve (SLN) and was identified by the electromyographic (EMG) signals obtained from the mylohyoid muscle. (3) Results: The injection of GLP-1 (20 pmol) into the mNTS reduced the swallowing frequency and extended the latency of the first swallow. These suppressive effects of GLP-1 were not observed after the fourth ventricular administration of orexin-A. After the injection of an orexin-1 receptor antagonist (SB334867) into the cNTS, an ineffective dose of GLP-1 (6 pmol) into the mNTS suppressed reflex swallowing. Similarly, the suppressive effects of orexin-A (1 nmol) were not observed after the injection of GLP-1 (6 pmol) into the mNTS. After the administration of a GLP-1 receptor antagonist (exendin-4(5-39)), an ineffective dose of orexin-A (0.3 nmol) suppressed reflex swallowing. (4) Conclusions: The presence of reciprocal inhibitory connections between GLP-1 receptive neurons and orexin-A receptive neurons in the NTS was strongly suggested.

P4412Association of sleep duration with cardio-metabolic risk leading to development of atherosclerotic cardiovascular disease

Background

Sleep duration, mostly of short duration, has emerged as a potential factor in adverse cardio-metabolic risk. We investigated the relationship between sleep duration and cardio-metabolic risk leading to atherosclerotic cardiovascular disease (ASCVD).

Purpose

We examined the association between sleep duration and cardio-metabolic risk in Japanese men.

Methods

This cross-sectional study was conducted using a sample of 6,907 apparent healthy men who had undergone medical examinations at the Health Planning Center of Nihon University Hospital between April, 2015 and May, 2016. The relationship between waist circumference, homeostasis model assessment of insulin resistance (HOMA-IR), HbA1c, non-high-density lipoprotein cholesterol (non-HDL-C) level, and sleep duration was evaluated.

Results

Both unusually short and long sleep durations were associated with waist circumference, impaired glucose tolerance and high non-HDL-C level (Figure). Compared with men sleeping 7 to 8 hours, the relative risk of abdominal obesity (defined according to the Japanese criteria for metabolic syndrome as a waist circumference of 85cm≥) among men sleeping ≥8 h was 1.27 (95% Confidence interval (CI), 1.05–1.55, p<0.01); the relative risk of a high HOMA-IR (2.0≥) level among men sleeping <5 h was 1.43 (95% CI, 1.00–2.05, p<0.05); among men sleeping ≥8 h the relative risk was 1.38 (95% CI, 1.08–1.77, p=0.01); the relative risk of a HbA1c level of ≥5.6% (defined as “high” by a specialized life style checkup program for the detection of symptoms of metabolic syndrome in Japan) among men sleeping <5 h was 1.39 (95% CI, 1.01–1.65, p<0.05); the relative risk of a non-HDL-C level of ≥170 mg/dL (defined as “high” by the Japanese Arteriosclerosis Society based on a lipid control target value for the primary prevention of ASCVD) among men sleeping ≥8 was 1.40 (95% CI, 1.13–1.76, p<0.01). These analyses were adjusted for age, psychological stress, and the use of cholesterol-lowering, blood-pressure lowering, and anti-diabetic medications.

Conclusion

The results suggest that unusually short and long sleep durations may increase cardio-metabolic risk. To further reduce the risk of ASCVD, it may be of particular importance to emphasize adequate sleep duration.

Effects of cevimeline on excitability of parasympathetic preganglionic neurons in the superior salivatory nucleus of rats

The superior salivatory nucleus (SSN) contains parasympathetic preganglionic neurons innervating the submandibular and sublingual salivary glands. Cevimeline, a muscarinic acetylcholine receptor (mAChR) agonist, is a sialogogue that possibly stimulates SSN neurons in addition to the salivary glands themselves because it can cross the blood-brain barrier (BBB). In the present study, we examined immunoreactivities for mAChR subtypes in SSN neurons retrogradely labeled with a fluorescent tracer in neonatal rats. Additionally, we examined the effects of cevimeline in labeled SSN neurons of brainstem slices using a whole-cell patch-clamp technique. Mainly M1 and M3 receptors were detected by immunohistochemical staining, with low-level detection of M4 and M5 receptors and absence of M2 receptors. Most (110 of 129) SSN neurons exhibited excitatory responses to application of cevimeline. In responding neurons, voltage-clamp recordings showed that 84% (101/120) of the neurons exhibited inward currents. In the neurons displaying inward currents, the effects of the mAChR antagonists were examined. A mixture of M1 and M3 receptor antagonists most effectively reduced the peak amplitude of inward currents, suggesting that the excitatory effects of cevimeline on SSN neurons were mainly mediated by M1 and M3 receptors. Current-clamp recordings showed that application of cevimeline induced membrane depolarization (9/9 neurons). These results suggest that most SSN neurons are excited by cevimeline via M1 and M3 muscarinic receptors.

Role of the lateral hypothalamus in submandibular salivary secretion during feeding in rats

To evaluate the role of the lateral hypothalamic area (LH) in the masticatory-salivary reflex, we investigated submandibular salivary secretion and the electromyographic (EMG) activity of the jaw-closer masseter muscle in sham-operated rats and rats with unilateral LH lesions. One week prior to surgery and recording, the rats were given daily experience of eating pellets; powder; or hard, medium or soft mash, all of which were composed of laboratory chow. Salivary secretion was induced during eating and grooming behavior. During eating, the powdered food induced the highest salivary flow rate, and the soft (wet) mash induced the lowest salivary flow rate. Conversely, the amount of food consumed (dry weight) was greatest when soft mash was provided and lowest when the powder or pellets (a dry diet) were provided. The EMG activity of the masseter muscle during eating was greatest during consumption of the pellets and weakest during consumption of the powder. LH lesions that were ipsilateral to the examined submandibular gland reduced salivary secretion to about 20-30% of the control value, whereas contralateral LH lesions reduced it to about 40-50% of the control value. Neither masseter muscle EMG activity nor food consumption was markedly affected by the presence of an LH lesion. These results suggest that the texture of food, especially its water content, affects the flow rate of saliva and that the LH is heavily involved in the masticatory-salivary reflex.

Development and external validation of a nomogram for overall survival after curative resection in serosa-negative, locally advanced gastric cancer

BACKGROUND

Few nomograms can predict overall survival (OS) after curative resection of advanced gastric cancer (AGC), and these nomograms were developed using data from only a few large centers over a long time period. The aim of this study was to develop and externally validate an elaborative nomogram that predicts 5-year OS after curative resection for serosa-negative, locally AGC using a large amount of data from multiple centers in Japan over a short time period (2001-2003).

PATIENTS AND METHODS

Of 39 859 patients who underwent surgery for gastric cancer between 2001 and 2003 at multiple centers in Japan, we retrospectively analyzed 5196 patients with serosa-negative AGC who underwent Resection A according to the 13th Japanese Classification of Gastric Carcinoma. The data of 3085 patients who underwent surgery from 2001 to 2002 were used as a training set for the construction of a nomogram and Web software. The data of 2111 patients who underwent surgery in 2003 were used as an external validation set.

RESULTS

Age at operation, gender, tumor size and location, macroscopic type, histological type, depth of invasion, number of positive and examined lymph nodes, and lymphovascular invasion, but not the extent of lymphadenectomy, were associated with OS. Discrimination of the developed nomogram was superior to that of the TNM classification (concordance indices of 0.68 versus 0.61; P < 0.001). Moreover, calibration was accurate.

CONCLUSIONS

We have developed and externally validated an elaborative nomogram that predicts the 5-year OS of postoperative serosa-negative AGC. This nomogram would be helpful in the assessment of individual risks and in the consideration of additional therapy in clinical practice, and we have created freely available Web software to more easily and quickly predict OS and to draw a survival curve for these purposes.

Differential involvement of two cortical masticatory areas in submandibular salivary secretion in rats

To evaluate the role of the masticatory area in the cerebral cortex in the masticatory-salivary reflex, we investigated submandibular salivary secretion, jaw-movement trajectory and electromyographic activity of the jaw-opener (digastric) and jaw-closer (masseter) muscles evoked by repetitive electrical stimulation of the cortical masticatory area in anesthetized rats. Rats have two cortical masticatory areas: the anterior area (A-area) in the orofacial motor cortex, and the posterior area (P-area) in the insular cortex. Our defined P-area extended more caudally than the previous reported one. P-area stimulation induced vigorous salivary secretion (about 20 µl/min) and rhythmical jaw movements (3-4 Hz) resembling masticatory movements. Salivary flow persisted even after minimizing jaw movements by curarization. A-area stimulation induced small and fast rhythmical jaw movements (6-8 Hz) resembling licking of solutions, but not salivary secretion. These findings suggest that P-area controls salivary secretion as well as mastication, and may be involved in the masticatory-salivary reflex.

Analysis of DNA endoreplication in the brain neurons in the terrestrial slug, Limax valentianus

DNA endoreplication is the DNA synthesis without cell division, resulting in the generation of a nucleus containing a larger amount of genomic DNA compared to a normal diploid genome. There are many such giant neurons in the molluscan brain that are generated as a result of repeated endoreplication. However, it has been controversial whether the endoreplication is the whole genome replication (polyploidy) or the local amplification of the genes that are necessary for the neuron's function (polyteny/polysomy). Here in this study, we investigated these two possibilities by (1) immunohistochemical analysis of the distribution of 5'-bromodeoxyuridine incorporated into the nuclei of the brain neurons, and by (2) quantitative genomic PCR directed to two different genes expressed in specific brain regions. Our data supported the view that the DNA endoreplication is the whole genome replication rather than the local amplification of a specific genomic region.

Fourth ventricular administration of ghrelin induces relaxation of the proximal stomach in the rat

The effects of fourth ventricular administration of ghrelin on motility of the proximal stomach were examined in anesthetized rats. Intragastric pressure (IGP) was measured using a balloon situated in the proximal part of the stomach. Administration of ghrelin into the fourth ventricle induced relaxation of the proximal stomach in a dose-dependent manner. Significant reduction of IGP was observed at doses of 3, 10, or 30 pmol. The administration of ghrelin (10 or 30 pmol) with growth hormone secretagogue receptor (GHS-R) antagonist ([d-Lys3] GHRP-6; 1 nmol) into the fourth ventricle did not induce a significant change in IGP. The sole administration of [d-Lys3] GHRP-6 also did not induce a significant change in IGP. Bilateral sectioning of the vagi at the cervical level abolished the relaxation induced by the administration of ghrelin (10 or 30 pmol) into the fourth ventricle, suggesting that relaxation induced by ghrelin is mediated by vagal preganglionic neurons. Microinjections of ghrelin (200 fmol) into the caudal part of the dorsal vagal complex (DVC) induced obvious relaxation of the proximal stomach. Similar injections into the intermediate part of the DVC did not induce significant change. Dose-response analyses revealed that the microinjection of 2 fmol of ghrelin into the caudal DVC significantly reduced IGP. These results revealed that ghrelin induced relaxation in the proximal stomach via GHS-R situated in the caudal DVC.

Immunohistochemical study on the distribution and origin of GABAergic nerve terminals in the superior salivatory nucleus

The superior salivatory nucleus (SSN) is the primary parasympathetic center controlling submandibular salivatory secretion. Our previous electrophysiological study revealed that many SSN neurons receive GABAergic and glycinergic synaptic inputs. In the present study, we examined the distribution of GABAergic and glycinergic nerve terminals, GABA(A) receptors in the SSN, and the origin of GABAergic nerve terminals innervating the SSN. Glutamic acid decarboxylase (GAD) and glycine transporter 2 (GLYT2) were used as markers of GABAergic and glycinergic nerve terminals, respectively. GAD- and GLYT2-positive nerve terminals and GABA(A) receptors were examined immunohistochemically in SSN neurons labeled by the retrograde axonal transport of FastBlue (FB) injected into the chorda-lingual nerve. The SSN neurons abundantly contained GAD-positive nerve terminals and GABA(A) receptors, suggesting that SSN neurons undergo strong GABAergic inhibition. The origin of GABAergic terminals was examined in neurons labeled by the retrograde transport of FluoroGold (FG) injected into the SSN. GAD was used as a marker of GABAergic neurons. Numerous FG-labeled neurons were found in the forebrain and brainstem. However, in FG-labeled neurons, GAD-positive neurons were occasionally observed in the reticular formation of the brainstem. These findings suggest that SSN neurons mainly receive GABAergic projections from the reticular formation.

Postnatal development of inhibitory synaptic transmission to superior salivatory neurons in rats

The primary parasympathetic center of the submandibular and sublingual salivary glands is the superior salivatory (SS) nucleus, and its neurons receive excitatory (glutamatergic) and inhibitory (GABAergic and glycinergic) synaptic transmissions in rats. In the present study, we focused on the postnatal development of inhibitory transmission to SS neurons. Gramicidin-perforated whole-cell patch-clamp recordings were performed in rat brainstem slices on postnatal day 2 (P2)-P14. Developmental changes in the intracellular Cl(-) concentration ([Cl(-)](in)) were examined based on the reversal potentials of total inhibitory postsynaptic currents (GABAergic plus glycinergic), which were evoked by electrical stimulation near the recording neuron. The [Cl(-)](in) in the P8-P14 group was significantly lower than in the P2-P7 group. The effect of GABA application at the resting potentials changed from depolarization to hyperpolarization around P8, suggesting that SS neurons acquired mature inhibitory systems around P8. The period at which GABA responses change from excitatory to inhibitory in SS neurons was discussed compared with those of the forebrain, brainstem, and spinal neurons.

Recovery of learning ability after the ablation of the procerebrum in the terrestrial slug, Limax valentianus

The procerebrum (PC) is indispensable for odor-aversion learning in Limax. On the other hand, the central nervous system (CNS) of some Pulmonata shows robustness against injury, recovering from nerve injury both at the histological and functional levels. To investigate whether the PC of Limax also shows robustness against nerve injury, we tested whether or not the slugs can acquire and retrieve odor-aversion memory after a long recovery period from PC ablation. When the recovery period is short (7 days), the PC-ablated slugs failed to avoid the conditioned odor. But when the recovery period is long (1 month), the PC-ablated slugs successfully avoided the conditioned odor. These results indicate that the CNS including the PC can recover from injury at least at the functional level.

Isotopic dependence of the giant monopole resonance in the even-A 112-124Sn isotopes and the asymmetry term in nuclear incompressibility

The strength distributions of the giant monopole resonance (GMR) have been measured in the even-A Sn isotopes (A=112-124) with inelastic scattering of 400-MeV alpha particles in the angular range 0 degrees -8.5 degrees . We find that the experimentally observed GMR energies of the Sn isotopes are lower than the values predicted by theoretical calculations that reproduce the GMR energies in 208Pb and 90Zr very well. From the GMR data, a value of Ktau = -550 +/- 100 MeV is obtained for the asymmetry term in the nuclear incompressibility.

Salivary secretion, taste and hyposalivation

Saliva has many essential functions. As the first digestive fluid in the alimentary canal, saliva is secreted in response to food, assisting intake and initiating the digestion of starch and lipids. During this process, saliva acts as a solvent of taste substances and affects taste sensitivity. Clinically, a more important role is in the maintenance of oral health, including the protection of teeth and mucosa from infections, maintenance of the milieu of taste receptors, and communication ability through speech. Variations in salivary flow can be affected, reversibly or irreversibly, by numerous physiological and pathological factors. Decreased salivary flow results in clinically significant oral discomfort that may manifest as increased caries, susceptibility to oral candidiasis, altered taste sensation or as a host of other problems. Hyposalivation is a condition that is frequently encountered in dental practice. The most common cause is the use of certain systemic medications, which put the elderly at greater risk because they are usually more medicated. Other causes include high doses of radiation and certain diseases such as Sjögren's syndrome. This article reviews the mechanism of salivary secretion, effect of saliva on taste, importance of saliva in oral health, and hyposalivation in relation to ageing, medicine and/or disease and management of hyposalivation.

Purinergic modulation of area postrema neuronal excitability in rat brain slices

ATP has been shown to excite neurons in various regions of the central nervous system. Whereas immunohistochemical studies show P2X receptors in the area postrema, the responsiveness of area postrema neurons to extracellular ATP has not been studied. To investigate the effects of purinoceptor activation on area postrema neuronal excitability, we performed whole-cell recordings from area postrema neurons in rat brain slices. Most area postrema neurons responded to ATP application, and most responses were excitatory. Voltage-clamp recordings showed three different types of response: (1) a postsynaptic or extrasynaptic excitatory response (inward currents; n=26/51 cells), (2) a presynaptic excitatory response (increased frequency of miniature excitatory postsynaptic currents with only a small direct postsynaptic current; n=24/51 cells, or (3) a postsynaptic inhibitory response (outward current; n=1/51). The excitatory responses were found in both of the two major electrophysiological cell classes, i.e. cells displaying I(h) and cells not displaying I(h), while the inhibitory responses were found in only cells not displaying I(h). Current-clamp recordings showed ATP-induced depolarization (n=13/15) or hyperpolarization (n=2/15) of membrane potential that modulated the frequency of action potentials. In the presence of CNQX, mEPSCs were abolished and bath-applied ATP did not generate mEPSCs, indicating that glutamate release was facilitated by the activation of presynaptically located ATP receptors. Our pharmacological results from studies with ATP, alphabetame-ATP, betame-ATP and PPADS indicate that the post- and/or extrasynaptic responses are most likely mediated by P2X(7) receptors and/or receptors composed of P2X(2) and P2X(5) subunits. We conclude that half of the presynaptic responses are most likely mediated by P2X(7) receptors and/or receptors composed of P2X(2) and P2X(5) subunits while the others also contain P2X(1) subunits. It is well known that P2X(7) subunit forms only homomultimeric P2X receptors. Finally, the present study suggests that purinoceptor activation may contribute to the control of several autonomic functions by area postrema neurons.

Variety of morphological and electrophysiological properties of area postrema neurons in adult rat brain slices

Whole-cell recordings were performed to examine the morphological properties of electrophysiologically classified area postrema (AP) neurons in rat brain slices. Using electrophysiological criteria, AP neurons were subdivided into three groups: (1) cells displaying both the hyperpolarization-activated cation current (I(h)) and the fast transient outward current (fast I(to)); (2) cells displaying only the fast I(to); (3) cells displaying only the slow I(to). All AP neurons had a single axon that was distinctly thinner than the cells' dendrites. No systematic differences, across groups, in the orientation of dendrites or axons were identified. Mean values of cell size and capacitance of neurons from group 3 were significantly larger than those of the other groups. Interestingly, a number of cells from groups 1 and 3 but not group 2 were found to extend their dendrites into the nucleus tractus solitarius (NTS), suggesting that AP neurons could receive vagal afferent inputs at their dendritic termini within the NTS. Although the AP has been implicated to contain uniformly shaped neurons, this study indicates the presence of significantly different subpopulations of AP neurons, which were characterized not only electrophysiologically but also morphologically.

Peripheral N-methyl-D-aspartate receptors modulate nonadrenergic noncholinergic lower esophageal sphincter relaxation in rabbits

We investigated the role of peripheral N-methyl-D-aspartate (NMDA) receptors in the myenteric plexus in mediating nonadrenergic noncholinergic (NANC) nitrergic relaxation of the lower esophageal sphincter (LES). Isometric contraction of LES strips from Japanese White rabbits was measured. NANC relaxation was induced by KCl (30 mM) in the presence of atropine and guanethidine. The concentration of 3',5'-cyclic guanosine monophosphate (cGMP) was measured using a radioimmunoassay. The muscle strips were exposed to diethyldithiocarbamic acid (DETCA; 3 mM) to inactivate Cu/Zn superoxide dismutase. MK801 (5-methyl-10,11-dihydroxy-5H-dibenzo(a,d)cyclohepten-5,10-imine) inhibited NANC relaxation in a concentration-dependent manner (EC50 = 1.5 x 10(-5) M), accompanied by a decrease in cGMP production. NMDA induced a concentration-dependent relaxation, which was antagonized by MK801. NMDA stimulated cGMP production, which was inhibited by N(G)-nitro-L-arginine. Superoxide dismutase (100 U/mL) shifted the concentration-response relationship of MK801-mediated inhibition of NANC relaxation to the right (EC50 = 3.4 x 10(-5) M), whereas catalase did not. Treatment with DETCA shifted the concentration-response relationships of pyrogallol-, ketamine- and MK801-mediated inhibition of NANC relaxation to the left. These findings suggest that the peripheral NMDA receptors mediate NANC smooth muscle relaxation, and modulate it, in part, through extracellular production of superoxide anions, thus eliminating the relaxant effect of endogenous nitric oxide.

Central neuropeptide Y induces proximal stomach relaxation via Y1 receptors in the dorsal vagal complex of the rat

Effects of neuropeptide Y (NPY) on motility of the proximal stomach was examined in anesthetized rats. Intragastric pressure was measured using a balloon situated in the proximal part of the stomach. Administration of NPY into the fourth ventricle induced relaxation of the proximal stomach in a dose-dependent manner. Administration of an Y1 receptor (Y1R) agonist [Leu31, Pro34]NPY induced a larger relaxation than NPY. The administration of an Y2 receptor agonist (NPY 13-36) did not induce significant changes in motility. Microinjections of [Leu31, Pro34]NPY into the caudal part of the dorsal vagal complex (DVC) induced relaxation of the proximal stomach. In contrast, similar injections into the intermediate part of the DVC increased IGP of the proximal stomach. Administration of NPY into the fourth ventricle did not induce relaxation after bilateral injections of the Y1R antagonist (1229U91) into the caudal DVC. These results indicate that NPY induces relaxation in the proximal stomach via Y1Rs situated in the DVC. Because bilateral vagotomy below the diaphragm abolished the relaxation induced by the administration of NPY into the fourth ventricle, relaxation induced by NPY is probably mediated by vagal preganglionic neurons. Intravenous injection of atropine methyl nitrate reduced relaxation induced by administration of NPY. Therefore, relaxation induced by NPY is likely mediated by peripheral cholinergic neurons.

The origin of sensory nerve fibers that innervate the submandibular salivary gland in the rat

The origin of sensory nerves that innervate the submandibular salivary gland was investigated in the rat. After application of wheat germ agglutinin-horseradish peroxidase to the cut endings of the sympathetic and parasympathetic nerve branches at the hilus of the gland, labeled cells were mainly found in the dorsal root ganglia and the trigeminal ganglion, respectively. The labeled neurons in these ganglia were of various sizes compared to unlabeled neurons, suggesting that the sensory nerves of the gland conduct various modalities of sensory information.

The sensitivity of hyperpolarization-activated cation current (Ih) to propofol in rat area postrema neurons

Area postrema neurons mediate various autonomic responses, including emesis. We examined the effects of propofol, a widely used anesthetic with antiemetic properties, on the hyperpolarization-activated cation current (Ih) in rat area postrema neurons using a slice patch-clamp technique. Although propofol suppressed Ih of area postrema neurons in a dose-dependent manner that was similar to what we observed for the hippocampal CA1 neurons, the IC50 for Ih in area postrema neurons (38 microM) was more than six times less than that found for hippocampal CA1 neurons (235 microM). We conclude that rat area postrema neurons are exquisitely sensitive to propofol. Given that reductions of Ih are associated with decreased excitability in neurons, we believe that the known antiemetic effects of propofol anesthesia are at least partly a result of a direct action on area postrema neurons to lower their excitability.

Nicotinic modulation of area postrema neuronal excitability in rat brain slices

We investigated the functions of nicotinic receptor activation on area postrema neurons by making whole-cell recordings in rat brainstem slices. Excitatory responses to nicotine application were found in approximately 78% (35/45) of all cells tested. Responsive cells included both the cells that display the hyperpolarization-activated cation current (I(h)) and cells that do not display I(h). An inhibitory effect of nicotine was never seen. Current-clamp recordings showed the nicotine-induced depolarization of a cell's membrane potential that could be sufficient to cause spontaneous firing. In voltage-clamp recordings, many cells showed nicotine-induced inward currents (18.3+/-3.2 pA, n=6) that persisted during pharmacological blockade of synaptic transmission (e.g., zero [Ca(2+)](out) and 5 mM [Mg(2+)](out), n=6/8). Other two cells, however, showed increases in the frequency of excitatory postsynaptic currents (EPSCs), which were blocked by CNQX (n=2/8). We analyzed miniature EPSCs (mEPSCs) recorded from cells that showed no inward currents but marked increases in the frequency of mEPSCs (0.8+/-0.2 to 4.8+/-1.7 Hz, n=4) during nicotine application. Nicotine augmented mEPSC amplitude (n=4); however, amplitude distribution was not significantly changed in two of four cells tested. We conclude that nicotinic receptors in the rat area postrema can excite cells via (1) a direct post- and/or extrasynaptic mechanism; and (2) an indirect enhancement of glutamate release.

Excitatory and inhibitory postsynaptic currents of the superior salivatory nucleus innervating the salivary glands and tongue in the rat

The excitatory and inhibitory synaptic inputs to parasympathetic preganglionic neurons in the superior salivatory (SS) nucleus were investigated in brain slices of neonatal (4-8 days old) rat using the whole-cell patch-clamp technique. The SS neurons innervating the submandibular and sublingual salivary glands and innervating the lingual artery in the anterior region of the tongue were identified by retrograde transport of a fluorescent tracer. Whole-cell currents were evoked by electrical stimulation of tissue surrounding the cell. These evoked postsynaptic currents were completely abolished by antagonists for N-methyl-D-aspartate (NMDA) glutamate, non-NMDA glutamate, gamma-aminobutyric acid type A (GABAA), and glycine receptors, suggesting that SS neurons receive glutamatergic excitatory, and GABAergic and glycinergic inhibitory synaptic inputs. In SS neurons for the salivary glands, the ratio of the NMDA component to the total excitatory postsynaptic current (EPSC) was larger than that of the non-NMDA component. This profile was reversed in the SS neurons for the tongue. In SS neurons for the salivary glands, the ratio of the GABAA component to the total IPSC was larger than the ratio of the glycine component to total inhibitory postsynaptic current (IPSC). The decay time constants of the GABAA component were slower than those for glycine. These characteristics of the excitatory and inhibitory inputs may be involved in determining the firing properties of the SS neurons innervating the salivary glands and the tongue.

Activation of presynaptic 5-HT3 receptors facilitates glutamatergic synaptic inputs to area postrema neurons in rat brain slices

Whole-cell voltage-clamp recordings were performed to investigate the serotonergic modulation of neurotransmitter release onto rat area postrema neurons in vitro. The bath application of serotonin (5-HT; 50 microM) or phenylbiguanide (PBA; 50 microM), a potent 5-HT3 receptor agonist, increased the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) or miniature EPSCs (mEPSCs) in 35 of 83 neurons (42%). These increases occurred in all electrophysiological cell classes. No cells exhibited a decrease in EPSC frequency. The majority of responding cells showed no inward currents during the application of serotonergic agonists (n = 34/35). However, the amplitude of mEPSCs was increased in 11/11 cells with 5-HT or 3/11 cells with PBA. ICS-205,930, a potent 5-HT3 receptor antagonist, markedly suppressed the 5-HT-induced facilitation of sEPSCs (n = 5) or mEPSCs (n = 5). An increase in the frequency of mEPSCs after PBA exposure was found, even with media containing Cd2+ (50 microM) or zero Ca2+. mEPSCs and evoked EPSCs were completely blocked in media containing the non-NMDA ionotropic receptor antagonist, CNQX (10 microM), indicating that EPSCs were glutamate events. These results suggest that glutamate release is increased in the area postrema by presynaptic 5-HT3 receptor activation. Furthermore, we present evidence that 5-HT3 receptor activation may be able to directly release glutamate from terminals, bypassing a requirement for voltage-dependent calcium entry into terminals. Such a mechanism may contribute to the chemosensitive function of area postrema neurons.

Role of the hyperpolarization-activated cation current (Ih) in pacemaker activity in area postrema neurons of rat brain slices

To clarify the functional properties of the hyperpolarization-activated cation current (Ih) as a pacemaker current in area postrema neurons, whole-cell recordings were made in visually identified cells in rat brain slices. The activation of Ih was identified in approximately 62 % of area postrema neurons tested. The cells displaying Ih showed a depolarizing "sag" in responses to hyperpolarizing current injection in current-clamp mode. The reversal potential for the Ih was -36 mV, and this was shown to depend on the external concentration of Na+ and K+ ions. Extracellular Cs+ ions (2 mM) and ZD7288 (100 microM), a potent selective Ih channel antagonist, blocked Ih and induced a membrane potential hyperpolarization, suggesting the sustained activation of Ih near the resting potential and a contribution from Ih to membrane potential maintenance at more depolarized levels. In contrast, extracellular Ba2+ ions caused a depolarization of the membrane potential, suggesting the blockade of inward rectifier K+ currents. ZD7288 decreased the spontaneous discharge rate by prolonging the slow depolarization between two spikes, with minimal effect on the amplitude of the afterhyperpolarization or action potential waveforms. Ih stabilized the latency of rebound action potentials. Ih was weakly activated by external 8-bromoadenosine 3',5' cyclic monophosphate (1 mM) or forskolin (50-100 microM), indicating that the Ih channel subtypes in area postrema cells could be modulated by intracellular cAMP. Our findings indicate that Ih contributes to the subthreshold membrane and firing properties of rat area postrema neurons and may regulate their resting membrane potential and firing patterns.

Suppression of the hyperpolarization-activated inward current contributes to the inhibitory actions of propofol on rat CA1 and CA3 pyramidal neurons

Intracellular and field potential recordings were taken from the hippocampal CA1 and CA3 neurons in rat brain slices to investigate the effects of 2,6 di-isopropylphenol (propofol) on the neuronal excitability during GABA(A)-C1 channel blockade by picrotoxin (100 microM). Propofol produced a membrane hyperpolarization and an inhibition of the magnitude of the 'voltage sag' that was mediated by the activation of a hyperpolarization-activated inward current (I(H)). Propofol (>100 microM) decreased the spontaneous discharge rate of epileptiform burst responses in CA1 neurons up to 38+/-6% of the control level. Propofol also markedly reduced the duration of both spontaneous and evoked epileptiform burst responses. A propofol-induced decrease in the spontaneous discharge rate in CA3 neurons was coincident with that in CA1 neurons. The effects of propofol on the membrane potential and spontaneous discharge rate but not on the duration of burst responses were duplicated by ZD7288 (potent selective antagonist for I(H) channels), indicating that the blockade of I(H) significantly contributes to reduction of cell's excitability. The present study suggests that various actions including suppressive effects on I(H) contribute to the anesthetic and anti-convulsant properties of propofol.

Mexiletine inhibits nonadrenergic noncholinergic lower oesophageal sphincter relaxation in rabbits

Nonadrenergic noncholinergic (NANC) nerves are known to be nitrergic and to have an important role in the regulation of gastrointestinal motility and function. Cardiac antiarrhythmic therapy in humans is accompanied by a high incidence of gastrointestinal side-effects. We investigated the effect of mexiletine, a class Ib antiarrhythmic drug, on NANC lower oesophageal sphincter relaxation. Mexiletine concentration dependently inhibited the NANC relaxation induced by 30 mM KCl (EC(50)=4.4 x 10(-6) M); the production of 3',5'-cyclic guanosine monophosphate (cGMP) after KCl stimulation was concentration dependently decreased. The relaxation induced by the exogenous nitric oxide (NO) donor, diethylamine NONOate (10(-5) M), was not inhibited by mexiletine, and the cGMP production after diethylamine NONOate application was not altered. Mexiletine did not alter the activity of NO synthase. These findings suggest that mexiletine inhibits NANC relaxation via NO-cGMP pathway modulation, possibly by inhibiting myenteric nitrergic neurotransmission in the lower oesophageal sphincter in rabbits.

Ketamine and midazolam differentially inhibit nonadrenergic noncholinergic lower esophageal sphincter relaxation in rabbits: role of superoxide anion and nitric oxide synthase

BACKGROUND

The authors previously reported that ketamine and midazolam inhibited nitric oxide-mediated nonadrenergic noncholinergic (NANC) lower esophageal sphincter (LES) relaxation nitric oxide-3',5'-cyclic guanosine monophosphate pathway modulation. The mechanisms inhibiting the NANC relaxation by ketamine and midazolam were investigated.

METHODS

The isometric tension of circular distal esophageal muscle strips from Japanese White rabbits was examined. NANC relaxation was induced by KCl (30 mm) in the presence of atropine (3 x 10(-6) m) and guanethidine (3 x 10(-6) m). Nitric oxide synthase activity in the absence and presence of ketamine and midazolam was analyzed using the biochemical conversion of L-[3H]arginine to L-[3H]citrulline.

RESULTS

The ketamine-induced inhibition of the NANC relaxation was partly reversed by superoxide dismutase (200, 400 U/ml) but not by catalase (100 U/ml). Ketamine concentration-dependently inhibited the relaxation induced by N-ethylethanamine:1,1-diethyl-2-hydroxy-2-nitrosohydrazine (diethylamine NONOate) and S-nitrosoglutathione. The NANC relaxation itself was not affected by superoxide dismutase. The midazolam-induced inhibition of the NANC relaxation was reversed neither by superoxide dismutase nor by catalase, and midazolam did not affect the relaxations induced by nitric oxide donors. The nitric oxide synthase activity was concentration-dependently suppressed by midazolam, but there was no marked effect of ketamine. Pyrogallol, a superoxide generator, inhibited the NANC and the diethylamine NONOate-induced relaxations. The pyrogallol-induced inhibition of the NANC relaxation was reversed by superoxide dismutase.

CONCLUSION

These findings suggest that ketamine inhibits NANC LES relaxation by the extracellular production of superoxide anion, and that midazolam inhibits it by the inhibition of nitric oxide synthase activity.

Area postrema mediates gastric motor response induced by apomorphine in rats

The effects of apomorphine administration on the autonomic responses were investigated in rats. Distinctive gastric motor responses were observed after the intravenous administration of apomorphine (0.1 mg/kg body weight). Gastric motor responses in the distal stomach induced by apomorphine administration were classified into two types. One type involved inhibition of phasic contractions which appeared just after the administration of apomorphine. The other involved an increase in the frequency of small phasic contractions accompanied by increased gastric tone appearing with a relatively longer delay. No relaxation was observed in either the proximal or distal stomach. These gastric motor responses showed a dose-response effect to the amount of apomorphine administered (0.002-0.1 mg/kg body weight). In addition, submandibular salivary secretion was observed in response to the intravenous administration of apomorphine at a dose of 3 or 10 mg/kg body weight. Pretreatment with domperidone (1 or 2 mg/kg body weight) or the ablation of the area postrema (AP) abolished the gastric motor response and salivary secretion induced by the administration of apomorphine. In conclusion, rats showed definitive autonomic phenomena in response to the administration of apomorphine. Dopamine 2-like receptors situated in the AP mediate apomorphine-induced autonomic phenomena in rats.

Central orexin facilitates gastric relaxation and contractility in rats

The effects of the intracisternal administration of synthetic orexin-A (3 nmol) on gastric motility were examined in rats. The administration of orexin but not a vehicle induced relaxation of the proximal stomach lasting for more than 30 min. Phasic contractions in the distal stomach were facilitated in response to the administration of orexin but not a vehicle. Facilitation in the distal stomach was not observed in the animals which underwent the sectioning of the bilateral vagi at the subdiaphragmatic level. Relaxation of the proximal stomach was observed in vagotomized animals but the magnitude of relaxation was significantly smaller than that in intact animals. These results suggest that central orexin facilitates distal stomach motility and relaxation of the proximal stomach via vagi.

Electrophysiological properties of the rat area postrema neurons displaying both the transient outward current and the hyperpolarization-activated inward current

We found coexistence of the transient outward potassium current (I(TO)) and the hyperpolarization-activated inward current (I(H)) in 26 of 82 area postrema neurons tested using the whole-cell patch-clamp technique in rat brain slices. Cells displaying both the I(TO) and the I(H) typically showed "voltage sag" and "rebound potentials" in response to hyperpolarizing current injection and repetitive firing with strong adaptation was seen with depolarizing current injection. When cells were held at membrane potentials more negative than the resting level (e.g., -85mV), the afterhyperpolarization was enhanced. Voltage clamp recordings were performed to examine the characteristics of I(TO) and I(H) in and the contributions of these currents to the electroresponsiveness of area postrema cells. We show, in this study, the voltage-dependent properties of I(H) and I(TO), and how these currents modulate the intrinsic membrane properties of area postrema cells. We discuss the functional significance of the specific subset of area postrema neurons whose cells have both I(H) and I(TO) channels.

Two distinct types of transient outward currents in area postrema neurons in rat brain slices

We investigated the electrophysiological properties of the area postrema neurons in acutely prepared rat brain slices using the whole-cell patch-clamp technique. Two different types of transient outward potassium current (I(to)), fast and slow, were found in the area postrema. Both the decay time constant and rise time were significantly faster in the fast I(to) than in the slow I(to). Both current-clamp and voltage-clamp recordings revealed that the activation of fast and slow I(to) contributes to generation of the different spiking patterns, late spiking and interrupted spiking, respectively. The activation and inactivation of both I(to) were strongly voltage-dependent. Curve fitting by the Boltzmann equation revealed no significant difference in the activation and inactivation curves for each I(to) except that the slope factor of inactivation was larger for fast I(to). Both I(to) were suppressed dose-dependently by application of 4-aminopyridine. Each spiking pattern was enhanced when cells were held at a more hyperpolarized membrane potential, i.e. a longer latency of the first spike or longer interspike interval between the first and second spikes. The voltage-dependent modulation of the spiking pattern was consistent with the voltage-dependent activation of I(to). The present study shows significant subdivisions of the area postrema neurons distinguished by a difference in the kinetics of I(to) and spiking patterns. We discuss the role of I(to) as the ionic current underlying neuronal excitability.

Role of saliva in the maintenance of taste sensitivity

Saliva is the principal fluid component of the external environment of the taste receptor cells and, as such, could play a role in taste sensitivity. Its main role includes transport of taste substances to and protection of the taste receptor. In the initial process of taste perception, saliva acts as a solvent for taste substances; salivary water dissolves taste substances, and the latter diffuse to the taste receptor sites. During this process, some salivary constituents chemically interact with taste substances. For example, salivary buffers (e.g., bicarbonate ions) decrease the concentration of free hydrogen ions (sour taste), and there are some salivary proteins which may bind with bitter taste substances. Another effect of saliva on taste transduction is that some salivary constituents can continuously stimulate the taste receptor, resulting in an alteration of taste sensitivity. For example, the taste detection threshold for NaCl is slightly above the salivary sodium concentrations with which the taste receptor is continuously stimulated. In contrast, saliva protects the taste receptor from damage brought about by dryness and bacterial infection, and from disuse atrophy via a decrease in transport of taste stimuli to the receptor sites. This is a long-term effect of saliva that may be related to taste disorders. These various effects of saliva on the taste perception differ depending on the anatomical relationship between the taste buds and oral openings of the ducts of the salivary glands. Many taste buds are localized in the trenches of the foliate and circumvallate papillae, where the lingual minor salivary glands (von Ebner's glands) secrete saliva. Taste buds situated at the surface of the anterior part of the tongue and soft palate are bathed with the mixed saliva secreted mainly by the three major salivary glands.

Evidence for insulating behavior in the electric conduction of (NH(3))K(3)C(60) systems

Microwave study using the cavity perturbation technique revealed that the conductivity of the antiferromagnet (NH(3))K(3-x)Rb(x)C(60) at 200 K is already 3-4 orders of magnitude smaller than those of superconductors, K(3)C(60) and (NH(3))(x)NaRb(2)C(60), and that the antiferromagnetic compounds are insulators below 250 K without metal-insulator transitions. The striking difference in the magnitude of the conductivity between these materials strongly suggests that the Mott-Hubbard transition in the ammoniated alkali fullerides is driven by a reduction of lattice symmetry from face-centered-cubic to face-centered-orthorhombic, rather than by the magnetic ordering.