Increased depression-like behaviors with altered brain dopamine metabolisms in male mice housed in large cages are alleviated by bupropion

Psycho-environmental stress-based animal models of anxiety and depression are useful for investigating pathological mechanisms and drug development. Although several rodent-based studies have reported the beneficial effects of environmental enrichment (EE) on brain plasticity and anxiety- and depression-like behaviors, other studies have reported inverse effects. Here, we found that housing male mice in EE involving large cages and other EE materials increased anxiety- and depression-like behaviors in open field and tail suspension tests (TST). We further confirmed that housing in large cages was sufficient to induce increased depression-like behaviors in the TST and reduce the saccharine preference percentage, a sign of anhedonia, in male mice. In these experiments, the number of animals per cage was equivalent to that in standard cage housing, suggesting that low density in large cages may be a determining factor for behavioral alteration. In mice housed in large cages, sex-specific dysregulation of brain monoamine systems was observed; dopamine turnover to homovanillic acid or norepinephrine in the prefrontal cortex was elevated in males, while serotonin turnover to 5-hydroxyindoleacetic acid in the amygdala was increased in females. Finally, we demonstrated that daily intraperitoneal injections of bupropion, a dopamine and norepinephrine reuptake inhibitor, counteracted large-cage housing-induced changes in depression- and anhedonia-like behaviors in male mice. Our results suggest that housing in large cages with a low density of mice is a novel paradigm to clarify the mechanisms of environmental stress-induced emotional dysregulation and to identify drugs or food factors to alleviate the dysregulation.

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.

Unstable mutant lysozymes are degraded through the interaction with calnexin homolog Cne1p in Saccharomyces cerevisiae

Cne1p is a yeast homolog of calnexin, which is a constituent of endoplasmic reticulum (ER)-associated protein quality control system in mammals. Cne1p may be involved in the degradation of misfolded lysozymes in Saccharomyces cerevisiae. To test this, c-Myc-tagged lysozymes were expressed in CNE1-deficient S. cerevisiae. The expression and secretion of an unstable lysozyme mutant G49N/D66H were enhanced and its intracellular localization was changed in the CNE1-deficient strain. Furthermore, when Cne1p was co-expressed with unstable lysozyme mutants (G49N/D66H, G49N/C76A, and K13D/G49N), its affinity to the misfolded mutant proteins was revealed by co-immunoprecipitation. The interaction with Cne1p was abrogated by the addition of tunicamycin, an inhibitor of N-glycosylation, indicating that N-linked carbohydrates might be necessary for protein binding to Cne1p. These results suggest that in yeasts, Cne1p interacts with misfolded lysozyme proteins possibly causing their retention in the ER and subsequent elimination via ER-associated degradation.

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.

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.

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.

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 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.

LIRF, a gene induced during hippocampal long-term potentiation as an immediate-early gene, encodes a novel RING finger protein

We describe here an LTP-induced gene, LIRF, which encodes a novel protein with RING finger and B30.2 domains in its N- and C-terminal portions, respectively. Each domain is encoded by one exon, suggesting that the organization of the gene was generated by exon shuffling. The amino acid sequences of the mouse, rat, and human LIRF proteins are highly conserved and contain a putative PEST sequence. LIRF is an immediate-early gene in hippocampal granule cells, and its expression is upregulated immediately after the induction of long-lasting long-term potentiation at perforant pathway-dentate gyrus synapses and returns to the basal level within 150 min. A heterologously expressed LIRF protein fused to EGFP localizes specifically to the cytoplasm in COS-7 cells. These findings suggest a possible involvement of LIRF in a limited, early phase of synaptic plasticity.

Spontaneous regression of hepatocellular carcinoma--a case report

We report a 72-year-old man with hepatocellular carcinoma, which showed spontaneous regression. He was diagnosed as having chronic hepatitis type C five years before admission. In January 1998, a liver mass was found by ultrasonography. In February, computed tomography showed a low-density mass, 3.5 cm in diameter in the S5 region. Although liver biopsy was not performed, findings obtained by computed tomography and ultrasonography indicated that the tumor was hepatocellular carcinoma. The levels of alpha-fetoprotein and PIVKA (protein induced by vitamin K antagonist)-II were increased to 1000 ng/mL and 2000 mAU/mL, respectively. The patient was admitted to our hospital in March 1998. At the time, the size of liver mass was reduced to 2.5 cm in diameter on computed tomography, and the tumor markers, alpha-fetoprotein and PIVKA-II, spontaneously decreased to the normal range. We considered that hepatocellular carcinoma of this patient regressed spontaneously. Because it was hard to exclude the possibility that the mass contained residual malignant cells, we resected the mass on April 28, 1998. Microscopically, the resected mass did not contain any malignant cells. The parenchyma surrounding tumor necrosis, which is reflected by severe inflammatory infiltration with lymphocytes, indicates spontaneous regression. Although the precise mechanism regarding spontaneous regression of hepatocellular carcinoma is not fully understood, either ischemia due to rapid growth of the tumor or some inflammatory mechanism may be involved in regression of hepatocellular carcinoma.

Development of a new heating needle for interstitial hyperthermia compatible with interstitial radiotherapy

PURPOSE

We have developed a new heating needle for interstitial hyperthermia compatible with brachytherapy. We studied the heating characteristics of interstitial needles and the usefulness of these needles for interstitial hyperthermia.

MATERIALS AND METHODS

As heating needles, we used MicroSelectron HDR interstitial needles. These needles were only heated at the metal tip, and were insulated in the middle and grounded from the top. The hyperthermia system was based on the principles of RF capacitive heating, and we used a Thermotron RF-8. We examined whether the temperature and the heating area could be elevated to a level required for hyperthermia.

RESULT

Good heating was obtained around the metal tip of the needle. The heating area of the longitudinal axis of the needle varied with the length of the metal part, while the transverse heating area of the needle was almost unchanged. If heating was performed while maintaining the elevation of temperature in each needle at the same level using variable coils (tuning box), heating was homogeneous over the regions in accordance with the arrangement of the needles.

CONCLUSION

With this heating system, the temperature rises easily, and a uniform temperature distribution can be obtained.

Propofol suppresses a hyperpolarization-activated inward current in rat hippocampal CA1 neurons

We examined the effect of propofol and thiopental, intravenous anesthetics, on the hyperpolarization-activated inward current (I(H)), whose functional role on the neuronal activity has been evaluated. Whole-cell recordings of I(H) evoked by hyperpolarizing step pulses were taken from hippocampal CA1 neurons in rat brain slices. Propofol reduced I(H) current in a dose-dependent manner. However, thiopental had no significant effect on the activation of I(H). According to the functional role of I(H), the suppression of I(H) should result in a reduction of neuronal activity. We suggest that the effectiveness of propofol as an anticonvulsant or an antiemetic is associated with the blockade of the I(H) channel.

Regulated expression of an actin-associated protein, synaptopodin, during long-term potentiation

We report NMDA receptor-dependent expression of synaptopodin mRNA in the dentate granule cells of the hippocampus following induction of long-term potentiation (LTP) in vivo. Synaptopodin did not belong to immediate-early genes, as de novo protein synthesis was required for the induction of synaptopodin gene transcription. An increased level of synaptopodin mRNA was observed at 75 min and 3.5 h after the onset of LTP. Importantly, there was correlation between the induction of mRNA expression and the persistence of LTP. Synaptopodin immunoreactivity was elevated specifically in synaptic layers, middle and outer molecular layers of dentate gyrus where LTP was induced. As synaptopodin is an actin-associated protein present in spine neck and implicated in the modulation of cell morphology, our results suggest that synaptopodin, by regulating the dynamics of the actin cytoskeleton, contributes to the morphological change in spine shape considered to be important for the maintenance of synaptic plasticity.

Intravenous anesthetics inhibit nonadrenergic noncholinergic lower esophageal sphincter relaxation via nitric oxide-cyclic guanosine monophosphate pathway modulation in rabbits

BACKGROUND

Nonadrenergic noncholinergic (NANC) nerves have important roles in the regulation of the lower esophageal sphincter (LES) motility and function. The effects of thiopental, ketamine, and midazolam on NANC LES relaxation were investigated.

METHODS

The isometric tension of circular muscle strips from Japanese White rabbits was examined. The 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). The modifications of the NANC and sodium nitroprusside (SNP; 10(-5) M)-induced relaxation by the anesthetics were examined. The content of 3',5'-cyclic guanosine monophosphate (cGMP) was measured by radioimmunoassay.

RESULTS

The KCl-induced relaxation was abolished by pretreating with tetrodotoxin (10(-6) M). The NANC relaxation was inhibited in the presence of N(G)-nitro-L-arginine (L-NNA; 3 x 10(-5) M), methylene blue (10(-6) M), apamin (10(-7) M), and glibenclamide (10(-5) M). The SNP-induced relaxation was inhibited by methylene blue but was not affected by tetrodotoxin, L-NNA, apamin, or glibenclamide. Ketamine (EC50 = 8.8 x 10(-5) M) and midazolam (EC50 = 4.8 x 10(-6) M) suppressed the NANC response in a concentration-dependent manner, leaving SNP-induced response unchanged. Thiopental altered neither of the relaxations. cGMP content was decreased in the presence of ketamine and midazolam.

CONCLUSION

The NANC relaxation was mediated by nitric oxide and by low-conductance calcium- and adenosine triphosphate-sensitive potassium channels of smooth muscle. The modulation of the nitric oxide-cGMP pathway was related, at least in part, to the inhibitory actions of ketamine and midazolam on the NANC LES relaxation.

Role of parabrachial nucleus in submandibular salivary secretion induced by bitter taste stimulation in rats

When rats lick a bitter taste solution such as quinine-hydrochloride, they secrete profuse amounts of saliva. The salivation has a higher flow rate than that induced by other qualities of taste stimulation: sweet, salty, and sour. The present study is aimed to clarify the neural mechanism of the quinine-evoked salivation by means of behavioral, neuroanatomical, and electrophysiological experiments. Behaviorally, submandibular salivary secretion and rejection behavior (gaping) were observed in normal rats, as well as in rats chronically decerebrated at the precollicular level. In chronically decerebrate rats, these quinine-evoked reactions were strongly suppressed by destruction of the medial part of the parabrachial nucleus, including the so-called taste area, and ventral part of the parabrachial nucleus, including the pontine reticular formation. Neuroanatomical study using a retrograde tracer, Fluoro-gold, revealed that the neurons sending their axons to the superior salivatory nucleus, parasympathetic secretory center, were located mainly in the pontine reticular formation ventral to the parabrachial nucleus, not in the parabrachial taste area. Extracellular neural activity was recorded from the parabrachial region in decerebrate rats, and responsiveness to taste stimulation, jaw movements, and electrical stimulation of the superior salivatory nucleus was examined. Neurons responsive to both taste stimulation and antidromic stimulation of the superior salivatory nucleus were found in the pontine reticular formation ventral to the parabrachial nucleus, which responded well to quinine and HCl taste stimuli. Neurons in the parabrachial taste area could respond to four qualities of taste stimulation, but not to antidromic stimulation of the salivary center. These results suggest that aversive taste information from the parabrachial taste area reaches the salivary secretory center via the reticular formation ventral to the parabrachial nucleus.

Neuronal activity in the putamen and the globus pallidus of rabbit during mastication

The pattern of jaw movements is changed during a masticatory sequence from ingestion of food to its deglutition. The masticatory sequence is divided into three distinct stages in the rabbit. However, the neural mechanism involved in the alteration of the masticatory stages is still unknown. This study was designed to determine whether neuronal activity in the putamen and globus pallidus is related to the alteration of the masticatory stages. Fifty-three percent of the recorded neurons showed significant alterations of activity during mastication. Of these neurons, 16% changed their firing frequency throughout the masticatory sequence (sequence-related neurons) and 84% changed their firing frequency with the transition of the masticatory stages (stage-related neurons). The stage-related neurons were classified into two groups based on their neuronal activity patterns observed during mastication, i.e. simple type and complex type. The former are the neurons that were either facilitated or inhibited once during mastication, and the latter are those showing the facilitation or inhibition twice or more during mastication. Complex-type neurons were observed more frequently in the globus pallidus than in the putamen. These results suggest that the basal ganglia is involved in mastication and may related to the transition between the masticatory stages.

A new expression cloning strategy for isolation of substrate-specific kinases by using phosphorylation site-specific antibody

Signal transduction from cell surface receptors to the nucleus is regulated in most part by protein phosphorylation. For the purpose of identification of kinases which play an important role at a particular phosphorylation step in a series of signal transduction pathways, we have developed a new expression-screening method using a phosphorylation site specific antibody and a vector encoding substrate polypeptide. We have applied this method for screening kinases which phosphorylate STAT3 at serine(727). In this screening, antibody (PS727 antibody) specifically recognizing STAT3 in which serine(727) is phosphorylated was first prepared. Escherichia coli, bacteria expressing a serine(727)-containing fragment of STAT3 which was fused to glutathione-S-transferase (GST) (GST-STAT3-WT) were infected by lambda phage cDNA expression libraries. Phosphorylation of GST-STAT3-WT was effectively performed in E. coli as expected, and clones positive for PS727 antibody immunoreactivity were selected. Isolated 53 clones encode four serine/threonine kinases; extracellular signal regulated kinase 1 (ERK1/p44-MAPK), dual specificity Yak1 related kinase (DYRK), dual specificity Yak1 related kinase 2 (DYRK2) and homeodomain interacting protein kinase 2 (HIPK2). These kinases have a potential to phosphorylate serine(727) in STAT3 protein also in mammalian cells. The present method is considered to be applicable in general to isolate kinases.

Propagation of synchronous burst discharges from entorhinal cortex to morphologically and electrophysiologically identified neurons of rat lateral amygdala

Intracellular and field potential recordings were taken from the lateral nucleus of the amygdala in a rat horizontal brain slice preparation that included hippocampal formation. Pyramidal cells comprised the majority of labeled cells (77%). Electrophysiological classification based on hyperpolarizing or depolarizing afterpotentials subdivided both the pyramidal and non-pyramidal cell classes, although pyramidal cells tended to have hyperpolarizing afterpotentials (70%) and non-pyramidal cells tended to have depolarizing afterpotentials (63%). Synchronous population bursts were triggered with single extracellular stimuli in the deep layers of entorhinal cortex. These events propagated from deep layers of entorhinal cortex into the lateral nucleus of the amygdala. Latencies were consistent with a direct entorhinal to amygdala projection. Individual lateral nucleus neurons exhibited responses ranging from a long burst response that included an initial period of 200 Hz firing and a tail of gamma frequency firing lasting over 100 ms (grade 1) to an epsp with no firing (grade 4). Half of pyramidal cells responding to events initiated in entorhinal cortex were found to receive epsps strong enough to trigger firing. Only one stellate neuron fired in response to entorhinal stimulation. Excitatory postsynaptic responses included NMDA and non-NMDA receptor mediated components. We demonstrate that synchronous population events can propagate from entorhinal cortex to the lateral nucleus of the amygdala and that pyramidal neurons of the lateral nucleus are more common targets than stellate neurons. We conclude that other synchronous events such as sharp waves and interictal spikes can spread from entorhinal cortex to amygdala in the same manner.

Water stimulation of the posterior oral cavity induces inhibition of gastric motility

The response of gastric motility to the administration of water and saline in the larynx and epiglottis was investigated in urethan-chloralose anesthetized rats. Administration of water inhibited motility of the distal stomach, but 0.15 M NaCl did not induce the inhibitory response. Bilateral sectioning of the superior laryngeal nerve (SLN) abolished the inhibitory response induced by water. Bilateral cervical vagotomies abolished the inhibitory responses, although spinal transection did not affect the inhibitory response. These inhibitory responses have been observed in immobilized animals. The degree of inhibition by water and hypotonic saline was negatively correlated with the sodium concentration. In contrast, the degree of inhibition to hypertonic saline was positively correlated with the sodium concentration. The proximal stomach also showed a reduction in intragastric pressure in response to the administration of water. These findings suggest that water-responsive afferent neurons in the SLN suppress gastric motility via the vagal efferent nerve.

Reflex secretion of proteins into submandibular saliva in conscious rats, before and after preganglionic sympathectomy

1. An indwelling catheter was placed in the left submandibular duct of rats, under pentobarbitone anaesthesia, and connected to an outflow cannula that emerged above the skull. 2. Saliva was collected from the outflow cannula in conscious rats, the same day after recovery from anaesthesia, under four different reflex conditions: grooming, heat exposure, rejection of a bitter tasting substance and feeding on softened chow, repeated in different orders. 3. Saliva flow was greatest for grooming and least for rejection. Protein concentrations were least with heat but much greater and similar for the other stimulations. Acinar peroxidase activity was high for feeding, intermediate for grooming and rejection, and again lowest with heat. Tubular tissue kallikrein activities were moderately low, being greatest with feeding and least with grooming. Secretory immunoglobulin A (SIgA) concentration was least with heat and similar for the other stimulations. 4. The next day, under pentobarbitone anaesthesia, the left preganglionic sympathetic trunk was sectioned (sympathetic decentralization) and, after recovery, the preceding stimulations were repeated. Flow of saliva showed little change, but protein and peroxidase concentrations and outputs decreased dramatically with grooming, rejection and feeding to levels similar to those with heat, which showed little change. Tissue kallikrein was lowered less dramatically, but the reductions in output were significant except with heat. Patterns of proteins resolved by electrophoresis changed for grooming, rejection and feeding and became similar to saliva from heat, which showed little change. No significant effects on SIgA concentrations occurred. 5. Gland weights from the sympathetically decentralized side were greater than from the intact side at the end of the experiments and histologically showed retention of acinar mucin. 6. Thus reflex sympathetic drive varied with the different stimulations; it was least during heat, but it had pronounced effects on acinar secretion of proteins during the other stimulations. At the same time this sympathetic drive had less impact on tissue kallikrein secretion from tubules and had little influence on flow or the concentration of SIgA secreted.

Isolated dissection of the celiac artery--a case report

Isolated arterial dissection, which occurs with the absence of aortic dissection, has been reported in carotid and renal arteries but rarely in visceral arteries. A case of isolated celiac artery dissection is reported here. A healthy 58-year-old man experienced sudden upper abdominal pain, which continued for several days. A body computed tomogram (CT) showed a multiple low-density wedge-shaped area in the spleen, which was diagnosed as splenic infarction, and an aneurysm with thrombus in the celiac artery. A selective angiogram showed dilatation of the celiac artery with wall irregularity, and proximal occlusion of the hepatic artery. The distal hepatic artery was fed by collateral arteries from the superior mesenteric artery. Splenic infarction was probably due to the embolism from the thrombus in the dissected celiac artery. The absence of other vascular lesions and causes or risks for the arterial dissection would suggest the occurrence of spontaneous dissection. The dissection of visceral arteries should be considered in diagnosing acute abdominal pain.

BMP2-induced apoptosis is mediated by activation of the TAK1-p38 kinase pathway that is negatively regulated by Smad6

Bone morphogenetic protein 2 (BMP2), a member of the transforming growth factor-beta (TGF-beta) superfamily, regulates a variety of cell fates and functions. At present, the molecular mechanism by which BMP2 induces apoptosis has not been fully elucidated. Here we propose a BMP2 signaling pathway that mediates apoptosis in mouse hybridoma MH60 cells whose growth is interleukin-6 (IL-6)-dependent. BMP2 dose-dependently induces apoptosis in MH60 cells even in the presence of IL-6. BMP2 has no inhibitory effect on the IL-6-induced tyrosine phosphorylation of STAT3, and the bcl-2 gene expression which is known to be regulated by STAT3, suggesting that BMP2-induced apoptosis is not attributed to alteration of the IL-6-mediated bcl-2 pathway. We demonstrate that BMP2 induces activation of TGF-beta-activated kinase (TAK1) and subsequent phosphorylation of p38 stress-activated protein kinase. In addition, forced expression of kinase-negative TAK1 in MH60 cells blocks BMP2-induced apoptosis. These results indicate that BMP2-induced apoptosis is mediated through the TAK1-p38 pathway in MH60 cells. We also show that MH60-derived transfectants expressing Smad6 are resistant to the apoptotic signal of BMP2. Interestingly, this ectopic expression of Smad6 blocks BMP2-induced TAK1 activation and p38 phosphorylation. Moreover, Smad6 can directly bind to TAK1. These findings suggest that Smad6 is likely to function as a negative regulator of the TAK1 pathway in the BMP2 signaling, in addition to the previously reported Smad pathway.

Identification and cataloging of genes induced by long-lasting long-term potentiation in awake rats

Maintenance of long-term potentiation (LTP) requires de novo gene expression. Here we report the direct isolation, using PCR-differential display, of genes whose expression level was altered after induction of long-lasting LTP in the hippocampus of freely moving awake rats. Differential display using 480 primer combinations revealed 17 cDNA bands that showed a reproducible change in expression level. These cDNAs represented at least 10 different genes (termed RM1-10), all of which showed up-regulation at 75 min after LTP induction and a return to basal expression levels within 24 h. Three of these genes were known only from expressed sequence tags (RM1-3), two were known genes whose up-regulation by LTP has not been described (GADD153/CHOP and ler5), and five were known genes whose up-regulation by LTP has already been reported (MAPK phosphatase, NGFI-A/zif268, vesl-1S/homer-1a, Ag2, and krox-20). We characterized the expression profiles of genes in the two former categories with respect to NMDA receptor dependency, tissue specificity, and developmental regulation using northern blotting and semiquantitative RT-PCR. The up-regulation of all five of these genes was NMDA receptor-dependent and correlated with the persistence of LTP, suggesting that these genes may play functional roles in prolonged LTP maintenance.

SD3212, a new antiarrhythmic drug, raises atrial fibrillation threshold in isolated rabbit hearts

SD3212 is a new antiarrhythmic drug which has class I, III, and IV effects. The purpose of this study was to elucidate the electrophysiological effects of this compound on a rabbit atrial fibrillation model, and to test a hypothesis that atrial fibrillation threshold is a quantitative indicator of atrial vulnerability. Whole hearts were excised from rabbits, and the aortas cannulated to perfuse the coronary arteries. Atrial fibrillation was induced with a burst stimulation of 50 Hz for 1 s while 3 microM acetylcholine (ACh) was perfused. When the right atrial appendage was paced at 200-ms intervals, SD3212 prolonged interatrial conduction time: control 30 +/- 1.2 ms, ACh 33 +/- 1.4 ms, ACh + SD 1 microM 37 +/- 2.4 ms, ACh + SD 3 microM 52 +/- 8.1 ms. The drug also prolonged the effective refractory period: control 80 +/-3.0 ms, ACh 48 +/- 3.8 ms, ACh + SD 1 microM 65 +/- 4.7 ms, ACh + SD 3 microM 98 +/- 15 ms. The rate of induction of atrial fibrillation by rapid pacing was 26% in Tyrode's solution, 85% in the presence of ACh, and 38% in the presence of ACh + SD 1 microM. The atrial fibrillation threshold decreased from 8.6 +/- 0.8mA (control) to 2.5 +/- 0.7 mA in the presence of ACh. It increased again to 7.8 +/- 1.0 mA in the presence of SD3212 (1 microM). SD3212 prolonged both the conduction time and refractory period. A reversed use-dependency was not prominent. These features caused antifibrillatory effects. Thus, the atrial fibrillation threshold seems to be a good quantitative indicator of atrial vulnerability.

Serotonergic modulation of the hyperpolarizing spike afterpotential in rat jaw-closing motoneurons by PKA and PKC

Intracellular recordings were obtained from rat jaw-closing motoneurons (JCMNs) in slice preparations to investigate the effects of serotonin (5-HT) on the postspike medium-duration afterhyperpolarization (mAHP) and an involvement of protein kinases in the effects. Application of 50 microM 5-HT caused membrane depolarization and increased input resistance in the most cells without affecting the mAHP, whereas not only membrane depolarization and an increase in input resistance, but also the suppression of the mAHP amplitude was induced by higher dose of 5-HT (100 or 200 microM). On the other hand, when the mAHP amplitude was increased by raising [Ca(2+)](o) from 2 to 6 mM, 5-HT-induced attenuation of the mAHP amplitude was enhanced, and even 50 microM 5-HT reduced the mAHP amplitude. This 5-HT-induced suppression of the mAHP could be mimicked by application of membrane-permeable cAMP analogue 8-Bromo-cAMP, potentiated by the cAMP-specific phosphodiesterase inhibitor Ro 20-1724 and antagonized by protein kinase A (PKA) inhibitor H89. The enhancement of the mAHP attenuation induced by 50 microM 5-HT under raised [Ca(2+)](o) was blocked by a protein kinase C (PKC) inhibitor chelerythrine, suggesting an involvement of PKC in this enhancement. On the other hand, the attenuation of the mAHP induced by PKC activator phorbol 12-myristate 13-acetate was blocked almost completely by H89, suggesting that the PKC action on the mAHP requires PKA activation. Neither 5-HT(1A) antagonist NAN-190 or 5-HT(4) antagonist SB 203186 blocked 5-HT-induced attenuation of the mAHP. We conclude that 5-HT induces dose-dependent attenuation of the mAHP amplitude through cAMP-dependent activation of PKA and that PKC-dependent PKA activation is also likely to be involved in the enhancement of 5-HT-induced attenuation of the mAHP under raised [Ca(2+)](o). Because the slope of the linear relationship between firing frequency and injected current was increased only when the mAHP amplitude was decreased by 5-HT, it is suggested that the relation between incoming synaptic inputs and firing output in JCMNs varies according to serotonergic effects on JCMNs and calcium-dependent modulation of its effects.

Noxious tooth pulp stimulation suppresses c-fos expression in the rat hippocampal formation

Changes in the expression of immediate early gene c-fos by noxious mechanical stimulation to the mandibular incisor pulp of rats were immunohistochemically examined in the hippocampus (Ammon's horn and dentate gyrus) and the retrohippocampus (subiculum, presubiculum, parasubiculum and entorhinal cortex). The highest control levels were found in subiculum, CA1, dentate and deep medial entorhinal cortex. Lower, but substantial levels were present in the other areas. Whereas weak dentinal stimulation caused increases in c-fos expression in some regions which were not statistically significant, strong tooth pulp stimulation caused a bilateral decrease in c-fos expression in every region except contralateral subiculum. These decreases reached statistical significance in superficial layer parasubiculum bilaterally (p<0.01), bilateral CA1 and ipsilateral side of superficial layer of medial entorhinal cortex (p<0.05). We suggest that inhibitory circuitry in hippocampal formation regions may be activated by peripheral noxious somatosensory inputs and this change in activity is accompanied by a change in the expression of the immediate early gene, c-fos.

Two types of parasympathetic preganglionic neurones in the superior salivatory nucleus characterized electrophysiologically in slice preparations of neonatal rats

1. The electrophysiological properties of parasympathetic preganglionic neurones in the superior salivatory nucleus were studied in thin- and thick-slice preparations of rats aged 1 and 2 weeks using the whole-cell patch-clamp technique. 2. The superior salivatory neurones were identified by a retrograde tracing method with dextran-tetramethylrhodamine-lysine. The injection of the tracer into the chorda-lingual nerve labelled the neurones innervating the submandibular ganglia and those innervating the intra-lingual ganglia, while the injection into the tip of the tongue labelled the latter group of neurones. 3. Firing characteristics were investigated mainly in the neurones of 6-8 days postnatal rats. In response to an injection of long depolarizing current pulses at hyperpolarized membrane potentials (< -80 mV) under a current clamp, the neurones labelled from the nerve displayed a train of action potentials with either a long silent period preceding the first spike (late spiking pattern) or a long silent period interposed between the first and second spikes (interrupted spiking pattern). The neurones labelled from the tongue invariably displayed the interrupted spiking pattern. 4. Under a voltage clamp, among the neurones from 6-8 days postnatal rats, those labelled from the nerve expressed either a fast or a slow transient outward current (A-current), while those labelled from the tongue invariably showed a slow transient outward current. Both the fast and slow A-currents were largely depressed by 1 mM 4-aminopyridine. 5. Similar fast and slow A-currents were observed in the neurones of rats aged 14-15 days. Both the time to peak and decay time constant of these A-currents were accelerated, suggesting a developmental trend of maturation in the activation and inactivation kinetics between 6 and 15 days postnatal. 6. Based on the differences in the firing pattern and outward current, the superior salivatory neurones can be separated into two distinct types. We discuss the functional aspects of these two types of neurones with reference to their target organs.

Neural activity of the superior salivatory nucleus in rats

We recorded the neural activity of the superior salivatory (SS) neurons in brain slice preparations from neonatal rats in vitro and in decerebrate anesthetized rats in vivo. In the in vitro experiment, the SS neurons were retrogradely labeled by the injection of Rhodamine into the chorda-lingual nerve (labeling SS neurons innervating the submandibular and intra-lingual ganglia) or into the anterior part of the tongue. The SS neurons labeled from the nerve were classifiable into two types: Type-I, tonic firing at a frequency of up to 30 Hz; and Type-II, phasic firing at a higher frequency of up to 70 Hz followed by tonic firing at 30-50 Hz. All of the SS neurons labeled from the tongue were Type-II. Since the anterior tongue is a non-glandular area, the type of cells may be involved in vasodilatation. Type-I neurons, which did not innervate the tongue, may be responsible for salivation. In the in vivo experiment, the reflex activity evoked by taste or mechanical stimulation was recorded from the axons of the SS neurons innervating the submandibular ganglia. These fibers also displayed two firing patterns. One was a tonic firing pattern discharging at 5-30 Hz. The other consisted of a transient firing (about 80 Hz) at the beginning of stimulation and then a prolonged firing at 5-40 Hz. The latter firing pattern was similar to that of the Type-II neurons. These findings suggest that the parasympathetic nerves of the salivary glands contain both the secretory- and vasodilator-type of SS neuron.

A triple coaxial catheter system for subselective visceral artery catheterization and embolization: preliminary clinical experience

We developed a triple coaxial catheter system (TCCS) which consists of a 6.1 Fr outer, a 4.1 Fr intermediate, and a 3.0 Fr inner catheter, all coated with a lubricant. The TCCS was used in seven patients with hepatic tumors, after several attempts to access a targeted vessel with conventional catheters and guidewires failed to reach the targeted vessel. No complications were encountered with the use of this system. TCCS may be a useful device for selective abdominal arteriography.

Cataloging altered gene expression during rat hippocampal long-term potentiation by means of differential display

We have employed mRNA differential display (DD) to generate a catalog of cDNAs whose expression in the hippocampus was regulated during long-term potentiation (LTP) in dentate gyrus of anesthetized rats. DD with 459 combinations of primer pairs revealed that 80 out of approximately 70000 bands displayed showed a reproducible change in their expression level. These cDNAs were categorized into seven groups according to changes in their temporal expression pattern. Some of these cDNAs were induced rapidly, but transiently, after the LTP induction, some induced rapidly and persistently, some induced slowly, and some down-regulated following LTP. This suggests that a complex molecular hierarchy underlies the maintenance of hippocampal LTP.

[Efficacy and safety of intramuscular imipenem/cilastatin (IPM/CS) for complicated urinary tract infections]

An intramuscular preparation of imipenem/cilastatin (IPM/CS, 500 mg/500 mg) was administered to 59 patients with complicated urinary tract infections (UTI; cystitis and pyelonephritis) to evaluate its efficacy and safety. The obtained results are summarized as follows: In patients with cystitis, evaluations based on daily frequencies of administration were also performed. 1) According to the treating doctors, the drug showed an overall efficacy rate of 80% (45/56 patients). The efficacy rate was 89% in patients with cystitis treated by a u.i.d. regimen. Among patients treated by a b.i.d. regimen, the efficacy rate was 67% for cystitis cases and 84% for pyelonephritis cases. 2) When clinical efficacy was assessed according to the criteria for UTI drug efficacy evaluation, the drug was 'markedly effective' in 14 patients, 'effective' in 23, and ineffective in 11 patients, for an efficacy rate of 77% (37/48 patients). 3) The microbiological eradication rate was 88% (59/67 strains). The rate was 95% (20/21 strains) for Gram-positive bacteria and 85% (39/46 strains) for Gram-negative bacteria. The efficacy for Enterobacter faecalis and Pseudomonas aeruginosa was 100% and 73%, respectively. 4) As side effects, pain at the injection site was reported by one patient and abnormal laboratory test values were observed in 2 patients. All of these reactions were mild and resolved shortly after the completion of treatment. Based on these findings, it is concluded that this intramuscular preparation of IPM/CS is effective for treating complicated urinary tract infections.

Role of calcium conductances on spike afterpotentials in rat trigeminal motoneurons

Intracellular recordings were obtained from rat trigeminal motoneurons in slice preparations to investigate the role of calcium conductances in the depolarizing and hyperpolarizing spike afterpotential (ADP and mAHP, respectively). The mAHP was suppressed by bath application of 1 microM apamin, 2 mM Mn2+, and 2 mM Co2+, and also by intracellular injection of ethylene glycol-bis(b-aminoethylenether)-N,N,N',N'-tetraacetic acid (EGTA), suggesting that the potassium conductance generating the mAHP is activated by Ca2+ influx. Mn2+ (2 mM) or Cd2+ (500 microM) reduced the ADP, whereas the ADP amplitude was increased by raising extracellular Ca2+ concentration from 2 to 8 mM by bath application of Ba2+ (0.5-5 mM) and by intracellular injection of EGTA. This would suggest that Ca2+ itself is likely to be the charge carrier generating the ADP. Focal application of omega-conotoxin GVIA (10-30 microM) suppressed the mAHP and enhanced the ADP, whereas focal application of omega-agatoxin IVA (10-100 microM) reduced the ADP amplitude without apparent effects on the mAHP. We conclude that Ca2+ influx through omega-agatoxin IVA-sensitive calcium channels is at least in part responsible for the generation of the ADP and that Ca2+ influx through omega-conotoxin GVIA-sensitive calcium channels contributes to the generation of the mAHP. Because of the selective suppression of the ADP and mAHP by omega-agatoxin IVA and omega-conotoxin GVIA, respectively, it is suggested that both calcium channels are separated geometrically in rat trigeminal motoneurons.

Regulation of masticatory force during cortically induced rhythmic jaw movements in the anesthetized rabbit

To examine the relationships between masticatory force, electromyogram (EMG) of masticatory muscles, and jaw movement pattern, we quantitatively evaluated the effects of changing hardness of a chewing substance on these three variables. Cortically induced rhythmic jaw movements of a crescent-shaped pattern were induced by electrical stimulation of the cerebral cortical masticatory area in the anesthetized rabbit. The axially directed masticatory force was recorded with a small force-displacement transducer mounted on the ground surface of the lower molars. EMGs were recorded from the masseter and digastric muscles simultaneously with jaw movements. Five test strips of polyurethane foam of different hardness were prepared and inserted between the upper molar and the transducer during the movements. The peak, impulse, and buildup speed of the masticatory force increased with strip hardness, whereas duration of the exerted force did not vary with strip hardness. The integrated activity and duration of the masseteric EMG bursts also increased with strip hardness. The integrated EMG activity of the digastric bursts was weakly related to strip hardness, whereas the duration was not. The minimum gape increased with strip hardness, but the maximum gape did not. The horizontal excursion of the jaw did not vary in a hardness-dependent manner, although it was greater in the cycles with strip application than in the cycles without strip application. Deprivation of periodontal sensation by cutting the nerves to the teeth reduced the buildup speed of the force, maximum gape, net gape, and horizontal jaw movements. The denervation also elongated the force duration and that of masseteric EMG bursts. However, the rate of the hardness-dependent changes in the above parameters did not alter after denervation. The latency of the masseteric EMG response to strip application was evaluated before and after denervation. In both conditions, it was > or = 6 ms in approximately 70% of the cycles and <6 ms in the remaining approximately 30%, which cannot be explained by a simple reflex mechanism. On the basis of the analysis of correlation coefficients, the masseteric integrated EMG seemed to be a good indicator of the peak and impulse of the masticatory force both before and after denervation. We conclude that periodontal afferents would be responsible for a quick buildup of masticatory force and that afferents other than those from periodontal tissue would contribute to the hardness-dependent change of masticatory force during cortically induced rhythmic jaw movements.

CD4- CD8- TCR alpha/beta+ suppressor T cells demonstrated in mice 1 day after thermal injury

We have described previously that CD8+ CD11b+ TCR gamma/delta+ type 2 T cells (BA-type 2 T cells) and suppressor macrophages (Sup-Mł) are generated in spleens of mice 3 to 5 days (Sup-Mł) and 4 to 9 days (BA-type 2 T cells) after thermal injury. In the present study, an additional suppressor T cell, characterized as CD3+ CD4- CD8- TCR alpha/beta+ T cells (double negative suppressor T cells, DN Sup-T cells), was demonstrated in mice 1 day after thermal injury. DN Sup-T cells inhibited the proliferation of lymphocytes stimulated with allogeneic cells or a lectin in a mixed lymphocyte reaction, and produced both type 1 and type 2 cytokines (interferon-gamma, interleukin-2, interleukin-4, and interleukin-10) when they were stimulated in vitro with anti-CD3 monoclonal antibody. These results suggest that DN Sup-T cells express phenotypic properties similar to natural suppressor cells and cytokine-producing profiles different from type 1 (Th1 cells and CTLs) and type 2 T cells (Th2 cells and CD8+ type 2 T cells). DN Sup-T cells may play a role on the burn-associated immunosuppression appearing in the acute phase of thermally injured individuals.

Modulation of jaw muscle spindle discharge during mastication in the rabbit

Discharges of jaw muscle spindles were recorded during chewing carrot from mesencephalic trigeminal nucleus (Mes V) in the awake rabbit to evaluate contribution of the muscle spindles to the development of complete sequences of masticatory movements. The Mes V spindle units were divided into two types according to the maximum firing rates during mastication, with a dividing line at 200 Hz; high-frequency units and low-frequency units. Although both types of units fired maximally during the jaw-opening phase of chewing cycles, their firing rates and pattern varied according to three sequential stages of mastication (stages I, IIa, and IIb). The high-frequency units often increased firing before the start of mastication and built up firing in the first few chewing cycles. Their maximal firing rate was sometimes lower during stage IIa (chewing stage) than during stage I (ingestion stage) and stage IIb (preswallowing stage), although the jaw movements were greater in stage IIa than in other stages. The phase relationship of the firing to a jaw movement cycle in stage IIa was consistent in individual units. The low-frequency units did not build up activity before the onset of movements. They fired mostly during the jaw-opening phase, but the peak of firing did not necessarily coincide with the time of maximal opening. It was concluded that the difference in the firing pattern among masticatory stages may be ascribed to a stage-dependent modulation of both fusimotor activity and jaw movement pattern.

Role of submandibular and sublingual saliva in maintenance of taste sensitivity recorded in the chorda tympani of rats

1. To evaluate the role of saliva in the maintenance of taste sensitivity, the activities in the rat chorda tympani innervating taste buds in the anterior part of the tongue were analysed. The effects of chronic extirpation of the submandibular and sublingual salivary glands were tested and compared with results after chronic oral administration of artificial saliva. 2. Removal of the salivary glands sharply decreased chorda tympani responses to four different taste stimuli by 7 days post-desalivation, while a stable response to cold water was observed by at least 28 days. 3. This selective decrease in taste responses was considerably recovered by 7-day-oral injection of artificial saliva (containing NaHCO3, KCl and/or mucin) or distilled water. However, the injection of the salt-containing artificial saliva induced significantly larger sucrose and smaller NaCl, HCl and quinine responses than did the injection of distilled water. 4. In our salivary manipulations, an alteration in the number of the functional sweet receptors was suggested by the cross-adaptation technique using NaHCO3, whereas sensitivity to the epithelial sodium transport blocker, amiloride, was stable in the NaCl response. 5. Salivary water and electrolytes which may participate in forming the external environment of the taste receptor cells modulated taste sensitivity in the chorda tympani.