Effects of CO2 on time-dependent changes in cardiorespiratory functions under sustained hypoxia.

Hypercapnia in addition to hypoxia affects the mammalian cardiorespiratory system and has been suggested to exert its effects on cardiorespiratory function by slightly different mechanisms to hypoxia. In the present study, we examined cardiorespiratory changes in urethane-anesthetized rats under hypocapnic (Hypo, 10% O2), isocapnic (Iso, 10% O2 and 4% CO2), and hypercapnic (Hyper, 10% O2 and 8% CO2) hypoxia for 2 h to clarify the effects of CO2 on sustained hypoxia-induced cardiorespiratory responses. Respiratory frequency increased the most in Hypo and tidal volume in Hyper. Minute ventilation, a product of respiratory frequency and tidal volume, increased the most in the latter group. Regarding cardiovascular variables during the hypoxic exposure period, heart rate and mean blood pressure both markedly decreased in Hypo. However, decreases in these parameters were small in Iso, and both increased over the pre-exposure level in Hyper. The present results suggest that CO2 interferes with the hypoxia-activated neural pathway via another pathway under sustained exposure to hypoxia.

Different sensitivity to the suppressive effects of isoflurane anesthesia on cardiorespiratory function in SHR/Izm, WKY/Izm, and Crl:CD (SD) rats.

Isoflurane is a widely used anesthetic, but its effects with increase in inspired concentration on cardiovascular function have not yet been clarified in rodents. Additionally, there are only a few studies comparing isoflurane-induced cardiorespiratory effects between rat strains. Thus, we investigated the differences in cardiorespiratory responsiveness to increasing concentration of inspired isoflurane in SHR/Izm, WKY/Izm and Crl:CD (SD) rats, by increasing the setting values of vaporizer's dial indicator. The rats were anesthetized with 1.5% isoflurane, and electrocardiograms, blood pressure, and respiratory rate were recorded simultaneously. Thereafter, the inspired concentration was increased stepwise to 2%, 3%, 4%, and 5%, and cardiorespiratory parameters were obtained at each concentration. Under anesthesia at more than 4%, although prolongation of the RR and PR intervals was observed in all strains, shortening of the QTC interval was found only in SHR/Izm rats. From frequency domain analysis of heart rate variability, an increase in LF/HF ratio and a decrease of HF components were observed in SHR/Izm and WKY/Izm rats, respectively, with 5% isoflurane anesthesia. Blood pressure and heart rate were remarkably reduced in SHR/Izm rats at higher concentrations, whereas the reduction was smallest in WKY/Izm rats among the three strains examined. Respiratory rate was inspired concentration-dependently decreased in all strains. These results suggested that SHR/Izm rats are more sensitive to suppressive effects of isoflurane anesthesia on cardiovascular function among these rat strains.

Functional chondroitin sulfate from Enteroctopus dofleini containing a 3-O-sulfo glucuronic acid residue.

There are several reports that chondroitin sulfate containing K-type units [GlcA (3S)-GalNAc (4S)] exhibiting similar levels of neurite outgrowth promoting activities as CS having high amounts of B-, D- and E-type disulfated disaccharides. Although CS containing K-type units possess important biological activities, there are only few sources, such as king crab cartilage, squid cartilage or sea cucumber. In this study, CS containing 13.9% of K-type units was found in octopus (Enteroctopus dofleini) cartilage using different substrate specificities of chondroitinases. The 2D NMR spectra showed cross-peaks assigned to protons on sugar ring of GlcA (3S), demonstrating the presence of K-type units in octopus CS. Furthermore, proportion of fucosylated disaccharide units in octopus CS was very low. Octopus CS showed high affinity for growth factors and stimulated neurite outgrowth of hippocampal neurons, similar to the activity of squid CS-E. These results strongly suggest that octopus cartilage is a rich source of CS-K and has important biological activities.

Immunohistochemical localization of dopamine D2 receptor in the rat carotid body.

Dopamine modulates the chemosensitivity of arterial chemoreceptors, and dopamine D2 receptor (D2R) is expected to localize in the glomus cells and/or sensory nerve endings of the carotid body. In the present study, the localization of D2R in the rat carotid body was examined using double immunofluorescence for D2R with various cell markers. D2R immunoreactivity was mainly localized in glomus cells immunoreactive to tyrosine hydroxylase or dopamine ß-hydroxylase (DBH), but not in S100B-immunoreactive sustentacular cells. Furthermore, D2R immunoreactivity was observed in petrosal ganglion cells and nerve bundles in the carotid body, but not in the nerve endings with P2X2 immunoreactivity. In the carotid ganglion, a few punctate D2R-immunoreactive products were detected in DBH-immunoreactive nerve cell bodies. These results showed that D2R was mainly distributed in glomus cells, and suggested that D2R plays a role in the inhibitory modulation of chemosensory activity in a paracrine and/or autocrine manner.

Differences in respiratory changes and Fos expression in the ventrolateral medulla of rats exposed to hypoxia, hypercapnia, and hypercapnic hypoxia.

Respiratory responses to hypoxia and/or hypercapnia, and their relationship to neural activity in the ventrolateral medulla (VLM), which includes the respiratory center, have not yet been elucidated in detail. We herein examined respiratory responses during exposure of 10% O2 (hypoxia), 10% CO2 (hypercapnia), and 10% O2-10% CO2 (hypercapnic hypoxia) using plethysmography. In addition to recording respiration, Fos expressions were examined in the VLM of the rat exposed to each gas to analyze neural activity. Respiratory frequency was increased in rats exposed to hypoxia, and Fos-positive neurons were observed in the caudal VLM (cVLM) and medial VLM (mVLM). Tidal volume was increased in rats exposed to hypercapnia, and Fos-positive neurons were observed in the rostral VLM (rVLM) includes the retrotrapezoid nucleus (RTN) and mVLM. Tidal volume was enhanced in rats exposed to hypercapnic hypoxia, similar to that in hypercapnia-exposed rats, and Fos-positive neurons were observed in the entire region of the VLM. In the mVLM and cVLM, double immunofluorescence showed Fos-immunoreactive nerve cells were also immunoreactive to dopamine ß-hydroxylase, the marker for A1/C1 catecholaminergic neuron. These results suggested that hypoxia and hypercapnia modulated rhythmogenic microcircuits in the mVLM via A1/C1 neurons and the RTN, respectively.

The effect of selective serotonin reuptake inhibitor (SSRI) on pain-related behavior in a rat model of neuropathic pain.

INTRODUCTION: Some antidepressants are effective for treating neuropathic pain independent of any effect on depression. Selective serotonin reuptake inhibitors (SSRIs) are one of the potential agents to treat neuropathic pain. The aims of this study were to compare the effects of SSRI and non-steroidal anti-inflammatory drugs (NSAIDs) on pain-related behavior and expression of cytokines in a rat model of neuropathic pain. MATERIALS AND METHODS: Spinal surgery was performed to apply nucleus pulposus (NP) to the dorsal root ganglion (DRG). NP animals were treated with saline (NP + S), meloxicam (NP + M), or low-dose or high-dose paroxetine (NP + PL and NP + PH), respectively. Behavioral testing was performed to investigate the mechanical withdrawal thresholds. The numbers of TNF-immunoreactive (IR) neurons in the DRG and of Iba1-IR microglia in the spinal cord (SC) were evaluated using immunohistochemistry. Expression of TNF in the DRG was examined using Western blots. RESULTS: The thresholds on days 14, 21, and 28 were higher in the drug-treated animals than in the NP + S group (p < 0.05). The number of TNF-IR neurons in DRGs from the NP + M group increased on day 2 and decreased on day 7, and TNF expression in DRGs was significantly higher in the NP + S group than in the NP + M group on days 7, 14. The number of Iba1-IR microglia in the SC was significantly higher in the NP + S group than in the NP + M, NP + PL, and NP + PH groups on days 7 and 14. CONCLUSION: An antidepressant might be a potential agent to treat lumbar disc herniation as well as NSAIDs.

Increased total volume and dopamine ß-hydroxylase immunoreactivity of carotid body in spontaneously hypertensive rats.

Under hypertension, it has been reported that the carotid body (CB) is enlarged and noradrenaline (NA) content in CB is increased. Therefore, it is hypothesized that morphological and neurochemical changes in CB are induced in hypertensive animal models. In the present study, we examined the morphological features and dopamine ß-hydroxylase (DBH) immunoreactivity in CB of spontaneously hypertensive rats (SHR/Izm) and Wistar Kyoto rats (WKY/Izm). The CB of SHR/Izm was elongated in terms of the cross section of center and was enlarged in the reconstructed images compared with that of WKY/Izm, and the total volume of CB in SHR/Izm (0.048 ± 0.004 mm³) was significantly (p<0.05) increased compared with the value in WKY/Izm (0.032 ± 0.006 mm³). By immunohistochemistry, immunoreactivity for tyrosine hydroxylase in CB was mainly observed in glomus cells and the immunostaining properties were similar between WKY/Izm and SHR/Izm. On the other hand, DBH immunoreactivity was mainly observed in nerve fibers around blood vessels and observed in a few glomus cells in CB of WKY/Izm. The number of glomus cells with strong DBH immunoreactivity was increased in SHR/Izm compared with that in WKY/Izm. In conclusion, the present study exhibited the enlargement of CB as three-dimensional image and revealed the enhanced immunoreactivity for DBH of glomus cells in SHR/Izm. These results suggest that the morphology of CB is affected by the effect of sympathetic nerve and that the signal transduction from CB is regulated by NA in glomus cells under hypertensive conditions.

Differences in tyrosine hydroxylase expression after short-term hypoxia, hypercapnia or hypercapnic hypoxia in rat carotid body.

In the carotid body (CB), it has been reported that the expressions of tyrosine hydroxylase (TH) mRNA and TH protein are enhanced by exposure to hypoxia. However, it is not known whether CO(2) affects the expression of TH in the CB. We examined the expression of TH mRNA and the immunoreactivity for TH in the CB of rats exposed to hypoxia (10% O(2)), hypercapnia (10% CO(2)) and hypercapnic hypoxia (10% O(2) and 10% CO(2)) for 2-24 h. The expression of TH mRNA in the CB was markedly enhanced in rats exposed to hypoxia for 4 h (6.6-fold), 6 h (6.0-fold) and 8 h (7.8-fold), and in rats exposed to hypercapnic hypoxia for 12 h (4.8-fold). The most intense TH immunoreactivity was observed in the CB from rats exposed to hypoxia for 12 and 24 h and to hypercapnic hypoxia for 24 h. The expressions of TH mRNA and the immunoreactivity for TH were not altered in the CB of rats exposed to hypercapnia. It is suggested that CO(2) does not affect TH expression in the CB, and that it inhibits hypoxia-enhanced TH expression.

Expression of Fos protein in brainstem after application of l-menthol to the rat nasal mucosa.

There are two functional pathways for the nasotrigeminal reflex: the spinal nucleus of trigeminal nerve (SPV) to the Kölliker-Fuse (KF) nucleus and the nucleus of solitary tract (NTS) to the lateral parabrachial nucleus (PBl). Although stimulation of the nasal mucosa by cool temperature induces respiratory depression, it is still unknown whether these nuclei are activated. In the present study, we examined the expression of Fos protein in rat brainstem neurons after nasal application of l-menthol, which is known to activate cold-sensitive nasal receptors. Application of l-menthol, but not paraffin oil, decreased the respiratory rate from 99.7+/-15.6 to 78.5+/-7.3 min(-1). Furthermore, a significantly higher density of Fos-immunoreactive cells was observed in the SPV and KF in the l-menthol rats than in the controls. In the SPV, the density of Fos-immunoreactive cells was highest at approximately 0.5mm rostral to the obex in both the l-menthol (48.5+/-11.5 cells/section) and paraffin oil (26.0+/-9.6 cells/section) groups. In the KF, the mean density of Fos-immunoreactive cells was highest at approximately 5.0mm rostral to the obex in both groups (l-menthol: 67.8+/-14.0 cells/section, control: 41.0+/-12.7 cells/section). The present study suggests that the SPV-KF pathway is important for the cold-induced respiratory depression.