Neonatal isoflurane exposure disturbs granule cell migration in the rat dentate gyrus.

It has been reported that neonatal isoflurane exposure causes behavioral abnormalities following neurodegeneration in animals and gamma-aminobutyric acid type A (GABAA) receptor activation during the synaptogenesis is considered to be one possible trigger. Additionally, the inhibitory effect of excitatory GABAA receptor signaling on the granule cell (GC) migration in the neonatal rat dentate gyrus (DG) was reported in a febrile seizure model. Then, we hypothesized that neonatal isoflurane exposure, which activates GABAA receptor, causes GC migration disturbances in the neonatal rat. Rat pups were injected with 5-bromo-2'-deoxyuridine (BrdU) and divided into five treatment groups, and double immunofluorescent staining targeting BrdU and homeobox prospero-like protein 1 (Prox1) was performed to examine the localization of BrdU/Prox1 colabeled cells, and then the GC migration was assessed. As a result, we found that the ectopic migration of GC after 2% isoflurane exposure on postnatal day 7 significantly increased after P21. The number of hilar ectopic GCs was influenced by the concentration of isoflurane and the exposure day but not by carbon dioxide exposure. Our main finding is that neonatal isoflurane anesthesia disturbs the migration of GCs in the rat DG, which may be one possible mechanism underlying the neurotoxicity following neonatal isoflurane anesthesia.

Isoflurane induces c-Fos expression in the area postrema of the rat.

INTRODUCTION: Volatile anesthetics are speculated to cause postoperative nausea and vomiting via stimulation of the chemoreceptor trigger zone (CTZ). However, the precise mechanism underlying the emetic action of these drugs is not well understood. In this study, we assessed whether isoflurane induced the expression of c-Fos, a neuronal activation marker, in the area postrema (AP), the locus of the CTZ, in rats, which do not have vomiting action. MATERIALS AND METHODS: Male rats were exposed to 1.3% isoflurane for 0-240 min, or to various concentrations of isoflurane (0, 1.3%, or 2.6%) for 120 min. Finally, the rats were exposed to 1.3% isoflurane for 120 min after ondansetron administration. After the treatments, immunohistochemistry of the rat AP was performed using c-Fos antibody staining. RESULTS: One-way analysis of variance showed that isoflurane exposure significantly increased c-Fos expression in the AP; however, the rats pretreated with 4 mg/kg ondansetron showed significantly decreased c-Fos expression. Moreover, we evaluated the effect of the anesthetic on inducing pica in the rats, and found that kaolin intake was not influenced by isoflurane exposure. CONCLUSION: Overall, these results suggest that isoflurane activates AP neurons and may be involved in the emetic mechanism of isoflurane. This study further suggests the feasibility of using rats as a model for studying emetic mechanisms of drugs, despite their lack of vomit action.

Influence of nitrous oxide on granule cell migration in the dentate gyrus of the neonatal rat.

For several decades, the neurotoxicities of anesthetics to the developing brain have been reported by many researchers focusing on various phenomena such as apoptosis, neurodegeneration, electrophysiological aberrations, and behavioral abnormalities. According to these reports, signals via N-methyl-D-aspartate receptors (NMDA-r) and/or γ-aminobutyric acid type A receptors (GABAA-r) are implicated in the anesthetic neurotoxicity. On the other hand, during brain development, NMDA-r and GABAA-r are also recognized to play primary roles in neural cell migration. Therefore, anesthetics exposed in this period may influence the neural cell migration of neonates, and increase the number of hilar ectopic granule cells, which are reported to be a cause of continuous neurological deficits. To examine this hypothesis, we investigated immunohistochemically granule cell distribution in the hippocampal dentate gyrus of Wistar/ST rats after nitrous oxide (N2O) exposure. At postnatal day (P) 6, 5-bromo-2'-deoxyuridine (BrdU) was administered to label newly generated cells. Then, rats were divided into groups (n = 6 each group), exposed to 50% N2O at P7, and evaluated at P21. As a result, we found that ectopic ratios (ratio of hilar/total granule cells generated at P6) were decreased in rats at P21 compared with those at P7, and increased in N2O exposed rats for over 120 min compared with the other groups. These results suggest that 50% N2O exposure for over 120 min increases the ratios of ectopic granule cells in the rat dentate gyrus.

Left subclavian artery malperfusion due to thoracic outlet syndrome during total vertebrectomy for invasive lung cancer: a case report.

Thoracic outlet syndrome (TOS) can interrupt blood flow to upper limbs by vascular compression. We report a case of a 52-year-old man who presented left subclavian artery malperfusion due to TOS during total vertebrectomy (Th2-4) in the prone position for invasive lung cancer. At the time of resection of the vertebral bodies, his left radial systolic blood pressure had begun to drop intermittently and we noticed an interarm pressure difference. Accordingly, we began to monitor the right radial artery pressure and found that only the left radial artery pressure decreased as a result of compressive force from the surgical site. The operation was continued with intermittent malperfusion of the left arm, and when it was prolonged, we asked the surgeons to release the compression. No symptoms of ischemia or nerve injuries in the left arm were observed after the surgery. Retrospective review of his preoperative enhanced computed tomography images suggested a slightly compressed left subclavian artery in the costoclavicular space. Combination of the prone position and a specific upper limb position may be a risk factor for intraoperative TOS. An interarm blood pressure difference is a clue to detect accidental arterial TOS during general anesthesia.

Nociceptin/orphanin FQ slows inspiratory rhythm via its direct effects on the pre-Bötzinger complex.

In a previous study, we showed that in an in vitro en bloc preparation of newborn rats perfused with standard [K(+)] (6.2mM) and high [K(+)] (11.2mM) artificial cerebrospinal fluid (aCSF), nociceptin/orphanin FQ (N/OFQ) suppresses bursting of pre-inspiratory neurons with 1:1 coupling to the fictive inspiration. However, it is unclear whether the pre-Bötzinger complex (preBötC) is involved in the N/OFQ-induced slowing. Using in vitro en bloc preparations with and without the retrotrapezoid nucleus/parafacial respiratory group (RTN/pFRG) perfused with high [K(+)] aCSF, we found the following: (1) there were no differences in the effects of N/OFQ on the inspiratory rhythm between the preparations with and without the RTN/pFRG, (2) N/OFQ decreased the input resistance of inspiratory neurons (Insps) in the preparations without the RTN/pFRG and suppressed their ectopic firing activities, and (3) N/OFQ suppressed the spontaneous firing of Insps under a chemical synaptic transmission blockade. In conclusion, it is possible that the preBötC is involved in N/OFQ-induced inspiratory rhythm slowing.

Dexmedetomidine suppresses long-term potentiation in the hippocampal CA1 field of anesthetized rats.

PURPOSE: The aim of this study was to evaluate the effect of dexmedetomidine (DEX) on hippocampal synaptic activity in vivo. METHODS: The adult rats used for this study received a intraperitoneal bolus injection of 3, 10, 30, or 100 µg/kg of DEX or an equivalent volume of saline. Electrophysiological recording of the hippocampal CA1 region was initiated 20 min after drug administration. The results are expressed as the percentages of the population spike amplitude measured just before high-frequency stimulation (HFS). The electrophysiological data were analyzed with an area under the curve (AUC) of 10-60 min after HFS. Moreover, to investigate the sedative dose of DEX in rats, we recorded the duration of loss of spontaneous movement after the administration of each dose of DEX. RESULTS: Intraperitoneal administration of DEX at doses of 30 and 100 µg/kg induced a range of sedative effects. The AUC measurements were significantly lower in the 30 and 100 µg/kg groups than in those injected with vehicle (vehicle: 8.81 ± 0.49, n = 7; DEX 30 µg/kg: 6.02 ± 0.99, n = 6; DEX 100 µg/kg: 5.10 ± 0.43, n = 5; P < 0.05). CONCLUSION: The results of our in vivo study reveal that sedative doses of DEX impaired the induction of hippocampal long-term potentiation (LTP). These findings may signify a causal link between DEX-induced sedative action and hippocampal LTP suppression, providing a better understanding of the mechanisms underlying the DEX-induced sedative and/or amnestic effect.

Co-existing liver disease increases the risk of postoperative thrombocytopenia in patients undergoing hepatic resection: implications for the risk of epidural hematoma associated with the removal of an epidural catheter.

PURPOSE: A common surgical diagnosis for hepatic resection in Japan is hepatocellular carcinoma secondary to chronic viral hepatitis. It is known that chronic liver disease causes a decrease in blood platelet count. We retrospectively reviewed the perioperative changes in blood platelet count associated with hepatic resection at a Japanese institution and evaluated the incidence and risk factors for postoperative thrombocytopenia, which may increase the potential risk of epidural hematoma. METHODS: We analyzed the data of 165 patients who underwent hepatic resection between 1 March 2010 and 30 June 2012 at Hokkaido University Hospital. The criterion of the platelet count for the unsafe removal of epidural catheter was <100,000/µL. Logistic regression was used to model the association between postoperative thrombocytopenia and co-existing liver disease, estimated blood loss and type of hepatic resection. RESULTS: After hepatic resection, 42.4 % of patients without preoperative thrombocytopenia experienced thrombocytopenia. The presence of co-existing liver disease was identified as a risk factor for postoperative thrombocytopenia [odds ratio 3.17 (95 % confidence interval 1.63-6.18)]. There was no epidural hematoma in the 149 patients who had epidural anesthesia. CONCLUSION: Hepatic resection can cause postoperative thrombocytopenia that may increase the potential risk of epidural hematoma associated with catheter removal, and the presence of co-existing liver disease heightens concerns for postoperative crucial thrombocytopenia.

Neonatal exposure to sevoflurane causes significant suppression of hippocampal long-term potentiation in postgrowth rats.

BACKGROUND: The inhaled anesthetic sevoflurane is commonly used for neonates in the clinical setting. Recent studies have indicated that exposure of neonatal rodents to sevoflurane causes acute widespread neurodegeneration and long-lasting neurocognitive dysfunction. Although acute toxic effects of sevoflurane on cellular viability in the hippocampus have been reported in some studies, little is known about the effects of neonatal sevoflurane exposure on long-term hippocampal synaptic plasticity, which has been implicated in the processes of learning and memory formation. Our study is the first to examine the long-term electrophysiological impact of neonatal exposure to a clinically relevant concentration of sevoflurane. METHODS: On postnatal day 7, rats were exposed to sevoflurane (1% or 2% for 2 hours) with oxygen. To eliminate the influence of blood gas abnormalities caused by sevoflurane-induced respiratory suppression, a group of rats were exposed to a high concentration of carbon dioxide (8% for 2 hours) to duplicate respiratory disturbances caused by 2% sevoflurane exposure. RESULTS: Exposure of neonatal rats to 2% sevoflurane for 2 hours caused significant suppression of long-term potentiation (LTP) induction in the postgrowth period. There was no significant difference between the control group and the CO2-exposed group in LTP induction, indicating that sevoflurane-induced LTP suppression was not caused by blood gas abnormalities. CONCLUSION: Our present findings indicate that neonatal exposure to sevoflurane at a higher concentration can cause alterations in the hippocampal synaptic plasticity that persists into adulthood.

Neonatal exposure to high concentration of carbon dioxide produces persistent learning deficits with impaired hippocampal synaptic plasticity.

Although respiratory complications with blood gas abnormalities contribute significantly to neurodevelopment in the immature brain, little is known about the mechanisms via which blood gas abnormalities, such as hypoxic hypercapnia, impair neurocognitive outcomes. To investigate the possible long-term consequences of neonatal exposure to hypoxic hypercapnia regarding learning ability, we investigated the effect of neonatal hypoxic hypercapnia on later functions in the hippocampus, which is a structure that has been implicated in many learning and memory processes. Neonatal rat pups (postnatal day 7; P7) were exposed to a high concentration of carbon dioxide (CO2; 13%) for 2 or 4h. Exposure to CO2 in P7 rat pups caused blood gas abnormalities, including hypercapnia, hypoxia, and acidosis, and disrupted later learning acquisition, as assessed in 10-week-old adult rats subjected to a Morris water maze test. Induction of long-term potentiation (LTP) in the synapses of the hippocampal CA1 area was also impaired, whereas the paired-pulse responses of population spikes exhibited a significant increase, in CO2-exposed rats, suggesting decreased recurrent inhibition in the hippocampus. Such long-lasting modifications in hippocampal synaptic plasticity may contribute to the learning impairments associated with perinatal hypoxic hypercapnia and acidosis.

[Survey of patients presented with severely difficult intubation in Hokkaido University Hospital (2005-2010)].

BACKGROUND: Recently, in addition to bronchofiberscope, the new equipments to manage difficult intubation are available. However, it is unknown whether the incidence of difficult intubation decreases or not. In order to determine the incidence of severe difficult intubation, we conducted a survey of patients who presented with severely difficult intubation during 2005-2010. METHODS: From data of patients in whom tracheal intubation was attempted in the operating rooms in Hokkaido university hospital from January 2005 to December 2010, the data was collected on the patients who presented with severely difficult intubation, defined as the inability to secure tracheal intubation in less than 20 min from induction of anesthesia. RESULTS: A total of 21,982 tracheal intubations were attempted during the study period. The incidence of severely difficult intubation was 0.3% (65 intubations for 58 patients). There was no significant difference among the years in the incidence of severely difficult intubation. CONCLUSIONS: The incidence of severely difficult intubation was 0.3% in Hokkaido university hospital during 2005-2010.

Neonatal administration with dexmedetomidine does not impair the rat hippocampal synaptic plasticity later in adulthood.

BACKGROUND AND OBJECTIVE: The use of dexmedetomidine (DEX), a selective alpha-2 agonist, in pediatric practice is expanding as a result of its desirable properties. To clarify the long-term neurological consequences of neonatal administration of DEX, we investigated the long-term effects of neonatal administration of DEX on hippocampal synaptic activity. METHODS: The rat pups received a bolus intraperitoneal injection of either 5 or 10 µg·kg(-1) DEX, or an equivalent volume of vehicle on postnatal day 7 (P7). Nine weeks after administration, evoked potentials (population spike, PS) and long-term potentiation (LTP) in the hippocampal CA1 region of rats were studied in vivo. RESULTS: Dexmedetomidine had a considerable sedative effect at these doses with little respiratory depression on P7. Nine weeks after administration of DEX, the amplitude of PS in the two treated groups was similar to that in the control group. DEX-treated rats showed no impairment in the induction of LTP. Furthermore, the response in PS to the paired stimuli was not impaired by neonatal administration of DEX. CONCLUSION: These findings demonstrate that a single administration of DEX to rats on P7 preserves hippocampal synaptic plasticity as well as synaptic transmission later in life. In view of the some evidence that have demonstrated the permanent detrimental impact of commonly used anesthetics on neurological outcomes after neonatal exposure, our findings may suggest the relative safety of DEX administered as a sedative agent to neonatal animals with regard to the development of hippocampal synaptic functions.

[Coagulation profiles following donor hepatectomy and implications for the risk of epidural hematoma associated with epidural anesthesia].

BACKGROUND: Continuous epidural analgesia has become an accepted technique used in laparotomy including liver resections. Although American Society of Regional Anesthesia and Pain Medicine recommends that epidural catheter be removed with prothrombin time-international normalized ratio (PT-INR) less than 1.5, it is possible that liver surgery causes coagulation disturbances. We examined the postoperative changes in coagulation profiles of living liver donors to elucidate whether hepatectomy increases the risk of epidural hematoma related to removal of epidural catheters or not. METHODS: From January 2007 to October 2009, 42 living liver related transplantations were performed in Hokkaido University Hospital. We reviewed the donor data including PT-INR obtained during perioperative days [preoperative, immediately postoperative, postoperative day 1, 3 and 7] and epidural catheter-related-complications, retrospectively. RESULTS: While in all donors values of PT-INR obtained during preoperative periods were within normal limits, 14 donors had a PT-INR over 1.5 during postoperative periods. There was no epidural hematoma case in this study. CONCLUSIONS: Our study suggested that hepatectomy increases the risk of epidural hematoma related to removal of epidural catheters, even in the living liver transplant donors with normal liver function.

Effects of sevoflurane on respiratory rhythm oscillators in the medulla oblongata.

Using in vitro newborn rat brainstem-spinal cord preparations with and without the parafacial respiratory group (pFRG), we examined the effects of the volatile anaesthetic sevoflurane on the respiratory rhythm oscillators of the pFRG and the preBötzinger complex (preBötC). Our study indicated that sevoflurane depressed pre-inspiratory neurons (Pre-Is) in the pFRG via gamma-aminobutyric acid-A (GABA(A))ergic and glycinergic inhibition and that it depressed preBötC inspiratory neurons via GABA(A)ergic but not via glycinergic inhibition. We also found that sevoflurane had stimulant effects on the respiratory rhythm oscillators. Our results shed light on respiratory rhythm generation. In all preparations (n=16) in which Pre-Is activity was recorded, inspiratory-related cervical motor output remained after application of 0.47 mM sevoflurane, despite the disappearance of the burst activity of Pre-Is. This finding shows that Pre-Is are not essential for respiratory rhythm generation and suggests that sevoflurane, when applied at a proper concentration, might offer a pharmacological means to eliminate pFRG function while preserving preBötC activity.

Altered synaptic transmission in rat anterior cingulate cortex following peripheral nerve injury.

BACKGROUND: Patients with neuropathic pain present not only with persistent pain but also a complex set of additional symptoms, including mood disorders and cognitive disturbance. Given the important roles of the anterior thalamic nuclei (ATN) and anterior cingulate cortex (ACC) in the cognitive and emotional aspects of pain, investigation of the properties of ATN-ACC synapses will help us to understand the mechanisms underlying neuropathic pain. METHODS: We studied changes in ATN-evoked ACC excitatory postsynaptic potentials (EPSPs) induced by neuropathic pain in a rat model under halothane anaesthesia. RESULTS: Neuropathic pain caused significant suppression of EPSPs in the ACC compared with rats subjected to sham surgery. Similar to previous evidence, acute inflammatory pain induced by formalin injection into the hind paw significantly increased synaptic efficacy in the ACC compared with naive rats. Neither of the pain paradigms altered the paired-pulse responses. CONCLUSIONS: A possible explanation for the neuropathic pain-related suppression of EPSPs is that the ACC was already sufficiently active at baseline as a result of neuropathic pain, and ATN stimulation could not further increase the already elevated level of ACC activity. This abnormal excitability of the ATN-ACC synapse may be important in understanding the mechanism underlying neuropathic pain, particularly with respect to the affective and cognitive aspects.

Nociceptin/orphanin FQ causes non-quantal slowing of respiratory rhythm in brainstem-spinal cord preparation from newborn rat.

Nociceptin/orphanin FQ (N/OFQ) is the endogenous agonist of the N/OFQ peptide receptor, an inhibitory G protein-coupled receptor. N/OFQ acts as a neuromodulator to depress respiratory rhythm in the brainstem. Although the mechanisms of respiratory rhythm generation remain poorly understood, the pre-inspiratory neuron (Pre-I) and the pre-Bötzinger complex (preBötC) inspiratory neuron (Insp) network in the rostral ventrolateral medulla (RVLM) have been proposed to be essential for respiratory rhythm generation. Opioids presumably cause quantal slowing via selective depression of preBötC Insps. However, it is unclear whether N/OFQ depresses respiratory rhythm via the same mechanism. In this study, using in vitro newborn rat en bloc preparations, we examined the slowing pattern of N/OFQ (quantal or non-quantal) and the effects of N/OFQ on the extracellularly recorded discharge of Pre-Is and Insps in the RVLM. N/OFQ caused non-quantal slowing with a synchronous decrease in burst rates of Insps and of C4 discharge whereas the intraburst spike number in Insps remained unchanged. It also caused a significant decrease in burst rates and intraburst spike numbers in Pre-Is, while the 1:1 coupling of Pre-Is bursts to C4 bursts was preserved. When superfusate K(+) was elevated from 6.2 to 11.2mM, Pre-I activity was increasingly uncoupled from C4 bursts. After the application of N/OFQ in a high [K(+)] superfusate, the 1:1 coupling of Pre-Is to C4 bursts was restored. We conclude that N/OFQ suppresses burst and spike generation of Pre-Is, and that suppression of Pre-Is activity with synchronous coupling to the Insps network contributes to N/OFQ-induced non-quantal slowing.

Anatomical features of the right internal jugular vein in infants and young children undergoing heart surgery for congenital disease: comparison between cyanotic and noncyanotic patients.

PURPOSE: It has been reported that children with cyanotic heart disease have elevated systemic levels of vascular endothelial growth factor, which may be related to the development of vessels. However, it is unknown whether the anatomical features of the internal jugular vein (IJV) differ between cyanotic and noncyanotic children. In this study, we compared anatomical information about the IJV of these two groups of patients. METHODS: We measured the distance between the right IJV and the right carotid artery (distance), the diameter of the IJV (diameter), and the depth of the IJV from the skin (depth), using an ultrasound device, in 100 children (0-34 months) undergoing heart surgery for congenital disease. First, we evaluated the relationship of these measurement values with patient demographic data (age, height, and body weight). Next, we evaluated the effect of the 15 degrees Trendelenburg position on these measurement values. RESULTS: There were 62 cyanotic and 38 noncyanotic patients. Distance and diameter, but not depth, were well correlated with the demographic data in both patient groups. Diameter in cyanotic patients was highly correlated with the demographic data. Clinically significant changes in the measurement values were not observed in the 15 degrees Trendelenburg position compared with the horizontal position in either patient group. CONCLUSION: The anatomical features of the right IJV in infants and young children with congenital heart disease were not different in cyanotic and noncyanotic patients, except for the relationship between diameter and the demographic data. In the small patients examined in our study (72% of them were infants), the diameter of the IJV was not sufficiently enlarged by the Trendelenburg position, regardless of whether the patients were cyanotic or noncyanotic.

Isoflurane bidirectionally modulates the paired-pulse responses in the rat hippocampal CA1 field in vivo.

BACKGROUND: We studied the effects of isoflurane on hippocampal synaptic transmission and paired-pulse plasticity, under in vivo intact interneuron circuitry. METHODS: Using rats chronically implanted with electrodes, excitatory postsynaptic potential (EPSP) and population spike amplitude (PSA) were measured in the hippocampal CA1 field by stimulating Schaffer collaterals. The lungs of the rats were mechanically ventilated with 0.25-1.5 minimum alveolar anesthetic concentration (MAC) isoflurane. A control value was obtained in the absence of isoflurane. RESULTS: Isoflurane depressed EPSP responses and enhanced synaptic efficacy. PSA was not depressed except under high concentrations, presumably reflecting a well-balanced combination with the decreased EPSP and enhanced synaptic efficacy. Low concentrations of isoflurane (0.25 and 0.5 MAC) increased paired-pulse facilitation (PPF), whereas a high concentration of isoflurane (1.5 MAC) prolonged the paired-pulse depression. CONCLUSIONS: Isoflurane appeared to affect multiple sites of CA1 synapses: 1) the depression of presynaptic glutamatergic transmission as shown by depressed EPSP and increased PPF; 2) the depression of pyramidal neurons as shown by prolonged PPF and depressed PSA under high concentration; and 3) the depression of interneurons as shown by the greater synaptic efficacy. The degree of each of these inhibitory effects seemed to vary at different concentrations, and the overall direction of the synaptic properties may depend on the balances between these inhibitory effects in vivo.