Comparison of the effect of surgical versus transcatheter aortic valve replacement on the development of postoperative acute kidney injury.

Acute kidney injury (AKI) frequently occurs after cardiac surgery. Recently, transcatheter aortic valve implantation (TAVI), a less invasive option for aortic stenosis (AS), has been increasingly performed, particularly in elderly patients. We retrospectively investigated and compared the incidence and risk factors of postoperative AKI in patients who underwent surgical aortic valve replacement (SAVR) and TAVI. This was a retrospective single-center study. Seven days postoperatively, data were obtained from medical records. Patients were classified into SAVR and TAVI groups based on age, according to the policy of the Japanese Circulation Society. A total of 155 patients underwent surgery for AS between January 2020 and December 2021. Variables included age, sex, risk score, preoperative left ventricular ejection fraction, hypertension, and renal dysfunction. AKI was defined in accordance with the Kidney Disease: Improving Global Outcomes criteria. A total of 33 SAVR and 79 TAVI procedures were included in this study. The incidences of AKI in the SAVR and TAVI groups were 45.5% and 43.0%, respectively. No significant differences existed between the two groups. Weight (p = 0.0392) and pre-renal dysfunction (p = 0.0308) affected the incidence of AKI in the SAVR group, whereas no such variables were identified in the TAVI group. Within the current age-based treatment selection criteria for AS, no significant difference in the incidence of AKI was observed between the two procedures.Although preoperative renal function may be associated with postoperative AKI, further studies are required to select the optimal surgical procedure for patients with renal dysfunction.

Genome-Wide Association Study Identifies Genetic Polymorphisms Associated with Estimated Minimum Effective Concentration of Fentanyl in Patients Undergoing Laparoscopic-Assisted Colectomy.

Sensitivity to opioids varies widely among individuals. To identify potential candidate single-nucleotide polymorphisms (SNPs) that may significantly contribute to individual differences in the minimum effective concentration (MEC) of an opioid, fentanyl, we conducted a three-stage genome-wide association study (GWAS) using whole-genome genotyping arrays in 350 patients who underwent laparoscopic-assisted colectomy. To estimate the MEC of fentanyl, plasma and effect-site concentrations of fentanyl over the 24 h postoperative period were estimated with a pharmacokinetic simulation model based on initial bolus doses and subsequent patient-controlled analgesia doses of fentanyl. Plasma and effect-site MECs of fentanyl were indicated by fentanyl concentrations, estimated immediately before each patient-controlled analgesia dose. The GWAS revealed that an intergenic SNP, rs966775, that mapped to 5p13 had significant associations with the plasma MEC averaged over the 6 h postoperative period and the effect-site MEC averaged over the 12 h postoperative period. The minor G allele of rs966775 was associated with increases in these MECs of fentanyl. The nearest protein-coding gene around this SNP was DRD1, encoding the dopamine D1 receptor. In the gene-based analysis, the association was significant for the SERP2 gene in the dominant model. Our findings provide valuable information for personalized pain treatment after laparoscopic-assisted colectomy.

Effects of rs958804 and rs7858836 single-nucleotide polymorphisms of the ASTN2 gene on pain-related phenotypes in patients who underwent laparoscopic colectomy and mandibular sagittal split ramus osteotomy.

BACKGROUND: Opioids are widely used as effective analgesics, but opioid sensitivity varies widely among individuals. The underlying genetic and nongenetic factors are not fully understood. Based on the results of our previous genome-wide association study, we investigated the effects of single nucleotide polymorphisms (SNPs) of the astrotactin 2 (ASTN2) gene on pain-related phenotypes in surgical patients. METHODS: We investigated the effects of two SNPs, rs958804 T/C and rs7858836 C/T, of the ASTN2 gene on eight and seven pain-related phenotypes in 350 patients who underwent laparoscopic colectomy (LAC) and 358 patients who underwent mandibular sagittal split ramus osteotomy (SSRO), respectively. In both surgical groups, intravenous fentanyl patient-controlled analgesia (PCA) was used for postoperative analgesia, and 24-hour postoperative PCA fentanyl use was the primary endpoint. RESULTS: The association analyses among the two SNPs and pain-related traits showed that 24-hour fentanyl use was significantly associated with the two SNP genotypes in both surgical groups. The Mann-Whitney test showed that 24-hour fentanyl use was lower in patients with the C allele than in patients with the TT genotype of the rs958804 T/C SNP (P = .0019 and .0200 in LAC and SSRO patients, respectively), and it was lower in patients with the T allele than in patients with the CC genotype of the rs7858836 C/T SNP (P = .0017 and .0098 in LAC and SSRO patients, respectively). CONCLUSION: The two SNPs of the ASTN2 gene were consistently associated with fentanyl requirements after two different types of surgery. These findings may contribute to personalized pain control.

Genome-wide scan identifies candidate loci related to remifentanil requirements during laparoscopic-assisted colectomy.

AIM:  Opioids are widely used as effective analgesics, but opioid sensitivity is well known to vary widely among individuals. We explored the genetic factors that contribute to individual differences in intraoperative opioid sensitivity by performing a genome-wide association study. PATIENTS & METHODS: We conducted a multistage genome-wide association study in subjects who underwent laparoscopic-assisted colectomy. RESULTS: A nonsynonymous SNP, rs199670311, within the TMEM8A gene region and intronic SNPs, including rs4839603, within the SLC9A9 gene region were significantly associated with intraoperative opioid requirements (p = 3.409 × 10-8 in the dominant model for rs199670311; p = 4.162 × 10-6 and p = 4.229 × 10-6 in the additive and recessive models, respectively, for rs4839603). The A and T alleles of the rs199670311 and rs4839603 SNPs, respectively, were associated with lower opioid sensitivity in patients. CONCLUSION: Our findings provide valuable information for personalized pain treatment during laparoscopic-assisted colectomy.

Opposite Associations Between the rs3845446 Single-Nucleotide Polymorphism of the CACNA1E Gene and Postoperative Pain-Related Phenotypes in Gastrointestinal Surgery Versus Previously Reported Orthognathic Surgery.

UNLABELLED: Cav2.3 (R-type) voltage-activated Ca(2+) channels (VACCs), encoded by the calcium channel, voltage-dependent, R-type, α1E subunit (CACNA1E) gene, are responsible for transmission of somatic inflammatory pain, and activation of antinociception elicited by visceral inflammatory pain stimuli. Carriers of the minor G allele of the rs3845446 single-nucleotide polymorphism (SNP) of the CACNA1E gene reportedly exhibit a decrease in opioid requirements to control typical somatic inflammatory pain after orthognathic surgery (ie, a painful cosmetic surgery), suggesting the downregulation of Cav2.3 VACC function that is responsible for transmission of somatic inflammatory pain in these carriers. Gastrointestinal surgery involves somatic and visceral inflammatory pain, in which visceral inflammatory pain stimuli activate Cav2.3 VACC-mediated antinociception. Unknown is whether pain-related phenotypes after gastrointestinal surgery are affected in these carriers. The present study used a correlational design to examine the effect of the rs3845446 SNP on postoperative pain-related phenotypes in 2 groups of patients who underwent gastrointestinal surgery. Carriers of the minor G allele had greater opioid requirements after laparoscopic colectomy when intravenous patient-controlled analgesia was used, and reported higher pain scores after open gastrointestinal surgery when postoperative analgesia was managed with continuous epidural analgesia and rescue analgesics. These results suggest that pain-related phenotypes after gastrointestinal surgery are enhanced in carriers of the minor G allele of the rs3845446 SNP, possibly through impairment of Cav2.3 VACC function that is responsible for the activation of visceral inflammatory pain stimulus-elicited antinociception. PERSPECTIVE: Carriers of the minor allele of the rs3845446 SNP of the CACNA1E gene required more opioid or reported higher pain scores after gastrointestinal surgery, and required less opioid after orthognathic surgery. The difference may result from the presence of visceral inflammatory pain stimulus that activates Cav2.3 VACCs-mediated antinociception.

Genome-wide association study identifies candidate loci associated with postoperative fentanyl requirements after laparoscopic-assisted colectomy.

AIMS: Opioids are widely used as effective analgesics, but opioid sensitivity is well known to vary widely among individuals and the underlying genetic factors are not fully understood, thus hampering efficient pain treatment. We explored the genetic factors that contribute to individual differences in opioid sensitivity by performing a genome-wide association study. METHODS: We conducted a multistage genome-wide association study in subjects who underwent laparoscopic-assisted colectomy (LAC). RESULTS: A nonsynonymous SNP in the LAMB3 gene region, rs2076222, was strongly associated with postoperative opioid requirements. The C allele of this best-candidate SNP was associated with lower opioid sensitivity and/or higher pain sensitivity in the patient subjects. CONCLUSION: Our findings provide valuable information for personalized pain treatment after LAC, in which the C allele of the rs2076222 SNP is associated with lower opioid sensitivity and requires more opioid analgesic after LAC.

The effects of dexmedetomidine administration on the pulmonary artery pressure and the transpulmonary pressure gradient after the bidirectional superior cavopulmonary shunt.

The hemodynamic effects of dexmedetomidine (DEX) on pulmonary artery pressure (PAP) are not fully understood in patients with a single-ventricle physiology. The objective of this retrospective study was to characterize the effect of perioperative DEX infusion on PAP and the transpulmonary pressure gradient after a bidirectional superior cavopulmonary shunt (BCPS) operation. We retrieved physiologic data including the heart rate, incidence of cardiac pacing, systolic and diastolic arterial blood pressure (ABP), and superior vena cava (SVC) and inferior vena cava (IVC) pressures from the medical records of all patients <12 months of age who underwent a BCPS operation. Patients with an additional Norwood or Damus-Kaye-Stansel procedure, those with additional pulmonary blood flow, and those without both a SVC and an IVC catheter were excluded from the present study. Following the BCPS operation, the SVC pressure is equivalent to the PAP. Similarly, the IVC pressure is equivalent to the common atrial pressure (CAP). Accordingly, we can directly assess the transpulmonary pressure gradient, defined as the difference between the PAP and the CAP, using simultaneous SVC and IVC pressure measurements. Twenty-nine patients were included in the present study. We did not find any increase in the PAP, CAP, PAP/systolic ABP ratio, or the transpulmonary pressure gradient as of 6 h after admission to the intensive care unit when the patients were treated with DEX infusion at a median (interquartile ranges) dose of 0.6 mcg/kg/h (0.4, 0.64 mcg/kg/h). We concluded that the administration of DEX to children with a single-ventricle physiology is acceptable.

[General anesthesia for a pregnant patient with PAPA syndrome].

A 31-year-old female, with 22 weeks of pregnancy, presented with sudden onset of severe headache. CT scan showed diffuse subarachnoid hemorrhage. A cerebral angiogram showed dissecting aneurysm of right cerebral artery. To obliterate the aneurysm and prevent rupture, the patient underwent coil embolization via an endovascular approach under general anesthesia because the procedure under sedation with local anesthesia was too risky for re-bleeding. The patient has been diagnosed as PAPA syndrome. Although the arthritis was now stable and she was taking no drug, remarkable osteoarthritis was observed. The cervical spine X ray demonstrated no cervical ankylosis. As patient was sedated with propofol, airway examination could not be done except noticing thyromental distance of seven centimeters. Patient's trachea was intubated using Macintosh size #3 laryngoscope blade and a 7.0 non-styletted tracheal tube at the first attempt without any problems (Cormack grade I). Anesthesia was maintained with sevoflurane, fentanyl and remifentanil. After the end of endovascular surgery, the patient was transferred to the intensive care unit under mechanical ventilation. She was weaned from mechanical ventilation 2 days later but consciousness was unclear. Right incomplete paralysis was also observed. MRI revealed vasospasm on the bilateral internal carotid artery. The patient underwent percutaneous tansluminalangioplasty coil and intraarterial injection of fasudil hydrochloride under local anesthesia. The consciousness recovered fully and the paralysis was improved. The patient delivered the baby by Caesarean sections under combined spinal and epidural anesthesia at 36 weeks without any problems with both the mother and baby.

The impact of intraoperative vasopressin infusion in complex neonatal cardiac surgery.

OBJECTIVES: Although recent advances have led to a better understanding of the beneficial effects of vasopressin on haemodynamics in paediatric cardiac surgery, not much information is available on the adverse effects. The objective of this study was to assess the impact of intraoperative vasopressin infusion on postoperative liver, renal and haemostatic function and lactate levels in neonates undergoing cardiac surgery. METHODS: We reviewed data from 34 consecutive neonates who had undergone complex cardiac surgery. The cohort was divided into two groups according to the use of vasopressin. Seventeen patients received vasopressin [vasopressin (+) group], and 17 patients did not [vasopressin (-) group]. RESULTS: No differences between the groups in terms of age, weight, cardiopulmonary bypass time, Risk Adjustment for Congenital Heart Surgery-1 score or the comprehensive Aristotle score were seen. No differences in the systolic or diastolic arterial blood pressures, heart rate or inotropic score upon admission to the intensive care unit were observed between the groups. No adverse effects on the aminotransferase levels were seen. The vasopressin (+) group had higher urea and creatinine levels. All the patients except one received peritoneal dialysis on the day of surgery. Thirteen patients in the vasopressin (+) group and 7 patients in the vasopressin (-) group continued to require peritoneal dialysis on postoperative day 5 (POD 5) (P = 0.04). The platelet count had decreased to a significantly lower level in the vasopressin (+) group on POD 5 [97 x 10(3)/mm(3) (range: 40-132 x 10(3)/mm(3))]. A tendency toward a high lactate concentration was seen in the vasopressin (+) group. In comparison with the vasopressin (-) group, the number of patients whose lactate level remained above 2.0 mmol/l was higher in the vasopressin (+) group on PODs 2 and 3 (17 patients vs 8 patients, P < 0.01 and 15 patients vs 7 patients, P = 0.01, respectively). CONCLUSIONS: These findings suggest that the intraoperative use of vasopressin extends the period of peritoneal dialysis, reduces platelet counts and delays the recovery of the lactate concentration. Intraoperative vasopressin infusion should not be used routinely, but only in catecholamine-refractory shock.

Donepezil reverses buprenorphine-induced central respiratory depression in anesthetized rabbits.

Buprenorphine is a mixed opioid receptor agonist-antagonist used in acute and chronic pain management. Although this agent's analgesic effect increases in a dose-dependent manner, buprenorphine-induced respiratory depression shows a marked ceiling effect at higher doses, which is considered to be an indicator of safety. Nevertheless, cases of overdose mortality or severe respiratory depression associated with buprenorphine use have been reported. Naloxone can reverse buprenorphine-induced respiratory depression, but is slow-acting and unstable, meaning that new drug candidates able to specifically antagonize buprenorphine-induced respiratory depression are needed in order to enable maximal analgesic effect without respiratory depression. Acetylcholine is an excitatory neurotransmitter in central respiratory control. We previously showed that a long-acting acetylcholinesterase inhibitor, donepezil, antagonizes morphine-induced respiratory depression. We have now investigated how donepezil affects buprenorphine-induced respiratory depression in anesthetized, paralyzed, and artificially ventilated rabbits. We measured phrenic nerve discharge as an Index of respiratory rate and amplitude, and compared discharges following the injection of buprenorphine with discharges following the injection of donepezil. Buprenorphine-induced suppression of the respiratory rate and respiratory amplitude was antagonized by donepezil (78.4 +/- 4.8 %, 92.3% +/- 22.8 % of control, respectively). These findings indicate that systemically administered donepezil restores buprenorphine-induced respiratory depression in anesthetized rabbits.

Donepezil reverses buprenorphine-induced central respiratory depression in anesthetized rabbits

Buprenorphine is a mixed opioid receptor agonist-antagonist used in acute and chronic pain management. Although this agent's analgesic effect increases in a dose-dependent manner, buprenorphine-induced respiratory depression shows a marked ceiling effect at higher doses, which is considered to be an indicator of safety. Nevertheless, cases of overdose mortality or severe respiratory depression associated with buprenorphine use have been reported. Naloxone can reverse buprenorphine-induced respiratory depression, but is slow-acting and unstable, meaning that new drug candidates able to specifically antagonize buprenorphine-induced respiratory depression are needed in order to enable maximal analgesic effect without respiratory depression. Acetylcholine is an excitatory neurotransmitter in central respiratory control. We previously showed that a long-acting acetylcholinesterase inhibitor, donepezil, antagonizes morphine-induced respiratory depression. We have now investigated how donepezil affects buprenorphine-induced respiratory depression in anesthetized, paralyzed, and artificially ventilated rabbits. We measured phrenic nerve discharge as an Índex of respiratory rate and amplitude, and compared discharges following the injection of buprenorphine with discharges following the injection of donepezil. Buprenorphine-induced suppression of the respiratory rate and respiratory amplitude was antagonized by donepezil (78.4 ± 4.8 percent, 92.3 percent ± 22.8 percent of control, respectively). These findings indicate that systemically administered donepezil restores buprenorphine-induced respiratory depression in anesthetized rabbits.

Neural mechanisms of sevoflurane-induced respiratory depression in newborn rats.

BACKGROUND: Sevoflurane-induced respiratory depression has been reported to be due to the action on medullary respiratory and phrenic motor neurons. These results were obtained from extracellular recordings of the neurons. Here, the authors made intracellular recordings of respiratory neurons and analyzed their membrane properties during sevoflurane application. Furthermore, they clarified the role of gamma-aminobutyric acid type A receptors in sevoflurane-induced respiratory depression. METHODS: In the isolated brainstem-spinal cord of newborn rat, the authors recorded the C4 nerve burst as an index of inspiratory activity. The preparation was superfused with a solution containing sevoflurane alone or sevoflurane plus the gamma-aminobutyric acid type A receptor antagonist picrotoxin or bicuculline. Neuronal activities were also recorded using patch clamp techniques. RESULTS: Sevoflurane decreased C4 burst rate and amplitude. Separate perfusion of sevoflurane to the medulla and to the spinal cord decreased C4 burst rate and amplitude, respectively. Both picrotoxin and bicuculline attenuated the reduction of C4 burst rate. Sevoflurane reduced both intraburst firing frequency and membrane resistance of respiratory neurons except for inspiratory neurons. CONCLUSION: Under the influence of sevoflurane, the region containing inspiratory neurons, i.e., the pre-Bötzinger complex, may determine the inspiratory rhythm, because reduced C4 bursts were still synchronized with the bursts of inspiratory neurons within the pre-Bötzinger complex. In contrast, the sevoflurane-induced decrease in C4 burst amplitude is mediated through the inhibition of phrenic motor neurons. gamma-Aminobutyric acid type A receptors may be involved in the sevoflurane-induced respiratory depression within the medulla, but not within the spinal cord.

CO2-sensitivity of GABAergic neurons in the ventral medullary surface of GAD67-GFP knock-in neonatal mice.

We investigated the CO2 responsiveness of GABAergic neurons in the ventral medullary surface (VMS), a putative chemoreceptive area using a 67-kDa isoform of GABA-synthesizing enzyme (GAD67)-green fluorescence protein (GFP) knock-in neonatal mouse, in which GFP is specifically expressed in GABAergic neurons. The slice was prepared by transversely sectioning at the level of the rostral rootlet of the XII nerve and the rostral end of the inferior olive in mock cerebrospinal fluid (CSF). Each medullary slice was continuously superfused with hypocapnic CSF. GFP-positive neurons in the VMS were selected by using fluorescent optics and their membrane potentials and firing activities were analyzed with a perforated patch recording technique. Thereafter, superfusion was changed from hypocapnic to hypercapnic CSF. In 4 out of 8 GABAergic neurons in the VMS, perfusion with hypercapnic CSF induced more than a 20% decrease in the discharge frequency and hyperpolarized the neurons. The remaining 4 GFP-positive neurons were CO2-insensitive. GABAergic neurons in the VMS have chemosensitivity. Inhibition of chemosensitive GABAergic neural activity in the VMS may induce increases in respiratory output in response to hypercapnia.

Antagonism of morphine-induced central respiratory depression by donepezil in the anesthetized rabbit.

Morphine is often used in cancer pain and postoperative analgesic management but induces respiratory depression. Therefore, there is an ongoing search for drug candidates that can antagonize morphine-induced respiratory depression but have no effect on morphine-induced analgesia. Acetylcholine is an excitatory neurotransmitter in central respiratory control and physostigmine antagonizes morphine-induced respiratory depression. However, physostigmine has not been applied in clinical practice because it has a short action time, among other characteristics. We therefore asked whether donepezil (a long-acting acetylcholinesterase inhibitor used in the treatment of Alzheimer's disease) can antagonize morphine-induced respiratory depression. Using the anesthetized rabbit as our model, we measured phrenic nerve discharge as an index of respiratory rate and amplitude. We compared control indices with discharges after the injection of morphine and after the injection of donepezil. Morphine-induced depression of respiratory rate and respiratory amplitude was partly antagonized by donepezil without any effect on blood pressure and end-tidal C02. In the other experiment, apneic threshold PaC02 was also compared. Morphine increased the phrenic nerve apnea threshold but this was antagonized by donepezil. These findings indicate that systemically administered donepezil partially restores morphine-induced respiratory depression and morphine-deteriorated phrenic nerve apnea threshold in the anesthetized rabbit.

Antagonism of morphine-induced central respiratory depression by donepezil in the anesthetized rabbit

Morphine is often used in cancer pain and postoperative analgesic management but induces respiratory depression. Therefore, there is an ongoing search for drug candidates that can antagonize morphine-induced respiratory depression but have no effect on morphine-induced analgesia. Acetylcholine is an excitatory neurotransmitter in central respiratory control and physostigmine antagonizes morphine-induced respiratory depression. However, physostigmine has not been applied in clinical practice because it has a short action time, among other characteristics. We therefore asked whether donepezil (a long-acting acetylcholinesterase inhibitor used in the treatment of Alzheimer's disease) can antagonize morphine-induced respiratory depression. Using the anesthetized rabbit as our model, we measured phrenic nerve discharge as an index of respiratory rate and amplitude. We compared control indices with discharges after the injection of morphine and after the injection of donepezil. Morphine-induced depression of respiratory rate and respiratory amplitude was partly antagonized by donepezil without any effect on blood pressure and end-tidal C0(2). In the other experiment, apneic threshold PaC0(2) was also compared. Morphine increased the phrenic nerve apnea threshold but this was antagonized by donepezil. These findings indicate that systemically administered donepezil partially restores morphine-induced respiratory depression and morphine-deteriorated phrenic nerve apnea threshold in the anesthetized rabbit.

Association of nicotinic acetylcholine receptors with central respiratory control in isolated brainstem-spinal cord preparation of neonatal rats.

Nicotine exposure is a risk factor in several breathing disorders Nicotinic acetylcholine receptors (nAChRs) exist in the ventrolateral medulla, an important site for respiratory control. We examined the effects of nicotinic acetylcholine neurotransmission on central respiratory control by addition of a nAChR agonist or one of various antagonists into superfusion medium in the isolated brainstem-spinal cord from neonatal rats. Ventral C4 neuronal activity was monitored as central respiratory output, and activities of respiratory neurons in the ventrolateral medulla were recorded in whole-cell configuration. RJR-2403 (0.1-10 mM), alpha4beta2 nAChR agonist induced dose-dependent increases in respiratory frequency. Non-selective nAChR antagonist mecamylamine (0.1-100 mM), alpha4beta2 antagonist dihydro-beta-erythroidine (0.1-100 mM), alpha7 antagonist methyllycaconitine (0.1-100 mM), and a-bungarotoxin (0.01-10 mM) all induced dose-dependent reductions in C4 respiratory rate. We next examined effects of 20 mM dihydro-beta-erythroidine and 20mM methyllycaconitine on respiratory neurons. Dihydro-beta-erythroidine induces hyperpolarization and decreases intraburst firing frequency of inspiratory and preinspiratory neurons. In contrast, methyllycaconitine has no effect on the membrane potential of inspiratory neurons, but does decrease their intraburst firing frequency while inducing hyperpolarization and decreasing intraburst firing frequency in preinspiratory neurons. These findings indicate that alpha4beta2 nAChR is involved in both inspiratory and preinspiratory neurons, whereas alpha7 nAChR functions only in preinspiratory neurons to modulate C4 respiratory rate.

Association of nicotinic acetylcholine receptors with central respiratory control in isolated brainstem-spinal cord preparation of neonatal rats

Nicotine exposure is a risk factor in several breathing disorders Nicotinic acetylcholine receptors (nAChRs) exist in the ventrolateral medulla, an important site for respiratory control. We examined the effects of nicotinic acetylcholine neurotransmission on central respiratory control by addition of a nAChR agonist or one of various antagonists into superfusion medium in the isolated brainstem-spinal cord from neonatal rats. Ventral C4 neuronal activity was monitored as central respiratory output, and activities of respiratory neurons in the ventrolateral medulla were recorded in whole-cell configuration. RJR-2403 (0.1-10mM), a4b2 nAChR agonist induced dose-dependent increases in respiratory frequency. Non-selective nAChR antagonist mecamylamine (0.1-100mM), a4b2 antagonist dihydro-b-erythroidine (0.1-100mM), a7 antagonist methyllycaconitine (0.1-100mM), and a-bungarotoxin (0.01-10mM) all induced dose-dependent reductions in C4 respiratory rate. We next examined effects of 20mM dihydro-b-erythroidine and 20mM methyllycaconitine on respiratory neurons. Dihydro-b-erythroidine induces hyperpolarization and decreases intraburst firing frequency of inspiratory and preinspiratory neurons. In contrast, methyllycaconitine has no effect on the membrane potential of inspiratory neurons, but does decrease their intraburst firing frequency while inducing hyperpolarization and decreasing intraburst firing frequency in preinspiratory neurons. These findings indicate that a4b2 nAChR is involved in both inspiratory and preinspiratory neurons, whereas a7 nAChR functions only in preinspiratory neurons to modulate C4 respiratory rate.