Antenatal anxiety symptoms outperform antenatal depression symptoms and suicidal ideation as a risk factor for postpartum suicidal ideation

BACKGROUND AND OBJECTIVES

Suicidal ideation (SI) during the postpartum phase is linked with suicide, a leading cause of death during this period. Antenatal depression and anxiety symptoms have both been linked with increased risk for postpartum SI. However, research aimed at examining the relative contributions of antenatal anxiety and depression symptoms towards postpartum SI remains nascent. In this study, we investigated the relative contribution of antenatal anxiety symptoms, depression symptoms, and SI towards postpartum SI.

DESIGN

These data are from a longitudinal study in which American mothers were assessed during pregnancy and again at six- to eight weeks postpartum.

METHODS

Data were analyzed using correlations and logistic regression models.

RESULTS

Antenatal anxiety symptoms and antenatal depression symptoms were significantly correlated with postpartum SI. Results from a logistic regression model indicated that antenatal anxiety symptoms (T1; OR = 1.185 [1.125, 1.245], p = .004), but not antenatal depression symptoms (T1; OR = 1.018 [0.943, 1.093], p = .812) or antenatal SI (T1; OR = 1.58 [0.11, 22.29], p = 0.73), were significantly associated with postpartum SI.

CONCLUSIONS

Antenatal anxiety symptoms, depression symptoms, and SI were positively associated with postpartum SI. When examined simultaneously, anxiety symptoms during the antenatal phase (but not depression symptoms or SI) predicted SI in the postpartum phase.

Developmental Differences in Relations Between Episodic Memory and Hippocampal Subregion Volume During Early Childhood

Episodic memory shows striking improvement during early childhood. However, neural contributions to these behavioral changes are not well understood. This study examined associations between episodic memory and volume of subregions (head, body, and tail) of the hippocampus-a structure known to support episodic memory in school-aged children and adults-during early childhood (n = 45). Results revealed significant positive relations between episodic memory and volume of the hippocampal head in both the left and right hemispheres for 6- but not 4-year-old children, suggesting brain-behavior relations vary across development. These findings add new information regarding neural mechanisms of change in memory development during early childhood and suggest that developmental differences in hippocampal subregions may contribute to age-related differences in episodic memory ability.

Elective surgery: a comparison of in-patient versus day surgery practices in Ireland

BACKGROUND

Currently, there is a paucity of research which has assessed practices at the point of care for day surgery patient.

AIM

To outline the patient journey from first referral for surgery and identify structures and processes which facilitate or constrain the provision of day surgery.

METHOD

A retrospective medical charts review of 200 consecutively presenting patients undergoing elective surgery in two Irish teaching hospitals. Data collection was completed from January 2009 to March 2009. This analysis spanned from first referral to the hospital until discharge and follow up.

RESULTS

Great variability was noted in practices between the two hospitals. While some of the differences in practice become barriers to increased rates of day surgery, others did not have an impact.

CONCLUSION

This study echoes findings of other similar studies in that management of patients undergoing elective surgery which varies significantly across Irish hospitals.

National survey of the provision of day surgery across public and private hospitals in Ireland

BACKGROUND

Day surgery (DS) is viewed as the optimal environment for many surgical procedures. Yet, Irish DS rates are low compared to international figures.

AIMS

To describe the current provision of DS in Ireland and to identify barriers to its expansion.

METHODS

Thirty-seven public hospitals and 17 private hospitals providing DS were surveyed during July/August 2009.

RESULTS

Thirty-seven hospitals replied (67%) (30 public, 7 private). DS beds ranged from 3 to 39. Fourteen (38%) had dedicated DS units, and no unit had a consultant in charge. Twenty-one (57%) provided pre-assessment with 36 (96%) providing patient information leaflets both pre- and post-operatively. Stay-in rate was less than 5%. Eight units had reviewed the adverse event rates following DS. Seven barriers to optimizing DS were identified, the main one being lack of dedicated DS theatres.

Clinicopathologic factors predicting complete pathological response to neoadjuvant chemoradiotherapy in esophageal cancer

Multimodal therapy comprising neoadjuvant chemotherapy and radiation therapy prior to radical resection is increasingly utilized in gastroesophageal cancer. The achievement of a complete pathological response (pCR) or a major response is associated with an improved survival. However, up to 70% of patients show an incomplete or no response to the neoadjuvant regimen, and the identification of factors which predict a response would be of considerable clinical benefit. A retrospective analysis of a prospectively updated esophageal cancer database was performed. The predictive values of the following clinicopathological factors were investigated: age, sex, tobacco, alcohol, weight, clinical history, tumor type, site, length, width, morphology and differentiation. Statistical analysis was performed using Chi-square test with Pearson's test or Kruskal-Wallis test. One hundred and seventy-six patients were identified who had undergone neo-adjuvant chemoradiotherapy at St James's Hospital Dublin, between January 1990 and June 2003. A complete pathological response was seen in 40 cases (23%). There was a significant (P < 0.05) relationship between response to chemoradiotherapy and pretreatment tumor length. The median tumor length in the pCR group was 2 cm (1-5 cm) compared with 3 cm (2-7 cm) in non-responders (P < 0.05). Body weight, sex, tobacco or alcohol usage, tumor site, or differentiation were not predictive of response, although a trend (P = 0.08) was observed for squamous cell cancer compared with adenocarcinoma. Smaller tumor length was predictive of a greater response to chemotherapy and radiation therapy. This may reflect different tumor biology, perhaps with acquired resistance to treatment-induced apoptosis in the larger tumors. A simpler explanation is that the existing dose and treatment schedule for combination chemoradiotherapy is suboptimal in patients with larger tumors.

Molecular load of pathologically occult metastases in pelvic lymph nodes is an independent prognostic marker of biochemical failure after localized prostate cancer treatment

PURPOSE

Thirty percent of patients treated with curative intent for localized prostate cancer (PC) experience biochemical recurrence (BCR) with rising serum prostate-specific antigen (sPSA), and of these, approximately 50% succumb to progressive disease. More discriminatory staging procedures are needed to identify occult micrometastases that spawn BCR.

PATIENTS AND METHODS

PSA mRNA copies in pathologically normal pelvic lymph nodes (N0-PLN) from 341 localized PC patients were quantified by real-time reverse-transcriptase polymerase chain reaction. Based on comparisons with normal lymph nodes and PLN with metastases and on normalization to 5 x 10(6) glyceraldehyde-3'-phosphate dehydrogenase mRNA copies, normalized PSA copies (PSA-N) and a threshold of PSA-N 100 or more were selected for continuous and categorical multivariate analyses of biochemical failure-free survival (BFFS) compared with established risk factors.

RESULTS

At median follow-up of 4 years, the BFFS of patients with PSA-N 100 or more versus PSA-N less than 100 was 55% and 77% (P = .0002), respectively. The effect was greatest for sPSA greater than 20 ng/mL, 25% versus 60% (P = .014), Gleason score 8 or higher, 21% versus 66% (P = .0002), stage T3c, 18% versus 64% (P = .001), and high-risk group (50% v 72%; P = .05). By continuous analysis PSA-N was an independent prognostic marker for BCR (P = .049) with a hazard ratio of 1.25 (95% CI, 1.001 to 1.57). By categorical analysis, PSA-N 100 or more was an independent variable (P = .021) with a relative risk of 1.98 (95% CI, 1.11 to 3.55) for BCR compared with PSA-N less than 100.

CONCLUSION

PSA-N 100 or more is a new, independent molecular staging criterion for localized PC that identifies high-risk group patients with clinically relevant occult micrometastases in N0-PLN, who may benefit from additional therapy to prevent BCR.

Unusual cause of a perforated stomach

A case of gastric perforation 2 months following insertion of a gastric balloon is reported. The literature is reviewed regarding the complications and success rates inherent in such balloon devices. This is the first case report of an intra-gastric balloon causing gastric perforation.

Loss of Bcl-2 expression in Barrett's dysplasia and adenocarcinoma is associated with tumor progression and worse survival but not with response to neoadjuvant chemoradiation

Esophageal adenocarcinoma arising on a background of Barrett's esophagus is increasing in incidence. A molecular understanding of both the progression of Barrett's esophagus and the factors determining the response of adenocarcinoma to neoadjuvant therapy is required, and this study focused on the role of proteins regulated by the bcl-2 family of genes, which are important regulators of programmed cell death (apoptosis). In total, 48 patients (36 men, 12 women) with Barrett's adenocarcinoma were studied. All patients received preoperative chemoradiotherapy followed by surgery. Bcl-2, bax and bcl-x protein expression were detected by standard avidin-biotin peroxidase method. Bcl-2, bax and bcl-x expression were detected in 84%, 80%, and 76%, respectively, of normal squamous mucosa. An increasing degree of dysplasia in Barrett's mucosa both before and after chemoradiotherapy was significantly associated with a reduction of bcl-2 expression (P = 0.03 and 0.009, respectively). Bcl-2 expression was significantly associated with tumor differentiation (P = 0.03) and a trend towards earlier T stage (P = 0.08), but not with nodal status. Pre-therapeutic bcl-2, bax and bcl-x protein expression (27%, 75%, and 87.5%, respectively) were not associated with tumor response or resistance to therapy. Bcl-2-positive patients had a significantly improved survival compared with bcl-2-negative tumors. A significant reduction of bcl-2 expression is associated with the progression of Barrett's mucosa to adenocarcinoma. Bcl-2 expression was associated with improved survival. Preoperative chemoradiotherapy induces expression of bax and bcl-x protein. The pretreatment expression of bcl-2 and related proteins did not predict response or resistance to neoadjuvant chemoradiotherapy, suggesting that regulators of apoptosis alone do not determine the response of Barrett's adenocarcinoma to neoadjuvant therapy.

Spontaneous and inducible apoptosis in oesophageal adenocarcinoma

The use of neoadjuvant chemoradiotherapy prior to surgery in the treatment of oesophageal adenocarcinoma has increased in recent years, and up to 25% of patients will have a complete pathological response to the neoadjuvant therapy. Many patients will not respond, however, and the knowledge of molecular factors predicting response or resistance to chemoradiotherapy is required to enhance treatment results. An understanding of apoptosis and cell proliferation may be relevant and this study focused on apoptotic indices and cell-cycle related (Ki-67, p53 and bcl-2) protein expression in a cohort of 42 patients with primary oesophageal adenocarcinoma. We documented that apoptosis occurs among viable (proliferating) tumour cells in all adenocarcinoma cases examined in this study. Pre-operative chemoradiotherapy significantly increased apoptosis and significantly decreased cell proliferation (estimated by Ki-67 expression). Immunohistochemically detected p53 and bcl-2 gene products had no regulatory role in the apoptotic process. The cumulative expression of p53 protein is significantly associated with increasing proliferation activity. Evaluation of apoptosis in pre-treatment specimens may have potential utility in predicting the efficacy of treatment. Assessment of the tumours proliferation activity by Ki-67 expression might identify patients who are at risk of developing metastatic disease.

A pathological study of tumour regression in oesophageal adenocarcinoma treated with preoperative chemoradiotherapy

AIMS

To measure residual tumour in oesophageal adenocarcinoma treated with preoperative chemoradiotherapy, to correlate specific pathological variables with survival, and to describe morphological changes in tumour and non-neoplastic tissue resulting from preoperative treatment.

METHODS

Resection specimens from 47 cases of oesophageal adenocarcinoma treated with preoperative 5-fluorouracil/cisplatin and radiotherapy were reviewed. Residual tumour was assessed in terms of tumour regression grade (TRG), pTNM stage, lymphovascular space invasion, and resection margin involvement. Survival analysis was performed using the Kaplan-Meier method and log rank test. Cox's proportional hazard model was used for multivariate analysis.

RESULTS

A complete pathological response (TRG1) was present in eight cases. The absence of residual tumour was confirmed by negative immunohistochemical staining for MNF116. Tumour corresponding to TRG2 was present in five cases, to TRG3 in nine, to TRG4 in 22, and to TRG5 in three. By multivariate analysis, pN0 status (n = 35) had a positive effect on survival (p = 0.04) and TRG had no significant effect on survival (p = 0.06). Patients with pN0 tumours had a median survival of 48 months versus eight months for those with pN1 tumours (log rank test, p < 0.0001). We found that giant fibroblasts were discernible from single large residual tumour cells on haematoxylin and eosin alone.

CONCLUSION

Response to preoperative chemoradiotherapy in oesophageal adenocarcinoma is variable. Although there are as yet no reliable predictors of response to treatment, patients who are identified at diagnosis as having negative loco-regional lymph nodes should benefit considerably from this treatment approach.

Application of the privacy principles to general practice

BACKGROUND

There are escalating requirements for general practitioners to comply with recognised privacy principles. With amendments to the Commonwealth Privacy Act (1988) imminent, there is an urgent need to formulate methods for applying these principles to general practice.

OBJECTIVE

The article provides an explanation of the origins of the privacy principles and a simple self audit which general practitioners can use to assess the extent to which their usual practices conform with them.

DISCUSSION

A careful review of the principles indicates that new measures will be needed before most general practices will be able to approach required standards of conduct. Practical strategies for achieving best practice are discussed and challenges confronting general practices in applying the principles are canvassed. Ethics committees should be used more often to provide independent review of practice policies and proposals to use patient information in new ways. General practitioners can expect increasing scrutiny and debate concerning confidentiality. In order to maintain patient trust in GPs as responsible data custodians, the privacy principles can be seen as a quality improvement tool.

The mouse gene encoding the testis-specific isoform of Poly(A) binding protein (Pabp2) is an expressed retroposon: intimations that gene expression in spermatogenic cells facilitates the creation of new genes

The gene encoding the testis-specific isoform of mouse poly(A) binding protein (Pabp2) has been isolated and sequenced. Unexpectedly, comparison of the sequence of genomic and cDNAs demonstrated that the Pabp2 gene lacks introns, whereas all other functional Pabp genes in plants, amphibians, and mammals contain introns. Thus, the mouse Pabp2 gene is a retroposon, created by synthesizing a reverse transcriptase copy of a processed mRNA and inserting the copy into the genome. The Pabp2 retroposon is unusual because it is functional: previous work demonstrates that its promoter drives the accumulation of Pabp2 mRNA in meiotic and early haploid spermatogenic cells, and the Pabp2 mRNA encodes a protein whose size and RNA-binding specificities are characteristic of PABP in plants, yeast, and mammals (Kleene et al. 1994). Two novel factors can be implicated in the retention of function of the Pabp2 retroposon. First, the promoter of the Pabp2 gene is not derived from its intron-containing progenitor, Pabp1. Second, mRNAs encoding somatic PABP isoform, PABP1, are present at high levels in meiotic and haploid spermatogenic cells. Both features contrast with the phosphoglycerate kinase 2 retroposon, which is believed to compensate for the depletion of the somatic isoform due to X-chromosome inactivation in meiotic spermatogenic cells. We also document that more functional retroposons are expressed in meiotic and haploid spermatogenic cells than in any other tissue and speculate that transcriptional derepression in spermatogenic cells favors the creation of expressed retroposons.

Protecting patient confidentiality in hospitals

As new methods of electronic data storage and distribution appear in hospitals, new challenges in protecting confidentiality have emerged. At the same time, demands for 'seamless' care and the desire to share information between clinicians are motivating hospitals to relax barriers to the transfer of patient information. Increasing numbers of users at multiple sites compound the difficulty of ensuring information systems security. Hospital policy may demand that requests by patients to restrict the distribution of personal information be respected, while existing electronic systems are not able to deliver on this promise. Compliance with the Information Privacy Principles of the Commonwealth Privacy Act 1988 and the Australian Standard 4400-1995 'Personal privacy protection in health care information systems' will provide a useful framework for managing these challenges. However, their implementation will require some forethought.

Prospective evaluation of a composite scoring system for mammographically detected cytologically assessed impalpable breast abnormalities

The aim of all breast screening programmes is a reduction in deaths from the disease. It is hoped that this can be achieved with minimal intervention in the patient cohort who do not have cancer. In this study we have assessed the efficacy of a combination of mammographic and cytological scoring systems in the evaluation of 208 women with screen-detected non-palpable breast lesions. All mammograms were scored 1-5 and those with a score of 3 or more required needle localization. A cytology score of 1 to 5 was generated for each patient according to a similar system and an aggregate score for each patient was achieved by the addition of the mammographic and cytology score. Ninety-three of the 208 patients had malignancy--the positive predictive value for mammography alone in this series was 45%. All 58 patients who had an aggregate score of 8 or greater had cancer. The 60 patients who had an aggregate score of 4 had benign disease on excision biopsy. We suggest that a 'wait and repeat mammogram' approach is appropriate in patients with grade 3 mammography and benign (grade 1) cytology. Patients with an intermediate aggregate score of 5-7 should have an excision biopsy and those with an aggregate score of 8 could have definitive surgery rather than excision biopsy. Application of this aggregate scoring technique would enhance the delivery of more appropriate surgery to a majority of patients with screen-detected breast abnormalities.

Measurement of carotid body blood flow in cats by use of radioactive microspheres

To resolve the controversy regarding carotid body blood flow, we used the radioactive microsphere technique for determination of tissue blood flow. We also measured the blood flow to several other tissues in the cat. Blood flow experiments were performed on 13 cats that were anesthetized, paralyzed, and mechanically ventilated with air. Different numbers of differently labeled 9-, 15-, and 25-micron microspheres were injected via a catheter into the left atrium. It was determined that one injection of 5 x 10(6) 15-micron microspheres was appropriate for the determination of carotid body blood flow. Flows to the carotid bodies and other organs by use of this protocol were as follows (ml.min-1.100 g-1, means +/- SE): carotid bodies, 1,417 +/- 143; adrenal glands, 406 +/- 89; left kidney, 355 +/- 69; right kidney, 375 +/- 74; heart, 201 +/- 39; liver 81 +/- 14; pancreas, 80 +/- 21; superior cervical ganglia, 62 +/- 9; carotid artery wall, 2.4 +/- 1.1. The blood flow to the carotid bodies was the highest for any organ. This measurement provides new evidence that tissue blood flow to the carotid body is very high. This high flow is consistent with the prompt physiological reflex functions of the carotid body.

Carotid body chemosensory function in prolonged normobaric hyperoxia in the cat

The effects of normobaric hyperoxia on carotid body chemosensory function in the cat were studied. The hypothesis was that carotid body chemosensory function would be affected by chronic exposure to 100% O2 at sea level. It was based on the assumptions that carotid body tissue is exposed to high PO2 because of its high blood flow and that its O2 chemosensing mechanism is sensitive to O2 radical-induced reactions. Twelve cats were exposed to 100% O2 for 60-67 h, and 10 control cats were maintained in room air at sea level. They were anesthetized with pentobarbital sodium (Nembutal), and chemosensory afferents from a cut carotid sinus nerve were isolated and identified. The responses of single or a few clearly identifiable chemoreceptor afferents to isocapnic hypoxia and hypercapnia during hyperoxia and to the bolus injections of cyanide, nicotine, and dopamine were studied. We found that chronic hyperoxia severely blunted or eliminated the O2-sensitive response of the carotid chemoreceptors while augmenting the hypercapnic response. The response to cyanide but not to nicotine and dopamine were attenuated. Thus the hypoxic and hypercapnic responses that normally interact were separable. The lack of the cyanide response was consistent with the lack of the hypoxic response, suggesting a possible shared mechanism of carotid chemoreceptor response. Qualitatively normal responses to dopamine and nicotine indicated that the respective receptors were relatively intact after chronic exposure to hyperoxia and that the sensory nerves themselves were not affected by the prolonged O2 exposure.

Cat carotid body chemoreceptor responses before and after nicotine receptor blockade with alpha-bungarotoxin

The nature of nicotine receptors in the carotid body was studied in anesthetized, paralyzed and artificially ventilated cats. Chemoreceptor discharge in single or few-fiber preparations of the carotid sinus nerve was measured during isocapnic hypoxia, hyperoxic hypercapnia and in response to nicotine injections before and after administration of alpha-bungarotoxin (10 cats) and after alpha-bungarotoxin plus mecamylamine (7 cats) which binds to neuromuscular-type nicotine cholinergic receptors. alpha-Bungarotoxin caused a slight enhancement of the chemoreceptor response to hypoxia without affecting the chemoreceptor stimulation by nicotine. Mecamylamine (1-5 mg, i.v.), a ganglionic-type nicotinic receptor blocker, had no further effect on the response to hypoxia while it completely abolished the chemoreceptor stimulation by nicotine. Thus the nicotinic receptors in the cat carotid body which elicit excitation of chemosensory fibers appear to be of the ganglionic-type. Blockade of neuromuscular and ganglionic types of nicotinic receptors in the carotid body by alpha-bungarotoxin and mecamylamine does not attenuate the chemosensory responses to either hypoxia or hypercapnia. These nicotinic receptors therefore, do not appear to play an essential role in hypoxic or hypercapnic chemoreception in the cat carotid body.

Adrenergic mechanisms in oxygen chemoreception in the cat aortic body

Sixteen cats were studied to test the hypothesis that oxygen chemoreception in the cat aortic body is dependent on the beta-adrenergic mechanism. The chemoreceptor activity was measured from a few aortic chemoreceptor afferents in each cat, anesthetized with alpha-chloralose (60 mg X kg-1). Three types of experiments were conducted. Aortic chemoreceptor responses to steady-state hypoxia (PaO2 range, 100-30 Torr) were measured (a) before and during intravenous infusion of the beta-receptor agonist, isoproterenol (0.5 micrograms X kg-1) in nine spontaneously breathing cats, and (b) before and after intravenous injection of the beta-receptor antagonist, propranolol (1 mg X kg-1) in seven cats which were paralyzed and artificially ventilated. In the third category (c) the stimulatory effect of hypotension on aortic chemoreceptor activity was measured in six of the seven cats in group (b) before and after propranolol injection. Isoproterenol infusion only moderately stimulated aortic chemoreceptor activity. This stimulation was blocked by propranolol. However, propranolol did not attenuate aortic chemoreceptor responses to hypoxia or to hypotension. We conclude that the beta-receptor adrenergic mechanism does not mediate oxygen chemoreception in the cat aortic body.

Separation of carotid body chemoreceptor responses to O2 and CO2 by oligomycin and by antimycin A

The cat carotid chemoreceptor O2 and CO2 responses can be separated by oligomycin and by antimycin A. Both of these agents greatly diminish or abolish the chemoreceptor O2 response but not the nicotine or CO2 responses. After either oligomycin or antimycin, the responses to increases and decreases in arterial CO2 partial pressure (PaCO2) consisted of increases and decreases in activity characterized respectively by exaggerated overshoots and undershoots. These were eliminated by the carbonic anhydrase inhibitor, acetazolamide, suggesting that they resulted from changes in carotid body tissue pH. The steady-state PaCO2 response remaining after oligomycin was no longer dependent on arterial O2 partial pressure (PaO2). All effects of antimycin were readily reversible in about 20 min. The separation of the responses to O2 and CO2 indicates that there may be at least partially separate pathways of chemoreception for these two stimuli. The similarity of the oligomycin and antimycin results supports the metabolic hypothesis of chemoreception.

Adaptive response of carotid body chemoreceptors to CO2

Carotid body chemoreceptor responses to sudden changes in pETCO2 (end-tidal tracheal CO2 partial pressure) and paCO2 (arterial CO2 partial pressure) from one stable state to another at a constant level of PETO2 (end-tidal tracheal O2 partial pressure) and paO2 (arterial O2 partial pressure) were studied in 18 anesthetized cats. Chemoreceptor activity was recorded from single or pauci-fiber filaments of a cut sinus nerve. During a hypercapnic stimulus by CO2 inhalation the discharge rate rapidly increased to a peak and then adapted to a lower level in 20-30 s showing an overshoot in the response. Likewise, withdrawal of the hypercapnic stimulus was followed by an undershoot in chemoreceptor activity. Hypoxia decreased the latency of the response and increased the overshoot and stable state responses to hypercapnia. The responses to step paCO2 increases by blood perfusion were qualitatively similar but the latency and time to peak amplitude were shorter and the peak amplitude was larger at any given perfusate pO2. The stable state responses to a given paCO2 achieved by CO2 inhalation or by blood perfusion were similar. The transient overshoot and undershoot in the activity produced by the increase and decrease in paCO2 were blocked by acetazolamide, a carbonic anhydrase inhibitor. The results are best explained by postulating that in the carotid body tissue, H+ is generated from CO2 in one compartment in the presence of carbonic anhydrase and is transported to another containing the receptor site in a pO2 dependent way--a high pO2 attenuating and a low pO2 augmenting it.

Responses of aortic chemoreceptors before and after pneumothorax in the cat

That the response of aortic chemoreceptors to hypercapnia is considerably smaller than that of carotid chemoreceptors is well accepted, but the mechanism for the difference is not known. It has been suggested that surgical exposure of the carotid body may contribute to the difference. Accordingly, the response of aortic body chemoreceptors to CO2 would be expected to resemble quantitatively that of carotid chemoreceptors after exposure of the aortic bodies by pneumothorax. The effect of opening the chest on aortic and carotid chemoreceptor responses to several levels of arterial CO2 and O2 tension and arterial blood pressure were studied in anesthetized cats. The activity of aortic chemoreceptors increased in spite of a decreased stimulus level in the thoracic cavity after pneumothorax. The activity remained higher than the control at all levels of arterial CO2 and O2 tension and arterial blood pressure. However, the slopes of CO2 response curves, which were initially small, did not change after pneumothorax. Thus a change in the normal environment of the aortic bodies by experimental manipulation did not cause the aortic chemoreceptor responses to resemble those of carotid chemoreceptors.

Carotid body O2 chemoreception and mitochondrial oxidative phosphorylation

The effect on carotid chemoreceptor afferents of oligomycin, an inhibitor of mitochondrial oxidative phosphorylation that does not affect energy conservation, was studied in 20 cats that were anesthetized, paralyzed, and artificially ventilated. Responses of single or a few chemoreceptor afferents to changes in arterial O2 tension (PaO2) at constant arterial CO2 tension were recorded. In addition, responses to nicotine, cyanide, and antimycin A or carbonyl cyanide p-tri-fluoromethoxyphenylhydrazone (FCCP) were tested in normoxia. Oligomycin (50-500 microgram) was administered by close intra-arterial injection, and the same tests were repeated at timed intervals. Initially, oligomycin caused vigorous stimulation of carotid chemoreceptor activity. Subsequently, although the afferent fibers were still active and could be vigorously stimulated by nicotine, they no longer responded to changes in PaO2 or to doses of cyanide, antimycin A, or FCCP. These results separate stimulation of chemoreceptor afferents by hypoxia and metabolic inhibitors and uncouplers from that by nicotine and suggest that intact oxidative phosphorylation, required for maintenance of the intracellular high-energy phosphate levels, forms the basis of O2 chemoreception in the carotid body.

Metabolic regulation of aortic chemoreceptor responses to CO2

Modification of the unusually feeble responses of aortic chemoreceptors to CO2 was studied in cats which were anethetized, paralyzed, artificially ventilated and maintained at 38 degrees C. The inhibitor of oxidative phosphorylation, oligomycin, strikingly augmented the initial responses to CO2 of aortic chemoreceptors just as for carotid chemoreceptors, indicating that the basic mechanism of chemoreception might be regulated in part through energy metabolism.

Comparison of aortic and carotid chemoreceptor responses to hypercapnia and hypoxia

A quantitative comparison of the responses between aortic and carotid chemoreceptors to steady-state levels of arterial CO2 and O2 partial pressure was made in 35 cats anesthetized, paralyzed, and artificially ventilated. The measurements on the two receptors were made simultaneously in 6 cats and separately in 29 cats. The response of aortic chemoreceptors to a CO2 stimulus was a fraction of that of carotid chemoreceptors, and the response to hypoxia was relatively blunted. The differences between the two chemoreceptors are quantitative rather than qualitative. Since a low arterial CO2 partial pressure stimulus is known to attenuate the hypoxic response of carotid chemoreceptors, it is suggested that the low CO2 response of aortic body chemoreceptors is responsible for their blunted hypoxic response.

Relative responses of aortic body and carotid body chemoreceptors to carboxyhemoglobinemia

The effects of carbon monoxide inhalation and of consequent carboxyhemoglobinemia (HbCO) on the discharge rates of aortic body and carotid body chemoreceptor afferents were investigated in 18 anesthetized cats. In 10 experiments both aortic and carotid chemoreceptor activities were monitored simultaneously. Carbon monoxide inhalation during normoxia always stimulated aortic chemoreceptors before carotid chemoreceptors, and the steady-state response of aortic chemoreceptors to HbCO was greater than that of most carotid chemoreceptors. Only 2 of the 18 carotid chemoreceptor fibers tested showed a distinct increase in activity in response to moderate increases in HbCO%. Thus, oxyhemoglobin contributed substantially to maintain tissue PO2 of all aortic chemoreceptors and of a few carotid chemoreceptors. Hyperoxia diminished the response of both aortic and carotid chemoreceptors to HbCO, indicating a lowered tissue PO2 as the stimulus source. We hypothesize that the aortic bodies have a much lower perfusion relative to their O2 utilization compared to the carotid bodies. As a consequence, the aortic chemoreceptors are able to act as a sensitive monitor of O2 delivery and to generate a circulatory chemoreflex for O2 homeostasis. carotid chemoreceptors monitor O2 tension and initiate strong reflex effects on the level of ventilation.

Interaction of dopamine and haloperidol with O2 and CO2 chemoreception in carotid body

Effects of dopamine and of a dopaminergic blocker, haloperidol, on the responses of carotid body chemoreceptors to hypoxia and hypercapnia were investigated in 16 anesthetized cats. Intravenous infusion of dopamine (10-20 micrograms.min-1) decreased carotid body chemoreceptor responses to hypoxia and hypercapnia. The effect was greater at higher levels of arterial oxygen and carbon dioxide tension (PaO2 and PaCO2) stimulus. Thus, the magnitude of the dopamine effect depended on the degree of both PO2- and PCO2-mediated excitation of the receptors. Haloperidol potentiated responses to both hypoxia and hypercapnia but apparently did not stimulate the receptors in the absence of these stimuli. Potentiation by haloperidol and inhibition by dopamine of excitatory effects due to PaO2 decrease and PaCO2 increase are complementary. The data suggest that chemoreception of dopamine, O2, and CO2 converge at some site in the carotid body. Persistence of hypoxic and hypercapnic responses, following dopamine-blocking doses of haloperidol, does not support the theory that regulation of dopamine release is responsible for O2 and CO2 chemoreception in carotid body of the cat.

Relative responses of aortic body and carotid body chemoreceptors to hypotension

Responses to acute arterial blood pressure changes of a single or a few chemoreceptor afferents from the aortic body and carotid body at constant arterial blood gases and pH were measured in 16 adult cats. During normocapnic normoxia and moderate hypoxia (arterial oxygen tension of 60 Torr) an induced hypotension of 80 Torr increased strikingly the discharge rate of all aortic chemoreceptors but not of most carotid chemoreceptors; hypotension down to the level of 50 Torr stimulated most carotid chemoreceptors only slightly. Hyperoxia eliminated the stimulatory effect of this degree of hypotension on carotid chemoreceptors; it did not affect aortic chemoreceptors to the same extent. Hypoxia augmented the effect on aortic chemoreceptors more than the effect on carotid chemoreceptors. Thus the effect of hypotension was dependent on arterial oxygen tension. The greater effect of hypotension on aortic body chemoreceptor activity indicates a greater normal circulatory constraint for the aortic body. Accordingly, aortic chemoreceptors are more suited to monitor circulatory changes in O2 flow, and carotid chemoreceptors are more suited to monitor arterial gas pressure changes due to respiration.

Relative latency of responses of chemoreceptor afferents from aortic and carotid bodies

Discharges from aortic and carotid body chemoreceptor afferents were simultaneously recorded in 18 anesthetized cats to test the hypothesis that aortic chemoreceptors, because of their proximity to the heart, respond to changes in arterial blood gases before carotid chemoreceptors. We found that carotid chemoreceptor responses to the onset of hypoxia and hypercapnia, and to the intravenously administered excitatory drugs (cyanide, nicotine, and doxapram), preceded those of aortic chemoreceptors. Postulating that this unexpected result was due to differences in microcirculation and mass transport, we also investigated their relative speed of responses to changes in arterial blood pressure. The aortic chemoreceptors responded to decreases in arterial blood pressure before the carotid chemoreceptors, supporting the idea that the aortic body has microcirculatory impediments not generally present in the carotid body. These findings strengthened the concept that carotid bodies are more suited for monitoring blood gas changes due to respiration, whereas aortic bodies are for monitoring circulation.

Aortic body chemoreceptor responses to changes in PCO2 and PO2 in the cat

Responses of aortic chemoreceptor afferents to a range of arterial carbon dioxide tension (Paco2) changes at various levels of arterial oxygen tension (Pao2) were investigated in 18 cats anesthetized with alpha-chloralose and maintained at 38 degrees C. Aortic chemoreceptor activity, end-tidal oxygen pressure, end-tidal carbon dioxide pressure, and arterial blood pressure were continuously monitored. Arterial blood gases were measured in steady states. Single or a few clearly identifiable afferents were studied during changes and steady states of Pao2 and Paco2. All the aortic chemoreceptor afferent discharge rates increased with Paco2 increases from hypercapnia (10-15 Torr) to normocapnia and moderate hypercapnia (30-50 Torr) and with Pao2 decreases from above 400 to 30 Torr. Hypoxia augmented the response to Paco2 most effectively in the range of 10-40 Torr. At any Pao2, the discharge rate reached a plateau with sufficient intensity of hypercapnia. The Paco2 stimulus threshold at a Pao2 of 440 Torr was about 15 Torr, and at a Pao2 of 60 Torr it was 10 Torr. In the transition from hypocapnia to hypercapnia, responses increased gradually, usually without an overshoot. The steady-state responses to Paco2 of the majority of aortic chemoreceptors resembled those of carotid chemoreceptors. The responses of both receptors can be attributed to the same basic type of mechanism.