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The rat has been widely used as a disease model in a laboratory setting, resulting in an abundance of genetic and phenotype data from a wide variety of studies. These data can be found at the Rat Genome Database (RGD, http://rgd.mcw.edu/ ), which provides a platform for researchers interested in linking genomic variations to phenotypes. Quantitative trait loci (QTLs) form one of the earliest and core datasets, allowing researchers to identify loci harboring genes associated with disease. These QTLs are not only important for those using the rat to identify genes and regions associated with disease, but also for cross-organism analyses of syntenic regions on the mouse and the human genomes to identify potential regions for study in these organisms. Currently, RGD has data on >1,900 rat QTLs that include details about the methods and animals used to determine the respective QTL along with the genomic positions and markers that define the region. RGD also curates human QTLs (>1,900) and houses >4,000 mouse QTLs (imported from Mouse Genome Informatics). Multiple ontologies are used to standardize traits, phenotypes, diseases, and experimental methods to facilitate queries, analyses, and cross-organism comparisons. QTLs are visualized in tools such as GBrowse and GViewer, with additional tools for analysis of gene sets within QTL regions. The QTL data at RGD provide valuable information for the study of mapped phenotypes and identification of candidate genes for disease associations.

The Rat Genome Database (RGD) was started >10 years ago to provide a core genomic resource for rat researchers. Currently, RGD combines genetic, genomic, pathway, phenotype and strain information with a focus on disease. RGD users are provided with access to structured and curated data from the molecular level through the organismal level. Those users access RGD from all over the world. End users are not only rat researchers but also researchers working with mouse and human data. Translational research is supported by RGD’s comparative genetics/genomics data in disease portals, in GBrowse, in VCMap and on gene report pages. The impact of RGD also goes beyond the traditional biomedical researcher, as the influence of RGD reaches bioinformaticians, tool developers and curators. Import of RGD data into other publicly available databases expands the influence of RGD to a larger set of end users than those who avail themselves of the RGD website. The value of RGD continues to grow as more types of data and more tools are added, while reaching more types of end users.

The Gene Ontology (GO) (http://www.geneontology.org) is a community bioinformatics resource that represents gene product function through the use of structured, controlled vocabularies. The number of GO annotations of gene products has increased due to curation efforts among GO Consortium (GOC) groups, including focused literature-based annotation and ortholog-based functional inference. The GO ontologies continue to expand and improve as a result of targeted ontology development, including the introduction of computable logical definitions and development of new tools for the streamlined addition of terms to the ontology. The GOC continues to support its user community through the use of e-mail lists, social media and web-based resources.

Objectives Our model of a systemic–pulmonary shunt exhibits enhanced reactivity of pulmonary arteries contralateral to a localized shunt between the left lower lobe pulmonary artery and aorta relative to those of ipsilateral or control pulmonary arteries 48 hours after anastomosis. We examined the contribution of nitric oxide, cyclooxygenase, lipoxygenase, or cytochrome P450 production to mediating this enhanced reactivity. Methods We created a surgical end-to-side anastomosis of the left lower lobe pulmonary artery to the aorta. Forty-eight hours later, we tested tension of pulmonary artery rings from the right and left lower lobes for contraction to the thromboxane mimetic U46619 in the presence of vehicle or inhibitors of nitric oxide synthase, cyclooxygenase, cytochrome P450, or lipoxygenase. Western blots of pulmonary artery homogenates were probed for endothelial nitric oxide synthase or isoforms metabolizing arachidonic acid. Eicosanoid products from intact pulmonary artery rings were detected using labeled arachidonic acid and high-performance liquid chromatography separation. Results Enhanced reactivity of unshunted right pulmonary arteries over that of left pulmonary arteries from high-flow hosts was not eliminated by inhibitors of nitric oxide synthase, cyclooxygenase, cytochrome P450. Treatment with 2 different lipoxygenase inhibitors, nordihydroguaiaretic acid and cinnamyl-3,4-dihydroxy- α -cyanocinnamate, closed the difference in contractility of shunted and unshunted pulmonary arteries. Pulmonary arteries contralateral to shunts metabolized arachidonic acid to 12-hydroxyeicosatetraenoic acid in greater quantities than analogous pulmonary arteries from the experimental left or control pulmonary arteries. Conclusions Forty-eight hours after anastomosis, enhanced reactivity of contralateral pulmonary arteries is attributable in part to increased lipoxygenase products as opposed to nitric oxide or other eicosanoid products.

Previously, we reported that the hypoxic ventilatory response (HVR) in rats was weakest at postnatal day (P) P13, concomitant with neurochemical changes in respiratory nuclei. A major determinant of minute ventilation (V̇e) is reportedly the metabolic rate [O2consumption (V̇o2) and CO2production (V̇co2)]. The present study aimed at testing our hypothesis that daily metabolic rates changed in parallel with ventilation during development and that a weak HVR at P13 was attributable mainly to an inadequate metabolic rate in hypoxia. Ventilation and metabolic rates were monitored daily in P0–P21 rats. We found that 1) ventilation and metabolic rates were not always correlated, and V̇e/V̇o2and V̇e/V̇co2ratios were not constant during development; 2) metabolic rate and V̇e/V̇o2and V̇e/V̇co2ratios at P0–P1 were significantly different from the remaining first postnatal week in normoxia and hypoxia; 3) at P13, metabolic rates and V̇e/V̇o2and V̇e/V̇co2ratios abruptly increased in normoxia and were compromised in acute hypoxia, unlike more stable trends during the remaining second and third postnatal weeks; and 4) the respiratory quotient (V̇co2/V̇o2) was quite stable in normoxia and fluctuated slightly in hypoxia from P0 to P21. Thus our data revealed heretofore unsuspected metabolic adjustments at P0–P1 and P13. At P0–P1, ventilation and metabolic rates were uncorrelated, whereas at P13, they were closely correlated under normoxia and hypoxia. The findings further strengthened the existence of a critical period of respiratory development around P13, when multiple physiological and neurochemical adjustments occur simultaneously.

To characterize structural and functional injuries following a single dose of whole-thorax irradiation that might be survivable after a nuclear attack/accident.Rats were exposed to 5 or 10 Gy of X-rays to the whole thorax with other organs shielded. Non-invasive measurements of breathing rate and arterial oxygen saturation, and invasive evaluations of bronchoalveolar lavage fluid, (for total protein, Clara cell secretory protein), vascular reactivity and histology were conducted for at least 6 time points up to 52 weeks after irradiation.Irradiation with 10 Gy resulted in increased breathing rate, a reduction in oxygen saturation, an increase in bronchoalveolar lavage fluid protein and attenuation of vascular reactivity between 4-12 weeks after irradiation. These changes were not observed with the lower dose of 5 Gy. Histological examination revealed perivascular edema at 4-8 weeks after exposure to both doses, and mild fibrosis beyond 20 weeks after 10 Gy.Single-dose exposure of rat thorax to 10 but not 5 Gy X-irradiation resulted in a decrease in oxygen uptake and vasoreactivity and an increase in respiratory rate, which paralleled early pulmonary vascular pathology. Vascular edema resolved and was replaced by mild fibrosis beyond 20 weeks after exposure, while lung function recovered.

Previously, we found heightened expression of inhibitory neurochemicals and depressed expression of excitatory neurochemicals with a sudden drop in metabolic activity around postnatal day (P) 12 in rat brainstem respiratory nuclei, suggesting that this period is a critical window during which respiratory control or regulation may be distinctly different. To test this hypothesis, the hypoxic ventilatory responses (HVR) to 10% oxygen were tested in rats every day from P0 to P21. Our data indicate that (1) during normoxia (N), breathing frequency (f) increased with age, peaking at P13, followed by a gradual decline, whereas both tidal volume (V(T)) and minute ventilation (.V(E) ) significantly increased in the second postnatal week, followed by a progressive increase in V(T) and a relative plateau in .V(E); (2) during 5 min of hypoxia (H), .V(E) exhibited a biphasic response from P3 onward. Significantly, the ratio of .V(E)(H) to .V(E)(N) was generally > 1 during development, except for P13-16, when it was < 1 after the first 1-2 min, with the lowest value at P13; (3) the H : N ratio for f, V(T) and .V(E) during the first 30 s and the last minute of hypoxia all showed a distinct dip at P13, after which the V(T) and .V(E) values rose again, while the f values declined through P21; and (4) the H : N ratios for f, V(T) and .V(E) averaged over 5 min of hypoxia all exhibited a sudden fall at P13. The f ratio remained low thereafter, while those for V(T) and .V(E) increased again with age until P21. Thus, hypoxic ventilatory response is influenced by both f and V(T) before P13, but predominantly by V(T) after P13. The striking changes in normoxic ventilation as well as HVR at or around P13, together with our previous neurochemical and metabolic data, strongly suggests that the end of the second postnatal week is a critical period of development for brainstem respiratory nuclei in the rat.

Abstract —In the brain, pressure-induced myogenic constriction of cerebral arteriolar muscle contributes to autoregulation of cerebral blood flow (CBF). This study examined the role of 20-HETE in autoregulation of CBF in anesthetized rats. The expression of P-450 4A protein and mRNA was localized in isolated cerebral arteriolar muscle of rat by immunocytochemistry and in situ hybridization. The results of reverse transcriptase–polymerase chain reaction studies revealed that rat cerebral microvessels express cytochrome P-450 4A1, 4A2, 4A3, and 4A8 isoforms, some of which catalyze the formation of 20-HETE from arachidonic acid. Cerebral arterial microsomes incubated with [ 14 C]arachidonic acid produced 20-HETE. An elevation in transmural pressure from 20 to 140 mm Hg increased 20-HETE concentration by 6-fold in cerebral arteries as measured by gas chromatography/mass spectrometry. In vivo, inhibition of vascular 20-HETE formation with N -methylsulfonyl-12,12-dibromododec-11-enamide (DDMS), or its vasoconstrictor actions using 15-HETE or 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid (20-HEDE), attenuated autoregulation of CBF to elevations of arterial pressure. In vitro application of DDMS, 15-HETE, or 20-HEDE eliminated pressure-induced constriction of rat middle cerebral arteries, and 20-HEDE and 15-HETE blocked the vasoconstriction action of 20-HETE. Taken together, these data suggest an important role for 20-HETE in the autoregulation of CBF. ( Circ Res. 2000;87:60-65.)

The purpose of these studies was to test the hypothesis that carotid chemoreceptor activity is necessary for postnatal maturation of the ventilatory control system. By using a lateral surgical access, 17 piglets were carotid body denervated (CBD) and 14 were sham denervated at 3–25 days of age. After surgery, there was no irregular breathing in any group. There was no significant hypoventilation when CBD was performed at less than 5 days of age ( n = 5) and only a mild (arterial[Formula: see text] 5 Torr; P < 0.05) to moderate, transient (arterial [Formula: see text] 8 Torr; P < 0.5) hypoventilation in piglets denervated at 10–15 ( n = 6) and 20–25 ( n = 6) days of age, respectively. Three weeks after surgery, both breathing of a hypoxic gas mixture and jugular venous NaCN injections elicited a hyperpnea in the CBD piglets that was attenuated compared with that in sham CBD piglets. In the CBD piglets, there was no response to injections of NaCN in the carotid arteries, but there was a response to NaCN injected into the proximal descending aorta, suggesting the residual peripheral chemosensitivity was of aortic origin. Carotid chemoreceptor-intact piglets had carotid and aortic NaCN chemosensitivity by 2 days of age. The carotid response persisted for the 40 days of the study, but the aortic reflex persisted only until ∼8 days of age. We conclude that 1) the major effect of CBD per se in neonatal piglets is age-dependent hypoventilation and 2) there is a high degree of plasticity in peripheral chemosensitivity in neonates that may contribute to minimizing the changes in breathing after CBD.

The objective of the present study was to determine in goats whether carotid body denervation (CBD) at 1–3 days of age causes permanent changes in breathing greater than those that occur after CBD in adult goats. Goats underwent CBD ( n = 6) or sham CBD ( n = 3) surgery at 1–3 days of age. In addition, one unoperated control animal was studied. Bolus intravenous injections of NaCN 2 days postsurgery verified successful CBD surgery. However, at 3, 11, and 18 mo of age, the CBD goats had regained a NaCN response that did not differ ( P > 0.10) from that of intact goats. Intracarotid NaCN injections elicited a hyperpnea in the sham CBD but not the CBD goats. Only one animal exhibited highly irregular breathing [characterized by prolonged (>9-s) apneas] after CBD, and the irregularity disappeared by 3 mo of age. One CBD goat died at 35 days of age, and autopsy revealed that death was associated with pneumonia. After 3 mo of age, there were no statistically significant differences ( P > 0.10) between sham and CBD goats in eupneic breathing, hypoxia and CO2 sensitivity, and the exercise hyperpnea. It is, therefore, concluded that CBD at 1–3 days of age in goats does not appear to affect selected aspects of respiratory control after 3 mo of age, conceivably because of the emergence of other functional chemoreceptors that compensate for the loss of the carotid chemoreceptor.

In adult and neonatal goats, we chronically implanted thermodes on the ventrolateral (VLM) medullary surface to create reversible neuronal dysfunction and thereby gain insight into the role of superficial VLM neurons in control of breathing in anesthetized, awake and asleep states. Consistent with data of others, cooling caudal area M and rostral area S caused sustained apnea under anesthesia. However, in the awake and NREM sleep states, cooling at this site caused only a modest reduction in breathing, indicating that neurons at this site are not critical for respiratory rhythm in these states. Moreover, data in the awake state over multiple conditions suggest neurons at this site do not integrate all intracranial and carotid chemoreception. The data suggest though that neurons at this site have a facilitatory-like effect on breathing both unrelated and related to intracranial chemoreception. We believe that this facilitation serves a function similar to the facilitation provided by the carotid chemoreceptors and by sources associated with wakefulness. Accordingly, elimination/attenuation of any one of these three influences (caudal M rostral S VLM, wakefulness, carotid chemoreception) results in a slight decrease in breathing, removal of two of the three results in a greater decrease in breathing, and removal of all three results in sustained apnea.

Background The Clinical Measurement Ontology (CMO), Measurement Method Ontology (MMO), and Experimental Condition Ontology (XCO) were originally developed at the Rat Genome Database (RGD) to standardize quantitative rat phenotype data in order to integrate results from multiple studies into the PhenoMiner database and data mining tool. These ontologies provide the framework for presenting what was measured, how it was measured, and under what conditions it was measured. Results There has been a continuing expansion of subdomains in each ontology with a parallel 2–3 fold increase in the total number of terms, substantially increasing the size and improving the scope of the ontologies. The proportion of terms with textual definitions has increased from ~60% to over 80% with greater synchronization of format and content throughout the three ontologies. Representation of definition source Uniform Resource Identifiers (URI) has been standardized, including the removal of all non-URI characters, and systematic versioning of all ontology files has been implemented. The continued expansion and success of these ontologies has facilitated the integration of more than 60,000 records into the RGD PhenoMiner database. In addition, new applications of these ontologies, such as annotation of Quantitative Trait Loci (QTL), have been added at the sites actively using them, including RGD and the Animal QTL Database. Conclusions The improvements to these three ontologies have been substantial, and development is ongoing. New terms and expansions to the ontologies continue to be added as a result of active curation efforts at RGD and the Animal QTL database. Use of these vocabularies to standardize data representation for quantitative phenotypes and quantitative trait loci across databases for multiple species has demonstrated their utility for integrating diverse data types from multiple sources. These ontologies are freely available for download and use from the NCBO BioPortal website at http://bioportal.bioontology.org/ontologies/1583 (CMO), http://bioportal.bioontology.org/ontologies/1584 (MMO), and http://bioportal.bioontology.org/ontologies/1585 (XCO), or from the RGD ftp site at ftp://rgd.mcw.edu/pub/ontology/.

The Rat Genome Database (RGD) is the premier repository of rat genomic and genetic data and currently houses >40 000 rat gene records as well as human and mouse orthologs, >2000 rat and 1900 human quantitative trait loci (QTLs) records and >2900 rat strain records. Biological information curated for these data objects includes disease associations, phenotypes, pathways, molecular functions, biological processes and cellular components. Recently, a project was initiated at RGD to incorporate quantitative phenotype data for rat strains, in addition to the currently existing qualitative phenotype data for rat strains, QTLs and genes. A specialized curation tool was designed to generate manual annotations with up to six different ontologies/vocabularies used simultaneously to describe a single experimental value from the literature. Concurrently, three of those ontologies needed extensive addition of new terms to move the curation forward. The curation interface development, as well as ontology development, was an ongoing process during the early stages of the PhenoMiner curation project. Database URL: http://rgd.mcw.edu

The Rat Genome Database (RGD) is the premier resource for genetic, genomic and phenotype data for the laboratory rat, Rattus norvegicus. In addition to organizing biological data from rats, the RGD team focuses on manual curation of gene–disease associations for rat, human and mouse. In this work, we have analyzed disease-associated strains, quantitative trait loci (QTL) and genes from rats. These disease objects form the basis for seven disease portals. Among disease portals, the cardiovascular disease and obesity/metabolic syndrome portals have the highest number of rat strains and QTL. These two portals share 398 rat QTL, and these shared QTL are highly concentrated on rat chromosomes 1 and 2. For disease-associated genes, we performed gene ontology (GO) enrichment analysis across portals using RatMine enrichment widgets. Fifteen GO terms, five from each GO aspect, were selected to profile enrichment patterns of each portal. Of the selected biological process (BP) terms, ‘regulation of programmed cell death’ was the top enriched term across all disease portals except in the obesity/metabolic syndrome portal where ‘lipid metabolic process’ was the most enriched term. ‘Cytosol’ and ‘nucleus’ were common cellular component (CC) annotations for disease genes, but only the cancer portal genes were highly enriched with ‘nucleus’ annotations. Similar enrichment patterns were observed in a parallel analysis using the DAVID functional annotation tool. The relationship between the preselected 15 GO terms and disease terms was examined reciprocally by retrieving rat genes annotated with these preselected terms. The individual GO term–annotated gene list showed enrichment in physiologically related diseases. For example, the ‘regulation of blood pressure’ genes were enriched with cardiovascular disease annotations, and the ‘lipid metabolic process’ genes with obesity annotations. Furthermore, we were able to enhance enrichment of neurological diseases by combining ‘G-protein coupled receptor binding’ annotated genes with ‘protein kinase binding’ annotated genes. Database URL: http://rgd.mcw.edu

Dysfunction through cooling of neurons near the ventrolateral medullary (VLM) surface results in apnea in the anesthetized state, whereas similar neuronal dysfunction in the awake state only modestly decreases breathing. The purpose of this study was to investigate effects on breathing, as measured by diaphragm electromyogram (EMGdi), of VLM neuronal dysfunction during NREM sleep, a naturally occurring change in state. In six goats, thermodes for cooling were chronically implanted between the first hypoglossal rootlet and the pontomedullary junction (area M and area S). During wakefulness and NREM sleep, bilateral VLM cooling (thermode temp = 20 degrees C) for 30 sec decreased EMGdi mean activity and minute EMGdi (p0.05) and lengthened the time between diaphragm contractions. During NREM sleep, reductions in mean and minute EMGdi during cooling tended to be greater than during waking, but not significantly. However, following carotid body denervation. VLM cooling caused prolonged apnea during NREM sleep but only a brief apnea in the awake state. The data suggest that either intact VLM neuronal mechanisms or intact carotid afferents are necessary for sustained EMGdi activity during NREM sleep.

The present study was designed to determine whether neurons near the ventral medullary surface (VMS) that are important to control of breathing in adult mammals are also important to control of breathing in neonates. In 7-day-old goats (n = 22), the VMS was surgically exposed under halothane anesthesia. Stainless steel thermodes (2 x 2 mm) were used to cool (20 degrees C) and thereby create neuronal dysfunction of discrete VMS sites. Bilateral cooling under anesthesia 0-2 or 2-4 mm lateral to the midline between the exit of cranial nerves VI and XII resulted in a reduction (P < 0.05) of breathing and most often in apnea. Cooling caudal or rostral to this area did not have a consistent effect on breathing. In 7-day-old goats (n = 8), 3 x 3-mm thermodes were chronically implanted bilaterally on the VMS surface between the exit of cranial nerves VI and XII. The goats recovered and were studied over several days thereafter. VMS cooling while the goats were awake caused breathing to decrease (P < 0.05), but apnea was never observed. The decrease was less (P < 0.05) than while the goats were anesthetized. After 10 s of cooling, the hypopnea while the goats were awake was uniform during eupnea, hypercapnia, hyperoxia, and hypoxia, but after 10 s of cooling, the decrease was relatively greater (P < 0.05) during hyperoxia and hypercapnia. These effects of VMS cooling are qualitatively the same as in adult goats; thus the data are consistent with mature VMS contribution to the control of breathing in neonatal goats.

To gain insight into the role of cerebral lactic acidosis in the hypoxic ventilatory response, we administered dichloroacetate (DCA) intravenously to inhibit lactic acid production in 7 awake goats (40-70 kg) during 0.5 h of normoxia (inspired O2 fraction = 0.209) and 5 h of poikilocapnic hypoxia (inspired O2 fraction = 0.125). On separate days, these goats were also studied with a continuous saline infusion (18 ml/h iv) during 5 h of normoxia and hypoxia. Arterial PCO2 (PaCO2) did not change during the 5-h normoxic period. During hypoxia, arterial PO2 fell significantly (P < 0.05) with both saline (from 111.3 to 39.0 Torr) and DCA (from 111.8 to 42.0 Torr) infusions. PaCO2 decreased (P < 0.05) during the first 0.5 h of both the saline and DCA hypoxia protocols. The decrease was greater (P < 0.05) during DCA (from 36.5 to 33.5 Torr) than during saline infusion (from 37.7 to 36.3 Torr). With saline infusion, PaCO2 decreased (P < 0.05) by 4.9 Torr between 0.5 and 5.0 h of hypoxia. However, over this period of DCA hypoxia, PaCO2 did not significantly decrease (P = 0.05). We conclude that the enhanced hyperventilation with DCA during acute hypoxia is consistent with brain lactic acidosis depressing breathing. Absence of additional significant hyperventilation after 0.5 h of DCA hypoxia suggests that a time-dependent alleviation of brain lactic acidosis might normally contribute to ventilatory acclimatization to hypoxia.

The laboratory rat, Rattus norvegicus, is an important model of human health and disease, and experimental findings in the rat have relevance to human physiology and disease. The Rat Genome Database (RGD, http://rgd.mcw.edu) is a model organism database that provides access to a wide variety of curated rat data including disease associations, phenotypes, pathways, molecular functions, biological processes, and cellular components for genes, quantitative trait loci, and strains. We present an overview of the database followed by specific examples that can be used to gain experience in employing RGD to explore the wealth of functional data available for the rat.

It has been postulated that the so-called area S of the ventrolateral medulla (VLM) integrates peripheral chemoreceptor activity; thus cooling-induced dysfunction of neurons in this VLM area should functionally eliminate carotid chemoreceptor stimulation of breathing. Accordingly, carotid chemoreceptor denervation (CBD) should not alter the breathing effects of VLM neuronal dysfunction. To test this hypothesis in awake goats, chronically implanted thermodes were used to cool the VLM and thereby cause reversible neuronal dysfunction in all or portions of VLM areas M and S. Within 5 s after initiation of cooling approximately 60–100% of areas M and S in (P < 0.05) uniformly over conditions of eupnea, hypercapnia, and hypoxia. Between 10 and 20 s of cooling, the reduction in VI was approximately 10% greater (P < 0.05) during hypercapnia than during eupnea and hypoxia. For the remaining 10 s of cooling and for approximately 1 min after cooling, VI increased to and above control for all conditions. For all conditions, CBD accentuated the depression of VI during cooling, causing VI to decrease (P < 0.05) 10–40% more than before CBD. After CBD, the greatest effect on VI of cooling was again during hypercapnia. Thus the carotid bodies in intact goats appear to sense blood gas errors caused during VLM cooling to minimize the decreases in VI. We conclude that the data from this study do not support the concept that the VLM integrates carotid chemoreceptor activity.

Regions within the rostral ventral medullary surface (RVMS) play an important role in cardiorespiratory responses to CO 2 during anesthesia. Activity within a RVMS area, in which local cooling elicited marked ventilatory and blood pressure reductions, was measured as 660 nm scattered light changes in 5 goats following 5% CO 2 challenges during waking and anesthetic states. During wakefulness, hypercapnia elicited a substantial, short latency transient (1–1.5 min) activity increase, followed by a sustained decrease. Stimulus cessation elicited a large and rapid off-transient activity increase which persisted for ≈20 min. In contrast, during halothane anesthesia, the initial activation was absent, and the later activity decline and off-response were much reduced. We conclude that biphasic RVMS activity responses emerge to CO 2 stimulation, and are state-dependent.

The objective was to determine whether there is an inhomogeneous response of respiratory muscles during cooling-induced ventrolateral medullary (VLM) neuronal dysfunction in anesthetized and awake goats. Thermodes for cooling were chronically implanted on all or portions of rostral, intermediate, and caudal areas of the VLM of 16 adult goats. Electromyograms (EMGs) were obtained from chronically implanted wires in the diaphragm (di), transversus abdominis (TA), and triangularis sterni (TS) muscles. During some periods of cooling in 9 of 16 anesthetized airway-intubated goats, complete cessation of EMGdi coincided with a reduced yet sustained inspiratory flow. In six awake tracheotomized goats, VLM cooling decreased (P < 0.05) EMGdi duration and minute activity more than inspiratory duration and minute ventilation. Cooling thus decreased activation of the diaphragm more than activation of other respiratory muscles. On the other hand, during VLM cooling in 3 of 10 airway-intact awake goats, cessation of inspiratory flow coincided with sustained EMGdi, suggesting that cooling decreased stimulation of the upper airway muscles more than stimulation of the diaphragm. Finally, VLM cooling in a majority of goats decreased EMGTA and EMGTS more than EMGdi. We conclude that VLM neuronal dysfunction has a differential effect on respiratory muscles of adult anesthetized and awake goats.

Two questions were addressed in this study: 1) Does respiratory resistive unloading (inspired O2 fraction = 0.21, inspired He fraction = 0.79) elicit a compensatory reduction in stimulation of the diaphragm? 2) Do diaphragm and lung afferents contribute to compensatory responses to unloading? Ten intact (I), five diaphragm-deafferented (DD), four hilar nerve-denervated (HND), and seven DD+HND adult ponies were studied at rest and during mild and moderate treadmill exercise. During steady-state unloading at rest, duration of the diaphragm electromyogram (EMGdi) was less (P < 0.05) than control in I ponies, but there were no additional significant changes in breathing or blood gases. Unloading during mild and moderate exercise increased (P < 0.05) pulmonary ventilation in all groups, and this response did not differ (P > 0.05) among the groups. With unloading during exercise, arterial PCO2 was within 1 Torr of control except in the DD+HND ponies, which were 1–2 Torr hypocapnic (P < 0.05). During exercise, the duration and rate of rise of the EMGdi were reduced (P < 0.05) below control, beginning at about the third unloaded breath. The decrease in rate of rise was usually not sustained, inasmuch as there was a gradual return toward control over 2 min of unloading. There were no consistent group differences in these EMGdi responses. We conclude that resistive unloading during mild and moderate exercise in ponies results in a transient reduction in neural drive to the diaphragm that is not critically dependent on diaphragm and pulmonary afferents.

This study was done to determine 1) whether goats demonstrate the roll-off phenomenon, i.e., a secondary decrease in minute ventilation (VE), after an initial hyperventilation during various levels of hypoxia and, if so, 2) whether roll-off could be due to changes in metabolic rate. We hypothesized that roll-off occurs in the goat during hypoxia but is not due to hypometabolism. To answer question 1, eight unanesthetized adult goats were exposed to 15–20 min of hypoxia at 0.15, 0.12, and 0.09 inspired O2 fraction (FIO2), resulting in 60, 40, and 30 Torr arterial PO2, respectively. Goats were fitted with a face mask connected to a spirometer to measure VE, and arterial blood gas samples were obtained via carotid arterial catheters. Roll-off was seen with 0.15 and 0.12 FIO2, whereas VE steadily increased with 0.09 FIO2. During hypoxia, arterial PCO2 fell 2, 3, and 7 Torr at 0.15, 0.12, and 0.09 FIO2, respectively. In the second series of experiments, nine different goats were exposed to 30 min of 0.12 FIO2. O2 consumption and CO2 production were measured five times during baseline and hypoxia. VE increased to 32% above baseline values after 2 min of hypoxia and then gradually decreased by 18%. Changes in breathing frequency and tidal volume contributed to the roll-off. O2 consumption decreased (P = 0.0029, analysis of variance) and CO2 production increased (P = 0.0027) during hypoxia, although both changes were small (< 7%) compared with the eventual 18% decrease in VE. We conclude that the adult goat demonstrates the roll-off phenomenon during moderate levels of hypoxia. (ABSTRACT TRUNCATED AT 250 WORDS)

To gain insight into central and peripheral contributions to changes in breathing during hypoxia, we compared effects on breathing of reducing inspired PO2 (hypoxic hypoxia) with reducing arterial O2 content (CaO2) through elevation of carboxy-hemoglobin (COHb) (CO hypoxia). Twelve awake ponies were studied during 1 h of breathing room air followed by 6 h when COHb was increased to 25% and CaO2 was decreased by 17%. When COHb was increased, arterial PCO2 (PaCO2) increased gradually to 1.3 Torr above (P < 0.05) control level between 30 and 45 min of CO exposure. Pulmonary ventilation (VE) decreased (P = 0.09) approximately 1 liter the first 30 min of CO exposure. After approximately 45 min, PaCO2 began to decrease, steadily reaching 1.5 Torr below (P < 0.05) control level by 4.5 h of CO hypoxia. VE did not change significantly after 30 min of elevated COHb. Eight ponies were also studied during 5 h of hypoxic hypoxia (arterial PO2 approximately 40 Torr). PaCO2 decreased 5 Torr (P < 0.05) within 5 min of hypoxia and decreased another 4 Torr (P < 0.05) between 30 min and 5 h of hypoxia consistent with hypoxic ventilatory acclimatization. VE increased (P < 0.05) within 3 min of hypoxic hypoxia but then decreased (P < 0.05; VE roll off) toward control and did not increase significantly with acclimatization. Because CO and hypoxic hypoxia both decrease brain oxygenation but only hypoxic hypoxia increases carotid chemoreceptor activity, we conclude that initial hypoventilation with CO hypoxia and VE roll off with hypoxic hypoxia are consistent with hypoxic ventilatory depression within the brain. In addition, hyperventilation with prolonged CO hypoxia is consistent with a central nervous system mechanism contributing to this phase of hypoxic ventilatory acclimatization in ponies.

Periodic oscillations in pulmonary ventilation (VI), tidal volume (VT), and inspiratory and expiratory times (TI and TE) were studied during normoxia (arterial PO2 = 95 Torr) and 48 h of hypoxia (arterial PO2 = 40–50 Torr) in awake intact (n = 8) and carotid body-denervated (CBD; n = 8) ponies. Periodic oscillations were identified by fast-Fourier transformation of breath-by-breath data and quantitated by determining the power ratio of significant periodic oscillations to total power of data sequence. Periodic oscillations of 0.063–0.500 cycles/breath were observed in all parameters during both normoxia and hypoxia. During normoxia, CBD accentuated periodicity of VT (P < 0.02) and VI (P < 0.01) but did not change TI or TE periodicity (P > 0.05). These findings suggest that carotid chemoreceptors serve to stabilize breathing (i.e., decrease periodicity) during normoxia, conceivably because of their shorter response time compared with that of central chemoreceptors. During certain periods of hypoxia, periodicity of VT and VI was significantly (P < 0.05) increased in intact ponies. The response to hypoxia in CBD ponies was variable, with VI periodicity significantly (P < 0.05) increasing, decreasing, or unchanging. Because some CBD ponies significantly changed their periodicity during hypoxia compared with normoxia, we conclude that carotid chemoreceptors are not requisite for hypoxia-induced changes in periodic breathing. In addition, our observations in both groups of ponies during normoxia and hypoxia suggest that multiple mechanisms may lead to periodic oscillations in breathing.

At model organism databases data is curated for numerous biological categories using various ontologies and vocabularies. The Rat Genome Database (RGD) uses four different ontologies to standardize annotation information for genes and their associations with disease, phenotypes, and pathways. For manual gene curation this is all done in a single user interface of a web-based annotation tool developed at RGD. The same interface can be used for the curation of QTLs and strains. The development of the tool has been achieved through a collaboration of curators and software developers. Features have been tailored to the needs of the curators to allow optimum efficiency of the data entry portion of the curation process. Annotations using the Gene Ontology, Mammalian Phenotype Ontology, Pathway Ontology, and Disease Ontology can be done simultaneously in the same user interface. The search function of the tool has multiple options, giving the curators the opportunity to specify the search according to the immediate need. For ontology terms, gene, QTL, and strain objects the tool searches RGD data tables. For references the tool searches both internal and PubMed reference IDs. If an abstract reference is not already found at RGD, the tool automatically downloads the reference and assigns an RGD ID to it. Data objects, ontology terms, and references can be stored in multiples, providing various options for composing annotations. An editing step allows the composed annotation line to be altered before entering it in the database. The tool displays all current annotations for any gene that is selected. A second editing function is available by hyperlink for any pre-existing annotation displayed in the tool. The curation software has more than doubled literature curation production since replacing spreadsheet curation.

Breathing, diaphragmatic and transversus abdominis electromyograms (EMGdi and EMGta, respectively), and arterial blood gases were studied during normoxia (arterial PO2 = 95 Torr) and 48 h of hypoxia (arterial PO2 = 40–50 Torr) in intact (n = 11) and carotid body-denervated (CBD, n = 9) awake ponies. In intact ponies, arterial PCO2 was 7, 5, 9, and 11 Torr below control (P less than 0.01) at 1 and 10 min and 5 and 24–48 h of hypoxia, respectively. In CBD ponies, arterial PCO2 was 3–4 Torr below control (P less than 0.01) at 4, 5, 6, and 24 h of hypoxia. In intact ponies, pulmonary ventilation, mean inspiratory flow rate, and rate of rise of EMGdi and EMGta changed in a multi-phasic fashion during hypoxia; each reached a maximum during the 1st h (P less than 0.05), declined between 1 and 5 h (P less than 0.05), and increased between 5 and 24–48 h of hypoxia. As a result of the increased drive to the diaphragm, the mean EMGdi was above control throughout hypoxia (P less than 0.05). In contrast, as a result of a sustained reduction in duration of the EMGta, the mean EMGta was below control for most of the hypoxic period. In CBD ponies, pulmonary ventilation and mean inspiratory flow rate did not change during chronic hypoxia (P greater than 0.10). In these ponies, the rate of rise of the EMGdi was less than control (P less than 0.05) for most of the hypoxic period, which resulted in the mean EMGdi to also be less than control (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

We investigated changes in arterial PCO2 (PaCO2) and pulmonary ventilation (VE) in normal, carotid chemoreceptor-denervated, and hilar nerve-denervated ponies during intravenous lactic acid infusion at rest and treadmill exercise at 1.8 mph-5% grade (mild) and 1.8 mph-15% grade (moderate). Lactic acid, (0.5 M) infusion of 0.10, 0.13, and 0.20 ml.min-1.kg-1 at rest and mild and moderate exercise increased arterial [H+] linearly throughout the 10 min of acid infusion. At 10 min of infusion, arterial [H+] had increased approximately 20 nmol/l (0.2 pH units) for each condition and group. Under most conditions, the temporal pattern of PaCO2 during acid infusion was biphasic. At rest and during mild exercise in all groups, and in carotid chemoreceptor-denervated ponies during moderate exercise, PaCO2 increased approximately 2 Torr (P less than 0.05) during the first 2 min of acid infusion. However, in normal ponies during moderate exercise, PaCO2 was not changed from control in the first 2 min of infusion. Between 2 and 10 min of infusion at rest and mild and moderate exercise in all groups, there was a 5-Torr significant decrease in PaCO2, which did not differ (P greater than 0.10) between groups. VE increased between 15-30 s and 2 min of infusion, but VE changed minimally between 2 and 10 min of infusion at rest and exercise in all groups of ponies. We conclude that lactacidosis does increase VE at rest and submaximal exercise in the pony.(ABSTRACT TRUNCATED AT 250 WORDS)

We studied the changes in breathing and respiratory muscle electromyograms (EMG) during passively induced increases in end-expiratory lung volume (EELV) in awake normal (N), hilar nerve-denervated (HND), carotid body-denervated (CBD), and HND + CBD ponies. EELV was increased by applying continuous negative pressure (-10 and -20 cmH2O) around the torso of the standing pony. In all groups, negative pressure produced sustained increases in EELV that were linearly related to the degree of negative pressure. Elevated EELV decreased breathing frequency (f) in N and CBD ponies but increased f in HND and HND + CBD ponies. When EELV was increased, tidal volume was unchanged or above control in N ponies but was below or near control in the other groups. In all groups during elevated EELV, arterial PCO2 initially decreased but then increased relative to control with isocapnia achieved after approximately 1.5 min. In all groups, the elevated EELV was accompanied by increased stimulation of the diaphragm as indicated by increased rate of rise of the integrated EMG (P less than 0.05). During elevated EELV, the duration of diaphragm EMG was reduced, but only in HND ponies was this reduction significant (P less than 0.05). In N ponies, the major effect of elevated EELV on the expiratory transversus abdominis (TA) muscle was an increase (P less than 0.05) in duration of activity and therefore total activity. The work of breathing was thus presumably shifted more to this muscle during elevated EELV. These changes in TA timing were not observed in HND and HND + CBD ponies during elevated EELV. We conclude that elevation of EELV, which presumably places the diaphragm on a less favorable portion of its length-tension relationship, results in compensatory increased stimulation of the diaphragm that is not critically dependent on hilar and carotid chemoreceptor afferents. However, hilar afferents do contribute to the changes in diaphragm and TA duration of activity during elevated EELV.

The objective of the present study was to determine the effect of elevated inspired CO2 on respiratory dead space (VD) of 12 normal, 8 carotid body-denervated (CBD), 7 hilar nerve-denervated (HND), and 6 CBD+HND ponies. The Fowler technique was used to determine VD on a breath-by-breath basis while the ponies breathed room air and inspired CO2 at 3 and 6%. During room air breathing, tidal volume (VT) and VD were greater in HND ponies than in normal and CBD ponies (P less than 0.05), and VT was less and VD/VT was greater after CBD than before CBD. For all groups. VD, VT, and breathing frequency (f) increased and VD/VT decreased significantly (P less than 0.01) with increasing inspired CO2. During CO2 breathing, VT and VD were higher (P less than 0.05) in the HND ponies than in all other groups, the decrease (P less than 0.05) in VD/VT was greatest in the CBD+HND group, and f was lower in the HND and HND+CBD than in the normal and CBD ponies. In addition, when inspired CO2 was increased from 0 to 6%, the decrease in VD/VT was greater and the increase in arterial PCO2 was less (P less than 0.05) after CBD than before CBD. For 70% of the ponies in all groups, VD increased linearly with increases in VT; for most of the remainder, VD tended to plateau at higher values of VT.

The major objective was to determine in ponies whether factors in addition to changes in blood PCO2 contribute to changes in plasma [H+] during submaximal exercise. Measurements were made to establish in vivo plasma [H+] at rest and during submaximal exercise, and CO2 titration of blood was completed for both in vitro and acute in vivo conditions. In 19 ponies arterial plasma [H+] was decreased from rest 4.5 neq/l (P less than 0.05) during the 7th min of treadmill running at 6 mph, 5% grade (P less than 0.5). A 5.6-Torr exercise hypocapnia accounted for approximately 2.9 neq/l of this reduced [H+]. The non-PCO2 component of this alkalosis was approximately neq/l, and it was due presumably to a 1.7-meq/l increase from rest in the plasma strong ion difference (SID). Despite the arterial hypocapnia, mixed venous PCO2 was 2.7 Torr above rest during steady-state exercise. Nevertheless, mixed venous plasma [H+] was 1.2 neq/l above rest during exercise, which was presumably due to the increase in SID. Also studied was the effect of submaximal exercise on whole blood CO2 content (CCO2). In vitro, at a given PCO2 there was minimal difference in CCO2 between rest and exercise blood, but plasma [HCO3-] was greater for exercise blood than for rest blood. In vivo, during steady-state exercise, arterial plasma blood. In vivo, during steady-state exercise, arterial plasma [HCO3-] was unchanged or slightly elevated from rest, but CaCO2 was 4 vol% below rest.(ABSTRACT TRUNCATED AT 250 WORDS)

Previously, we found heightened expression of inhibitory neurochemicals and depressed expression of excitatory neurochemicals with a sudden drop in metabolic activity around postnatal day (P) 12 in rat brainstem respiratory nuclei, suggesting that this period is a critical window during which respiratory control or regulation may be distinctly different. To test this hypothesis, the hypoxic ventilatory responses (HVR) to 10% oxygen were tested in rats every day from P0 to P21. Our data indicate that (1) during normoxia (N), breathing frequency (f) increased with age, peaking at P13, followed by a gradual decline, whereas both tidal volume (V(T)) and minute ventilation (.V(E) ) significantly increased in the second postnatal week, followed by a progressive increase in V(T) and a relative plateau in .V(E); (2) during 5 min of hypoxia (H), .V(E) exhibited a biphasic response from P3 onward. Significantly, the ratio of .V(E)(H) to .V(E)(N) was generally1 during development, except for P13-16, when it was1 after the first 1-2 min, with the lowest value at P13; (3) the H : N ratio for f, V(T) and .V(E) during the first 30 s and the last minute of hypoxia all showed a distinct dip at P13, after which the V(T) and .V(E) values rose again, while the f values declined through P21; and (4) the H : N ratios for f, V(T) and .V(E) averaged over 5 min of hypoxia all exhibited a sudden fall at P13. The f ratio remained low thereafter, while those for V(T) and .V(E) increased again with age until P21. Thus, hypoxic ventilatory response is influenced by both f and V(T) before P13, but predominantly by V(T) after P13. The striking changes in normoxic ventilation as well as HVR at or around P13, together with our previous neurochemical and metabolic data, strongly suggests that the end of the second postnatal week is a critical period of development for brainstem respiratory nuclei in the rat.

Prenatal and postnatal exposure to cigarette smoke is associated with an increased incidence of the sudden infant death syndrome, although the cause(s) for this is unknown. Tobacco glycoprotein (TGP), a group of proteins purified from cured tobacco leaves and present in cigarette smoke, have been shown to cause anaphylaxis in excised hearts and lungs of adult rabbits that were neonatally sensitized to TGP and later rechallenged. We sought to determine whether anaphylaxis occurred in live infant rabbits who were neonatally sensitized to TGP. At the age of 1 day, 12 animals were sensitized to TGP (0.1mg in 0.25 cc alum) via intraperitoneal injection (i.p.i.) followed by a booster ipi at the age of 30 days (TGP-S). Seven animals received i.p.i. of antigen-free alum only (controls). All animals underwent an intravenous TGP challenge at age 42+/-2 days. Heart rate (HR) and respiratory rate (RR) were recorded for 2 min prior to and 5 min after the challenge. Baseline HR (approximately 260) and RR (approximately 120) were similar in all animals. Seven TGP-S animals developed apnea (1.9-4.7s) within 60s of the challenge while none of the controls did. The TGP-S also became bradycardic (the lowest HR over 50 consecutive beats), with the HR decreasing from 260 to 220 vs the controls, whose HR remained constant (approximately 250). We conclude that some rabbits neonatally sensitized to TGP develop apnea and bradycardia upon further intravenous TGP challenge. These studies suggest that cigarette smoke exposure may be associated with a higher rate of SIDS via an anaphylactic mechanism.

This review provides a summary and prospective on the importance of carotid/peripheral chemoreceptors to the control of breathing during physiologic conditions. For several days after carotid body denervation (CBD), adult mammals hypoventilate (+10 mmHg increase in Pa(CO(2))) at rest and during exercise and CO(2) sensitivity is attenuated by about 60%. In addition, if the rostral ventrolateral medulla is cooled during NREM sleep after CBD, a sustained apnea is observed. Eventually, days or weeks after CBD, a peripheral ventilatory chemoreflex redevelops and there is a normalization of breathing (rest and exercise) and CO(2) sensitivity. The site (s) of the regained chemosensitivity has not been established. This plasticity/redundancy after CBD appears greater in neonates than in adult mammals. These data suggest the carotid and other peripheral chemoreceptors provide an important excitatory input to medullary respiratory neurons that is essential for breathing when wakeful stimuli and central chemoreceptors are absent.

Forster, H. V., L. G. Pan, T. F. Lowry, T. Feroah, W. M. Gershan, A. A. Whaley, M. M. Forster, and B. Sprtel. Breathing of awake goats during prolonged dysfunction of caudal M ventrolateral medullary neurons. J. Appl. Physiol.84(1): 129–140, 1998.—Cooling the caudal M ventrolateral medullary (VLM) surface for 30 s results in a sustained apnea in anesthetized goats but only a 30% decrease in breathing in awake goats. The purpose of the present study was to determine, in the awake state, the effect of prolonged (minutes, hours) caudal M neuronal dysfunction on eupneic breathing and CO2 sensitivity. Dysfunction was created by ejecting excitatory amino acid receptor antagonists or a neurotoxin on the VLM surface through guide tubes chronically implanted bilaterally on a 10- to 12-mm2portion of the caudal M VLM surface of 12 goats. Unilateral and bilateral ejections (1 μl) of selective antagonists for N-methyl-d-aspartic acid or non- N-methyl-d-aspartic acid receptors had no significant effect on eupneic breathing or CO2 sensitivity. Unilateral ejection of a nonselective excitatory amino acid receptor antagonist generally had no effect on eupneic breathing or CO2 sensitivity. However, bilateral ejection of this antagonist resulted in a significant 2-Torr hypoventilation during eupnea and a significant reduction in CO2 sensitivity to 60 ± 9% of control. Unilateral ejection of the neurotoxin kainic acid initially stimulated breathing; however, breathing then returned to near control with no incidence of apnea. After the kainic acid ejection, CO2 sensitivity was reduced significantly to 60 ± 7% of control. We conclude that in the awake state a prolonged dysfunction of caudal M VLM neurons results in compensation by other mechanisms (e.g., carotid chemoreceptors, wakefulness) to maintain near-normal eupneic breathing, but compensation is more limited for maintaining CO2 sensitivity.

The increase in pulmonary ventilation (V e ) during the first minutes of hypoxia is not sustained as after several minutes V e decreases or “rolls-off” toward control levels. We hypothesized that intravenous infusion of theophylline, by blocking the central inhibitory effects on breathing of adenosine, would attenuate the hypoxic V e roll-off. Twelve unanesthetized adult goats were exposed for 20 min to a 12% O 2 -88% N 2 gas mixture. In some studies, theophylline was infused intravenously (IV) for 20 min before and during the hypoxia. The highest infusion rate of 6.0–8.0 mg/min was sufficient to totally prevent the arterial hypertension and bradycardia that occurred with IV infusion of 4 mg·min −1 of adenosine. Nine of the 12 goats demonstrated V e roll-off without the theophylline infusion. In goats that demonstrated V e roll-off without theophylline, a significant ( P e roll-off was observed even at the highest theophylline infusion rate. We therefore conclude that the V e roll-off during hypoxia is not primarily or critically mediated by adenosine in awake, adult goats.

The rostral ventrolateral medullary surface (VMS) plays a major state-dependent role in the control of breathing; its role during hypoxia remains speculative. We therefore assessed activity within the rostral VMS by measuring reflectance of scattered light in 5 goats during normoxia, hypoxia, and hyperoxia in awake and halothane anesthetic states. Within the first minute of hypoxia, light reflectance began to decrease in the awake state; reflectance reached a stable nadir within 30 min about 10 and 17% below control values (P < 0.01), at 12 and 10% inspired O2, respectively. In the anesthetized state, reflectance decreased (P < 0.01) by 6% at 10% inspired O2. After 30 min in the awake state, reflectance returned (P < 0.01) toward control values, reaching a stable level at 7 and 11% below control at 12 and 10% inspired O2, respectively (P < 0.05). Hyperoxia resulted in a 1% increase (P < 0.05) in reflectance. Changes in reflectance during hypoxia did not consistently parallel changes in breathing, heart rate, or arterial blood pressure. We conclude that, a) decreased reflectance during hypoxia results, in part, from increased neural activity, and b) state exerts a substantial effect on the response of VMS areas to hypoxia.

It has been reported that the caudal ventrolateral medulla (VLM) is important in central chemoreception and the control of breathing. The objective of this study was to determine in adult goats the effects on breathing of neuronal dysfunction of this caudal VLM region (area L; caudal to rostral hypoglossal nerve rootlet). Thermodes were chronically implanted on the VLM to cool neurons and thereby cause neuronal dysfunction. During awake and (halothane) anesthetized states, cooling the caudal VLM for 20 s to 20 degrees C did not alter breathing (P > 0.10). However, between 20 and 30 s of cooling and during recovery from cooling 0–4 mm caudal to the rostral hypoglossal rootlet, there was a 12 (awake) to 25% (anesthetized) increase (P < 0.05) in breathing. This tachypneic hyperpnea was uniform over conditions of eucapnia, hypercapnia, and hypoxia and resulted from reduced inspiratory time that increased frequency. We conclude that in goats inhibitory neurons are located in area L and the lateral caudal ventral medulla.

In three previously reported studies, we had documented that the normal exercise hyperventilation in ponies is accentuated by carotid body denervation (CBD), not affected by hilar nerve pulmonary vagal denervation (HND), and mildly attenuated by spinal cord ablation of the dorsal lateral columns at L2 (SA). In the present study, we hypothesized that if redundancy of control existed in exercising ponies, then multiple denervations of theoretically important pathways in the same animal might attenuate the ventilatory response to exercise in a way not predictable by the individual lesion experiments alone. There were three major findings in the various combinations of CBD, HND, and SA in ponies during treadmill exercise. First, the combination of CBD with HND or SA resulted generally in an accentuation of the hypocapnia during exercise that was predictable on the basis of CBD alone. However, in one pony that showed a hypercapnic exercise response after SA alone, CBD subsequently caused a greater exercise hypercapnia. Second, HND in a CBD or SA pony did not affect the exercise arterial PCO2 response, which is consistent with previous data showing the lack of an HND effect in otherwise intact ponies. Third, in ponies with all three denervations together, the predominant response was an increase, not a decrease, in the exercise hyperventilation; this increase was greater than that predicted from the individual lesions. We conclude that these data do not provide evidence of redundancy in mechanism for the exercise hyperpnea other than instances of carotid chemoreceptor error sensing when hypercapnia occurs during exercise.

Our objective was to investigate the role of the ventrolateral medulla (VLM) in the control of breathing during the awake state. In 17 awake adult goats, chronically implanted thermodes were used to cool the VLM and thereby cause reversible neuronal dysfunction in all or portions of the area between the first hypoglossal rootlet and the ponto-medullary junction (so-called area M (rostral) and area S). Within 5 s after the initiation of cooling, 60–100% of areas M and S, pulmonary ventilation (VE) decreased uniformly over conditions of eucapnia, hypercapnia, hypoxia, and exercise (P < 0.05). Between 10 and 20 s of cooling, the reduction in VE was approximately 10% greater during eucapnia and hypercapnia than during hypoxia and exercise (P < 0.05). For the remaining 10 s of cooling and for about 1 min after cooling, VE increased to and above control level. Cooling only rostral area M or only caudal area M-rostral area S affected breathing qualitatively in the same manner as when 60–100% of areas M and S were cooled. However, cooling caudal area S had effects that differed significantly (P < 0.05) from more rostral cooling in that the initial decrease in VE was attenuated and the subsequent increase was accentuated. The initial uniform decreased VE during cooling suggests that superficial VLM nonchemoreceptor neurons facilitate breathing. The subsequent relatively greater effect of cooling during eucapnia and hypercapnia probably reflects dysfunction of chemoreceptor-related neurons that normally stimulate breathing. The stimulation of breathing during the later stages and after cooling may suggest that some VLM neurons inhibit breathing.

The ventrolateral medulla (VLM) has been reported to be important as a source of tonic facilitation of dorsal respiratory neurons and as a site critical for respiratory rhythmogenesis. We investigated these theories in awake and anesthetized goats (n = 13) by using chronically implanted thermodes to create reversible neuronal dysfunction at superficial VLM sites between the first hypoglossal rootlet and the pontomedullary junction (area M (rostral) and area S). During halothane anesthesia (arterial PCO2 = 57.4 +/- 4.5 Torr), bilateral cooling (thermode temperature = 20 degrees C) of 60–100% of areas M and S for 30 s produced a sustained apnea (46 +/- 4 s) that lasted beyond the period of cooling. While the animals were awake (arterial PCO2 = 36.0 +/- 1.9 Torr), cooling the identical region in the same goats resulted in a decrease (approximately 50%) in pulmonary ventilation, with a brief apnea seen only in one goat. Reductions in both tidal volume and frequency were observed. Qualitatively similar responses were obtained when cooling caudal area M-rostral area S and rostral area M, but the responses were less pronounced. Minimal effects were seen in response to cooling caudal area S. During anesthesia, breathing is critically dependent on superficial VLM neurons, whereas in the awake state these neurons are not essential for the maintenance of respiratory rhythm. Our data are consistent with these superficial VLM neuronal regions providing tonic facilitation to more dorsal respiratory neurons in both the anesthetized and awake states.

The Rat Genome Database (RGD) is the premier repository of rat genomic and genetic data and currently houses over 40 000 rat gene records, as well as human and mouse orthologs, 1857 rat and 1912 human quantitative trait loci (QTLs) and 2347 rat strains. Biological information curated for these data objects includes disease associations, phenotypes, pathways, molecular functions, biological processes and cellular components. RGD uses more than a dozen different ontologies to standardize annotation information for genes, QTLs and strains. That means a lot of time can be spent searching and browsing ontologies for the appropriate terms needed both for curating and mining the data. RGD has upgraded its ontology term search to make it more versatile and more robust. A term search result is connected to a term browser so the user can fine-tune the search by viewing parent and children terms. Most publicly available term browsers display a hierarchical organization of terms in an expandable tree format. RGD has replaced its old tree browser format with a ‘driller’ type of browser that allows quicker drilling up and down through the term branches, which has been confirmed by testing. The RGD ontology report pages have also been upgraded. Expanded functionality allows more choice in how annotations are displayed and what subsets of annotations are displayed. The new ontology search, browser and report features have been designed to enhance both manual data curation and manual data extraction. Database URL: http://rgd.mcw.edu/rgdweb/ontology/search.html

To determine the effect of hypoxia on metabolic rate (VO2) of ponies, on 2 days we studied ponies that were breathing room air for 1 h followed by 5 h of either hypoxic hypoxia (fractional concn of inspired O2 = 0.126) or 5 h of CO hypoxia. Control arterial PO2 was 103 +/- 1.2 Torr, and at 5 min and 5 h of hypoxic hypoxia, arterial PO2 was 53.1 +/- 1.8 and 41.0 +/- 1.8 Torr, respectively. There was a time-dependent hypocapnia and alkalosis during hypoxic hypoxia. During CO hypoxia, carboxyhemoglobin increased to 25% after 30 min and remained constant thereafter. With increased carboxyhemoglobin, arterial PCO2 was 1.3 Torr above (P < 0.05) and 1.5 Torr (P < 0.05) below control levels after 30 min and 3 h, respectively. There were no significant (P > 0.10) changes in VO2 during either hypoxic or CO hypoxia. However, in 50% of the ponies, VO2, pulmonary ventilation, and rectal temperature increased and shivering was evident after 30 min of hypoxia. Peak values of pulmonary ventilation, VO2, and shivering occurred at approximately 2 h with a subsequent return toward control levels. We conclude that, in contrast to smaller mammals, acute hypoxia does not depress VO2 of ponies. The hypermetabolism and hyperthermia during chronic hypoxia in some ponies may reflect a transient failure in thermoregulation.

The objective of the present study was to determine whether lung and diaphragm afferents contribute to the changes in respiratory muscle activity when end-expiratory lung volume (EELV) is changed in ponies. We studied the responses of the diaphragm and the transversus abdominis (TA) muscles to passive increases in EELV in awake intact (I), diaphragm-deafferented (DD), pulmonary vagal- (hilar nerve) denervated (HND), and DD + HND ponies. Negative pressure of -10 or -20 cmH2O applied around the ponies′ torsos [positive transrespiratory (TR) pressure] increased (P < 0.05) EELV in all ponies; the increases were more (P < 0.05) in HND and less (P < 0.05) in DD than in I ponies. In I ponies, positive TR pressure increased (P < 0.05) the rate of rise of the integrated diaphragmatic electromyogram (EMG), reflecting increased drive to the muscle. This increase was less (P < 0.05) in DD and HND than in I ponies. In DD + HND ponies, there was no significant (P > 0.10) change in drive to the diaphragm during positive TR pressure. In I ponies, positive TR pressure increased (P < 0.05) the duration and mean activity of the TA EMG. In HND and DD + HND ponies, the TA EMG was not altered by positive TR pressure. I and DD ponies decreased (P < 0.05) breathing frequency but maintained tidal volume (VT) during positive TR pressure. HND and DD+HND ponies increased breathing frequency (P < 0.05) and decreased (P < 0.05) VT during positive TR pressure. We conclude that, during positive TR pressure when the diaphragm is presumably at a mechanical disadvantage, diaphragm and vagal afferents mediate increased drive to the diaphragm to prevent VT from decreasing. In addition, during positive TR pressure, vagal afferents mediate an increase in duration of TA activity, which minimizes the increase in EELV.

We determined the effect of pulmonary vagal (hilar nerve) denervation (HND) and diaphragm deafferentation (DD) on inspiratory load compensation. We studied awake intact (I; n = 10), DD (n = 5), HND (n = 4), and DD+HND (n = 7) ponies at rest and during mild (1.8 mph, 5% grade) and moderate (1.8 mph, 15% grade) treadmill exercise before, during, and after resistance of the inspiratory circuit was increased from approximately 1.5 to approximately 20 cmH2O.l–1.s. During the first loaded breath in I ponies at rest, inspiratory time (TI) increased, expiratory time decreased, and inspiratory drive increased. There were minimal changes after the first breath, and inspiratory minute ventilation (VI) and arterial PCO2 did not change (P > 0.10) from control values. On the first loaded breath during exercise, TI increased but inspiratory drive either did not change or decreased from control values. TI and drive increased after the first breath, but the increases were insufficient to maintain VI and arterial PCO2 at control levels. First-breath load compensation remained after DD, HND, and DD+HND, but after DD+HND tidal volume and VI were compensated 5–10% less (P < 0.05) than in I ponies. In all groups inspiratory drive, tidal volume, and VI were markedly augmented on the first breath after loading was terminated with a gradual return toward control. We conclude that diaphragm and pulmonary afferents contribute to but are not essential for inspiratory load compensation in awake ponies.

In humans, attenuating carotid chemoreceptor activity by hyperoxia does not alter arterial PCO2 (PaCO2) during submaximal exercise, yet a transient hypercapnia occurs in carotid chemoreceptor-resected (CBR) asthmatic subjects during submaximal exercise. We hypothesized that this difference was due to asthma and not CBR causing the abnormal response. Accordingly, we determined the temporal pattern of PaCO2 during mild and moderate exercise in chemoreceptor-intact asthmatic (n = 10) and nonasthmatic subjects (n = 10). We also hypothesized that hyperoxia alters PaCO2 during exercise if exercise already has disrupted PaCO2 homeostasis. Accordingly, we studied, during exercise, asthmatic subjects while hyperoxic; nonasthmatic subjects during loaded breathing of room air, which increased PaCO2; and nonasthmatic subjects during loaded breathing while hyperoxic. While breathing room air, neither asthmatic nor nonasthmatic subjects maintained arterial isocapnia during exercise. An increase in PaCO2 between rest and exercise and between mild exercise and 1st min of moderate exercise was greater in asthmatic than in nonasthmatic subjects (P < 0.05). In six asthmatic subjects that were hypercapnic breathing room air during exercise, hypercapnia was accentuated by hyperoxia. The ventilatory load in nonasthmatic subjects resulted in a work load-dependent hypercapnia (P < 0.01) accentuated (P < 0.01) by hyperoxia. We conclude that normally in humans the carotid chemoreceptors contribute minimally to the hyperpnea of submaximal exercise. However, when PaCO2 is increased from resting values during exercise, then the chemoreceptors serve to augment ventilation and thereby minimize the hypercapnia.