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Biomedical subjects

M H O'Neal

Publications and source records attributed to M H O'Neal.

7 recordsLinked to original sources
PubMed2001

Differential expression of connexin26 and connexin32 in the pre-Bötzinger complex of neonatal and adult rat.

The pre-Bötzinger complex (pre-BötC) is hypothesized to be the site for respiratory rhythm generation in mammals. Studies examining the cellular mechanisms mediating rhythm generation have focused on the role of chemically mediated synaptic interactions; however, electrotonic synaptic interactions (i.e., electrotonic coupling), which occur by means of gap junctions, may also play a role. Here, we used immunoblot and immunohistochemical analyses to determine whether the pre-BötC contains the gap junction proteins necessary for electrotonic communication and whether the presence and distribution of these gap junction proteins show a developmental change in expression. We found that both connexin26 (Cx26) and connexin32 (Cx32) were expressed in pre-BötC neurons of neonatal and adult rats; however, the relative amounts and their distribution varied by age. Cx26 labeling was seen in a high proportion of pre-BötC neurons in neonatal rats < or = 7 days postnatal (P7) but declined with increasing age. In contrast, Cx32 labeling was sparse in pre-BötC neurons of neonatal rats < or = P7, but increased with increasing age; the highest proportion was seen in adult rats. These data suggest the potential for gap junctional communication in the pre-BötC of both neonatal and adult rats, and we propose that the gap junction proteins Cx26 and Cx32 form the neuroanatomic substrate for this gap junctional communication, which may be important in the synchronization of neural activity generating respiratory rhythm.

Aging↗
PubMed2001

Localization of connexin26 and connexin32 in putative CO(2)-chemosensitive brainstem regions in rat.

Recent studies have suggested that cell-to-cell coupling, which occurs via gap junctions, may play a role in CO(2) chemoreception. Here, we used immunoblot and immunohistochemical analyses to investigate the presence, distribution, and cellular localization of the gap junction proteins connexin26 (Cx26) and connexin32 (Cx32) in putative CO(2)-chemosensitive brainstem regions in both neonatal and adult rats. Immunoblot analyses revealed that both Cx subtypes were expressed in putative CO(2)-chemosensitive brainstem regions; however, regional differences in expression were observed. Immunohistochemical experiments confirmed Cx expression in each of the putative CO(2)-chemosensitive brainstem regions, and further demonstrated that Cx26 and Cx32 were found in neurons and Cx26 was also found in astrocytes in these regions. Thus, our findings suggest the potential for gap junctional communication in these regions in both neonatal and adult rats. We propose that the gap junction proteins Cx26 and Cx32, at least in part, form the neuroanatomical substrate for this gap junctional communication, which is hypothesized to play a role in central CO(2) chemoreception.

Animals↗
PubMed2000

CO(2)/H(+) chemoreception in the cat pre-Bötzinger complex in vivo.

We examined the effects of focal tissue acidosis in the pre-Bötzinger complex (pre-BötC; the proposed locus of respiratory rhythm generation) on phrenic nerve discharge in chloralose-anesthetized, vagotomized, paralyzed, mechanically ventilated cats. Focal tissue acidosis was produced by unilateral microinjection of 10-20 nl of the carbonic anhydrase inhibitors acetazolamide (AZ; 50 microM) or methazolamide (MZ; 50 microM). Microinjection of AZ and MZ into 14 sites in the pre-BötC reversibly increased the peak amplitude of integrated phrenic nerve discharge and, in some sites, produced augmented bursts (i.e., eupneic breath ending with a high-amplitude, short-duration burst). Microinjection of AZ and MZ into this region also reversibly increased the frequency of eupneic phrenic bursts in seven sites and produced premature bursts (i.e., doublets) in five sites. Phrenic nerve discharge increased within 5-15 min of microinjection of either agent; however, the time to the peak increase and the time to recovery were less with AZ than with MZ, consistent with the different pharmacological properties of AZ and MZ. In contrast to other CO(2)/H(+) brain stem respiratory chemosensitive sites demonstrated in vivo, which have only shown increases in amplitude of integrated phrenic nerve activity, focal tissue acidosis in the pre-BötC increases frequency of phrenic bursts and produces premature (i.e., doublet) bursts. These data indicate that the pre-BötC has the potential to play a role in the modulation of respiratory rhythm and pattern elicited by increased CO(2)/H(+) and lend additional support to the concept that the proposed locus for respiratory rhythm generation has intrinsic chemosensitivity.

Acetazolamide↗
PubMed1980

Transcutaneous oxygen monitoring during exercise stress testing.

Transcutaneous oxygen tension (tcPO2) was compared with simultaneous arterial oxygen tension (PaO2) in 3 normal young adults and 4 pediatric lung disease patients at rest and during exercise to assess the usefulness of tcPO2 monitoring during exercise stress testing. At rest, the regression coefficient of tcPO2 on PaO2 was 0.78 +/- 0.03 (SEM) (r = 0.924; P < 0.0005). During exercise, the regression coefficient of tcPO2 on PaO2 was 0.88 +/- 0.02 (r = 0.958; P < 0.0005), indicating that tcPO2 approximates PaO2 equally well at rest and during exercise. After a step change in inspired oxygen concentration (FIO2) from 0.21 to 0.17, there was no significant difference in the tcPO2 time constant at rest (66.2 +/- 8.5 s) and during exercise (73.0 +/- 3.1 s). Neither PaO2 nor tcPO2 fell in normal subjects during graded exercise stress testing. However, in 3 of 4 pediatric lung disease patients, there were decreases in both PaO2 (40.7 +/- 11.6 Hg) and tcPO2 (28.7 +/- 10.0 mm Hg) during 7 exercise stress tests. These results indicate that tcPO2 approximates PaO2 equally well at rest and during exercise.

Adolescent↗
PubMed1980

Pulmonary function abnormalities in thalassemia patients on a hypertransfusion program.

Pulmonary function tests were performed in 12 thalassemia patients on a hypertransfusion program (age 18.4 +/- 2.6 SEM years) to determine the presence of any abnormalities of lung function. These included spirometry, expiratory flow rates, body plethysmography, single-breath nitrogen washout, single breath carbon monoxide diffusing capacity, and arterial blood gases. Only one patient had normal pulmonary function. Arterial hypoxemia was present in ten of 12 patients at rest. The total lung capacity (TLC) was normal. The residual volume was abnormally increased in five of 12 patients. The slope of phase III of single breath nitrogen washout curve was abnormal in five of 12 patients, but the closing volume was normal. The maximal expiratory flow rate at 60% total lung capacity was decreased in four of 12 patients, suggesting the presence of small airway disease. The single breath carbon monoxide diffusing capacity was normal in all patients. These pulmonary function abnormalities did not correlate with age or the cumulative amount of iron via blood transfused. The small airway obstruction, hyperinflation; and hypoxemia observed in thalassemia patients on a hypertransfusion program may result from the basic disease, iron deposition in the lungs, or other factors.

Adolescent↗