This thesis concerns the possible existence of central nervous system (CNS) chemosensitive mechanisms influencing sympathetic activity. The thesis is based on observations of sympathetic neuron and cardiovascular responses to CNS ischemia, systemic hypoxia and systemic hypercapnia. Investigation of the pressor response to cerebral ischemia in the cat indicates that it is mediated by superficial regions of the ventral medulla also involved in the pressor response to central hypercapnia. Experiments concerning the sympathetic response to systemic hypoxia in the CNS-intact sino-aortic denervated cat revealed a two-component response of the firing rates of single sympathetic preganglionic neurons (SPN), the mass activity of the cervical sympathetic trunk, and the neurogenic component of hindlink vascular resistance (N-HLVR). The response consisted of: (i) an increase of all three variables during extreme hypoxia, and (ii) a decrease during moderate hypoxia. The hypoxic sympatho-depression resulted from loss of central respiratory input to SPNs as well as of respiration-independent input. The hypoxic sympatho-excitation involved only the latter input. Investigation of the sympathetic response to systemic hypercapnia in the acute C$ sb1$ spinal cat demonstrated a direct relationship between SPN firing rate or N-HLVR and arterial PCO$ sb2$ between normocapnia and severe hypercapnia. N-HLVR also increased in this preparation during systemic hypoxia.

No description available.

The fatigue of the human diaphragm during resting ventilation^was found to be determined by the fraction of the maximal trans-^diaphragmatic pressure used at each inspiration (Pdi/Pdi(' )max) and the fraction of the breathing cycle time spent in inspiration (T(,I)/T(,TOT)). A fatigue threshold relation was found between the Pdi/Pdi(' )max and the T(,I)/T(,TOT). This fatigue threshold corresponds to a quadratic hyperbola function given by the product (Pdi/Pdi(' )max) times (T(,I)/T(,TOT)). This product was termed the diaphragmatic tension-time index (TTdi) and at the fatigue threshold is equal to .15 (TTdi crit). Above TTdi crit the endurance time is limited and is accompanied by a progressive shift of the EMG power spectrum towards lower frequencies. The rate of shift of the EMG power spectrum is proportional to the endurance time. Patients with chronic obstructive lung disease breathe at rest closer to the fatigue threshold than normals secondary to an increased airway resistance and a decreased Pdi max. Minor modifications of the breathing cycle in those patients were found to cause diaphragmatic fatigue. / Diaphragmatic blood flow (Qdi)(' )in dogs was measured during static continuous and intermittent stimulated contractions. Qdi(' )was found to be related to the TTdi and to be maximal at a TTdi of .20. At higher and lower TTdi,(' )Qdi decreases and is zero at TTdi of .75. When the TTdi was greater than .20, a post contraction hyperaemia was present and increased as a function of TTdi, thus indicating that the(' )Qdi was limited in the preceding contractions.

Na+/H+ exchangers (NHE) are integral membrane proteins that catalyze the electroneutral exchange of Na+ (or K+) for H+. The nine human isoforms identified to date share the same topology of twelve membrane-spanning domains and a cytoplasmic regulatory tail, and diverge in their tissue expressions and subcellular localizations. This thesis focused on the identification and characterization of proteins interacting with the ubiquitous NHE6 isoform, which resides predominantly in recycling endosomes. Recent yeast two-hybrid (Y2H) screening of a human brain cDNA library using the regulatory tail of NHE6 as a probe resulted in the tentative identification of about 250 partial or full-length NHE6-interacting proteins. Thirty other potential NHE6-interacting partners were identified by isolating NHE6 complexes from embryonic kidney 293 cells by tandem affinity purification (TAP) and subjecting them to mass spectrometry analysis. The interaction between NHE6 and eight of these proteins (four from each Y2H and TAP analyses) was tested by co-immunoprecipitation, co-localization by immunofluorescence microscopy and in vitro GST-fusion protein pull-down assays. We show that apolipoprotein D interacts weakly with NHE6, while myosin light chain kinase and the mitochondrial ATP synthase subunit-alpha are true NHE6-binding partners. The remaining five proteins exhibited poor and/or non-reproducible association with NHE6.

There exists no adequate objective measure of vestibular function and consequently clinicians cannot easily estimate degree of vestibular dysfunction or dizziness. This study aimed to evaluate new objective measures of vestibular function by determining (1) how these measures relate to subjective clinical estimates of vestibular function and (2) whether these measures can identify patients with true vestibular dizziness. / Net $ {$slow-phase + saccadic$ }$ gaze stabilization and active comfortable torsal-head rotation were used to objectively characterize vestibulo-ocular and vestibulospinal function, respectively, in 39 dizzy patients and 30 normals. Blinded clinical ranking of apparent vestibular function of the patients was obtained from history and clinical examination. / It was found (1) that clinical rankings were significantly correlated (r$ rm sb{s}$:0.39, p $<$ 0.02) to a new objective parameter based on both vestibulo-ocular and vestibulospinal measures, and (2) that an objective measure of both vestibulo-ocular and vestibulospinal function permitted most dizzy patients and normal subjects to be identified (sensitivity: 87%, specificity: 83%).

Acute myocardial ischemia is the main cause of ventricular tachycardia and ventricular fibrillation. Reentrant activity is the most common mechanism of these ventricular arrhythmias, and is often initiated from the border zone between the ischemic and normal tissue. Theoretical studies have suggested that spiral-wave activity may be one form of reentrant arrhythmia. Our study explores the possible relation between spiral-wave activity and ischemia-induced ventricular arrhythmias. We numerically simulate reentrant activity in a two-dimensional sheet of ventricular myocardium which contains an ischemic area. We construct this ischemic area by increasing the extracellular potassium concentration in that area. When pacing the sheet with a sequence of stimuli delivered at a sufficiently high frequency, different types of spiral waves are initiated either within the ischemic area itself or in the normal area close to the ischemic boundary, depending on the potassium concentration in the ischemic area. The formation of the spiral wave is influenced by several factors such as the frequency of stimulation, the geometry of the ischemic area, and the exact level of the extracellular potassium concentration in the ischemic area. Future work should model the ischemic area more realistically with a spatially-extended border zone.

Free and microencapsulated hepatocytes in an alginate-polylysine-alginate artificial membrane (APA), were implanted intraperitoneally into the Gunn rat, the animal model for Crigler-Najjar syndrome, to reduce serum bilirubin level. Hepatocytes from guinea pigs, Wistar and Sprague-Dawley rats whether free or microencapsulated were equally effective in lowering serum bilirubin levels in the Gunn rat. Buffalo rat hepatocytes however, were immunorejected unless microencapsulated. Decrease in serum bilirubin was concomitant with the appearance of conjugated bilirubin in the bile of Gunn rats as demonstrated by HPLC analysis. Microcapsules containing guinea pig hepatocytes showed less fibrosis than microcapsules containing hepatocytes from different strains of rats and empty microcapsules. In the Gunn rat there is significant accumulation of bilirubin in various tissues which affects the net removal of bilirubin upon implantation of the encapsulated hepatocytes. This deposition increases with time and it is organ-dependent. The kinetic data of UDP-glucuronosyltransferase (UDPGT) indicated that it is a multisubunit enzyme in which there is cooperative binding of the substrate to the subunits. The binding of bilirubin showed positive cooperativity while the binding of UDPGA exhibited kinetics with mixed cooperativity. Encapsulated hepatocytes when incubated with bilirubin and UDP-glucuronic acid can form bilirubin conjugates. This was shown by HPLC analysis.The comparison of UDPGT activity between liver homogenate, intact hepatocytes and encapsulated hepatocytes showed that there is mass transfer resistance of the APA membrane.

In the rat, catecholamine conjugates, particularly dopamine conjugates, are widely distributed in cerebrospinal fluid, sympathetically innervated tissues, plasma, erythrocytes and urine. Sulfoconjugated dopamine, norepinephrine and epinephrine are detected in small quantities, whereas glucuronoconjugation seems to occur only in dopamine, and is by far the predominant form of dopamine conjugation. On the other hand, in man, sulfoconjugation is normally the sole form of catecholamine conjugation. Glucuronoconjugated dopamine constitutes the bulk not only of dopamine, but also of total catecholamines in rat cerebrospinal fluid, plasma and urine, which sharply contrasts with the composition of catecholamines in peripheral tissues where the bulk of total catecholamines is free norepinephrine (in sympathetically innervated tissues) or epinephrine (in adrenals). Sulfo- and glucuronoconjugated catecholamines in rat cerebrospinal fluid are central in origin, whereas the adrenal medulla and peripheral postganglionic sympathetic neurons are important sources of peripheral conjugated catecholamines. In response to stress, rat plasma free catecholamine surges occur with concomitant substantial falls in sulfoconjugated dopamine, norepinephrine and epinephrine as well as glucuronoconjugated dopamine. Under stress, a large portion of rat plasma conjugated dopamine, mainly glucuronoconjugated dopamine is not only deconjugated to free dopamine, but probably also converted to free norepinephrine and epinephrine. Adrenalectomy abolishes these normal stress-induced responses to plasma conjugated catecholamines in the rat. These findings led to the following conclusions. (1) Glucuronoconjugation is an important pathway in the metabolism of central and peripheral dopamine in the rat. (2) In the metabolism of catecholamines, conjugation is qualitatively distinct from O-methylation and deamination in that conjugation represents an intermediate and reversible process, whereas O-methylatio

The functions of somatostatin, norepinephrine and epinephrine in regulation of rhythmic growth hormone secretion were evaluated in male Sprague-Dawley rats. Three experimental strategies were used: (1) the chronic cannulation model to assess the effects of stress, lateral hypothalamic stimulation, monosodium glutamate, and pharmacologic agents on growth hormone dynamics, (2) biochemical mapping of central somatostatinergic pathways involved in growth hormone regulation, and (3) an in vitro perifusion system to study somatostatin release. / It is shown that exictatory and inhibitory neural inputs must be intact to maintain normal rhythmic growth hormone secretion. Growth hormone rises are generated by hypothalamic neurons that liberate a growth hormone releasing factor. These neurons are activated by adrenergic (and probably noradrenergic) inputs. The periventricular and amygdalofugal somatostatinergic systems control ebbs in plasma growth hormone and stress- or lateral hypothalamic stimulation-induced growth hormone suppression. Catecholaminergic regulation of somatostatin release is not defined clearly.

No description available.