Aerobic exercise such as cycling is known to elicit a post-exercise hypotensive (PEH) response. However, it is not known if swim exercise produces a similar effect in normotensive individuals. We tested the hypothesis that an acute bout of swimming would elicit a PEH response that is less compared to an equivalent bout of cycling. 10 trained and 11 untrained normotensive (SBP/DBP < 120/80 mmHg) individuals (23±1 years) underwent 30 min intensity-matched cycling and swimming sessions to assess changes in BP and cardiovascular responses. While PEH was similar between modalities within groups, the magnitude and temporality of change in BP following swimming was significantly different (p < 0.01) between groups, with untrained participants showing a significant PEH response. Attenuation of PEH in trained individuals was reflective of a significant increase in sympathetic outflow and slower vagal reactivation, suggesting training in an aquatic environment leads to alterations in post-exercise BP regulatory mechanisms.

The effective of additional muscle mass in a priming exercise on cardiac output (Q) and pulmonary oxygen uptake (VO2) kinetics (mean response time, s) were determined in cyclists. Outcomes were measured over four trials, each consisting of a 6-minute legs alone (UAL) or arms and legs (ULO) warm-up, 3 minute passive recovery, then 6 minutes leg cycling (PAL, PLO; respectively). Q was significantly higher preceding exercise onset with PAL compared to PLO or ULO (0.72 ± 0.13 vs. 0.58 ± 0.09, 0.43 ± 0.09 L∙min-1; respectively, P < 0.05). Q kinetics did not differ between unprimed (ULO: 38.9 ± 8.6) and primed exercise regardless of muscle mass (PLO: 38.6 ± 11.0; PAL: 40.7 ± 11.3). VO2 kinetics were faster (P < 0.05) with PAL (36.9 ± 6.0) compared to ULO (58.7 ± 10.5). Muscle mass employed during priming exercise had only slight effect on subsequent VO2 and Q responses.

This thesis tested the hypothesis that ethanol suppresses respiratory muscle activity by effects at the central motor pool and/or by state-dependent regulation of motor activity via influences on sleep/arousal processes. Ten rats were implanted with electroencephalogram and neck electrodes to record sleep-wake states, and genioglossus and diaphragm electrodes for respiratory recordings. Studies were performed following intraperitoneal injection of ethanol (1.25g/kg) or vehicle. The effects on genioglossus activity of ethanol (0.025-1M) or vehicle applied directly to the hypoglossal motor nucleus were also determined in sixteen isoflurane-anaesthetized rats. The results of these studies suggest that ethanol at physiologically relevant concentrations promoted sleep, and altered electroencephalogram and postural motor activities indicative of a sedating effect. The lack of effect on genioglossus activity with ethanol applied directly to the hypoglossal motor pool suggests that the suppression observed with systemic administration may be mediated via effects on state-dependent processes rather than direct effects at the motor pool per se.

Transforming growth factor-beta 1 (TGF-β1) is a multifunctional cytokine that orchestrates key events of development, disease and repair in the central nervous system (CNS). To investigate the effects of chronically producing TGF-β1 on synaptic structure and synaptic transmission, I performed immunohistochemistry and immunoblot of brain tissues from transgenic mice (TGF-β1 mice) that over-express active form of TGF-β1 from astrocytes in the CNS. Immunohistochemical assays showed that synaptophysin increased in the CA3 subfield whereas calbindin-D28K decreased in the mossy fibres. Immunoblot analysis revealed that several α-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptor subunit proteins were up-regulated in the hippocampus of TGF-β1 mice. To examine the direct effect of TGF-β1 alone on glutamatergic synaptic activity, cultured hippocampal neurons were treated with or without TGF-β1. Electrophysiological recordings displayed that TGF-β1 significantly increased the amplitude of glutamate-evoked current (p<0.05). Taken together, these data suggest that TGF-β1 modulates hippocampal glutamatergic synaptic protein expression and regulates synaptic transmission.

Rationale: Vascular remodeling and right-ventricular (RV) dysfunction are features of refractory pulmonary hypertension (PHT) in human neonates. These features are replicated in rats chronically exposed to hypoxia (13% O2), in which increased pulmonary vascular resistance (PVR) was acutely normalized by Y-27632, a Rho-kinase (ROCK) inhibitor, but not by inhaled nitric oxide. Objective: To examine the reversing effects of sustained ROCK inhibition on haemodynamic (RV dysfunction and increased PVR) and structural (RV hypertrophy and arterial wall remodeling) changes of chronic hypoxic PHT. Methods: Rat pups were exposed to air or hypoxia from birth for up to 21 days and received Y-27632 (15 mg/kg/b.i.d.) or vehicle from day 14. Results: Y-27632 normalised RV dysfunction and reversed remodeling secondary to chronic hypoxia. These changes were accompanied by increased apoptosis of smooth muscle and attenuated endothelin-1 expression in pulmonary arteries. Conclusion: ROCK inhibitors hold promise as a rescue therapy for refractory PHT in neonates.

GABA and GABA type A receptor (GABAAR) are expressed in pancreatic β-cells and comprise an autocrine signaling system. How the GABA-GABAAR system is regulated is unknown. In this study, I investigated insulin’s effect on this system in the INS-1 β-cell line. I found that GABA evoked current (IGABA) in INS-1 cells, resulting in membrane depolarization. Perforated-patch recordings showed that pre-treatment of insulin or zinc-free insulin suppressed IGABA in INS-1 cells (p < 0.01). Radioimmunossay showed that GABA (30 μM) increased C-peptide secretion from INS-1 cells, which was blocked by GABAAR antagonist picrotoxin, indicating that GABA increased insulin secretion through activation of GABAAR. However, insulin significantly reduced the stimulatory effect of GABA on C-peptide secretion (p < 0.05). These data suggest that GABA released from β-cells positively regulates insulin secretion via GABAAR activation, and that insulin negatively regulates the β-cell secretory pathway likely via inhibiting the GABA-GABAAR system in β-cells.

Background: Intracellular glucocorticoid receptors (GRs) mediate the regulation of lung development, including alveolarization, by glucocorticoids (GCs). One potential approach to determining the role of GC-GR signalling in alveolar formation would be by pharmacologic blockade. Hypothesis: CP472555, a novel GR antagonist with negligible anti-PR activity, is a suitable tool for the study of GC-GR regulation of rat alveolarization. Design/Methods: CP472555 doses needed to block GR were estimated in vitro in fetal rat lung primary cultures. Postnatally, a variety of doses were administered intraperitoneally over a range of days. Results: During postnatal days (PN)0-PN10, when GC levels are low, CP472555 induced changes consistent with GR agonist activity. While GC levels increase after PN11, animals exposed to CP472555 from PN11-PN21 exhibit changes consistent with anti-GR antagonist activity. Conclusion: CP472555 causes a degree of GR blockade sufficient to permit further pharmacological investigation of the role of endogenous GC-GR signalling at the end of alveolarization.

The mechanisms underlying the generation of rapid eye movement (REM) sleep are poorly understood. Despite a lack of direct support, neurons maximally active during REM sleep (REM sleep-active) located in the pedunculopontine tegmental nucleus (PPTn) are hypothesized to generate this state and its component phenomenology. This hypothesis has never been directly tested, since the results of selectively inhibiting this cell-group have never been determined. Using microdialysis, electrophysiology, histochemical and pharmacological methods in freely-behaving rats (n=22) instrumented for sleep-wake state and respiratory muscle recordings, I selectively inhibited REM sleep-active PPTn neurons. Contrary to the prevailing hypothesis, I showed that REM sleep-active PPTn neurons suppress REM sleep by limiting the frequency of its onset. These neurons also shape the impact of REM sleep on breathing. REM sleep-active PPTn neurons restrain behavioural activation of upper-airway musculature during REM sleep, while depressing breathing rate and respiratory activation of the upper-airway musculature across sleep-wake-states.

Increased intracellular calcium (Ca2+) is required for vascular smooth muscle cell (VSMC) proliferation through mechanisms that are not well-known. Preventing calmodulin (CaM)-cyclin E interaction with a synthetic peptide inhibits VSMC proliferation in a cyclin E-dependent manner, without increasing de-differentiation or cell death, or affecting re-endothelialization or collagen deposition. Moreover, in situ Ca2+-sensitive phosphorylation and degradation of the cell cycle inhibitor p27Kip1 (p27) in VSMC is specific to G1 and dependent on camodulin kinase-II (CaMK-II) and the proteasome, but not MEK. Lastly, IQGAP1 binding to CaM increases during G1 with no change in total IQGAP1 expression across the cell cycle. Therefore, we determined the clinical potential of an established mechanism (CaM/cyclin E), the existence of a putative mechanism (CaMK-II/p27), and a target novel mechanism (CaM-IQGAP1). Characterization of calcium-sensitive mechanisms of VSMC cycle control could form the basis for new drug-eluting stent agents that have increased selectivity for rapidly dividing VSMC.

The specialized myocytes of the ventricular conduction system (VCS) coordinate ventricular contraction and are critical for efficient pumping by the heart. Impaired VCS conduction is characteristic of inherited forms of cardiac conduction disorders. Here we show that the Iroquois homeobox 3 (Irx3) transcription factor is preferentially expressed in the developing and mature VCS. Loss of Irx3 in mice results in slowed VCS conduction and prolonged QRS duration with right bundle branch block, caused by reduction (42%) in VCS-specific connexin 40 (Cx40) expression and VCS fiber hypoplasia, absent in littermate controls. Therefore, we show that the role of Irx3 in the heart is two-fold, whereby Irx3 (1) indirectly regulates Cx40 gene expression, by repressing a repressor of Cx40 transcript, and (2) controls VCS maturation, possibly in an Nkx2-5-dependent manner. To our knowledge, this is the first report of a role for Irx3 in regulating the development and function of the VCS.