Biomedical subjects

S Gorbey

Publications and source records attributed to S Gorbey.

3 recordsLinked to original sources

PubMed2005

Circadian periodicity of cerebral blood flow revealed by laser-Doppler flowmetry in awake rats: relation to blood pressure and activity.

Cardiovascular parameters such as arterial blood pressure (ABP) and heart rate display pronounced circadian variation. The present study was performed to detect whether there is a circadian periodicity in the regulation of cerebral perfusion. Normotensive Sprague-Dawley rats (SDR, approximately 15 wk old) and hypertensive (mREN2)27 transgenic rats (TGR, approximately 12 wk old) were instrumented in the abdominal aorta with a blood pressure sensor coupled to a telemetry system for continuous recording of ABP, heart rate, and locomotor activity. After 5-12 days, a laser-Doppler flow (LDF) probe was attached to the skull by means of a guiding device to measure changes in brain cortical blood flow (CBF). After the animals recovered from anesthesia, measurements were taken for 3-4 days. The time series were analyzed with respect to the midline estimating statistic of rhythm (i.e., mean value of a periodic event after fit to a cosine function), amplitude, and acrophase (i.e., phase angle that corresponds to the peak of a given period) of the 24-h period. The LDF signal displayed a significant circadian rhythm, with the peak occurring at around midnight in SDR and TGR, despite inverse periodicity of ABP in TGR. This finding suggests independence of LDF periodicity from ABP regulation. Furthermore, the acrophase of the LDF was consistently found before the acrophase of the activity. From the present data, it is concluded that there is a circadian periodicity in the regulation of cerebral perfusion that is independent of circadian changes in ABP and probably is also independent of locomotor activity. The presence of a circadian periodicity in CBF may have implications for the occurrence of diurnal alterations in cerebrovascular events in humans.

Animals↗

PubMed2005

Inverse blood pressure rhythm of transgenic hypertensive TGR(mREN2)27 rats: role of norepinephrine and expression of tyrosine-hydroxylase and reuptake1-transporter.

Transgenic hypertensive TGR(mREN2)27 rats (TGR) exhibit an inverse circadian blood pressure profile from the age of 8 to 9 wk. To investigate the role of the sympathetic nervous system in this pathological blood pressure rhythm, we examined postnatal changes in catecholamine concentration, expression of tyrosine-hydroxylase (TH), and norepinephrine (NE) reuptake(1)-transporter (NET) in the heart, adrenal glands, and hypothalamus of non-hypertensive TGR at an age of 4 wk and of hypertensive TGR at an age of 10 wk and compared these to normotensive, age-matched Sprague-Dawley rats. Rats were kept under synchronized light:dark (LD) conditions of 12:12 h. Blood pressure and heart rate were monitored by radiotelemetry, catecholamines by high performance liquid chromatography, expression of TH and NET (mRNA) by RT-PCR, and TH protein by Western blots. In normotensive 4 wk-old Sprague-Dawley rats, cardiac NE concentrations were circadian phase-dependent with lower values at ZT12.5, with no differences observed, in 10-wk-old animals. At both ages however, sympathetic tone was higher during the dark phase, as shown by a higher turnover of NE. This observation confirms earlier data, which indicate that the endogenous amine concentration may not mirror its turnover rate. TGR at either age had lower cardiac NE as well as lower TH expression and did not display a circadian phase-dependency. The increased cardiac NE turnover rate in the dark phase in non-hypertensive TGR was lost in hypertensive rats. Both cardiac NE concentrations and TH expression decreased with age in both strains. In adrenal glands, NE and epinephrine (E) were not circadian phase-dependent in both strains but increased with age. NE concentrations in the hypothalamus were neither circadian phase-dependent nor different in both strains and at both ages. However, sympathetic tone of NE in the hypothalamus, as indicated by the turnover rate, was greater during the dark phase in both strains at an age of 10 wk. Expression of TH and NET were greatly reduced in adrenal glands when compared to Sprague-Dawley rats; whereas, expression of TH in the hypothalamus was significantly increased in hypertensive TGR. These data indicate that the transgene in TGR leads to an increased central stimulation of the sympathetic nervous system and to a consecutive down-regulation in the peripheral organs. It is of interest that rhythmicity in the studied parameters was lost in hypertensive TGR, except in the turnover of NE in the hypothalamus. We concluded that the data on key mechanisms of regulation of the sympathetic system in TGR cannot explain the inverse blood pressure rhythm observed in this transgenic rat strain.

Animals↗

PubMed1999

Population forecasting with endogenous migration: an application to trans-Tasman migration.

"This article focuses on forecasting migration between Australia and New Zealand (trans-Tasman migration), which is largely visa-free and therefore resembles internal migration. Net trans-Tasman migration is a major component of New Zealand population change and is embedded in this article in a Bayesian or unrestricted vector autoregression (VAR) model, which includes foreign and domestic economic variables. When time series of net migration are available, this approach provides a useful input into forecasting population growth in the short run in the absence of major policy changes. This conclusion applies equally to interregional migration and to unrestricted international migration between economically integrated nations."

Australia↗