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SYMPATHECTOMY AND CARDIOVASCULAR SPECTRAL COMPONENTS IN CONSCIOUS NORMOTENSIVE RATS
No full textWe examined the extent to which sympathetic influences are reflected by spectral powers of blood pressure and pulse interval in specific frequency bands in spontaneously behaving Wistar-Kyoto rats subjected to continuous intraarterial blood pressure recording. The rats were pretreated with 6-hydroxydopamine (150 mg/kg twice in 1 week, n=19) to produce chemical sympathectomy or received vehicle (n=15). In the sympathectomized group, additional monitoring sessions were performed with rats under alpha-adrenergic receptor blockade with phenoxybenzamine (n=8), beta-receptor blockade with propranolol (n=7), or cholinergic receptor blockade with atropine (n=8). Blood pressure signals were analyzed by a computer to calculate spectral powers (fast Fourier transform) in the low-frequency (0.025 to 0.1 Hz), mid-frequency (0.1 to 0.6 Hz), and high-frequency (0.8 to 3.0 Hz) bands. In sympa thectomized rats, low-frequency power of blood pressure was 70% greater than in intact rats, whereas mid-frequency power was 60% smaller (P<.05 for both) and high-frequency power was unchanged. High-frequency power of pulse interval was also unchanged in sympathectomized rats, whereas low- and mid-frequency powers were reduced by approximately 50% (P<.05). No further alterations in spectral powers were observed by adding alpha- or beta-adrenergic blockade to sympathectomy, whereas adding cholinergic blockade caused a striking reduction in all pulse interval powers. Thus, mid-frequency blood pressure power depends on sympathetic but also to a substantial extent on nonsympathetic influence influences do not contribute to low-frequency blood pressure power, having instead a restraining effect. The low- and mid-frequency pulse interval powers depend on both sympathetic and vagal influences. Thus, no blood pressure or pulse interval power in the mid- and low-frequency ranges can be regarded as a specific marker of sympathetic activity
Sympathetic, parasympathetic and non-autonomic contributions to cardiovascular spectral powers in unanesthetized spontaneously hypertensive rats
No full textObjective: To determine whether spectral powers of blood pressure and pulse interval can specifically reflect sympathetic and parasympathetic effects in unanesthetized, free-moving spontaneously hypertensive rats (SHR). Design: Spectral powers were observed before and after various autonomic interventions in chronically instrumented rats. Materials and methods: Chemical sympathectomy was produced in 12-week-old SHR by repeated injections of 6-hydroxydopamine, while control rats were given vehicle alone. Chronic arterial and venous catheters were inserted in the femoral artery and vein. Blood pressure was recorded beat-to-beat for 90 min in free-moving rats; further recording sessions were obtained under additional alpha-receptor blockade with phenoxybenzamine at 1 mg/kg and/or additional cholinergic blockade with atropine at 0.8 mg/kg. Off-line computer analysis (fast Fourier transform) provided estimates of low- (0.025-0.1 Hz), mid- (0.1-0.6 Hz) and high-frequency (0.8-3.0 Hz) powers for blood pressure and pulse interval over consecutive periods of 100 s. Results: The most noticeable findings were that sympathectomy produced a striking increase in the low-frequency power of blood pressure and a tendency (borderline statistical significance) to reduce the mid-frequency power of blood pressure. Additional ct-receptor blockade had no effect on any spectral power whereas additional cholinergic blockade caused a further increase in the low-frequency blood pressure power and a drastic reduction in all pulse interval powers. Conclusions: In the unanesthetized SHR, sympathetic activity opposes low-frequency and marginally promotes mid-frequency blood pressure fluctuations; the pulse interval spectral expression of vagal effects is spread throughout the range of frequencies explored and is not confined to the high-frequency band. These data indicate that in SHR no spectral power can specifically reflect the effects of either autonomic limb
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
LIMITATIONS OF USING BLOOD-PRESSURE SPECTRAL PEAKS AS INDEXES OF SYMPATHETIC ACTIVITY IN SHR AND WKY RATS
No full textSympathovagal interplay in the control of overall blood pressure variability in unanesthetized rats.
No full textThe role of sympathetic and parasympathetic influences in the control of overall blood pressure variability was studied in chronically instrumented, freely behaving Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) subjected to sympathectomy by 6-hydroxydopamine (100 micrograms/kg ip) twice in 1 wk (effectiveness verified by abolition of pressor and tachycardic response to tyramine, 150 mg/kg i.v.) and/or to cholinergic blockade by atropine (0.7 mg/kg i.v.). Overall heart rate and blood pressure variabilities were measured as variation coefficients computed beat to beat on 90-min blood pressure recordings. As compared with the vehicle-treated controls, sympathectomized rats had much larger blood pressure variability (WKY, +61%, SHR, +86%, both P < 0.01). Cholinergic blockade superimposed to sympathectomy caused heart rate variability to markedly fall and the already augmented blood pressure variability to further rise 47% in WKY and 28% in SHR (both P < 0.01). Prolonged observation of the animals revealed the systematic occurrence of rapid blood pressure falls occurring at the onset of locomotor activity, accounting for a substantial fraction of the sympathectomy-related increase in blood pressure variability. It is concluded that 1) under undisturbed daily life conditions, sympathetic influences oppose blood pressure variations, presumably by adjusting their vasoconstrictor influences to compensate for the metabolic vasodilation occurring in functionally active tissues; 2) when sympathetic vascular control is lost, vagally mediated heart rate variations oppose the rise in blood pressure variability, possibly via rapid changes in cardiac output that partly offset the fluctuations in total peripheral resistance; and 3) chronic hypertension fails to alter these cardiovascular regulatory mechanisms
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Enhanced vascular reactivity in the sympathectomized rat: studies in vivo and in small isolated resistance arteries.
Full text linkOBJECTIVE: In the conscious rat, sympathectomy (6-hydroxydopamine pretreatment, 100 mg/kg intraperitoneally, twice in the previous 5-6 days) induces, among various homeostatic modifications, the frequent occurrence of sudden and wide oscillations of blood pressure. Since one of the mechanisms underlying this, as yet unexplained, phenomenon may be an enhanced vascular reactivity, we tested the hypothesis that sympathectomized rats exhibit such a hyper-reactivity. We examined the response to a variety of vasoactive agents both in vivo (chronically instrumented conscious animals) and in vitro (small isolated resistance arteries). DESIGN AND METHODS: Wistar-Kyoto sympathectomized rats (6-hydroxydopamine pretreatment, n = 19) and control rats (vehicle pretreatment, n = 23) were studied. In conscious animals, concentration-blood pressure response curves to intra-venous bolus injections of vasopressin, phenylephrine and angiotensin II were obtained. In isolated vessels, concentration-wall tension response curves were obtained for norepinephrine, phenylephrine, vasopressin, serotonin and potassium. Vasodilator responses to acetylcholine (with or without L-NAME), bradykinin and sodium nitroprusside were also evaluated after precontraction with norepinephrine (mesenteric arteries) or vasopressin (cerebral arteries). RESULTS: In sympathectomized rats in vivo the pressor responses to vasopressin, phenylephrine and angiotensin II were significantly larger than in control rats, the difference amounting to 46.5, 40.2 and 57.1%, respectively (all P < 0.05). In vitro, the vascular reactivity of isolated cerebral arteries was similar in sympathectomized and control rats. In contrast, the mesenteric arteries showed significantly increased contractions in sympathectomized compared to control rats in response to norepinephrine, phenylephrine and vasopressin but not to serotonin and potassium, whereas the vasodilator responses to acetylcholine and sodium nitroprusside (but not to bradykinin and acetylcholine+L-NAME) were reduced. CONCLUSIONS: In conclusion, we showed that sympathectomy produces complex alterations of vascular reactivity both in vivo and in isolated vessels, which shift the balance of the sensitivity of the vessel between vasoconstrictor and vasodilating agents towards an increased constriction. These results are unlikely to simply reflect denervation supersensitivity; their underlying receptor, post-receptor and/or contractile mechanisms are yet to be identified
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