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Biomedical subjects

T Segura

Publications and source records attributed to T Segura.

28 records · Page 2Linked to original sources
PubMed1991

Cardiovascular responses to bicuculline in the paraventricular nucleus of the rat.

The present study was undertaken to determine whether gamma-aminobutyric acid in the paraventricular nucleus contributes to the regulation of cardiovascular function. Blood pressure and heart rate were recorded and plasma catecholamines were measured in conscious rats receiving microinfusions of either artificial cerebrospinal fluid or a gamma-aminobutyric acid antagonist, bicuculline methiodide, bilaterally into the paraventricular nucleus. Artificial cerebrospinal fluid had no effect on any of the recorded variables. In contrast, infusion of bicuculline into the region of the paraventricular nucleus produced increases in blood pressure (20 +/- 2 mm Hg), heart rate (110 +/- 11 beats/min), and plasma concentrations of norepinephrine (640 +/- 107 pg/ml) and epinephrine (1,266 +/- 267 pg/ml). Pretreatment with a ganglionic blocking agent abolished both the blood pressure (-1 +/- 2 mm Hg) and heart rate (5 +/- 18 beats/min) effects. Bilateral adrenal medullectomy reduced the changes in plasma norepinephrine concentrations (81 +/- 14 pg/ml) significantly and abolished the changes in plasma epinephrine concentrations (5 +/- 4 pg/ml). Conversely, adrenal medullectomy reduced the pressor effects (18 +/- 2 mm Hg) only slightly while the heart rate responses were attenuated (42 +/- 9 beats/min) by approximately 50%. These results suggest that an endogenous gamma-aminobutyric acid system exerts a tonic inhibitory effect on the sympathetic nervous system at the level of the paraventricular nucleus of the hypothalamus.

Adrenal Medulla↗
PubMed1989

Evidence of an endogenous forebrain GABAergic system capable of inhibiting baroreceptor-mediated vasopressin release.

In conscious rats, intracerebroventricular (i.c.v.) injections of gamma-aminobutyric acid (GABA), a GABA-uptake inhibitor (nipecotic acid), and artificial CSF (aCSF) were restricted to forebrain regions and their effect on baroreceptor-mediated arginine-vasopressin (AVP) release was studied. AVP release was stimulated by the hypotension resulting from combined treatment with a converting enzyme inhibitor (CEI) and chlorisondamine (CHLOR), a ganglionic blocking agent. CEI + CHLOR reduced mean arterial pressure (MAP) from 118 +/- 2 to 63 +/- 2 mm Hg, but pressure then rose to a compensated level of 78 +/- 1 mm Hg. The compensation in MAP was shown to be AVP-dependent at the end of the experiment since the vascular AVP antagonist, d(CH2)5Tyr(Me)AVP, reduced MAP from 78 +/- 1 to 63 +/- 1 mm Hg. While AVP was contributing to MAP maintenance, GABA (15, 50 and 150 micrograms) caused dose-related reductions in MAP (5 +/- 1.7 +/- 1 and 11 +/- 2 mm Hg, respectively). Nipecotic acid (3-350 micrograms) also caused dose-related reductions in MAP (from 3 +/- 1 to 15 +/- 2 mm Hg), while aCSF had no effect on MAP. Pretreatment with d(CH2)5Tyr(Me)AVP, antagonized completely the depressor effects of GABA and nipecotic acid. In other rats, blood samples were taken to measure the changes in plasma AVP concentrations (pAVP) induced by CEI + CHLOR and subsequent treatment with aCSF or nipecotic acid (175 micrograms). Hypotension induced by CEI + CHLOR caused a significant increase in pAVP. Forebrain-restricted nipecotic acid significantly suppressed pAVP (61 +/- 8% reduction; P less than 0.05 vs aCSF). These data provide evidence of an endogenous forebrain GABAergic system which, when activated, can inhibit baroreceptor-mediated AVP release.

Animals↗
PubMedDate not supplied

Microembolic signal monitoring in hemispheric acute ischaemic stroke: a prospective study.

BACKGROUND AND PURPOSE: There are few data on the occurrence of microembolic signals (MES) in the acute phase of ischaemic stroke. The objective of our work was to systematically study the frequency of MES in non-selected patients with a first-ever hemispheric transient ischemic attack (TIA) or acute cerebral infarction, and to evaluate the clinical usefulness of MES detection. METHODS: 182 consecutive patients with hemispheric TIA or acute cerebral infarction, and 54-age-matched healthy controls were studied. Bilateral transcranial Doppler ultrasound (TCD) monitoring was performed for at least 30 min with a mean time from stroke onset to TCD of 69 h. Stroke severity on admission, early recurrent stroke and dependency on discharge were investigated. RESULTS: MES were detected in 20.5% of patients with arterial sources of embolism, 17. 1% of patients with potential sources of cardioembolism and 5% of patients with cryptogenic stroke. They were not registered, however, in lacunar infarctions (p < 0.001). Stroke severity on admission of patients with MES was greater than that of patients without MES (47. 1 vs. 19.4% with the Canadian Stroke Scale < or =6.5; p = 0.009). Early recurrent stroke was more frequent in patients with MES (11.8%) than in those without MES (4.2%) although the difference was not statistically significant. Multiple logistic regression analysis showed that MES increased the risk of dependency on discharge (odds ratio, 4.2; 95% CI, 1.2-14.9; p = 0.01) independently of age, stroke severity on admission and presence of an arterial or cardiac embolic source. CONCLUSIONS: There is a strong association of MES in the acute phase of stroke with known potential arterial and cardiac embolic sources. MES have an independent predictive value of poor outcome.

Acute Disease↗
PubMedDate not supplied

[Unusual bulbar infarct and occlusion of the vertebral artery].

INTRODUCTION: Isolated bulbar infarcts are infrequent. Because of the vascular anatomy the lateral region is the most commonly affected, and in this clinical disorder the various signs and symptoms are grouped together as the so-called Wallenberg's syndrome. Since the introduction of magnetic resonance (MR) it has been possible to correlate the extent and site of the laterobulbar area involved with the most probable vascular topography and etiopathogenesis. CLINICAL CASE: We describe the case of a 69 year old female patient with all the symptoms of Wallenberg's syndrome and two potential causes of stroke (emboliogenic cardiopathy and atherothrombotic vascular occlusion), in whom MR showed the presence of an isolated bulbar lesion of unusual morphology which had previously been described as being of thrombotic origin. CONCLUSIONS: In spite of the small area of the brain involved, in laterobulbar infarcts MR permits definition of different topographic patterns of ischemic lesions. Some of these patterns have been correlated with the specific aetiology of an infarct. Therefore there is twice the importance of cerebral MR in cases of suspicion of lateral bulbar ischaemia, since it not only assists in diagnosis and its clinicopathological correlations, but also, as in our case, helps to have a clinical suspicion of the most likely etiopathogenesis of the stroke.

Aged↗
PubMedDate not supplied

[Pharmacological targets in neurodegenerative diseases].

The frequency, morbidity and complexity of neurodegenerative diseases (NDD) make them the greatest therapeutic challenge to Medicine today. These diseases are characterized by a decreased number of cells in certain neuronal populations, which is clinically reflected in the appearance of specific symptoms. In this study, we will centre our attention on the two fundamental lines of action that, from a pharmacological point of view, are available for the treatment of NDD. The first is aetiopathogenic, and is aimed at stopping cell death and promoting the recovery of cell populations. The second line is physiopathological and seeks to prevent, delay or palliate the appearance of the symptoms indicating an alteration in the levels of neurotransmitters, and its chief objective is to maintain them. Pharmacology has already provided neurologists with a wide range of tried and tested drugs, yet the results obtained in research laboratories in the last few years seem to indicate that the number of therapeutic possibilities are very likely to rise sharply in the future. Progress made in genomics and the better understanding of cellular biochemical cycles allow us to expect that this century will finally be that of the Neurosciences, and that Neurology, without losing its cognitive essence, will start to be considered to be a speciality that is as therapeutic as it is diagnostic.

Adjuvants, Immunologic↗
PubMedDate not supplied

[Normal values of cerebral vasomotor reactivity using the Breath-Holding Test].

INTRODUCTION: Cerebral circulation has its own mechanism for regulating blood flow so that a constant supply can be maintained despite the variations that take place in systemic variables. This mechanism is called cerebral vasomotor reactivity (CVR) and it can be measured using a number of different tests. Transcranial Doppler ultrasonography (TDU) is one of them. To measure cerebral vasomotor reactivity by means of TDU, intravenous infusion of acetazolamide, inhalation of CO2 or voluntary breath-holding can be employed to stimulate vasodilatation. This last method is called the Breath-Holding Test and can be offered as a percentage increase in flow velocity (PIV) weighted by the time the breath is held -what is then known as the Breath-Holding Index (BHI). Given the growing interest in CVR in vascular pathology of the brain, we have calculated the normal values for the breath-holding test in our area. PATIENTS AND METHODS: The sample used in the study was made up of subjects of both sexes over the age of 18. Patients with a history of strokes, chest diseases, cervical or intracranial vascular stenoses, haematological disorders and clinical pictures suggesting sleep apnea were excluded. CVR was measured using TDU and the breath-holding test in the middle cerebral artery and the basilar artery, by means of the percentage increase of flow velocity, which was weighted by breath-holding time. RESULTS: The mean BHI value was 1.45 +/- 0.50 in the middle cerebral artery, and 1.52 +/- 0.60 in the basilar artery, the respective PIV values being 31.6 +/- 12.3% in the middle cerebral artery and 32.8 +/- 15.1% in the basilar artery. The CVR determined by this test was similar in the two arteries. Significant differences were found among age groups but not between sexes. CONCLUSIONS: The Breath-Holding Test is a simple method for measuring CVR. In this article we report the normal values for our area. Although differences were obtained according to age groups, none were found according to sex or between the middle cerebral and the basilar arteries. These findings can be used as a reference in ultrasonography laboratories in our country.

Adult↗