Biomedical subjects

Isabel Rocha

Publications and source records attributed to Isabel Rocha.

6 recordsLinked to original sources

PubMed2005

Evolutionary programming as a platform for in silico metabolic engineering.

BACKGROUND: Through genetic engineering it is possible to introduce targeted genetic changes and hereby engineer the metabolism of microbial cells with the objective to obtain desirable phenotypes. However, owing to the complexity of metabolic networks, both in terms of structure and regulation, it is often difficult to predict the effects of genetic modifications on the resulting phenotype. Recently genome-scale metabolic models have been compiled for several different microorganisms where structural and stoichiometric complexity is inherently accounted for. New algorithms are being developed by using genome-scale metabolic models that enable identification of gene knockout strategies for obtaining improved phenotypes. However, the problem of finding optimal gene deletion strategy is combinatorial and consequently the computational time increases exponentially with the size of the problem, and it is therefore interesting to develop new faster algorithms. RESULTS: In this study we report an evolutionary programming based method to rapidly identify gene deletion strategies for optimization of a desired phenotypic objective function. We illustrate the proposed method for two important design parameters in industrial fermentations, one linear and other non-linear, by using a genome-scale model of the yeast Saccharomyces cerevisiae. Potential metabolic engineering targets for improved production of succinic acid, glycerol and vanillin are identified and underlying flux changes for the predicted mutants are discussed. CONCLUSION: We show that evolutionary programming enables solving large gene knockout problems in relatively short computational time. The proposed algorithm also allows the optimization of non-linear objective functions or incorporation of non-linear constraints and additionally provides a family of close to optimal solutions. The identified metabolic engineering strategies suggest that non-intuitive genetic modifications span several different pathways and may be necessary for solving challenging metabolic engineering problems.

Algorithms↗

PubMed2005

Cerebellar haemorrhage as a cause of neurogenic pulmonary edema - case report.

The neurogenic pulmonary edema is a rare clinical situation caused by an imbalance characterized by an excessive sympathetic outflow. It is observed mostly in young patients, is associated with brain or spinal cord haemorrhage, trauma, tumours or infections and is usually fatal. A case of neurogenic pulmonary edema in a 27-year-old woman is presented, caused by a cerebellar haemorrhage due to a vermian and paravermian arteriovenous malformation rupture. The vermian and hemispheric haemorrhage injuring the sub-lobule IX-b of the uvula induced a disruption of both carotid baroreceptor and chemoreceptor reflexes control mechanisms. Medical treatment with controlled ventilation, PEEP, diuretics and morphine reverted the pulmonary edema. After surgical treatment of the haemorrhage and cerebellar AVM the patient recovered to an almost normal social and professional life. The cerebellar lesion induced a temporary vermian sub lobule IX-b dysfunction that was responsible for the sympathetic storm that evoked the neurogenic pulmonary edema.

Adult↗

PubMed2004

Effect of stimulation of anterior hypothalamic area on urinary bladder function of the anesthetized rat.

The hypothalamus is a key area for the integration of the autonomic features of affective behavior. Hypothalamic defence area (HDA) stimulation evokes major cardiorespiratory changes as well as modifications of general autonomic activity both in the anesthetized and conscious animal. Micturition is due to an increase in pelvic parasympathetic activity and, in the cat, the anterior hypothalamus has been implicated in urinary bladder control with the demonstration of a dorsolateral vesicoconstrictor pathway and a ventromedial inhibitory pathway. In this study we have investigated the effect of electrical and chemical stimulation of the HDA on bladder pressure and contractions in rat. Female rats (n = 15) were anesthetized, paralyzed and ventilated artificially. Arterial blood pressure, heart rate, urinary bladder pressure and pelvic nerve activity were recorded. HDA was electrically (1 ms, 100 Hz, 5-10 s train at intensities up to 150 micro A) and chemically (sodium glutamate, 50 nl, 2mM) stimulated. For statistical analysis the t-test was used, data were expressed as mean +/- SEM. Values of t were taken as significant when p < 0.05.HDA stimulation at 100-150 micro A evoked changes of both mean blood pressure (mBP) and bladder pressure (BlP). However, stimulation at < 30 micro A allowed a distinction within HDA of two different regions, at the same antero-posterior and lateral level, but separated 100-150 micro m in depth, which evoked differential effects on blood pressure and urinary bladder pressure. Results show that low intensity stimulation at ventral sites evoked a significant increase of mBP (from 102 +/- 5.9 to 127 +/- 8.6 mmHg, n = 10, p < 0.0001) with little changes of BlP (from 12 +/- 2.2 to 16 +/- 2.9 cmH(2)O, n = 10, p < 0.0005), whilst at more dorsal sites significant increases of BlP were elicited (from 12 +/- 8.3 to 38 +/- 4.6 cmH(2)O,n = 10, p < 0.0001) with only a small rise of mBP (from 102 +/- 6.2 to 111 +/- 9.8 mmHg, n = 10, p < 0.005). Glutamate injections at dorsal sites evoked a rise of BlP (from 11 +/- 2.2 to 30 +/- 3.0 cmH(2)O (n = 5; p < 0.0001) with small changes in BP, whilst at ventral sites (n = 4) glutamate microinjections evoked changes in BP but not of BlP. In conclusion stimulation at different sites within HDA can elicit separate changes in BP and BlP.

Anesthesia↗

PubMed2003

Effect of losartan microinjections into the NTS on the cardiovascular components of chemically evoked reflexes in a rabbit model of acute heart ischemia.

In the acute phase of myocardial infarction (MI) there are modifications of the autonomic outflow with an increase in the sympathetic tone and changes in cardiovascular reflexes. Activation of angiotensin AT1 receptors in the nucleus tractus solitarii (NTS) inhibits the baroreceptor and enhances the carotid chemoreflex. In this study, we investigated the role of NTS-AT1 receptors on the cardiovascular reflex responses evoked on stimulation of carotid chemoreflex and cardiac chemosensitive fibres in the acute phase of MI. We also test the hypothesis that changes in cardiovascular responses to activation of carotid chemo and cardiac chemosensitive reflexes are secondary to changes in haemodynamic conditions due to infarction or to the activation of nociceptors of the heart. Rabbits were anaesthetised, paralysed and artificially ventilated. Carotid chemoreceptors and cardiac chemosensitive fibres were stimulated with lobeline and ATP, respectively. Arterial blood pressure, electrocardiogram and heart rate were monitored. A craniotomy was made to expose the caudal portions of the medulla and a multibarreled glass microelectrode was inserted in order to allow the identification of NTS and the microinjection of losartan (an angiotensin AT1 receptor antagonist). The heart was exposed by a midline thoracotomy and cardiac ischemia was produced by ligating the left descending coronary artery. The carotid chemoreflex and cardiac chemosensitive reflexes were evoked before and following the coronary ligation. The effect of losartan injection into the NTS on these reflexes was also assessed. In control experiments reflexes were assessed before and after the administration of capsaicin and procainamide. Results show that the activation of carotid chemoreflex elicited a greater increase of blood pressure and bradycardia after MI and that this was partially reversed by losartan microinjection after MI. Also the stimulation of cardiac chemosensitive fibres evoked a larger decrease on blood pressure and heart rate after MI and these were also partially reversed by losartan. The same enhancement of cardiovascular carotid chemo and cardiac chemosensitive receptors was observed after administration of capsaicin on the ventricular surface but not after procainamide. In conclusion, this study strongly suggests that, at NTS level, angiotensin AT1 receptors are involved in the modifications of autonomic outflow observed in the acute phase of MI.

Acute Disease↗

PubMed2003

Angiotensin AT1 receptor antagonist losartan and the defence reaction in the anaesthetised rat. Effect on the carotid chemoreflex.

Modulation at the level of the nucleus tractus solitarii (NTS) appears to be an effective way of controlling cardiovascular reflexes. Angiotensin II acting on angiotensin AT1 receptors at the central nervous system appears to have an important role in these modulatory processes. The hypothalamic defence area (HDA) is a potential source of descending fibres containing angiotensin II that innervate the NTS. We investigated the effect of AT1 receptor blockade in the NTS on the response to stimulation of HDA in anaesthetised rats treated with the neuromuscular blocking agent pancuronium bromide. The characteristic increase in heart rate, blood pressure and phrenic nerve activity evoked by electrical stimulation of HDA is decreased by the microinjection of the AT1 receptor antagonist losartan into the NTS and the cardiovascular response to carotid body chemical stimulation is also reduced. These results support the hypothesis that AT1 receptors in the NTS play a role in the modulation of cardiovascular reflexes, and modify the influence exerted on the processing of these reflexes by other areas of the central nervous system.

Anesthesia↗

PubMed2002

Attenuation of the carotid body chemoreflex during the stimulation of the posterior vermis in the anaesthetised rabbit.

The purpose of this study was to investigate the effects of electrical and chemical stimulation of the sub-lobule IX-b of the cerebellar uvula on the cardiorespiratory responses evoked on stimulation of the carotid chemoreceptors in the anaesthetised and paralysed rabbit. Recordings of arterial blood pressure, ECG, heart rate and phrenic nerve activity were evaluated. Sub-lobule IX-b was activated electrically (1 ms, 20 microA, 100 Hz, 4-s train) and stimulated chemically with sodium glutamate microinjections (2 mM, pH=7.4 +/- 0.1) using bipolar concentric or multibarrelled microelectrodes. Carotid body chemoreflexes were evoked by the retrograde injection of sodium cyanide (0.1%, 0.1 ml) into the blood supply of the carotid body through a cannula inserted in the external carotid artery. The interaction of uvula stimulation and the carotid chemoreceptor reflex was studied by following the chemoreceptor stimulus with a stimulus to the uvula. Electrical and chemical stimulation of the uvula evoked a characteristic bradycardia and a depressor response together with a decrease in phrenic nerve activity. Carotid body stimulation evoked a decrease in heart rate accompanied by an increase of both arterial blood pressure and phrenic nerve activity. However, simultaneous delivery of the two stimuli resulted in a depressor response together with a decrease of phrenic nerve activity and an increased bradycardia. These data suggest that stimulation of the cerebellar uvula exerts an inhibitory control of the chemoreflex efficacy as far as respiratory activity and blood pressure is concerned.

Anesthesia↗