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Biomedical subjects

M Velasco

Publications and source records attributed to M Velasco.

At least 181 records · Page 10Linked to original sources
PubMed1986

Subcortical correlates of the P300 potential complex in man to auditory stimuli.

Bipolar and referential responses correlated to the surface P300 auditory potential complex (components N2, P3 and N4) were studied in different subcortical structures of parkinsonian and epileptic patients with implanted electrodes used as an electrophysiological procedure for surgical treatment. Bipolar and referential subcortical responses were recorded from a wide subcortical region which included subthalamo-thalamic (Sth-Th), dorsothalamic (DTh), orbitofronto-hippocampal (OFH) and striatal (STR) structures. They were formed by 3 consecutive components C, D and E correlated to components N2, P3 and N4 of the surface responses. Component D correlated to surface P3 was either absent or very small in all subcortical bipolar responses and in referential responses recorded from OFH structures. Polarity of bipolar component C was inverted between DTh and OFH while that of bipolar component E was inverted between Sth-Th and DTh, between OFH and STR and between Sth-Th and STR. Polarity of the referential component C was inverted between STh-Th and DTh and between OFH and STR while that of referential components D and E remained unchanged along all subcortical structures. Referential components C-E and D attained maximal amplitudes and minimal latencies at the subthalamic and at the medial geniculate thalamic nucleus regions respectively. From here, their amplitudes decreased and latencies increased with distance in other structures rostrally and caudally located, with the exception of those at the orbitofrontal (components C-E) and dorsal thalamic and striatal regions (component D) where no amplitude-latency gradients were observed.

Electroencephalography↗
PubMed1986

Alumina cream-induced focal motor seizures in cats: bilateral lesions of the mesencephalic reticular formation.

The effect of bilateral lesions of the mesencephalic reticular formation on the EEG-EMG patterns of types B and C alumina cream-induced focal motor seizures was studied in cats with chronically implanted electrode and cannula lesion systems. EEG patterns included number, amplitude, and contralateral propagation of type B spikes and occurrence and duration of type C tonic-clonic discharges. EMG patterns included changes in muscular multiple-unit activity time locked to the onset of type B spikes and to the onset and end of type C tonic-clonic EEG paroxysmal discharges. The lesions persistently blocked the orienting response to visual, auditory, and tactile stimuli to both sides in all cats and produced other neurologic symptoms partially or totally recovered in some cats. The lesions significantly increased the number, amplitude, and contralateral propagation of type B EEG spikes and the occurrence, but not the duration, of type C EEG tonic-clonic discharges. Ipsi- and contralateral adversion of the tonic phase were completely blocked and the muscular contractions of the clonic phase were reduced and delayed. These facts suggest that in intact epileptic cats, the mesencephalic reticular formation has an ascending suppressive influence on the mechanism related to EEG spike generation and precipitation of seizures but also a descending facilitatory control on the corticospinal epileptic impulses mediated through pyramidal and extrapyramidal pathways.

Aluminum Oxide↗
PubMed1986

Neglect induced by thalamotomy in humans: a quantitative appraisal of the sensory and motor deficits.

Stereotactic lesions for the treatment of tremor and rigidity in patients with Parkinson's disease are occasionally followed by neglect of the use of contralateral extremities for spontaneous movement when there are no specific sensory or motor deficits. A group of patients with neglected extremities was compared with a group of patients in which thalamotomy did not produce neglect. Neglect was shown by changes in motor performance, somatosensory evoked potentials (SEP) and electroencephalographic frequency induced by the lesion, as well as radiological evidence of brain atrophy and place and extension of lesions. Reaction time to both auditory and somatosensory stimuli was significantly increased only in the extremities contralateral to the lesion of patients with neglect; tremor decreased equally in both groups, and other motor abilities remained unchanged. P-200 component of SEP decreased in amplitude and increased in latency only in cases with neglect, particularly ipsilateral to the lesion; early components and mean electroencephalographic frequency remained unchanged. Brain atrophy was significant in patients with neglect, particularly for the posterior portion of the 3rd ventricle. No differences in size and location of the lesions were found between the groups. Results indicate that this type of neglect is not secondary to lesions in specific sensory of motor pathways, but to lesions of structures coupling sensorimotor functions and the process of attention and that midline thalamic nuclei atrophy precipitates the neglect, perhaps by critically decreasing the amount of reticulothalamocortical projections engaged in selective attention.

Adult↗
PubMed1985

Effects of prazosin and alphamethyldopa on blood lipids and lipoproteins in hypertensive patients.

The effects of prazosin and alphamethyldopa on blood lipids and lipoproteins were assessed in 20 patients with mild or moderate arterial hypertension. Parameters measured included serum cholesterol (CHO), triglycerides (TG), high density lipoprotein-cholesterol (HDL-CHO), insulin (I), glucose (G), and non-esterified fatty acids (NEFA). Prazosin -4 mg/day for 6 weeks in hydrochlorothiazide-treated patients lowered blood pressure by 18.6/17.2 (systolic/diastolic pressure) mmHg. There was a significant decrease in CHO (-5.8%), in I (-16.5%), and in NEFA (-3.0%), and a significant increase in HDL-CHO (+15.5%). Alphamethyldopa 250-750 mg/day for 6 weeks in hydrochlorothiazide-treated patients lowered blood pressure by 18.8/14.6 (systolic/diastolic pressure) mmHg, accompanied by a non-significant decrease in CHO and TG, and significant increases in HDL-CHO (+10.3%), G (+8.5%) and NEFA (+6.4%). Thus, prazosin appears to have a more beneficial effect on blood lipids and lipoproteins than alphamethyldopa.

Adult↗
PubMed1985

Haemodynamic effects of enalapril, a new converting enzyme inhibitor, in hypertensive patients.

The haemodynamic effects of enalapril (EN), a new, long-acting, nonsulphhydryl converting enzyme inhibitor, were evaluated by non-invasive methods in 10 adult patients with mild to moderate essential hypertension (EH). Patients were randomly assigned, double blind to 2 treatment groups (EN 20 mg o.d. or 10 mg b.d.) for 4 weeks, and were crossed over to the other dosage regimen after a 2-week washout period. Measurements included mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), limb blood flow (LBF), plasma aldosterone (ALD), plasma renin activity (PRA) and systolic time intervals (STI). Both regimens (b.d. and o.d.) significantly reduced MAP (15.3% and 16.3%, respectively), total peripheral resistance (20.3% and 21.8%, respectively), limb vascular resistance (24.1% and 24.9%) and ALD (33.5% and 36.9%) and increased CO (7.8% and 8.7%), LBF (10.9% and 11.6%) and PRA (10.4% and 9.5%). No significant change was observed in HR or STI. EN 20 mg o.d. or 10 mg b.d. reduced arterial pressure to a similar extent through a fall in total peripheral resistance. An increase in CO was also observed.

Adult↗
PubMed1985

Subcortical correlates of the somatic, auditory and visual vertex activities in man. I. Bipolar EEG responses and electrical stimulation.

Bipolar responses correlated to somatic, auditory and visual vertex activities were studied in different subcortical structures of patients with implanted electrodes used as an electrophysiological procedure for surgical treatment. In addition, we studied the subjective responses of patients to electrical stimulation of subcortical structures where vertex-like activities (VA) were recorded, in order to determine their possible role in somatic, auditory and visual sensations. Typical subcortical VA evoked by somatic, auditory and visual stimuli, were recorded together from a single structure of a non-specific system including: reticulo-, medial dorsal-thalamic, orbito-frontal, limbic and striatal structures. Typical subcortical VA were formed by 4 consecutive components: O, A, B and C correlated to P1, N1, P2 and N2 of the surface VA. Polarity of component A was inverted between reticulo- and medial-thalamic structures while that of component B was inverted between medial thalamic and dorsal thalamic and between fronto-limbic and striatal structures. Typical subcortical VA were absent within specific thalamic nuclei and pathways in presence or absence of short latency responses evoked by specific sensory stimuli. Atypical subcortical VA of 1, 2 and 3 sensory modalities with inconsistent amplitudes, latencies and polarities were recorded from an intermediate zone surrounding and between specific and non-specific structures. Electrical stimulation of the non-specific structures at the reticulo- and medial thalamic levels elicited sensation of falling down and increase tension and tremor of the contralateral hand while no subjective responses were elicited by the stimulation at the dorsal thalamic, fronto-limbic and striatal levels. Stimulation of the specific structures and the intermediate zone elicited somatic, auditory and visual sensations with and without and apparent topographical organization, respectively.

Cerebral Cortex↗
PubMed1985

Alumina cream induced focal motor epilepsy in cats. VI. Excision of the perilesional cortex.

The effect of surgical excision of dorsolateral, ventromedial and combined (dorsolateral-ventromedial) perilesional cortices on EMG-EEG patterns of alumina cream induced focal motor seizures was studied in cats with chronically implanted electrodes. EMG patterns included clinical convulsions and related EMG-multiple unit activity. EEG patterns included number, amplitude, polarity and contralateral propagation of type B isolated spikes and type C tonic-clonic paroxysmal discharges. (1) Dorsolateral decortications abolished isolated jerks and related EMG-multiple unit activity and blocked propagation with no effect on number, amplitude and polarity of EEG spikes of type B seizures (epilepsia partialis continua). Dorsolateral decortications reduced contraversion and repetitive jerks and related EMG-multiple unit activity with no changes in number, amplitude, polarity and propagation of EEG tonic-clonic paroxysmal discharges of type C seizures (adversive epilepsy). (2) Ventromedial decortications decreased the number but neither changed jerks and related EMG-multiple unit activity nor amplitude, polarity, propagation of EEG spikes of type B seizures. Ventromedial decortications abolished contraversion and jerks and related EMG-multiple unit activity and reduced number, amplitude and duration with no changes in polarity and propagation of EEG paroxysmal discharges of type C seizures. (3) Combined decortications abolished jerks, contraversion and related EMG-multiple unit activity with a variable effect on EEG patterns of type B and C seizures. In 4 cats, combined decortications abolished while in other 2 cats decreased the amplitude and reversed the polarity of type B spikes and reversed the polarity and blocked the propagation of type C paroxysmal discharges.

Aluminum Oxide↗
PubMed1985

Comparative effects of topical perfusions of pentylenetetrazol in the mesencephalon and cerebral cortex of cats.

Push-pull perfusions of pentylenetetrazol (PTZ) were carried out in the mesencephalon and cerebral cortex (orbitofrontal, motor, and suprasylvian) of "encéphale isolé" cats, while EEG recordings from motor cortices and EMG of facial muscles were obtained. There were significant differences between perfusions in the mesencephalic reticular formation (MRF) and in the cerebral cortex: (i) EEG spikes not accompanied by muscular contractions occurred during perfusion of cerebral cortex (motor cortex included), but never with perfusions in MRF. (ii) In some instances muscular tonic and clonic contractions occurred in the absence of EEG spikes when perfusing the mesencephalon, but never with cortical perfusions. (iii) Both MRF and cortical perfusions induced EEG spikes accompanied by myoclonic seizures; however, muscular seizures were practically of the same amplitude in both sides after perfusion of the MRF and were predominant in the contralateral side after cortical perfusions. In addition, significantly less perfusion time (total dose) of PTZ was needed to induce such events in the MRF than in the cerebral cortex. (iv) Generalized seizures induced by cortical perfusions showed a clear predominance of contractions in the muscles contralateral to the perfusion site, whereas perfusions in the MRF induced generalized seizures indistinguishable from those produced by i.v. administration of PTZ. Results suggest that PTZ generalized seizures, closely resembling the so called "primary generalized seizures," result from activation of the MRF, whereas PTZ acting in the cerebral cortex produces a model of focal convulsions that may become secondarily generalized.

Administration, Topical↗
PubMed1984

Phasic paradoxical sleep precipitates focal motor and limbic seizures.

The facilitatory or inhibitory effect of paradoxical sleep (PxS) was investigated in two models of focal epilepsy: focal motor seizures induced by alumina cream in the frontal cortex and limbic seizures produced by intra-amygdaloid kainic acid microinjections in cats. We found that phasic episodes of PxS could trigger both types of seizures. Interictal spikes were generally blocked during PxS. We conclude that PxS exerts facilitatory or inhibitory effects depending on the particular event under analysis and the degree of epileptogenicity. The capacity of phasic PxS to precipitate focal ictal discharges may depend on ponto-limbic excitatory influences.

Aluminum Hydroxide↗
PubMed1984

Systemic and cardiac haemodynamic interactions between guanfacine and hydrallazine in hypertensive patients.

The effect of guanfacine and hydrallazine on cardiovascular haemodynamics and on sympathetic nervous activity has been studied in 16 patients with essential hypertension. Two groups of patients were investigated: in Group A guanfacine brought the blood pressure back to normal (diastolic blood pressure less than or equal to 90 mmHg), and in Group B diastolic blood pressure was greater than 90 mmHg and required the addition of hydrallazine. Guanfacine significantly decreased heart rate, plasma renin activity and urinary excretion of noradrenaline, without altering cardiac contractility. In Group B, guanfacine 2 to 6 mg/day produced a significant decrease in blood pressure from 178.7/112.4 to 164.4/102.9 mmHg and in heart rate from 77.1 to 62.7 beats/min after 4 weeks of treatment. Guanfacine did not significantly alter preejection period, cardiac output or total peripheral resistance. Hydrallazine 50 to 300 mg/day caused a further reduction in blood pressure from 164.4/102.9 to 150.7/90.2 mmHg and an increase in heart rate from 62.7 to 72.1 beats/min. Limb blood flow was increased from 4.55 to 5.93 ml/100 g/min and limb vascular resistance was decreased from 39.55 to 23.6 mmHg 100 g X min/ml. Hydrallazine also caused a slight increase in plasma renin activity and urinary excretion of noradrenaline. It is concluded that guanfacine is a useful agent to block a hydrallazine-induced increase in sympathetic nervous activity.

Adult↗
PubMed1984

Fine-needle biopsy of the pancreas using real-time ultrasonography.

Percutaneous fine-needle biopsy of the pancreas by real-time ultrasonography was performed in 45 patients with suspected pancreatic carcinoma. True-positive diagnoses were obtained in 27 cases, 11 examinations yielded true-negative results, 3 results were false-negative, 2 were equivocal, and 2 samples were inadequate. The overall success rate was 84.4%. No false-positive cytologic diagnoses were made. Complications were not seen in any of the patients. The results confirm the effectiveness, safety, and relatively low cost of this procedure.

Adult↗
PubMed1984

Alumina cream-induced focal motor seizures in cats. V. Unilateral lesions of the brain-stem reticular formation.

The effect of unilateral mesencephalic (MRF) and pontine (PRF) lesions on EEG-EMG patterns of type B and C alumina cream induced focal motor seizures was studied on cats with chronically implanted electrode and cannula lesion systems. EEG patterns included number, amplitude and contralateral propagation of type B spikes and occurrence and duration of type C tonic-clonic discharges. EMG patterns included changes in muscular multiple unit activity (EMG-MUA) time locked to the onset of type B spikes and to the onset (tonic OTCD) and the end (clonic ETCD) of type C tonic-clonic EEG paroxysmal discharges. (1) MRF lesions ipsilateral to the cortical epileptogenic focus significantly increased number, amplitude and propagation of type B EEG spikes and the occurrence, but not the duration, of type C EEG tonic-clonic discharges. They also reduced amplitude of type B muscular jerks and blocked type C tonic contradversion with a significant decrease in EMG-MUA time locked to the onset of type B spikes and type C paroxysmal EEG discharges. (2) PRF lesions contralateral to the cortical epileptogenic focus produced an effect on muscular contractions of type B and C seizures similar to that produced by ipsilateral MRF lesions. PRF lesions, however, did not significantly change the EEG patterns of type B and C seizures. (3) Neither MRF lesions contralateral nor PRF lesions ipsilateral to the cortical epileptogenic focus produced significant changes on EEG and EMG patterns of types B and C epileptic seizures.

Aluminum Oxide↗