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Biomedical subjects

H Maldonado

Publications and source records attributed to H Maldonado.

71 records · Page 4Linked to original sources
PubMed1976

Specific and nonspecific multiple unit activities during the onset of pentylenetetrazol seizures. II. Acute lesions interrupting nonspecific system connections.

Nonspecific cortical, thalamic, mesencephalic, and pontine multiple unit activities (MUA) and changes in EEG and MUS of the sciatic nerve after threshold pentylenetetrazol activation were studied in three groups of animals in which neuronal connections were interrupted at three different levels of the central nervous system: spinal, mesencephalic, and prethalamic. Maximal increments of nonspecific MUA and maximal increments and maximal decrements of sciatic MUA after pentylenetetrazol from each group of lesioned animals were statistically compared with tose observed in intact animals. 1. Pentylenetetrazol threshold for producing cortical tonic-clonic EEG discharges was increased in animals with nesencephaic and prethalamic lesions but was not modified in animals with spinal transection. 2. Cortical MUA maximal increment was significantly decreased in mesencephalic and prethalamic lesioned animals, whereas thalamic MUA maximal increment was significantly decreased in mesencephalic and significantly increased in prethalamic lesioned animals. Pontine MUA maximal increment was significantly increased in spinal, mesencephalic, and prethalamic lesioned animals, and mesencephalic M-A maximal increment was not significantly modified in either prethalamic lesioned or in spinal transected animals. 3. Sciatic MUA maximal increment and maximal decrement were significatly decreased in spinal transected animals, whereas only maximal increment was significantly decreased in mesencephalic and only maximal decrement was significantly decreased in prethalamic lesioned animals. These results based on lesion experiments permit us to infer than under normal cinditions the development of generalized seizures induced by threshold pentylenetetrazol injection is highly dependent upon the neuronal interactions between nonspecific structures at different levels of the central nervous system. The possible nature of these neuronal interactions in the intact animals is discussed.

Animals↗
PubMed1976

[Identification and lesion of prelemniscal radiation in the surgical treatment of tremor].

In a group of 40 patients operated on for the relief of tremor using stereotaxic techniques, the radiological location and electrophysiological characteristics of the optimum target were studied. The optimum target was defined as the place where the minimal lesion produced by the insertion of a 1.5 mm diameter electrode produced immediate cessation of tremor in the contralateral extremities. It was found that the optimum target is located in the subthalamus. Within this area electrical stimulation did not elicit sensory of pyramidal responses, but increased the amplitude of tremor. The study of somatic evoked potentials produced by stimulation of contralateral median nerve confirmed that the area does not correspond to a specific sensory system (medial lemniscus). By recording multiple unit activity a spontaneous 5 cycle per second rhythmic pattern, similar to that described for the VL thalamic nucleus, was occasionally seen. Finally, through an IBM 1130 computer the radiological location of those electrodes in the target area was approximated to a line, representing a vector whose orientation in space could be compared with that of different anatomical structures, and corresponded to the prelemniscal radiation. We concluded that the target area herein described is part of a reticulothalamic system that conveys tremogrogenic impulses to the pyramidal system and from here to the periphery.

Computers↗
PubMed1975

Differential effect of thalamic and subthalamic lesions on early and late components of the somatic evoked potentials in man.

The effect of thalamic (Vo), subthalamic (Raprl) and combined (Vo-Raprl) unilateral lesions on early and late components of the somatic evoked potentials (SEPs) was investigated in a group of 16 cases operated on for the treatment of contralateral dyskinetic movements. In these cases, SEPs were independently produced by stimulation of the left and right median nerves and recorded at the corresponding somatosensory scalp regions. In addition, EEG frequencies and reaction time (RT) were independently and bilaterally determined. These tests were performed before and after operation and changes in SEP, EEG and RT were quantitatively evaluated in relation to both ipsilateral preoperative and contralateral postoperative controls. 1. All cases with either thalamic or combined lesions involving Vo nucleus showed an ipsilateral reduction in amplitude of late SEP components and EEG frequency and a contralateral increase RT. A peculiar form of "inattention" to the contralateral hand was also found. Quantitative evaluation of the total group showed significant amplitude reduction in late SEP components in relation to both ipsilateral preoperative and contralateral postoperative controls. Changes in EEG and RT were only significant in relation to their preoperative ipsilateral controls. 2. Two cases with subthalamic lesions and quick postoperative recovery showed no apparent change in SEP, EEG and RT. Three cases with similar lesions and slow postoperative recovery showed bilateral decrease in amplitude of late SEP components, EEG frequency and increase in RT. Clinical inattention to contralateral hand was also found in all these cases. Quantitative evaluation of the total group showed no significant changes in these parameters in relation to preoperative controls. 3. None of these lesions produced changes in early SEP components or somatosensory deficits at the contralateral hand.

Attention↗
PubMedDate not supplied

Ethanol affects context memory and long-term habituation in the crab Chasmagnathus.

A shadow moving overhead acts as a danger stimulus and elicits an escape response in the crab Chasmagnathus granulatus that habituates promptly and for a long period. The effect of acute ethanol treatment on this long-term memory was analyzed. A single injection of 0.01, 0.05, or 0.1 micrograms ethanol (ET)/g given 30 min before iterated presentation of a visual danger stimulus failed to affect short-term habituation. Posttraining ethanol (0.01 to 0.1 microgram/g) produces a dose-dependent impairment of long-term habituation, but pretraining ethanol had no amnestic effect. However, a retention deficit confined to context memory was disclosed with both pre- and posttraining ethanol. Results from experiments with double injection (posttraining and pretesting injections) account for the retention impairment in terms of true amnesia (failure to acquire memory) but not due to state-dependence or retrieval deficit. The nonamnestic effect of pretraining ethanol upon long-term habituation is explained by a nonespecific depressing effect caused by interaction between iterative presentation of the danger stimulus and drug-induced internal state during training.

Animals↗
PubMedDate not supplied

Multidisciplinary analysis of patients with extratemporal complex partial seizures. I. Intertest agreement.

In 15 patients we hypothesized the origin of epilepsies to be 'extratemporal' based on videotaped seizures and surface EEG. Neuropsychological tests and neuroimaging (CAT, MRI, and PET scans) were then compared to the hypothesized ictal sites. Neuropsychological tests were abnormal in 86.6% and FDG-PET scans were abnormal in 73%. The neuropsychological tests and PET localized or lateralized areas of dysfunction to the same sites as electroclinical characteristics did in 85% of patients (P less than 0.01, Fisher exact test). No statistically significant correlation between lesion sites on CT and MRI and the ictal origin was observed due to the high proportion of normal or non-specific scans. These observations should be verified in a larger series of extratemporal seizures.

Adolescent↗
PubMedDate not supplied

Melasma in men. A clinical and histologic study.

Melasma is characterized by a facial hypermelanosis of light to dark brown color, being more common in women of Hispanic origin. In this study, 27 men with melasma were evaluated clinically and histologically to compare their features with those of previous studies. Three patterns of localization were recognized, namely, centrofacial, malar, and mandibular. On the basis of Wood's light examination, an epidermal, a dermal, and a mixed type were identified. Epidermal hyperpigmentation only and epidermal and dermal hyperpigmentation were found in histologic analysis of the cases. Significant etiologic factors included exposure to sunlight in 66.6% as well as a familial predisposition in 70.4% of the cases. This study demonstrated that melasma in men shares the same clinicohistologic characteristics as in women, but hormonal factors do not seem to play major significant role.

Adult↗
PubMedDate not supplied

Vascular trauma: late sequelae and treatment.

58 patients presenting with late manifestations of vascular trauma underwent operative correction at an average of 37.2 months from the date of injury. False aneurysms alone were seen in 23 patients, arteriovenous fistulae in another 35, and both lesions concurrently in 6 patients. Excellent results were achieved in 54 patients, fair results in 4 patients, and only 3 patients required later reoperation despite the chronic nature of these lesions.

Adolescent↗
PubMedDate not supplied

Caveolae a new subcellular transport organelle.

Recent advances have allowed the identification and characterization of well defined vesicular subcellular organelles involved in multiple basic cellular physiological processes, with demonstrated clinical relevance. Among these, three particular subcellular organelles have received special attention based on their proven and postulated participation in the sorting and targeting of small-and large-molecular weight molecules during exocytosis and endocytosis, and in cell signaling and transduction events. These have characteristic proteinaceous coat structures that allows their classification accordingly, into what has been described as clathrin coated vesicles and COP-coated vesicles and caveolae. In this review article a brief description of clathrin-coated vesicles and COP-coated vesicles is presented. Caveolae (CAV), in turn, constitute a novel subcellular organelle that has received special attention based on its proven and postulated participation in transcytosis, potocytosis, and in cell signaling and transduction events. In this review of the literature a more extensive discussion is presented of CAV. In this context the article discusses the structural features of caveolae, its constituent protein caveolin(s), the functional aspects of this new organelle, and its postulated clinical relevance.

Caveolin 1↗