Biomedical subjects

E Salinas

Publications and source records attributed to E Salinas.

At least 55 records · Page 3Linked to original sources

PubMed1996

A model of multiplicative neural responses in parietal cortex.

Visual responses of neurons in parietal area 7a are modulated by a combined eye and head position signal in a multiplicative manner. Neurons with multiplicative responses can act as powerful computational elements in neural networks. In the case of parietal cortex, multiplicative gain modulation appears to play a crucial role in the transformation of object locations from retinal to body-centered coordinates. It has proven difficult to uncover single-neuron mechanisms that account for neuronal multiplication. Here we show that multiplicative responses can arise in a network model through population effects. Specifically, neurons in a recurrently connected network with excitatory connections between similarly tuned neurons and inhibitory connections between differently tuned neurons can perform a product operation on additive synaptic inputs. The results suggest that parietal responses may be based on this architecture.

Animals↗

PubMed1996

Acquired transmission-blocking immunity to Plasmodium vivax in a population of southern coastal Mexico.

Naturally acquired transmission-blocking immunity to Plasmodium vivax was studied in three groups of patients from the southern coast of Mexico: primary cases (Group A, 61% of the study population), secondary cases with the prior infection seven or more months earlier (Group B, 23%), and secondary cases with the previous malaria experience within six months of the present study (Group C, 16%). Anopheles albimanus mosquitoes were fed with patients' infected blood cells in the presence of autologous or control serum, with or without heat-inactivation. Patients from all three groups had transmission-blocking immunity, although the quality and quantity of this blocking activity was significantly higher in the two secondary patient groups (B and C). Only primary malaria cases produced transmission-enhancing activity (23% of the cases), which was dependent on heat-labile serum components. The levels of patient group transmission-blocking immunity and mosquito infectivity were used to calculate the probabilities of a mosquito becoming infective after taking a blood meal from a P. vivax-infected patient from any one of the three groups. This probability was 0.025, with Group A patients providing the major source of these infections (92% risk from Group A and 4% risk for Groups B and C).

Adolescent↗

PubMed1995

Anti-syntaxin antibodies inhibit calcium-dependent catecholamine secretion from permeabilized chromaffin cells.

Adrenomedullary chromaffin cells release catecholamines in response to the intracellular calcium rise upon stimulation by different secretagogues. The presence of syntaxin 1, a protein presumably involved in docking of synaptic vesicles to presynaptic membranes, has been investigated in chromaffin cells. The study using two different monoclonal antibodies shows that syntaxin 1 is present in the chromaffin cell membrane fraction. Functional experiments demonstrate that anti-syntaxin antibodies inhibit calcium-dependent secretion in permeabilized cells. These results suggest that syntaxin 1 is an important component of the secretory machinery in chromaffin cells.

Adrenal Medulla↗

PubMed1995

Evidence for an altered luteinizing hormone sensitivity to naloxone in pathological hyperprolactinaemia.

OBJECTIVE: The underlying mechanisms involved in the pathogenesis of amenorrhoea in hyperprolactinaemic states still remain unclear. Conflicting information exists on the role of endogenous opiates on gonadotrophin disturbances in this pathological condition. In this study we have undertaken a detailed investigation of LH and PRL secretion before and during administration of naloxone, an opioid receptor blocker, in hyperprolactinaemic women with or without ovarian function in order to assess the role of ovarian steroids upon naloxone induced LH and PRL release. DESIGN: Five anovulatory and six ovulatory subjects with hyperprolactinaemia were studied before and during naloxone infusion. Five normo-prolactinaemic ovulatory subjects were included as controls. All ovulatory subjects were studied during the luteal phase of a menstrual cycle. Blood was sampled every 10-20 minutes over a 16-hour period on two alternate days. On study day 1 (control day), subjects received two sets of saline infusion every 6 hours and one saline bolus at the beginning of the seventh hour; on study day 3 (naloxone day), they received a saline infusion during the first 6 hours, an intravenous bolus of naloxone (20 mg) at the beginning of the seventh hour and then a continuous naloxone infusion (1.6 mg/hour) during the ensuing 6 hours. Pituitary LH responsiveness and reserve were assessed on both study days by the subsequent administration of 5 and 95 micrograms of GnRH 4 hours before the completion of each sampling period. MEASUREMENTS: Serum concentrations of LH, PRL, oestradiol and progesterone were determined by radioimmunoassay. LH and PRL pulse detection and characteristics were analysed by the Cluster program. RESULTS: Serum PRL levels in hyperprolactinaemic anovulatory and ovulatory subjects were significantly elevated above the normal range. Oestradiol and progesterone serum levels during the luteal phase in women with hyperprolactinaemia and regular menses were similar to those in control ovulatory subjects. Mean LH concentrations increased during naloxone infusion (P < 0.05) in ovulatory hyperprolactinaemia and controls, whereas PRL increased (P < 0.05) only in the group of control subjects. LH pulse amplitude and pulse interval were increased by naloxone (P < 0.05) in all the ovulatory subjects, with no significant changes in anovulatory hyperprolactinaemic women. PRL pulse characteristics were modified significantly by naloxone only in the control group. On day 1, GnRH administration increased LH in all groups, whereas a consistently lower pituitary LH response was observed after naloxone (day 3). Serum PRL levels significantly increased after GnRH administration on day 1 only in normal women, whilst on day 3 this GnRH-dependent PRL releasing effect was significantly attenuated. CONCLUSIONS: The absence of stimulatory effects of naloxone on LH in anovulatory hyperprolactinaemia implies that endogenous opiates do not play a significant role in the mechanisms governing hypothalamic amenorrhoea in this syndrome. The results in subjects with ovulatory hyperprolactinaemia suggest the existence of an active role of ovarian steroids on naloxone induced LH release. These data, along with those previously reported in normal women throughout the menstrual cycle, are consistent with the concept that sex steroid hormones contribute to the underlying mechanisms involved in the opioidergic control of LH and PRL release. Whether PRL by itself or through other non-opioid neuroendocrine pathways alters the hypothalamic-gonadotroph unit still requires further investigation.

Adolescent↗

PubMed1995

Transfer of coded information from sensory to motor networks.

During sensory-guided motor tasks, information must be transferred from arrays of neurons coding target location to motor networks that generate and control movement. We address two basic questions about this information transfer. First, what mechanisms assure that the different neural representations align properly so that activity in the sensory network representing target location evokes a motor response generating accurate movement toward the target? Coordinate transformations may be needed to put the sensory data into a form appropriate for use by the motor system. For example, in visually guided reaching the location of a target relative to the body is determined by a combination of the position of its image on the retina and the direction of gaze. What assures that the motor network responds to the appropriate combination of sensory inputs corresponding to target position in body- or arm-centered coordinates? To answer these questions, we model a sensory network coding target position and use it to drive a similarly modeled motor network. To determine the actual motor response we use decoding methods that have been developed and verified in experimental work. We derive a general set of conditions on the sensory-to-motor synaptic connections that assure a properly aligned and transformed response. The accuracy of the response for different numbers of coding cells is computed. We show that development of the synaptic weights needed to generate the correct motor response can occur spontaneously through the observation of random movements and correlation-based synaptic modification. No error signal or external teaching is needed during this process. We also discuss nonlinear coordinate transformations and the presence of both shifting and nonshifting receptive fields in sensory/motor systems.

Animals↗

PubMed1994

Vector reconstruction from firing rates.

In a number of systems including wind detection in the cricket, visual motion perception and coding of arm movement direction in the monkey and place cell response to position in the rat hippocampus, firing rates in a population of tuned neurons are correlated with a vector quantity. We examine and compare several methods that allow the coded vector to be reconstructed from measured firing rates. In cases where the neuronal tuning curves resemble cosines, linear reconstruction methods work as well as more complex statistical methods requiring more detailed information about the responses of the coding neurons. We present a new linear method, the optimal linear estimator (OLE), that on average provides the best possible linear reconstruction. This method is compared with the more familiar vector method and shown to produce more accurate reconstructions using far fewer recorded neurons.

Animals↗

PubMed1994

Plasmodium vivax sporozoite rates from Anopheles albimanus in southern Chiapas, Mexico.

Anopheles albimanus mosquitoes were collected from August 1984 to November 1987 on intra- and peridomicile human bait in Rancheria El Gancho, Chiapas, Mexico. The mosquitoes were desiccated and stored in silicon chambers from 3 mo to 3 yr post-collection prior to being assayed using a direct enzyme-linked immunosorbent assay to detect Plasmodium vivax predominant-type sporozoite protein. Peridomicile-collected mosquitoes had a 10-fold higher sporozoite rate than those collected indoors, but only the latter correlate significantly with the seasonal human parasite index. Mosquito sporozoite burden was also significantly higher in the peridomicile-collected population.

Animals↗

PubMed1994

Effects of transmission-blocking immunity on Plasmodium vivax infections in Anopheles albimanus populations.

Two colonized populations of Anopheles albimanus isolated from the Suchiate region, Chiapas State, Mexico, were compared for their susceptibility to coindigenous Plasmodium vivax. Groups of mosquitoes were fed in vitro with either autologous donor blood or the same blood cells substituted with serum negative for anti-gametocyte antibody. Significant differences in susceptibility between the 2 colonies were encountered if the autologous blood from a patient was fed to mosquitoes: mean infection rates of AnA2-positive groups was double that in AnA1 mosquitoes. Consistent for both colonies, only 23.6% of samples positive from malaria-negative serum-substituted blood were infected with an autologous blood feed. Vector competence in these mosquito populations was partially linked to the human populations's immune response to the parasite.

Animals↗

PubMed1993

Magnetic resonance imaging or arthrographic diagnosis of internal derangement of the temporomandibular joint. Correlation comparison study with arthroscopic surgical confirmation.

Although arthrography has long been considered a gold standard for the diagnosis of internal derangements of the temporomandibular joint, magnetic resonance imaging has rapidly proved to be a valuable tool for other insights into soft tissue structures. The goals of this study were twofold: (1) to compare the diagnostic efficacy of arthrography with magnetic resonance imaging and (2) to compare these results with the actual arthroscopic findings. The correlation between arthroscopic examination and independent fluoroscopic arthrogram and magnetic resonance imaging was high for the diagnosis of anterior disk displacement, as were the correlations between arthroscopic examinations and fluoroscopic arthrograms on diagnosing disk perforations. These findings, together with the apparent specialized abilities of the arthroscopic examination to yield information on the quality of the surface tissues (e.g., cartilage degeneration, synovitis, proliferations) led us to conclude that diagnostic arthroscopy may prove to be as valuable to the maxillofacial surgeon for the diagnosis of intracapsular temporomandibular joint disorders as it is for the orthopedic surgeon in diagnosing other joint disorders.

Adolescent↗

PubMed1993

Studies on the reliability of a novel absorption-lipophilicity approach to interpret the effects of the synthetic surfactants on drug and xenobiotic absorption.

Some theoretical principles of the absorption/lipophilicity approach, which attempts to explain the effects of the synthetic surfactants on xenobiotic and drug intestinal absorption, are reviewed and experimentally checked by examining the correlations obtained between "in situ" absorption constants, ka, found in rat colon, and "in vitro" lipophilicity indexes, K', for two compound series (secondary aliphatic amines and phenylalkylamines) in the absence and in the presence of the nonionic surfactant Polysorbate 80, in the intestinal perfusion fluid. Evidence is given for the following actions of the synthetic surfactant: at its critical micelle concentration (CMC), it increases the polarity of the absorbing membrane and, at the same time, it disrupts the aqueous stagnant diffusion layer adjacent to the mucosal barrier. When a supramicellar concentration (SMC) is used, the above actions are almost totally masked by the micellar solubilization of the tested amines, which decreases their absorption constants relative to those found at CMC, as markedly as solute lipophilicity increases. As a consequence of these actions, the correlations between ka and K', which are clearly hyperbolic in free solution, become potential in the presence of the surfactant at its CMC, whereas at SMC a bilinear correlation is obtained. Absorption via lipophilic ionized species seems to take place for both compound series. Mathematical and physicochemical interpretations of this behaviour are outlined, and biopharmaceutical implications of these phenomena are discussed.

Amines↗

PubMed1992

Physical anhedonia in major depressive disorder.

Physical anhedonia, evaluated by the score on the physical anhedonia scale (PAS) of Chapman et al. [J. Abnorm. Psychol. 4 374-382 (1976)] was studied in 61 patients, who met RDC criteria for major depressive disorder and in 61 normal subjects. The depressed patients scored significantly higher than the normal group and presented a continuous distribution. Physical anhedonia of depressed patients seems related to the severity of the depression and does not appear to identify a qualitatively distinct subgroup.

Adult↗

PubMed1989

[Short-term treatment of meningococcal infections].

Based upon our previous experience on the treatment of meningococcal infections with satisfactory evolution when the fourth day of therapy was finalized and taking into account published experiences with four or less days of therapy, we realized a study on the efficacy of a four days therapy when venial meningococcal infections but of seven days when the serious ones. The results obtained were like the former ones we published concerning to death rate but having inferior number of complications. The results of our study suggest that meningococcal infections may be successfully treated according to seriousness, with a four or seven-day course of intravenous penicillin G (300,000 UI/kg/day) distributed in six "aliquots" each four hours. The possibility of a four-days therapy, not taking into account seriousness, is considered for every meningococcal infections.

Adolescent↗

PubMed1988

Laboratory oviposition, fecundity and egg hatching ability of colonized Anopheles albimanus from southwestern Mexico.

Fecundity, oviposition patterns and egg hatching characteristics were studied in two colonies of Anopheles albimanus isolated from the Pacific coast of southern Mexico. Fecundity was inversely proportional to the cage space available to the female and was influenced by the bloodmeal source, feeding method and previous feeding history. The length of the gonotrophic cycle decreased with succeeding experience from a mean 6.6 in the first to 2.6 days for the fifth cycle. Oviposition timing was also dependent on availability of oviposition substrate. Hatching success of eggs increased significantly when the oviposition site was witheld until 48 hr post-bloodmeal.

Animals↗

PubMed1981

Acute ethylene oxide intoxication.

A case of acute ethylene oxide intoxication is described in which neurological involvement was present. Three recurrent seizures over a period of an hour were observed in a 43-year-old female. The patient continued to complain of malaise and inability to perform minor motor tasks up to one week after discharge. Neurological evaluation conducted three weeks after toxic exposure was completely normal. A two-month follow-up showed the patient to be asymptomatic without recurrence of symptoms.

Acute Disease↗

PubMedDate not supplied

Anhedonia and blunted affect in major depressive disorder.

The relation between anhedonia and affective flattening was studied in 61 normal subjects and 61 major depressives. Affective flattening and anhedonia were defined by the following self-rating scales: Fawcett-Clark Pleasure Capacity Scale (FCPCS), Hardy Displeasure Capacity Scale (HDCS), FCPCS-PP (subscale of physical pleasure), and HDCS-PD (subscale of physical displeasure). The depressives are more sensitive to displeasure and more anhedonic than controls. Concerning physical stimulations (FCPCS-PP and HDCS-PD) in the depressed group, anhedonia and affective flattening are not linked, suggesting that physical anhedonia is not secondary to low emotional reactivity (affective flattening) and constitutes an independent dimension.

Adult↗

PubMedDate not supplied

Posterior chamber silicone intraocular lens for the correction of myopia: an experimental study in rabbits.

PURPOSE: To establish whether ocular lesions arise after implantation of posterior chamber silicone intraocular lenses (IOL) for the correction of high myopia. METHODS: Twenty-three posterior chamber silicone IOL were implanted in 23 eyes of the same number of pigmented rabbits. After different follow-up time (from one week to one year) the eyes were enucleated and processed for histopathological study after determining the protein concentration in the aqueous humor. The IOL were removed for staining and examination, and adhered cells were counted. Ten eyes analogous to those operated upon were used as controls. RESULTS: Intense inflammation was observed in the early postoperative period in all cases. Protein concentration in the aqueous humor was initially high and decreased over time, though without reaching normal values at one year. Mono- and multinucleated cells were seen adhering to the IOL, though they decreased in number over time and were practically absent after one year. Friction between the posterior surface of the iris and the IOL had no clinical repercussions. The only pigment accumulations were in the iris and in the peritrabecular zone. There were no significant differences in the accumulation of granules in relation to IOL diameter or power. Excluding three cataracts morphologically similar to traumatic cataracts, five lens opacifications were observed: two were anterior subcapsular cataracts, and the other three were only precapsular deposits. The IOL had no synechiae to the ocular tissues. CONCLUSIONS: Opacification of the lens is the main concern with implanted posterior chamber silicone IOL. Larger series of eyes must be analysed to establish the true incidence and reversibility of these opacities.

Animals↗

PubMedDate not supplied

[A validity study of continuous Doppler].

INTRODUCTION: Ultrasound is regularly used for the detection of carotid stenosis which can be treated surgically. This technique includes continuous Doppler, which together with study of blood flow in the orbit is very useful and should be used systematically, not only in certain cases. We present a study of the usefulness of this technique in our Cerebral Vascular Pathology Laboratory. PATIENTS AND METHODS: We selected 708 patients studied sequentially over 10 years with continuous Doppler and conventional angiography (gold standard). The data obtained independently with each technique were compared in order to establish the degree of concordance between them and the corresponding indicators of validity. Contingency tables were drawn up for different cut-off points corresponding to the different degrees of stenosis (50, 70 and 100%). The parameters for validity (sensitivity, specificity, predictive value and precision) were calculated in each case. RESULTS: The percentage coincidence of the two techniques was 91.95%. At the cut-off points there was a high degree of precision (> 94.35%). The specificity and negative predictive value of Doppler compared with angiography was over 95% and 96% respectively. CONCLUSIONS: The validity markers obtained in our laboratory support the technique using continuous Doppler as the ideal non-invasive diagnostic method for carotid stenosis and this means that its systematic use is to be recommended in patients with suspected extracranial carotid disease. Moreover, the low cost of the equipment used as compared with other more sophisticated techniques should lead to its more widespread use as a first-line diagnostic method in all Neurology departments.

Adult↗

PubMedDate not supplied

[Spontaneous intracranial hypotension].

INTRODUCTION AND CLINICAL CASE: A 38 year old woman, with no previous history of trauma, presented complaining of interscapular pain followed by pulsating headache clearly related to posture, alleviated on lying down and worse on standing up. Subsequently, she also complained of diplopia. On examination there was paresia of the left sixth cranial nerve. Low opening pressure on lumbar puncture confirmed the presence of intracranial hypotension. The protein level of the cerebrospinal fluid was slightly raised. On CT the cortical sulci and small ventricles had disappeared. Cerebral MR (without gadolinium) showed marked diffuse meningeal hyper-intensity and apparent absence of the basal cisterni. Isotopic cisternography showed a pattern compatible with hypotension, without signs of fistulas. On spinal MR no spinal meningeal defects were seen. With conservative treatment the patient improved in a few days and the headache and diplopia disappeared. The absence of traumatism or spinal operations mean that the hypotension may be considered to be spontaneous. We discuss the CSF, neuroimaging and cisternography findings characteristic of the spontaneous intracranial hypotension syndrome. CONCLUSION: Unawareness of this syndrome, the particular neuroimaging changes and the usual CSF anomalies may lead to confusion over diagnosis, leading to the use of invasive techniques unsuitable for a condition which often has a good prognosis and in which the symptoms resolve in a few days or weeks with conservative treatment.

Abducens Nerve↗