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Biomedical subjects

A Polo

Publications and source records attributed to A Polo.

At least 55 records · Page 3Linked to original sources
PubMed1995

Effect of pharmacologically induced mydriasis on the normal variability of retinal oscillatory potentials in man.

In this study we describe certain aspects of normal variability of oscillatory potentials, with particular reference to interaction between pupil size and stimulus intensity. The mean latencies of the earlier oscillatory potentials, O1 and O2, were significantly shorter when adopting the dilated pupil condition than when stimulating with a normal pupil. This occurred at various light intensities, although the difference was more significant at the highest intensity. O1 and O2 latencies became significantly longer as the stimulus intensity was progressively reduced. The latencies of the later components O3 and O4 were unaffected. The O1 and O2 amplitudes were not influenced by pupil size, but a significant reduction occurred with the progressive decrease in stimulus intensity. The later components O3 and O4 are greatly reduced in amplitude after pupil dilatation using higher stimulus intensities; the O4 potential may even disappear in 10% of the cases. These data provide further support for the existence of two distinct behavior patterns for earlier and later oscillatory potentials. Although light adaptation may affect oscillatory potentials, we suggest that in our experimental conditions, oscillatory potential changes may occur as a result of the activity of the neural modulating system, not only as a result of photoreceptor interaction.

Adult↗
PubMed1995

Neurophysiological and urodynamic examinations in the functional assessment of the spinal cord below the injury site.

We examined the characteristics of specific components of the evoked electrospinogram (EESG) in response to tibial nerve stimulation in 28 patients with traumatic injury of the dorsal and cervical spinal cord. The data were correlated with clinical, urodynamic and additional neurophysiological findings. In the majority of patients (82%), 11 with complete and 12 with partial spinal cord lesions, the lumbar components of the EESG were normal. In 4 of these patients with complete lesion above T2 the dorsal EESG was absent. In 5 cases (18%), the lumbosacral EESG was altered in the presence of an atypical clinical syndrome characterized by persistent urinary retention associated with lower leg atrophy and reduced tendon jerks. In these cases, MRI provided evidence of an unexpected sacral lesion. Unlike the dorsal EESG reflecting the afferent dorsal column volley, the lumbar components of the EESG are usually unaffected by interruption of the cord pathways; these last events thus originate from segmental neuronal activity, the involvement of which bears witness to additional lumbosacral damage.

Adolescent↗
PubMed1995

Dynamic F wave from lower limbs: value and clinical application.

We evaluated changes in F wave from the lower limbs after walking in normals. Twenty-two healthy subjects ranging in age from 24 to 74 years (mean 40.2 SD 15.2) were investigated. The peroneal nerve was examined in 16 subjects and the posterior tibial nerve in 22 subjects on the dominant side. F waves were evaluated at rest and 1 minute and 10 minutes after effort testing consisting in prolonged walking for 15 minutes. F wave minimum, maximum and mean latencies, chronodispersion, duration, persistence and amplitude were evaluated. Only chronodispersion showed a significant decrease for both the peroneal and tibial nerve (p < 0.05) after walking. Moreover we evaluated the F wave after effort in five patients affected by neurogenic claudication: three patients presented a further slowing of proximal conduction, while two patients exhibited a transitory conduction block. In conclusion, F wave changes observed in dynamic conditions in normals probably reflect a synchronization of motorneuron firing requiring a certain amount of descending facilitation. On the other hand, the marked F wave changes after effort observed in patients increase the sensitivity of this method in the clinical setting and may provide insights into the pathophysiologic basis of neurogenic claudication.

Adult↗
PubMed1994

LIGA20, a lyso derivative of ganglioside GM1, given orally after cortical thrombosis reduces infarct size and associated cognition deficit.

A bilateral photochemically induced thrombotic lesion of rat sensorimotor cortex (approximately 3 mm in diameter and 25 mm3 in volume) is associated with a persistent cognition (learning and memory) deficit, which was evaluated with water maze tasks. The N-dichloroacetylsphingosine derivative of lysoGM1 (LIGA20) administered after the lesion either i.v. or per or reduces the infarct size by 30-40% and attenuates the associated cognition deficits, presumably by limiting the extent of damage of neurons at risk located in the surroundings of the infarcted core (i.e., area penumbra). The LIGA20 protection is dose and time dependent. Maximal protection is afforded by a single dose of LIGA20 of 34 mumol/kg i.v. 1 hr after lesion or by a dose of 270 mumol/kg per os when administered 1 hr and 24 hr after the lesion. The protective effect of LIGA20 can be observed when the drug is administered i.v. up to 6 hr after the lesion. The protective efficacy of the oral administration of LIGA20 is related to its physiochemical properties, which, unlike those of GM1, allow absorption from the gastrointestinal tract. LIGA20 given orally reaches the brain promptly and rapidly inserts into the neuronal membranes. Here, by an unknown molecular mechanism, LIGA20 selectively reduces the pathological amplification of Ca2+ signaling elicited by persistent stimulation of ionotropic glutamate receptors in the area penumbra.

Administration, Oral↗
PubMed1994

Cortical output modulation after rapid repetitive movements.

Transcranial magnetic stimulation was used to evaluate changes in motor cortex excitability after rapid repetitive movements in five healthy subjects aged 23-30 years, by considering the amplitude of motor evoked potentials (MEPs) at rest and after one minute of maximal frequency repetitive abduction-adduction movements of the thumb. In addition, M and F waves were evaluated by stimulating the median nerve at the wrist. All of the examined subjects showed a clear modification in post-exercise MEP amplitudes, with a mean maximal reduction of 50-60% in comparison with basal values and complete recovery after a period of about 35 minutes. The time course of this phenomenon showed a triphasic pattern: (I) a rapid decrease phase up to the fifth minute; (II) a maximal depression phase for a period of about ten minutes; (III) a slow return to basal values. No significant changes were observed in post-exercise M and F waves. These results show the existence of a reversible modulation of the excitability of the upper motor neuron after rapid repetitive movements. It is likely that this modulation takes place at the level of the motor cortex and that its anatomo-functional substrate is represented by the activation of inhibitory intracortical circuits.

Adult↗
PubMed1994

Brain content of glycosphingolipids after oral administration of monosialogangliosides GM1 and LIGA20 to rats.

Natural (GM1) and semisynthetic [113-Neu-5-AcGgOse4-2-D-erythro-1,3- dihydroxy-2-dichloroacetylamide-4-trans-octadecene (LIGA20)] glycosphingolipids, given parenterally, protect neurones against glutamate-induced death without producing the side effects typical of glutamate receptor antagonists. Chronic glutamate-related neurotoxicity (e.g., in recurring strokes in elderly hypertensive patients, and in Parkinson disease) could be prevented also by glycosphingolipids treatment, but this therapeutic intervention will require a protracted administration of orally active glycosphingolipids. Here we demonstrate that 3-6 h after oral administration of 68 mumol/kg of LIGA20 and GM1 to rats, the brain content of LIGA20 is 50-fold higher than that of GM1. The brain concentration of LIGA20 remains elevated for at least 12-24 h. Because the LIGA20 that reaches the brain is slowly metabolized, repeated oral administrations of this glycosphingolipid can yield to its accumulation in brain, and can yield various brain levels depending on the dose and frequency of drug administration. In contrast this is not possible with GM1, which given orally for 7 d, cannot accumulate in brain in pharmacologically significant concentrations.

Administration, Oral↗
PubMed1994

Spinal somatosensory evoked potentials in patients with tethered cord syndrome.

We studied the electrophysiological changes occurring in six patients with tethered cord syndrome. Evidence of spinal malformations was provided by magnetic resonance imaging. The functional assessment of the spinal cord was performed by analysing both spinal and cortical somatosensory evoked potentials. The evoked electrospinogram was recorded from the thoracic and lumbosacral spinous processes. The N22 lumbosacral potential was selectively affected, being rostrocaudally displaced and reduced in amplitude or even absent in patients with neurological signs indicating a segmental lower cord lesion. Inter-peak somatosensory evoked potentials latency was normal in all cases, suggesting that ascending axonal potentials in the dorsal column fibres may be synchronized. Segmental potentials of the lumbosacral response, originating from the post-synaptic activity of dorsal horn interneurons, are selectively affected in this syndrome resulting from the rostrocaudal displacement of the spinal cord due to tethering. Our findings in the clinical field are consistent with previous experimental evidence indicating a different sensitivity of the gray vs. white matter to progressive stretching.

Adult↗
PubMed1994

Variability of tibial nerve early cortical potentials in normal subjects.

The aim of the study was to calculate and test the variability of several tibial nerve SEP parameters, particularly scalp amplitude distribution, with a view to obtaining more reliable clinico-electrophysiological correlations. The parameters were evaluated in 20 healthy subjects using a simple, easily reproducible recording method. The absolute latency of the P40 wave was greater than that of the N37 wave, except in two cases. Paradoxical lateralization was present in all subjects. On the basis of the scalp amplitude distribution of the ipsi- and contralateral potentials, three distinct groups were identified: a) dominance of ipsilateral P40, 29 sides; b) dominance of P37, 15 sides; and c) equivalent amplitude of P37 and ipsilateral P40, 5 sides. The individual amplitude values of these potentials were plotted on a normogram. The results suggest that (i) the absence of one or more early cortical SEPs may be considered abnormal; (ii) when SEP scalp lateralization is present, it may be useful to compare the amplitude distribution of the individual components in normal and pathological populations; and (iii) for this purpose, lateralized potentials are more reliable owing to their lower degree of amplitude dispersion.

Adult↗
PubMed1993

A histochemical and immunohistochemical study of digestive enzymes and hormones during the larval development of the sea bream, Sparus aurata L.

The distribution of different hydrolytic enzymes and the localization of the hormones which regulate glucose metabolism during development of the digestive tract of the sea bream, Sparus aurata L., were studied. The yolk sac contains trypsin, glucose-6-phosphatase, ATPases and acid and alkaline phosphatase activities. Positive insulin, glucagon and somatostatin cells were observed in the pancreas and in the lumen of the intestinal tract during endogenous feeding. From hatching until 3 days later, the digestive tract of sea bream larvae shows no enzymatic activities. During exogenous feeding, the activities of the phosphatases and trypsin generally increase, as do the amounts of the hydrolytic enzymes and trypsin, as well as the pancreatic and intestinal hormones. The enzymatic activities gradually decrease from the anterior part towards the posterior part of the digestive tract.

Acid Phosphatase↗
PubMed1993

Molecular parameters of semisynthetic derivatives of gangliosides and sphingosine in monolayers at the air-water interface.

The molecular parameters (molecular area, surface potential, collapse pressure, dipole moment contributions) of semisynthetic derivatives of ganglioside GM1 and of sphingosine were studied in lipid monolayers at the air-NaCl (145 mM, pH 5.6) interface at 22 +/- 0.3 degrees C. The chemical modifications included alterations of the fatty acyl chain moiety linked to the 2-amino position of the sphingosine (Sph) base. The compounds studied were PKS-1 (N-acetyl Sph), PKS-2 (N-chloroacetyl Sph), PKS-3 (N-dichloroacetyl Sph), PKS-4 (N-trichloroacetyl Sph), Lyso-GM1 (ganglioside GM1 lacking the N-linked fatty acyl chain and the N-acetyl group on the sialic acid), Liga-4 (N-acetyl, lyso[NeuAc]GM1) and Liga-20 (N-dichloroacetyl, lyso[NeuAc]GM1). Relatively small modifications of the chemical structure of sphingolipids introduce dramatic consequences on their surface molecular properties. The absence of the long chain fatty acyl moiety and of the N-acetyl group on the neuraminic acid in Lyso-GM1 leads to a more condensed behavior and to an increase of the collapse pressure compared with GM1. The acetylation or chloroacetylation at the 2-amino position in Liga-4 and Liga-20 induce an expansion of the surface pressure-area isotherm and a decrease of the collapse pressure. The limiting molecular areas of GM1 derivatives, taken at the collapse pressure point, are consistent with the oligosaccharide chain being oriented approximately perpendicularly to the interface. Sphingosine shows a liquid expanded isotherm. The acetylation and successive chlorination of the acetyl residue at the 2-amino position of Sph cause a progressive increase in the limiting molecular area. The variation of the resultant dipole moment under compression, calculated from the surface potential values, suggests the reorientation of selective groups within these molecules that depend on the degree of intermolecular packing. Thermodynamic-geometric correlations on the basis of the molecular parameters of these derivatives suggest that small alterations of the substituent group at the 2-amino position of Sph could have large and amplified consequences on the type, curvature and stability of the possible self-aggregated structure that these lipids may form in aqueous medium.

Air↗
PubMed1993

Effects of halothane and isoflurane on beta-endorphin release in children.

We compared the effects of halothane and isoflurane with 50% nitrous oxide (seven children each) on plasma beta-endorphin concentrations in a group of 14 children aged 1 to 6 years. The findings were compared for four periods of anaesthesia: basal, induction, maintenance and recovery. Beta-endorphin release was most increased with isoflurane, especially during the maintenance period. Measurements of haemodynamic parameters (heart rate and blood pressure) showed diastolic blood pressure significantly lower after isoflurane anaesthesia. The findings suggest that the use of isoflurane for paediatric inhaled isoflurane anaesthesia leads to a more marked surgical stress adaptation effect than the use of halothane.

Anesthesia, Inhalation↗
PubMed1993

Stimulation of brain pregnenolone synthesis by mitochondrial diazepam binding inhibitor receptor ligands in vivo.

Evidence that neurosteroids are potent modulators of the action of GABA at GABAA receptors has prompted the investigation of the mechanism that controls brain neurosteroid synthesis by glial cell mitochondria in vivo. In vitro studies suggest that the interaction of the diazepam binding inhibitor (DBI)--a polypeptide that is abundant in steroidogenic cells--with glial mitochondrial DBI receptors (MDRs) is a crucial step in the physiological regulation of neurosteroid biosynthesis. MDRs bind 4'-chlorodiazepam (4'-CD), N,N-di-n-hexyl-2-(4-fluorophenyl)-indol-3-acetamide (FGIN-1-27), and the isoquinoline carboxamide PK 11195 with high affinity, and these ligands have been used to investigate whether the stimulation of glial MDRs increases brain pregnenolone production in vivo. Adrenalectomized and castrated (A-C) male rats (to eliminate peripheral sources of pregnenolone) were pretreated with trilostane (to prevent pregnenolone metabolism to progesterone), and the pregnenolone content in brain regions dissected after fixation with a 0.8-s exposure to microwave irradiation focused to the head was determined by HPLC followed by specific radioimmunoassay. The forebrain and cerebellum of A-C rats contained 4-7 ng of pregnenolone/g of tissue, and the olfactory bulb contained 10-14 ng/g. These concentrations of brain pregnenolone are only 30-40% lower than those of sham-operated rats. In contrast, the plasma pregnenolone content of sham-operated rats was 2-3 ng/ml, but it was only 0.15-0.20 ng/ml in the plasma of A-C rats. In A-C rats, treatment with the MDR ligands 4'-CD and FGIN-1-27 increased the pregnenolone content in the brain but failed to change the plasma or peripheral tissue content of this steroid. The effect of 4'-CD on brain pregnenolone content was maximal (70-100% increase) at the dose of 18 mumol/kg, 5-10 min after intravenous injection. The effect of oral administration of FGIN-1-27 on brain pregnenolone content was maximal (80-150% increase) at doses of 400-800 mumol/kg and peaked at approximately 1 h. That this effect of FGIN-1-27 was mediated by the MDR was documented by pretreatment with the MDR partial agonist PK 11195 (100 mumol/kg, i.p.). PK 11195 did not affect basal brain pregnenolone content but prevented the accumulation of brain pregnenolone induced by FGIN-1-27. FGIN-1-27 and 4'-CD failed to increase the brain concentration of dehydroepiandrosterone in A-C rats. These data suggest that glial cell MDRs play a role in neurosteroid biosynthesis in vivo.

Adrenalectomy↗
PubMed1993

Stimulation of brain steroidogenesis by 2-aryl-indole-3-acetamide derivatives acting at the mitochondrial diazepam-binding inhibitor receptor complex.

The 2-aryl-indole-3-acetamide derivatives, 2-hexyl-indole-3-acetamide (FGIN-1-27) and 2-hexyl-indole-3-acetamide-N-benzene-tricarboxylic acid (FGIN-1-44) displaced [3H]1-(2-chlorophenyl)-N-methyl-N-(1- methylpropyl)-3-isoquinoline-carboxamide([3H]PK 11195) and [3H]4-chlorodiazepam ([3H]4'CD) from binding sites located on the rat brain mitochondrial DBI receptor complex (MDRC) with Ki values in the nanomolar range. Both 2-aryl-indole-3-acetamide derivatives acted as agonists at the MDRC and thereby stimulated the rate of pregnenolone synthesis in isolated rat brain mitochondria; this effect was inhibited by PK 11195, an MDRC ligand that does not possess steroidogenic activity. FGIN-1-27 and FGIN-1-44 failed to bind to other transmitter receptors, including gamma-aminobutyric-A receptors. When administered orally to rats, both FGIN-1-27 and FGIN-1-44 reduced fear of novelty in the elevated plus maze test. This action was prevented by PK 11195, but not by flumazenil. FGIN-1-44, which was rapidly converted to FGIN-1-27 in the rat brain, was 3 to 4 times more potent than FGIN-1-27 in reducing fear of novelty because of its greater bioavailability. FGIN-1-27 increased the brain pregnenolone content in adrenalectomized-castrated rats pretreated with trilostane (in order to prevent metabolism of pregnenolone to progesterone). This increase was blocked by pretreatment with PK 11195. Although FGIN-1-27 and FGIN-1-44 increased the corticosterone concentration in adrenal glands and plasma of hypophysectomized rats in a PK 11195-sensitive manner, both drugs failed to increase adrenal steroidogenesis in sham-operated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗
PubMed1992

Retinal oscillatory potential abnormalities in patients with chronic renal failure, before and after dialytic treatment.

Nineteen patients with chronic renal failure were studied, oscillatory potentials (OPs) being recorded shortly before and after dialytic treatment. Mean values of either onset latency (O1 latency) and duration of the complex (O1-N4 inter-peak latency) were found to be significantly longer in patients than in controls (p < 0.001). Most of the patients (12) showed a pathological prolongation of latency (> 2.5 SD). Amplitude changes also affected OPs, but earlier components were reduced to a lesser degree than the later ones, as shown by statistical analysis. Moreover, seven patients showed an almost complete loss of O3 and O4 peaks. Latency changes may be transiently reversed by dialysis, suggesting a functional impairment of the retinal response; the loss of later components is a more persistent abnormality probably related with a structural damage.

Adult↗
PubMed1992

Polyneuritis cranialis: clinical and electrophysiological findings.

A 13 year old boy, developed bilateral facial weakness, dysphonia and dysphagia acutely after a febrile illness. Neurological examination and MRI of the brain were normal. The CSF protein level increased. Blink reflex monitoring during clinical recovery was consistent with demyelination of the lower cranial nerves innervating the branchial arch musculature, a rare variant of Guillain-Barré syndrome.

Adolescent↗
PubMed1992

Evoked potentials before and after anemia correction with recombinant human erythropoietin in end-stage renal disease.

Subclinical involvement of the nervous system in uremic adults has been detected by modern neurophysiological techniques. Chronic anemia is one of the possible factors responsible for neural dysfunction in uremia. We evaluated neurophysiological (brainstem auditory and somatosensory evoked potential) abnormalities and their possible modification following anemia correction with recombinant human erythropoietin in 14 children with end-stage renal disease maintained by hemodialysis. Only peripheral and 8th cranial nerve electrophysiological data are significantly abnormal in our patients, and they are not acutely modified by anemia correction. These data confirm the importance of electrophysiological testing of uremic children for detecting nervous system involvement at an early stage and for monitoring the efficacy of its management.

Adolescent↗