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Biomedical subjects

G Benedek

Publications and source records attributed to G Benedek.

At least 73 records · Page 4Linked to original sources
PubMed1996

Human oscillatory potentials: components of rod origin.

Oscillatory potentials (OPs) evoked by white flashing light after dark or light adaptation (WDA and WLA conditions) and those evoked by blue flashing light stimulation against a dark background (BDA condition) were recorded in 16 healthy volunteers. When blue flashing light was employed over a scotopic background, the two major OPs of this response (OP2 and OP3) appeared with a latency time that sharply coincided with the third (OP3) and fourth (OP4) components of the OPs evoked by white flashes. The results provide evidence in support of the notion that various elements of OPs represent the activities of different retinal mechanisms, of which OP3 and OP4 seem to be of rod origin.

Adolescent↗
PubMed1995

Oxidation of gamma II-crystallin solutions yields dimers with a high phase separation temperature.

Aqueous solutions of the bovine eye lens protein gamma II (or gamma B)-crystallin at neutral pH show a gradual increase in phase separation temperature, Tph, when allowed to stand for several weeks at room temperature without reducing agents. In a typical experiment, the Tph of the protein solution (218 mg/ml) increases from 2.5 +/- 1 degree C to 32.5 +/- 1 degree C after 21 days, and a new protein species, gamma IIH, is formed. The Tph of pure gamma IIH is at least 40 degrees C higher than that of pure gamma II. The average apparent hydrodynamic radius is 36 A for gamma IIH compared to 26 A for gamma II. The molecular mass of gamma IIH is approximately 41.5 kDa compared to 20 kDa for native gamma II. Therefore, gamma IIH is probably a dimer of gamma II crystallin. gamma IIH has a lower thiol content than gamma II and is not formed in the presence of dithiothreitol. We conclude that gamma IIH is a thiol oxidation product of gamma II-crystallin and is a dimer containing an intermolecular disulfide crosslink. Thus, some oxidative modifications of protein thiol groups lead to an increase in net attractive interactions between proteins. As a result, Tph increases and protein aggregates are formed. These two microscopic changes produce the increased light scattering associated with lens opacification.

Animals↗
PubMed1995

Organization of the colliculo-suprageniculate pathway in the cat: a wheat germ agglutinin-horseradish peroxidase study.

A wheat germ-agglutinated horseradish peroxidase (WGA-HRP) tracing technique was used to label the cell bodies of neurons in the superior colliculus that send projections into the visually sensitive region of the suprageniculate nucleus (Sg) in the feline thalamus. After determination of the position of the Sg by detecting characteristic single-unit responses to moving visual stimuli, WGA-HRP was injected into the Sg in five pentobarbital-anesthetized cats. The animals were than sacrificed, and serial frozen sections of the midbrain were processed for the demonstration of peroxidase activity. A total of 2,736 WGA-HRP-stained neurons were located within the ipsilateral superior colliculus (SC), and a few labeled cells were consistently found bilaterally in the external nuclei of the inferior colliculus. In each cat, a small but significant fraction of the labeled cells were encountered contralateral to the injection. Medial SC neurons tended to project to the posterior Sg, and lateral SC neurons tended to project to more rostral Sg. However, labeled cells were distributed homogeneously along the rostrocaudal extent of the SC, indicating the absence of a well defined topographic relationship. Nor was the Sg injection site location related to the laminar distribution of SC projection neurons. In all cases, the majority of the labeled cells were found in layer IV (49.0%), with fewer cells in layers III (17.5%) layer V (20.0%), and layer VI (11.8%). No labeled cells were located in layer I, although a few were located in the deep part of layer II. Five types of SC projection cells were distinguished morphologically. Of the 258 labeled cells that could be characterized, 25% were stellate cells, 25% vertical cells, 20% granular cells, 17% triangular cells, and 12% horizontal cells. The average diameter of 226 cells ranged between 8 and 47 microns. We conclude that a mixed population of SC cells projects to the Sg; the morphological heterogeneity and the distribution of these cells suggests that several functionally different pathways may be involved in the colliculothalamic pathway and in the processing of visual input in the SC.

Animals↗
PubMed1995

Bilateral projections from the superior colliculus to the suprageniculate nucleus in the cat: a WGA-HRP/double fluorescent tracing study.

Following WGA-HRP injection into the right suprageniculate nucleus of the cat brain, retrogradely-labeled neurons were found not only in the ipsilateral, but also in the contralateral superior colliculi. After WGA-HRP injection into the unilateral superior colliculus, anterogradely-labeled axon terminals were observed in the bilateral suprageniculate nuclei, and electron microscopic examination revealed that these were large terminals which made asymmetric synaptic contacts with dendrites. When a different kind of fluorescent tracer was injected into each suprageniculate nucleus (Fast blue and Nuclear yellow), double-labeled neurons were observed in the rostral and middle portions of both superior colliculi. These results suggest that there are direct bilateral projections from the superior colliculus to the suprageniculate nuclei, and that some of these projections originate from branching colliculo-suprageniculate axons.

Animals↗
PubMed1994

Mydriatic and antinociceptive effects of intrathecal dexmedetomidine in conscious rats.

A comparison was made of the dose-effect relationship of intrathecally applied dexmedetomidine as concerns its mydriatic and antinociceptive effects in rats. Pupil diameter was measured with a photographic method without anesthesia. Antinociception was measured by means of the tail-withdrawal test. The intrathecal (i.t.) administration of dexmedetomidine led to dose-dependent antinociception (P < 0.05) and mydriasis (P < 0.001). Both effects reached their maximum 10 min after drug application. The tail-withdrawal latency was prolonged by 9 micrograms dexmedetomidine. Mydriasis appeared on administration of a 1 microgram dose and its degree was proportional to the dexmedetomidine dosage up to 12 micrograms. A significant correlation was not found between pupil diameter and tail-withdrawal latency in the same rat after any dexmedetomidine dose. Based on the present experiments, we conclude that the mydriatic effect of i.t. dexmedetomidine appears at a lower dose than its antinociceptive effect. Our results suggest that the assessment of pupillary response is a sensitive method for estimation of the supraspinal effect of i.t. administered alpha 2-adrenoceptor agonists.

Adrenergic alpha-Agonists↗
PubMed1994

Electrophysiologic alterations in patients with optic nerve hypoplasia.

The clinical and electrophysiologic data (electroretinograms and visual evoked potentials) were studied in 45 patients with optic nerve hypoplasia. The patients were divided into three fairly distinct groups on the basis of their electrophysiologic alterations. Group 1 consisted of 13 patients with almost extinguished visual evoked potentials and with mild electroretinographic alterations. These were the cases that are traditionally recognized as optic nerve hypoplasia. The serious visual impairment in these cases was accompanied by various developmental ophthalmologic and nonophthalmologic abnormalities. Group 2 included 26 patients without any significant visual evoked potential or electroretinographic alterations, but with overt funduscopic signs of optic nerve hypoplasia. These patients were consistently suffering from strabismus and/or amblyopia. The visual functions based on visual evoked potential and electroretinographic recordings could be fairly normal apart from a pathologic ophthalmoscopic picture characteristic of optic nerve hypoplasia. Group 3 included six patients with abnormal albeit well-recordable visual evoked potentials and subnormal or negative-type electroretinograms that suggested an accompanying retinal disease. This finding seems to prove that a subset of patients with optic nerve hypoplasia with nystagmus may have a primary retinal abnormality. Our study provides further evidence that optic nerve hypoplasia is not a uniform disease entity.

Adolescent↗
PubMed1994

An ultrasonographic method for the evaluation of dexmedetomidine on micturition in intact rats.

We describe a simple, noninvasive, nontraumatic, and reproducible ultrasonographic method to determine the effect of the alpha 2-adrenoceptor agonist dexmedetomidine in anesthetic dose (300 micrograms/kg subcutaneously) on the micturition reflex in intact rats. The bladder volumes were estimated by an ellipsoid equation. To validate the reliability of the method, an in vitro model assessment also was performed. The mean difference between estimated and instilled volumes were 27.3 microL (-21.61, 76.23). The highly significant correlation (r = 0.98, p < .001) indicates that the ultrasonography with the equation is a reliable tool. After the dexmedetomidine administration to intact rats, urine dribbling occurred at 30 +/- 4.8 min. The volume threshold for urination was 2100 +/- 100 microL. Although dribbling of the urine was observed almost continuously, significant differences were not observed between bladder volumes obtained at any time (from 10 to 100 min). This study indicates that the alpha 2-adrenoceptor agonist dexmedetomidine inhibits the micturition reflex in intact rats. The method described, which is both noninvasive and nonpainful, may therefore be widely used to quantify in small animals pharmacological effects on the urinary bladder.

Animals↗
PubMed1993

Suppression of phase separation in bovine gamma IV crystallin solutions: effect of modification by charged versus uncharged polar groups.

gamma IVa Crystallin, the ocular lens protein with the highest critical temperature (Tc) for phase separation, has been chemically modified with N-ethylmaleimide (NEM) at neutral pH. NEM, a polar but uncharged modifier reacts with the cysteine residues of the protein. A maximum of 80-85% of the thiol groups are modified and the phase separation temperature is lowered by about 10 degrees C at a protein concentration of 30 mg ml-1. The coexistence curve of the NEM-modified protein with nearly four out of the six cysteines modified was determined and compared with that obtained by modifying the protein with a charged reagent, N-bromoacetylethanolamine phosphate (NBAEP). NBAEP modifies both cysteine and methionine residues of gamma IVa crystallin. The results of these two modification studies indicate that for the same total degree of modification of the sulfur-containing residues, the suppression in Tc due to the charged NBAEP is at least twice as large as that due to the polar but uncharged NEM. In order to obtain some measure of the relative hydrophilicities of the two modifiers, we have estimated the free energies of hydration of the nonionic segments of NEM and NBAEP, using structural additivity schemes. We find that the intrinsic hydrophilicities of the nonionic segments of these two modifiers are nearly equal. Hence the much larger suppression of Tc resulting from NBAEP modification is most probably due to the strongly polar, doubly charged phosphate group.

Amino Acids↗
PubMed1993

Dexmedetomidine-induced decrease in cerebral blood flow is attenuated by verapamil in rats: a laser Doppler study.

This study was performed to examine the changes in local cortical blood flow (CoBF) after simultaneous administration of an alpha 2 adrenergic agonist (dexmedetomidine) and a calcium channel antagonist (verapamil) to urethane-anaesthetized rats. Dexmedetomidine (100 micrograms.kg-1) given intraperitoneally alone resulted in decreases in mean arterial blood pressure (MABP) (F[27,140] = 3.43; P < 0.01) and CoBF (F[27,140] = 4.22; P < 0.01), whereas the heart rate (HR) was increased (F[27,140] = 2.33; P < 0.01). Verapamil (2.5 mg.kg-1) given subcutaneously reduced the MABP (F[27,140] = 3.41; P < 0.01), but the HR and CoBF were not changed. Combined administration of the drugs decreased MAPB (F[27,140] = 5.37; P < 0.01), with no changes in CoBF and HR. The present data indicate that the calcium channel antagonist verapamil did not potentiate the haemodynamic effects of dexmedetomidine in rats, but rather attenuated the effect of dexmedetomidine on CoBF. This favourable interaction suggests a potential therapeutic role of these agents in maintaining cardiovascular stability during surgical interventions.

Adrenergic alpha-Agonists↗
PubMed1993

Spatial selectivity in the anterior ectosylvian visual area of the cat.

Pattern reversal visually evoked potentials (PR-VEPs) were recorded in the anterior ectosylvian visual area (AEV) of the cat, and the dependence of the PR-VEPs on the spatial frequency (SF) and the mean luminance of the stimulation was studied. Six SFs between 0.025 and 1 cycles per degree (c/d) and four light density levels between 2 x 10(-2) and 117 cd/m2 (candela per square meter) were tested. The latency of the first positive component (P1) and the amplitude measured between P1 and the first negative (N1) component were analyzed. The dependence of the PR-VEP latencies on the SF displayed a significant relationship, with a minimum at around 0.05 c/d. This relationship was consistent at all luminance levels tested. The dependence of the amplitudes on the SF gave a "low-pass" tuning curve at every luminance level. The higher the luminance level, the steeper was the curve. The cut-off SF of these curves was at around 1 c/d under photopic conditions and around 0.6 c/d under scotopic conditions. The contrast dependence of the PR-VEP amplitudes exhibited saturation at 0.5, which was much higher than that of either the striate cortex or other extrastriate visual cortical areas, but similar to that of the superior colliculus. These results provide further evidence in support of the notion of a tecto-extrageniculo-extrastriate visual pathway functioning separately from the geniculo-striate mechanisms.

Animals↗