PubMed Health⌕ Search

Biomedical subjects

G Mohn

Publications and source records attributed to G Mohn.

At least 37 records · Page 2Linked to original sources
PubMed1983

Visual discrimination learning under conditions of interocular conflict in hooded and albino rats.

Hooded and albino rats were trained on a paradigm of interocular conflict, in which the animals were trained on a discrimination of vertically inverted triangles with one eye, and on the reversed discrimination with the other eye on alternate days. Albino rats acquired the conflicting tasks as quickly as a single monocularly trained task. Hooded rats required considerably longer training on the conflicting discriminations. The role of some non-visual behavioral strategies in the performance of the conflicting tasks was explored, and possible mechanisms are discussed with reference to the different size of the ipsilateral optic projection in hooded and albino rats.

Animals↗
PubMed1983

Preferential looking acuity in preterm infants.

Acuity was measured in 48 prematurely born infants using the preferential looking technique. These quantitative results show that acuity development in these infants is related to conceptional rather than postnatal age, in agreement with the qualitative findings of previous studies. Severe intraventricular haemorrhage was accompanied by low visual acuity in two infants.

Cerebral Hemorrhage↗
PubMed1983

Optokinetic and spontaneous nystagmus in children with neurological disorders.

Binocular and monocular optokinetic nystagmus (OKN) was examined with EOG recordings in 26 visually impaired children with neurological disorders, aged 2.5 months to 15 years. Spontaneous and/or latent nystagmus, complicating the assessment of OKN, was seen in 73% of the children. Binocular OKN in 21 patients with positive visual functions was symmetrical in 5 cases, asymmetrical in 12 cases and could not be elicited in 4 patients. Monocular OKN was nearly always asymmetrical, with usually a superiority of the temporal-to-nasal (TN) components. Five blind children, 4 of them cortically blind, showed positive binocular and monocular OKN, suggesting that neural control of OKN in humans may be at least partly independent of the cortex. This, together with results from some of the sighted patients, indicates that in humans, cortical and subcortical contributions to OKN, and particularly to monocular nasal-to-temporal (NT) OKN, may be more complicated than had been thought.

Adolescent↗
PubMed1983

Behavioural and electrophysiological measures of visual functions in children with neurological disorders.

The preferential looking (PL) technique, pattern visual evoked potentials (VEPs) and (simple) tests for visual field size were used to assess visual functions in 37 children with neurological disorders, ranging in age from 10 weeks to 15 years. PL acuities were obtained for 23 out of 32 patients tested (70%). Acuity was nearly always lower than normal, which often, but not always, was related to ophthalmological or neurological defects. Pattern VEPs were recorded in 7 patients. In 3 out of 4 patients, VEP 'acuity' was much lower than PL acuity, possibly due to spontaneous eye movements. One of two cortically blind children had positive pattern VEPs. Visual field defects were seen in 21 out of 23 children tested with a simple method using a pair of white balls. In only one-third of these, the field defects could have been predicted by the neurological and/or ophthalmological conditions. In several cases, field size appeared to be affected by spontaneous and/or latent nystagmus. A simplified perimeter has been found very useful with children from the age of 4 years onwards.

Adolescent↗
PubMed1982

Mutagenic activity of 2-(2',4'-diaminophenoxy)ethanol in strains TA1538 and TA98 of Salmonella typhimurium.

The mutagenicity of 2-(2',4'-diaminophenoxy)ethanol (2,4-DAPE) was compared with that of 2,4-diaminoanisole (2,4-DAA), a chemically related compound previously used in hair-dye formulations. Both chemicals were tested in standard procedures with the Salmonella/microsome mutagenicity test as described by Ames and colleagues. In several experiments, which extended over a total period of 2 years, 2,4-DAA exhibited definite, but variable mutagenicity toward strain TA1538 when S9 preparations of rat liver induced with Aroclor 1254 were present in the incubation mixtures. The compound 2,4-DAPE did not exhibit detectable mutagenic activity when tested concomitantly under the same experimental conditions. We conclude that 2,4-DAPE is not mutagenic for Salmonella under conditions of the standard mammalian microsome assay with strain TA1538 and TA98 as indicators.

Animals↗
PubMed1982

Mutagenic activity of three isomeric N-nitroso-N-methylaminopyridines towards Escherichia coli K-12 in in vitro and animal-mediated assays.

Three isomeric nitrosomethylaminopyridines (2-NMPY, 3-NMPY, and 4-NMPY), of which only the 2-isomer exerts significant carcinogenic activity in rats, were tested in vitro and in the host-mediated assay for their activity to induce gene mutations in E. coli K-12 strain 343/113. Two related carcinogenic nitrosamines were also tested, namely, nitrosodimethylamine (NDMA) and nitrosomethylaniline (NMA). The in vitro mutagenicity tests were performed either without or in the presence of various fractions (S-9, microsomes, S-100) of rodent liver homogenates. The in vivo mutagenicity was determined in host-mediated assays, in which the indicator E. coli cells were recovered for the liver of treated animals. In experiments involving the S-9 liver fraction, only 2-NMPY among the nitrosomethylaminopyridines exerted a slight mutagenic effect. The low mutagenicity of this isomer, and the non-mutagenicity of the remaining 3- and 4-isomer could be partly explained in experiments involving microsomes and the S-100 fraction of rodent liver: 2-NMPY and 4-NMPY were activated to mutagenic factors by microsomes, but their mutagenic effect was completely abolished when S-100 was added. 3-NMPY, on the other hand, was directly mutagenic for E. coli but, again, its mutagenic potential was abolished when S-100 liver fraction was added to the incubation mixtures. NDMA was activated to mutagenic factors with both microsomes and S-9 fractions, whereas NMA could not be shown as mutagenically active under any of the present experimental conditions. It could be shown that the deactivating effect of the S-100 fraction was of nonenzymatic nature, and probably was due to the presence of thiol-containing "scavenger" molecules in this fraction. In the host-mediated assays, only the 2-isomer among the three exerted a mutagenic affect. The present results indicate that the three isomers investigated here are mutagenic either directly (3-NMPY) or upon microsomal activation (2-NMPY and 4-NMPY). The non-carcinogenicity of 3-NMPY and 4-NMPY, and the non-mutagenicity of these compounds in host-mediated assays, is probably the result of very efficient deactivation by cytosolic (thiol-group-containing?)factors.

Albumins↗
PubMed1982

[Functional eye testing in the mentally retarded].

Simple clinical testing procedures, devised by Sheridan, to test visual functions in young and/or handicapped children are discussed. Using these methods, combined with experience obtained in studying visuo-motor behaviour in cats, vision was tested in 30 severely mentally handicapped children. For 17 of these, it was unclear whether they possessed any usable visual functions. For 29 out of the 30 tested children it was possible to reach a reasonably confident conclusion regarding presence or absence of functional vision. Thirteen patients appeared to be functionally blind. In 17 children the size of the visual field could be determined; 7 showed normal, 10 restricted visual fields. In 6 children acuity could be measured. The importance of early detection of visual defects is discussed.

Child↗
PubMed1981

The role of the corpus callosum and some subcortical commissures in interocular transfer in the hooded rat.

The effect of sectioning the corpus callosum on interocular transfer of a brightness and a horizontal/vertical discrimination was examined in hooded rats. Lesions of the posterior portion of the callosum usually led to moderate transfer deficits, but considerable individual variation was found. Lesions involving only the anterior part of the callosum had little effect on transfer. This suggests a functional localisation in the corpus callosum of the rat similar to that seen in higher mammals. Section of the posterior and tectal commissures and the thalamic massa intermedia in addition to the callosum had no greater effect on transfer thatn callosal section alone. It is therefore unlikely that these structures play a crucial role in interocular transfer in the rat.

Animals↗
PubMed1981

Comparison of the mutagenic activity of dialkylnitrosamines in animal-mediated and in vitro assays using an Escherichia coli indicator.

An intrasanguineous host-mediated assay was used to establish the mutagenic potential of a series of dialkylnitrosamines to E. coli K12/343/113 in the liver and spleen of mice. For calibrating purposes, dose- and time-dependent kinetics of mutation induction by the model compound diethylnitrosamine in this assay was determined. Comparison with the results of the same compound in vitro reveals that activation in the intact liver of living mice is more efficient and proceeds for a longer period of time than during incubation in the presence of a liver homogenate. The mutagenicity of five other dialkylnitrosamines (dimethyl-, diethanol-, diisopropyl-, methylethyl-, and methyl-n-propylnitrosamine) was also determined. The results of host-mediated assays in livers and spleens of mice indicate a good correlation with the carcinogenic properties of these compounds as far as the effect on the liver is concerned. The mutagenic activity in vitro shows, however, a poor correlation with carcinogenicity data, mainly because some of the carcinogenicity data, mainly because some of the carcinogenic nitrosamines are not detectable in those tests. It is concluded that, under the present experimental conditions, intrasanguineous host-mediated assays are more sensitive and more representative of the carcinogenic activity of dialkylnitrosamines than in vitro assays using S-9 liver fractions.

Animals↗
PubMed1981

Effects of Syphacia muris and the anthelmintic fenbendazole on the microsomal monooxygenase system in mouse liver.

Mice given food containing fenbendazole to prevent a reinfection with Syphacia muris were treated with inducers of the hepatic microsomal monooxygenase system. Specific induction values and factors were the same as found previously in similar mice infected with Syphacia muris. There was a decrease in the total hepatic monooxygenase system by 20-40%, associated with a similar decrease in the total microsomal protein. As this was found in both experimental and control mice, the induction factors of the total values remained also unaltered. Thus infection by Syphacia muris not only retarded the growth of young mice but also accelerated the development of their hepatic monooxygenase system.

Animals↗
PubMed1980

Interocular transfer of two visual discriminations in hooded and albino rats.

Interocular transfer of a brightness and a pattern discrimination was compared in hooded and albino rats. Equally high levels of transfer were found in the two strains, and there was no difference in transfer between the two discriminations. The results indicate that interocular transfer in the rat does not necessarily depend on the uncrossed optic fibres, and that the commissures of the rat's brain are capable of efficient transfer.

Animals↗
PubMed1980

The inactivation of hexobarbital induced preferably by cyclohexane inhalation.

Female mice inhaled 2X10(-4) mol/l cyclohexane for 0.5--3 days. No change was seen after 0.5 days in the hexobarbital (HB) sleeping time and in its half-life in blood plasma. However, after 1 day there was a decrease by 50 and 60%, respectively. The steep increase in HB-inactivation between 0.5 and 1 day was seen at least 12 h before the main increase in ethylumbeliferone dealkylase and NADPH-P-450 reductase activity and in the cytochromes P-450 and b5 per liver. It could be prevented by actinomycin D and diminished to 25% by cycloheximide. Remarkably after 3 days of CH-inhalation, no more than 65--68% decrease of sleeping time and plasma half-life had been reached. It is concluded that the inactivation of HB is preferably induced compared to the dealkylase. However, it seems to come to a steady state during the main increase of dealkylase, reductase and cytochromes.

Animals↗
PubMed1975

Mutagenic activity of cyclophosphamide, ifosfamide, and trofosfamide in different genes of escherichia coli and salmonella typhimurium after biotransformation through extracts of rodent liver.

Experiments are performed to compare the mutagenic properties of the three phosphamide esters of nitrogen mustard, cyclophosphamide (CP), ifosfamide (IF), and trofosfamide (TF), in different bacterial systems. The systems include forward mutations leading to resistance against 5-methyltryptophan (MTR) and from galR-s18 to gal-+ in Escherichia coli 343/113, back mutations from arg56 to arg-+ in Escherichia coli 343/113 and back mutations from hisG46 to his-+ in Salmonella typhimurium TA1535. CP, IF, and TF are not mutagenic per se. After biotransformation through isolated rodent liver homogenates (S-9 fraction) all three compounds exhibit mutagenic activity in the order CP smaller than IF smaller than TF. Specific activating potential of mouse liver extracts is higher than that of rat liver. Except for back mutations in S. typhimurium TA1535, all mutation systems tested show a similar pattern of induction after treatment with CP, IF, and TF. However, because gal-+ mutations are not induced by CP under conditions where arg-+ and MTR are induced, it is suggested that more than one mutational system be used in routine mutagenicity testing.

Animals↗