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Biomedical subjects

G Horn

Publications and source records attributed to G Horn.

At least 127 records · Page 7Linked to original sources
PubMed1982

Differential effects of exposure to an imprinting stimulus on 'spontaneous' neuronal activity in two regions of the chick brain.

Young chicks were placed in running wheels and exposed for a total of 3 h to an imprinting stimulus: a rotating flashing red light. Revolutions made towards the stimulus minus revolutions made away from it were totalled and are referred to as approach counts. After exposure, chicks were anaesthetized and two vertical electrode penetrations were made, one through the visual projection area, hyperstriatum accessorium (HA), and one through the intermediate and medial part of hyperstriatum ventrale (IMHV), a region which has been implicated in the imprinting process. 'Spontaneous' impulse activity was recorded from neurones in these areas. In some of the chicks, after penetrating through HA, discharges evoked by diffuse retinal illumination were monitored and the zona hyperstriatum intercalatus/hyperstriatum dorsale (HI/HD) below HA was classified as being a visually responsive lamina (VRL) if responses were obtained to greater than or equal to 20 consecutive light flashes. In HA there was a positive correlation between spontaneous activity and approach counts in those chicks with a VRL; there was no significant correlation in those chicks without a VRL. In contrast, for IMHV the correlation between spontaneous activity and approach counts was negative and appeared to be independent of the presence or absence of a VRL.

Action Potentials↗
PubMed1982

A comparison between transient amnesias induced by two drugs (diazepam or lorazepam) and amnesia of organic origin.

The transient amnesias produced by drugs may have much in common with the more permanent amnesias associated with organic brain damage. This possibility was investigated using two benzodiazepines, diazepam and lorazepam, with medical student volunteers. In Experiment 1, 27 subjects received a 2ml intravenous injection of either diazepam (7.5 mg) or of lorazepam (3.0 mg) or of normal saline. In Experiment 2, a further 13 subjects were given lorazepam (2.5 mg) or saline. A double blind procedure was used. Neither drug had an appreciable effect on span-type short-term memory (except with 2-channel presentation). Both drugs produced severe anterograde amnesia in other forms of memory test: the amnesic effect of lorazepam lasted for several hours. This amnesia was not attributable to failures of perception. Lorazepam appeared to affect recognition even more than recall. In a test with lorazepam no evidence was obtained that the drug increases susceptibility to proactive interference. With both drugs, recall and recognition were unimpaired of material presented about 10 min before the injection; this shows that the drugs did not affect retrieval mechanisms.

Adult↗
PubMed1982

Electrochemical reduction pathways of anthracycline antibiotics.

The preparative electrochemical reduction of a series of anthracycline antibiotics was performed using the technique of large scale electrolysis and d. c. polarography for recording different reaction pathways. The reduction products were identified by mass spectrometric and chromatographic analyses. Only anthracyclines with sugar residues in the C-10 position chromatographic analyses. Only anthracyclines with sugar residues in the C-10 position (iremycin, roseorubicin A) were reduced reversibly by 2e- to the corresponding hydroquinones. All others with sugar residues in the C-7 position (daunomycin, 5-iminodaunomycin, adriamycin, carminomycin, beta-rhodomycin II, aclacinomycin A, 1-deoxypyrromycin) showed an irreversible behavior because of the reductive splitting of the glycosidic bond after formation of 7-deoxy compounds or -- if the C-11 OH-group was not present -- of dimers, respectively.

Anti-Bacterial Agents↗
PubMed1981

Neural mechanisms of learning: an analysis of imprinting in the domestic chick.

Learning is a complex set of processes involving the acquisition and storage of information. Imprinting in the domestic chick was studied to analyse the neural basis of storage. The recently hatched chick learns the characteristics of a visually conspicuous object by being exposed to it. When a chick is trained in this way, biochemical changes can be detected in the dorsal part of the forebrain. Through a series of experiments it was shown that these changes are unlikely to be non-specific consequences of training, but more probably reflect some aspect of the storage process. By using a radioautographic technique to localize the brain region more precisely, part of the hyperstriatum ventrale was implicated in this process. Bilateral destruction of the region before imprinting prevented acquisition, and bilateral destruction after imprinting impaired retention. After exposure for 140 min to an imprinting stimulus there was an increase in the area of contact between presynaptic and postsynaptic elements in the region. This effect was found on the left side only. Sequential lesions to left and right sides confirmed that there is a hemispheric asymmetry in the role of the region in the storage of information. The area receives input from the visual pathways and possibly from other sensory pathways, and projects to regions that are thought to be involved in the control of locomotor and viscero-endocrine functions. The results afford an opportunity for the further analysis both of storage and of the whole set of neural processes that underlie imprinting in the domestic chick.U

Age Factors↗
PubMed1981

Effects of restricted lesions of the chick forebrain on the acquisition of filial preferences during imprinting.

The effects of placing bilateral lesions in that part of the chick brain (IMHV) which was previously been implicated in imprinting, was studied in young domestic chicks. Twenty-four dark-reared chicks were matched in pairs on the basis of their approach activity during a 30 min period of exposure to one of two visual imprinting stimuli. Both members of the chick pair were then anaesthetized and bilateral lesions were made by radio-frequency coagulation in the IMHV of one chick; the other chick served as a sham-operated control. On the following day each chick was exposed for 2.5 h to the imprinting stimulus to which it had previously been exposed. After training, the preferences of all chicks were measured by comparing their approach to the training stimulus with that to the second stimulus. Sham-operated chicks showed a strong preference for the training stimulus; lesioned chicks showed none. Subsequently the latency of each chick to approach and accurately peck a shiny rod was measured. The two groups of chicks did not differ significantly in this test of visuomotor coordination. The area of tissue damaged by the lesion was reconstructed: IMHV was severely damaged with relatively little damage to other areas of the brain.

Animals↗
PubMed1981

Imprinting. An electron microscopic study of chick hyperstriatum ventrale.

Fourteen chicks were hatched and reared in darkness to approximately equal to 21 h when they were exposed to overhead illumination for 0.5 h and then to an imprinting stimulus (a pulsing red light) for 20 min. The chicks were then matched in pairs on the basis of their activity. One member of each pair was returned to the dark and the other was trained for a further 120 min. All chicks were killed approximately equal to 6.5 h after the onset of training and perfused with fixative. Blocks were removed bilaterally from a restricted part of the hyperstriatum ventrale and prepared for electron-microscopy. Various synaptic features were measured, all counts being performed 'blind'. In undertrained chicks the length of the synaptic apposition zone in this part of the left hemisphere was shorter than that in the right by a mean value of 35 +/- 11.4 (SEM) nm. Further training eliminated this difference. No other synaptic measurements were affected by prolonging the period of training.

Animals↗
PubMed1981

Imprinting. A study of cholinergic receptor sites in parts of the chick brain.

The distribution of cholinergic receptor binding sites was studied in certain areas of the chick brain, especially that part (IMHV) of hyperstriatum ventrale which has previously been implicated in the imprinting process. There was relatively little binding of [125I]-alpha-bungarotoxin in this region, as shown using an autoradiographic technique. In contrast muscarinic receptor sites, with an affinity for [3H]-quinuclidinyl benzilate (QNB), are present in relatively high concentration in a medial forebrain sample containing IMHV and also in a visual projection area, the hyperstriatum accessorium (HA). To assess the effects of imprinting on the concentration of QNB binding sites 26 young chicks were exposed to an imprinting stimulus (a pulsing red light) for 20 min. Thirteen of the chicks were returned to the dark and the other 13 were trained for a further 100 min. There was no effect of further training on specific QNB binding in HA or in the medial forebrain sample. In undertrained chicks there was a positive correlation between QNB binding in the medial forebrain sample of the left hemisphere and that in the right; there was no such relationship in overtrained birds. Mean QNB binding in the right medial forebrain sample was greater than in the left by 21%. There was no such hemispheric asymmetry in HA.

Animals↗
PubMed1981

[On the local efficacy of ciclopiroxolamine in onychomycoses (author's transl)].

An open, multicenter clinical trial of 6-cyclohexyl-1-hydroxy-4-methyl-2(1H)-pyridone, 2-aminoethanol salt (ciclopiroxolamine, Cic, Hoe 296, Batrafen) was performed in 150 patients with 246 nails afflicted by mycotic infection. Dermatophytes were observed in 96% of the initial cultures. A combination of 1% Cic solution and cream was applied, and a very strict nail toilet was performed. The mean duration of study was 12.7 +/- 5.6 weeks, followed by a 6 week follow-up period on the average. The share of pathologically changed nails of 35 +/- 16% was reduced to 8 +/- 10% of nail plate. In a total of 96% of patients, some of whom had only been treated for a brief period, a measurable improvement was observed, and 57% of the patients were free from signs of infection. Signs of intolerance or definite relapses were not observed.

Adolescent↗
PubMed1980

[Value of dietetics and general nutritional guidelines in the metaphylaxis of urinary calculi].

After a short historical survey the interest of our Socialist state in an optimum nutrition and nutritional education of the citizens is described. The importance of prophylaxis, therapy and metaphylaxis of urolithiasis is proved by the increasing morbidity rate of this disease (1-3%). Out of the series of vitamins above all the vitamin B6 is of importance in the oxalate lithiasis so that a diet rich in vitamin B6 is indicated. Of the quantity elements contained in nutrition calcium, phosphorus and magnesium are significant, wherefore the enteral supply of these elements is to be taken into consideration in the various kinds of urinary calculi. Furthermore, in carriers of calcium oxalate calculi nutrients rich in oxalic acid and in carriers of urinary calculi and in hyperuricaemia, respectively, nutrients rich in purine should be restricted. Adequate tables concerning the vitamin B6, Ca, P, Mg, oxalic acid and purine content of the nutrients are given. The increasing importance of the adiposity of carriers of uroliths is represented with the help of indices of our own urolith dispensary. Finally short references to diet for the 4 most important kinds of uroliths are proposed.

Diet↗
PubMed1979

An autoradiographic study of the chick brain after imprinting.

On the first day after hatching domestic chicks were exposed to an imprinting stimulus, a horizontal yellow slit of light moving upwards in a window and presented at a rate of 4 slits/sec. Chicks were exposed for either 45 min (undertrained) or 180 min (overtrained) on the first day of hatching (60 or 240 min in the case of 1 pair). On the second day all birds were exposed for a further 63 min. Twenty birds were matched in pairs and each chick received 1.1 muCi [14C]uracil/g body weight injected into the heart region before exposure on day 2. At 150 min after the injection the chicks were decapitated and serial coronal sections of their brains cut; alternate pairs of sections were prepared for autoradiography. The optical density for a number of major anatomical regions was measured. The measurements for each region were averaged over congruent to 0.6 mm 'slabs' of brain and expressed as a percentage of the mean of all measurements for that brain. Standardized mean optical density was significantly greater in undertrained chicks than in overtrained chicks in a part of the medial region of hyperstriatum ventrale (MHV) which extended across two adjacent slabs. The slabs were slightly posterior to the mid-point between anterior and posterior poles of the brain. In the next two, adjacent, anterior slabs the variances for MHV were significantly greater in undertrained chicks than in overtrained chicks. There were no other significant differences between brain regions. Taken together with previous studies these results suggest that the intermediate and medial part of hyperstriatum ventrale is intimately linked with the imprinting process.

Animals↗
PubMed1979

Effects of rhythmic hyperstriatal stimulation on chicks' preferences for visual flicker.

Chicks' preferences for the frequency of a flashing light can be modified by electrically stimulating the medial part of the hyperstriatum ventrale with trains of shocks at that frequency. Chicks stimulated with 1.5 pulse trains s-1 preferred a light flashing at 1.5 s-1 and chicks stimulated at 4.5 trains s-1 preferred a light flashing at 4.5 s-1. Three behavioural measures taken during the preference test, namely measures of movement, latency to approach and distress calls were not significantly influenced by the frequency of brain stimulation.

Animals↗