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Biomedical subjects

J Atkinson

Publications and source records attributed to J Atkinson.

At least 109 records · Page 6Linked to original sources
PubMed1977

The cardiovascular effects of caffeine in various forms.

We have investigated the influence of various procedures which alter the solubility of caffeine on its physiological effects. Pretreatment of caffeine prior to injection by a) addition of sodium salicylate or sodium benzoate, b) increase in temperature or c) preliminary dissolution in hydrochloric acid, did not change the cardiovascular effects when injected i.v. at equivalent doses in urethane-anaesthetized rats. Addition of chlorogenic acid, a molecule found in coffee and other plants and reported to modify, by complexation, the physiological effects of caffeine, had no significant effect on the depressor responses to caffeine but did diminish caffeine-induced tachycardia at high doses of caffeine (10 and 30 mg/kg i.v.).

Animals↗
PubMed1976

[The effect of coffee and coffee components on the stomach muscle].

The isolated stomach muscle strip preparation works well when given pure compounds which are stable and non-toxic. When complex test mixtures such as coffee are used, however, the results are more difficult to interpret. This is probably due to non-specific effects of such mixtures, e.g. induction of changes in organ bath pH, etc. In spite of the above remark, differences in the effects of decaffeinated and normal instant coffees were clearly seen. The so-called "wholesome" coffees gave results identical to those obtained with normal instant coffee. In general, coffee induced muscle contraction followed by relaxation. Choline (possibly together with potassium) would appear to be responsible for the contractions observed, and caffeine for the relaxation.

Animals↗
PubMed1976

Steroscopic discrimination in infants.

The ability to make discrimiations of binocular disparity was investigated in 2-month-old infnats by two methods: (a)fixation preference between patterns differing in the disparity they contained, and (b)recovery from habituation of high-amplitude sucking when there was a change in disparity in the visual reinforcer. The stimuli were random-dot steregrams. The results for both mthods indicated that at least some infants of this age could perform steroscopic discriminations and that both techniques were feasible for development for longitudinal studies of steroscopic vision.

Depth Perception↗
PubMed1976

The magic number 4 +/- 0: a new look at visual numerosity judgements.

Visual numerosity judgements were made for tachistoscopically presented linear arrays of dots or lines. The interelement interval (which could be specified in spatial frequency terms) was constant for a given array but varied across conditions. A clear limit in the accuracy of numerosity judgements was found to be set at 4 for regularly spaced elements with spatial frequencies below approximately 10 cycles/deg (element and interelement interval of 0-05 deg). This limit in terms of accuracy is accompanied by a fast and almost constant response time for arrays of 4 or less, compared to response times for arrays of more than 4 elements. The limit in accuracy falls to 2 elements rather than 4 for spacing narrower than 0-05 deg alghough with such spacing the elements are still easily resolved. The limit of 4 is found if the stimulus is a bright afterimage, lasting for approximately 60 s. This result suggests that the limit is independent of the time allowed for a single fixation and is a perceptual limit rather than a limit in some memory buffer. 'Numerosity' units are propsoed to account for the results.

Humans↗
PubMed1976

The dependence of the visual numerosity limit on orientation, colour, and grouping in the stimulus.

Visual numerosity judgements were made for tachistoscopically presented arrays of dots. The arrangement within the arrays was either linear or such that dots could be easily perceptually subdivided into two groups. Subdivision was either in terms of an orientation difference, a colour difference, or a spacing difference in the centre of the array. For a large difference in orientation between the two 'arms' of the array (90 degrees), or a large central space (three times the interdot interval) up to 8 dots were accurately perceived. This numerosity limit was twice that found for equivalent linear arrays, with no grouping. Although in terms of accuracy it seems that in these conditions the two groups within each array can be counted independently, there is no evidence for independent processing in terms of response times. From the results of a subsidiary experiment it seems likely that the slow response times in the subgrouping conditions are due to the necessity of processes other than counting (such as judgements of symmetry). For arrays where subgrouping was in teems of a colour difference, or an orientation difference of between approximately 45 degrees and 90 degrees, or a small central space of twice the interdot interval, there was an improvement in accuracy compared to equivalent linear arrays, but no evidence of independent processing, up to a limit of 4, in each of the subgroups. From these preliminary results, tentative proposals concerning 'numerosity' units and their properties are made.

Color↗
PubMed1976

Self-administration of caffeine by the rat.

Rats with permanently implanted right jugular vein cannulae were either pre-treated with increasing doses of caffeine for up to 98 h, or underwent no pre-treatment. Both groups were then presented with a lever, the pressing of which caused a self-injection of a caffeine solution. For both groups, some of the rats self-administered caffeine for up to 4 days and then their activity stopped; the other rats did not self-administered caffeine.

Animals↗
PubMed1975

An automatic device for the isolated rabbit heart preparation for testing cardioactive drugs.

An automatic device for the isolated rabbit heart is described. Test solutions are perfused from reservoirs via valves, the sequence and time of opening of which is controlled by a programmable unit. The perfusate was pushed through the heart at a constant flow-rate, with pressure measurement serving as an indicator of preparation stability. The system worked well giving reproducible results without tedious, repetitive manual work. The results obtained with caffeine were in line with those reported in the literature, there being a dose-dependent increase in rate and force of contraction.

Animals↗
PubMed1975

The effect of caffeine on barbiturate sleeping time and brain level.

The effect of caffeine and coffee on the sleeping time induced by barbital was tested in rats. It was found that caffeine pretreatment shortened barbital-induced sleeping time and that coffee had an effect in direct proportion to its caffeine content; decaffeinated coffee was without effect. It was hypothesized that the shortening was due to an interaction at the brain level. This hypothesis was tested using hexobarbital which is metabolized by the liver whereas barbital is only negligibly so metabolized. Pretreatment with caffeine was found to shorten the hexobarbital sleeping time even though the brain concentration of the latter was actually elevated. It was also shown that caffeine pretreatment was much less effective than phenobarbital pretreatment in stimulating the enzyme systems in the liver which metabolize hexobarbital, aminopyrine and ethylmorphine (in vitro). Consequently, it is concluded that caffeine stimulation of liver metabolism is a relatively minor factor in the shortening of barbiturate sleeping time by caffeine in comparison to the brain interaction of these two drugs.

Aminopyrine N-Demethylase↗