Appetite changes under free-living conditions during Ramadan fasting.

During the fasting month of Ramadan, Muslims abstain from food and drink from sunrise until sunset. This change of eating pattern provides an opportunity to investigate factors controlling hunger and thirst. A group of healthy Muslims (15 men and 26 women) living in Reading, U.K. made hourly ratings of their hunger, mood and thirst, and recorded their food and drink intake on specified days before, during and after Ramadan between January and March 1996. There were no significant changes in body weight over Ramadan. Rated hunger increased substantially during the daily fast, and hunger was higher for the women than the men during the earlier days of Ramadan, whereas later, on average, fasting levels of hunger were very similar for both sexes (significant gender x day interaction,p<0. 001). During Ramadan, the men tended to spend much of their time away from home, and may therefore have largely avoided eating-related cues during the daily fast. The women, however, were frequently involved in preparing food to be eaten later after sunset, which suggests an explanation for the results based on the external cue control of hunger. That is, unreinforced exposure to food cues in this context may have led to a decrease in the capacity of these cues to stimulate hunger.

Food choice and intake: towards a unifying framework of learning and feeding motivation.

The food choice and intake of animals (including humans) has typically been studied using frameworks of learning and feeding motivation. When used in isolation such frameworks could be criticized because learning paradigms give little consideration to how new food items are included or excluded from an individual's diet, and motivational paradigms do not explain how individuals decide which food to eat when given a choice. Consequently we are posed with the question of whether individuals actively interact with the food items present in their environment to learn about their nutritional properties? The thesis of this review is that individuals are motivated to actively sample food items in order to assess whether they are nutritionally beneficial or harmful. We offer a unifying framework, centred upon the concept of exploratory motivation, which is a synthesis of learning and paradigms of feeding motivation. In this framework information gathering occurs on two levels through exploratory behaviour: (i) the discrimination of food from nonfood items, and (ii) the continued monitoring and storage of information concerning the nutritional properties of these food items. We expect that this framework will advance our understanding of the behavioural control of nutrient intake by explaining how new food items are identified in the environment, and how individuals are able to monitor changes in the nutritional content of their food resource.

Does the study of feeding behaviour benefit from a teleonomic framework?

In this paper we respond to the criticisms of Provenza et al. (1998) that our framework of learning and feeding motivation (Day et al. 1998) resorts to higher order goals, which cannot be falsified by experimentation. We assert that in order to be able to predict the feeding behaviour of animals we first need to understand what they are trying to achieve (i.e. invoke teleonomy). We then detail our framework in such terms that one could envisage experiments that could quantitatively test its predictions. We contend that the framework of 'the self-organization of behaviour' proposed by Provenza et al. (1998) cannot lead to such quantitative predictions, since it is invoked to describe feeding behaviour of animals a posteriori. It is our own desire, by contrast, to assess feeding behaviour a priori, which leads us to propose and defend our framework of learning and feeding motivation.

Tissue culture of retinal glial cells.

In order to be able to investigate the properties and characteristics of glia in the retina, a monotypic culture of retinal glial cells is likely to be an important research vehicle. Several techniques are now available to produce cultures of glial cells from the retina. These methods generally result in cultures of Mueller cells rather than retinal astrocytes. Publications on glial cultures involved complex procedures for the isolation of the target cell. Recent developments have resulted in simpler procedures with the advantage that large numbers of cultures can be established quickly and easily. Glial cultures have already been used in a variety of studies, simpler methods of culture, particularly if these can be adapted for culture of human glial cells, will probably result in more extensive use of cultures to unravel the properties of retinal glia.

The morphological features of bovine meshwork cells in vitro and their synthetic activities.

The morphological characteristics of 3rd-passage cultured bovine meshwork cells were investigated, as were some of their synthetic activities. Growing meshwork cells had the ultrastructural characteristics of metabolically active cells whereas postconfluent cells formed gap junctions at their lateral borders and were closer in their fine structure to meshwork cells in vivo. The incorporation of 3H proline and 3H glucosamine was significantly greater in growing than postconfluent cultures. The normal bovine outflow system was rich in type I collagen but type V collagen and fibronectin was also evident. The 3rd-passage cells were shown to synthesize type I collagen, type V collagen and fibronectin. However, ultrastructural studies of the extracellular matrix which was produced in vitro demonstrated the presence of small fibrils with no distinctive banding pattern, unlike the larger collagen fibrils with a 640 A banding pattern seen in vivo.