No description available.

No description available.

No description available.

No description available.

No description available.

Some of the parameters of the process of chemical neuro- transmission at the locust excitatory neuromuscular synapse have been investigated. This has involved the application of two distinct procedures for purifying membrane proteins which exhibit pharmacological properties consistent with a neuroreceptor function. The first technique used chloroform/methanol mixtures to extract protein/lipid complexes (proteolipids) from the muscle. The second procedure adapted conventional subcellular fractionation techniques to yield a membrane fraction in an aqueous environment. Distinct high and low affinity binding sites for L-glutamate were detected in preparations obtained using both techniques. The chloroform/methanol extract was resolved by a chromatographic procedure and was shown to contain proteolipids which bound L-glutamate with high affinity (Kd = 8 muM) and low affinity (Kd = 50 muM) respectively. Competition studies with the high affinity site showed that binding of L-glutamate could be inhibited by L-aspartate and 2-amino-4-phosphonobutyric acid, whilst D-glutamate was without effect. The proteolipids which bound L-glutamate were further characterised by analysis of their associated phospholipids and unesterified fatty acids. The aqueous membrane preparation exhibited two L-glutamate- binding populations which could be defined by their sensitivities to sodium ions - a sodium-ion insensitive high affinity site (Kd = 0.53 muM) and a sodium-ion sensitive low affinity site (Kd = 21.6 muM). Binding of L-glutamate to the low affinity site was susceptible to freezing, sonicating and osmotically-shocking the membrane preparation. Binding of L-glutamate to the high affinity site was unaffected by such treatments. Competition studies indicated that only chlorpromazine, L-glutamyl-beta-hydroxamate and ouabain inhibited binding of L-glutamate at the low affinity site. These ligands were without effect at the high affinity site, where a wide range of ligands inhibited binding of L-glutamate, Kainie acid, quisqualic acid, hrmine hydrochloride and D,L-2-amino-4-phosphonobutyric acid were particularly potent inhibitors. L-aspartate was a potent inhibitor of binding of L-glutamate to both sites. It is concluded that the high affinity sites of both preparations are representative of neuroreceptor proteins for L-glutamate and as such supplement the larger body of electrophysiological evidence that supports the suggestion that transmission at the locust excitatory synapse is mediated by the amino acid. It is suggested that the low affinity sites represent uptake sites. They may function to remove neurally-released transmitter (L-glutamate) from the region of the synapse.

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No description available.

No description available.

For active tasks we have to appropriately allocate our gaze spatially and temporally so that we are fixating informative areas when the crucial information is available. We know that vision supports action, and several fundamental elements of how this is so have been established, for example that the eye leads the hand during action. What we do not know is whether the spatiotemporal allocation of gaze is consistent regardless of the task, the objects and the level of familiarity we have with the environment. In Chapter 3 we found that visual behaviour changes as a result of the task being undertaken, with more looks to task irrelevant objects, longer eye-hand latencies and more visually guided putdowns of objects made for tea making rather than sandwich making. Analysis revealed that the objects used in the two different tasks did affect eye-hand latencies. In Chapter 4 this issue was explored further and it was found that the properties of objects (glasses) such as glass type (where height may be the important factor) influenced visual guidance if the glass was empty during the set down, but that level of liquid contained, and the material it was made from impacted the likelihood of using visual guidance for a second putdown of the same glass. These results indicate flexibility in terms of the allocation of visual guidance depending on our knowledge of the object properties, and suggest that risk may be an important factor in this. The effect of familiarity with an environment was looked at in three ways. First in Chapter 5 we compared people making tea in familiar environments (their own kitchens) and in novel environments (their experimental partners kitchen). Second we explored the acquisition of familiarity by having participants perform a task in the same environment for 10 consecutive days (Chapter 6) and finally we investigated what information was encoded incidentally by having the participants from Chapter 6 perform a new task in the same environment for two subsequent days. We found that people were faster to complete the same task in a familiar environment than a novel one but that it was not just that search was facilitated and thus shorter, visual behaviours such as visual exploration and looks to task irrelevant objects were fewer when in familiar environments and several elements of the Object Related Action (ORA) also reduced in a temporal nature. We found that during the acquisition of familiarity people encoded information about the layout of objects in the scene which facilitated search in Chapter 7 but there appeared to be no such effect on the ORA, suggesting that object specific information for task irrelevant objects is not incidentally encoded. The findings of this thesis suggest that spatiotemporal allocation of gaze in natural tasks depends on the context of the environment, the properties of objects and our level of prior knowledge.