Landmark learning and visuo-spatial memories in gerbils.

The aim of this study is to understand what a rodent (Meriones unguiculatus) learns about the geometrical relations between a goal and nearby visual landmarks and how it uses this information to reach a goal. Gerbils were trained to find sunflower seeds on the floor of a light-tight, black painted room illuminated by a single light bulb hung from the ceiling. The position of the seed on the floor was specified by an array of one or more landmarks. Once training was complete, we recorded where the gerbils searched when landmarks were present but the seed was absent. In such tests, gerbils were confronted either with the array of landmarks to which they were accustomed or with a transformation of this array. Animals searched in the appropriate spot when trained to find seeds placed in a constant direction and at a constant distance from a single cylindrical landmark. Since gerbils look in one spot and not in a circle centred on the landmark, the direction between landmark and goal must be supplied by cues external to the landmark array. Distance, on the other hand, must be measured with respect to the landmark. Tests in which the size of the landmark was altered from that used in training suggest that distance is not learned solely in terms of the apparent size of the landmark as seen from the goal. Gerbils can still reach a goal defined by an array of landmarks when the room light is extinguished during their approach. This ability implies that they have already planned a trajectory to the goal before the room is darkened. In order to compute such a trajectory, their internal representation of landmarks and goal needs to contain information about the distances and bearings between landmarks and goal. For planning trajectories, each landmark of an array can be used separately from the others. Gerbils trained to a goal specified by an array of several landmarks were tested with one or more of the landmarks removed or with the array expanded. They then searched as though they had computed an independent trajectory for each landmark. For instance, gerbils trained with an array of two landmarks were tested with the distance between two landmarks doubled. The animals then searched for seeds in two positions, which were at the correct distance and in the right direction from each landmark.(ABSTRACT TRUNCATED AT 400 WORDS)

Strong metal-oxygen interaction in uracils. X-ray crystal structure of bis-(1,3-dimethyluracil)dichlorocopper(II).

An X-ray structure determination showed that in the compound bis-(1,3-dimethyluracil)-dichlorocopper(II) the uracil moiety is strongly bonded to the metal via the O(4) atom. Changes in the i.r. spectra on metal binding are discussed. Details of the structural parameters have been deposited as Supplementary Publications SUP 50091 (3 pages) at the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1978) 169, 5.

X-ray structure of a compound of cobalt with uridine 5'-monophosphate. Evidence for metal-phosphate bonding only.

An X-ray study of the crystal structure of a cobalt(II) complex with uridine 5'-monophosphate shows it to contain polymeric chains of composition [Co2(H2O)4 (5'-UMP)2]n. The cobalt atoms do not bind to the pyrimidine base moiety; instead each metal atom is octahedrally coordinated to four phosphate groups and two water molecules. Managanese(II) forms a similar compound.