Spatial information enhanced by non-spatial information in hippocampal granule cells

The hippocampus organizes sequential memory composed of non-spatial information (such as objects and odors) and spatial information (places). The dentate gyrus (DG) in the hippocampus receives two types of information from the lateral and medial entorhinal cortices. Non-spatial and spatial information is delivered respectively to distal and medial dendrites (MDs) of granule cells (GCs) within the molecular layer in the DG. To investigate the role of the association of those two inputs, we measured the response characteristics of distal and MDs of a GC in a rat hippocampal slice and developed a multi-compartment GC model with dynamic synapses; this model reproduces the response characteristics of the dendrites. Upon applying random inputs or input sequences generated by a Markov process to the computational model, it was found that a high-frequency random pulse input to distal dendrites (DDs) and, separately, regular burst inputs to MDs were effective for inducing GC activation. Furthermore, when the random and theta burst inputs were simultaneously applied to the respective dendrites, the pattern discrimination for theta burst input to MDs that caused slight GC activation was enhanced in the presence of random input to DDs. These results suggest that the temporal pattern discrimination of spatial information is originally involved in a synaptic characteristic in GCs and is enhanced by non-spatial information input to DDs. Consequently, the co-activation of two separate inputs may play a crucial role in the information processing on dendrites of GCs by usefully combing each temporal sequence.     

A newly-discovered population ofColobus angolensis in East Africa

A very isolated population ofColobus angolensis has been newly discovered in Tanzania. The monkey has white, long epaulettes and cheek hair, but no white pygal band. Its tail has somewhat of a brushy tip, and is grey in color. This may very well be a heretofore undescribed, and distinct subspecies.     

Transport of 1,5-anhydro-D-glucitol into insulinoma cells by a glucose-sensitive transport system

The uptake of 1,5-anhydro-D-glucitol (1,5-AG) occurs by passive mechanisms in cells or tissues that have passive glucose transporters. It is known that serum 1,5-AG concentrations are reduced in patients with diabetes mellitus. To elucidate the metabolism of this substance and its physiological role in pancreatic β-cells, we assayed 1,5-AG transport in the insulinoma-derived cell lines, RINr and MIN6. Both cell lines showed an insulin-insensitive, concentration-dependent uptake of 1,5-AG with a saturation time of approximately 120 min, and most of the 1,5-AG in the cytoplasm was in the free form. A biphasic saturation curve was obtained using a wide range of 1,5-AG concentrations, suggesting that accumulation was mediated by a high affinity and a low affinity transporter. The high affinity transporter had a K_m of 10.4 in RINr cells and 13.0 mM in MIN6 cells, and the low affinity transporter had a K_m of 131 in RINr cells and 211 mM in MIN6 cells. Uptake of 1,5-AG was markedly inhibited by phloretin and cytochalasin B, but was only slightly affected by phloridzin. Uptake of 1,5-AG was markedly inhibited by glucose at physiological concentrations (1.0–10 mM), as well as by galactose and mannose. The 1,5-AG concentration required to inhibit 2-deoxyglucose uptake exceeded that of glucose by >100 times, being much higher than the physiological concentrations of 1,5-AG. These results indicate that the 1,5-AG carrier system in insulinoma cells is distinct from that in either the somatic cells or renal tubular cells. These findings also suggest that a unique 1,5-AG transport system is present in pancreatic β-cells.