Dark-rearing delays the loss of NMDA-receptor function in kitten visual cortex.

Some features of the visual cortex develop postnatally in mammals. For example, geniculocortical axons that initially overlap throughout cortical layer IV segregate postnatally into two sets of interleaved eye-specific bands. NMDA (N-methyl-D-aspartate) receptors are necessary for eye-specific axon-segregation in the frog tectum, and as NMDA receptors play a greater part in synaptic transmission in early life and decrease in function during the period of axon segregation, they may be involved in the segregation of geniculocortical axons: they are well placed to do so as they transduce retinally derived signals essential for segregation. Rearing animals in the dark in early life delays segregation and prolongs the critical period for plasticity. We now report that dark-rearing of kittens also delays the loss of NMDA receptor function in the visual cortex, supporting the view that they play an important part in neuronal development and plasticity.     

Mapping human visual cortex with positron emission tomography

Positron-emission tomography (PET) can localize functions of the human brain by imaging regional cerebral blood flow (CBF) during voluntary behaviour. Functional brain mapping with PET, however, has been hindered by PET's poor spatial resolution (typically greater than 1 cm). We have developed an image-analysis strategy that can map functional zones not resolved by conventional PET images. Brain areas selectively activated by a behavioural task can be isolated by subtracting a paired control-state image from the task-state image, thereby removing areas not recruited by the task. When imaged in isolation the centre of an activated area can be located very precisely. This allows subtle shifts in response locale due to changes in task to be detected readily despite poor spatial resolution. As an initial application of this strategy we mapped the retinal projection topography of human primary visual cortex. Functional zones separated by less than 3 mm (centre-to-centre) were differentiated using PET CBF images with a spatial resolution of 18 mm. This technique is not limited to a particular brain area or type of behaviour but does require that the increase in CBF produced by the task be both intense and focal.     

Recombinant antibodies possessing novel effector functions

The introduction into lymphocytes of immunoglobulin-gene DNA that has been manipulated in vitro allows the production of novel antibodies. In this way, cell lines have been established that secrete hapten-specific antibodies in which the Fc portion has been replaced either with an active enzyme moiety or with polypeptide displaying c-myc antigenic determinants.     

The afterglow and elliptical host galaxy of the short gamma-ray burst GRB 050724

Despite a rich phenomenology, gamma-ray bursts (GRBs) are divided into two classes based on their duration and spectral hardness--the long-soft and the short-hard bursts. The discovery of afterglow emission from long GRBs was a watershed event, pinpointing their origin to star-forming galaxies, and hence the death of massive stars, and indicating an energy release of about 10(51) erg. While theoretical arguments suggest that short GRBs are produced in the coalescence of binary compact objects (neutron stars or black holes), the progenitors, energetics and environments of these events remain elusive despite recent localizations. Here we report the discovery of the first radio afterglow from the short burst GRB 050724, which unambiguously associates it with an elliptical galaxy at a redshift z = 0.257. We show that the burst is powered by the same relativistic fireball mechanism as long GRBs, with the ejecta possibly collimated in jets, but that the total energy release is 10-1,000 times smaller. More importantly, the nature of the host galaxy demonstrates that short GRBs arise from an old (> 1 Gyr) stellar population, strengthening earlier suggestions and providing support for coalescing compact object binaries as the progenitors.