Sensory systems

A key role of starburst amacrine cells in originating retinal directional selectivity and optokinetic eye movement.

Yoshida, K. et al. Neuron 30, 771–780 (2001) [Contents page]

Direction-selective ganglion cells in the retina respond to stimuli that are moving in one, but not in the opposite, direction. Yoshida et al. eliminated another type of retinal neuron — the starburst amacrine cells — and found that direction selectivity of ganglion cells was abolished. The optokinetic eye reflex that is normally elicited by moving stimuli was also abolished, indicating that starburst cells are crucial for detecting direction of movement.

Development

Synergy between Hoxa1 and Hoxb1 : the relationship between arch patterning and the generation of cranial neural crest.

Gavalas, A. et al. Development 128, 3017–3027 (2001) Pubmed

The Hox genes are well known for their roles in neural crest patterning. Gavalas et al. now propose an additional role in neural crest generation. In mouse embryos mutant for Hoxa1 and Hoxb1 in the ectoderm, rhombomere 4 (r4) was reduced in size and failed to generate neural crest. Although r4 crest cells normally migrate to the second pharyngeal arch, its early patterning was unaffected, indicating that this does not depend on neural crest.

Glia

Spontaneous astrocytic Ca 2+ oscillations in situ drive NMDA receptor-mediated neuronal excitation.

Parri, H. R. et al. Nature Neurosci. 4, 803–812 (2001) [Abstract]

The idea that glial cells can directly affect synaptic activity has received significant support. But in most cases, glial cells act as reactive elements; synaptic activity triggers a response in astrocytes, which then release transmitters that act back on the synapse. Parry et al. show that spontaneous Ca2+ waves among astrocytes can trigger NMDA (N-methyl-d-aspartate)-receptor-mediated responses in neighbouring neurons, providing evidence that glial cells do not solely react to synaptic activity, but can also participate directly in its generation.

Neurodegenerative disorders

Tauopathy in Drosophila : neurodegeneration without neurofibrillary tangles.

Wittmann, C. W. et al. Science 14 June 2001 (10.1126/science.1062382) Pubmed

Tau is a microtubule-binding protein that has been implicated in Alzheimer's disease. The authors found that expressing human tau in Drosophila caused neurodegeneration, which shared some of the features seen in humans. However, neurofibrillary tangles, a key characteristic of Alzheimer's disease, were absent in the fly, indicating that tangle formation might not be directly related to cell death. This genetic model might allow the identification of suppressors and enhancers of neurodegeneration.