In Brief

Synaptic physiology

Mossy fiber Zn²⁺ spillover modulates heterosynaptic N -methyl- d -aspartate receptor activity in hippocampal CA3 circuits. Ueno, S. et al. J. Cell Biol. 158, 215–220 (2002)

Careful monitoring in hippocampal slices indicates that Zn²⁺ is released from mossy fibre terminals in an activity-dependent manner, and that it diffuses from there to the neighbouring stratum radiatum. This increase in Zn²⁺ seems to be responsible for the inhibition of NMDA-receptor-mediated synaptic responses that follows mossy fibre stimulation. The high concentrations of Zn²⁺ in mossy fibre terminals might modulate synaptic plasticity in nearby hippocampal networks. Although previous work had shown that Zn²⁺ could modulate signalling homosynaptically, it now appears that spillover of Zn²⁺ allows its effects to be more widespread.

Synaptic plasticity

Dendritic spikes as a mechanism for cooperative long-term potentiation. Golding, N. L. et al. Nature 418, 326–331 (2002)

Golding et al. show that local, spatially restricted regenerative potentials, known as dendritic spikes, are produced by the activation of sodium and calcium channels following synaptic activation on distal dendrites of hippocampal CA1 pyramidal neurons. These spikes produce cooperative long-term potentiation by generating the postsynaptic depolarization and calcium entry that is needed to trigger potentiation, without requiring the backpropagation of action potentials.

Limbic system

CREB activity in the nucleus accumbens shell controls gating of behavioral responses to emotional stimuli. Barrot, M. et al. Proc. Natl Acad. Sci. USA 99, 11435–11440 (2002)

The authors show that both rewarding and aversive emotional stimuli activate CRE-mediated gene transcription in the nucleus accumbens shell. When the activity of CREB in this area was increased by gene transfer, reactions to rewarding, anxiogenic, aversive and painful stimuli were decreased, whereas a decrease in CREB caused increased responses. CREB seems to gate behavioural responses to emotional stimuli, regardless of their intrinsic value.

Cortical development

Conversion of cerebral cortex into basal ganglia in Emx2^−/−Pax6^Sey/Sey double-mutant mice. Muzio, L. et al. Nature Neurosci. 5, 737–745 (2002)

The authors set out to discover whether two homeobox genes, Emx2 and Pax6, are required to subdivide the telencephalon into cerebral cortex and basal ganglia during development. In mice, inactivating either gene alone caused only mild defects, but when both genes were knocked out simultaneously, most of the cortical tissue was transformed into striatum. This result indicates that the products of just two genes stand between a cortical and a striatal fate.