Hippocampus

Attractor dynamics in the hippocampal representation of the local environment. Wills, T. J. et al. Science 308, 873–876 (2005)

Place cells in the hippocampus respond to specific locations within an environment, and can 'remap' if an animal is moved to a different environment. Wills and colleagues allowed rats to forage in square and circular boxes made of different materials, so that their place cells would form representations of the two environments, and found that the place cell activity resembled attractor states: when rats were subsequently placed in boxes of varying shapes, the activity patterns switched abruptly and simultaneously from one representation to the other.

Synaptic physiology

Fast vesicle replenishment allows indefatigable signalling at the first auditory synapse. Griesinger, C. B. et al. Nature 435, 212–215 (2005)

Although the readily releasable pool of docked vesicles in the ribbon synapses of mammalian inner hair cells contains about the same number of vesicles as those of other synapses, ribbon synapses release vesicles more quickly and with greater temporal precision. Griesinger et al. used two-photon imaging of release sites in the cochlea to show that compartments in the cytoplasm of inner hair cells generate preformed vesicles, and that these vesicles are used to rapidly replenish the readily releasable pool.

Learning and Memory

Disrupting the melanin-concentrating hormone receptor 1 in mice leads to cognitive deficits and alterations of NMDA receptor function. Adamantidis, A. et al. Eur. J. Neurosci. 21, 2837–2844 (2005)

Mice that lack the gene for the melanin-concentrating hormone (MCH) receptor 1 show a specific deficit on an inhibitory passive avoidance test, and reduced responses to NMDA (N-methyl-D-aspartate) in CA1 hippocampal pyramidal neurons. Expression of the NMDA receptor 1 (NMDAR1) subunit in this region was reduced, which indicates that MCH might be involved in modulating the function or expression of NMDARs.

Genes and behaviour

Lhx6 delineates a pathway mediating innate reproductive behaviors from the amygdala to the hypothalamus. Choi, G. B. et al. Neuron 46, 647–660 (2005)

Innate reproductive or defensive behaviours are elicited in mammals by conspecific or predator signals, and are controlled by pathways from the amygdala to the hypothalamus. Choi et al. show that the pathway that mediates reproductive behaviour expresses the transcription factor LHX6, whereas the defensive pathway expresses other LHX proteins. The two pathways are anatomically segregated but converge in the ventromedial hypothalamus, and their opposite neurotransmitter phenotypes might allow a 'gate control' mechanism to integrate conflicting cues.