Simon Rumpel | PubMed Health

PubMed2005

Postsynaptic receptor trafficking underlying a form of associative learning.

To elucidate molecular, cellular, and circuit changes that occur in the brain during learning, we investigated the role of a glutamate receptor subtype in fear conditioning. In this form of learning, animals associate two stimuli, such as a tone and a shock. Here we report that fear conditioning drives AMPA-type glutamate receptors into the synapse of a large fraction of postsynaptic neurons in the lateral amygdala, a brain structure essential for this learning process. Furthermore, memory was reduced if AMPA receptor synaptic incorporation was blocked in as few as 10 to 20% of lateral amygdala neurons. Thus, the encoding of memories in the lateral amygdala is mediated by AMPA receptor trafficking, is widely distributed, and displays little redundancy.

Amygdala↗

PubMed2004

Silent synapses in the immature visual cortex: layer-specific developmental regulation.

Central glutamatergic synapses are thought to initially form as immature, so-called silent synapses showing exclusively N-methyl-d-aspartate receptor-mediated synaptic transmission. Postsynaptic insertion of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors during further development leads to a conversion into functional, mature synapses. Here, we tested the hypothesis that, according to the "inside first-outside last" pattern of neocortical layer formation and synaptogenesis, pyramidal cells in the superficial layers might show a higher fraction of silent synapses compared with pyramidal cells in the deep layers. We performed an electrophysiological analysis of glutamatergic synapses in acute rat visual cortex slices during postnatal development. In layer VI pyramidal neurons the incidence of silent synapses was high during the first postnatal week and strongly declined during further development. Surprisingly, in superficial cortical plate pyramidal neurons (immature layers II/III), the fraction of silent synapses was initially very low and increased up to the second postnatal week. Thereafter, a similar decline as found in layer VI pyramidal neurons was observed. Thus the developmental regulation of silent synapses was clearly different in pyramidal neurons from different neocortical layers. The almost complete absence of silent synapses at early stages in layer II/III pyramidal neurons indicates that an initially formed subset of synapses is constitutively functional. This might be important to enable spontaneous activity and latter activity-dependent maturation of synapses.

Animals↗