Cortical Interneuron Subtypes Vary in Their Axonal Action Potential Properties.

Unlabelled: The role of interneurons in cortical microcircuits is strongly influenced by their passive and active electrical properties. Although different types of interneurons exhibit unique electrophysiological properties recorded at the soma, it is not yet clear whether these differences are also manifested in other neuronal compartments. To address this question, we have used voltage-sensitive dye to image the propagation of action potentials into the fine collaterals of axons and dendrites in two of the largest cortical interneuron subtypes in the mouse: fast-spiking interneurons, which are typically basket or chandelier neurons; and somatostatin containing interneurons, which are typically regular spiking Martinotti cells.

Motor cortex feedback influences sensory processing by modulating network state.

Long-range corticocortical communication may have important roles in context-dependent sensory processing, yet we know very little about how these pathways influence their target regions. We studied the influence of primary motor cortex activity on primary somatosensory cortex in the mouse whisker system. We show that primary motor and somatosensory cortices undergo coherent, context-dependent changes in network state.

Active action potential propagation but not initiation in thalamic interneuron dendrites.

Inhibitory interneurons of the dorsal lateral geniculate nucleus of the thalamus modulate the activity of thalamocortical cells in response to excitatory input through the release of inhibitory neurotransmitter from both axons and dendrites. The exact mechanisms by which release can occur from dendrites are, however, not well understood. Recent experiments using calcium imaging have suggested that Na/K-based action potentials can evoke calcium transients in dendrites via local active conductances, making the backpropagating action potential a candidate for dendritic neurotransmitter release.

Influence of path integration versus environmental orientation on place cell remapping between visually identical environments.

To assess the effects of interactions between angular path integration and visual landmarks on the firing of hippocampal neurons, we recorded from CA1 pyramidal cells as rats foraged in two identical boxes with polarizing internal cues. In the same-orientation condition, following an earlier experiment by Skaggs and McNaughton, the boxes were oriented identically and connected by a corridor. In the opposite-orientation condition, the boxes were abutted by rotating them 90 degrees in opposite directions, so that their orientations differed by 180 degrees .