bluelogo.gif (1643 bytes)
Gatsby Computational Neuroscience Unit
Alexandra House, 17 Queen Square, LONDON, WC1N 3AR, UK
Tel: +44 (0) 20 7679 1176, Fax +44 (0) 20 7679 1173, admin@gatsby.ucl.ac.uk, www.gatsby.ucl.ac.uk

 

home
people
research
annual report
publications
seminars
travel
vacancies
the greater gatsby
search
ucl

 

WORKSHOP ON:
CENTRAL PROBLEMS IN SINGLE CELL COMPUTATION


16-18 September 2002
By invitation only

Venue
B10 Seminar Room, Alexandra House, 17 Queen Square, London, WC1N 3AR


Active properties of layer 2/3 pyramidal cell dendrites in vitro and in vivo
Fritjof Helmchen, Department of Cell Physiology, Max Planck Institut e for Medical Reserach, Germany
Pyramidal cells in layer 2/3 of neocortex are morphologically heterogeneous with somata located 150-550 Ám from the pia, an apical trunk of variable length, and apical tufts extending in layer 1. Integration of synaptic inputs arriving at the apical tuft critically depends on whether voltage-dependent ion channels are present in the dendrites. We therefore investigated active properties of layer 2/3 apical dendrites both in brain slices (in vitro) and in urethane-anesthetized rats (in vivo). Experiments were performed under as similar as possible conditions in somatosensory cortex of 28-day old rats using whole-cell patch-clamp recordings and calcium imaging. Both in vitro and in vivo, action potentials (AP) backpropagated in a decremental fashion along the apical trunk (measured using dendritic recordings). Backpropagation was actively supported by sodium channels because application of TTX caused a much stronger attenuation. Both in vitro and in vivo single action potentials evoked large calcium transients in the apical trunk but generally failed to evoke calcium influx in layer 1. In contrast, distal calcium influx could be induced by multiple APs delivered at high frequencies (>100 Hz). In addition, all-or-none regenerative dendritic potentials causing large distal calcium influx could be evoked by direct dendritic current injection. When paired with a somatic AP these distal dendritic events could cause a second rebound AP. We conclude that layer 2/3 pyramidal cell dendrites contain sodium and calcium channels, which are activated similarly in brain slices and during anesthesia. These active properties may allow layer 2/3 pyramidal neurons to associate basal and distal synaptic inputs.
Joint work with: Jack Waters, Matthew Larkum, Bert Sakmann