Compartmentalized and Binary Behavior of Terminal Dendrites in Hippocampal Pyramidal Neurons
Abstract number :
1.019
Submission category :
Year :
2001
Submission ID :
3065
Source :
www.aesnet.org
Presentation date :
12/1/2001 12:00:00 AM
Published date :
Dec 1, 2001, 06:00 AM
Authors :
D-S. Wei, PhD, Neurology, University of Maryland School of Medicine, Baltimore, MD; S.M. Thompson, PhD, Physiology, University of Maryland School of Medicine, Baltimore, MD; C-M. Tang, MD, PhD, Neurology, University of Maryland School of Medicine, Baltimo
RATIONALE: Dendrites are not passive antennae that simply receive synaptic inputs, but rather actively process and transform them as they are received. Terminal dendritic segments comprise 70-90% of the dendritic tree and receive the majority of synaptic inputs, but have been little studied due to their inaccessibility to conventional electrophysiological techniques.
METHODS: Whole-cell recording was used to study membrane potential changes generated by CA1 pyramidal cells in hippocampal slice cultures in response to fluorescence guided focal photolysis of caged glutamate at individual terminal dendritic branches (10 um diameter spot size).
RESULTS: Terminal dendrites generated passive graded subthreshold responses following brief glutamate pulses (1-3 ms). Active, cadmium-sensitive, all-or-none responses were generated following larger (3-10 ms) glutamate pulses. All-or-none responses in terminal branches were incapabale of triggering somato-dendritic action potentials. Calcium imaging revealed that subthreshold responses were confined to the vicinity of the focal photolysis, whereas all-or-none responses triggered calcium influx throughout an individual terminal dendrite, but did not propagate past branch points. All-or-none responses were preferentially triggered by NMDA receptor activation. The duration of the all-or-none response was prolonged 10-fold by intracellular BAPTA.
CONCLUSIONS: We conclude that strong stimulation of glutamatergic receptors in terminal dendrites can activate voltage-dependent calcium channels. These regenerative calcium spikes propagate throughout the stimulated dendritic branch until propagation ceases at branch points, presumably due to impedence mismatches. Terminal dendritic branches thus behave as individual compartments and are capable of highly non-linear behavior. Compartmentalized and binary behavior of terminal dendrites enables parallel non-linear computation and may contribute to the induction of synaptic plasticity.
Support: VA, NIH (CMT), and UMB Bressler Funds (SMT).