Related Experiment Videos
Variation in electrophysiology and morphology of hippocampal CA3 pyramidal cells
D K Bilkey1, P A Schwartzkroin
1Department of Neurological Surgery, University of Washington, Seattle 98195.
Insights
Pyramidal cells in the hippocampus can generate bursts of action potentials. Deep cells, located near the stratum pyramidale/oriens border, are more likely to exhibit burst-type firing than shallow cells.
Area of Science:
- Neuroscience
- Cellular Electrophysiology
- Hippocampal Anatomy
Background:
- Pyramidal cells in the CA3 region of the hippocampus exhibit burst-type firing.
- Previous research suggested a topographical distribution of burst-firing cells within CA3 subregions (CA3a vs. CA3b).
- The relationship between burst-type firing and specific cell morphology remained unclear.
Purpose of the Study:
- To investigate the relationship between pyramidal cell morphology and burst-type firing in hippocampal CA3 subregions.
- To determine if burst-firing cell distribution varies across CA3a, CA3b, and CA3c.
- To identify morphological correlates of burst-type firing.
Main Methods:
- Intracellular recordings from pyramidal cells in CA3 subregions (CA3a, b, c).
- Lucifer yellow filling of recorded cells to visualize gross morphology.
- Correlation of electrophysiological properties (burst-type firing) with morphological features (soma location, apical dendrite length).
Main Results:
- The proportion of burst-generating cells did not differ significantly across CA3 subregions.
- Cells with somata near the stratum pyramidale/oriens border ('deep' cells) were over twice as likely to exhibit burst-type firing compared to 'shallow' cells.
- Deep cells possessed a longer initial segment of their apical dendrite.
Conclusions:
- Burst-type firing in CA3 pyramidal cells is not dependent on subregion (CA3a, b, c) but is strongly correlated with soma location.
- The 'deep' cell morphology, characterized by a longer apical dendrite initial segment, is associated with burst-type firing.
- Findings support the hypothesis that ion channels on the apical dendrite's initial segment modulate burst-type responses.
Abstract:
A proportion of pyramidal cells in region CA3 of the mammalian hippocampus generate bursts of action potentials when stimulated with an intracellular injection of depolarizing current. Although a previous study has suggested that burst-type cells are more likely to be located in subregion CA3a than CA3b, it has been unclear if, or how, this burst-type firing was related to cell morphology. In the present study, a sample of pyramidal cells located in subregions CA3a, b and c were recorded intracellularly. Many of these cells were filled with Lucifer yellow, allowing correlation of gross morphology with electrophysiology. Contrary to previous results, it was determined that the proportion of cells which generated bursts did not differ significantly across CA3 subregions. It was found, however, that cells with somata located close to the stratum pyramidale (s.p.)/oriens border ('deep' cells) were more than twice as likely to generate burst-type responses than were cells located closer to stratum radiatum ('shallow' cells). One notable morphological feature of the deep cells was the greater length of the initial portion of their apical dendrite, as measured from soma to primary branching point. This observation is consistent with the hypothesis that burst-type responses are generated or modulated by ion channels on this section of the dendrite.