INTERACTIONS BETWEEN ORIENS, BASKET AND PYRAMIDAL CELLS DURING IN VITRO SEIZURE-LIKE EVENTS IN CA1 OF THE RAT HIPPOCAMPUS
Open Access
- Author:
- Parekh, Ruchi
- Graduate Program:
- Neuroscience
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 20, 2010
- Committee Members:
- Steven Schiff, Dissertation Advisor/Co-Advisor
Steven Schiff, Committee Chair/Co-Chair
Bernhard Luscher, Committee Member
Bruce Gluckman, Committee Member
Byron C Jones, Committee Member
John R Cressman, Committee Member
Jokubas Ziburkus, Committee Member - Keywords:
- 4-aminopyridine
hippocampus
seizures - Abstract:
- Network activity in the brain is shaped by interactions between cells. There is limited knowledge about such interactions in pathological conditions like epilepsy. Previous results from our laboratory showed unique interplay between pyramidal cells and oriens lacunosum-moleculare interneurons in rat hippocampal CA1 during in vitro seizure-like events (SLEs). To further investigate the interactions between different sub-types of interneurons and pyramidal cells, we performed simultaneous dual and triple whole cell patch and extracellular recordings in pyramidal, basket and oriens cells in the CA1 region of the rat hippocampus. Triple immunofluorescence confirmed the identity of patched cells. We measured spike frequency, spike and subthreshold correlation between these cells before, during and after single seizure-like events (SLEs) and during the inter-seizure intervals (ISIs). We confirmed our previous findings and found a distinctly different firing pattern between the perisomatically-innervating basket cells and the dendritically-innervating oriens cells during 4-aminopyridine induced SLEs in the presence of low magnesium. At the pre-ictal stage of the SLE the subthreshold correlation between pyramidal and basket cells is strong; oriens cells show high firing frequency, whereas the basket cells show a gradual increase. At the start of the SLE, the previously strong subthreshold correlations between pyramidal and basket cells decrease; all 3 cells show increased firing rates with basket and oriens cells reaching their maximum firing rates. Following this, subthreshold correlations for all 3 cells decrease; oriens cells go into depolarization block that is characterized by total spike failure, whereas pyramidal and basket cells continue firing. SLE termination is defined by conditions returning to pre-ictal dynamics. During the ISI all three cell types increase their firing activity at different times before onset of the subsequent seizure. Our findings further emphasize the importance of cell-type specific differences in interactions between excitatory and inhibitory cells during SLEs. Other similar cellular dynamics may be representative of the hippocampal circuitry under conditions that cause general hyperexcitability. We also show a significant gradual increase in spike rates in both the inhibitory and excitatory cells, starting at least a minute before seizure onset. These findings expand on the current knowledge of seizure formation patterns and can be used in studies of seizure prediction models.