IPSPs elicited in CA1 pyramidal cells by putative basket cells in slices of adult rat hippocampus

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Abstract
CA1 basket cells are identifiable by an axonal arbour largely confined to, and spanning, the entire depth of stratum pyramidale where they innervate pyramidal somata and proximal dendrites. Basket cells display a range of electrophysiological properties and the inhibitory postsynaptic potentials (IPSPs) they elicit in pyramidal cells vary widely in duration. To determine whether these parameters are correlated, we used paired intracellular recordings, with biocytin filling, in pyramidal cells of adult hippocampal slices, and studied γ‐aminobutyric acid (GABAA) IPSPs (n = 43) elicited by putative basket cells (n = 35) with axons largely confined to stratum pyramidale in simultaneously recorded pyramidal cells. Fast‐spiking interneurons elicited relatively brief IPSPs, while IPSPs elicited by burst‐firing cells were amongst the slowest. Regular spiking interneurons elicited fast and slow GABAA IPSPs, but any one interneuron elicited IPSPs with remarkably similar durations in two to four pyramidal targets. However, with different types of target for a single putative basket cell, IPSPs elicited in postsynaptic interneurons were briefer than in pyramidal cells. Vertical oriens cells with somata in stratum oriens and a narrow, sparse axonal arbour in stratum pyramidale in transverse hippocampal slices, elicited IPSPs whose rise times and half widths clustered around intermediate values. Durations of IPSPs in pyramidal cells thus correlate, to a degree, with the physiological properties of presynaptic basket cells. The seven‐fold range of durations observed (10–70 ms half widths) may underlie contributions made by different basket cells to hippocampal rhythms of different frequencies.