Differential surface density and modulatory effects of presynaptic GABAB receptors in hippocampal cholecystokinin and parvalbumin basket cells
Booker SA, Althof D, Degro CE, Watanabe M, Kulik Á, Vida I.
Brain Struct Funct. online article
The perisomatic domain of cortical neurons is under the control of two major GABAergic inhibitory interneuron types: CCK BCs and PV BCs. They are different in their presynaptic modulation of their synaptic output. Most GABAergic terminals contain GABABRs but their role in presynaptic inhibition and surface expression have not been characterized in the two BC types. We performed whole-cell recordings from CCK and PV BCs and PCs, as well as freeze-fracture replica-based quantitative immunogold EM of their synapses. Our results demonstrate that while both CCK and PV BCs contain functional GABABRs, their modulatory effects and relative abundance are different at these synapses: GABA release is dramatically inhibited by baclofen at CCK BC synapses, whereas a modarete reduction in inhibitory transmission is observed at PV BC synapses. Furthermore, GABABR activation has divergent effects on synaptic dynamics: PPD is enhanced at CCK BC synapses, but abolished at PV BC synapses. Consistent with the quantitative differences in presynaptic inhibition, virtually all CCK BC terminals contain GABABRs at high densities, but only 40% of PV BC terminals contain GABABRs at detectable levels. These findings add to an increasing list of differences between these two interneuron types, with implications for their network functions.
