Hippocampal interneuron types specifically related to complex behaviours
The morphological, neurochemical and electrophysiological characterization of inhibitory, GABAergic cell types in the hippocampus allowed the introduction of a detailed functional classification. Several lines of evidence underlies a division of labor between major interneuron classes in cortical information processing. The latest results led to the hypothesis that specificity can go as far as activity patterns of individual cell types are directly related tto complex behaviours. The example used in this talk include basket cells; they control the ensemble activity and synchronization of principal neurons and are divided into two major types with different connectivities and functions: one characterized by the expression of the calcium-binding protein parvalbumin (PV) while the other contains the neuropeptide CCK. The electrically and synaptically coupled ensembles of PV-containing basket cells are indispensable components of the oscillating cortical hardware; they represent the rigid (nonplastic) precision clockwork without which no cortical operations are possible. The activity of a similar syncytium of CCK-containing basket cells is superimposed on the PV basket cell-entrained network, conveying the emotional and motivational effects carried by subcortical pathways (containing serotonin, for example). Actions of the CCK cell ensemble are highly modifiable also by local neuromodulators and retrograde signal molecules, which may allow further fine-tuning of principal cell cooperation. Impairment of this tuning system likely results in mood disorders such as anxiety. Endocannabinoid signaling plays a crucial role in regulating postsynaptic effects of the CCK cell ensemble (i.e., the fine-tuning device) and therefore is an ideal target for the pharmacotherapy of anxiety-like behaviors.
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