| Perisomatic inhibition plays an essential role in the output and synchrony of network oscillations. Two non-overlapping classes of GABAergic interneurons, the parvalbumin-expressing (PV+) and the cholecystokinin-expressing (CCK+) basket cells, provide the main source of perisomatic inhibition in the hippocampus. The two classes of basket cells can be distinguished by several differences, such as their expression of pre- and postsynaptic receptors, firing properties, and different patterns of glutamatergic and subcortical input, which highlight the distinct roles that the basket cells play in shaping network dynamics. The basket cells are also associated with normal conditions such as higher cognitive processes, mood regulation, and in pathological states such as schizophrenia, anxiety disorders, and epilepsy.;In this dissertation, we provide new insight into the physiological modulation and the neuroanatomical and functional organization of perisomatic inhibition in the hippocampus and entorhinal cortex. The studies described here utilize pharmacological tools combined with single and paired electrophysiological recordings, and immunocytochemical methods to confirm the identity of the recorded cells.;In the Introduction, we present a general overview of perisomatic inhibition. Chapter 1 provides background into CCK, one of the most highly expressed neuropeptides in the brain, which we demonstrate in Chapter 2, acts to gate the two types of basket cells to shape perisomatic inhibition. Chapter 3 presents the distinct signaling mechanisms which enable CCK to exert its cell-type specific control over the basket cells, and in Chapter 4, we show for the first time, that CCK+ perisomatic inputs can segregate according to the projection patterns of their postsynaptic targets. |
