Carbachol-induced network oscillations in an in vitro limbic system brain slice

We employed simultaneous field potential record- ings from CA3, subiculum and entorhinal cortex in an in vitro brain slice preparation to understand the involvement of these limbic areas in the generation of the field potential oscillations that are induced by bath application of the muscarinic receptor agonist carbachol. Regularly spaced oscillations that mainly presented at theta frequency range (5–12 Hz) occurred synchronously in all three structures in the presence of carbachol. These oscillations, which disap- peared when slices were perfused with pirenzepine or with glutamatergic receptor antagonists, were categorized as short (<4 s) and long (>4 s) with short events oscillating at higher frequencies than long events. Field oscillations were highly synchronized between regions and latency anal- ysis revealed that they often initiated in the entorhinal cortex later than in the other two structures. Blocking GABAA recep- tors modified the activity patterns of both short and long oscillations and decreased their coherence in the theta fre- quency range. Finally, blocking KCC2 activity disclosed a pattern of recurrent short oscillations. Our results suggest that in the presence of carbachol both subiculum and CA3 most often drive theta generators in the entorhinal cortex and that these oscillations are influenced but not abolished by altering GABAA receptor signaling. ! 2017 IBRO. Published by Elsevier Ltd. All rights reserved.