Generation and modulation of network oscillations in the rodent prefrontal cortex in vitro

Fast network oscillations (~12-80 Hz) are recorded extensively in the mammalian cerebral cortex in vivo. They are thought to subserve the neuronal mechanism by which local and distant neuronal populations orchestrate their firing activity to process cognitive-related information. The rat medial prefrontal cortex (mPFC) is considered to be functionally and anatomically homologous to the primate prefrontal cortex. Earlier in vitro studies have demonstrated that the mPFC can sustain carbachol-induced persistent beta1 or kainate-induced transient low gamma frequency oscillations. We wished to establish an in vitro paradigm of carbachol (10 μM) / kainate (200 nM)-induced persistent fast network oscillations in the rat mPFC with the objective to investigate the distribution patterns and the mechanisms of these oscillations. Then we assessed the modulatory effects of the ascending catecholamine systems on fast network oscillations with exogenous application of dopamine and noradrenaline. Persistent fast network oscillations in the ventral mPFC were stronger, more rhythmic but slower (~25 Hz) than oscillations in the dorsal mPFC (~28 Hz). The regional difference in the oscillation amplitude was correlated to the strong presence of bursting cells in the ventral but not the dorsal regions. Across all regions in the mPFC, oscillations were stronger in layer 5. Oscillations relied on GABAA, kainate but not AMPA receptors. In the ventral mPFC, network oscillations were also dependent on NMDA receptor-mediated synaptic transmission. Dopamine (100 μM) reduced the oscillation strength and rhythmicity in the ventral mPFC. Instead, dopamine increased the power and rhythmicity of network oscillations in the dorsal mPFC. The region-dependent dopamine effect was correlated to the induced effects on synaptic inhibition and neuronal firing. Noradrenaline (30 μM) reduced the oscillation strength in the ventral mPFC, but caused no effect on the dorsal mPFC.