Relationship between EEG potentials and intracellular activity of striataland cortico-striatal neurons: an in vivo study under different anesthetics

The functions of the basal ganglia are achieved through excitation of stria tal output neurons (SONs) by converging cortical glutamergic afferents. We assessed the relationship between different patterns of activity in cortico -striatal (C-S) cells and the electrical behavior of SONs in vivo. Intracel lular activities of rat G-S neurons in the orofacial motor cortex and of SO Ns, located in the projection field of this cortical region, were recorded under different anesthetics, which generate various temporal patterns of co rtical activity. A surface electroencephalogram (EEG) of the orofacial moto r cortex was simultaneously performed with intracellular recordings and EEG waves were used as correlates of a coherent synaptic activity in cortical neurons. Under barbiturate anesthesia C-S neurons showed rhythmic (5-7 Hz) supra-threshold depolarizations in phase with large amplitude EEG waves. Th e correlative activity of SONs was characterized by large amplitude oscilla tion-like synaptic depolarizations that could trigger action potentials. Un der ketamine-xylazine anesthesia C-S neurons exhibited a step-like behavior consisting of depolarizing plateaus (up states), leading to multiple spike discharges, interrupted by hyperpolarizing periods (down states). The rela ted activity of SONs was step-like membrane potential fluctuations with fir ing confined to the early part of the striatal up state. In C-S neurons and SONs up states coincided with slow recurrent EEG waves (similar to1 Hz). F inally, under neurolept-analgesia an apparently disorganized EEG activity w as associated with a lack of rhythmic discharge in C-S neurons. This uncorr elated activity in C-S neurons resulted in an absence of spontaneous firing as well as of large amplitude synaptic depolarizations in SONs. In the pre sent study we demonstrate that SONs shape their input-output relationship b y filtering oct uncorrelated synaptic activity and that a minimal synchroni zation in the cortico-striatal afferents is required to produce significant synaptic depolarization in SONs.