No abstract

The external globus pallidus (GP) is a GABAergic node involved in motor control regulation and coordinates firing and synchronization in the basal ganglia–thalamic–cortical network through inputs and electrical activity. In Parkinson's disease, high GABA levels alter electrical activity in the GP and contribute to motor symptoms. Under normal conditions, GABA levels are regulated by GABA transporters (GATs). GAT type 1 (GAT-1) is highly expressed in the GP, and pharmacological blockade of GAT-1 increases the duration of currents mediated by GABA A receptors and induces tonic inhibition. The functional contribution of the pathway between the GP and the reticular thalamic nucleus (RTn) is unknown. This pathway is important since the RTn controls the flow of information between the thalamus and cortex, suggesting that it contributes to cortical dynamics. In this work, we investigated the effect of increased GABA levels on electrical activity in the RTn by obtaining single-unit extracellular recordings from anesthetized rats and on the motor cortex (MCx) by corticography. Our results show that high GABA levels increase the spontaneous activity rate of RTn neurons and desynchronize oscillations in the beta frequency band in the MCx. Our findings provide evidence that the GP exerts tonic control over RTn activity through the GP–reticular pathway and functionally contributes to cortical oscillation dynamics.

The external globus pallidus (GP) firing rate synchronizes the basal ganglia-thalamus-cortex network controlling GABAergic output to different nuclei. In this context, two findings are significant: the activity and GABAergic transmission of the GP modulated by GABA B receptors and the presence of the GP-thalamic reticular nucleus (RTn) pathway, the functionality of which is unknown. The functional participation of GABA B receptors through this network in cortical dynamics is feasible because the RTn controls transmission between the thalamus and cortex. To analyze this hypothesis, we used single-unit recordings of RTn neurons and electroencephalograms of the motor cortex (MCx) before and after GP injection of the GABA B agonist baclofen and the antagonist saclofen in anesthetized rats. We found that GABA B agonists increase the spiking rate of the RTn and that this response decreases the spectral density of beta frequency bands in the MCx. Additionally, injections of GABA B antagonists decreased the firing activity of the RTn and reversed the effects in the power spectra of beta frequency bands in the MCx. Our results proved that the GP modulates cortical oscillation dynamics through the GP-RTn network via tonic modulation of RTn activity.

Flavonoids are natural substances obtained from plants. Most flavonoids cross the blood-brain barrier and exert a wide range of effects on the central nervous system. These actions have been attributed to the modulation of GABA-A receptors. Although motor systems in the central nervous system express a high density of GABA-A receptors, physiological studies about the effects of flavonoids on motor nuclei are scarce. Among the nuclei of the basal ganglia, the globus pallidus is potentially important for the processing of information related to movement. The electrical activity of globus pallidus neurons depends on the GABAergic fibers coming from the striatum and recurrent collateral fibers. It is known that the basal activity of the globus pallidus is modified by blocking dopaminergic receptors. In the present work, we analyzed the effects of the local application of a flavonoid, (-)-epicatechin, on the spiking of globus pallidus neurons in chloral hydrate-anesthetized rats and determined whether (-)-epicatechin applied bilaterally to the globus pallidus can modify the catalepsy induced by systemic administration of haloperidol. The results showed that (-)-epicatechin increased the basal firing of globus pallidus neurons in a dose-dependent manner and antagonized the inhibitory effect of GABA. Bilateral infusion of (-)-epicatechin to the globus pallidus diminished the catalepsy induced by haloperidol.