Current approaches to characterize micro- and macroscale circuit mechanisms of Parkinson's disease in rodent models

Accelerating technological progress in experimental neuroscience is increasing the scale as well as specificity of both observational and perturbational approaches to study circuit physiology. While these techniques have also been used to study disease mechanisms, a wider adoption of these approaches in the field of experimental neurology would greatly facilitate our understanding of neurological dysfunctions and their potential treatments at cellular and circuit level. In this review, we will introduce classic and novel methods ranging from single-cell electrophysiological recordings to state-of-the-art calcium imaging and cell-type specific optogenetic or chemogenetic stimulation. We will focus on their application in rodent models of Parkinson’s disease while also presenting their use in the context of motor control and basal ganglia function. By highlighting the scope and limitations of each method, we will discuss how they can be used to study pathophysiological mechanisms at local and global circuit levels and how novel frameworks can help to bridge these scales.

3D-printed Recoverable Microdrive and Base Plate System for Rodent Electrophysiology

Extracellular recordings in freely moving animals allow the monitoring of brain activity from populations of neurons at single-spike temporal resolution. While state-of-the-art electrophysiological recording devices have been developed in recent years (e.g., µLED and Neuropixels silicon probes), implantation methods for silicon probes in rats and mice have not advanced substantially for a decade. The surgery is complex, takes time to master, and involves handling expensive devices and valuable animal subjects. In addition, chronic silicon neural probes are practically single implant devices due to the current low success rate of probe recovery. To successfully recover silicon probes, improve upon the quality of electrophysiological recording, and make silicon probe recordings more accessible, we have designed a miniature, low cost, and recoverable microdrive system. The addition of a novel 3D-printed skull baseplate makes the surgery less invasive, faster, and simpler for both rats and mice. We provide detailed procedural instructions and print designs, allowing researchers to adapt and flexibly customize our designs to their experimental usage.

Cortical direct current stimulation improves signal transmission between the motor cortices of rats

Transcranial direct current (DC) stimulation is a noninvasive brain stimulation technique that is now widely used to improve motor and cognitive function. The neuromodulatory effects of DC is considered to extend to nearby as well as remote brain areas from the site of stimulation because of current flowing into the brain and/or signal transmission in neuronal networks. However, the effects of DC on cortico-cortical neuronal transmission are not well known. In the present study, we focused on signal transmission from the primary (M1) to secondary (M2) motor cortex of rats. Intra-cortical microstimulation (ICMS) was applied to the M1 under DC conditions, and changes in synaptic activity in the M2 were examined using current-source density analyses. The synaptic input to the M2 superficial layers was enhanced during DC stimulation, while the synaptic input to the M2 deeper layers was increased after DC stimulation. These results suggest that DC stimulation improves cortico-cortical neuronal transmission from M1 to M2, and that the effectiveness of DC may be different among different projection neuron types in the M1.