Acute In Vivo Electrophysiological Recordings of Local Field Potentials and Multi-unit Activity from the Hyperdirect Pathway in Anesthetized Rats

Summary

In this study, the methodology is presented on how to perform multi-site in vivo electrophysiological recordings from the hyperdirect pathway under urethane anesthesia.

Abstract

Converging evidence shows that many neuropsychiatric diseases should be understood as disorders of large-scale neuronal networks. To better understand the pathophysiological basis of these diseases, it is necessary to precisely characterize in which way the processing of information is disturbed between the different neuronal parts of the circuit. Using extracellular in vivo electrophysiological recordings, it is possible to accurately delineate neuronal activity within a neuronal network. The application of this method has several advantages over alternative techniques, e.g., functional magnetic resonance imaging and calcium imaging, as it allows a unique temporal and spatial resolution and does not rely on genetically engineered organisms. However, the use of extracellular in vivo recordings is limited since it is an invasive technique that cannot be universally applied. In this article, a simple and easy to use method is presented with which it is possible to simultaneously record extracellular potentials such as local field potentials and multiunit activity at multiple sites of a network. It is detailed how a precise targeting of subcortical nuclei can be achieved using a combination of stereotactic surgery and online analysis of multi-unit recordings. Thus, it is demonstrated, how a complete network such as the hyperdirect cortico-basal ganglia loop can be studied in anesthetized animals in vivo.

Introduction

Recent cumulative evidence on different neuropsychiatric disorders such as Parkinson´s disease (PD) and schizophrenia strongly suggests that their pathophysiology is based on a critical dysfunction of extended neuronal circuits that often involve cortical and subcortical structures^1,2,3. According to this theory, the clinical manifestations of the diseases arise as a consequence of an impaired information processing capacity of a network of cells instead of single cells or specific neuronal elements^1,2,

Protocol

Experimental procedures were conducted in accordance with the German Animal Welfare Act (last revised in 2014) and European regulations (2010/63/EU). Experiments were approved by the local animal welfare authority (LaGeSo, Berlin), and conformed to local department and international guidelines.

NOTE: In the presented method two models of electrodes are used to record from the hyperdirect cortico-basal ganglia pathway that connects the primary motor cortex (M1) with the subthalamic nucleus (STN) and the substantia nigra pars reticulate (SNr). For epidural electrocorticogram (ECoG) recordings from the M1 custom-made low-impedance Ag/AgCl elec....

Results

With the herein used recording electrodes, it is possible to sample LFPs from the primary motor cortex, the subthalamic nucleus and the substantia nigra pars reticulata and MUA from the STN and SNr. Initially, LFPs and multi-unit activity are recorded together in a broad-band signal. Thereafter, LFPs and MUAs are separated by bandpass filters (0.05-250 Hz for LFPs and 300-4,000 Hz for MUA).

For the correct targeting of subcortic.......

Discussion

In the present study, the method is demonstrated how to record extracellular electrophysiological signals simultaneously from multiple sites of a given network using the example of the hyperdirect cortico-basal ganglia pathway that connects the M1 with the STN and SNr in rodents.

A critical step in the recording of small subcortical structures such as the STN is the precisely guided insertion of the recording electrodes into the target. In the presented method, taking care of two crucial steps.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Ag/AgCl custom epidural electrodes	Goodfellow GmbH D-61213 Bad Nauheim, Germany info@goodfellow.com	Product-ID AG005127 for 99.99% silver wire	Ag/AgCl electrodes will allow for better signal quality, but may only be used in acute experiments. Possible replacement: Stainless steel electrodes
Stereotaxic holder with acrylic block	David Kopf Instruments, 7324 Elmo Street, Tujunga, CA 91042, USA	Product ID Model 1770 Standard Electrode Holder	Make sure the acrylic block has recesses which suit the electrode setup for the desired target. Acrylic blocks can easily be modified with a file to obtain the desired configuration. Possible replacement: Self-constructed electrode holders
Tungsten microwire electrodes 1.5 MΩ impedance	Microprobes.com 18247-D Flower Hill Way  Gaithersburg, Maryland, 20879 USA	Product-ID WE3ST31.5A5-250um	The 1.5 MΩ is necessary to record MUA and LFP at the same time. Possible replacement: Microelectrodes of different materials can be used. The electrodes have to be straight, robust and as thin as possible.
Rat alignment tool	David Kopf Instruments, 7324 Elmo Street, Tujunga, CA 91042, USA	Product ID Model 944 Rat Alignment Tool	Allows the exact orientation of the brain to match stereotaxic atlases. Possible replacement: Stereotaxic holder with a cannula
Two-component dental acrylic	Associated Dental Products Ltd. Kemdent Works, Purton, Swindon Wiltshire, SN5 4HT, United Kingdom	Simplex Rapid Powder Clear 225g, Product code: ACR803; Simplex Rapid Liquid 150ml, Product code: ACR920	Depending in the electrodes used, superglue might be an easy alternative, if the electrodes are small and lightweight. Possible replacement: Superglue (Cyanacrylate-based)
Faraday cage	Self-construction		A proper Faraday cage will be the best protection from electromagnetic artifacts, but everything which can be formed into a box shape or applied to a frame and is made of conductive material may help. Possible replacement: Aluminum foil or copper mesh
Electrophysiological setup with recording software and online spike-sorting capabilities	OmniPlex® Neural Data Acquisition System Plexon Inc 6500 Greenville Avenue, Suite 700 Dallas, Texas 75206 USA		Offline sorting software is a potential alternative, multiple scripts and softwares can be found for free in the open source community.