In Vivo Intracellular Recording of Type-Identified Rat Spinal Motoneurons During Trans-Spinal Direct Current Stimulation

Summary

This protocol describes in vivo intracellular recording of rat lumbar motoneurons with simultaneous trans-spinal direct current stimulation. The method enables us to measure membrane properties and to record rhythmic firing of motoneurons before, during and after anodal or cathodal polarization of the spinal cord.

Abstract

Intracellular recording of spinal motoneurons in vivo provides a “gold standard” for determining the cells’ electrophysiological characteristics in the intact spinal network and holds significant advantages relative to classical in vitro or extracellular recording techniques. An advantage of in vivo intracellular recordings is that this method can be performed on adult animals with a fully mature nervous system, and therefore many observed physiological mechanisms can be translated to practical applications. In this methodological paper, we describe this procedure combined with externally applied constant current stimulation, which mimics polarization processes occurring within spinal neuronal networks. Trans-spinal direct current stimulation (tsDCS) is an innovative method increasingly used as a neuromodulatory intervention in rehabilitation after various neurological injuries as well as in sports. The influence of tsDCS on the nervous system remains poorly understood and the physiological mechanisms behind its actions are largely unknown. The application of the tsDCS simultaneously with intracellular recordings enables us to directly observe changes of motoneuron membrane properties and characteristics of rhythmic firing in response to the polarization of the spinal neuronal network, which is crucial for the understanding of tsDCS actions. Moreover, when the presented protocol includes the identification of the motoneuron with respect to an innervated muscle and its function (flexor versus extensor) as well as the physiological type (fast versus slow) it provides an opportunity to selectively investigate the influence of tsDCS on identified components of spinal circuitry, which seem to be differently affected by polarization. The presented procedure focuses on surgical preparation for intracellular recordings and stimulation with an emphasis on the steps which are necessary to achieve preparation stability and reproducibility of results. The details of the methodology of the anodal or cathodal tsDCS application are discussed while paying attention to practical and safety issues.

Introduction

Trans-spinal direct current stimulation (tsDCS) is gaining recognition as a potent method to modify spinal circuit excitability in health and disease^1,2,3. In this technique, a constant current is passed between an active electrode located above selected spinal segments, with a reference electrode located either ventrally or more rostrally⁴. Several studies have already confirmed that tsDCS can be used in managing certain pathological conditions, such as neuropathic pain⁵, spasticity⁶, spinal cord injury<....

Protocol

All procedures connected to this protocol have been accepted by the appropriate authorities (e.g., Local Ethics Committee) and follow the national and international rules on animal welfare and management.

NOTE: Each participant involved in the procedure has to be properly trained in basic surgical procedures and has to have a valid license for performing animal experiments.

1. Anesthesia and premedication

1. Anesthetize a rat with intraperitoneal injections.......

Discussion

If performed correctly, the surgical part of the described protocol should be completed within approximately three hours. One should take particular care in maintaining stable physiological conditions of an animal during the surgery, in particular body temperature and depth of anesthesia. Apart from obvious ethical considerations, a lack of proper anesthesia can result in excessive limb movements during nerve dissection or laminectomy and lead to damage to the preparation or a premature experiment termination. Upon paral.......

Materials

Name	Company	Catalog Number	Comments
Durgs and solutions	-	-	-
Atropinum sulfuricum	Polfa Warszawa	-	-
Glucose	Merck	346351	-
NaHCO3	Merck	106329	-
Pancuronium Jelfa	PharmaSwiss/Valeant	-	Neuromuscular blocker
Pentobarbital sodium	Biowet Puławy Sp. z o.o	-	Main anesthetic agent
Pottasium citrate	Chempur	6100-05-06	-
Tetraspan	Braun	-	HES solution
Surgical equipment	-	-	-
21 Blade	FST	10021-00	Scalpel blade
Cauterizer	FST	18010-00	-
Chest Tubes	Mila	CT1215	-
Dumont #4 Forceps	FST	11241-30	Muscle forceps
Dumont #5 Forceps	FST	11254-20	Dura forceps
Dumont #5F Forceps	FST	11255-20	Nerve forceps
Dumont #5SF Forceps	FST	11252-00	Pia forceps
Forceps	FST	11008-13	Blunt forceps
Forceps	FST	11053-10	Skin forceps
Hemostat	FST	13013-14	-
Rongeur	FST	16021-14	For laminectomy
Scissors	FST	15000-08	Vein scissors
Scissors	FST	15002-08	Dura scissors
Scissors	FST	14184-09	For trachea cut
Scissors	FST	104075-11	Muscle scissors
Scissors	FST	14002-13	Skin scissors
Tracheal tube	-	-	Custom made
Vein catheter	Vygon	1261.201	-
Vessel cannulation forceps	FST	18403-11	-
Vessel clamp	FST	18320-11	For vein clamping
Vessel Dilating Probe	FST	10160-13	For vein dissection
Sugrgical materials	-	-	-
Gel foam	Pfizer	GTIN 00300090315085	Hemostatic agent
Silk suture 4.0	FST	18020-40	-
Silk suture 6.0	FST	18020-60	-
Equipment	-	-	-
Axoclamp 2B	Molecular devices	discontinued	Intracellular amplifier/ new model Axoclamp 900A
CapStar-100 End-tidal CO2 Monitor	CWE	11-10000	Gas analyzer
Grass S-88	A-M Systems	discontinued	Constant current stimulator
Homeothermic Blanket Systems with Flexible Probe	Harvard Apparatus	507222F	Heating system
ISO-DAM8A	WPI	74020	Extracellular amplifier
Microdrive	-	-	Custom made/replacement IVM/Scientifica
P-1000 Microelectrode puller	Sutter Instruments	P-1000	Microelectrode puller
SAR-830/AP Small Animal Ventilator	CWE	12-02100	Respirator
Support frame	-	-	Custom made/replacement lab standard base 51601/Stoelting
Spinal clamps	-	-	Custom made/replacement Rat spinal adaptor 51695/Stoelting
TP-1 DC stimulator	WiNUE	-	tsDCS stimulator
Miscellaneous	-	-	-
1B150-4 glass capillaries	WPI	1B150-4	For microelectrodes production
Cotton wool	-	-	-
flexible tubing	-	-	For respirator and CO2 analyzer connection
MicroFil	WPI	MF28G67-5	For filling micropipettes
Silver wire	-	-	For nerve electrodes