Application of Passive Head Motion to Generate Defined Accelerations at the Heads of Rodents

Summary

The present protocol describes a custom-designed ''passive head motion'' system, which reproduces mechanical accelerations at rodents' heads generated during their treadmill running at moderate velocities. It allows dissecting mechanical factors/elements from the beneficial effects of physical exercise.

Abstract

Exercise is widely recognized as effective for various diseases and physical disorders, including those related to brain dysfunction. However, molecular mechanisms behind the beneficial effects of exercise are poorly understood. Many physical workouts, particularly those classified as aerobic exercises such as jogging and walking, produce impulsive forces at the time of foot contact with the ground. Therefore, it was speculated that mechanical impact might be implicated in how exercise contributes to organismal homeostasis. For testing this hypothesis on the brain, a custom-designed ''passive head motion'' (hereafter referred to as PHM) system was developed that can generate vertical accelerations with controlled and defined magnitudes and modes and reproduce mechanical stimulation that might be applied to the heads of rodents during treadmill running at moderate velocities, a typical intervention to test the effects of exercise in animals. By using this system, it was demonstrated that PHM recapitulates the serotonin (5-hydroxytryptamine, hereafter referred to as 5-HT) receptor subtype 2A (5-HT_2A) signaling in the prefrontal cortex (PFC) neurons of mice. This work provides detailed protocols for applying PHM and measuring its resultant mechanical accelerations at rodents' heads.

Introduction

Exercise is beneficial to treat or prevent several physical disorders, including lifestyle diseases such as diabetes mellitus and essential hypertension¹. Related to this, evidence has also been accumulated regarding the positive effects of exercise on brain functions². However, molecular mechanisms underlying the benefits of exercise for the brain remain primarily unelucidated. Most physical activities and workouts generate mechanical accelerations at the head, at least to some extent. Whereas various physiological phenomena are mechanically regulated, the importance of mechanical loading has, in most cases, been docume....

Protocol

All animal experiments were approved by the Institutional Animal Care and Use Committee of National Rehabilitation Center for Persons with Disabilities. 8-9 weeks old male Sprague-Dawley rats were used to measure accelerations at the head during treadmill running and PHM. 9-10 weeks old male C57BL/6 mice were used for behavior tests and histological analyses of the PFC. The animals were obtained from commercial sources (see Table of Materials).

1. Measurement of magnitudes of accelerations along x-, y-, and z-axes during treadmill running

1. Anesthetize the rat with inhalation of 1.5% isoflurane.

Results

The peak magnitude of the vertical accelerations at the rats' heads during their treadmill running at a moderate velocity (20 m/min) was approximately 1.0 × g (Figure 1C). The PHM system (Figure 1D) was set up to generate vertical acceleration peaks of 1.0 × g at the rodents' heads.

PHM application (2 Hz, 30 min/day for 7 days) to mice significantly attenuated their HTR as compared to the control mice (daily anesthet.......

Discussion

Using the developed PHM application system, we have shown that 5-HT signaling in their PFC neurons is mechanically regulated. Because of the complexity of exercise effects, it has been difficult to precisely dissect the consequence of exercise in the context of health promotion. The focus is on mechanical aspects to preclude the involvement or contribution of metabolic events that may occur with or subsequently to exercise activities, such as energy consumption. The method described here is expected to be more broadly us.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
5-hydroxytryptophan (5-HTP)	Sigma-Aldrich	H9772	Serotonin (5-HT) precursor
Brushless motor driver	Oriental motor	BMUD30-A2	Speed changer build-in motor driver
C57BL/6 mice	Oriental yeast company	C57BL/6J	Mice used in this study
Cryostat	Leica	CM33050S	Microtome to cut frozen samples
DC Motor	Oriental motor	BLM230-GFV2	Motor
Donkey anti-goat Alexa Fluor 568	Invitrogen	A-11057	Secondary antibody used for immunohistochemical staining
Donkey anti-mouse Alexa Fluor 647	Invitrogen	A-31571	Secondary antibody used for immunohistochemical staining
Donkey anti-rabbit Alexa Fluor 488	Invitrogen	A-21206	Secondary antibody used for immunohistochemical staining
Donkey serum	Sigma-Aldrich	S30-100ML	Blocker of non-specific binding of antibodies in immunohistochemical staining
Fluorescence microscope	Keyence	BZ-9000	Fluorescence microscope
Goat polyclonal anti-5-HT2A receptor	Santa Cruz Biotechnology	sc-15073	Primary antibody used for immunohistochemical staining
Isoflurane	Pfizer	v002139	Inhalation anesthetic
KimWipe	NIPPON PAPER CRECIA	S-200	Paper cloth for cleaning surfaces, parts, instruments in labratory
Liquid Blocker	Daido Sangyo	PAP-S	Marker used to make the slide surface water-repellent
Mouse monoclonal anti-NeuN (clone A60)	EMD Millipore (Merck)	MAB377	Primary antibody used for immunohistochemical staining
NinjaScan-Light	Switchscience	SSCI-023641	Accelerometer to measure accelerations
OCT compound	Sakura Finetek	45833	Embedding agent for preparing frozen tissue sections
ProLong Gold Antifade Mountant	Invitrogen	P36934	Mounting medium to prevent flourscence fading
Rabbit polyclonal anti-c-Fos	Santa Cruz Biotechnology	sc-52	Primary antibody used for immunohistochemical staining
Slide box	AS ONE	03-448-1	Opaque box to store slides
Spike2	Cambridge electronic design limited (CED)	N/A	Application software used to analyze acceleration
Sprague-Dawley rats	Japan SLC	Slc:SD	Rats used in this study
Treadmill machine	Muromachi	MK-680	System used in experiments of forced running of rats and mice