Unfixed Head and Closed Skull Weight Drop Method as a Rodent Model of Mild Traumatic Brain Injury (Mtbi) for Studies of Post-Traumatic Headache (PTH)

Summary

The protocol describes a rodent model of unfixed head mild traumatic brain injury induced by a weight drop allowing for free linear and rotational impact-related forces. The dynamics of this injury are similar to concussions that occur in humans and are useful to investigate underlying mechanisms involved in post-traumatic headache.

Abstract

Mild traumatic brain injury (mTBI) represents one of the major contributors to the overall global disability. Post-traumatic headache (PTH) is a frequent and often the most debilitating associated symptom. For some patients, headache resolves in the first weeks to 3 months following a mTBI, a condition defined as acute PTH (APTH). However, several individuals continue to experience ongoing or intermittent headaches that persist beyond 3 months, a condition defined as persistent PTH (PPTH). Many animal models of TBI have been developed. Often, these are performed by impacting the head of rodents whose motion is mechanically fixed and/or involves an open skull. The following protocol describes a model where the head is unfixed, allowing free linear and rotational forces induced by a standardized weight drop that has similarities to concussions that occur in many situations in humans. The headache in this model is characterized by initial transient tactile allodynia in the cephalic region that lasts for several days and reflects the pain-like feature of APTH. Tactile allodynia is also observed in the extra-cephalic body areas suggestive of central sensitization and PTH. Following resolution of the transient APTH, animals display long-lasting latent sensitization, where baseline pain responses are normal, but otherwise innocuous provocative stimuli provoke cephalic and hind paw tactile allodynia, suggesting the development of persistent sensitization that may underlie PPTH. The key advantages of this model include concussion-like injury dynamics (closed head injury, reproduction of both linear and rotational forces) and induction of transient pain-like features followed by a long-lasting (persistent) period of increased vulnerability to normally innocuous stimuli that may reinstate a headache-like response. This method may be used to investigate the underlying pathological mechanisms involved in the transition of APTH to PPTH and the evaluation of novel therapeutic strategies for the treatment or prevention of APTH and PPTH.

Introduction

Mild traumatic brain injury (mTBI), also known as concussion, represents the most prevalent type of closed head injury and is one of the leading causes of global disability^1,2,3,4,5. mTBI often affects civilians, military personnel, and veterans and can result from blunt trauma, acceleration, or deceleration forces, including falls, motor vehicle collisions, contact or collision sports, exposure to blasts, and additional mechanisms of injury^1,2. Pos....

Protocol

All procedures were approved by the ethical guidelines of the International Association for the Study of Pain regulations on animal welfare and the National Institutes of Health guidelines for the care and use of laboratory animals. The Institutional Animal Care and Use Committee of the University of Arizona previously approved the experimental procedures described in this protocol.

NOTE: The mTBI model described in this protocol is optimized for female or male C57/BL6J¹²

Discussion

Herein, we describe a mouse model of mTBI in which the head is unfixed, reproducing many biomechanical aspects of common human mild head injuries, including closed-skull, blunt force direct impact, and linear, rotational, acceleration, and shearing forces from unrestrained head movement. It is suggested that these similarities of the model to human concussion might allow for increased relevance of investigations of pathophysiological mechanisms associated with APTH and the transition to PPTH. The injury produced by this .......

Materials

Name	Company	Catalog Number	Comments
Clear PMMA chambers (10 x 10 x 20 cm)	NA	NA	in house
Disposable underpad	VWR	56617-014	Can be replaced by any brand of laboratory disposable underpad
Fluriso Isoflurane	Vet One	502017	Can be replaced by any animal laboratory isuflurane inhalational anesthesia
Inhalational anesthesia station	Parkland Scientific	PM1002	Can be replaced by any animal laboratory inhalational anesthesia station
LED lights for BLS exposure
Mesh stand (0.635 cm² grid) for behavioral testing	NA	NA	in house
Mono nylon filament for hindpaw region (0.6 g/3.84)	North Coast medical	NC12775-07
Mono nylon filament for periorbital region (0.4 g/3.61)	North Coast medical	NC12775-06
mTBI/Sham apparatus	NA	NA	in house
mTBI/sham induction-recording sheet of paper	NA	NA	Prepare the sheet according to the Supplementary Material
Pen	Fisher Scientific	NC1836221	Any brand of pen
Scotch Magic Clear tape 3M	Fisher Scientific	50-205-2453	Can be replaced by any brand of clear tape
Stopwatch	Fisher Scientific	06-662-56	Can be replaced by any brand of stopwatch
Tissue paper	Kleenex/Fisher Scientific	15-235-130	Can be replaced by any brand tissue paper (4.4” x 8.4”)