Scanning electron microscopy of the floor of the fourth ventricle in rats subjected to graded impact injury to the sensorimotor cortex.
OBJECTIVE
Respiratory dysfunction including apnea frequently follows head injury in humans. The purpose of this study was to identify any structural alterations in the region of brainstem respiratory nuclei that might account for immediate postinjury respiratory abnormalities in anesthetized experimental animals.


METHODS
Using scanning electron microscopy, the authors examined the floor of the fourth ventricle in injured rats after a piston strike to the sensorimotor cortex that depressed the dura 1, 2, or 4 mm. The rats were killed within minutes of injury. Cortical impact depths measuring either 1 or 2 mm (eight rats) produced no respiratory abnormalities, and the structural integrity of the ependymal lining of the ventricular floor in these animals was not compromised. Thirteen rats were subjected to impact to a 4-mm depth and 10 of these exhibited immediate temporary or permanent apnea. The medullae of nine of these rats were studied using scanning electron microscopy, and the fourth ventricular floors of all nine rats showed tears. Four rats that exhibited immediate, permanent apnea had tears in the caudal fourth ventricle floor near the obex, whereas five rats with no or only transient apnea had tears located more anteriorly, near the aqueduct or laterally. Changes in cerebrospinal fluid flow or pressure dynamics may have caused these tears. Light microscopy, focused near the area postrema, revealed a shearing defect through the ependyma of the fourth ventricular floor into the subjacent neuropil with a disruption of axonal pathways.


CONCLUSIONS
Respiratory neuronal network components lying within 2 mm of the area postrema may well have been disrupted by the caudal tears producing permanent apnea. A similar phenomenon could account for the transient or permanent postinjury apnea seen in humans with severe head injury.
Sarphie
T G
TG
Department of Cell Biology and Anatomy, Neurotrauma Research Laboratory, Louisiana State University Medical Center, New Orleans 70112, USA. tsarph@lsumc.edu
Carey
M E
ME
Davidson
J F
JF
Soblosky
J S
JS
D000818:Animals; D001049:Apnea / Q000209:etiology; D001369:Axons / Q000648:ultrastructure; D002535:Cerebral Aqueduct / Q000293:injuries / Q000648:ultrastructure; D002552:Cerebral Ventricles / Q000293:injuries / Q000648:ultrastructure*; D002555:Cerebrospinal Fluid / Q000502:physiology; D015170:Cerebrospinal Fluid Pressure / Q000502:physiology; D004388:Dura Mater / Q000293:injuries; D004805:Ependyma / Q000293:injuries / Q000648:ultrastructure; D008297:Male; D008526:Medulla Oblongata / Q000293:injuries / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D009044:Motor Cortex / Q000293:injuries* / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D012120:Respiration Disorders / Q000209:etiology; D012125:Respiratory Center / Q000293:injuries / Q000648:ultrastructure; D013003:Somatosensory Cortex / Q000293:injuries* / Q000648:ultrastructure