Repetitive Long-Term Hyperbaric Oxygen Treatment (HBOT) Administered after Experimental Traumatic Brain Injury in Rats Induces Significant Remyelination and a Recovery of Sensorimotor Function

<div><p>Cells in the central nervous system rely almost exclusively on aerobic metabolism. Oxygen deprivation, such as injury-associated ischemia, results in detrimental apoptotic and necrotic cell loss. There is evidence that repetitive hyperbaric oxygen therapy (HBOT) improves outcomes in traumatic brain-injured patients. However, there are no experimental studies investigating the mechanism of repetitive long-term HBOT treatment-associated protective effects. We have therefore analysed the effect of long-term repetitive HBOT treatment on brain trauma-associated cerebral modulations using the lateral fluid percussion model for rats. Trauma-associated neurological impairment regressed significantly in the group of HBO-treated animals within three weeks post trauma. Evaluation of somatosensory-evoked potentials indicated a possible remyelination of neurons in the injured hemisphere following HBOT. This presumption was confirmed by a pronounced increase in myelin basic protein isoforms, PLP expression as well as an increase in myelin following three weeks of repetitive HBO treatment. Our results indicate that protective long-term HBOT effects following brain injury is mediated by a pronounced remyelination in the ipsilateral injured cortex as substantiated by the associated recovery of sensorimotor function.</p></div

Schematic representation of the schedule of HBO treatments and associated analytical assays following induction of traumatic brain injury by fluid percussion.

<p>Schematic representation of the schedule of HBO treatments and associated analytical assays following induction of traumatic brain injury by fluid percussion.</p

Grouping of animals and number of animals per group and testing parameter.

<p>*Uneven number of animals is due to trauma- or anaesthesia-related loss of rats. ^#Different groups were implemented since this allowed for simultaneous analysis of these parameters. Biases in the results of the distinct testing parameters due to previous handling of the animals were thereby avoided, i.e. anaesthetics and interventions during MRI or SSEP did not affect behavioural potentials of the rats and vice versa. mTBI: moderate traumatic brain injury; sTBI: severe traumatic brain injury.</p

Modulation of myelin in the ipsilateral cortex at day 22 following induction of traumatic brain injury and HBO treatment.

<p>A. Quantitative analysis of myelin stained by Luxol Fast Blue. The ipsilateral hemisphere was analysed as a whole in order to avoid bias. Representation of the % tissue translucence of the ipsilateral hemisphere as compared to sham controls; a minimum of 4 successive brain slices per animal were analysed, *<i>p<0.05</i>, HBO-treated versus untreated animals; B. Exemplification of proteolipid protein (PLP) staining at day 22 following induction of traumatic brain injury and HBO treatment; number of animals see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0097750#pone-0097750-t001" target="_blank">Table 1</a>. Error bars represent ± standard error means.</p

Time-dependent changes in the central conduction times following traumatic brain injury and HBO treatment established by somatosensory-evoked potentials.

<p>A. Schematic representation of the somatosensory-evoked potential recording sites adapted from the human 10–20 system. B. The central conduction time (CCT) is calculated by subtracting the peak latency of the major response from the neck from the latency of the primary cortical response C. Time-dependent modulation in the central conduction time recorded at the ipsi- and contralateral hemisphere in treated and untreated brain injured rats. Open square: HBO-treated brain injured rats; open circle: untreated brain injured rats; ---- baseline recordings; The HBOT effect was not observed at all time points (repeated measures mixed model ANOVA; <i>F(1,20) = 0.38, n.s.</i>); however, there was a significant effect at 3 weeks. *<i>p<</i>0.05 (repeated measures ANOVA, Bonferonni corrected); ^#<i>p</i>≤0.003 (t-test), HBO-treated versus untreated injured animals. ^##<i>p<0.001</i> (ANOVA), HBO-treated animals versus sham controls; n = 5 for untreated, n = 12 for HBO-treated (uneven group sizes arise from missing data points in some animals, which were excluded in repeated measures mixed model ANOVA). Error bars represent ± standard error means.</p

Western blot analysis of time-dependent changes in myelin basic protein isoform expression in the ipsilateral cortex following traumatic brain injury and HBO treatment.

<p>A-D Myelin basic protein isoform expression at days 4, 11, 16 and 22 as percentage of expression in sham controls and representative western blot gels. Light grey bars: expression of isoform 21.5-kDa, grey bar: expression of isoform 18.5-kDa; dark grey bar: expression of isoform 17.2-kDa isoform; insert:, 1: sham, 2: brain injured animals, 3: injured and HBO-treated animals; western blot analysis was repeated at least twice per animal sample; n≥4 for each group. *<i>p<0.05</i>, HBO treated vs untreated injured animals; ^#<i>p<0.05</i> as compared to sham controls. Error bars represent ± standard error means.</p