Fig. 4
Intrathoracic pressure promotes fluid flow into the spinal white and grey matter. A Quantitative analysis of fluorescent ovalbumin (AFO-647) inflow into the spinal interstitium after intracisternal infusion was assessed on microscopic images. Grey and white matter were delineated on the channel immunostained with rat endothelial cell antigen (RECA). Microscopic fluorescence intensities within the spinal cord from: B, E, H whole coronal sections; C, F, I white matter; and D, G, J grey matter were measured at every level from C2 to T4. Experiments investigating the effects of: B–D respiration; E–G blood pressure; and, H–J heart rate on fluid flow were carried out. B–D There was significantly higher fluorescence within the whole axial section (B), grey matter (D), and white matter (C), in spontaneous breathing (SB) rats compared with the control groups. On post hoc analysis, the difference between SB and controls reached significance at C2 in all compartments of the spinal cord, from C2 to C4 compared to Controls, C2 and C4 compared to Normal controls in the white matter, and at C2 only in the grey matter. In the white matter and whole axial section (E–G), the intensity of AFO-647 signal was significantly lower in hypertensive rats compared with controls ventilated at a higher respiratory rate and normalised partial pressure of CO2 and pH (Normal). However, compared with the matched Controls, tracer fluorescence was higher in hypertensive rats. In the grey matter (G), tracer signal intensity was higher in hypertensive rats than either of the control groups. H–J Within the whole axial section and white matter, there was no difference in AFO-647 intensity between tachycardic rats and Normal control, but the tachycardic cohort had significantly higher fluorescence than Controls. Tracer signal was significantly higher in the grey matter in tachycardic animals compared with controls (J). Two-way analysis of variance (ANOVA) post hoc Bonferroni’s, *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001, mean ± SEM, n = 6/7 rats. (*) denotes significant difference to Controls, (†) denotes significant difference to Normal controls