Fig. 2

Negative intrathoracic pressure, hypertension and tachycardia increase tracer distribution along the spinal cord after grey matter injection. a fluorescent ovalbumin (AFO-647) was injected into the spinal grey matter. d Macroscopic distribution of AFO-647 in the whole neuraxis was imaged. A white-light image was produced to identify individual spinal levels and fluorescent images of the ventral and dorsal surface were taken. Macroscopic fluorescence was highest around the point of injection at C8, tapering rostrally and caudally. b, c Experiments investigating the effects of changes in respiration compared mechanically ventilated controls (MV) with spontaneous breathing (SB) animals. This tested the effect of positive intrathoracic pressures only (the MV animals were given a neuromuscular blockade to stop any diaphragmatic movement) with SB animals with both positive and negative intrathoracic pressures. e, f Experiments investigating the effects of blood pressure compared 2 groups of mechanically ventilated animals, a control group with low mean arterial pressure (Low MAP) and a group with hypertension (High MAP). g, h To test the effect of heart rate on tracer movement through the spinal cord, mechanically ventilated controls with low heart rate (HR) were compared with mechanically ventilated animals with tachycardia (High HR). SB, hypertensive and tachycardic rats all displayed significantly higher tracer intensity over both the ventral and dorsal surfaces. On post hoc analysis, the difference in tracer intensities reached significance at C5 in the respiration experiments. Two-way analysis of variance (ANOVA) post hoc Bonferroni’s *p < 0.05, **p < 0.01. All error bars are expressed as ± SEM, n = 10 rats