Glyceryl trinitrate for the treatment of ischaemic stroke: Determining efficacy in rodent and ovine species for enhanced clinical translation.

Hypertension is a leading risk factor for death and dependency after ischaemic stroke. However, administering anti-hypertensive medications post-stroke remains contentious with concerns regarding deleterious effects on cerebral blood flow and infarct expansion. This study sought to determine the effect of glyceryl trinitrate (GTN) treatment in both lissencephalic and gyrencephalic pre-clinical stroke models. Merino sheep underwent middle cerebral artery occlusion (MCAO) followed by GTN or control patch administration (0.2 mg/h). Monitoring of numerous physiologically relevant measures over 24 h showed that GTN administration was associated with decreased intracranial pressure, infarct volume, cerebral oedema and midline shift compared to vehicle treatment (p < 0.05). No significant changes in blood pressure or cerebral perfusion pressure were observed. Using optical imaging spectroscopy and laser speckle imaging, the effect of varying doses of GTN (0.69-50 µg/h) on cerebral blood flow and tissue oxygenation was examined in mice. No consistent effect was found. Additional mice undergoing MCAO followed by GTN administration (doses varying from 0-60 µg/h) also showed no improvement in infarct volume or neurological score within 24 h post-stroke. GTN administration significantly improved numerous stroke-related physiological outcomes in sheep but was ineffective in mice. This suggests that, whilst GTN administration could potentially benefit patients, further research into mechanisms of action are required.

Decreased haemodynamic response and decoupling of cortical gamma-band activity and tissue oxygen perfusion after striatal interleukin-1 injection.

BACKGROUND: Neurovascular coupling describes the mechanism by which the energy and oxygen demand arising from neuronal activity is met by an increase in regional blood flow, known as the haemodynamic response. Interleukin 1 (IL-1) is a pro-inflammatory cytokine and an important mediator of neuronal injury, though mechanisms through which IL-1 exerts its effects in the brain are not fully understood. In this study, we set out to investigate if increased cerebral levels of IL-1 have a negative effect on the neurovascular coupling in the cortex in response to sensory stimulation. METHODS: We used two approaches to measure the neuronal activity and haemodynamic changes in the anaesthetised rat barrel somatosensory cortex in response to mechanical whisker stimulation, before and for 6 h after intra-striatal injection of interleukin-1ß or vehicle. First, we used two-dimensional optical imaging spectroscopy (2D-OIS) to measure the size of the functional haemodynamic response, indicated by changes of oxyhaemoglobin (HbO2) and total haemoglobin (HbT) concentration. In the same animals, immunostaining of immunoglobulin G and SJC-positive extravasated neutrophils was used to confirm the pro-inflammatory effects of interleukin-1ß (IL-1ß). Second, to examine the functional coupling between neuronal activity and the haemodynamic response, we used a 'Clark-style' electrode combined with a single sharp electrode to simultaneously record local tissue oxygenation (partial pressure oxygen, pO2) in layer IV/V of the stimulated barrel cortex and multi-unit activity (MUA) together with local field potentials (LFPs), respectively. RESULTS: 2D-OIS data revealed that the size of the haemodynamic response to mechanical whisker stimulation declined over the 6 h following IL-1ß injection whereas the vehicle group remained stable, significant differences being seen after 5 h. Moreover, the size of the transient increases of neuronal LFP activity in response to whisker stimulation decreased after IL-1ß injection, significant changes compared to vehicle being seen for gamma-band activity after 1 h and beta-band activity after 3 h. The amplitude of the functional pO2 response similarly decreased after 3 h post-IL-1ß injection, whereas IL-1ß had no significant effect on the peak of whisker-stimulation-induced MUA. The stimulation-evoked increases in gamma power and pO2 correlated significantly throughout the 6 h in the vehicle group, but such a correlation was not observed in the IL-1ß-injected group. CONCLUSIONS: We conclude that intra-striatal IL-1ß decouples cortical neuronal activity from its haemodynamic response. This finding may have implications for neurological conditions where IL-1ß plays a part, especially those involving reductions in cerebral blood flow (such as stroke).

Delayed reperfusion deficits after experimental stroke account for increased pathophysiology.

Cerebral blood flow and oxygenation in the first few hours after reperfusion following ischemic stroke are critical for therapeutic interventions but are not well understood. We investigate changes in oxyhemoglobin (HbO2) concentration in the cortex during and after ischemic stroke, using multispectral optical imaging in anesthetized mice, a remote filament to induce either 30 minute middle cerebral artery occlusion (MCAo), sham surgery or anesthesia alone. Immunohistochemistry establishes cortical injury and correlates the severity of damage with the change of oxygen perfusion. All groups were imaged for 6 hours after MCAo or sham surgery. Oxygenation maps were calculated using a pathlength scaling algorithm. The MCAo group shows a significant drop in HbO2 during occlusion and an initial increase after reperfusion. Over the subsequent 6 hours HbO2 concentrations decline to levels below those observed during stroke. Platelets, activated microglia, interleukin-1α, evidence of BBB breakdown and neuronal stress increase within the stroked hemisphere and correlate with the severity of the delayed reperfusion deficit but not with the ΔHbO2 during stroke. Despite initial restoration of HbO2 after 30 min MCAo there is a delayed compromise that coincides with inflammation and could be a target for improved stroke outcome after thrombolysis.