Oral free session: New findings from surgical sheep models
| Thursday, November 28, 2024 |
| 10:30 AM - 11:00 AM |
| Blackwattle Bay Room 1 & 2, Level R |
Speaker
Dr Lindsea Booth
Researcher
Florey Institute
Neuroinflammation in cardiopulmonary bypass
10:30 AM - 10:45 AMAbstract:
Background: Intraoperative cerebral tissue inflammation and hypoxia may contribute to neurocognitive disorders following cardiopulmonary bypass (CPB). However, the contributions of general anaesthesia (GA), surgical trauma and CPB are unclear.
Methods: In adult female sheep, we investigated the systemic inflammatory response, cerebral tissue oxygenation and the extent of microglia activation (biomarker of neuroinflammation) across cerebral cortical regions during GA and surgical trauma with and without CPB (N=5-10/group). Sheep were studied while conscious, during GA and surgical site injury, with and without CPB.
Results: Plasma TNF-alpha (3.7 [1.4] vs. 1.6 [0.9] ng/mL; mean [standard deviation]; P=0.0004), and IL-6 levels (4.0 [2.1] vs. 1.5 [0.9] ng/mL; P = 0.029) were significantly higher at 1.5 hours, with a further increase in IL-6 at 3 hours (7.0 [3.7] vs. 1.8 [0.9] ng/mL; P < 0.0001) in animals undergoing CPB compared with those that did not. Although cerebral tissue perfusion and oxygen tension were preserved throughout CPB, immunohistochemistry showed pronounced neuroinflammation with greater microglia circularity within the frontal cortex of sheep that underwent CPB compared with those that did not (0.34 [0.02] vs. 0.30 [0.01]; P = 0.029). Moreover, microglia had fewer branches within the parietal (7.7 [1.0] vs. 10.9 [1.3]; P = 0.001) and temporal (7.8 [0.5] vs. 9.9 [1.4]; P= 0.020) cortices in sheep that underwent CPB.
Conclusion: CPB enhanced the release of pro-inflammatory cytokines beyond that initiated by GA and surgical trauma. This systemic inflammation was associated with widespread neuroinflammation despite an absence of cerebral hypoperfusion and hypoxemia. The frontal, cortex appear to be particularly susceptible to neuroinflammation during CPB. These data provide direct evidence of CPB-induced neuroinflammation in a clinically relevant large animal model and provide the scientific rationale to develop targeted drugs to mitigate postoperative neurocognitive disorders in humans.
Methods: In adult female sheep, we investigated the systemic inflammatory response, cerebral tissue oxygenation and the extent of microglia activation (biomarker of neuroinflammation) across cerebral cortical regions during GA and surgical trauma with and without CPB (N=5-10/group). Sheep were studied while conscious, during GA and surgical site injury, with and without CPB.
Results: Plasma TNF-alpha (3.7 [1.4] vs. 1.6 [0.9] ng/mL; mean [standard deviation]; P=0.0004), and IL-6 levels (4.0 [2.1] vs. 1.5 [0.9] ng/mL; P = 0.029) were significantly higher at 1.5 hours, with a further increase in IL-6 at 3 hours (7.0 [3.7] vs. 1.8 [0.9] ng/mL; P < 0.0001) in animals undergoing CPB compared with those that did not. Although cerebral tissue perfusion and oxygen tension were preserved throughout CPB, immunohistochemistry showed pronounced neuroinflammation with greater microglia circularity within the frontal cortex of sheep that underwent CPB compared with those that did not (0.34 [0.02] vs. 0.30 [0.01]; P = 0.029). Moreover, microglia had fewer branches within the parietal (7.7 [1.0] vs. 10.9 [1.3]; P = 0.001) and temporal (7.8 [0.5] vs. 9.9 [1.4]; P= 0.020) cortices in sheep that underwent CPB.
Conclusion: CPB enhanced the release of pro-inflammatory cytokines beyond that initiated by GA and surgical trauma. This systemic inflammation was associated with widespread neuroinflammation despite an absence of cerebral hypoperfusion and hypoxemia. The frontal, cortex appear to be particularly susceptible to neuroinflammation during CPB. These data provide direct evidence of CPB-induced neuroinflammation in a clinically relevant large animal model and provide the scientific rationale to develop targeted drugs to mitigate postoperative neurocognitive disorders in humans.
Biography
Lindsea Booth is an Allan and Maria Myers Senior Research Fellow and head of the Neurocardiovascular Physiology Group at the Florey Institute, University of Melbourne. Her research is focused on understanding how the brain communicates with other vital organs (heart and kidneys) in disease. Her laboratory uses state-of-art genetic engineering techniques to investigate how we can modify brain and nerve function to improve health outcomes.
Dr Ruslan Pustovit
Research Fellow
Florey Institute Of Neuroscience And Mental Health
Seizure-induced changes in cardiac and renal sympathetic nerve activity associated with hypertension, tachycardia and heart arrythmias in non-anaesthetised sheep
10:45 AM - 11:00 AMAbstract:
Background. Sudden unexpected death in epilepsy (SUDEP) is the most frequent epilepsy-related cause of death and occurs primarily after repeated generalised tonic-clonic seizures (GTCS). Tachycardia occurs in 82% of patients with epilepsy and is associated with a dysregulation in sympathetic and parasympathetic activity, which have been hypothesized to contribute toward SUDEP. Since the effects of seizure on sympathetic outflow to the heart and kidney are unknown, we investigated the seizure-induced changes in sympathetic nerve activity to these two vital organs.
Aim. To determine the changes in cardiac and renal sympathetic nerve activity and associated cardiovascular changes in an unanaesthetised sheep model of proconvulsant seizure.
Methods. Adult female Merino sheep were surgically instrumented to record mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), electrocardiogram (ECG), cardiac sympathetic nerve activity (CSNA) and renal SNA (RSNA). The effect of GTCS induced by intravenous administration of pentylenetetrazole (PTZ) (5.0 mg/kg/min for 4 minutes intravenous infusion) was compared with baseline measurements before the seizures.
Results. Intravenous infusion of PTZ in unanaesthetised sheep induced GTCSs that lasted 202±38 sec. By 10 min post-seizure, MAP (79±5 to 129±6 mmHg, P<0.0001), HR (80±5 to 124±2 beats/min, P<0.0001) and CO (4.1±0.2 to 7.9±0.5 L/min, P<0.0001) had increased and remained significantly above baseline for 60 min (n=12). Sinus arrhythmias and premature atrial/ventricular beats occurred in 9 out of 12 sheep with GTCS, either during the seizure or in the first 10 minutes afterwards. CSNA (n=3) was significantly increased, whereas RSNA (n=3) was completely abolished during the GTCS. Return of CSNA and RSNA to baseline levels depended on the severity of seizure and differed between sheep.
Conclusions. Pharmacologically induced seizures in unanaesthetised sheep led to a significant elevation in CSNA, but inhibition of RSNA. This selective increase in sympathetic drive to the heart was associated with tachycardia, arrhythmias and repolarisation changes suggesting that it may promote SUDEP. These findings provide a mechanistically based therapeutic target to decrease the adverse cardiac effects of seizures and reduce the incidence of SUDEP.
Aim. To determine the changes in cardiac and renal sympathetic nerve activity and associated cardiovascular changes in an unanaesthetised sheep model of proconvulsant seizure.
Methods. Adult female Merino sheep were surgically instrumented to record mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), electrocardiogram (ECG), cardiac sympathetic nerve activity (CSNA) and renal SNA (RSNA). The effect of GTCS induced by intravenous administration of pentylenetetrazole (PTZ) (5.0 mg/kg/min for 4 minutes intravenous infusion) was compared with baseline measurements before the seizures.
Results. Intravenous infusion of PTZ in unanaesthetised sheep induced GTCSs that lasted 202±38 sec. By 10 min post-seizure, MAP (79±5 to 129±6 mmHg, P<0.0001), HR (80±5 to 124±2 beats/min, P<0.0001) and CO (4.1±0.2 to 7.9±0.5 L/min, P<0.0001) had increased and remained significantly above baseline for 60 min (n=12). Sinus arrhythmias and premature atrial/ventricular beats occurred in 9 out of 12 sheep with GTCS, either during the seizure or in the first 10 minutes afterwards. CSNA (n=3) was significantly increased, whereas RSNA (n=3) was completely abolished during the GTCS. Return of CSNA and RSNA to baseline levels depended on the severity of seizure and differed between sheep.
Conclusions. Pharmacologically induced seizures in unanaesthetised sheep led to a significant elevation in CSNA, but inhibition of RSNA. This selective increase in sympathetic drive to the heart was associated with tachycardia, arrhythmias and repolarisation changes suggesting that it may promote SUDEP. These findings provide a mechanistically based therapeutic target to decrease the adverse cardiac effects of seizures and reduce the incidence of SUDEP.
Biography
Dr Ruslan Pustovit was recruited by Prof John Furness and started his first postdoctoral position at the Department of Anatomy and Neuroscience at the University of Melbourne. His research focused on the enteric nervous system and ways to stimulate it to improve the gastrointestinal function in people with spinal cord injury and neurodegenerative diseases.
In 2023, Ruslan was recruited by Prof Yugeesh Lankadeva to join his research group to lead the new project as part of a Cardiovascular Health MRFF grant – Investigating the role of seizures on cardiac arrhythmia in driving sudden unexpected death in epilepsy. Dr Pustovit has established a new seizure model in sheep and demonstrated detrimental impact seizures have on heart and brain function, which provides an ideal translational testbed for drug development.
