The Effect Of Isoflurane-Anesthesia On The Neurovascular Coupling During Acute Ictal Events In Mice

Background:Unambiguously identifying an epileptic focus with high spatial resolution is a challenge,especially in cases where no anatomic abnormality can be detected.Neurovascular coupling describes the intimate relationship between neuronal activation,increased metabolism,and the resulting rise in cerebral blood flow,or functional hyperemia required to adequately oxygenate active neurons.Neurovascular couplingbased brain mapping techniques are often applied in clinic despite the unclear ictal neurovascular coupling mechanisms,which have been derived primarily from recordings in anesthetized animals with a limited spatial sampling of the ictal core.Objectives:We were going to investigate the relationship between neuronal activities and hemodynamic signals in ictal event in awake and anesthetized mice,and describe the mechanism of the difference between the two states,and explore a better signal for seizure mapping based on neurovascular coupling brain imaging.Method:Focal injection of 4-Aminopyridine(4-AP)was employed to create an acute neocortical seizure model in both anesthetized and awake Thy1-GCa MP6 f transgenic mice.The local field potential(LFP)was recorded through the 4-AP electrode.Meanwhile,a “temporal separation” technique was employed to simultaneously image wide-field calcium and a multispectral intrinsic optical signal.Finally,dextranconjugated fluorescein isothiocyanate(FITC-dx)was injected intravenously to investigate the role of vasodilation in our imaging results.Result:In awake mice,three different calcium propagation patterns were observed.In 9/17 seizures,the calcium signal remained ipsilateral.In 6/17 seizures,the seizure activity first propagated throughout the ipsilateral cortex and then jumped to the homotopic location to the 4-AP injection site in the contralateral hemisphere.In the remaining 2events,the seizure first propagated throughout the ipsilateral cortex and then contiguously propagated to the contralateral cortex.Isoflurane increases highfrequency activity in the LFP,reduces the accuracy of the calcium signal,and restricts contralateral electrographic spread.Anesthesia likewise blunts the hemodynamic response leading to a profound increase in the area of the rise in deoxygenated hemoglobin(Hbr)and rendering the “epileptic dip”.The destruction of endothelial cells by FITC-dx caused a similar decrease in oxygenated hemoglobin(Hb O)and an increase in Hbr.For awake and anesthetized mapping of ictal event,the signal derived from cerebral blood volume(CBV),or total hemoglobin(Hb T),provides the most reliable signal for mapping both the ictal onset and spread.Conclusion:(1)Ictal event has a variety of propagation patterns and mechanisms,but isoflurane-anesthesia will limit the propagation.Brain functional imaging under anesthesia may not unambiguously identify epileptogenic foci.(2)Isoflurane-anesthesia can affect the neuronal activities and blunt the hemodynamic response during seizures compared with unanesthesia.The mechanism of neurovascular coupling during ictal events in isoflurane-anesthetized mice is different from that in awake mice.(3)Isoflurane may reduce vascular functional hyperemia by interfering with endothelial cells and affect hemodynamics during seizures.(4)The CBV-based imaging techniques should be more accurate than blood oxygen level dependent(BOLD)-based imaging techniques for seizure mapping in awake and anesthetized patients and animals.