Electrical stimulation of cerebellar fastigial nucleus fails to rematch blood flow and metabolism in focal ischemic infarctions

Integrity of Cerebellar Fastigial Nucleus Intrinsic Neurons Is Critical for the Global Ischemic Preconditioning

Excitation of intrinsic neurons of cerebellar fastigial nucleus (FN) renders brain tolerant to local and global ischemia. This effect reaches a maximum 72 h after the stimulation and lasts over 10 days. Comparable neuroprotection is observed following sublethal global brain ischemia, a phenomenon known as preconditioning. We hypothesized that FN may participate in the mechanisms of ischemic preconditioning as a part of the intrinsic neuroprotective mechanism. To explore potential significance of FN neurons in brain ischemic tolerance we lesioned intrinsic FN neurons with excitotoxin ibotenic acid five days before exposure to 20 min four-vessel occlusion (4-VO) global ischemia while analyzing neuronal damage in Cornu Ammoni area 1 (CA1) hippocampal area one week later. In FN-lesioned animals, loss of CA1 cells was higher by 22% compared to control (phosphate buffered saline (PBS)-injected) animals. Moreover, lesion of FN neurons increased morbidity following global ischemia by 50%. Ablation of FN neurons also reversed salvaging effects of five-minute ischemic preconditioning on CA1 neurons and morbidity, while ablation of cerebellar dentate nucleus neurons did not change effect of ischemic preconditioning. We conclude that FN is an important part of intrinsic neuroprotective system, which participates in ischemic preconditioning and may participate in naturally occurring neuroprotection, such as "diving response".

Efficacy of transcranial alternating current stimulation over bilateral mastoids (tACSbm) on enhancing recovery of subacute post-stroke patients

BACKGROUND AND AIMS

Transcranial alternating current stimulation (tACS) offers another method of non-invasive brain stimulation in post-stroke rehabilitation. Because it is not known if tACS over bilateral mastoids (tACS_bm) can promote the functional recovery in subacute post-stroke patients, we wish to learn the effect of tACS_bm on improving neurological function and intracranial hemodynamics of subacute post-stroke patients.

METHODS

Sixty subacute post-stroke patients (mean age: 65.4 ± 9.8 years), 15 to 60 days after the onset, were randomly assigned to receiving 15 sessions of usual rehabilitation program without (n = 30) or with tACS_bm (20 Hz and < 400 μA for 30-min; n = 30). The outcome measures included the NIH Stroke Scale (NIHSS) and measures of intracranial hemodynamics before and after treatment.

RESULTS

At the fifteenth session, when compared with the baseline, the mean NIHSS scores of the patients in the tACS_bm group had significantly a larger decrease [18.3 ± 2.6 vs. 10.8 ± 2.7; p < 0.001] than that of the control group [19.1 ± 2.7 vs. 13.0 ± 2.4] [F(1,54) = 4.29, p = 0.043]. After both the first and fifteenth sessions, compared with the control group, the mean blood flow velocity (MFVs) of the tACS_bm group had significantly larger increase in the MCA, ACA, and PCA (p < 0.001), the Gosling pulsatility index (PI) of the tACS_bm group had also significantly larger decline in the MCA, ACA, and PCA than that of the control group (p < 0.001). The best predictor of the changes in the NIHSS scores was the decline in the pulsatility index in the vascular territory of both lesional and non-lesional MCA measured by the end of the last treatment session.

CONCLUSIONS

tACS_bm appeared to be effective for enhancing patients' functional recovery and cerebral hemodynamics in the subacute phase. The extent of recovery seems to be associated with the decline of the resistance in vascular bed of the main cerebral arteries. The mechanisms behind this effect should be explored further through research.

Electrical stimulation of cerebellar fastigial nucleus: mechanism of neuroprotection and prospects for clinical application against cerebral ischemia

For around two decades, electrical fastigial nucleus stimulation (FNS) has been demonstrated to induce neuroprotection involving multiple mechanisms. In this review, we summarize the protective effects of FNS against cerebral ischemia through the inhibition of electrical activity around the lesion, excitotoxic damage on neurons, and brain inflammatory response, as well as apoptosis. Moreover, FNS has been reported to promote nerve tissue repair, reconstruction, and neurological rehabilitation and improve stroke-related complications including poststroke cognitive dysfunction, depression, and abnormal heart rate variability. We thus further discuss the potential of FNS for clinical applications. Given the absence of any risk of inducing sublethal damage, FNS may offer a new approach to preconditioned neuroprotection against cerebral ischemia.

Electrical forepaw stimulation during reversible forebrain ischemia decreases infarct volume

BACKGROUND AND PURPOSE

Functional stimulation is accompanied by increases in regional cerebral blood flow which exceed metabolic demands under normal circumstances, but it is unknown whether functional stimulation is beneficial or detrimental in the setting of acute ischemia. The aim of this study was to determine the effect of forepaw stimulation during temporary focal ischemia on neurological and tissue outcome in a rat model of reversible focal forebrain ischemia.

METHODS

Sprague-Dawley rats were prepared for temporary occlusion of the right middle cerebral artery (MCA) using the filament model. Cerebral blood flow in the MCA territory was continuously monitored with a laser-Doppler flowmeter. Subdermal electrodes were inserted into the dorsal forepaw to stimulate either the forepaw ipsilateral or contralateral to the occlusion starting 1 minute into ischemia and continuing throughout the ischemic period. A neurological evaluation was undertaken after 24 hours of reperfusion, and animals were then euthanized and brain slices stained with 2,3,5-triphenyltetrazolium chloride. Cortical and striatal damage was measured separately.

RESULTS

The cortical and striatal infarct volumes were both significantly reduced in the contralateral stimulated group compared with the ipsilateral stimulated group (48% total reduction). There were no statistically significant differences in the neurobehavioral scores between the 2 groups, or in the laser-Doppler flow measurements from the MCA core.

CONCLUSIONS

Functional stimulation of ischemic tissue may decrease tissue damage and improve outcome from stroke. Although the precise mechanism of this effect remains to be determined, functional stimulation could readily be translated to clinical practice.

Neurogenic neuroprotection

1. Stimulation of the rostral-ventromedial pole of the cerebellar fastigial nucleus exerts powerful effects on systemic and cerebral circulation. 2. Excitation of fibers passing through the fastigial nucleus evokes sympathoactivation and increases in arterial pressure. 3. Increase in cerebral blood flow evoked by excitation of fibers passing through the FN is mediated by intrinsic brain mechanisms independently of metabolism. 4. Excitation of the fastigial nucleus neurons in contrast decreases arterial pressure and cerebral blood flow. The latter probably is secondary to the suppression of brain metabolism. 5. Excitation of the fastigial nucleus neurons significantly decreases damaging effects of focal and global ischemia on the brain. 6. The fastigial nucleus-evoked neuroprotection can be conditioned: 1-h stimulation protects the brain for up to 3 weeks. 7. Other brain structures such as subthalamic cerebrovasodilator area and dorsal periaqueductal gray matter also produce long-lasting brain salvage when stimulated. 8. More than one mechanism may account for neurogenic neuroprotection. 9. Early neuroprotection, which develops immediately after the stimulation, involves opening of potassium channels. 10. Delayed long-lasting neuroprotection may involve changes in genes expression resulting in suppression of inflammatory reaction and apoptotic cascade. 11. It is conceivable that intrinsic neuroprotective system exists within the brain, which renders the brain more tolerant to adverse stimuli when activated. 12. Knowledge of the mechanisms of neurogenic neuroprotection will allow developing new neuroprotective approaches.

Electrical stimulation of the dorsal periaqueductal gray decreases volume of the brain infarction independently of accompanying hypertension and cerebrovasodilation

We investigated whether selective stimulation of neurons of the sympathoinhibitory ventral periaqueductal gray (VPAG), or sympathoexcitatory dorsal periaqueductal gray (DPAG), differentially modulates CBF and EEG and exerts neuroprotection. Electrical stimulation of either regions of PAG comparably elevated AP and CBF, whereas chemical stimulation with the D,L-homocysteine produced either sympathoinhibition accompanied by decrease in CBF from ventral region or sympathoexcitation accompanied by increase in CBF from dorsal region in nonspinalized rats. The CBF effects evoked from DPAG and VPAG by chemical stimulation were preserved in spinalized rats supporting that the evoked CBF responses result directly from stimulation and are not secondary to AP changes. Stimulation of either region, whether chemical or electrical, synchronized the EEG. To explore whether PAG stimulation might protect the brain against ischemic injury, in other rats the VPAG or DPAG were stimulated for 1 h (50 Hz, 1 s on/1 s off, 75-100 microA) and the middle cerebral artery occluded 72 h later. Stimulation of the DPAG, but not VPAG, significantly reduced infarction volumes relative to sham-stimulated controls as determined 24 h after occlusion. Elevations of AP and CBF did not differ between groups. We conclude: (a). intrinsic neurons of D- and VPAG differentially regulate CBF; (b). neurons of DPAG are neuroprotective independently of changes in CBF and/or AP. The DPAG effect on infarct volume may be related to the central neuroprotective pathway evoked by stimulation of the cerebellar FN.

Inducible nitric oxide synthase expression in the ischemic core and penumbra after transient focal cerebral ischemia in mice

The present observations examined the hypothesis that the iNOS expression in the ischemic penumbra after a transient focal ischemic insult is involved in the recruitment of penumbra into infarction. The middle cerebral artery in mice was occluded for 2 h by an intraluminal filament and then recirculated. The measurement of iNOS activity, iNOS protein formation and NO concentration in the ischemic core and penumbra, and the determination of infarct volume were performed at 6, 12, 24 and 48 h after reperfusion. iNOS protein and iNOS enzymatic activity appeared at 6 h, peaked at 24 h, and declined at 48 h in the penumbra after reperfusion. iNOS protein was not detectable in contralateral area and in sham-operated brains. The time course of iNOS protein, enzymatic activity and NO concentration in the penumbra but not in the core matched the process of infarct maturation. Treatment with iNOS inhibitor aminoguanidine (100 mg.kg(-1), i.p.) at 6 and 12 h after reperfusion inhibited iNOS activity by 88.0 +/- 10.4% and reduced NO concentration by 48.5 +/- 8.3% in the penumbra, and lessened infarct size by 48.8 +/- 7.2%. The iNOS activity and NO level in the core were not affected by the administration of aminoguanidine. These results suggest that iNOS expression in the ischemic penumbra is involved in the recruitment of penumbra into infarction and thereby contributing to the enlargement of infarct.

Stimulation of the subthalamic vasodilator area and fastigial nucleus independently protects the brain against focal ischemia

We investigated whether stimulation of the functionally discrete subthalamic region, subthalamic cerebrovasodilator area (SVA), which increases cerebral blood flow (CBF) when excited, would, like stimulation of cerebellar fastigial nucleus (FN), produce central neurogenic neuroprotection. A 1-h electrical stimulation of SVA or FN reduced infarctions triggered by permanent occlusion of middle cerebral artery (MCA) by 48-55% in Sprague-Dawley rats and by 59% in Fisher rats. The salvaging effect of SVA stimulation, similar to FN, was long lasting and reduced the volume of infarctions placed 72 h or 10 days later by 58 and 26%, respectively, in Fisher rats. Bilateral lesioning of FN neurons by the microinjection of ibotenic acid 5 days before SVA stimulation did not affect SVA-evoked neuroprotection. Bilateral lesions of SVA neurons administered 5 days before FN stimulation had no effect on FN-induced neuroprotection but reversed the stimulus-locked increase in CBF accompanying FN stimulation. This study demonstrates that (1) excitation of neurons and/or fibers projecting through the SVA reduces ischemic infarctions as substantially as excitation of FN neurons; (2) the effects are long-lasting and not attributable to increases in cerebral blood flow, changes in blood gases or brain temperature, or rat strain; (3) the neuroprotective effects of SVA and FN stimulation are mutually independent and (4) FN-evoked cerebrovasodilation is mediated by SVA neurons. The SVA and FN are part of a neuronal system in CNS, which is distributed and, when excited, acts to protect the brain from ischemic injury.

Role of potassium channels in the central neurogenic neuroprotection elicited by cerebellar stimulation in rat

Electrical stimulation of the cerebellar fastigial nucleus (FN) in spontaneously hypertensive (SHR), Wistar-Kyoto (WKY) and Fisher rats reduced, by approximately 50%, the infarctions produced by occlusion of the middle cerebral artery. Blockade of ATP-dependent potassium (K-ATP) channels with glibenclamide (i.c.v.) abolished salvage only in the SHR rat. While blockade of K-ATP channels failed to abolish salvage in WKY and Fisher rats, participation of potassium channels in neurogenic neuroprotection cannot be excluded.

Intrinsic neurons of fastigial nucleus mediate neurogenic neuroprotection against excitotoxic and ischemic neuronal injury in rat

Electrical stimulation of the cerebellar fastigial nucleus (FN) elevates regional cerebral blood flow (rCBF) and arterial pressure (AP) and provides long-lasting protection against focal and global ischemic infarctions. We investigated which neuronal element in FN, perikarya or axons, mediates this central neurogenic neuroprotection and whether it also protects against excitotoxicity. In anesthetized rats, the FN was stimulated for 1 hr, and ibotenic acid (IBO) was microinjected unilaterally into the striatum. In unstimulated controls, the excitotoxic lesions averaged approximately 40 mm3. Stimulation of FN, but not dentate nucleus (DN), significantly reduced lesion volumes up to 80% when IBO was injected 15 min, 72 hr, or 10 d, but not 30 d, thereafter. In other rats, intrinsic neurons of FN or DN were destroyed by pretreatment with IBO. Five days later, the FN was stimulated, and 72 hr later, IBO was microinjected into the striatum. Lesions of FN, but not DN, abolished neuroprotection but not the elevations of rCBF and AP elicited from FN stimulation. Excitotoxic lesions of FN, but not DN, also abolished the 37% reduction in focal ischemic infarctions produced by middle cerebral artery occlusion. Excitation of intrinsic FN neurons provides long-lasting, substantial, and reversible protection of central neurons from excitotoxicity, as well as focal ischemia, whereas axons in the nucleus, probably collaterals of ramified brainstem neurons, mediate the elevations in rCBF, which do not contribute to neuroprotection. Long-lived protection against a range of injuries is an unrecognized function of FN neurons transmitted over pathways distinct from those regulating rCBF.

Neuroprotective electrical stimulation of cerebellar fastigial nucleus attenuates expression of periinfarction depolarizing waves (PIDs) and inhibits cortical spreading depression

In rat, electrical stimulation of the cerebellar fastigial nucleus (FN) for 1 h reduces the volume of focal ischemic infarctions produced by occluding the middle cerebral artery (MCAO), even 10 days later. The mechanism by which this 'central neurogenic neuroprotection' salvages ischemic brain is not known but does not result from changes in cerebral perfusion. MCAO also triggers periodic periinfarction depolarizing waves (PIDs) in the ischemic penumbra, the territory of salvage. These may contribute to neuronal death and promote infarct expansion. Conceivably, FN stimulation, which can otherwise modify cortical excitability, may alter the development of PIDs. We investigated in anesthetized rats whether FN stimulation modifies PIDs expression and, if so, the threshold for evoking cortical spreading depression (CSD), a process sharing characteristics with PIDs and an index of cortical excitability. Stimulation of FN immediately or 72 h before MCAO decreased infarction volumes by approximately 45% (p<0.01), increased PID latency >10-fold, and decreased the number of PIDs by >50% (p<0.001). In normal rats, stimulation of FN increased the threshold current for eliciting CSD by 175% and slowed its propagation velocity by 35% (p<0.01 for each) immediately, but not 72 h, after FN stimulation. We conclude: FN stimulation elicits long-lasting suppression of PIDs in parallel with neuroprotection. However, PIDs suppression over time is unlikely to result from a major increase in cortical tolerance to depolarization and probably is not the principal mechanism of salvage.

Stimulation of cerebellar fastigial nucleus inhibits interleukin-1beta-induced cerebrovascular inflammation

Electrical stimulation of the cerebellar fastigial nucleus (FN) in rat protects the brain against ischemia. We studied whether FN could reduce the cerebrovascular inflammation as a mechanism of protection. FN or dentate nucleus (sham controls) was electrically stimulated for 1 h, and 72 h later rats were either injected with interleukin (IL)-1beta into the striata or processed to analyze inflammatory responses in isolated brain microvessels. In striata, IL-1beta induced a recruitment of leukocytes that was reduced by 50% by FN stimulation. In isolated microvessels, IL-1beta induced the transient and dose-dependent upregulation of the mRNAs encoding for the inducible nitric oxide synthase (NOS-2), intercellular adhesion molecule 1 (ICAM-1), and inhibitory kappaB-alpha (IkappaB-alpha), an inhibitor of nuclear factor-kappaB. FN stimulation decreased the upregulation of NOS-2 and ICAM-1 mRNAs, whereas it increased IkappaB-alpha mRNA expression. Dentate nucleus stimulation did not mimic the FN actions. These findings suggest that FN stimulation may render brain microvessels refractory to IL-1beta by overproduction of IkappaB-alpha and support the hypothesis that alteration of microvascular inflammation may contribute to the central neurogenic neuroprotection elicited from the FN.

Cerebellar stimulation reduces inducible nitric oxide synthase expression and protects brain from ischemia

A focal infarction produced by occlusion of the middle cerebral artery (MCAO) in spontaneously hypertensive rats induced expression of inducible nitric oxide synthase (iNOS) mRNA, measured by competitive reverse transcription-polymerase chain reaction. The mRNA appeared simultaneously in the ischemic core and penumbra at 8 h, peaked between 14 and 24 h, and disappeared by 48 h. At 24 h, inducible nitric oxide synthase (iNOS)-like immunoreactivity was present in the endothelium of cerebral microvessels and in scattered cells, probably representing leukocytes or activated microglia. Electrical stimulation of the cerebellar fastigial nucleus (FN) for 1 h, 48 h before MCAO, reduced infarct volumes by 45% by decreasing cellular death in the ischemic penumbra. It also reduced by >90% the expression of iNOS mRNA and protein in the penumbra, but not core, and decreased by 44% the iNOS enzyme activity. We conclude that excitation of neuronal networks represented in the cerebellum elicits a conditioned central neurogenic neuroprotection associated with the downregulation of iNOS mRNA and protein. This neuroimmune interaction may, by blocking the expression of iNOS, contribute to neuroprotection.

Stimulation of cerebellum protects hippocampal neurons from global ischemia

We investigated whether electrical stimulation of the cerebellar fastigial nucleus (FN) can protect pyramidal neurons of the CA1 zone of dorsal hippocampus from delayed neuronal death caused by global ischemia. Stimulation of the FN for 1 h prior to transient 4-vessel occlusion in anesthetized rats salvaged 57% (p < 0.01) of pyramidal neurons from degeneration. This effect could be preconditioned. Sham simulation of FN or stimulation of the rostral ventrolateral medulla (RVL) were without effect (p > 0.5). Excitation of intrinsic neuronal pathways represented in FN can protect central neurons from global as well as focal ischemic degeneration. The brain contains systems designed to protect it from ischemia by mechanisms of central neurogenic neuroprotection acting independently of actions on cerebral blood flow.

Central neurogenic neuroprotection: central neural systems that protect the brain from hypoxia and ischemia

The brain can protect itself from ischemia and/or hypoxia by two distinct mechanisms which probably involve two separate systems of neurons in the CNS. One, which mediates a reflexive neurogenic neuroprotection, emanates from oxygen-sensitive sympathoexcitatory reticulospinal neurons of the RVLM. These cells, excited within seconds by reduction in blood flow or oxygen, initiate the systemic vascular components of the oxygen conserving (diving) reflex. They profoundly increase rCBF without changing rCGU and, hence, rapidly and efficiently provide the brain with oxygen. Upon cessation of the stimulus the systemic and cerebrovascular adjustments return to normal. The system mediating reflex protection projects via as-yet-undefined projections from RVLM to upper brainstem and/or thalamus to engage a small population of neurons in the cortex which appear to be dedicated to transducing a neuronal signal into vasodilation. It also appears to relay the central neurogenic vasodilation elicited from other brain regions, including excitation of axons innervating the FN. This mode of protection would be initiated under conditions of global ischemia and/or hypoxemia because the signal is detected by medullary neurons. The second neuroprotective system is represented in intrinsic neurons of the cerebellar FN and mediates a conditioned central neurogenic neuroprotection. The response can be initiated by excitation of intrinsic neurons of the FN and does not appear dependent upon RVLM. The pathways and transmitters that mediate the effect are unknown. The neuroprotection afforded by this network is long-lasting, persisting for almost two weeks, and is associated with reduced excitability of cortical neurons and reduced immunoreactivity of cerebral microvessels. This mode of neuroprotection, moreover, is not restricted to focal ischemia, as we have demonstrated that it also protects the brain against global ischemia and excitotoxic cell death. That the brain may have neuronal systems dedicated to protecting itself from injury, at first appearing to be a novel concept, is, upon reflection, not surprising since the brain is not injured in naturalistic behaviors characterized by very low levels of rCBF, diving and hibernation. An understanding of the pathways, transmitters, and molecules engaged in such protection may provide new insights into novel therapies for a range of disorders characterized by neuronal death.

Autonomic and vasomotor regulation

The cerebellum not only modulates the systemic circulation, but also profoundly influences cerebral blood flow (rCBF) and metabolism (rCGU), and initiates long-term protection of the brain from ischemia. Electrical stimulation of the rostral ventral pole of the fastigial nucleus (FN), elevates arterial pressure (AP), releases vasoactive hormones, elicits consummatory behavioral and other autonomic events and site specifically elevates rCBF independently of changes in rCGU. Cerebral vasodilation results from the antidromic excitation of axons of brain stem neurons which innervate cerebellum and, through their collaterals, neurons in the rostral ventrolateral reticular nucleus (RVL). RVL neurons initiate cerebral vasodilation over polysynaptic vasodilator pathways which engage a population of vasodilator neurons in the cerebral cortex. In contrast, intrinsic neurons of FN, when excited, elicit widespread reductions in rCGU and, secondarily, rCBF, along with sympathetic inhibition. Electrical stimulation of FN can reduce the volume of a focal cerebral infarction produced by occlusion of the middle cerebral artery by 50%. This central neurogenic neuroprotection is long lasting (weeks) and is not due to changes in rCBF or rCGU. Rather, it appears to reflect alterations in neuronal excitability and/or downregulation of inflammatory responses in cerebral vessels. The FN, therefore, appears to be involved in widespread autonomic, metabolic, and behavioral control, independent of motor control. The findings imply that the FN receives inputs from neurons, probably widely represented in the central autonomic core, which may provide continuing information processing of autonomic and behavioral states. The cerebellum may also widely modulate the state of cortical reactivity to ischemia, hypoxia, and possibly other neurodegenerative events.