Despite progress in reducing ischemic stroke damage, complete protection remains elusive. Here we demonstrate that, after permanent occlusion of a major cortical artery (middle cerebral artery; MCA), single whisker stimulation can induce complete protection of the adult rat cortex, but only if administered within a critical time window. Animals that receive early treatment are histologically and behaviorally equivalent to healthy controls and have normal neuronal function. Protection of the cortex clearly requires reperfusion to the ischemic area despite permanent occlusion. Using blood flow imaging and other techniques we found evidence of reversed blood flow into MCA branches from an alternate arterial source via collateral vessels (inter-arterial connections), a potential mechanism for reperfusion. These findings suggest that the cortex is capable of extensive blood flow reorganization and more importantly that mild sensory stimulation can provide complete protection from impending stroke given early intervention. Such non-invasive, non-pharmacological intervention has clear translational potential.
Summary Experience alters cortical networks through neural plasticity mechanisms. During a developmental critical period, the most dramatic consequence of occluding vision through one eye (monocular deprivation) is a rapid loss of excitatory synaptic inputs to parvalbumin-expressing (PV) inhibitory neurons in visual cortex. Subsequent cortical disinhibition by reduced PV cell activity allows for excitatory ocular dominance plasticity. However, the molecular mechanisms underlying critical period synaptic plasticity are unclear. Here we show that brief monocular deprivation during the critical period down-regulates neuregulin-1(NRG1)/ErbB4 signaling in PV neurons, causing retraction of excitatory inputs to PV neurons. Exogenous NRG1 rapidly restores excitatory inputs onto deprived PV cells through downstream PKC-dependent activation and AMPA receptor exocytosis, thus enhancing PV neuronal inhibition to excitatory neurons. NRG1 treatment prevents the loss of deprived eye visual cortical responsiveness in vivo. Our findings reveal molecular, cellular and circuit mechanisms of NRG1/ErbB4 in regulating the initiation of critical period visual cortical plasticity.
The maturation of inhibitory circuits in the juvenile cortex triggers a critical period of plasticity in visual system development. Although several manipulations of inhibition can alter its timing, none have reactivated critical period plasticity in adulthood. We developed a transplantation method to reactivate critical period plasticity in the adult visual cortex. Transplanted embryonic inhibitory neurons from the medial ganglionic eminence reinstate ocular dominance plasticity in adult recipients. Transplanted inhibitory cells develop cell-type appropriate molecular characteristics and visually evoked responses. In adult mice impaired by deprivation during the juvenile critical period, transplantation also recovers both visual cortical responses and performance on a behavioral test of visual acuity. Plasticity and recovery are induced when the critical period would have occurred in the donor animal. These results reveal that the focal reactivation of visual cortical plasticity using inhibitory cell transplantation creates a new critical period that restores visual perception after childhood deprivation.
When delivered within 1 and in most cases 2 hours of permanent middle cerebral artery occlusion (pMCAO), mild sensory stimulation (intermittent single whisker stimulation) was shown to be completely neuroprotective according to assessment with multiple techniques 24 hours after pMCAO in a rodent model of ischemic stroke (Lay et al., 2010). The acute effect of stimulation treatment on the ischemic cortex however, had yet to be reported. Here we characterize cortical function and perfusion during the 120 minute whisker stimulation period in four experimental groups with treatment initiated 0, 1, 2 hours (protected groups) or 3 hours post-pMCAO (unprotected group) using multiple techniques. According to functional imaging, a gradual return of evoked whisker functional representation to baseline levels was initiated with treatment onset and completed within the treatment period. Evoked neuronal activity and reperfusion to the ischemic area also showed a gradual recovery in protected animals. Surprisingly, a similar recovery profile was observed in response to treatment in all protected animals, irrespective of treatment onset time. Non-stimulated pMCAO control group data demonstrate that reperfusion is not spontaneous. This makes the complete protection observed in the majority of animals stimulated at 2 hours post-pMCAO even more surprising as these animals recovered despite having been in this severely ischemic state for two full hours. In summary, when delivered within a 2 hour window post- pMCAO, whisker stimulation treatment initiated reperfusion and a gradual recovery of cortical function that was completed or nearly completed within the treatment period.
Stroke is the fourth leading cause of death in the United States and the leading cause of long-term disability. Ischemic stroke, due to an interruption in blood supply, is particularly prevalent; 87% of all strokes are ischemic. Unfortunately, current options for acute treatment are extremely limited and there is a great need for new treatment strategies. This review will discuss evidence that mild sensory stimulation can completely protect the jeopardized brain from an impending stroke in a rodent model. When delivered within the first 2 hours following ischemic onset, this stimulation results in complete protection, including a full reestablishment of cortical function, sensorimotor capabilities, and blood flow. Identical stimulation, however, initiated 3 hours following ischemic onset, results in an increase in damage compared with untreated animals. The protective effect is not specific to a single sensory modality, anesthesia, or age, and increasing evoked cortical activity by increasing stimulation accelerates recovery. Taken together, these findings demonstrate that cortical activity is a critical factor for protection and suggest a new, exciting potential avenue for the development of acute stroke treatment strategies that may produce a noninvasive, drug-free, equipment-free, and side effect-free means of protecting from ischemic stroke.
Background and Purpose Using a rodent model of ischemia (permanent middle cerebral artery occlsion; pMCAO), our lab previously demonstrated that 4.27 minutes of patterned single whisker stimulation delivered over 120 minutes can fully protect from impending damage when initiated within two hours of pMCAO (“early”). When initiated three hours post-pMCAO (“late”), stimulation resulted in irreversible damage. Here we investigate the effect of altering pattern, distribution, or amount of stimulation in this model. Methods We assessed the cortex using functional imaging and histological analysis with altered stimulation treatment protocols. In two groups of animals we administered the same number of whisker deflections but in a random rather than patterned fashion, distributed either over 120 minutes or condensed into 10 minutes post-pMCAO. We also tested increased (full whisker array versus single whisker) stimulation. Results Early random whisker stimulation (condensed or dispersed) resulted in protection equivalent to early patterned stimulation. Early full whisker array patterned stimulation also resulted in complete protection, but promoted faster recovery. Late full whisker array patterned stimulation however, resulted in loss of evoked function and infarct volumes larger than those sustained by single whisker counterparts. Conclusions When induced early on after ischemic insult, stimulus-evoked cortical activity, irrespective of the parameters of peripheral stimulation that induced it, seems to be the important variable for neuroprotection.
Background--Accumulated research has shown that the older adult brain is significantly more vulnerable to stroke than the young adult brain. Although recent evidence in young adult rats demonstrates that single-whisker stimulation can result in complete protection from ischemic damage after permanent middle cerebral artery occlusion (pMCAO), it remains unclear whether the same treatment would be effective in older animals.
Stroke is a leading cause of death, disability, and socioeconomic loss worldwide. The majority of all strokes result from an interruption in blood flow (ischemia). Middle cerebral artery (MCA) delivers a great majority of blood to the lateral surface of the cortex, is the most common site of human stroke, and ischemia within its territory can result in extensive dysfunction or death. Survivors of ischemic stroke often suffer loss or disruption of motor capabilities, sensory deficits, and infarct. In an effort to capture these key characteristics of stroke, and thereby develop effective treatment, a great deal of emphasis is placed upon animal models of ischemia in MCA. Here we present a method of permanently occluding a cortical surface blood vessel. We will present this method using an example of a relevant vessel occlusion that models the most common type, location, and outcome of human stroke, permanent middle cerebral artery occlusion (pMCAO). In this model, we surgically expose MCA in the adult rat and subsequently occlude via double ligature and transection of the vessel. This pMCAO blocks the proximal cortical branch of MCA, causing ischemia in all of MCA cortical territory, a large portion of the cortex. This method of occlusion can also be used to occlude more distal portions of cortical vessels in order to achieve more focal ischemia targeting a smaller region of cortex. The primary disadvantages of pMCAO are that the surgical procedure is somewhat invasive as a small craniotomy is required to access MCA, though this results in minimal tissue damage. The primary advantages of this model, however, are: the site of occlusion is well defined, the degree of blood flow reduction is consistent, functional and neurological impairment occurs rapidly, infarct size is consistent, and the high rate of survival allows for long-term chronic assessment.
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