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Intracerebral hemorrhage (ICH) remains a common and debilitating form of stroke. This neurological emergency must be diagnosed and treated rapidly yet effectively. In this article, we review the medical, surgical, repair, and regenerative treatment options for managing ICH. Topics of focus include the management of blood pressure, intracranial pressure, coagulopathy, and intraventricular hemorrhage, as well as the role of surgery, regeneration, rehabilitation, and secondary prevention. Results of various phase II and III trials are incorporated. In summary, ICH patients should undergo rapid evaluation with neuroimaging, and early interventions should include systolic blood pressure control in the range of 140 mmHg, correction of coagulopathy if indicated, and assessment for surgical intervention. ICH patients should be managed in dedicated neurosurgical intensive care or stroke units where continuous monitoring of neurological status and evaluation for neurological deterioration is rapidly possible. Extravasation of hematoma may be helpful in patients with intraventricular extension of ICH. The goal of care is to reduce mortality and enable multimodal rehabilitative therapy.

Background Electrical stimulation of the cerebellar fastigial nucleus (FN) reduces the infarct size induced by middle cerebral artery occlusion in rats. FN stimulation confers long‐lasting protection from brain injury; however, its underlying mechanism is not yet understood. We aimed to elucidate the mechanism by which FN stimulation exerts neuroprotection. We hypothesized that the neuroprotective effect of FN stimulation involves activation of cholinergic pathways, which increases reactive oxygen species (ROS) production by opening mitochondrial K + ATP channels, thus leading to an increase in UCP4 (uncoupling protein 4) expression and subsequent neuroprotection. Methods FN stimulation was performed for 1 hour in rats. The UCP4 protein and mRNA levels were measured by western blot, dot blot, and in situ hybridization. Carbachol was applied following UCP4‐promoter tdTomato reporter vector transfection of the rat primary cortical cell culture (in vitro) and rat brain (in vivo). We observed cellular UCP4 expression using fluorescence microscopy. UCP4 expression in the cell culture in response to diazoxide application was determined by a reverse transcription‐polymerase chain reaction and western blotting. Results Whereas FN stimulation increased UCP4 protein and mRNA levels, carbachol administration induced UCP4 expression in vitro and in vivo. The attenuation of this effect by atropine suggests that FN‐induced UCP4 expression involves the cholinergic pathway. The opening of mitochondrial K + ATP channels with diazoxide increased the production of ROS and led to increased UCP4 expression. In contrast, quenching ROS with superoxide dismutase reversed the effect of diazoxide on UCP4 expression. Therefore, the opening of mitochondrial K + ATP channels increased ROS production, which subsequently enhanced UCP4 expression and attenuated ROS generation. Conclusion Neuroprotective effect of FN stimulation involves activation of the cholinergic pathways, which increases ROS production by opening mitochondrial K + ATP channels, leading to increased expression of neuroprotective UCP4.

The trigeminocardiac reflex (TCR) is a well-recognized brainstem reflex that represents a unique interaction between the brain and the heart through the Vth and Xth cranial nerves and brainstem nuclei. The TCR has mainly been reported as an intraoperative phenomenon causing cardiovascular changes during skull-base surgeries. However, it is now appreciated that the TCR is implicated during non-neurosurgical procedures and in nonsurgical conditions, and its complex reflex pathways have been explored as potential therapeutic options in various neurological and cardiovascular diseases. This narrative review presents an in-depth overview of hypothetical and experimental models of the TCR phenomenon in relation to the Vth and Xth cranial nerves. In addition, primitive interactions between these 2 cranial nerves and their significance are highlighted. Finally, therapeutic models of the complex interactions of the TCR and areas for further research will be considered.

Mild traumatic brain injuries (mTBIs) are the most common type of brain injury. Timely diagnosis of mTBI is crucial in making ‘go/no-go’ decision in order to prevent repeated injury, avoid strenuous activities which may prolong recovery, and assure capabilities of high-level performance of the subject. If undiagnosed, mTBI may lead to various short- and long-term abnormalities, which include, but are not limited to impaired cognitive function, fatigue, depression, irritability, and headaches. Existing screening and diagnostic tools to detect acute and early-stage mTBIs have insufficient sensitivity and specificity. This results in uncertainty in clinical decision-making regarding diagnosis and returning to activity or requiring further medical treatment. Therefore, it is important to identify relevant physiological biomarkers that can be integrated into a mutually complementary set and provide a combination of data modalities for improved on-site diagnostic sensitivity of mTBI. In recent years, the processing power, signal fidelity, and the number of recording channels and modalities of wearable healthcare devices have improved tremendously and generated an enormous amount of data. During the same period, there have been incredible advances in machine learning tools and data processing methodologies. These achievements are enabling clinicians and engineers to develop and implement multiparametric high-precision diagnostic tools for mTBI. In this review, we first assess clinical challenges in the diagnosis of acute mTBI, and then consider recording modalities and hardware implementation of various sensing technologies used to assess physiological biomarkers that may be related to mTBI. Finally, we discuss the state of the art in machine learning-based detection of mTBI and consider how a more diverse list of quantitative physiological biomarker features may improve current data-driven approaches in providing mTBI patients timely diagnosis and treatment.

Subarachnoid hemorrhage (SAH) in 95% of cases results in long-term disabilities due to brain damage, pathogenesis of which remains uncertain. Hindrance of cerebrospinal fluid (CSF) circulation along glymphatic pathways is a possible mechanism interrupting drainage of damaging substances from subarachnoid space and parenchyma. We explored changes in CSF circulation at different time following SAH and possible role of brain tissue factor (TF). Fluorescent solute and fluorescent microspheres injected into cisterna magna were used to track CSF flow in mice. SAH induced by perforation of circle of Willis interrupted CSF flow for up to 30 days. Block of CSF flow did not correlate with the size of hemorrhage. Following SAH, fibrin deposits were observed on the brain surface including areas without visible blood. Block of astroglia-associated TF by intracerebroventricular administration of specific antibodies increased size of hemorrhage, decreased fibrin deposition and facilitated spread of fluorophores in sham/naïve animals. We conclude that brain TF plays an important role in localization of hemorrhage and also regulates CSF flow under normal conditions. Targeting of the TF system will allow developing of new therapeutic approaches to the treatment of SAH and pathologies related to CSF flow such as hydrocephalus.

We observed fine fibrin deposition along the paravascular spaces in naive animals, which increased dramatically following subarachnoid hemorrhage (SAH). Following SAH, fibrin deposits in the areas remote from the hemorrhage. Traditionally it is thought that fibrinogen enters subarachnoid space through damaged blood brain barrier. However, deposition of fibrin remotely from hemorrhage suggests that fibrinogen chains Aα, Bβ, and γ can originate in the brain. Here we demonstrate in vivo and in vitro that astroglia and neurons are capable of expression of fibrinogen chains. SAH in mice was induced by the filament perforation of the circle of Willis. Four days after SAH animals were anesthetized, transcardially perfused and fixed. Whole brain was processed for immunofluorescent (IF) analysis of fibrin deposition on the brain surface or in brains slices processed for fibrinogen chains Aα, Bβ, γ immunohistochemical detection. Normal human astrocytes were grown media to confluency and stimulated with NOC-18 (100 μM), TNF-α (100 nM), ATP-γ-S (100 μM) for 24 h. Culture was fixed and washed/permeabilized with 0.1% Triton and processed for IF. Four days following SAH fibrinogen chains Aα IF associated with glia limitans and superficial brain layers increased 3.2 and 2.5 times (p < 0.05 and p < 0.01) on the ventral and dorsal brain surfaces respectively; fibrinogen chains Bβ increased by 3 times (p < 0.01) on the dorsal surface and fibrinogen chain γ increased by 3 times (p < 0.01) on the ventral surface compared to sham animals. Human cultured astrocytes and neurons constitutively expressed all three fibrinogen chains. Their expression changed differentially when exposed for 24 h to biologically significant stimuli: TNFα, NO or ATP. Western blot and RT-qPCR confirmed presence of the products of the appropriate molecular weight and respective mRNA. We demonstrate for the first time that mouse and human astrocytes and neurons express fibrinogen chains suggesting potential presence of endogenous to the brain fibrinogen chains differentially changing to biologically significant stimuli. SAH is followed by increased expression of fibrinogen chains associated with glia limitans remote from the hemorrhage. We conclude that brain astrocytes and neurons are capable of production of fibrinogen chains, which may be involved in various normal and pathological processes.

Background The trigeminocardiac reflex (TCR) is defined as sudden onset of parasympathetic dysrhythmias including hemodynamic irregularities, apnea, and gastric hypermotility during stimulation of sensory branches of the trigeminal nerve. Since the first description of the TCR in 1999, there is an ongoing discussion about a more emergent clinical definition. In this work, the author worked out an approach to such an improved definition. Methods In this study, a grounded theory approach was used. Literature about TCR was systematically identified through PubMed (MEDLINE), EMBASE (Ovid SP), and ISI Web of Sciences databases from 1/2005 until 8/2015. TCR was defined as a drop of heart rate (HR) below 60 bpm or 20% to the baseline. A grounded theory approach was used to analyze and interpret the data through a synthesis by the researcher’s perspectives, values, and positions. Results Out of the included studies, the authors formed available data to an update of the understanding of changes in hemodynamic parameters (HR and blood pressure) in a TCR. According to this update, an HR deceleration should be a constant observation to identify a TCR episode while a drop in blood pressure should probably not being fixed to a certain percentage of decrease. Conclusion The here presented working definition improves our understanding of the TCR. It leads the way to a new understanding of the TCR for a proper clinical definition.

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”.

Following traumatic brain injury (TBI), ischemia and hypoxia play a major role in further worsening of the damage, a process referred to as ‘secondary injury’. Protecting neurons from causative factors of secondary injury has been the guiding principle of modern TBI management. Stimulation of trigeminal nerve induces pressor response and improves cerebral blood flow (CBF) by activating the rostral ventrolateral medulla. Moreover, it causes cerebrovasodilation through the trigemino-cerebrovascular system and trigemino-parasympathetic reflex. These effects are capable of increasing cerebral perfusion, making trigeminal nerve stimulation (TNS) a promising strategy for TBI management. Here, we investigated the use of electrical TNS for improving CBF and brain oxygen tension (PbrO2), with the goal of decreasing secondary injury. Severe TBI was produced using controlled cortical impact (CCI) in a rat model, and TNS treatment was delivered for the first hour after CCI. In comparison to TBI group, TBI animals with TNS treatment demonstrated significantly increased systemic blood pressure, CBF and PbrO2 at the hyperacute phase of TBI. Furthermore, rats in TNS-treatment group showed significantly reduced brain edema, blood-brain barrier disruption, lesion volume, and brain cortical levels of TNF-α and IL-6. These data provide strong early evidence that TNS could be an effective neuroprotective strategy.

Inflammatory conditions characterized by excessive peripheral immune responses are associated with diverse alterations in brain function, and brain-derived neural pathways regulate peripheral inflammation. Important aspects of this bidirectional peripheral immune-brain communication, including the impact of peripheral inflammation on brain region-specific cytokine responses, and brain cholinergic signaling (which plays a role in controlling peripheral cytokine levels), remain unclear. To provide insight, we studied gene expression of cytokines, immune cell markers and brain cholinergic system components in the cortex, cerebellum, brainstem, hippocampus, hypothalamus, striatum and thalamus in mice after an intraperitoneal lipopolysaccharide injection. Endotoxemia was accompanied by elevated serum levels of interleukin (IL)-1β, IL-6 and other cytokines and brain region-specific increases in Il1b (the highest increase, relative to basal level, was in cortex; the lowest increase was in cerebellum) and Il6 (highest increase in cerebellum; lowest increase in striatum) mRNA expression. Gene expression of brain Gfap (astrocyte marker) was also differentially increased. However, Iba1 (microglia marker) mRNA expression was decreased in the cortex, hippocampus and other brain regions in parallel with morphological changes, indicating microglia activation. Brain choline acetyltransferase (Chat ) mRNA expression was decreased in the striatum, acetylcholinesterase (Ache) mRNA expression was decreased in the cortex and increased in the hippocampus, and M1 muscarinic acetylcholine receptor (Chrm1) mRNA expression was decreased in the cortex and the brainstem. These results reveal a previously unrecognized regional specificity in brain immunoregulatory and cholinergic system gene expression in the context of peripheral inflammation and are of interest for designing future antiinflammatory approaches.

The photic sneeze reflex (PSR) is a condition of uncontrollable sneezing episodes in response to bright light. This reflex often manifests as a mild phenomenon but may cause devastating consequences in some situations (aeroplane pilots, car drivers, etc.). Its exact mechanism is poorly understood. Interestingly, the roles of the fifth and tenth cranial nerves, brainstem nuclei and inciting patterns closely mimic a well-known brainstem reflex, known as the trigeminocardiac reflex (TCR). In this critical review, we hypothesize that the PSR can be a variant of the TCR. This concept will lead to a better understanding of the PSR and sharpens the TCR characteristics and open the doors for new research possibilities.

Diving response is a powerful integrative response targeted toward survival of the hypoxic/anoxic conditions. Being present in all animals and humans it allows to survive adverse conditions like diving. Earlier we discovered that forehead stimulation affords neuroprotective effect decreasing infarction volume triggered by permanent occlusion of the middle cerebral artery in rats. We hypothesized that cold stimulation of the forehead induces diving response in rats, which, in turn, exerts neuroprotection. We compared autonomic (AP, HR, CBF) and EEG responses to the known diving response-triggering stimulus, ammonia stimulation of the nasal mucosa, cold stimulation of the forehead, and cold stimulation of the glabrous skin of the tail base in anesthetized rats. Responses in AP, HR, CBF and EEG to cold stimulation of the forehead and ammonia vapors instillation into the nasal cavity were comparable and differed significantly from responses to the cold stimulation of the tail base. Excitotoxic lesion of the subthalamic vasodilator area, which is known to participate in CBF regulation and to afford neuroprotection upon excitation, failed to affect autonomic components of the diving response evoked by forehead cold stimulation or nasal mucosa ammonia stimulation. We conclude that cold stimulation of the forehead triggers physiological response comparable to the response evoked by ammonia vapor instillation into the nasal cavity, which considered as stimulus triggering protective diving response. These observations may explain the neuroprotective effect of the forehead stimulation. Data demonstrate that subthalamic vasodilator area does not directly participate in the autonomic adjustments accompanying diving response, however, it is involved in diving-evoked modulation of EEG. We suggest that forehead stimulation can be employed as a stimulus capable of triggering oxygen-conserving diving response and can be used for neuroprotective therapy.

Electrical stimulation of the cerebellar fastigial nucleus (FN) elicits a prolonged ( approximately 10 days) and substantial (50-80%) protection against ischemic and excitotoxic injuries. The mechanism(s) of protection are unknown. We investigated whether FN stimulation directly protects brain cells against apoptotic cell death in an in vitro rat brain slice culture model. Rats were electrically stimulated in FN or, as control, the cerebellar dentate nucleus (DN). Coronal slices through the forebrain were explanted, exposed to staurosporine, harvested, and analyzed for caspase-3 activity by a fluorescence assay. FN, but not DN, stimulation significantly reduced staurosporine-induced caspase-3 activity by 39 +/- 7% at 3 h, 31 +/- 3% at 6 h and 26 +/- 4% at 10 h of incubation. Immunocytochemistry revealed FN-specific reductions in activated caspase-3 mainly in glial-like cells throughout the forebrain. FN stimulation also results in a 56.5% reduction in cytochrome c release upon staurosporine incubation. We conclude that neuroprotection elicited from FN stimulation can directly modify the sensitivity of brain cells to apoptotic stimuli and thereby suppress staurosporine induced apoptosis in adult rat brain slices. This model indicates that neuroprotection can be studied in vitro and provides new insight into the potential role of glial cells in ischemic protection of neurons induced by FN stimulation.

Background: Universally present in animals diving response triggered by stimulation of the trigeminal nerve is known as "oxygen conserving reflex". This powerful integrative response includes apnea, bradycardia, and blood flow redistribution targeted to protect the brain against hypoxia. We hypothesized that diving response triggered by forehead stimulation can be neuroprotective in rat. Methods: Male Sprague-Dawley rats were anesthetized, intubated, and artificially ventilated while blood gases and body temperature were maintained at physiologic levels. Arterial pressure, heart rate and temperature and in some cases, CBF were monitored. The forehead skin selectively was continuously selectively cooled or electrically stimulated for one hour. Middle cerebral artery was permanently occluded and infarction volume was determined 24 hours later. Results: Forehead cooling to +11 °C decreased infarction volume by 31% compared to control (58±14 mm3 vs. 87±12 mm3, corrected for edema, p

We report a novel single neural probe for real-time simultaneous monitoring of multiple neurochemicals and direct-current electrocorticography (DC-ECoG). A major advance of this probe is the inclusion of two iridium oxide reference electrodes to improve sensor accuracy. The ECoG reference electrode is identical to the ECoG recording electrodes to significantly improve DC stability, while the reference for electrochemical sensors has 10-fold lower polarization rate to minimize the small current-induced drift in the reference electrode potential. In vitro, the single probe selectively measured oxygen (r(2)=0.985 ± 0.01, concentration range=0-60 mmHg, limit of detection=0.4 ± 0.07 mmHg) and glucose (r(2)=0.989 ± 0.009, concentration range=0-4mM, limit of detection=31 ± 8 µM) in a linear fashion. The performance of the single probe was assessed in an in vivo needle prick model to mimic sequelae of traumatic brain injury. It successfully monitored the theoretically expected transient brain oxygen, glucose, and DC potential changes during the passage of spreading depolarization (SD) waves. We envision that the developed probe can be used to decipher the cause-effect relationships between multiple variables of brain pathophysiology with the high temporal and spatial resolutions that it provides.

Cerebral blood flow (CBF) plays a critical role in the exchange of nutrients and metabolites at the capillary level and is tightly regulated to meet the metabolic demands of the brain. After major brain injuries, CBF normally decreases and supporting the injured brain with adequate CBF is a mainstay of therapy after traumatic brain injury. Quantitative and localized measurement of CBF is therefore critically important for evaluation of treatment efficacy and also for understanding of cerebral pathophysiology. We present here an improved thermal flow microsensor and its operation which provides higher accuracy compared to existing devices. The flow microsensor consists of three components, two stacked-up thin film resistive elements serving as composite heater/temperature sensor and one remote resistive element for environmental temperature compensation. It operates in constant-temperature mode (~2 °C above the medium temperature) providing 20 ms temporal resolution. Compared to previous thermal flow microsensor based on self-heating and self-sensing design, the sensor presented provides at least two-fold improvement in accuracy in the range from 0 to 200 ml/100 g/min. This is mainly achieved by using the stacked-up structure, where the heating and sensing are separated to improve the temperature measurement accuracy by minimization of errors introduced by self-heating.

SAH, blood accumulation in subarachnoid space (SS), is caused by rupture of intracranial aneurisms or by TBI. CSF circulating throughout SS and brain parenchyma forms glymphatic pathways for waste removal. We explored alterations to CSF circulation following SAH in C57BL mice at various time after perforation SAH. Fluorescent microspheres (μS, 0.02, 1.0 mm) were injected into the cisterna magna (CM). One hour later, their spread across the brain was monitored using in vivo multiphoton or ex vivo fluorescence microscopy. In naive mice, from CM μS spread to the brain stem, paraarterially along Willis circle, and further along middle cerebral artery and the ventral surface vessels toward the olfactory bulb. Caudally μS spread down the spinal cord. One hour after SAH, μS were confined to the CM and brain stem region limited by the rostral pons border indicating significant CSF flow impairment. The number of μS distributed to the spinal cord was also greatly reduced. Four days post SAH CSF flow remained arrest...

The trigeminocardiac reflex (TCR) is defined as the sudden onset of parasympathetic dysrhythmia, sympathetic hypotension, apnea, or gastric hypermotility during stimulation of any of the sensory branches of the trigeminal nerve. Clinically, the TCR has been reported in all the surgical procedures in which a structure innervated by the trigeminal nerve is involved. Although, there is an abundant literature with reports of incidences and risk factors of the TCR; the physiological significance and function of this brainstem reflex has not yet been fully elucidated. In addition, there are complexities within the TCR that requires examination and clarification. There is also a growing need to discuss its cellular mechanism and functional consequences. Therefore, the current review provides an updated examination of the TCR with a particular focus on the mechanisms and diverse nature of the TCR.

Stimulation of the ophthalmic branch of the trigeminal nerve can trigger a complex response known as the diving response (DR). Universally expressed in all animals, the DR is targeted to enable them to survive anoxic conditions. In the response, severe hypoxia or anoxia, complex multisystem and multilevel changes diminish oxygen consumption and activate endogenous protective mechanisms. The salient features of the DR are apnea, bradycardia, and peripheral vasoconstriction. Bradycardia decreases myocardial oxygen consumption, peripheral vasoconstriction limits both the blood supply and oxygen use by “nonvital” organs. Although the brain’s blood supply remains stable, neurogenic mechanisms diminish brain activity in order to decrease brain metabolism. Along with the slowing of oxygen consumption, neurogenic neuroprotective mechanisms are activated to increase the brain’s tolerance of hypoxia at system and cellular levels.

In Sprague-Dawley rats symmetrical sites of the parietal cortex were microinjected with ibotenic acid (IBO, 10microg in 1microl) to lesion local neurons or with saline (1microl). Five days later, changes of cortical cerebral blood flow (CBF) in response to hypoxia and stimulation of the subthalamic vasodilator area (SVA) were measured using laser-Doppler flowmetry (LDF). The baseline CBF over the IBO- and saline-injected cortical sites did not differ significantly, but spontaneous waves of CBF were abolished over the lesioned sites. Elevations of CBF evoked by hypoxia or stimulation of SVA were attenuated by 54% and 88%, respectively (P < 0.05) over the lesioned sites, compared to saline-injected or non-injected sites. Hypercarbic cerebrovasodilation was comparable over all sites. We conclude that the SVA-evoked increase of CBF and about 50% of the hypoxia-evoked increase of CBF are mediated by excitation of cortical neurons.

In anesthetized spinalized rat, electrical stimulation of the nucleus tractus solitarius (NTS) synchronizes the EEG by increasing the power of 4-6-Hz waves (>100%; P

We sought to identify the medullary relay area mediating the elevations of regional cerebral blood flow (rCBF) and synchronization of the electroencephalogram (EEG) in the rat cerebral cortex elicited by hypoxic excitation of reticulospinal sympathoexcitatory neurons of the rostral ventrolateral medulla (RVLM). In anaesthetized spinalized rats electrical stimulation of RVLM elevated rCBF (laser-Doppler flowmetry) by 31 ± 6 %, reduced cerebrovascular resistance (CVR) by 26 ± 8 %, and synchronized the EEG, increasing the power of the 5–6 Hz band by 98 ± 25 %. Stimulation of a contiguous caudal region, the medullary cerebral vasodilator area (MCVA), had comparable effects which, like responses of RVLM, were replicated by microinjection of L-glutamate (5 nmol, 20 nl). Microinjection of NaCN (300 pmol in 20 nl) elevated rCBF (17 ± 5 %) and synchronized the EEG from RVLM, but not MCVA, while nicotine (1.2 nmol in 40 nl) increased rCBF by 13 ± 5 % and synchronized the EEG from MCVA. In intact rats nicotine lowered arterial pressure only from MCVA (101 ± 3 to 52 ± 9 mmHg). Bilateral electrolytic lesions of MCVA significantly reduced, by over 59 %, elevations in rCBF and, by 78 %, changes in EEG evoked from RVLM. Bilateral electrolytic lesions of RVLM did not affect responses from MCVA. Anterograde tracing with BDA demonstrated that RVLM and MCVA are interconnected. The MCVA is a nicotine-sensitive region of the medulla that relays signals elicited by excitation of oxygen-sensitive reticulospinal neurons in RVLM to reflexively elevate rCBF and slow the EEG as part of the oxygen-conserving (diving) reflex initiated in these neurons by hypoxia or ischaemia. Hypoxia or ischaemia of the medulla oblongata increases sympathetic nerve activity, elevates arterial pressure (AP), and induces expiratory apnoea and bradycardia (Dampney et al. 1979; Sun et al. 1992; Reis et al. 1994; Golanov & Reis, 1996a) in rat. It also increases regional cerebral blood flow (rCBF), but not regional cerebral glucose utilization (rCGU), and synchronizes the EEG (Golanov & Reis, 1994, 1996a). This integrated response simulates, in most respects, the diving reflex (Blix & Folkow, 1983), the prototypical oxygen-conserving reflex of mammals. The autonomic responses have been attributed to direct hypoxic excitation of tonically active sympathoexcitatory reticulospinal vasomotor neurons of the rostral ventrolateral reticular nucleus of the medulla (RVLM) (Sun & Reis, 1994a). In vivo these neurons are selectively, rapidly and reversibly excited by blockade of the respiratory chain by microinjection or microiontophoresis of NaCN (histotoxic hypoxia) (Sun & Reis, 1993). Moreover, restricted lesions of RVLM block the systemic and cerebrovascular responses to ischaemia and/or hypoxaemia (Dampney & Moon, 1980; Underwood et al. 1994; Golanov & Reis, 1996a). Indeed, to protect the brain from lack of oxygen may be an important function of the RVLM (Reis et al. 1994). Reticulospinal neurons of the RVLM function as premotor neurons, acting to initiate the integrated responses to hypoxia by activation of effector (motor) neurons distributed elsewhere in the CNS. Thus, the sympathetic responses can be attributed to activation of the RVL-spinal sympathoexcitatory pathway (Sun & Reis, 1996a), apnoea from activation through short intramedullary projections of the adjacent ventral respiratory cell group (Kita et al. 1994; Sun & Reis, 1996b), and bradycardia – from excitation of medullary cardiovagal neurons (Ross et al. 1984; Benarroch et al. 1986). However, the pathway(s) through which rCBF and the EEG are modified is unknown. Since the RVLM does not innervate the cerebral cortex (Ruggiero et al. 1989), the projection must be indirect. In this study we investigate whether a small area of the ventrolateral medulla serves to relay the signals generated by hypoxic excitation of the RVLM to elevate rCBF and synchronize the EEG in the cerebral cortex of rats. We report that an heretofore unrecognized paraambigual region of the bulbar reticular formation, which we term the medullary cerebral vasodilator area (MCVA), subserves this role.

Reticulospinal sympathoexcitatory neurons of rostral ventrolateral medulla (RVL) are selectively excited by hypoxia to elevate arterial pressure (AP) and cerebral blood flow (rCBF), that are elements of the oxygen-conserving (diving) reflex. We investigated whether KATP+-channels participate in this. Tolbutamide and glibenclamide, KATP+-channel blockers, microinjected into RVL in anesthetized rats, dose-dependently and site-specifically elevated AP and rCBF and potentiated responses to hypoxemia. KATP+-channels may mediate hypoxic excitation of oxygen-sensing RVL neurons.

Spontaneous ultra-slow oscillations in brain signals are ubiquitous, although their source and function remain unknown. A new study now reports that this activity is correlated between functionally related areas across hemispheres in humans.

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.

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% (p0.01) 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 (p0.5). 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.

The cerebellar fastigial nucleus (FN) was electrically stimulated for 1 h in anesthetized rats and the middle cerebral artery occluded at various times thereafter. Stimulation of the FN but not dentate nucleus reduced the volume of the focal infarction to 50%. Protection persisted for 10 but disappeared by 30 d. Intrinsic neuronal pathways which function to condition central neurogenic neuroprotection can protect the brain from ischemic injury by processes independent of cerebral blood flow.

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.

Electrical stimulation of the cerebellar fastigial nucleus (FN) elevates regional cerebral blood flow (rCBF) independently of cerebral metabolism (rCGU) throughout brain. One hour of FN stimulation also reduces, by up to 50%, the volume of the focal ischemic infarction produced by occlusion of the middle cerebral artery in rat. Protected areas correspond to the ischemic penumbra. Neuroprotection, while reversible, persists for weeks after 1h of stimulation. It cannot be attributed to increasing rCBF and/or reducing rCGU to improve matching of flow and metabolism. Conditional stimulation of FN initiates long-lived inhibition of expression of peri-infarction depolarizing waves, possibly by altering potassium-channel function and suppresses induction of inducible nitric oxide synthase (iNOS) and ICAM in cerebral microvessels. The brain contains intrinsic networks which may protect the brain from ischemic injury, possibly by producing widespread and longterm suppression of electrical excitability and/or and expression of proinflammatory molecules.

The pedunculopontine-laterodorsal tegmental nuclear complex was identified as a major source of brainstem afferents terminating in the fastigial cerebellar nucleus and/or ventrolateral reticular nucleus (n.Rvl). Collaterals from the pedunculopontine nucleus (Ch5 area) to rostral [vasopressor] regions of the fastigial nucleus and ventral reticular formation were revealed with a combined retrograde tracing technique. The data implicate acetylcholine as a transmitter and raise the hypothesis that the identified afferents may contribute to the autonomic and behavioral responses to midline cerebellar stimulation.

Abnormalities of cerebrovascular circulation are one of the salient consequences of traumatic brain injury. Severity of cerebral blood flow disregulation is associated with the negative clinical outcome. Regulation of cerebral blood flow is complex and differs from regulation of blood flow in other vascular beds. Basic vascular tone formed by interaction of vascular smooth muscle cells and endothelium provides background for other regulatory mechanisms. Understanding of traumatic brain injury-induced abnormalities of basic vascular tone formation and its adjustment using isolated brain vessel model is important for unveiling the pathophysiological mechanisms of brain trauma and development of new therapeutic approaches.

1. We sought to determine whether hypoxic stimulation of neurons of the rostral ventrolateral reticular nucleus (RVL) would elevate regional cerebral blood flow (rCBF) in anaesthetized paralysed rats. 2. Microinjection of sodium cyanide (NaCN; 150-450 pmol) into the RVL rapidly (within 1-2 s), transiently, dose-dependently and site-specifically elevated rCBF1 measured by laser Doppler flowmetry, by 61.3 +/- 22.1% (P < 0.01), increased arterial pressure (AP; +30 +/- 8 mmHg; P < 0.01)1 and triggered a synchronized 6 Hz rhythm of EEG activity. 3. Following cervical spinal cord transection, NaCN and also dinitrophenol (DNP) significantly (P < 0.05) elevated rCBF and synchronized the EEG but did not elevate AP; the response to NaCN was attenuated by hyperoxia and deepening of anaesthesia. 4. Electrical stimulation of NaCN-sensitive sites in the RVL in spinalized rats increased rCBF measured autoradiographically with 14C iodoantipyrine (Kety method) in the mid-line thalamus (by 182.3 +/- 17.2%; P < 0.05) and cerebral cortex (by 172.6 +/- 15.6%; P < 0.05) regions, respectively, directly or indirectly innervated by RVL neurons, and in the remainder of the brain. In contrast regional cerebral glucose utilization (rCGU), measured autoradiographically with 14C-2-deoxyglucose (Sokoloff method), was increased in proportion to rCBF in the mid-line thalamus (165.6 +/- 17.8%, P < 0.05) but was unchanged in the cortex. 5. Bilateral electrolytic lesions of NaCN sensitive sites of RVL, while not altering resting rCBF or the elevation elicited by hypercarbia (arterial CO2 pressure, Pa,CO2, approximately 69 mmHg), reduced the vasodilatation elicited by normocapnic hypoxaemia (arterial O2 pressure, Pa,O2, approximately 27 mmHg) by 67% (P < 0.01) and flattened the slope of the Pa,O2-rCBF response curve. 6. We conclude that the elevation of rCBF produced in the cerebral cortex by hypoxaemia is in large measure neurogenic, mediated trans-synaptically over intrinsic neuronal pathways, and initiated by excitation of oxygen sensitive neurons in the RVL.

We recorded neurons in rat cerebral cortex with activity relating to the neurogenic elevations in regional cerebral blood flow (rCBF) coupled to stereotyped bursts of EEG activity, burst-cerebrovascular wave complexes, appearing spontaneously or evoked by electrical stimulation of rostral ventrolateral medulla (RVL) or fastigial nucleus (FN). Of 333 spontaneously active neurons only 15 (5%), in layers 5-6, consistently (P < 0.05, chi-square) increased their activity during the earliest potential of the complex, approximately 1.3 s before the rise of rCBF, and during the minutes-long elevation of rCBF elicited by 10 s of stimulation of RVL or FN. The results indicate the presence of a small population of neurons in deep cortical laminae whose activity correlates with neurogenic elevations of rCBF. These neurons may function to transduce afferent neuronal signals into vasodilation.

In non-pulsatile cardiopulmonary bypass surgery, middle cerebral artery blood flow velocity (BFV) is characterized by infra-slow oscillations of approximately 0.06Hz, which are paralleled by changes in total EEG power variability (EEG-PV), measured in 2s intervals. Since the origin of these BFV oscillations is not known, we explored their possible causative relationships with oscillations in EEG-PV at around 0.06Hz. We monitored 28 patients undergoing non-pulsatile cardiopulmonary bypass using transcranial Doppler sonography and scalp electroencephalography at two levels of anesthesia, deep (prevalence of burst suppression rhythm) and moderate (prevalence of theta rhythm). Under deep anesthesia, the EEG bursts suppression pattern was highly correlative with BFV oscillations. Hence, a detailed quantitative picture of the coupling between electrical brain activity and BFV was derived, both in deep and moderate anesthesia, via linear and non linear processing of EEG-PV and BFV signals, resorting to widely used measures of signal coupling such as frequency of oscillations, coherence, Granger causality and cross-approximate entropy. Results strongly suggest the existence of coupling between EEG-PV and BFV. In moderate anesthesia EEG-PV mean dominant frequency is similar to frequency of BFV oscillations (0.065±0.010Hz vs 0.045±0.019Hz); coherence between the two signals was significant in about 55% of subjects, and the Granger causality suggested an EEG-PV→BFV causal effect direction. The strength of the coupling increased with deepening anesthesia, as EEG-PV oscillations mean dominant frequency virtually coincided with the BFV peak frequency (0.062±0.017Hz vs 0.060±0.024Hz), and coherence became significant in a larger number (65%) of subjects. Cross-approximate entropy decreased significantly from moderate to deep anesthesia, indicating a higher level of synchrony between the two signals. Presence of a subcortical brain pacemaker that drives vascular infra-slow oscillations in the brain is proposed. These findings allow to suggest an original hypothesis explaining the mechanism underlying infra-slow neurovascular coupling.

Rilmenidine and idazoxan reduce the volume of focal ischemic infarctions produced by occlusion of the middle cerebral artery in the rat by 33% and 29%, respectively, by preserving neurons within the ischemic penumbra. In contrast, the alpha 2-selective antagonist SKF-86466 is without effect. The neuroprotective action of rilmenidine is dose dependent and parallels its antihypertensive actions. Neuroprotection cannot be attributed to changes in cerebral blood flow. We conclude that the neuroprotection produced by rilmenidine is attributable to an interaction with imidazoline receptors (IRs). However, the mechanism of action is not obvious. If it results from an action within the penumbra (direct), it is mediated by mitochondrial I-2 receptors on astrocytes, since cortical neurons are devoid of IRs. Neuroprotection might occur by selectively stimulating Ca2+ uptake into astrocytes, and thereby reducing Ca2+ uptake into neurons. Alternatively, rilmenidine may act indirectly to activate pathways in the brain that are neuroprotective. Neuroprotection may be a therapeutic target for rilmenidine and allied agents that act at central IRs.

Objective. Direct-current electrocorticography (DC-ECoG) allows a more complete characterization of brain states and pathologies than traditional alternating-current recordings (AC-ECoG). However, reliable recording of DC signals is challenging because of electrode polarization-induced potential drift, particularly at low frequencies and for more conducting materials. Further challenges arise as electrode size decreases, since impedance is increased and the potential drift is augmented. While microelectrodes have been investigated for AC-ECoG recordings, little work has addressed microelectrode properties for DC-signal recording. In this paper, we investigated several common microelectrode materials used in biomedical application for DC-ECoG. Approach. Five of the most common materials including gold (Au), silver/silver chloride (Ag/AgCl), platinum (Pt), Iridium oxide (IrOx), and platinum-iridium oxide (Pt/IrOx) were investigated for electrode diameters of 300 μm. The critical characteristics such as polarization impedance, AC current-induced polarization, long-term stability and low-frequency noise were studied in vitro (0.9% saline). The two most promising materials, Pt and Pt/lrOx were further investigated in vivo by recording waves of spreading depolarization, one of the most important applications for DC-ECoG in clinical and basic science research. Main results. Our experimental results indicate that IrOx-based microelectrodes, particularly with composite layers of nanostructures, are excellent in all of the common evaluation characteristics both in vitro and in vivo and are most suitable for multimodal monitoring applications. Pt electrodes suffer high current-induced polarization, but have acceptable long-term stability suitable for DC-ECoG. Major significance. The results of this study provide quantitative data on the electrical properties of microelectrodes with commonly-used materials and will be valuable for development of neural recordings inclusive of low frequencies.

To determine whether the neuroprotection elicited from electrical stimulation of the cerebellar fastigial nucleus (FN) is attributable to the elevation in regional cerebral blood flow (rCBF), we compared the effects in spontaneously hypertensive rats of stimulation of the rostral ventrolateral medulla (RVL) or FN on (a) a focal ischemic lesion produced by middle cerebral artery (MCA) occlusion, and (b) the changes in rCBF, measured by laser-Doppler flowmetry for 1.5 h, over regions corresponding to the ischemic core (parietal cortex), penumbra (occipital cortex), and nonischemic area (contralateral parietal cortex). Stimulation of FN for 1 h following MCA occlusion reduced infarction 24 h later by 52%. Stimulation of RVL was ineffective. Changes in the lesion were confined to the penumbra. FN and RVL stimulation comparably and significantly increased rCBF up to 185% in unlesioned animals. Following MCA occlusion, stimulation of FN or RVL and hypercarbia failed to elevate rCBF in the ischemic area but did so in the nonischemic area, even though in the same animals only FN stimulation reduced infarction 24 h later. We conclude that (a) the neuroprotection elicited from FN is not the result of an increase in rCBF but results from another mechanism, possibly reduction of metabolism in penumbra, and (b) the pathways mediating central neurogenic vasodilation and neuroprotection are, in part, distinct.

We investigated whether inhibition of nitric oxide (NO) biosynthesis with N-ω-nitro-l-arginine (NNA), a competitive inhibitor of NO synthase (NOS), would modify the volume of the focal ischemic infarction produced by occlusion of the middle cerebral artery (MCA) in spontaneously hypertensive rats. NNA was infused for 1 h (2.4 mg/kg/h) immediately following occlusion of the MCA. NNA increased lesion volume 24 h later by 32% over controls (150.8 ± 16.6 to 199.2 ± 17.4 mm3; p < 0.001, n = 6). This effect was antagonized by co-infusion of l- but not d-arginine. The antihypertensive rilmenidine (0.75 mg/kg) reduced the lesion by 27% (p < 0.05, n = 4). Changes in lesion size were confined to the penumbra. NNA increased arterial pressure (AP) (118 ± 8.9 to 149 ± 16.0 mm Hg; p < 0.01, n = 3) but did not change regional CBF. However, elevation of AP did not change the lesion volume or distribution. We conclude that inhibition of the constitutive form of NOS in vivo increases the volume of focal ischemic infarction as a consequence of reduced NO biosynthesis. The absence of NO availability may extend lesion formation by inhibition of reactive hyperemia, platelet disaggregation, and/or release of neuroprotective neuromodulators in the penumbra, which may counteract and override any of its neurotoxic actions.

Trigeminocardiac reflex (TCR) is a brainstem reflex that manifests as sudden onset of hemodynamic perturbation in blood pressure (MABP) and heart rate (HR), as apnea and as gastric hypermotility during stimulation of any branches of the trigeminal nerve. The molecular and clinical knowledge about the TCR is in a constant growth since 1999, what implies a current need of a review about its definition in this changing context. Relevant literature was identified through searching in PubMed (MEDLINE) and Google scholar database for the terms TCR, oculocardiac reflex, diving reflex, vasovagale response. The definition of the TCR varies in clinical as well as in research studies. The main difference applies the required change of MABP and sometimes also HR, which most varies between 10% and 20%. Due to this definition problem, we defined, related to actual literature, 2 major (plausibility, reversibility) and 2 minor criteria (repetition, prevention) for a more proper identification of the TCR in a clinical or research setting. Latest research implies that there is a need for a more extended classification with 2 additional subgroups, considering also the diving reflex and the brainstem reflex. In this review, we highlighted criteria for proper definition and classification of the TCR in the light of increased knowledge and present a thinking model to overcome this complexity. Further we separately discussed the role of HR and MABP and their variation in this context. As another subtopic we gave attention to is the chronic TCR; a variant that is rarely seen in clinical medicine.

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 μA) 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.