Adaptive plasticity in tachykinin and tachykinin receptor expression after focal cerebral ischemia is differentially linked to gabaergic and glutamatergic cerebrocortical circuits and cerebrovenular endothelium

Transient Opening of the Blood-Brain Barrier by Vasoactive Peptides to Increase CNS Drug Delivery: Reality Versus Wishful Thinking?

BACKGROUND

The blood-brain barrier inhibits the central nervous system penetration of 98% of small molecule drugs and virtually all biologic agents, which has limited progress in treating neurologic disease. Vasoactive peptides have been shown in animal studies to transiently disrupt the blood-brain barrier and regadenoson is currently being studied in humans to determine if it can improve drug delivery to the brain. However, many other vasoactive peptides could potentially be used for this purpose.

METHODS

We performed a review of the literature evaluating the physiologic effects of vasoactive peptides on the vasculature of the brain and systemic organs. To assess the likelihood that a vasoactive peptide might transiently disrupt the blood-brain barrier, we devised a four-tier classification system to organize the available evidence.

RESULTS

We identified 32 vasoactive peptides with potential blood-brain barrier permeabilityaltering properties. To date, none of these are shown to open the blood-brain barrier in humans. Twelve vasoactive peptides increased blood-brain barrier permeability in rodents. The remaining 20 had favorable physiologic effects on blood vessels but lacked specific information on permeability changes to the blood-brain barrier.

CONCLUSION

Vasoactive peptides remain an understudied class of drugs with the potential to increase drug delivery and improve treatment in patients with brain tumors and other neurologic diseases. Dozens of vasoactive peptides have yet to be formally evaluated for this important clinical effect. This narrative review summarizes the available data on vasoactive peptides, highlighting agents that deserve further in vitro and in vivo investigations.

Bee Pollen and Probiotics May Alter Brain Neuropeptide Levels in a Rodent Model of Autism Spectrum Disorders

Neuropeptides play a major role in maintaining normal brain development in children. Dysfunction of some specific neuropeptides can lead to autism spectrum disorders (ASD) in terms of social interaction and repetitive behavior, but the exact underlying etiological mechanisms are still not clear. In this study, we used an animal model of autism to investigate the role of bee pollen and probiotic in maintaining neuropeptide levels in the brain. We measured the Alpha-melanocyte-stimulating hormone (α-MSH), Beta-endorphin (β-End), neurotensin (NT), and substance P (SP) in brain homogenates of six studied groups of rats. Group I served as control, given only PBS for 30 days; Group II as an autistic model treated with 250 mg PPA/kg BW/day for 3 days after being given PBS for 27 days. Groups III-VI were denoted as intervention groups. G-III was treated with bee pollen (BP) 250 mg/kg body weight/day; G-IV with Lactobacillus paracaseii (LB) (109 CFU/mL) suspended in PBS; G-V with 0.2 g/kg body weight/day Protexin^®, a mixture of probiotics (MPB); and G-VI was transplanted with stool from normal animals (FT) for 27 days prior to the induction of PPA neurotoxicity on the last 3 days of study (days 28–30). The obtained data were analyzed through the use of principal component analysis (PCA), discriminant analysis (DA), hierarchical clustering, and receiver operating characteristic (ROC) curves as excellent statistical tools in the field of biomarkers. The obtained data revealed that brain levels of the four measured neuropeptides were significantly reduced in PPA-treated animals compared to healthy control animals. Moreover, the findings demonstrate the ameliorative effects of bee pollen as a prebiotic and of the pure or mixed probiotics. This study proves the protective effects of pre and probiotics against the neurotoxic effects of PPA presented as impaired levels of α-MSH, β-End, NT, and SP.

Role of Monoamine Oxidase Activity in Alzheimer's Disease: An Insight into the Therapeutic Potential of Inhibitors

Despite not being utilized as considerably as other antidepressants in the therapy of depression, the monoamine oxidase inhibitors (MAOIs) proceed to hold a place in neurodegeneration and to have a somewhat broad spectrum in respect of the treatment of neurological and psychiatric conditions. Preclinical and clinical studies on MAOIs have been developing in recent times, especially on account of rousing discoveries manifesting that these drugs possess neuroprotective activities. The altered brain levels of monoamine neurotransmitters due to monoamine oxidase (MAO) are directly associated with various neuropsychiatric conditions like Alzheimer’s disease (AD). Activated MAO induces the amyloid-beta (Aβ) deposition via abnormal cleavage of the amyloid precursor protein (APP). Additionally, activated MAO contributes to the generation of neurofibrillary tangles and cognitive impairment due to neuronal loss. No matter the attention of researchers on the participation of MAOIs in neuroprotection has been on monoamine oxidase-B (MAO-B) inhibitors, there is a developing frame of proof indicating that monoamine oxidase-A (MAO-A) inhibitors may also play a role in neuroprotection. The therapeutic potential of MAOIs alongside the complete understanding of the enzyme’s physiology may lead to the future advancement of these drugs.

Overview of the Neuroprotective Effects of the MAO-Inhibiting Antidepressant Phenelzine

Phenelzine (PLZ) is a monoamine oxidase (MAO)-inhibiting antidepressant with anxiolytic properties. This multifaceted drug has a number of pharmacological and neurochemical effects in addition to inhibition of MAO, and findings on these effects have contributed to a body of evidence indicating that PLZ also has neuroprotective/neurorescue properties. These attributes are reviewed in this paper and include catabolism to the active metabolite β-phenylethylidenehydrazine (PEH) and effects of PLZ and PEH on the GABA-glutamate balance in brain, sequestration of reactive aldehydes, and inhibition of primary amine oxidase. Also discussed are the encouraging findings of the effects of PLZ in animal models of stroke, spinal cord injury, traumatic brain injury, and multiple sclerosis, as well other actions such as reduction of nitrative stress, reduction of the effects of a toxin on dopaminergic neurons, potential anticonvulsant actions, and effects on brain-derived neurotrophic factor, neural cell adhesion molecules, an anti-apoptotic factor, and brain levels of ornithine and N-acetylamino acids.

Molecular pathogenesis of spontaneous abortions - Whole genome copy number analysis and expression of angiogenic factors

OBJECTIVE

To study two major molecular alterations in spontaneous abortions (SA) with unexplained etiology - fetal genomic anomalies and the endometrial expression of main angiogenic factors VEGFA/VEGFR2 and chemokines SDF-1/CXCR4.

MATERIALS AND METHODS

Whole genome copy number analysis by arrayCGH or Next Generation Sequencing (NGS) was applied for detection of fetal genomic imbalances. The abortive decidua of SA without fetal aneuploidies was further investigated for expression levels of the abovementioned factors using real time PCR analysis. A total of 30 abortive materials were collected from spontaneous abortions after exclusion of known predisposing factors.

RESULTS

In 21 of 30 spontaneous abortions (70%), genomic anomalies were discovered by whole genome copy number analysis. Numerical anomalies were detected in 90% of aberrant cases, and in 10% - structural aberrations were revealed. An increased expression for essential factors of angiogenesis was identified in spontaneous abortions' tissues - 3.44 times for VEGFA and 10.29 times for VEGFR2. We found an average of 14 times increase in the expression levels of SDF-1 and 3.21 times for its receptor CXCR4.

CONCLUSION

We could suggest the occurrence of increased angiogenesis in SA without fetal aneuploidies, compared to the control tissues, which could lead to increased oxidative stress and fetal loss.

High serum substance P levels and mortality after malignant middle cerebral artery infarction

PURPOSE

Previously our team found higher serum substance P concentrations at day 1 of a malignant middle cerebral artery infarction (MMCAI) in non-surviving than in surviving patients. Thus, the objective of this study was to determine whether serum substance P levels during the first week of MMCAI could predict mortality.

METHODS

We included patients with MMCAI defined as computed tomography findings of acute infarction in at least of 50% of the territory and Glasgow Coma Scale ≤8. We determined serum concentrations of substance P on days 1, 4 and 8 of MMCAI. Thirty-day mortality was the study end-point.

RESULTS

Serum substance P concentrations at days 1 (p < .001), 4 (p < .001), and 8 (p = .001) of MMCAI in non-surviving (n = 34) were higher than in surviving patients (n = 34). Receiver operating characteristic analyses showed that serum substance P concentrations at days 1, 4, and 8 of MMCAI had an area under curve (95% confidence intervals) to predict 30-day mortality of 0.77 (0.66-0.87; p < .001), 0.82 (0.69-0.91; p < .001) and 0.85 (0.72-0.94; p < .001) respectively.

CONCLUSIONS

The two new findings of our study are that non-surviving MMCAI patients showed higher serum substance P levels at day 1, 4 and 8 than surviving, and that those levels could predict 30-day mortality.

NK1-r Antagonist Treatment Comparable to Decompressive Craniectomy in Reducing Intracranial Pressure Following Stroke

Background and Purpose: The morbidity and early mortality associated with stroke is largely attributable to cerebral edema and elevated intracranial pressure (ICP). Existing pharmacotherapies do not target the underlying pathophysiology and are often ineffective in sustainably lowering ICP, whilst decompressive craniectomy (DC) surgery is life-saving yet with surgical/peri-operative risk and increased morbidity in the elderly. Accordingly, there is an urgent need for therapies that directly target the mechanisms of edema genesis. Neurogenic inflammation, mediated by substance P (SP) binding to the tachykinin NK1 receptor (NK1-r), is associated with blood-brain barrier (BBB) disruption, cerebral edema and poor outcome post-stroke. NK1-r antagonist treatment ameliorates BBB dysfunction and cerebral edema in rodent stroke models. However, treatment has not been investigated in a large animal model, an important step toward clinical translation. Consequently, the current study compared the efficacy of NK1-r antagonist treatment to DC surgery in reducing ICP post-stroke in a clinically relevant ovine model.

Methods: Anesthetized female Merino sheep (65 ± 6 kg, 18–24 months) underwent sham surgery (n = 4) or permanent middle cerebral artery occlusion (n = 22). Stroke animals were randomized into one of 5 treatments: 1×NK1 bolus (4 h), 2×NK1 bolus (4 h;9 h), 3×NK1 bolus (4 h;9 h;14 h), DC surgery (performed at 4 h) or saline vehicle. ICP, blood pressure and blood gasses were monitored for 24 h post-stroke. At 24 h post-stroke anesthetized animals underwent MRI followed by perfusion and brains removed and processed for histological assessment.

Results: 2×NK1, 3×NK1 administration or DC surgery significantly (p < 0.05) reduced ICP compared to vehicle. 1×NK1 was ineffective in sustainably lowering ICP. On MRI, midline shift and cerebral edema were more marked in vehicles compared to NK1-r treatment groups.

Conclusion: Two or three boluses of NK1-r antagonist treatment reduced ICP comparable to DC surgery, suggesting it may provide a novel alternative to invasive surgery for the management of elevated ICP.

Human microglia and astrocytes constitutively express the neurokinin-1 receptor and functionally respond to substance P

Background

The tachykinin substance P (SP) is recognized to exacerbate inflammation at peripheral sites via its target receptor, neurokinin 1 receptor (NK-1R), expressed by leukocytes. More recently, SP/NK-1R interactions have been associated with severe neuroinflammation and neuronal damage. We have previously demonstrated that NK-1R antagonists can limit neuroinflammatory damage in a mouse model of bacterial meningitis. Furthermore, we have since shown that these agents can attenuate bacteria-induced neuronal and glial inflammatory mediator production in nonhuman primate (NHP) brain explants and isolated neuronal cells, and following in vivo infection.

Methods

In the present study, we have assessed the ability of NHP brain explants, primary human microglia and astrocytes, and immortalized human glial cell lines to express NK-1R isoforms. We have utilized RT-PCR, immunoblot analysis, immunofluorescent microscopy, and/or flow cytometric analysis, to quantify NK-1R expression in each, at rest, or following bacterial challenge. Furthermore, we have assessed the ability of human microglia to respond to SP by immunoblot analysis of NF-kB nuclear translocation and determined the ability of this neuropeptide to augment inflammatory cytokine release and neurotoxic mediator production by human astrocytes using an ELISA and a neuronal cell toxicity assay, respectively.

Results

We demonstrate that human microglial and astrocytic cells as well as NHP brain tissue constitutively express robust levels of the full-length NK-1R isoform. In addition, we demonstrate that the expression of NK-1R by human astrocytes can be further elevated following exposure to disparate bacterial pathogens or their components. Importantly, we have demonstrated that NK-1R is functional in both human microglia and astrocytes and show that SP can augment the inflammatory and/or neurotoxic immune responses of glial cells to disparate and clinically relevant bacterial pathogens.

Conclusions

The robust constitutive and functional expression of the full-length NK-1R isoform by human microglia and astrocytes, and the ability of SP to augment inflammatory signaling pathways and mediator production by these cells, support the contention that SP/NK-1R interactions play a significant role in the damaging neuroinflammation associated with conditions such as bacterial meningitis.

The Role of Neurogenic Inflammation in Blood-Brain Barrier Disruption and Development of Cerebral Oedema Following Acute Central Nervous System (CNS) Injury

Acute central nervous system (CNS) injury, encompassing traumatic brain injury (TBI) and stroke, accounts for a significant burden of morbidity and mortality worldwide, largely attributable to the development of cerebral oedema and elevated intracranial pressure (ICP). Despite this, clinical treatments are limited and new therapies are urgently required to improve patient outcomes and survival. Originally characterised in peripheral tissues, such as the skin and lungs as a neurally-elicited inflammatory process that contributes to increased microvascular permeability and tissue swelling, neurogenic inflammation has now been described in acute injury to the brain where it may play a key role in the secondary injury cascades that evolve following both TBI and stroke. In particular, release of the neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP) appear to be critically involved. In particular, increased SP expression is observed in perivascular tissue following acute CNS injury, with the magnitude of SP release being related to both the frequency and degree of the insult. SP release is associated with profound blood-brain barrier disruption and the subsequent development of vasogenic oedema, as well as neuronal injury and poor functional outcomes. Inhibition of SP through use of a neurokinin 1 (NK1) antagonist is highly beneficial following both TBI and ischaemic stroke in pre-clinical models. The role of CGRP is more unclear, especially with respect to TBI, with both elevations and reductions in CGRP levels reported following trauma. However, a beneficial role has been delineated in stroke, given its potent vasodilatory effects. Thus, modulating neuropeptides represents a novel therapeutic target in the treatment of cerebral oedema following acute CNS injury.

The Role of Substance P in Secondary Pathophysiology after Traumatic Brain Injury

It has recently been shown that substance P (SP) plays a major role in the secondary injury process following traumatic brain injury (TBI), particularly with respect to neuroinflammation, increased blood–brain barrier (BBB) permeability, and edema formation. Edema formation is associated with the development of increased intracranial pressure (ICP) that has been widely associated with increased mortality and morbidity after neurotrauma. However, a pharmacological intervention to specifically reduce ICP is yet to be developed, with current interventions limited to osmotic therapy rather than addressing the cause of increased ICP. Given that previous publications have shown that SP, NK1 receptor antagonists reduce edema after TBI, more recent studies have examined whether these compounds might also reduce ICP and improve brain oxygenation after TBI. We discuss the results of these studies, which demonstrate that NK1 antagonists reduce posttraumatic ICP to near normal levels within 4 h of drug administration, as well as restoring brain oxygenation to near normal levels in the same time frame. The improvements in these parameters occurred in association with an improvement in BBB integrity to serum proteins, suggesting that SP-mediated increases in vascular permeability significantly contribute to the development of increased ICP after acute brain injury. NK1 antagonists may therefore provide a novel, mechanistically targeted approach to the management of increased ICP.

CD74-immunoreactive activated M1 microglia are shown late in the gerbil hippocampal CA1 region following transient cerebral ischemia

Activated M1 microglia secrete proinflammatory cytokines into damaged brain areas. The present study examined activated M1 microglial morphology and expression in the hippocampal Cornu Ammonis (CA) 1 region, which is vulnerable to transient ischemia. Transient cerebral ischemia was performed for 5 min in gerbils, and neuronal death in the CA1 region following transient cerebral ischemia was confirmed using cresyl violet staining, neuronal nuclear antigen immunohistochemistry and Fluoro-Jade B histofluorescent staining. In addition, CA1 regions were stained for cluster of differentiation (CD) 74, a marker for activated M1 microglia and a ligand for macrophage migration inhibitory factor In sham-operated animals, no CD74 immunoreactivity was observed in the hippocampal CA1 region. CD74 immunoreactivity was not observed in the hippocampal CA1 region until 3 days post-ischemic insult; however, elevated CD74 immunoreactivity was detected in the CA1 region from 5 days post-ischemia. Double immunofluorescence staining for CD74 and ionized calcium-binding adapter molecule 1, a marker for M1 microglial cells, confirmed the expression of CD74 on this microglial subtype. These results indicated that M1 microglia are activated late in the hippocampal CA1 region following ischemic stroke. Therefore, optimizing the timing of therapeutic intervention may reduce activated M1 microglial-induced neuronal damage.

The Therapeutic Potential of Targeting Substance P/NK-1R Interactions in Inflammatory CNS Disorders

The inflammatory responses of resident central nervous system (CNS) cells are now known to play a critical role in the initiation and progression of an array of infectious and sterile neuroinflammatory disorders such as meningitis, encephalitis, Parkinson's disease, Alzheimer's disease and multiple sclerosis (MS). Regulating glial inflammatory responses in a timely manner is therefore critical in preserving normal CNS functions. The neuropeptide substance P is produced at high levels within the CNS and its selective receptor, the neurokinin 1 receptor (NK-1R), is abundantly expressed by neurons and is present on glial cell types including microglia and astrocytes. In addition to its functions as a neurotransmitter in the perception of pain and its essential role in gut motility, this tachykinin is widely recognized to exacerbate inflammation at peripheral sites including the skin, gastrointestinal tract and the lungs. Recently, a number of studies have identified a role for substance P and NK-1R interactions in neuroinflammation and described the ability of this neuropeptide to alter the immune functions of activated microglia and astrocytes. In this review article, we describe the expression of substance P and its receptor by resident CNS cells, and we discuss the ability of this neuropeptide to exacerbate the inflammatory responses of glia and immune cells that are recruited to the brain during neurodegenerative diseases. In addition, we discuss the available data indicating that the NK-1R-mediated augmentation of such responses appears to be detrimental during microbial infection and some sterile neurodegenerative disorders, and propose the repurposed use of NK-1R antagonists, of a type that are currently approved as anti-emetic and anti-anxiolytic agents, as an adjunct therapy to ameliorate the inflammatory CNS damage in these conditions.

Dysregulation of Chemokine/Chemokine Receptor Axes and NK Cell Tissue Localization during Diseases

Chemokines are small chemotactic molecules that play key roles in physiological and pathological conditions. Upon signaling via their specific receptors, chemokines regulate tissue mobilization and trafficking of a wide array of immune cells, including natural killer (NK) cells. Current research is focused on analyzing changes in chemokine/chemokine receptor expression during various diseases to interfere with pathological trafficking of cells or to recruit selected cell types to specific tissues. NK cells are a heterogeneous lymphocyte population comprising several subsets endowed with distinct functional properties and mainly representing distinct stages of a linear development process. Because of their different functional potential, the type of subset that accumulates in a tissue drives the final outcome of NK cell-regulated immune response, leading to either protection or pathology. Correspondingly, chemokine receptors, including CXCR4, CXCR3, and CX₃CR1, are differentially expressed by NK cell subsets, and their expression levels can be modulated during NK cell activation. At first, this review will summarize the current knowledge on the contribution of chemokines to the localization and generation of NK cell subsets in homeostasis. How an inappropriate chemotactic response can lead to pathology and how chemokine targeting can therapeutically affect tissue recruitment/localization of distinct NK cell subsets will also be discussed.

Serum Levels of Substance P and Mortality in Patients with a Severe Acute Ischemic Stroke

Substance P (SP), a member of tachykinin family, is involved in the inflammation of the central nervous system and in the appearance of cerebral edema. Higher serum levels of SP have been found in 18 patients with cerebral ischemia compared with healthy controls. The aim of our multi-center study was to analyze the possible association between serum levels of SP and mortality in ischemic stroke patients. We included patients with malignant middle cerebral artery infarction (MMCAI) and a Glasgow Coma Scale (GCS) lower than 9. Non-surviving patients at 30 days (n = 31) had higher serum concentrations of SP levels at diagnosis of severe MMCAI than survivors (n = 30) (p < 0.001). We found in multiple regression an association between serum concentrations of SP higher than 362 pg/mL and mortality at 30 days (Odds Ratio = 5.33; 95% confidence interval = 1.541-18.470; p = 0.008) after controlling for age and GCS. Thus, the major novel finding of our study was the association between serum levels of SP and mortality in patients suffering from severe acute ischemic stroke.

NK1 tachykinin receptor treatment is superior to capsaicin pre-treatment in improving functional outcome following acute ischemic stroke

Previous results from our laboratory have shown that blockade of the substance P (SP) pathway with an NK1 tachykinin receptor antagonist significantly reduces blood brain barrier breakdown, cerebral edema and functional deficits following ischemic stroke. However, it is unclear whether removal of all neuropeptides is more efficacious than blocking SP alone. As such, the aim of the present study was to determine the effect of neuropeptide depletion with capsaicin pre-treatment on functional outcome following acute ischemic stroke in rats. Animals received 125 mg/kg of capsaicin or equal volume of saline vehicle, administered subcutaneously over a 3-day period. At 14 days following treatment animals were subject to 2h of middle cerebral artery occlusion followed by reperfusion. A subset of animals was treated with an NK1 tachykinin receptor antagonist (NAT) or vehicle at 4h after the onset of stroke only. The functional outcome of animals was assessed for a 7-day period following stroke using a rotarod device, the bilateral asymmetry test, modified neurological severity score, open field and angleboard. Although capsaicin pre-treatment improved outcome, treatment with an NK1 tachykinin receptor antagonist was superior in improving post-stroke functional outcome. This data suggests that some neuropeptides may play a beneficial role following stroke, whilst others such as SP are deleterious.

A survey from 2012 of evidence for the role of neuroinflammation in neurotoxin animal models of Parkinson's disease and potential molecular targets

Parkinson's disease (PD) is a neurodegenerative movement disorder that results from the progressive loss of dopaminergic neurons in the midbrain substantia nigra pars compacta (SNpc). The specific molecular events that cause PD are currently not known; however, progress to better understand PD pathogenesis has been made using various animal models of the disease. In this review, we have highlighted reports from 2012 in which neurochemical/neurotoxins have been used in rodents to specifically address the role of neuroinflammation in the development and/or progression of PD-like pathology and in particular nigral degeneration. A number of studies have been summarized in which plausible pro-inflammatory, anti-inflammatory, or therapeutic agents targeting inflammatory pathways were introduced and/or investigated by various groups for neuroprotective effects. From these studies, it is clear that neuroinflammation acts to exacerbate the toxic outcomes that are set in motion within neurons following exposure to neurotoxins. Additionally, it is noted that future work is still needed to better understand the underlying mechanisms mediating the neuroinflammatory and neurotoxic phenotypes reported in rodent models of PD-like pathology to maximize the translation potential of these interventions to the clinic to prevent and/or delay PD onset and/or progression in humans.

The role of substance p in ischaemic brain injury

Stroke is a leading cause of death, disability and dementia worldwide. Despite extensive pre-clinical investigation, few therapeutic treatment options are available to patients, meaning that death, severe disability and the requirement for long-term rehabilitation are common outcomes. Cell loss and tissue injury following stroke occurs through a number of diverse secondary injury pathways, whose delayed nature provides an opportunity for pharmacological intervention. Amongst these secondary injury factors, increased blood-brain barrier permeability and cerebral oedema are well-documented complications of cerebral ischaemia, whose severity has been shown to be associated with final outcome. Whilst the mechanisms of increased blood-brain barrier permeability and cerebral oedema are largely unknown, recent evidence suggests that the neuropeptide substance P (SP) plays a central role. The aim of this review is to examine the role of SP in ischaemic stroke and report on the potential utility of NK1 tachykinin receptor antagonists as therapeutic agents.

Transmitter- and hormone-activated Ca(2+) responses in adult microglia/brain macrophages in situ recorded after viral transduction of a recombinant Ca(2+) sensor

In vitro studies show that microglia, the resident immune cells of the brain, express neurotransmitter and neuropeptide receptors which are linked to Ca(2+) signaling. Here we describe an approach to obtain Ca(2+) recordings from microglia in situ. We injected a retrovirus encoding a calcium sensor into the cortex of mice 2 days after stimulation of microglial proliferation by a stab wound injury. Microglial cells were identified with tomato lectin in acute slices prepared 3, 6, 21 and 42 days after the injury. The membrane current profile and the ameboid morphology indicated that microglial cells were activated at day 6 while at day 42 they resembled resting microglia. We recorded transient Ca(2+) responses to application of ATP, endothelin-1, substance P, histamine and serotonin. The fluorescence amplitude of ATP was increased only at day 6 compared to other time points, while responses to all other ligands did not vary. Only half of the microglial cells that responded to ATP also responded to endothelin-1, serotonin and histamine. Substance P, in contrast, showed a complete overlap with the ATP responding microglial population at day 6, at day 42 this population was reduced to 55%. Cultured cells were less responsive to these ligands. This study shows that in situ microglia consist of heterogeneous populations with respect to their sensitivity to neuropeptides and -transmitters.

A substance P antagonist improves outcome when administered 4 h after onset of ischaemic stroke

Previous studies have suggested that substance P (SP) plays a critical role in the development of brain oedema and functional deficits following traumatic brain injury and that SP receptor antagonism may improve outcome. No studies have described such a role in ischemic stroke. The present study characterized the effects of the NK1 tachykinin receptor antagonist, n-acetyl-L-tryptophan (NAT), on blood-brain barrier (BBB) breakdown, oedema formation, infarct volume and functional outcome following reversible ischemic stroke in rats. Ischemia was induced using a reversible thread model of middle cerebral artery occlusion where occlusion was maintained for 2 h before reperfusion. Animals received either NAT or equal volume saline vehicle intravenously at 2 h post-reperfusion. Ischaemic stroke resulted in increased perivascular SP immunoreactivity at 24 h. Administration of NAT significantly reduced oedema formation and BBB permeability at 24 h post-ischemia and significantly improved functional outcome as assessed over 7 days. There was no effect on infarct volume. We conclude that inhibition of SP activity with a NK1 tachykinin receptor antagonist is effective in reducing cerebral oedema, BBB permeability and functional deficits following reversible ischemia and may therefore represent a novel therapeutic approach to the treatment of ischaemic stroke.

Kinin receptor antagonists as potential neuroprotective agents in central nervous system injury

Injury to the central nervous system initiates complex physiological, cellular and molecular processes that can result in neuronal cell death. Of interest to this review is the activation of the kinin family of neuropeptides, in particular bradykinin and substance P. These neuropeptides are known to have a potent pro-inflammatory role and can initiate neurogenic inflammation resulting in vasodilation, plasma extravasation and the subsequent development of edema. As inflammation and edema play an integral role in the progressive secondary injury that causes neurological deficits, this review critically examines kinin receptor antagonists as a potential neuroprotective intervention for acute brain injury, and more specifically, traumatic brain and spinal cord injury and stroke.

Substance P immunoreactivity increases following human traumatic brain injury

Recent experimental evidence suggests that neuropeptides, and in particular substance P (SP), are released following traumatic brain injury (TBI) and may play a significant role in the aetiology of cerebral edema and increased intracranial pressure. Whether SP may play a similar role in clinical TBI remains unknown and was investigated in the current study. Archival post-mortem material was selected from patients who had sustained TBI, had died and had undergone post-mortem and detailed neuropathological examination (n = 13). A second cohort of patients who had died, but who showed no neuropathological abnormality (n = 10), served as case controls. Changes in SP immunoreactivity were examined in the cerebral cortex directly beneath the subdural haematoma in 7 TBI cases and in proximity to contusions in the other 6 cases. Increased SP perivascular immunoreactivity was observed after TBI in 10/13 cases, cortical neurones in 12/13 and astrocytes in 10/13 cases. Perivascular axonal injury was observed by amyloid precursor protein (APP) immunoreactivity in 6/13 TBI cases. Co-localization of SP and APP in a small subset of perivascular fibres suggests perivascular axonal injury could be a mechanism of release of this neuropeptide. The abundance of SP fibres around the human cerebral microvasculature, particularly post capillary venules, together with the changes observed following TBI in perivascular axons, cortical neurones and astrocytes suggest a potentially important role for substance P in neurogenic inflammation following human TBI.

Substance P antagonists as a therapeutic approach to improving outcome following traumatic brain injury

Although a number of secondary injury factors are known to contribute to the development of morphological injury and functional deficits following traumatic brain injury, accumulating evidence has suggested that neuropeptides, and in particular substance P, may play a critical role. Substance P is released early following acute injury to the CNS as part of a neurogenic inflammatory response. In so doing, it facilitates an increase in the permeability of the blood-brain barrier and the development of vasogenic edema. At the cellular level, substance P has been shown to directly result in neuronal cell death; functionally, substance P has been implicated in learning and memory, mood and anxiety, stress mechanisms, emotion-processing, migraine, emesis, pain, and seizures, all of which may be adversely affected after brain injury. Inhibition of post-traumatic substance P activity, either by preventing release or by antagonism of the neurokinin-1 receptor, has consistently resulted in a profound decrease in development of edema and marked improvements in functional outcome. This review summarizes the current evidence supporting a role for substance P in acute brain injury.

Substance P is associated with the development of brain edema and functional deficits after traumatic brain injury

Brain edema and swelling is a critical factor in the high mortality and morbidity associated with traumatic brain injury (TBI). Despite this, the mechanisms associated with its development are poorly understood and interventions have not changed in over 30 years. Although neuropeptides and neurogenic inflammation have been implicated in peripheral edema formation, their role in the development of central nervous system edema after brain trauma has not been investigated. This study examines the role of the neuropeptide, substance P (SP), in the development of edema and functional deficits after brain trauma in rats. After severe diffuse TBI in adult male rats, neuronal and perivascular SP immunoreactivity were increased markedly. Perivascular SP colocalized with exogenously administered Evans blue, supporting a role for SP in vascular permeability. Inhibition of SP action by administration of the neurokinin-1 (NK1) antagonist, N-acetyl-L-tryptophan, at 30 mins after trauma attenuated vascular permeability and edema formation. Administration of the NK1 antagonist also improved both motor and cognitive neurologic outcomes. These findings suggest that SP release is integrally linked to the increased vascular permeability and edema formation after brain trauma, and that treatment with an NK1 receptor antagonist reduces edema and improves neurologic outcome.

Differential regulation of CXCL12 and PACAP mRNA expression after focal and global ischemia

Pituitary adenylate cyclase activating peptide (PACAP) and the chemokine stromal cell-derived factor (SDF-1) have been implicated in neuroprotection, neurogenesis, and regeneration. Focal ischemia is associated with rapid upregulation of PACAP in perifocal neurons and delayed induction of SDF-1 in hypoxic/ischemic tissues, the latter process being involved in the recruitment of stem cells and inflammatory cells. Here, we studied mRNA patterns of PACAP, SDF-1 and the cognate receptors PAC1 and CXCR4 by in situ hybridization in the rat hippocampus after transient global ischemia, a rat model for programmed death of CA1 pyramidal neurons. Cell death in CA1 was not associated with local induction of PACAP and SDF-1 expression or recruitment of CXCR4-expressing infiltrates. However, there was a transient, almost complete loss of SDF-1 expression in microvessels in all hippocampal regions. Granule cells transiently showed a decrease of SDF-1 and an increase of PACAP expression. While PAC1 mRNA was moderately decreased throughout the hippocampus, CXCR4 expression was selectively increased in the subgranular layer. We propose that altered PACAP and SDF-1 gene expression in granule cells plays a role in regulated neurogenesis after global ischemia. The finding that programmed neuronal death after global ischemia was not associated with SDF-1 upregulation or recruitment of CXCR4-expressing cells is in sharp contrast to SDF-1/CXCR4-mediated infiltration of infarct tissue after focal ischemia. Hence, the different modes of neuronal death after focal and global ischemia are associated with distinct SDF-1 and PACAP gene regulation patterns and distinct reorganization mechanisms.

Regional and cellular localization of the CXCl12/SDF-1 chemokine receptor CXCR7 in the developing and adult rat brain

The chemokine stromal cell-derived factor-1 (SDF-1) regulates neuronal development via the chemokine receptor CXCR4. In the adult brain the SDF-1/CXCR4 system was implicated in neurogenesis, neuromodulation, brain inflammation, tumor growth, and HIV encephalopathy. Until the recent identification of RDC1/CXCR7 as the second SDF-1 receptor, CXCR4 was considered to be the only receptor for SDF-1. Here we provide the first map of CXCR7 mRNA expression in the embryonic and adult rat brain. At embryonic stages, CXCR7 and CXCR4 were codistributed in the germinative zone of the ganglionic eminences, caudate putamen, and along the routes of GABAergic precursors migrating toward the cortex. In the cortex, CXCR7 was identified in GABAergic precursors and in some reelin-expressing Cajal-Retzius cells. Unlike CXCR4, CXCR7 was abundant in neurons forming the cortical plate and sparse in the developing dentate gyrus and cerebellar external germinal layer. In the adult brain, CXCR7 was expressed by blood vessels, pyramidal cells in CA3, and mature dentate gyrus granule cells, which is reminiscent of the SDF-1 pattern. CXCR7 and CXCR4 overlapped in the wall of the four ventricles. Further neuronal structures expressing CXCR7 comprised the olfactory bulb, accumbens shell, supraoptic and ventromedial hypothalamic nuclei, medial thalamus, and brain stem motor nuclei. Also, GLAST-expressing astrocytes showed signals for CXCR7. Thus, CXCR4 and CXCR7 may cooperate or act independently in SDF-1-dependent neuronal development. In mature neurons and blood vessels CXCR7 appears to be the preponderant SDF-1-receptor.

Effects of Lipopolysaccharide on56Fe-Particle Radiation-Induced Impairment of Synaptic Plasticity in the Mouse Hippocampus

Space radiation, including high-mass, high-Z, high-energy particles (HZE; e.g. (56)Fe), represents a significant health risk for astronauts, and the central nervous system (CNS) may be a vulnerable target. HZE-particle radiation may directly affect neuronal function, or during immunological challenge, it may alter immune system-to-CNS communication. To test these hypotheses, we exposed mice to accelerated iron particles ((56)Fe; 600 MeV/nucleon; 1, 2, 4 Gy; brain only) and 1 month later prepared hippocampal slices to measure the effects of radiation on neurotransmission and synaptic plasticity in CA1 neurons. In a model of immune system-to-CNS communication, these electrophysiological parameters were measured in irradiated mice additionally challenged with the peripheral immunological stressor lipopolysaccharide (LPS) injected intraperitoneally 4 h before the slice preparation. Exposure to (56)Fe particles alone increased dendritic excitability and inhibited plasticity. In control mice (0 Gy), LPS treatment also inhibited synaptic plasticity. Paradoxically, in mice exposed to 2 Gy, the LPS treatment restored synaptic plasticity to levels similar to those found in controls (0 Gy, no LPS). Our results indicate that HZE-particle radiation alters normal electrophysiological properties of the CNS and the hippocampal response to LPS.

Pituitary adenylate cyclase-activating polypeptide is up-regulated in cortical pyramidal cells after focal ischemia and protects neurons from mild hypoxic/ischemic damage

The protective effect of pituitary adenylate cyclase-activating polypeptide (PACAP) in stroke models is poorly understood. We studied patterns of PACAP, vasoactive intestinal peptide, and the PACAP-selective receptor PAC1 after middle cerebral artery occlusion and neuroprotection by PACAP in cortical cultures exposed to oxygen/glucose deprivation (OGD). Within hours, focal ischemia caused a massive, NMDA receptor (NMDAR)-dependent up-regulation of PACAP in cortical pyramidal cells. PACAP expression dropped below the control level after 2 days and was normalized after 4 days. Vasoactive intestinal peptide expression was regulated oppositely to that of PACAP. PAC1 mRNA showed ubiquitous expression in neurons and astrocytes with minor changes after ischemia. In cultured cortical neurons PACAP27 strongly activated Erk1/2 at low and p38 MAP kinase at higher nanomolar concentrations via PAC1. In astrocyte cultures, effects of PACAP27 on Erk1/2 and p38 were weak. During OGD, neurons showed severely reduced Erk1/2 activity and dephosphorylation of Erk1/2-regulated Ser112 of pro-apoptotic Bad. PACAP27 stimulation counteracted Erk1/2 inactivation and Bad dephosphorylation during short-term OGD but was ineffective after expanded OGD. Consistently, PACAP27 caused MEK-dependent neuroprotection during mild but not severe hypoxic/ischemic stress. While PACAP27 protected neurons at 1-5 nmol/L, full PAC1 activation by 100 nmol/L PACAP exaggerated hypoxic/ischemic damage. PACAP27 stimulation of astrocytes increased the production of Akt-activating factors and conferred ischemic tolerance to neurons. Thus, ischemia-induced PACAP may act via neuronal and astroglial PAC1. PACAP confers protection to ischemic neurons by maintaining Erk1/2 signaling via neuronal PAC1 and by increasing neuroprotective factor production via astroglial PAC1.

Patterns of SDF-1alpha and SDF-1gamma mRNAs, migration pathways, and phenotypes of CXCR4-expressing neurons in the developing rat telencephalon

Cortical GABAergic neurons originate in the ventral telencephalon, invade the cortex via tangential migration, and integrate into the cortical plate by surface-directed and ventricle-directed migration. In mice lacking CXCR4 or SDF-1, GABAergic neurons fail to complete their migration. It is presently unknown which parts of the migration of CXCR4-expressing GABAergic neurons are driven by SDF-1. Here we compared patterns of SDF-1 isoforms and CXCR4 in the developing rat telencephalon. In the ventral telencephalon, radial glia, striatal, and migratory GABAergic neurons expressed CXCR4. Tangentially migrating CXCR4-expressing neurons populated the marginal zone and started to invade the lateral intermediate zone at embryonic day (E)14. Until E17 the spread of CXCR4-expressing neurons in the dorsomedial direction was accompanied by progressive upregulation of SDF-1alpha in the dorsomedial intermediate/subventricular zone. In the meninges, SDF-1alpha and SDF-1gamma were expressed persistently. During invasion of the cortical plate the orientation of CXCR4-immunoreactive neurons changed gradually from tangential (E17/E18) to radial (postnatal day [P] 0), which was paralleled by downregulation of SDF-1alpha in the intermediate/subventricular zone. At E17, CXCR4-immunoreactive cells were colabeled with markers for ventral forebrain-derived neurons (Dlx) but not markers for glutamatergic (Tbr) or subplate (calretinin) neurons. Postnatally, calretinin- and somatostatin-expressing but not parvalbumin-expressing GABAergic neurons or pyramidal cells contained CXCR4. Pyramidal cells and few large blood vessels expressed SDF-1alpha, while microvessels contained SDF-1gamma transcripts. In summary, SDF-1alpha is expressed along cortical but not subcortical migration routes of GABAergic neurons. We propose that regulated expression of SDF-1 in the intermediate/subventricular zone influences lateromedial tangential migration of CXCR4-expressing GABAergic neurons.

Membrane glycoprotein M6a interacts with the micro-opioid receptor and facilitates receptor endocytosis and recycling

Using a yeast two-hybrid screen, the neuronal membrane glycoprotein M6a, a member of the proteolipid protein family, was identified to be associated with the mu-opioid receptor (MOPr). Bioluminescence resonance energy transfer and co-immunoprecipitation experiments confirmed that M6a interacts agonist-independently with MOPr in human embryonic kidney 293 cells co-expressing MOPr and M6a. Co-expression of MOPr with M6a, but not with M6b or DM20, exists in many brain regions, further supporting a specific interaction between MOPr and M6a. After opioid treatment M6a co-internalizes and then co-recycles with MOPr to cell surface in transfected human embryonic kidney 293 cells. Moreover, the interaction of M6a and MOPr augments constitutive and agonist-dependent internalization as well as the recycling rate of mu-opioid receptors. On the other hand, overexpression of a M6a-negative mutant prevents mu-opioid receptor endocytosis, demonstrating an essential role of M6a in receptor internalization. In addition, we demonstrated the interaction of M6a with a number of other G protein-coupled receptors (GPCRs) such as the delta-opioid receptor, cannabinoid receptor CB1, and somatostatin receptor sst2A, suggesting that M6a might play a general role in the regulation of certain GPCRs. Taken together, these data provide evidence that M6a may act as a scaffolding molecule in the regulation of GPCR endocytosis and intracellular trafficking.

PET imaging of neurokinin-1 receptors with [(18)F]SPA-RQ in human subjects: assessment of reference tissue models and their test-retest reproducibility

[(18)F]SPA-RQ (substance P antagonist receptor quantifier) labels the substance P-preferring (NK(1)) receptor in human brain. A prior study showed that [(18)F]SPA-RQ brain uptake can be quantified with a reference tissue method and thereby avoid invasive blood sampling. The purposes of this study were to compare three different reference tissue methods and to assess test-retest reproducibility. Eight healthy subjects underwent two [(18)F]SPA-RQ scans. We calculated the binding potential (BP), which is proportional to receptor density, from both regional volume of interest and voxel-wise data. We compared three reference tissue methods: simplified reference tissue model, multilinear reference tissue model (MRTM), and its two-parameter version (MRTM2). The three methods generated equivalent values of regional BP, but MRTM2 was the most resistant to noise. Temporally stable values of BP were obtained with 240 min of imaging data. MRTM2 had excellent test-retest reproducibility, with high reliability (intraclass correlation > 0.9) and low variability (< 10%). In addition to regional volume of interest analysis, we also created parametric images of BP, variability, and reliability based on voxel-wise time-activity data. The reproducibility of parametric BP was also good, with variability < 20% and reliability > 0.7 in gray matter regions. In conclusion, a two-parameter reference tissue method (MRTM2) provided reproducible and reliable measurements of [(18)F]SPA-RQ brain uptake using 240 min of both regional and voxel-wise data.

Substance P in traumatic brain injury

Recent evidence has suggested that neuropeptides, and in particular substance P (SP), may play a critical role in the development of morphological injury and functional deficits following acute insults to the brain. Few studies, however, have examined the role of SP, and more generally, neurogenic inflammation, in the pathophysiology of traumatic brain injury and stroke. Those studies that have been reported suggest that SP is released following injury to the CNS and facilitates the increased permeability of the blood brain barrier, the development of vasogenic edema and the subsequent cell death and functional deficits that are associated with these events. Inhibition of the SP activity, either through inhibition of the neuropeptide release or the use of SP receptor antagonists, have consistently resulted in profound decreases in edema formation and marked improvements in functional outcome. The current review summarizes the role of SP in acute brain injury, focussing on its properties as a neurotransmitter and the potential for SP to adversely affect outcome.

TRPV1 activation results in disruption of the blood-brain barrier in the rat

We have examined the role of TRPV1 activation in disrupting the blood-brain barrier by measuring the permeability of single pial venular capillaries in anaesthetized rats. Capsaicin application to the brain surface resulted in increased permeability, maximal 2.1+/-0.12 x 10(-6) cm s(-1) (mean+/-s.e.m.) with log EC50 -4.5+/-0.10. Substance P methyl ester gave a similar response (maximal 2.0+/-0.07, n = 6, log EC50 -4.8+/-0.07), but the selective NK2 agonist, beta-Ala8-NKA(4-10) peptide, had no effect. Although CGRP decreased the permeability of venules (log EC50 10.3+/-0.11), its receptor antagonist CGRP(8-37) had no effect on the response to capsaicin. The TRPV1 antagonist capsazepine (1 mM) reduced the response to capsaicin (100 microM), from 1.78+/-0.15 to 0.63+/-0.10 (n = 4). The NK1 receptor antagonists GR205171 (100 microM) and SDZ NKT 376 (1 mM) also reduced the response to capsaicin (from 1.75+/-0.14 to 0.46+/-0.08; n = 6, and from 1.85+/-0.13 to 0.48+/-0.05; n = 5, respectively), indicating that capsaicin acts via TRPV1 in series with NK(1). Starch microspheres were used to produce transient focal ischaemia. Permeability was increased on reperfusion to a greater extent and more rapidly in vessels with diameter greater than 40 microm than those less than 15 microm. Capsazepine given intraperitoneally during ischaemia reduced the permeability increase in small venules from 5.9+/-0.3 to 2.4+/-0.1, and from 11.4+/-0.8 to 5.1+/-0.9 in large venules. In conclusion, the TRPV1 receptor is active in the brain microvasculature and has its permeability-increasing effect via substance P. It also plays a role in the immediate blood-brain barrier disruption following ischaemia-reperfusion.

Tachykinins and excitotoxicity in cerebellar granule cells

The tachykinins represent an important group of neuropeptides that are widely distributed both in the central and peripheral nervous system where they perform several functions connected with neuronal modulation, often in synergy with glutamate excitatory transmission. While a great deal of data is available on their distribution and many studies have been performed by molecular, biochemical, and immunohistochemical techniques, much less is known about their physiological role, in particular in the cerebellum. This review is an attempt to summarize the diverse evidence suggesting a role for tachykinins in cerebellar granule neurons.

Substance P receptor mediated maintenance of chronic inflammation in EAE

Substance P (SP) is a modulatory, pro-inflammatory neuropeptide. We investigated the role of the SP receptor, neurokinin-1 (NK-1), in EAE. Our data show that in the chronic phase, mice lacking NK-1 have improved mobility and decreased numbers of LFA-1 high CD4+ T cells and MOG-specific, IFN-gamma producing CD4+ T cells. SR140333, an NK-1 antagonist, administered alone during the chronic phase of EAE was not sufficient to ameliorate symptoms. These results indicate that SP, through NK-1, contributes to maintenance of CNS inflammation, and combining NK-1 antagonists with conventional anti-inflammatory treatments may enhance the success of treatments for diseases like multiple sclerosis.

Neuroprotection by endogenous and exogenous PACAP following stroke

We investigated the effects of PACAP treatment, and endogenous PACAP deficiency, on infarct volume, neurological function, and the cerebrocortical transcriptional response in a mouse model of stroke, middle cerebral artery occlusion (MCAO). PACAP-38 administered i.v. or i.c.v. 1 h after MCAO significantly reduced infarct volume, and ameliorated functional motor deficits measured 24 h later in wild-type mice. Infarct volumes and neurological deficits (walking faults) were both greater in PACAP-deficient than in wild-type mice, but treatment with PACAP reduced lesion volume and neurological deficits in PACAP-deficient mice to the same level of improvement as in wild-type mice. A 35,546-clone mouse cDNA microarray was used to investigate cortical transcriptional changes associated with cerebral ischemia in wild-type and PACAP-deficient mice, and with PACAP treatment after MCAO in wild-type mice. 229 known (named) transcripts were increased (228) or decreased (1) in abundance at least 50% following cerebral ischemia in wild-type mice. 49 transcripts were significantly up-regulated only at 1 h post-MCAO (acute response transcripts), 142 were up-regulated only at 24 h post-MCAO (delayed response transcripts) and 37 transcripts were up-regulated at both times (sustained response transcripts). More than half of these are transcripts not previously reported to be altered in ischemia. A larger percentage of genes up-regulated at 24 hr than at 1 hr required endogenous PACAP, suggesting a more prominent role for PACAP in later response to injury than in the initial response. This is consistent with a neuroprotective role for PACAP in late response to injury, i.e., even when administered 1 hr or more after MCAO. Putative injury effector transcripts regulated by PACAP include beta-actin, midline 2, and metallothionein 1. Potential neuroprotective transcripts include several demonstrated to be PACAP-regulated in other contexts. Prominent among these were transcripts encoding the PACAP-regulated gene Ier3, and the neuropeptides enkephalin, substance P (tachykinin 1), and neurotensin.

Increased substance P immunoreactivity and edema formation following reversible ischemic stroke

Previous results from our laboratory have shown that neurogenic inflammation is associated with edema formation after traumatic brain injury (TBI). This neurogenic inflammation was characterized by increased substance P (SP) immunoreactivity and could be attenuated with administration of SP antagonists with a resultant decrease in edema formation. Few studies have examined whether neurogenic inflammation, as identified by increased SP immunoreactivity, occurs after stroke and its potential role in edema formation. The present study examines SP immunoreactivity and edema formation following stroke. Experimental stroke was induced in halothane anaesthetized male Sprague-Dawley rats using a reversible thread model of middle cerebral artery occlusion. Increased SP immunoreactivity at 24 hours relative to the non-infarcted hemisphere was observed in perivascular, neuronal, and glial tissue, and within the penumbra of the infarcted hemisphere. It was not as apparent in the infarct core. This increased SP immunoreactivity was associated with edema formation. We conclude that neurogenic inflammation, as reflected by increased SP immunoreactivity, occurs following experimental stroke, and that this may be associated with edema formation. As such, inhibition of neurogenic inflammation may represent a novel therapeutic target for the treatment of edema following reversible, ischemic stroke.

Autocrine peptide mediators of cerebral endothelial cells and their role in the regulation of blood-brain barrier

A unique feature of cerebral endothelial cells (CECs) is the formation of the blood-brain barrier (BBB), which contributes to the stability of the brain microenvironment. CECs are capable of producing several substances mediating endothelium-dependent vasorelaxation or vasoconstriction, regulating BBB permeability, and participating in the regulation of cell-cell interactions during inflammatory and immunological processes. The chemical nature of these mediators produced by CECs ranges from gaseous anorganic molecules (e.g. nitric oxide) through lipid mediators (e.g. prostaglandins) to peptides. Peptide mediators are a large and diverse family of bioactive molecules which can elicit multiple effects on cerebral endothelial functions. In this review, we summarize current knowledge of peptide mediators produced by CECs, such as adrenomedullin, angiotensin, endothelin and several others and their role in the regulation of BBB functions.

AMPA receptors are modulated by tachykinins in rat cerebellum neurons

The peptides of the tachykinin family are widely distributed within the mammalian peripheral and central nervous systems and play a well-recognized role as neuromodulators, although their direct action on cerebellum granule cells have not yet been demonstrated. We have examined the effect of the best known members of the family, substance P (SP), neurokinin A (NKA), and neurokinin B (NKB) on alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors from rat cerebellar granule cells in culture to assess the ability of these peptides to regulate the glutamatergic input. Both NKA and NKB, but not SP, produce a significant enhancement of ionic current through AMPA receptors activated by the agonist kainate in 53.5 and 46% of patched neurons, respectively. This effect was not observable in the presence of MEN 10,627 and Trp(7)betaAla(8), NKA and NKB competitive antagonist receptors, respectively, indicating that the current modulations were mediated by the respective receptors. NKB also produces a significant enhancement of ionic current through the AMPA receptors activated directly by its agonist AMPA and cyclothiazide, an allosteric modulator that selectively suppresses desensitization of AMPA receptors. The presence of NK3 receptors was demonstrated in these neurons by RT-PCR amplification of total RNA extracted from cerebellar granule cells, using NK3-specific primer pairs. Immunocytochemistry experiments, using a specific polyclonal antibody directed against NK3, also confirmed the presence of NK3 receptors and their co-localization with the GLUR2 AMPA subunit in about 54% of cerebellar granule neurons. This study adds the tachykinins to the list of neuromodulators capable of exerting a excitatory action on cerebellar granule cells.

Expression of the mu-opioid receptor is induced in dentate gyrus granule cells after focal cerebrocortical ischaemia and stimulation of entorhinal afferents

Focal ischaemia in the cerebral cortex affects the inducibility of long-term potentiation (LTP) in the hippocampus. This impairment of hippocampal function may result from excessive activation of cortico-hippocampal afferents and subsequent perturbation of hippocampal LTP-relevant transmitter systems, which include opioids. Here, we tested if permanent focal ischaemia and electrical afferent stimulation influence the expression of the mu-opioid receptor (MOR) in the rat hippocampus. In the applied ischaemia model, the entire ipsilateral cortical hemisphere and hippocampus experienced sustained excitation as indicated by a long-lasting increase in the expression of arg 3.1/arc (ARG) mRNA, a marker for neuronal activity. Expression of MOR mRNA and protein was strongly increased in granule cells, which contain very low MOR levels under normal conditions, but not in gamma-aminobutyric acid (GABA)ergic neurons, which express the MOR constitutively. In the molecular layer, which contains the dendrites of granule cells, focal ischaemia caused a redistribution of MOR-like immunoreactivity. In contrast to the dentate gyrus, MOR expression was unaltered in the hippocampus proper and in non-infarcted cortical areas. Repetitive high-frequency stimulation of cortico-hippocampal perforant path afferents induced strong MOR mRNA expression throughout the granular layer. However, weak tetanization sufficient to induce LTP and ARG expression did not influence MOR mRNA levels. Taken together, we provide direct evidence for the induction of MOR expression in granule cells experiencing sustained excitation by cortical afferents. In activated, MOR-expressing granule cells, inhibitory opioids may counter-regulate glutamatergic excitation by the perforant path.

The temperature-sensitive ion channel TRPV2 is endogenously expressed and functional in the primary sensory cell line F-11

In sensory neurons heat is transduced by a subfamily of TRP channels sharing sequence homology with the capsaicin-sensitive vanilloid receptor subtype 1 (TRPV1), but differing in their thermal response thresholds. To identify a neuronal cell line endogenously expressing noxious heat-transducing ion channels, we examined F-11 cells, a hybridoma derived from rat dorsal root ganglia and mouse neuroblastoma. Using RT-PCR, transcripts homologous to TRPV2 and TRPV4, but not to TRPV1 or TRPV3, were found. We isolated a full-length cDNA of 2.4 kb coding for a 757-amino acid protein corresponding to mouse TRPV2, which was further characterized by immunocytochemistry and electrophysiology. Using the whole-cell patch-clamp technique, we observed a heat-evoked increase in outward and inward currents with a threshold of 51.6 +/- 0.2 degrees C. The current-voltage relationship stimulated by a temperature of 52 degrees C was characterized by an outward rectification with a reversal potential close to -10 mV. Heat-evoked currents could be inhibited by ruthenium red. There was no activation by stimulation with capsaicin or 2-aminoethoxydiphenyl borate. Our results indicate that F-11 cells express functional noxious heat-sensitive TRPV2 channels. Thus, we propose that F-11 cells represent a valuable in vitro model to characterize the properties of TRPV2 in a native neuronal environment.

An immunocytochemical study on specific amacrine cell subpopulations in the rat retina after ischemia

Transient retinal ischemia leads to the loss of neurons in the inner retina. In an accompanying paper [F. Dijk, S. Van Leeuwen, W. Kamphuis, Differential effects of ischemia/reperfusion on amacrine cell subtype-specific transcript levels in the rat retina, Brain Res., 1026 (2004) 194-204] we present the results of a study on the effects of experimentally induced retinal ischemia on transcript levels of genes expressed by distinct subpopulations of amacrine cells. In response to 60-min ischemia, three different patterns of changes in transcript levels were found, indicating a differential vulnerability of amacrine subtypes: (i) a gradual decrease of transcript level without recovery (parvalbumin; PV); (ii) a gradual decrease, with varying rates and degrees, followed by partial recovery after 72 h of reperfusion (choline acetyltransferase (ChAT), calretinin (CR) and glycine transporter (Glyt1)); (iii) no significant changes (substance P (SP)). In order to verify whether the degree of cell loss can be predicted from the quantified alterations in gene expression level, immunocytochemical stainings were carried out. A 60-min ischemic period was administered to the rat eye by raising the intraocular pressure, followed by a reperfusion period lasting between 2 h and 4 weeks. Cryosections were immunostained for Glyt1, PV, ChAT, CR, and SP. Double-labelling with apoptosis marker TUNEL was used to demonstrate cell type-specific apoptosis. Following ischemia, the numbers of detected PV-, Glyt1, ChAT-, and CR-immunopositive somata showed a substantial, but differential, reduction at 1-4 weeks after ischemia. The total amount of immunoreactivity present in the inner plexiform layer (IPL) also decreased. The extent of alterations derived from immunocytochemical staining was greater than was anticipated from the decrease of transcript levels. Only for SP, no significant decrease in number of cells or in the intensity of immunoreactivity in IPL was observed, which is in agreement with the absence of significant changes in transcript levels. In conclusion, retinal ischemia/reperfusion differentially affects amacrine cell populations. Although both protein and mRNA levels are reduced, transcript levels are less attenuated. Caution must be applied in the use of real-time quantitative PCR (qPCR) screening as a tool to assess the cellular pattern of neurodegeneration in the retina.

Peptidergic and non-peptidergic innervation and vasomotor responses of human lenticulostriate and posterior cerebral arteries

The aim of the present study was to compare in man the innervation pattern and the functional responses to neuronal messengers in medium sized lenticulostriate and branches of the posterior cerebral arteries (PCA). The majority of the nerve fibers found were sympathetic and displayed specific immunoreactivity for tyrosine hydroxylase (TH) and neuropeptide Y (NPY). Only few nerve fibers displayed vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP) and substance P (SP) immunoreactivity. In both arteries, the contractions induced by noradrenaline (NA), NPY and 5-hydroxytryptamine (5-HT) and the relaxant responses induced by acetylcholine (ACh), VIP and pituitary adenylate cyclase activating peptide-27 (PACAP) as well as CGRP and SP were compared in vitro. In conclusion, there was no major difference in innervation pattern or vasomotor sensitivity (pEC50 and pIC50 values) between the two vessels. However, the general pattern indicates stronger vasomotor responses (Emax and Imax) in the PCA branches as compared to the lenticulostriate arteries which may lend support for the clinical observation of a difference in stroke expression between the two vascular areas.

Neuropeptide release influences brain edema formation after diffuse traumatic brain injury

The mechanisms associated with edema formation after traumatic brain injury (TBI) have not been fully elucidated. In peripheral tissue injury, the neurogenic component of inflammation plays a significant role in increased vascular permeability and edema formation. However, few studies have examined the role of neuropeptide induced neurogenic inflammation following TBI. Adult male Sprague-Dawley rats were either left untreated, or pre-treated with capsaicin (125 mg/kg s.c.) or equal volume vehicle, and injured 14 days later using the 2-meter impact-acceleration model. Subgroups of animals were assessed for blood brain barrier (BBB) permeability (Evans Blue), brain edema (wet weight/dry weight) and functional outcome (Barnes maze and Rotarod) for up to 2 weeks post-trauma. Increased BBB permeability was present in untreated animals between 3 and 6 h after injury but not at later time-points. Edema was maximal at 5 h after trauma, declined and then significantly increased over the 5 days post-trauma. In contrast, capsaicin pre-treated, neuropeptide-depleted animals exhibited no significant increase in BBB permeability or edema compared to vehicle treated animals after injury. Notably, motor and cognitive impairments were significantly reduced in the capsaicin-pretreated animals. We conclude that neurogenic inflammation contributes to the development of edema and posttraumatic deficits after diffuse TBI.

Neurogenic inflammation is associated with development of edema and functional deficits following traumatic brain injury in rats

The present study has used capsaicin-induced neuropeptide depletion to examine the role of neurogenic inflammation in the development of edema and functional deficits following traumatic brain injury (TBI). Adult, male rats were treated with capsaicin (neuropeptide-depleted) or equal volume vehicle (controls) 14 days prior to induction of moderate/severe diffuse TBI. Injury in vehicle treated control animals resulted in acute (4-5 h) edema formation, which was confirmed as being vasogenic in origin by diffusion weighted magnetic resonance imaging and the presence of increased permeability of the blood-brain barrier (BBB) to Evans blue dye. There was also a significant decline in brain magnesium concentration, as assessed by phosphorus magnetic resonance spectroscopy, and the development of profound motor and cognitive deficits. In contrast, capsaicin pre-treatment resulted in a significant reduction in post-traumatic edema formation (p < 0.001), BBB permeability (p < 0.001), free magnesium decline (p < 0.01) and both motor and cognitive deficits (p < 0.001). We conclude that neurogenic inflammation may play an integral role in the development of edema and functional deficits following TBI, and that neuropeptides may be a novel target for development of interventional pharmacological strategies.

Rapid, transient, and dose-dependent expression of hsp70 messenger RNA in the rat brain after morphine treatment

Induction of Hsp70 in the brain has been reported after intake of drugs of abuse like amphetamine and lysergic acid diethylamide. In this investigation, gene expression of Hsp70 and other heat shock genes in the rat brain was studied in response to morphine. Twenty milligrams per kilogram morphine intraperitoneally resulted in a marked induction of Hsp70 messenger RNA (mRNA) expression in the frontal cortex with a maximum increase of 13.2-fold after 2 hours. A moderate increase of Hsp27 mRNA expression (6.7-fold) could be observed after 4 hours, whereas mRNA expression of Hsp90 and of the constitutive Hsc70 did not exceed a mean factor of 1.8-fold during the 24 hours interval. The increase in Hsp70 mRNA was dose dependent, showing a significant elevation after doses ranging from 10 to 50 mg/kg morphine. In situ hybridization revealed enhanced Hsp70 mRNA expression mainly in cortical areas, in the hippocampus, in the paraventricular and supraoptic nuclei of the hypothalamus, in the locus coeruleus, as well in the pineal body. The double in situ hybridization technique revealed increased Hsp70 mRNA expression mainly in VGLUT1-positive neurons and to a lesser extent in olig1-positive oligodendroglia. Immunohistochemistry revealed a marked increase of Hsp70 protein in neuronal cells and blood vessels after 12 hours. In contrast to animal experiments, morphine did not increase Hsp70 mRNA expression in vitro in micro-opioid receptor (MOR1)-expressing human embryonic kidney 293 cells, suggesting no direct MOR1-mediated cellular effect. To exclude a body temperature-related morphine effect on Hsp70 mRNA expression, the temperature was recorded. Five to 20 mg/kg resulted in hyperthermia (maximum 40.6 degrees), whereas a high dose (50 mg/kg) that produced the highest mRNA induction, showed a clear hypothermia (minimum 37.2 degrees C). These findings argue against the possibility that Hsp70 induction by morphine is caused by its effect on body temperature. It may be speculated that increased expression of Hsp70 after morphine application protects brain structures against potentially hazardous effects of opiates.