Introduction: Increasing evidence indicates that neurodegenerative diseases, including Alzheimer’s disease (AD), are a product of gene-by-environment interplay. The immune system is a major contributor mediating these interactions. Signaling between peripheral immune cells and those within the microvasculature and meninges of the central nervous system (CNS), at the blood-brain barrier, and in the gut likely plays an important role in AD. The cytokine tumor necrosis factor (TNF) is elevated in AD patients, regulates brain and gut barrier permeability, and is produced by central and peripheral immune cells. Our group previously reported that soluble TNF (sTNF) modulates cytokine and chemokine cascades that regulate peripheral immune cell traffic to the brain in young 5xFAD female mice, and in separate studies that a diet high in fat and sugar (HFHS) dysregulates signaling pathways that trigger sTNF-dependent immune and metabolic responses that can result in metabolic syndrome, which is a risk factor for AD. We hypothesized that sTNF is a key mediator of peripheral immune cell contributions to gene-by-environment interactions to AD-like pathology, metabolic dysfunction, and diet-induced gut dysbiosis. Methods: Female 5xFAD mice were subjected to HFHS diet for 2 months and then given XPro1595 to inhibit sTNF for the last month or saline vehicle. We quantified immune cell profiles by multi-color flow cytometry on cells isolated from brain and blood; metabolic, immune, and inflammatory mRNA and protein marker biochemical and immunhistological analyses, gut microbiome, and electrophysiology in brain slices were also performed. Results: Here, we show that selective inhibition of sTNF signaling via the biologic XPro1595 modulates the effects of an HFHS diet in 5xFAD mice on peripheral and central immune profiles including CNS-associated CD8+ T cells, the composition of gut microbiota, and long-term potentiation deficits. Discussion: Obesogenic diet induces immune and neuronal dysfunction in 5xFAD mice and sTNF inhibition mitigates its effects. A clinical trial in subjects at risk for AD due to genetic predisposition and underlying inflammation associated with peripheral inflammatory co-morbidities will be needed to investigate the extent to which these findings translate to the clinic.

Stroke is a multiphasic process involving a direct ischemic brain injury which is then exacerbated by the influx of immune cells into the brain tissue. Activation of brain endothelial cells leads to the expression of adhesion molecules such vascular cell adhesion molecule 1 (VCAM-1) on endothelial cells, further increasing leukocyte recruitment. Polymerase δ-interacting protein 2 (Poldip2) promotes brain vascular inflammation and leukocyte recruitment via unknown mechanisms. This study aimed to define the role of Poldip2 in mediating vascular inflammation and leukocyte recruitment following cerebral ischemia. Cerebral ischemia was induced in Poldip2+/+ and Poldip2+/− mice and brains were isolated and processed for flow cytometry or RT-PCR. Cultured rat brain microvascular endothelial cells were used to investigate the effect of Poldip2 depletion on focal adhesion kinase (FAK)-mediated VCAM-1 induction. Poldip2 depletion in vivo attenuated the infiltration of myeloid cells, inflammatory monocytes/macrophages and decreased the induction of adhesion molecules. Focusing on VCAM-1, we demonstrated mechanistically that FAK activation was a critical intermediary in Poldip2-mediated VCAM-1 induction. In conclusion, Poldip2 is an important mediator of endothelial dysfunction and leukocyte recruitment. Thus, Poldip2 could be a therapeutic target to improve morbidity following ischemic stroke.

Degeneration of locus ceruleus (LC) neurons and dysregulation of noradrenergic signaling are ubiquitous features of Parkinson's disease (PD). The LC is among the first brain regions affected by α-synuclein (asyn) pathology, yet how asyn affects these neurons remains unclear. LC-derived norepinephrine (NE) can stimulate neuroprotective mechanisms and modulate immune cells, while dysregulation of NE neurotransmission may exacerbate disease progression, particularly nonmotor symptoms, and contribute to the chronic neuroinflammation associated with PD pathology. Although transgenic mice overexpressing asyn have previously been developed, transgene expression is usually driven by pan-neuronal promoters and thus has not been selectively targeted to LC neurons. Here we report a novel transgenic mouse expressing human wild-type asyn under control of the noradrenergic-specific dopamine β-hydroxylase promoter (DBH-hSNCA). These mice developed oligomeric and conformation-specific asyn in LC neurons, alterations in hippocampal and LC microglial abundance, upregulated GFAP expression, degeneration of LC fibers, decreased striatal DA metabolism, and age-dependent behaviors reminiscent of nonmotor symptoms of PD that were rescued by adrenergic receptor antagonists. These mice provide novel insights into how asyn pathology affects LC neurons and how central noradrenergic dysfunction may contribute to early PD pathophysiology.SIGNIFICANCE STATEMENT ɑ-Synuclein (asyn) pathology and loss of neurons in the locus ceruleus (LC) are two of the most ubiquitous neuropathologic features of Parkinson's disease (PD). Dysregulated norepinephrine (NE) neurotransmission is associated with the nonmotor symptoms of PD, including sleep disturbances, emotional changes such as anxiety and depression, and cognitive decline. Importantly, the loss of central NE may contribute to the chronic inflammation in, and progression of, PD. We have generated a novel transgenic mouse expressing human asyn in LC neurons to investigate how increased asyn expression affects the function of the central noradrenergic transmission and associated behaviors. We report cytotoxic effects of oligomeric and conformation-specific asyn, astrogliosis, LC fiber degeneration, disruptions in striatal dopamine metabolism, and age-dependent alterations in nonmotor behaviors without inclusions.

Degeneration of locus coeruleus (LC) neurons and dysregulation of noradrenergic signaling are ubiquitous features of Parkinson’s disease (PD). The LC is among the first brain regions affected by α-synuclein (asyn) pathology, yet how asyn affects these neurons remains unclear. LC-derived norepinephrine (NE) can stimulate neuroprotective mechanisms and modulate immune cells, while dysregulation of NE neurotransmission may exacerbate disease progression, particularly non-motor symptoms, and contribute to the chronic neuroinflammation associated with PD pathology. Although transgenic mice overexpressing asyn have previously been developed, transgene expression is usually driven by pan-neuronal promoters and thus has not been selectively targeted to LC neurons. Here we report a novel transgenic mouse expressing human wild-type asyn under control of the noradrenergic-specific dopamine β-hydroxylase promoter. These mice developed oligomeric and conformation-specific asyn in LC neurons, alterations in hippocampal and LC microglial abundance, upregulated GFAP expression, degeneration of LC fibers, decreased striatal dopamine (DA) metabolism, and age-dependent behaviors reminiscent of non-motor symptoms of PD that were rescued by adrenergic receptor antagonists. These mice provide novel insights into how asyn pathology affects LC neurons and how central noradrenergic dysfunction may contribute to early PD pathophysiology. Significance statement α-synuclein (asyn) pathology and loss of neurons in the locus coeruleus (LC) are two of the most ubiquitous neuropathologic features of Parkinson’s disease (PD). Dysregulated NE neurotransmission is associated with the non-motor symptoms of PD including sleep disturbances, emotional changes such as anxiety and depression, and cognitive decline. Importantly, loss of central NE may contribute to the chronic inflammation in, and progression of, PD. We have generated a novel transgenic mouse expressing human asyn in LC neurons to investigate how increased asyn expression affects the function of the central noradrenergic transmission and associated behaviors. We report cytotoxic effects of oligomeric and conformation-specific asyn, astrogliosis, LC fiber degeneration, disruptions in striatal dopamine metabolism, and age-dependent alterations in non-motor behaviors without inclusions. ### Competing Interest Statement The authors have declared no competing interest.

AbstractBackgroundSporadic Alzheimer’s disease (AD) is a product of complex gene‐environment (GxE) interactions. Central‐peripheral immune cell crosstalk and traffic across the blood‐brain barrier (BBB) have been implicated in AD pathophysiology by recent studies that demonstrate a T‐cell signature in AD brain, gut dysbiosis in AD patients, and a significant epidemiological association between metabolic syndrome, obesity, and type‐2 diabetes with increased incidence of AD. Soluble tumor necrosis factor (sTNF), a known regulator of BBB and gut‐epithelial barrier permeability in chronic systemic inflammatory diseases that is increased in AD patient blood, was investigated as a regulator of immune cell traffic and AD‐like pathology in a mouse model of amyloid pathology subjected to an obesogenic diet.MethodTo investigate the effects of chronic peripheral inflammation on neuroinflammation and AD‐associated pathology, 2‐month old female 5xFAD (Tg) or non‐Tg mice were fed a high‐fat high‐carbohydrate diet (HFHC) or a balanced control diet (CD) for 8 weeks. After 4 weeks of diet, BBB‐permeant XPro®1595 was given subcutaneously every third day to selectively inhibit sTNF signaling. Neuroimmunological, histological, biochemical, genomic, and transcriptomic analyses were used to analyze effects on blood and brain immune populations, BBB permeability, inflammatory gene and protein expression, and gut microbiome.ResultHFHC‐fed Tg mice showed decreased T cell numbers in the blood and increased Ly6C+ T cells in the brain as compared to Tg mice fed CD or non‐Tg HFHC‐fed mice. Tg mice fed HFHC diet displayed increased hippocampal TNF and ZO‐1 mRNA, modestly increased Aβ burden, and marked increases of Iba1+ cells. Analysis of gut microbiota revealed significant beta diversity genotype‐ and diet‐dependent differences between Tg and non‐Tg mice, synergy in GxE interactions, and the ability of XPro®1595 to reverse many of these features.ConclusionTogether, these data suggest that an obesogenic diet enhances BBB permeability, disrupts innate and adaptive immune cell populations in the blood, promotes gut dysbiosis, and enhanced traffic of immune cells to the CNS through sTNF‐dependent mechanisms. Clinical trials in patients with MCI/early AD are underway to investigate the ability of a weekly dose of XPro1595 to reduce underlying inflammation without immunosuppression via selective targeting of sTNF.

Over 5 million people are estimated to have Alzheimer's disease (AD) in the United States; this number is expected to triple by 2050. Epidemiological studies indicate that modifiable risk factors characterized by elevated peripheral inflammation such as hypertension, and metabolic syndrome are linked to development of neurodegenerative disease, including AD, and controlling blood pressure (BP) protects against AD. Importantly, African Americans (AA) are disproportionately affected by both vascular risk factors and AD than whites. Using multiplexed immunoassays and deep-immunophenotyping by flow cytometry, here we tested the hypothesis that inflammation is associated with degree of CSF tau and Aβ accumulation in a cohort of middle- aged (45-65 yrs), cognitively normal individuals at high risk for AD based on race, AD parental history and an overrepresentation of the ApoE4 allele. AA individuals had lower CSF total tau, and phospho-tau as compared to whites. We regressed CSF Aβ and tau protein levels on plasma and CSF inflammatory factors after adjusting for appropriate confounders (Aβ42 and the 42:40 ratio: age, sex, AA, systolic, and ApoE4; phospho-tau and total tau: age, sex, AA, and systolic BP). Phospho-tau negatively associated with plasma CRP. Experiments are ongoing to immunophenotype CSF and blood via flow cytometry. This investigation will aid in understanding the relationship and role of central and peripheral inflammation in individuals at high risk for Alzheimer's disease.

Each year, over 50 million Americans suffer from persistent pain, including debilitating headaches, joint pain, and severe back pain. Although morphine is amongst the most effective analgesics available for the management of severe pain, prolonged morphine treatment results in decreased analgesic efficacy (i.e., tolerance). Despite significant headway in the field, the mechanisms underlying the development of morphine tolerance are not well understood. The midbrain ventrolateral periaqueductal gray (vlPAG) is a primary neural substrate for the analgesic effects of morphine, as well as for the development of morphine tolerance. A growing body of literature indicates that activated glia (i.e., microglia and astrocytes) facilitate pain transmission and oppose morphine analgesia, making these cells important potential targets in the treatment of chronic pain. Morphine affects glia by binding to the innate immune receptor toll-like receptor 4 (TLR4), leading to the release of proinflammatory cytokines and opposition of morphine analgesia. Despite the established role of the vlPAG as an integral locus for the development of morphine tolerance, most studies have examined the role of glia activation within the spinal cord. Additionally, the role of TLR4 in the development of tolerance has not been elucidated. This review attempts to summarize what is known regarding the role of vlPAG glia and TLR4 in the development of morphine tolerance. These data, together, provide information about the mechanism by which central nervous system glia regulate morphine tolerance, and identify a potential therapeutic target for the enhancement of analgesic efficacy in the clinical treatment of chronic pain.

Physical and psychosocial maltreatment experienced before the age of 18, termed early life adversity (ELA), affects an estimated 39% of the world's population, and has long-term detrimental health and psychological outcomes. While adult phenotypes vary following ELA, inflammation and altered stress responsivity are pervasive. Cytokines, most notably tumor necrosis factor (TNF), are elevated in adults with a history of ELA. While soluble TNF (solTNF) drives chronic inflammatory disease, transmembrane TNF facilitates innate immunity. Here, we test whether solTNF mediates the behavioral and molecular outcomes of adolescent psychological stress by administering a brain permeable, selective inhibitor of solTNF, XPro1595. Male and female C57BL/6 mice were exposed to an aggressive rat through a perforated translucent ball ('predatory stress') or transported to an empty room for 30 min for 30 days starting on postnatal day 34. Mice were given XPro1595 or vehicle treatment across the last 15 days. Social interaction, sucrose preference, and plasma inflammation were measured at 2 and 4 weeks, and open field behavior, adiposity, and neuroinflammation were measured at 4 weeks. Chronic adolescent stress resulted in increased peripheral inflammation and dysregulated neuroinflammation in adulthood in a sex-specific manner. Abnormal social and open field behavior, fat pad weight, and fecal boli deposition were noted after 30 days; solTNF antagonism ameliorated the effects of stress. Together, these data support our hypothesis, and suggest that targeting solTNF with XPro1595 may improve quality of life for individuals with a history of adolescent stress.

Over 5 million people are estimated to have Alzheimer's disease (AD) in the United States; this number is expected to triple by 2050. Epidemiological studies indicate that modifiable risk factors characterized by elevated peripheral inflammation such as hypertension and metabolic syndrome are linked to development of neurodegenerative disease, including AD, and controlling blood pressure (BP) protects against AD. Importantly, African Americans (AA) are disproportionately affected by both vascular risk factors and AD than whites. Using multiplexed immunoassays, deep-immunophenotyping by flow cytometry, and cognitive tests, here we tested the hypothesis that cognition negatively correlates with inflammation in a cohort of middle- aged (45-65 yrs), cognitively normal individuals at high risk for AD based on parental history and an overrepresentation of the ApoE4 allele. AA individuals had higher plasma and CSF CRP and plasma IL-6, and lower plasma IL-8 and CSF NGAL than whites. We regressed cognitive scores on plasma and CSF inflammatory factors after adjusting for appropriate confounders (age, sex, education, and ApoE4). MOCA score, which assesses global cognition, negatively associated with plasma NGAL and IL-10, and CSF IL-10, Buschke score, which assesses verbal memory, negatively associated with plasma IL-8, TNF and NGAL, and positively associated with CSF IFNγ. When controlling only for APOE4, verbal memory was positively associated with plasma NGAL and CSF IL-6 and negatively associated with plasma TNF and CSF IL-10 and IL-8. Executive function, as measured by TrailsB score positively associated with CSF IL-8 and TNF protein; when controlling only for APOE4, TrailsB score positively associated with CSF IL-8. Language, as measured by MINT score was positively associated with plasma TNF. Experiments are ongoing to immunophenotype CSF and blood via flow cytometry. This investigation will aid in understanding the relationship and role of central and peripheral inflammation on cognition in individuals at high risk for AD.

between individuals of the same neighborhood. Results:A limited activity space modifies the association between neighborhood socioeconomic status and dementia incidence. In people whose activity space was limited to their neighborhood (n1⁄4772, 11%), living in a deprived neighborhood was associated with a higher risk of dementia (3C deprivation score: T3 HR 1⁄4 1.45, 95% CI 1.01-2.06); conversely living in an advantaged neighborhood was associated with a lower risk (Table 1). These results were not evidenced for peoplewhose activity spacewas not limited.Conclusions:This study shows the role of activity space in health inequalities, in addition to highlighting the importance of the living environment on cognitive ageing. If confirmed in different populations, these findings would help to identify groups at risk, best target for prevention. 1. Letellier N et al. (2017). Sex-specific association between neighborhood characteristics and dementia: The Three-City cohort. Alzheimers Dement.

Peripheral immune cell signaling has been shown to play an important role in neuroinflammatory diseases, such as Alzheimer's disease (AD). Cytokine and chemokine mechanisms regulate peripheral immune cell trafficking to inflamed tissues, such as the brain. The cytokine, soluble Tumor Necrosis Factor (solTNF), has been shown to be elevated in AD patients. SolTNF regulates blood-brain barrier permeability, and is produced by central and peripheral immune cells. Therefore, we hypothesize that sTNF is a key mediator of peripheral immune cell contributions to AD-like pathology. Peripheral inflammation may accelerate neurodegeneration by increasing neuroinflammation, altering blood brain barrier integrity, and promoting peripheral immune cell trafficking to the CNS. Therefore, we aim to determine the effect of chronic high-fat high-carbohydrate (HFHC) diet-induced peripheral inflammation on neuroinflammation and neuronal health in a model of AD. The 5xFAD mouse model of AD was fed a high-fat high-carbohydrate (HFHC) or a control diet (CD) for 8 weeks. After 4 weeks of diet, XPro®1595, a BBB-permeant peptide, was used to selectively inhibit solTNF signaling. Tight junction proteins and central inflammatory gene expression were evaluated by qPCR. Immune cell populations in the brain were assessed using flow cytometry. 5xFAD mice fed a HFHC diet and treated with saline had increased TNF mRNA expression in the hippocampus. XPro®1595 eliminated this diet effect. Independent of genotype, mice given HFHC diet and saline had increased hippocampal ZO-1 gene expression compared to CD-fed mice given saline. XPro®1595 reversed this diet effect. HFHC diet treatment also impacted brain immune populations. 5xFAD mice had increased CD8+ T cell percentages in the brain when fed HFHC. CD8+ T cells were also increased in HFHC diet-fed Tg mice as compared with HFHC nonTg mice. An increase in Ly6C+ T cells was observed in HFHC diet-fed Tg mice versus CD fed mice, suggesting an increased migration of CD8+ (cytotoxic) T cells into the brain. Experiments are ongoing to assess additional effects of solTNF in AD pathogenesis. Diet-induced obesity alters immune cell populations and promotes BBB-associated alterations that may impact neuroinflammation and increase the risk for AD; targeting solTNF may be a therapeutic path forward.

Morphine remains one of the most widely prescribed opioids for alleviation of persistent and/or severe pain; however, multiple preclinical and clinical studies report that morphine is less efficacious in females compared to males. Morphine primarily binds to the mu opioid receptor, a prototypical G-protein coupled receptor densely localized in the midbrain periaqueductal gray. Anatomical and physiological studies conducted in the 1960s identified the periaqueductal gray, and its descending projections to the rostral ventromedial medulla and spinal cord, as an essential descending inhibitory circuit mediating opioid-based analgesia. Remarkably, the majority of studies published over the following 30 years were conducted in males with the implicit assumption that the anatomical and physiological characteristics of this descending inhibitory circuit were comparable in females; not surprisingly, this is not the case. Several factors have since been identified as contributing to the dimorphic effects of opioids, including sex differences in the neuroanatomical and neurophysiological characteristics of the descending inhibitory circuit and its modulation by gonadal steroids. Recent data also implicate sex differences in opioid metabolism and neuroimmune signaling as additional contributing factors. Here we cohesively present these lines of evidence demonstrating a neural basis for sex differences in opioid modulation of pain, with a focus on the PAG as a sexually dimorphic core of descending opioid-induced inhibition and argue for the development of sex-specific pain therapeutics.

Recent studies about the gut‐brain axis suggest that high fat high fructose (HFHF) consumption is associated with chronic peripheral inflammation due to disruption of gut flora. Some evidence suggests that chronic peripheral inflammation may increase blood‐brain barrier (BBB) permeability. This may lead to increase in neuroinflammation and development of neurodegenerative diseases. The current study aims to observe the relationship between HFHF diet and BBB trafficking. We hypothesize that peripheral inflammation induced by HFHF diet will increase BBB permeability allowing for increased peripheral monocyte trafficking to the brain. To test this hypothesis, a mouse with red fluorescent protein (RFP) driven by the chemokine receptor 2 (CCR2), was treated with HFHF or control diet (CD) for five weeks to induce chronic inflammation. CCR2 is expressed on peripheral monocytes and to a lesser degree on microglia in the brain. To differentiate between resident microglia and brain infiltrating peripheral monocytes, tissue sections were stained with CD169, a marker specific for peripheral monocytes. Brain sections from CCR2‐RFP mice were stained by immunofluorescence in the hippocampal areas of CA1, CA3, and the dentate gyrus as these areas are affected in the neurodegenerative Alzheimer's Disease. CD169 and CCR2 stained cells were quantified using mean intensity to determine the effects of diet on infiltrating peripheral monocytes. In CA3, CCR2 CD mice presented with significantly decreased CCR2 and CD169 mean intensity as compared with WT CD mice (p=0.048, p=0.03). This may be because the Tg only has one allele of CCR2, permitting less trafficking than WT mice, which have two alleles. In CA1, there was a main effect of diet such that Tg HFHF treated mice showed a significant decrease in CD169 mean intensity compared to Tg CD (p=0.02). The low number of animals, the old age of the animals, and the time treated with diet may have impacted our findings. The current data did not support our hypothesis that HFHF diet increases peripheral trafficking across the BBB. Future directions include repeating this experiment with more animals, and treating the animals with HFHF diet for a longer period.Support or Funding InformationWork was funded by the NIH NIA RO1 RF1AG051514 (MGT) and the APS IOSP Fellowship.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Efforts to identify fluid biomarkers of Parkinson’s disease (PD) have intensified in the last decade. As the role of inflammation in PD pathophysiology becomes increasingly recognized, investigators aim to define inflammatory signatures to help elucidate underlying mechanisms of disease pathogenesis and aid in identification of patients with inflammatory endophenotypes that could benefit from immunomodulatory interventions. However, discordant results in the literature and a lack of information regarding the stability of inflammatory factors over a 24-h period have hampered progress.

Obesity and hypertension contribute to increased risk for neurodegenerative diseases, including Alzheimer's disease (AD). Peripheral inflammation, induced by unhealthy diet influences brain function, increases blood brain barrier (BBB) permeability, and induces brain inflammation. However, the exact mechanism by which chronic peripheral inflammation impacts AD-like pathology is unknown. Elevated levels of TNF in the CSF and plasma have been reported in AD patients. TNF promotes brain inflammation, increased BBB permeability, and altered regulation of immune cell trafficking. Here we tested the hypothesis that soluble TNF mediates the effects of an obesogenic diet on AD-like pathology and peripheral immune cell traffic to the CNS. We fed 5xFAD (Tg) mice a diet high in fructose and fat (HFHF) or a control diet (CD) for 2 months to induce low grade-chronic peripheral inflammation. After one month, we inhibited peripheral and central soluble TNF signaling with the BBB-permeant peptide XPro1595, and assessed immune cell populations in the brain and blood via flow cytometry, inflammatory gene expression (qPCR), and microglia activation and amyloid (IHC) in AD-relevant brain regions. We found that diet impacts immune populations in the blood and brain. Within the blood Tg mice had increased frequency of CD11b+ monocytes; within this population Ly6Clo monocytes were increased, while MHCII+ monocytes were decreased. Four weeks of HFHF diet decreased the frequency of CD4+ T cells within the blood of Tg mice as compared to non-Tg CD mice. Following 8 weeks of HFHF diet, the frequency of CD45hiLy6ChiCD11b+ cells in the brain of Tg mice was reduced while the frequency of CD8+ T cells was increased as compared to non-Tg mice. Analysis of inflammation-related gene expression in the CNS is underway for correlation with changes in central and peripheral immunophenotypes. An additional cohort of mice is being treated with XPro1595 to investigate the hypothesis that inhibition of soluble TNF can mitigate diet-induced alterations in immune cell profiles centrally and peripherally and delay AD-like pathology. An obesogenic diet alters innate and adaptive immune cell populations in the blood and brain of 5xFAD mice and may promote neuroinflammation which may in turn accelerate AD-like pathology.

Although morphine remains the primary drug prescribed for alleviation of severe or persistent pain, both preclinical and clinical studies have shown that females require two to three times more morphine than males to produce comparable levels of analgesia. In addition to binding to the neuronal μ-opioid receptor, morphine binds to the innate immune receptor toll-like receptor 4 (TLR4) localized primarily on microglia. Morphine action at TLR4 initiates a neuroinflammatory response that directly opposes the analgesic effects of morphine. Here, we test the hypothesis that the attenuated response to morphine observed in females is the result of increased microglia activation in the periaqueductal gray (PAG), a central locus mediating the antinociceptive effects of morphine. We report that, whereas no overall sex differences in the density of microglia were noted within the PAG of male or female rats, microglia exhibited a more “activated” phenotype in females at baseline, with the degree of activation a significant predictor of morphine half-maximal antinociceptive dose (ED50) values. Priming microglia with LPS induced greater microglia activation in the PAG of females compared with males and was accompanied by increased transcription levels of IL-1β and a significant rightward shift in the morphine dose–response curve. Blockade of morphine binding to PAG TLR4 with (+)-naloxone potentiated morphine antinociception significantly in females such that no sex differences in ED50 were observed. These results demonstrate that PAG microglia are sexually dimorphic in both basal and LPS-induced activation and contribute to the sexually dimorphic effects of morphine in the rat. SIGNIFICANCE STATEMENT We demonstrate that periaqueductal gray (PAG) microglia contribute to the sexually dimorphic effects of morphine. Specifically, we report that increased activation of microglia in the PAG contributes to the attenuated response to morphine observed in females. Our data further implicate the innate immune receptor toll-like receptor 4 (TLR4) as an underlying mechanism mediating these effects and establish that TLR4 inhibition in the PAG of females reverses the sex differences in morphine responsiveness. These data suggest novel methods to improve current opioid-based pain management via inhibition of glial TLR4 and illustrate the necessity for sex-specific research and individualized treatment strategies for the management of pain in men and women.

CSF IFNγ and serum IL-8 positively correlated with UPDRS components at baseline in PD subjects. (PDF 563 kb)