Oxytocin, Dopamine, and Opioid Interactions Underlying Pair Bonding: Highlighting a Potential Role for Microglia.

Pair bonds represent some of the strongest attachments we form as humans. These relationships positively modulate health and well-being. Conversely, the loss of a spouse is an emotionally painful event that leads to numerous deleterious physiological effects, including increased risk for cardiac dysfunction and mental illness. Much of our understanding of the neuroendocrine basis of pair bonding has come from studies of monogamous prairie voles (Microtus ochrogaster), laboratory-amenable rodents that, unlike laboratory mice and rats, form lifelong pair bonds. Specifically, research using prairie voles has delineated a role for multiple neuromodulatory and neuroendocrine systems in the formation and maintenance of pair bonds, including the oxytocinergic, dopaminergic, and opioidergic systems. However, while these studies have contributed to our understanding of selective attachment, few studies have examined how interactions among these 3 systems may be essential for expression of complex social behaviors, such as pair bonding. Therefore, in this review, we focus on how the social neuropeptide, oxytocin, interacts with classical reward system modulators, including dopamine and endogenous opioids, during bond formation and maintenance. We argue that an understanding of these interactions has important clinical implications and is required to understand the evolution and encoding of complex social behaviors more generally. Finally, we provide a brief consideration of future directions, including a discussion of the possible roles that glia, specifically microglia, may have in modulating social behavior by acting as a functional regulator of these 3 neuromodulatory systems.

A Novel Interaction of Translocator Protein 18 kDa (TSPO) with NADPH Oxidase in Microglia.

In the brain neuropil, translocator protein 18 kDa (TSPO) is a stress response protein that is upregulated in microglia and astrocytes in diverse central nervous system pathologies. TSPO is widely used as a biomarker of neuroinflammation in preclinical and clinical neuroimaging studies. However, there is a paucity of knowledge on the function(s) of TSPO in glial cells. In this study, we explored a putative interaction between TSPO and NADPH oxidase 2 (NOX2) in microglia. We found that TSPO associates with gp91phox and p22phox, the principal subunits of NOX2 in primary murine microglia. The association of TSPO with gp91phox and p22phox was observed using co-immunoprecipitation, confocal immunofluorescence imaging, and proximity ligation assay. We found that besides gp91phox and p22phox, voltage-dependent anion channel (VDAC) also co-immunoprecipitated with TSPO consistent with previous reports. When we compared lipopolysaccharide (LPS) stimulated microglia to vehicle control, we found that a lower amount of gp91phox and p22phox protein co-immunoprecipitated with TSPO suggesting a disruption of the TSPO-NOX2 subunits association. TSPO immuno-gold electron microscopy confirmed that TSPO is present in the outer mitochondrial membrane but it is also found in the endoplasmic reticulum (ER), mitochondria-associated ER membrane (MAM), and in the plasma membrane. TSPO localization at the MAM may represent a subcellular site where TSPO interacts with gp91phox and p22phox since the MAM is a point of communication between outer mitochondria membrane proteins (TSPO) and ER proteins (gp91phox and p22phox) where they mature and form the cytochrome b558 (Cytb558) heterodimer. We also found that an acute burst of reactive oxygen species (ROS) increased TSPO levels on the surface of microglia and this effect was abrogated by a ROS scavenger. These results suggest that ROS production may alter the subcellular distribution of TSPO. Collectively, our findings suggest that in microglia, TSPO is associated with the major NOX2 subunits gp91phox and p22phox. We hypothesize that this interaction may regulate Cytb558 formation and modulate NOX2 levels, ROS production, and redox homeostasis in microglia.

From the Cover: 7,8-Dihydroxyflavone Rescues Lead-Induced Impairment of Vesicular Release: A Novel Therapeutic Approach for Lead Intoxicated Children.

Childhood lead (Pb2+) intoxication is a public health problem of global proportion. Lead exposure during development produces multiple effects on the central nervous system including impaired synapse formation, altered synaptic plasticity, and learning deficits. In primary hippocampal neurons in culture and hippocampal slices, Pb2+ exposure inhibits vesicular release and reduces the number of fast-releasing sites, an effect associated with Pb2+ inhibition of NMDA receptor-mediated trans-synaptic Brain-Derived Neurotrophic Factor (BDNF) signaling. The objective of this study was to determine if activation of TrkB, the cognate receptor for BDNF, would rescue Pb2+-induced impairments of vesicular release. Rats were chronically exposed to Pb2+ prenatally and postnatally until 50 days of age. This chronic Pb2+ exposure paradigm enhanced paired-pulse facilitation of synaptic potentials in Schaffer collateral-CA1 synapses in the hippocampus, a phenomenon indicative of reduced vesicular release probability. Decreased vesicular release probability was confirmed by both mean-variance analysis and direct 2-photon imaging of vesicular release from hippocampal slices of rats exposed to Pb2+in vivo. We also found a Pb2+-induced impairment of calcium influx in Schaffer collateral-CA1 synaptic terminals. Intraperitoneal injections of Pb2+ rats with the TrkB receptor agonist 7,8-dihydroxyflavone (5 mg/kg) for 14-15 days starting at postnatal day 35, reversed all Pb2+-induced impairments of presynaptic transmitter release at Schaffer collateral-CA1 synapses. This study demonstrates for the first time that in vivo pharmacological activation of TrkB receptors by small molecules such as 7,8-dihydroxyflavone can reverse long-term effects of chronic Pb2+ exposure on presynaptic terminals, pointing to TrkB receptor activation as a promising therapeutic intervention in Pb2+-intoxicated children.

TSPO Finds NOX2 in Microglia for Redox Homeostasis.

During the past decade, translocator protein 18 kDa (TSPO), previously named peripheral benzodiazepine receptor, has gained a great deal of attention based on its use as a clinical biomarker of neuroinflammation with therapeutic potential. However, there is a paucity of knowledge on the function(s) of TSPO in glial cells. Here, we identify a novel function of TSPO in microglia that is not associated with steroidogenesis. We propose that a TSPO interaction with NADPH oxidase (NOX2) links the generation of reactive oxygen species (ROS) to the induction of an antioxidant response to maintain redox homeostasis. This line of investigation may provide a greater understanding of TSPO glial cell biology, and the knowledge gained may prove beneficial in devising therapeutic strategies.

TSPO in a murine model of Sandhoff disease: presymptomatic marker of neurodegeneration and disease pathophysiology.

Translocator protein (18 kDa), formerly known as the peripheral benzodiazepine receptor (PBR), has been extensively used as a biomarker of active brain disease and neuroinflammation. TSPO expression increases dramatically in glial cells, particularly in microglia and astrocytes, as a result of brain injury, and this phenomenon is a component of the hallmark response of the brain to injury. In this study, we used a mouse model of Sandhoff disease (SD) to assess the longitudinal expression of TSPO as a function of disease progression and its relationship to behavioral and neuropathological endpoints. Focusing on the presymptomatic period of the disease, we used ex vivo [(3)H]DPA-713 quantitative autoradiography and in vivo [(125)I]IodoDPA-713 small animal SPECT imaging to show that brain TSPO levels markedly increase prior to physical and behavioral manifestation of disease. We further show that TSPO upregulation coincides with early neuronal GM2 ganglioside aggregation and is associated with ongoing neurodegeneration and activation of both microglia and astrocytes. In brain regions with increased TSPO levels, there is a differential pattern of glial cell activation with astrocytes being activated earlier than microglia during the progression of disease. Immunofluorescent confocal imaging confirmed that TSPO colocalizes with both microglia and astrocyte markers, but the glial source of the TSPO response differs by brain region and age in SD mice. Notably, TSPO colocalization with the astrocyte marker GFAP was greater than with the microglia marker, Mac-1. Taken together, our findings have significant implications for understanding TSPO glial cell biology and for detecting neurodegeneration prior to clinical expression of disease.

Novel BAC Mouse Model of Huntington's Disease with 225 CAG Repeats Exhibits an Early Widespread and Stable Degenerative Phenotype.

BACKGROUND: Unusually large CAG repeat expansions (>60) in exon one of Huntingtin (HTT) are invariably associated with a juvenile-onset form of Huntington's disease (HD), characterized by a more extensive and rapidly progressing neuropathology than the more prevalent adult-onset form. However, existing mouse models of HD that express the full-length Htt gene with CAG repeat lengths associated with juvenile HD (ranging between ~75 to ~150 repeats in published models) exhibit selective neurodegenerative phenotypes more consistent with adult-onset HD. Objective: To determine if a very large CAG repeat (>200) in full-length Htt elicits neurodegenerative phenotypes consistent with juvenile HD. METHODS: Using a …bacterial artificial chromosome (BAC) system, we generated mice expressing full-length mouse Htt with ~225 CAG repeats under control of the mouse Htt promoter. Mice were characterized using behavioral, neuropathological, biochemical and brain imaging methods. RESULTS: BAC-225Q mice exhibit phenotypes consistent with a subset of features seen in juvenile-onset HD: very early motor behavior abnormalities, reduced body weight, widespread and progressive increase in Htt aggregates, gliosis, and neurodegeneration. Early striatal pathology was observed, including reactive gliosis and loss of dopamine receptors, prior to detectable volume loss. HD-related blood markers of impaired energy metabolism and systemic inflammation were also increased. Aside from an age-dependent progression of diffuse nuclear aggregates at 6 months of age to abundant neuropil aggregates at 12 months of age, other pathological and motor phenotypes showed little to no progression. CONCLUSIONS: The HD phenotypes present in animals 3 to 12 months of age make the BAC-225Q mice a unique and stable model of full-length mutant Htt associated phenotypes, including body weight loss, behavioral impairment and HD-like neurodegenerative phenotypes characteristic of juvenile-onset HD and/or late-stage adult-onset HD.

Impact of decision aids in a sustained implementation at a breast care center.

OBJECTIVE: We examined the reach and impact of five decision aids (DAs) routinely distributed to breast cancer patients as part of a shared decision making demonstration project. METHODS: From 2005 to 2008, we surveyed patients' change in knowledge and decisional conflict (DC) before and after their review of DAs. Using bivariate tests, we identified significant predictors of change in knowledge or decisional conflict and entered significant predictors into a multivariate regression model. RESULTS: We distributed 1553 DAs to 1098 patients and received 549 completed surveys. The DAs were associated with increased knowledge and decreased DC. For knowledge, significant predictors of above-average change included: lower baseline knowledge and viewing the surgery decision aid. For decisional conflict, significant predictors of above-average change included: higher decisional conflict; viewing any of the early-stage cancer DAs; and Hispanic ethnicity. CONCLUSIONS: DAs used in routine care were associated with significant knowledge gains and reductions in decisional conflict. Some subsets of patients (those reporting low baseline knowledge, high DC, or Hispanic ethnicity) may benefit more than others. PRACTICE IMPLICATIONS: Breast cancer patients benefit overall from routine distribution of DAs. Our exploratory findings may be useful in generating hypotheses to identify target populations who would most benefit from reviewing DAs.

Expanding the reach of decision and communication aids in a breast care center: a quality improvement study.

OBJECTIVE: One academically based breast cancer clinic implements decision and communication aids as part of routine clinical care. This quality improvement study aimed to expand reach of these supportive materials and services with budget-neutral program changes. METHODS: We used program theory and continuous quality improvement to design changes to our program. We calculated reach as the number of new patient visits for which we administered decision and communication aids. We compared reach before and after the program changes. RESULTS: Program changes included: reassigning program outreach tasks from over-committed to under-utilized personnel; deploying personnel in floating rather than fixed schedules; and creating a waitlist so service delivery was dynamically reallocated from overbooked to underbooked personnel. Before these changes, we reached 208 visitors with decision aids, and 142 visitors with communication aids. Changes were associated with expanded reach, culminating in program year 2008 with the delivery of 936 decision aids and 285 communication aids. CONCLUSIONS: We observed over a fourfold increase in decision aid reach and a twofold increase in communication aid reach. We attribute increases to recent program changes. PRACTICE IMPLICATIONS: This study illustrates how program theory and quality improvement methods can contribute to expanded reach of decision and communication aids.

Implementing decision and communication aids to facilitate patient-centered care in breast cancer: a case study.

OBJECTIVE: Decision Services (DS) provide support for breast cancer patients at the University of California, San Francisco to help ensure patient-centered care. METHODS: We examined a case study to explore whether our program practices matched our program theory, and what the patient in the case thought was effective and ineffective about our decision support interventions. RESULTS: The patient relied on a decision aid to educate her husband about her condition; felt that her question list contributed to a productive and efficient consultation with her oncologist; credited an audio-recording with helping her remember to follow-up with a genetic counselor; and reviewed the consultation summary 30 days into treatment in order to reflect on her decision. The patient rated the interventions highly on surveys, and experienced desirable reductions in decisional conflict, and improvements in knowledge. However, the question-prompting intervention was associated with a small decrease in self-efficacy, and the patient criticized the decision aid for omitting mention of a prognostic test. CONCLUSION: This case illustrates how decision support interventions can be deployed to promote patient-centered care. PRACTICE IMPLICATIONS: Breast care centers should consider distributing decision aids and assisting patients in listing questions, recording consultations, and obtaining written consultation summaries.

Monitoring the implementation of Consultation Planning, Recording, and Summarizing in a breast care center.

OBJECTIVE: We implemented and monitored a clinical service, Consultation Planning, Recording and Summarizing (CPRS), in which trained facilitators elicit patient questions for doctors, and then audio-record, and summarize the doctor-patient consultations. METHODS: We trained 8 schedulers to offer CPRS to breast cancer patients making treatment decisions, and trained 14 premedical interns to provide the service. We surveyed a convenience sample of patients regarding their self-efficacy and decisional conflict. We solicited feedback from physicians, schedulers, and CPRS staff on our implementation of CPRS. RESULTS: 278 patients used CPRS over the 22-month study period, an exploitation rate of 32% compared to our capacity. 37 patients responded to surveys, providing pilot data showing improvements in self-efficacy and decisional conflict. Physicians, schedulers, and premedical interns recommended changes in the program's locations; delivery; products; and screening, recruitment and scheduling processes. CONCLUSION: Our monitoring of this implementation found elements of success while surfacing recommendations for improvement. PRACTICE IMPLICATIONS: We made changes based on study findings. We moved Consultation Planning to conference rooms or telephone sessions; shortened the documents produced by CPRS staff; diverted slack resources to increase recruitment efforts; and obtained a waiver of consent in order to streamline and improve ongoing evaluation.