Microglia, the brain's resident immune cells and phagocytes, are emerging as critical regulators of developing synaptic circuits in the healthy brain after having long been thought to function primarily during central nervous system (CNS) injury or disease. Recent work indicates that microglia engulf synapses in the developing brain; however, how microglia know which synapses to target for removal remains a major open question. For my dissertation research, I studied microglia-mediated pruning in the retinogeniculate system and sought to identify the molecules regulating microglial engulfment of synaptic inputs. I discovered that "eat me" and "don't eat me" signals, immune molecules known for either promoting or inhibiting macrophage phagocytosis of cells or debris, localize to the dorsal lateral geniculate nucleus of the thalamus (dLGN) and direct retinogeniculate refinement. We found that "eat me" signal C3 and its microglial receptor, CR3, are required for normal engulfment, and that loss of either of these molecules leads to a reduction in phagocytosis and sustained deficits in refinement. These data suggest that microglia-mediated pruning may be analogous to the removal of non-self material by phagocytes in the immune system. To test this hypothesis, I examined whether protective signals are required to prevent excess microglial engulfment, as they prevent phagocytosis of self cells in the immune system. I found that protective "don't eat me" signal CD47 is required to prevent excess microglial engulfment and retinogeniculate pruning during development. Moreover, another "don't eat me signal", CD200, also prevents overpruning. Together, these findings indicate that immune molecules instruct microglia as to which synapses to engulf and present a model in which a balance of stimulatory and inhibitory cues is necessary to guide remodeling of immature synaptic circuits. These data shed new light on mechanisms regulating synaptic refinement and microglial function in the healthy, developing CNS, and may have implications for disorders characterized by immune dysregulation and circuit disconnectivity, such as autism spectrum disorder (ASD) and schizophrenia.

Focused ultrasound (FUS) can temporarily increase blood-brain barrier (BBB) permeability and locally deliver therapeutic agents to the brain. To date, applications of FUS for treatment of Alzheimer’s disease (AD) have not been explored. Here, I propose that FUS can facilitate a rapid reduction in amyloid-β peptide (Aβ) pathology in a mouse model of AD. Firstly, FUS was used to enhance delivery of an antibody directed against Aβ, which aggregates and forms extracellular plaques. FUS mediated the delivery of antibodies to the targeted right cortex by 4 hours post-treatment and antibodies remained bound to Aβ plaques for 4 days. At 4 days post-treatment, stereological quantification of plaque burden demonstrated a significant reduction of 23%. Secondly, FUS treatment alone resulted in a significant reduction in plaque load (13%). I then investigated effects of FUS that may contribute to Aβ plaque reduction, specifically the delivery of endogenous antibodies to the brain and, activation of microglia and astrocytes. Endogenous immunoglobulin was found bound to plaques within the treated cortex at 4 days post-FUS. Western blot analysis confirmed that immunoglobulin levels were increased significantly. Further, FUS led to a time-dependent increase in glial response. The expression of ionized calcium-binding adaptor molecule 1, a marker of phagocytic microglia, was increased at 4 hours and 4 days, and it was resolved by 15 days. Astrocytes had a slightly delayed response, with an increase in the expression of glial fibrillary acidic protein at 4 days, which declined by 15 days. After 4 days, microglia and astrocytes had significantly greater volumes and surface areas, signifying enhanced activation in the FUS-treated cortex, without an apparent increase in cell count. Co-localization of Aβ within activated glia revealed a significant increase in Aβ internalization following FUS. In conclusion, it was demonstrated that the delivery of exogenous antibodies by FUS, and FUS alone can lead to plaque reduction. Mechanisms by which FUS alone reduces plaque load may include entry of endogenous antibodies to the brain and the induction of a transient glial response. This work details acute effects of FUS that highlight the promise of this delivery method for AD treatment.

Focused ultrasound (FUS) can temporarily increase blood-brain barrier (BBB) permeability and locally deliver therapeutic agents to the brain. To date, applications of FUS for treatment of Alzheimer’s disease (AD) have not been explored. Here, I propose that FUS can facilitate a rapid reduction in amyloid-β peptide (Aβ) pathology in a mouse model of AD. Firstly, FUS was used to enhance delivery of an antibody directed against Aβ, which aggregates and forms extracellular plaques. FUS mediated the delivery of antibodies to the targeted right cortex by 4 hours post-treatment and antibodies remained bound to Aβ plaques for 4 days. At 4 days post-treatment, stereological quantification of plaque burden demonstrated a significant reduction of 23%. Secondly, FUS treatment alone resulted in a significant reduction in plaque load (13%). I then investigated effects of FUS that may contribute to Aβ plaque reduction, specifically the delivery of endogenous antibodies to the brain and, activation of microglia and astrocytes. Endogenous immunoglobulin was found bound to plaques within the treated cortex at 4 days post-FUS. Western blot analysis confirmed that immunoglobulin levels were increased significantly. Further, FUS led to a time-dependent increase in glial response. The expression of ionized calcium-binding adaptor molecule 1, a marker of phagocytic microglia, was increased at 4 hours and 4 days, and it was resolved by 15 days. Astrocytes had a slightly delayed response, with an increase in the expression of glial fibrillary acidic protein at 4 days, which declined by 15 days. After 4 days, microglia and astrocytes had significantly greater volumes and surface areas, signifying enhanced activation in the FUS-treated cortex, without an apparent increase in cell count. Co-localization of Aβ within activated glia revealed a significant increase in Aβ internalization following FUS. In conclusion, it was demonstrated that the delivery of exogenous antibodies by FUS, and FUS alone can lead to plaque reduction. Mechanisms by which FUS alone reduces plaque load may include entry of endogenous antibodies to the brain and the induction of a transient glial response. This work details acute effects of FUS that highlight the promise of this delivery method for AD treatment.

No description available.

G-CSF is routinely used to treat neutropenia/leukopenia or to increase hematopoietic stem cell generation in bone marrow donors. G-CSF and its receptor, G-CSFR, are produced by various cell types both in the peripheral circulation and within brain. As a consequence, exogenous administration of G-CSF results in a broad spectrum of effects involving hematopoietic, immune and central nervous systems. G-CSF administration in a mouse model of Alzheimer's disease (AD) has revealed both cognitive benefits and disease modifying effects: a) decreased Aβ plaque burden, b) increased microgliosis, c) increased neurogenesis and d) improved performance in radial arm water maze (RAWM). In clinical studies, G-CSF plasma levels were found to be lower in patients with early AD in comparison to healthy age matched controls. A course of G-CSF administration in humans is known to increase levels of circulating hematopoietic stem cells (CD34 cells), monocytes and neutrophils in patients with neutropenia and when administered to patients with AD, there is also a similar increase in absolute monocyte count, CD34 cells and total neutrophils. The extent to which the beneficial effects of G-CSF in AD depend on monocyte infiltration into CNS, compared to direct neurotrophic actions of G-CSF on the CNS, is not known. The overall goal of this study was to investigate and understand the effects of G-CSF in an AD mouse model, but more specifically to distinguish the actions of G-CSF that affect the peripheral monocyte population from the direct actions on CNS. The first approach was to examine in vitro effects of G-CSF within a monocytic cell line (THP-1) and a neuronal cell line (SH-SY5Y). The second approach was to study effects of G-CSF on infiltration of bone marrow-derived cells into the brain by utilizing a chimeric GFP+ APP/PS1 AD mouse model. The third approach was to assess the effects of G-CSF on hippocampal neurogenesis in both a wild-type and AD mouse model. Comparison of the monocytic and neuronal cell lines showed a) G-CSF interacts with its cognate receptor with different binding kinetics and with a greater affinity for the monocyte G-CSFR, b) the number of G-CSF receptors in neurons is greater than in monocytes, and c) the anti-apoptotic response in neurons occurs at lower concentrations of G-CSF than in monocytes. Various concentrations of G-CSF increased proliferation of both the monocytic and neuronal cell line in vitro. G-CSF did not improve migratory properties of the monocytic cell line, either adhesiveness or migration through a membrane. In vivo G-CSF treatment (250μg/kg s.c. qod for 2 ½ weeks) in both the AD chimeric and non-chimeric AD mice resulted in increased microgliosis and decreased amyloid plaque burden in the hippocampus. In the chimeric AD mice, G-CSF treatment did not increase infiltration of GFP+ bone marrow derived cells (BMDC) into brain parenchyma and did not increase adhesion to microvasculature. In the non-chimeric AD mice there was improvement of neurogenesis to non-transgenic levels after G-CSF treatment and an increase in synaptogenesis in the CA1 region of the hippocampus. The effects of G-CSF on the endogeneous microglial population are most likely responsible for the increase in microgliosis, as no significant increase of BMDC infiltration into the brain parenchyma was found in vivo. The enhanced proliferation and improved viability of the neuronal cell line after G-CSF treatment may explain the improvement in neurogenesis and significant increase in synaptogenesis seen in the AD mouse model. The actions of G-CSF on neural stem/progenitor cells to stimulate hippocampal neurogenesis and to enhance resident microglial capacity to decrease amyloid burden are the most likely mechanisms responsible for the behavioral improvement seen in the AD mouse model.

Background: Spinal cord injury (SCI) is heterogeneous in nature and can be complicated by inflammation and scarring in the subarachnoid space (arachnoiditis). The constellation of traumatic injury and arachnoiditis can lead to extensive intraparenchymal cysts or post-traumatic syringomyelia (PTS), due to alterations in fluid flow and pressure dynamics in the subarachnoid space. Hypothesis: Intrathecal injection of a bioengineered hydrogel containing hyaluronan (HA) will improve functional recovery following severe spinal cord injury associated with arachnoiditis. Methods: Acute to subacute pathophysiological events were characterized in non-injured sham rats, rats receiving a clip compression/contusion injury (SCI), rats receiving an intrathecal kaolin injection (Arachnoiditis) and in rats receiving SCI plus kaolin injection (PTS). Next, a HA containing hydrogel (HAMC) or artificial cerbralspinal fluid (aCSF) control was injected into the subarachnoid space 24 hours following PTS injury. To assess treatment efficacy, subacute pathophysiology was assessed as was long-term neurobehavioural and neuroanatomical recovery. Finally, in vitro studies examined the effect of HA on TLR4 activation using lipopolysaccharide in primary rat microglial cultures. Results: PTS animals exhibited a greater parenchymal injury response as compared to the sum of SCI alone or arachnoiditis alone. Injection of HAMC reduced the extent of scarring and inflammation in the subarachnoid space and improved neurobehavioural and neuroanatomical recovery relative to aCSF controls. These improvements were associated with reduced chondroitin sulfate proteoglycan and IL-1α expression and a trend towards and axonal preservation. In vitro studies demonstrated that HA is capable of reducing TLR4 mediated inflammation in microglia. Conclusions: Acute arachnoiditis potentiates the intensity of intraparenchymal inflammatory and scarring events following SCI. When HAMC was injected intrathecally following PTS injury, it mitigated some of the pernicious effects of arachnoiditis. Part of the therapeutic action of HAMC can be attributed to the ability of HA to reduce TLR4 mediated inflammation in microglia, possibly through an extracellular mechanism.

Teleost retinal ganglion cells can regenerate severed axons following injury, something their mammalian counterparts cannot do. In the teleost, successful regeneration has been attributed in part to microglial cell activities including the phagocytosis of myelin. Although the regulation of microglial phagocytosis has been studied in mammals, in the teleost it is largely unexamined. The present study was designed to identify mediators of microglial phagocytosis released by injured goldfish optic nerve during the course of regeneration. We found that microglial phagocytosis was significantly enhanced in the presence of a 7 day regenerating nerve or medium conditioned by the nerve (CM). When either nerve or CM was incubated with microglia along with an antibody against tumour necrosis factor alpha (TNFalpha), this effect was neutralized. The L929 cell cytotoxicity assay further demonstrated TNFalpha activity in the CM. However, Western blot analysis did not confirm this result. Therefore, further work is necessary to clearly establish the presence of TNFalpha.

Dissertation (Ph.D.)--University of South Florida, 2007. / Title from PDF of title page. Document formatted into pages; contains 142 pages. Includes vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Vita. "May 2007" Includes bibliographical references.

Dissertation (Ph.D.)--University of South Florida, 2007. / Includes vita. Includes bibliographical references (leaves 128-139). Also available online.