IH-exposed Mice Research Articles

Chronic Intermittent Hypoxia during Sleep Causes Browning of Interscapular Adipose Tissue Accompanied by Local Insulin Resistance in Mice

Obstructive sleep apnea (OSA) is a highly prevalent condition, characterized by intermittent hypoxia (IH), sleep disruption, and altered autonomic nervous system function. OSA has been independently associated with dyslipidemia, insulin resistance, and metabolic syndrome. Brown adipose tissue (BAT) has been suggested as a modulator of systemic glucose tolerance through adaptive thermogenesis. Reductions in BAT mass have been associated with obesity and metabolic syndrome. No studies have systematically characterized the effects of chronic IH on BAT. Thus, we aimed to delineate IH effects on BAT and concomitant metabolic changes. C57BL/6J 8-week-old male mice were randomly assigned to IH during sleep (alternating 90 s cycles of 6.5% FIO2 followed by 21% FIO2) or normoxia (room air, RA) for 10 weeks. Mice were subjected to glucose tolerance testing and 18F-FDG PET-MRI towards the end of the exposures followed by BAT tissues analyses for morphological and global transcriptomic changes. Animals exposed to IH were glucose intolerant despite lower total body weight and adiposity. BAT tissues in IH-exposed mice demonstrated characteristic changes associated with "browning"-smaller lipids, increased vascularity, and a trend towards higher protein levels of UCP1. Conversely, mitochondrial DNA content and protein levels of respiratory chain complex III were reduced. Pro-inflammatory macrophages were more abundant in IH-exposed BAT. Transcriptomic analysis revealed increases in fatty acid oxidation and oxidative stress pathways in IH-exposed BAT, along with a reduction in pathways related to myogenesis, hypoxia, and IL-4 anti-inflammatory response. Functionally, IH-exposed BAT demonstrated reduced absorption of glucose on PET scans and reduced phosphorylation of AKT in response to insulin. Current studies provide initial evidence for the presence of a maladaptive response of interscapular BAT in response to chronic IH mimicking OSA, resulting in a paradoxical divergence, namely, BAT browning but tissue-specific and systemic insulin resistance. We postulate that oxidative stress, mitochondrial dysfunction, and inflammation may underlie these dichotomous outcomes in BAT.

Intermittent hypoxia mediated by TSP1 dependent on STAT3 induces cardiac fibroblast activation and cardiac fibrosis.

Intermittent hypoxia (IH) is the predominant pathophysiological disturbance in obstructive sleep apnea (OSA), known to be independently associated with cardiovascular diseases. However, the effect of IH on cardiac fibrosis and molecular events involved in this process are unclear. Here, we tested IH in angiotensin II (Ang II)-induced cardiac fibrosis and signaling linked to fibroblast activation. IH triggered cardiac fibrosis and aggravated Ang II-induced cardiac dysfunction in mice. Plasma thrombospondin-1 (TSP1) content was upregulated in both IH-exposed mice and OSA patients. Moreover, both in vivo and in vitro results showed IH-induced cardiac fibroblast activation and increased TSP1 expression in cardiac fibroblasts. Mechanistically, phosphorylation of STAT3 at Tyr705 mediated the IH-induced TSP1 expression and fibroblast activation. Finally, STAT3 inhibitor S3I-201 or AAV9 carrying a periostin promoter driving the expression of shRNA targeting Stat3 significantly attenuated the synergistic effects of IH and Ang II on cardiac fibrosis in mice. This work suggests a potential therapeutic strategy for OSA-related fibrotic heart disease.

The antioxidant α-lipoic acid attenuates intermittent hypoxia-related renal injury in a mouse model of sleep apnea.

Oxidative stress and inflammation are proposed to mediate kidney diseases that occur in patients with obstructive sleep apnea (OSA). We examined the hypothesis that α-lipoic acid (LA) prevents renal injury in a mouse model of sleep apnea. Twenty male mice received either intermittent hypoxia (IH) or intermittent air (IA) with or without a LA-enriched diet for 60 days. Plasma and urine samples were collected at the end of study, and kidneys were harvested for protein analysis. Animals in the IH + LA group had lower levels (p < 0.05) of plasma oxidative stress (8-isoprostane) and inflammation (TNF-α). Renal oxidative stress was also reduced in mice in the IH + LA (p < 0.05) compared with IH-exposed mice that were fed regular diet. Renal cellular apoptosis and tubular injury were reduced in the IH + LA group. Treatment with LA attenuated IH-induced glomerular hypertrophy and increased albuminuria. Treatment with LA prevents IH-induced renal injury in mice. LA may be a potential therapy for reducing renal dysfunction in patients with OSA. LA can also increase oxidative stress in healthy animals.

Low-Frequency Intermittent Hypoxia Suppresses Subcutaneous Adipogenesis and Induces Macrophage Polarization in Lean Mice.

BackgroundThe relationship between obstructive sleep apnoea (OSA) and metabolic disorders is complex and highly associated. The impairment of adipogenic capacity in pre-adipocytes may promote adipocyte hypertrophy and increase the risk of further metabolic dysfunction. We hypothesize that intermittent hypoxia (IH), as a pathophysiologic feature of OSA, may regulate adipogenesis by promoting macrophage polarization.MethodsMale C57BL/6N mice were exposed to either IH (240 seconds of 10% O2 followed by 120 seconds of 21% O2, i.e., 10 cycles/hour) or intermittent normoxia (IN) for 6 weeks. Stromal-vascular fractions derived from subcutaneous (SUB-SVF) and visceral (VIS-SVF) adipose tissues were cultured and differentiated. Conditioned media from cultured RAW 264.7 macrophages after air (Raw) or IH exposure (Raw-IH) were incubated with SUB-SVF during adipogenic differentiation.ResultsAdipogenic differentiation of SUB-SVF but not VIS-SVF from IH-exposed mice was significantly downregulated in comparison with that derived from IN-exposed mice. IH-exposed mice compared to IN-exposed mice showed induction of hypertrophic adipocytes and increased preferential infiltration of M1 macrophages in subcutaneous adipose tissue (SAT) compared to visceral adipose tissue. Complementary in vitro analysis demonstrated that Raw-IH media significantly enhanced inhibition of adipogenesis of SUB-SVF compared to Raw media, in agreement with corresponding gene expression levels of differentiation-associated markers and adipogenic transcription factors.ConclusionLow frequency IH exposure impaired adipogenesis of SAT in lean mice, and macrophage polarization may be a potential mechanism for the impaired adipogenesis.

Sleep-disordered breathing, circulating exosomes, and insulin sensitivity in adipocytes.

BackgroundSleep-disordered-breathing (SDB), which is characterized by chronic intermittent hypoxia (IH) and sleep fragmentation (SF), is a prevalent condition that promotes metabolic dysfunction, particularly among patients suffering from obstructive hypoventilation syndrome (OHS). Exosomes are generated ubiquitously, are readily present in the circulation, and their cargo may exert substantial functional cellular alterations in both physiological and pathological conditions. However, the effects of plasma exosomes on adipocyte metabolism in patients with OHS or in mice subjected to IH or SF mimicking SDB are unclear.MethodsExosomes from fasting morning plasma samples from obese adults with polysomnographically-confirmed OSA before and after 3 months of adherent CPAP therapy were assayed. In addition, C57BL/6 mice were randomly assigned to (1) sleep control (SC), (2) sleep fragmentation (SF), and (3) intermittent hypoxia (HI) for 6 weeks, and plasma exosomes were isolated. Equivalent exosome amounts were added to differentiated adipocytes in culture, after which insulin sensitivity was assessed using 0 nM and 5nM insulin-induced pAKT/AKT expression changes by western blotting.ResultsWhen plasma exosomes were co-cultured and internalized by human naïve adipocytes, significant reductions emerged in Akt phosphorylation responses to insulin when compared to exosomes obtained after 24 months of adherent CPAP treatment (n=24; p<0.001), while no such changes occur in untreated patients (n=8). In addition, OHS exosomes induced significant increases in adipocyte lipolysis that were attenuated after CPAP, but did not alter pre-adipocyte differentiation. Similarly, exosomes from SF- and IH-exposed mice induced attenuated p-AKT/total AKT responses to exogenous insulin and increased glycerol content in naïve murine adipocytes, without altering pre-adipocyte differentiation.ConclusionsUsing in vitro adipocyte-based functional reporter assays, alterations in plasma exosomal cargo occur in SDB, and appear to contribute to adipocyte metabolic dysfunction. Further exploration of exosomal miRNA signatures in either human subjects or animal models and their putative organ and cell targets appears warranted.

Intermittent hypoxia causes histological kidney damage and increases growth factor expression in a mouse model of obstructive sleep apnea.

Epidemiological studies demonstrate an association between obstructive sleep apnea (OSA) and accelerated loss of kidney function. It is unclear whether the decline in function is due to OSA per se or to other confounding factors such as obesity. In addition, the structural kidney abnormalities associated with OSA are unclear. The objective of this study was to determine whether intermittent hypoxia (IH), a key pathological feature of OSA, induces renal histopathological damage using a mouse model. Ten 8-week old wild-type male CB57BL/6 mice were randomly assigned to receive either IH or intermittent air (IA) for 60 days. After euthanasia, one kidney per animal was paraformaldehyde-fixed and then sectioned for histopathological and immunohistochemical analysis. Measurements of glomerular hypertrophy and mesangial matrix expansion were made in periodic acid–Schiff stained kidney sections, while glomerular transforming growth factor-β1 (TGF-β1), connective tissue growth factor (CTGF) and vascular endothelial growth factor-A (VEGF-A) proteins were semi-quantified by immunohistochemistry. The antigen-antibody reaction was detected by 3,3′-diaminobenzidine chromogen where the color intensity semi-quantified glomerular protein expression. To enhance the accuracy of protein semi-quantification, the percentage of only highly-positive staining was used for analysis. Levels of TGF-β, CTGF and VEGF-A proteins in the kidney cortex were further quantified by western blotting. Cellular apoptosis was also investigated by measuring cortical antiapoptotic B-cell lymphoma 2 (Bcl-2) and apoptotic Bcl-2-associated X (Bax) proteins by western blotting. Further investigation of cellular apoptosis was carried out by fluorometric terminal deoxynucleotidyl transferase (TdT) dUTP Nick-End Labeling (TUNEL) staining. Finally, the levels of serum creatinine and 24-hour urinary albumin were measured as a general index of renal function. Our results indicate that mice exposed to IH have an increased glomerular area (by 1.13 fold, p< 0.001) and expansion of mesangial matrix (by 1.8 fold, p< 0.01). Moreover, the glomerular expressions of TGF-β1, CTGF and VEGF-A proteins were 2.7, 2.2 and 3.8-fold higher in mice exposed to IH (p< 0.05 for all). Furthermore, western blotting protein analysis demonstrates that IH-exposed mice express higher levels of TGF-β1, CTGF and VEGF-A proteins by 1.9, 4.0 and 1.6-fold (p< 0.05 for all) respectively. Renal cellular apoptosis was greater in the IH group as shown by an increased cortical Bax/Bcl-2 protein ratio (p< 0.01) and higher fluorometric TUNEL staining (p< 0.001). Finally, 24-hr urinary albumin levels were higher in mice exposed to IH (43.4 μg vs 9.7 μg, p< 0.01), while there were no differences in serum creatinine levels between the two groups. We conclude that IH causes kidney injury that is accompanied by glomerular hypertrophy, mesangial matrix expansion, increased expression of glomerular growth factors and an increased cellular apoptosis.

Role of Cyclooxygenase-2 on Intermittent Hypoxia-Induced Lung Tumor Malignancy in a Mouse Model of Sleep Apnea

An adverse role for obstructive sleep apnea (OSA) in cancer epidemiology and outcomes has recently emerged from clinical and animal studies. In animals, intermittent hypoxia (IH) mimicking OSA promotes tumor malignancy both directly and via host immune alterations. We hypothesized that IH could potentiate cancer aggressiveness through activation of the cyclooxygenase-2 (COX-2) pathway and the concomitant increases in prostaglandin E2 (PGE2). The contribution of the COX-2 in IH-induced enhanced tumor malignancy was assessed using celecoxib as a COX-2 specific inhibitor in a murine model of OSA bearing Lewis lung carcinoma (LLC1) tumors. Exposures to IH accelerated tumor progression with a tumor associated macrophages (TAMs) shift towards a pro-tumoral M2 phenotype. Treatment with celecoxib prevented IH-induced adverse tumor outcomes by inhibiting IH-induced M2 polarization of TAMs. Furthermore, TAMs isolated from IH-exposed mice treated with celecoxib reduced the proliferation of LLC1 naïve cells, while the opposite occurred with placebo-treated IH-exposed mice. Finally, in vitro IH exposures of murine macrophages and LLC1 cells showed that both cell types increased PGE2 release in response to IH. These results suggest a crucial role for the COX-2 signaling pathway in the IH-exacerbated malignant processes, and designate macrophages and lung adenocarcinoma cells, as potential sources of PGE2.

Altered CD8+ T-Cell Lymphocyte Function and TC1 Cell Stemness Contribute to Enhanced Malignant Tumor Properties in Murine Models of Sleep Apnea.

The presence of obstructive sleep apnea (OSA) in patients with cancer appears to be accompanied by poorer outcomes. However, the mechanisms underlying such association are unknown. Tumor infiltrating lymphocytes (TILs), including CD8+ T cells, function as cytotoxic T lymphocytes (CTLs) and mount immune responses to cancer by the release of cytolytic enzymes, including granzyme B (GzmB), perforin (Prf), and cytokines such as interferon (IFN)-γ. Using established in vivo mouse models, we investigated CD8+ T cells and cancer stem cells (CSCs) in intermittent hypoxia (IH) and sleep fragmentation (SF) in the context of tumor environment. Both IH and SF promoted increased tumor growth and invasion toward adjacent tissues compared to controls. The number and frequency of GzmB-producing CD8+ T cells per milligram of tumor tissue was significantly reduced in IH-exposed mice with impaired cytolytic function in both the groups and correlated with tumor weight. We also found that Oct4+ and CD44+CD133+ expressing CSCs were considerably increased in IH and SF tumors, respectively. Reductions in GzmB in intratumoral CD8+ T cells in combination with the changes in tumor microenvironment that maintain the ability of CSCs to self-renew and even confer this capability to the nonstem population are compatible with reduced immunosurveillance and adverse tumor outcomes in animal models of OSA.

Normoxic Recovery Mimicking Treatment of Sleep Apnea Does Not Reverse Intermittent Hypoxia-Induced Bacterial Dysbiosis and Low-Grade Endotoxemia in Mice.

Intermittent hypoxia (IH) mimicking obstructive sleep apnea (OSA) significantly modifies gut microbiota in mice. However, whether these IH-induced gut microbiome changes are reversible after restoring normal oxygenation (the equivalent of effective OSA therapy) is unknown. The aim of this study was to investigate gut microbiota composition and circulating endotoxemia after a post-IH normoxic period in a mouse model of OSA. Ten mice were subjected to IH (40 sec 21% O2-20 sec 5% O2) for 6 h/day for 6 w and 10 mice breathing normoxic air (NM) were used as controls. After exposures, both groups were subjected to 6 w in normoxia. Microbiome composition of fecal samples was determined by 16S ribosomal RNA (rRNA) pyrosequencing. Bioinformatic analysis was performed by Quantitative Insights into Microbial Ecology. Plasma lipopolysaccharide (LPS) levels were measured by endotoxin assay. After normoxic recovery, the Chao and Shannon indices of each group suggested similar bacterial richness and diversity. 16S rRNA pyrosequencing analysis showed that IH-exposed mice had a significant decrease in the abundance of Bacteroidetes and a significant increase of Firmicutes and Deferribacteres compared to the NM group. After normoxic recovery, circulating LPS concentrations were higher in the IH group (P < 0.009). Moreover, the IH group showed a negative and significant correlation between the abundance of Lactobacillus and Ruminococcus and significant positive correlations between the abundance of Mucispirillum and Desulfovibrio and plasma LPS levels, respectively. Even after prolonged normoxic recovery after IH exposures, gut microbiota and circulating endotoxemia remain negatively altered, suggesting that potential benefits of OSA treatment for reversing OSA-induced changes in gut microbiota may either require a longer period or alternative interventions.

Tumor Cell Malignant Properties Are Enhanced by Circulating Exosomes in Sleep Apnea

OSA is associated with increased cancer incidence and mortality. Exosomes are vesicles secreted by most cells. They are released into the bloodstream and play a role in tumor progression and metastasis. We evaluated whether the chronic intermittent hypoxia (IH) that characterizes OSA leads to release of tumor-promoting exosomes in the circulation. C57/B6 male mice were randomized to 6weeks of IH or room air (RA). Asubgroup was injected with TC1 lung carcinoma cells in the left flank after 2weeks of IH. Exosomes from mouse plasma and from 10 adult human patients with OSA before and after treatment for 6weeks were cocultured with mouse TC1 and human adenocarcinoma cells lines. Malignant tumor properties such as proliferation, migration, invasion, and endothelial monolayer disruption were assessed, as was micro-RNA (miRNA), exosomal content, and transcriptomic effects of exosomes on TC1 cells invitro to identify target genes. Application of IH-induced exosomes from either IH-exposed tumor-bearing (IH+) or non-tumor-bearing (IH-) mice significantly promoted TC1 malignant properties. Similarly,before adherent treatment, exosomes from patients with OSA significantly enhanced proliferation and migration of human adenocarcinoma cells compared with after adherent treatment. Eleven distinct miRNAs emerged in IH-exposed mice, and their gene targets in TC1 cells were identified. Circulating exosomes released under IH conditions invivo selectively enhance specific properties of lung tumor cell cultures. Thus, plasma exosomes participate in the increased tumor aggressiveness observed in patients with OSA.

Cardiovascular dysfunction in adult mice following postnatal intermittent hypoxia.

Ex-premature infants are at higher risk for hypertension and cardiovascular disease as adults, although the mechanisms underlying such increased risks are unknown. We hypothesize that postnatal exposure to intermittent hypoxia (IH) leads to cardiovascular dysfunction in adulthood with alterations of the renin-angiotensin pathway. Neonatal mice were exposed to IH for 4 wk. At the age of 3 mo, various cardiovascular measurements were obtained. IH-exposed mice exhibited higher systolic blood pressure, impaired baroreflex responses, and decreased heart rate variability. Furthermore, IH-exposed mice manifested evidence of endothelial dysfunction, as shown by reduced reperfusion indices after tail vessel occlusion and impaired vasodilatory responses to acetylcholine. CD31(+) endothelial cells isolated from mesenteric arteries of IH-exposed mice expressed higher levels of angiotensin-converting enzyme and reactive oxygen species; plasma angiotensin-II levels were also significantly higher in these animals. In addition, DNA methylation patterns of the Ace1 and the Agt genes in these cells were congruent with their expression patterns. Our results suggest that exposures to postnatal IH alter the normal development of the renin-angiotensin system and promote the occurrence of cardiovascular dysfunction during adulthood in mice.

Abstract 15724: Intermittent Hypoxia Induces Early Pro-Atherogenic Changes in Aortic Wall Macrophages in a Murine Model of Obstructive Sleep Apnea

Background: OSA is a highly prevalent condition throughout the lifespan, and has emerged as an independent risk factor for atherosclerosis. Macrophages play a key role in the pathogenesis of atherosclerosis through shifts in the continuum between the pro-inflammatory M1 and the athero-protective M2. We hypothesized that Intermittent Hypoxia (IH) during the sleep period, a model for OSA, will induce shifts towards a pro-atherogenic state in the spectrum of macrophages within the aortic vascular wall. Methods: 8-week old male C57BL/6J mice were exposed to IH for 12-hr/day during the light period or to room air (RA) for 6 weeks and were kept on a regular low-fat chow. Following exposure, full-length aortas were dissected and enzymatically digested. Single cell suspensions were prepared and cells were incubated with antibodies for macrophage markers previously implicated in atherogenesis and metabolic dysregulation - CD11b, F4/80, Ly6c, CD36, and CD64, and analyzed by FACS. Results: Macrophages were defined as CD11b+/F4/80+ cells. Significant increases in the percentage of macrophages emerged in IH-exposed mice (6.4%±0.3 vs. 8%±0.3, p=0.003, n=19-20/group). Furthermore, IH induced shifts in the macrophage population toward an M1 pro-inflammatory phenotype. Specifically, IH group showed significantly higher expression of Ly6c, (MFI:522±23 vs. 699±43, p=0.004, n=12/group) and increased the percentage of Ly6c+(hi) cells (9.2% vs. 11.7%, p=0.03). Conversely, tissue-resident marker CD64 expression in the aortic macrophages was down-regulated following IH exposures (MFI:3207±453 vs. 2967±483, p=0.03, n=12/group), while scavenger receptor CD36 expression was increased in the IH-exposed group (MFI:1694±56 vs.2129±209, p=0.005). Conclusion: Intermittent hypoxia during the sleep period leads to early expansion of the macrophage population in the aortic wall in a relatively resistant animal model for development of atherosclerosis, i.e., in the absence of a high-fat diet or of high atherogenic risk predisposing gene knockout. Furthermore IH induces changes in macrophage phenotypes, including a shift towards a pro-inflammatory phenotype, and recruitment of bone-marrow derived macrophages expressing indicators of metabolic activation.

Intermittent hypoxia-induced changes in tumor-associated macrophages and tumor malignancy in a mouse model of sleep apnea.

An increased cancer aggressiveness and mortality have been recently reported among patients with obstructive sleep apnea (OSA). Intermittent hypoxia (IH), a hallmark of OSA, enhances melanoma growth and metastasis in mice. To assess whether OSA-related adverse cancer outcomes occur via IH-induced changes in host immune responses, namely tumor-associated macrophages (TAMs). Lung epithelial TC1 cell tumors were 84% greater in mice subjected to IH for 28 days compared with room air (RA). In addition, TAMs in IH-exposed tumors exhibited reductions in M1 polarity with a shift toward M2 protumoral phenotype. Although TAMs from tumors harvested from RA-exposed mice increased TC1 migration and extravasation, TAMs from IH-exposed mice markedly enhanced such effects and also promoted proliferative rates and invasiveness of TC1 cells. Proliferative rates of melanoma (B16F10) and TC1 cells exposed to IH either in single culture or in coculture with macrophages (RAW 264.7) increased only when RAW 264.7 macrophages were concurrently present. Our findings support the notion that IH-induced alterations in TAMs participate in the adverse cancer outcomes reported in OSA.

Exogenous erythropoietin administration attenuates intermittent hypoxia-induced cognitive deficits in a murine model of sleep apnea

BackgroundIn rodents, exposure to intermittent hypoxia (IH), a hallmark of obstructive sleep apnea (OSA), is associated with neurobehavioral impairments, increased apoptosis in the hippocampus and cortex, as well as increased oxidant stress and inflammation. Such findings are markedly attenuated in rodents exposed to sustained hypoxia 9SH) of similar magnitude. The hypoxia-sensitive gene erythropoietin (EPO) has emerged as a major endogenous neuroprotectant, and could be involved in IH-induced neuronal dysfunction.Methods and ResultsIH induced only transiently increased expression of EPO mRNA in hippocampus, which was continued in (SH)-exposed mice. IH, but not SH, adversely affected two forms of spatial learning in the water maze, and increased markers of oxidative stress. However, on a standard place training task, mice treated with exogenously administered EPO displayed normal learning, and were protected from the spatial learning deficits observed in vehicle-treated (C) littermates exposed to IH. Moreover, anxiety levels were increased in IH as compared to normoxia, while no changes in anxiety emerged in EPO-treated mice. Additionally, C mice, but not EPO-treated IH-exposed mice had significantly elevated levels of NADPH oxidase expression, as well as increased MDA and 8-OHDG levels in cortical and hippocampal lysates.ConclusionsThe oxidative stress responses and neurobehavioral impairments induced by IH during sleep are mediated, at least in part, by imbalances between EPO expression and increased NADPH oxidase activity, and thus pharmacological agents targeting EPO expression in CNS may provide a therapeutic strategy in sleep-disordered breathing.

Hippocampal spine-associated Rap-specific GTPase-activating protein induces enhancement of learning and memory in postnatally hypoxia-exposed mice

Spine-associated Rap-specific GTPase-activating protein (SPAR) is a postsynaptic protein that forms a complex with postsynaptic density (PSD)-95 and N-methyl- d-aspartate receptors (NMDARs), and morphologically regulates dendritic spines. Mild intermittent hypoxia (IH, 16.0% O 2, 4 h/day for 4 weeks) is known to markedly enhance spatial learning and memory in postnatal developing mice. Here, we report that this effect is correlated with persistent increases in SPAR expression as well as long-term potentiation (LTP) in the hippocampus of IH-exposed mice. Furthermore, an infusion of SPAR antisense oligonucleotides into the dorsal hippocampus disrupted elevation of SPAR expression, preventing enhanced hippocampal LTP in IH-exposed developing mice and also reducing LTP in normoxic mice, without altering basal synaptic transmission. In SPAR antisense-treated mice, acquisition of the Morris water maze spatial learning task was impaired, as was memory retention in probe trails following training. This study provides the first evidence that SPAR is functionally required for synaptic plasticity and contributes to the IH-induced enhancement of spatial learning and memory in postnatal developing mice.