Enduring Behavioral Effects Induced by Birth by Caesarean Section in the Mouse.

Birth by Caesarean (C)-section impacts early gut microbiota colonization and is associated with an increased risk of developing immune and metabolic disorders. Moreover, alterations of the microbiome have been shown to affect neurodevelopmental trajectories. However, the long-term effects of C-section on neurobehavioral processes remain unknown. Here, we demonstrated that birth by C-section results in marked but transient changes in microbiome composition in the mouse, in particular, the abundance of Bifidobacterium spp. was depleted in early life. Mice born by C-section had enduring social, cognitive, and anxiety deficits in early life and adulthood. Interestingly, we found that these specific behavioral alterations induced by the mode of birth were also partially corrected by co-housing with vaginally born mice. Finally, we showed that supplementation from birth with a Bifidobacterium breve strain, or with a dietary prebiotic mixture that stimulates the growth of bifidobacteria, reverses selective behavioral alterations in C-section mice. Taken together, our data link the gut microbiota to behavioral alterations in C-section-born mice and suggest the possibility of developing adjunctive microbiota-targeted therapies that may help to avert long-term negative consequences on behavior associated with C-section birth mode.

Intervention strategies for cesarean section-induced alterations in the microbiota-gut-brain axis.

Microbial colonization of the gastrointestinal tract is an essential process that modulates host physiology and immunity. Recently, researchers have begun to understand how and when these microorganisms colonize the gut and the early-life factors that impact their natural ecological establishment. The vertical transmission of maternal microbes to the offspring is a critical factor for host immune and metabolic development. Increasing evidence also points to a role in the wiring of the gut-brain axis. This process may be altered by various factors such as mode of delivery, gestational age at birth, the use of antibiotics in early life, infant feeding, and hygiene practices. In fact, these early exposures that impact the intestinal microbiota have been associated with the development of diseases such as obesity, type 1 diabetes, asthma, allergies, and even neurodevelopmental disorders. The present review summarizes the impact of cesarean birth on the gut microbiome and the health status of the developing infant and discusses possible preventative and restorative strategies to compensate for early-life microbial perturbations.

Transferring the blues: Depression-associated gut microbiota induces neurobehavioural changes in the rat.

The gut microbiota interacts with the host via neuroimmune, neuroendocrine and neural pathways. These pathways are components of the brain-gut-microbiota axis and preclinical evidence suggests that the microbiota can recruit this bidirectional communication system to modulate brain development, function and behaviour. The pathophysiology of depression involves neuroimmune-neuroendocrine dysregulation. However, the extent to which changes in gut microbiota composition and function mediate the dysregulation of these pathways is unknown. Thirty four patients with major depression and 33 matched healthy controls were recruited. Cytokines, CRP, Salivary Cortisol and plasma Lipopolysaccharide binding protein were determined by ELISA. Plasma tryptophan and kynurenine were determined by HPLC. Fecal samples were collected for 16s rRNA sequencing. A Fecal Microbiota transplantation was prepared from a sub group of depressed patients and controls and transferred by oral gavage to a microbiota-deficient rat model. We demonstrate that depression is associated with decreased gut microbiota richness and diversity. Fecal microbiota transplantation from depressed patients to microbiota-depleted rats can induce behavioural and physiological features characteristic of depression in the recipient animals, including anhedonia and anxiety-like behaviours, as well as alterations in tryptophan metabolism. This suggests that the gut microbiota may play a causal role in the development of features of depression and may provide a tractable target in the treatment and prevention of this disorder.

Prenatal stress-induced alterations in major physiological systems correlate with gut microbiota composition in adulthood.

Early-life adverse experiences, including prenatal stress (PNS), are associated with a higher prevalence of neurodevelopmental, cardiovascular and metabolic disorders in affected offspring. Here, in a rat model of chronic PNS, we investigate the impact of late gestational stress on physiological outcomes in adulthood. Sprague-Dawley pregnant dams were subjected to repeated restraint stress from embryonic day 14 to day 20, and their male offspring were assessed at 4 months of age. PNS induced an exaggeration of the hypothalamic-pituitary-adrenal (HPA) axis response to stress, as well as an elevation of blood pressure and impairment of cognitive function. Altered respiratory control was also observed, as demonstrated by increased variability in basal respiratory frequency and abnormal frequency responses to both hypoxic and hypercapnic challenges. PNS also affected gastrointestinal neurodevelopment and function, as measured by a decrease in the innervation density of distal colon and an increase in the colonic secretory response to catecholaminergic stimulation. Finally, PNS induced long lasting alterations in the intestinal microbiota composition. 16S rRNA gene 454 pyrosequencing revealed a strong trend towards decreased numbers of bacteria in the Lactobacillus genus, accompanied by elevated abundance of the Oscillibacter, Anaerotruncus and Peptococcus genera in PNS animals. Strikingly, relative abundance of distinct bacteria genera significantly correlated with certain respiratory parameters and the responsiveness of the HPA axis to stress. Together, these findings provide novel evidence that PNS induces long-term maladaptive alterations in the gastrointestinal and respiratory systems, accompanied by hyper-responsiveness to stress and alterations in the gut microbiota.

The impact of microbiota on brain and behavior: mechanisms & therapeutic potential.

There is increasing evidence that host-microbe interactions play a key role in maintaining homeostasis. Alterations in gut microbial composition is associated with marked changes in behaviors relevant to mood, pain and cognition, establishing the critical importance of the bi-directional pathway of communication between the microbiota and the brain in health and disease. Dysfunction of the microbiome-brain-gut axis has been implicated in stress-related disorders such as depression, anxiety and irritable bowel syndrome and neurodevelopmental disorders such as autism. Bacterial colonization of the gut is central to postnatal development and maturation of key systems that have the capacity to influence central nervous system (CNS) programming and signaling, including the immune and endocrine systems. Moreover, there is now expanding evidence for the view that enteric microbiota plays a role in early programming and later response to acute and chronic stress. This view is supported by studies in germ-free mice and in animals exposed to pathogenic bacterial infections, probiotic agents or antibiotics. Although communication between gut microbiota and the CNS are not fully elucidated, neural, hormonal, immune and metabolic pathways have been suggested. Thus, the concept of a microbiome-brain-gut axis is emerging, suggesting microbiota-modulating strategies may be a tractable therapeutic approach for developing novel treatments for CNS disorders.

Microbiota and neurodevelopmental windows: implications for brain disorders.

Gut microbiota is essential to human health, playing a major role in the bidirectional communication between the gastrointestinal tract and the central nervous system. The microbiota undergoes a vigorous process of development throughout the lifespan and establishes its symbiotic rapport with the host early in life. Early life perturbations of the developing gut microbiota can impact neurodevelopment and potentially lead to adverse mental health outcomes later in life. This review compares the parallel early development of the intestinal microbiota and the nervous system. The concept of parallel and interacting microbial-neural critical windows opens new avenues for developing novel microbiota-modulating based therapeutic interventions in early life to combat neurodevelopmental deficits and brain disorders.

Neuroprotective and cognitive enhancing effects of a multi-targeted food intervention in an animal model of neurodegeneration and depression.

Rising neurodegenerative and depressive disease prevalence combined with the lack of effective pharmaceutical treatments and dangerous side effects, has created an urgent need for the development of effective therapies. Considering that these disorders are multifactorial in origin, treatments designed to interfere at different mechanistic levels may be more effective than the traditional single-targeted pharmacological concepts. To that end, an experimental diet composed of zinc, melatonin, curcumin, piperine, eicosapentaenoic acid (EPA, 20:5, n-3), docosahexaenoic acid (DHA, 22:6, n-3), uridine, and choline was formulated. This diet was tested on the olfactory bulbectomized rat (OBX), an established animal model of depression and cognitive decline. The ingredients of the diet have been individually shown to attenuate glutamate excitoxicity, exert potent anti-oxidant/anti-inflammatory properties, and improve synaptogenesis; processes that all have been implicated in neurodegenerative diseases and in the cognitive deficits following OBX in rodents. Dietary treatment started 2 weeks before OBX surgery, continuing for 6 weeks in total. The diet attenuated OBX-induced cognitive and behavioral deficits, except long-term spatial memory. Ameliorating effects of the diet extended to the control animals. Furthermore, the experimental diet reduced hippocampal atrophy and decreased the peripheral immune activation in the OBX rats. The ameliorating effects of the diet on the OBX-induced changes were comparable to those of the NMDA receptor antagonist, memantine, a drug used for the management of Alzheimer's disease. This proof-of-concept study suggests that a diet, which simultaneously targets multiple disease etiologies, can prevent/impede the development of a neurodegenerative and depressive disorders and the concomitant cognitive deficits.

Autistic-like behavioural and neurochemical changes in a mouse model of food allergy.

Food allergy has been suggested to contribute to the expression of psychological and psychiatric traits, including disturbed social behaviour and repetitive behaviour inherent in autism spectrum disorders (ASD). Most research in this field receives little attention, since fundamental evidence showing direct effects of food allergic immune responses on social behaviour is very limited. In the present study, we show that a food allergic reaction to cow's milk protein, induced shortly after weaning, reduced social behaviour and increased repetitive behaviour in mice. This food allergic reaction increased levels of serotonin (5-hydroxytryptamine; 5-HT) and the number of 5-HT positive cells, and decreased levels of 5-hydroxyindoleacetic acid (5-HIAA) in the intestine. Behavioural changes in food allergic mice were accompanied by reduced dopaminergic activity in the prefrontal cortex. Furthermore, neuronal activation (c-Fos expression) was increased in the prefrontal cortex and reduced in the paraventricular nucleus of the hypothalamus after exposure to a social target. We hypothesize that an intestinal allergic response regulates complex, but critical, neuroimmune interactions, thereby affecting brain circuits involved in social interaction, repetitive behaviour and cognition. Together with a genetic predisposition and multiple environmental factors, these effects of allergic immune activation may exacerbate behavioural abnormalities in patients with ASD.

The neuro-immune axis: prospect for novel treatments for mental disorders.

Disturbed bidirectional pathways between the (central) nervous system and immune system have been implicated in various mental disorders, including depressive and neurodevelopmental disorders. In this minireview, the role of the neuro-immune axis and its targetability in relation to major depression and autism spectrum disorder will be discussed. All together, the management of these and possibly other multi-factorial mental disorders needs a new and integrated therapeutic approach. Pharmacologically bioactive molecules as well as medical nutrition targeting the (gut)-immune-brain axis could be such an approach.

Minocycline restores spatial but not fear memory in olfactory bulbectomized rats.

We investigated the effects of minocycline, a microglia suppressant, on olfactory bulbectomized (OBX) rats, a model of cognitive and behavioral impairments arising from neurodegenerative processes. Previously, we demonstrated that the major OBX-induced behavioral and cognitive impairments develop between day 3 and 7 following bulbectomy. Here we show that the onset of these cognitive changes parallel in time with signs of microglia activation (increased mRNA levels of IL-1ß and CD68) in hippocampus. Next, rats were treated with minocycline (50mg/kg, i.p.) once daily for 4 weeks. OBX surgery was done at day 3 of drug treatment. Animals were tested in a battery of behavioral assays: open field, passive avoidance (fear learning and memory-acquired prior to OBX) and T-maze (spatial memory, conducted post bulbectomy). Minocycline normalized OBX-induced hyperactivity in the open field. Minocycline failed to prevent fear memory loss, but protected the OBX rats against hippocampal-dependent spatial memory deficit. Our findings suggest that treatment with minocycline may be effective in the early phase of a neurodegenerative disease.

Celecoxib delays cognitive decline in an animal model of neurodegeneration.

Cyclooxygenase-2 (COX-2) is thought to play a role in the pathogenesis of various neurodegenerative disorders. However, clinical trials with COX-2 inhibitors have yielded contradictory results. In the present study we investigated whether COX-2 plays a role in the behavioral and cognitive impairments seen in olfactory bulbectomized rats. These impairments arise from neurodegenerative processes. First, we determined the time course of the OBX-induced behavioral (hyperactivity) and cognitive changes (fear memory) and how these correlate with changes in COX-2 mRNA expression in hippocampus. This experiment showed that the major impairments in behavior and cognition developed between Days 3 and 14 after OBX surgery, which correlated with changes in mRNA levels of COX-2, which increased at Days 7 and 14 after surgery but not anymore at day 28. In a subsequent experiment, rats were treated, starting two days before surgery, with the COX-2 inhibitor celecoxib (10 mg/kg, dissolved in drinking water) for 4 weeks. OBX-induced hyperactivity in the open field was normalized after 2 weeks of celecoxib treatment, but not longer after 4 weeks. Celecoxib partly rescued fear learning and memory deficits without affecting spatial memory. The effects of celecoxib on fear memory lasted up to 1 week posttreatment, but disappeared thereafter. Our results show that COX-2 plays a limited role (both in magnitude and time) in the development of the OBX syndrome.

Memantine partly rescues behavioral and cognitive deficits in an animal model of neurodegeneration.

Memantine, a non-competitive NMDA receptor antagonist, is used for the treatment of Alzheimer's disease (AD) and off-label as an anti-depressant. Here we investigated possible anti-depressant, cognitive enhancing and neuroprotective effects of memantine in the olfactory bulbectomized (OBX) rat. OBX is used as a screening model for antidepressants and shows cognitive disturbances. In Experiment I, memantine treatment started 14 days after OBX surgery (this setup is similar to what we use for screening of potential antidepressants) and 2 days before surgery in experiment II. In both experiments, memantine (20 mg/kg, p.o) was administered once daily for 28 days. Animals were tested in the open field (locomotor activity), passive avoidance (fear learning and memory), and holeboard (spatial acquisition and memory) before and after the bulbectomy. Memantine, when administered before surgery, prevented OBX-induced hyperactivity and partly fear memory loss. These behavioral effects were present for at least 3 weeks after cessation of treatment. Memantine, however did not improve spatial memory. When administered 2 weeks after OBX surgery, memantine was ineffective in normalizing open field hyperactivity and improving cognitive deficits. Interestingly, after the animals were retrained in passive avoidance, memantine- treated OBX rats (both in experiment I and II) showed improved fear learning and memory. Our findings suggest that memantine has both neuroprotective and cognitive enhancing effects without antidepressant-like properties in the OBX rat. Based on our results, we propose that memantine may be more beneficial to AD patients when administered early in the disease process.

Simvastatin improves learning and memory in control but not in olfactory bulbectomized rats.

RATIONALE: Olfactory bulbectomy (OBX) in a laboratory rodent leads to numerous behavioral deficits and involves cognitive and motor changes that are used to model major depression, but may also be a valuable tool in the study of neurodegenerative disorders like Alzheimer's disease. OBJECTIVES: This experiment evaluated the effects of simvastatin, a cholesterol-lowering drug with putative neuroprotective properties, on OBX-induced behavioral changes. RESULTS: Chronic administration of simvastatin, starting 48 h after surgery, did not have any behavioral effect in OBX rats, as tested in open field, passive avoidance and object-recognition paradigms. In control rats, simvastatin treatment resulted in an improved performance in both the passive avoidance and the object-in-place task. CONCLUSION: In the present study, simvastatin treatment enhanced cognition in intact rats, but had no effect in OBX rats. These results are in line with the idea that statins may attenuate (early) age-associated cognitive decline in humans.

Changes in sensitivity of response distributions to changing reinforcement ratios during exposure to ephedrine, caffeine, and ephedrine-caffeine combinations.

Changes in the sensitivity of response distributions to changes in reward distribution (reinforcer distribution sensitivity) were examined when rats were exposed to low and moderate doses of caffeine, ephedrine, and caffeine-ephedrine combinations. The data show significant decreases in sensitivity in response distributions to changes in reward schedule values during exposure to caffeine and ephedrine/caffeine combinations, whereas ephedrine alone resulted in overmatching comparable with baseline and NaCl conditions. Rats treated either with 3.0-mg/kg or 10.0-mg/kg doses of caffeine and all combinations of ephedrine at doses of 1.8 or 5.6 mg/kg with caffeine at 3.0 or 10.0 mg/kg showed reduced sensitivity in response distributions to differences in reinforcement schedule ratios. In contrast, when rats were exposed to ephedrine at 1.8 or 5.6 mg/kg, they maintained or increased the degree of overmatching. Although reinforcer distribution sensitivity was altered, drug exposure did not significantly affect the absolute rates of responding. Bias varied after exposure to caffeine, ephedrine, and their combinations, but not systematically. Finally, whereas the estimates of goodness of fit (r2) to the matching equation showed some decreases during drug exposure, these were neither statistically significant nor correlated with drug dose. These results suggest differential effects of ephedrine and caffeine on the sensitivity of response distributions to changes in reinforcement ratio distributions, with deleterious effects of caffeine and ephedrine/caffeine combinations.