A GABAB receptor antagonist rescues functional and structural impairments in the perirhinal cortex of a mouse model of CDKL5 deficiency disorder.

CDKL5 (cyclin-dependent kinase-like 5) deficiency disorder (CDD) is a severe neurodevelopmental encephalopathy characterized by early-onset epilepsy and intellectual disability. Studies in mouse models have linked CDKL5 deficiency to defects in neuronal maturation and synaptic plasticity, and disruption of the excitatory/inhibitory balance. Interestingly, increased density of both GABAergic synaptic terminals and parvalbumin inhibitory interneurons was recently observed in the primary visual cortex of Cdkl5 knockout (KO) mice, suggesting that excessive GABAergic transmission might contribute to the visual deficits characteristic of CDD. However, the functional relevance of cortical GABAergic circuits abnormalities in these mutant mice has not been investigated so far. Here we examined GABAergic circuits in the perirhinal cortex (PRC) of Cdkl5 KO mice, where we previously observed impaired long-term potentiation (LTP) associated with deficits in novel object recognition (NOR) memory. We found a higher number of GABAergic (VGAT)-immunopositive terminals in the PRC of Cdkl5 KO compared to wild-type mice, suggesting that increased inhibitory transmission might contribute to LTP impairment. Interestingly, while exposure of PRC slices to the GABAA receptor antagonist picrotoxin had no positive effects on LTP in Cdkl5 KO mice, the selective GABAB receptor antagonist CGP55845 restored LTP magnitude, suggesting that exaggerated GABAB receptor-mediated inhibition contributes to LTP impairment in mutants. Moreover, acute in vivo treatment with CGP55845 increased the number of PSD95 positive puncta as well as density and maturation of dendritic spines in PRC, and restored NOR memory in Cdkl5 KO mice. The present data show the efficacy of limiting excessive GABAB receptor-mediated signaling in improving synaptic plasticity and cognition in CDD mice.

Pre- and postnatal exposure to glyphosate-based herbicide causes behavioral and cognitive impairments in adult mice: evidence of cortical ad hippocampal dysfunction.

Glyphosate-based herbicides (GBH) are the most widely used pesticides worldwide. Despite considerable progress in describing the neurotoxic potential of GBH, the harmful effects on brain cytoarchitecture and behavior are still unclear. Here, we addressed the developmental impact of GBH by exposing female mice to 250 or 500 mg/kg doses of GBH during both pregnancy and lactation and then examined the downstream effects at the behavioral, neurochemical and molecular levels. We show that pre- and neonatal exposure to GBH impairs fertility and reproduction parameters as well as maternal behavior of exposed mothers. In offspring, GBH was responsible for a global delay in innate reflexes and a deficit in motor development. At the adult age, exposed animals showed a decrease of locomotor activity, sociability, learning and short- and long-term memory associated with alterations of cholinergic and dopaminergic systems. Furthermore, GBH-activated microglia and astrocytes, sign of neuroinflammation event in the medial prefrontal cortex and hippocampus. At the molecular level, a down-regulation of brain-derived neurotrophic factor (BDNF) expression and an up-regulation of tyrosine-related kinase receptor (TrkB), NR1 subunit of NMDA receptor as well as tumor necrosis factor α (TNFα) were found in the brain of GBH-exposed mice. The present work demonstrates that GBH induces numerous behavioral and cognitive abnormalities closely associated with significant histological, neurochemical and molecular impairments. It also raises fundamental concerns about the ability of current safety testing to assess risks of pesticide exposure during developmental periods of central nervous system.

Glyphosate-based herbicide exposure affects cognitive flexibility and social cognition in adult mice.

Glyphosate (Gly) is the active ingredient of several widely used herbicide formulations. Studies on Gly and glyphosate-based herbicide (GBH) exposure in different experimental models have suggested that the nervous system represented a key target for its toxicity, especially the prefrontal cortex (PFC). However, it is still unknown whether exposure to GBH affects higher brain functions dependent on PFC circuitry. The present work aimed to examine the effects of subtoxic doses of GBH on social cognition and cognitive flexibility as two functions belonging to higher brain function in mice. To do so, adult male mice were exposed daily to GBH by gavage at doses of 250 or 500 mg/kg for a sub-chronic period lasting 6 weeks. Then, mice were subjected to behavioral testing using the three-chamber and the Barnes maze paradigms. Our results indicate that GBH did not affect sociability. However, we found that GBH affects social cognition expressed by a lower discrimination index in the three-chamber test. Moreover, spatial memories evaluated during the probe trial, and cognitive flexibility evaluated during the reversal probe, were affected in mice exposed to GBH. Based on these results, exposure to subtoxic doses of GBH led to neurobehavioral alterations affecting the integrity of social cognition and cognitive flexibility functions. Finally, these data urge a thorough investigation of the cellular and molecular mechanisms underlying these alterations.

Anxiety and Gene Expression Enhancement in Mice Exposed to Glyphosate-Based Herbicide.

Growing evidence demonstrates that serotonin (5-HT) depletion increases activity in the amygdala and medial prefrontal cortex (mPFC), ultimately leading to anxiety behavior. Previously, we showed that glyphosate-based herbicides (GBHs) increased anxiety levels and reduced the number of serotoninergic fibers within the mPFCs and amygdalas of exposed mice. However, the impact of this 5-HT depletion following GBH exposure on neuronal activity in these structures is still unknown. In this study, we investigated the effects of GBH on immediate early gene (IEG) activation within the mPFCs and amygdalas of treated mice from juvenile age to adulthood and its subsequent effects on anxiety levels. Mice were treated for subchronic (6 weeks) and chronic (12 weeks) periods with 250 or 500 mg/kg/day of GBH and subjected to behavioral testing using the open field and elevated plus maze paradigms. Then, we analyzed the expression levels of c-Fos and pCREB and established the molecular proxies of neuronal activation within the mPFC and the amygdala. Our data revealed that repeated exposure to GBH triggers anxiogenic behavior in exposed mice. Confocal microscopy investigations into the prelimbic/infralimbic regions of the mPFC and in basolateral/central nuclei of the amygdala disclosed that the behavioral alterations are paralleled by a robust increase in the density and labelling intensity of c-Fos- and pCREB-positive cells. Taken together, these data show that mice exposed to GBH display the hyperactivation of the mPFC-amygdala areas, suggesting that this is a potential mechanism underlying the anxiety-like phenotype.

Behavioral and Immunohistochemical Study of the Effects of Subchronic and Chronic Exposure to Glyphosate in Mice.

Many epidemiological studies have described an adolescent-related psychiatric illness and sensorimotor deficits after Glyphosate based herbicide (GBH) exposure. GBH exposure in animal models of various ages suggests that it may be neurotoxic and could impact brain development and subsequently, behavior in adulthood. However, its neurotoxic effects on adolescent brain remain unclear and the results are limited. The present study was conducted to evaluate the neurobehavioral effects of GBH following acute, subchronic (6 weeks) and chronic (12 weeks) exposure (250 or 500 mg/kg/day) in mice treated from juvenile age until adulthood. Mice were subjected to behavioral testing with the open field (OF), the elevated plus maze, the tail suspension and Splash tests (STs). Their behaviors related to exploratory activity, anxiety and depression-like were recorded. After completion of the behavioral testing, adult mice were sacrificed and the expression of tyrosine hydroxylase (TH) in the substantia nigra pars compacta (SNc) and serotonin (5-HT) in the dorsal raphe nucleus (DRN), the basolateral amygdala (BLA) and the ventral medial prefrontal cortex (mPFC) was evaluated using immunohistochemical procedure. Our results indicate that unlike acute exposure, both subchronic and chronic exposure to GBH induced a decrease in body weight gain and locomotor activity, and an increase of anxiety and depression-like behavior levels. In addition, the immunohistochemical findings showed that only the chronic treatment induced a reduction of TH-immunoreactivity. However, both subchronic and chronic exposure produced a reduction of 5-HT-immunoreactivity in the DRN, BLA and ventral mPFC. Taken together, our data suggest that exposure to GBH from juvenile age through adulthood in mice leads to neurobehavioral changes that stem from the impairment of neuronal developmental processes.

Prenatal Paraquat exposure induces neurobehavioral and cognitive changes in mice offspring.

In the present work, we investigated developmental toxicity of Paraquat (PQ), from the 1st or 6th day of mating and throughout the gestation period. We have examined several parameters, including toxicity indices, reproductive performance, sensorimotor development, as well as anxiety and cognitive performance of the offspring. Our results showed that exposure to 20mg/kg of Paraquat during the first days of pregnancy completely prevents pregnancy in treated mice, but from the 6th day of pregnancy, an alteration in fertility and reproductive parameters was observed. In offspring, the PQ was responsible for an overall delay of innate reflexes and a deficit in motor development. All exposed animals showed a decrease in the level of locomotor activity, increased levels of anxiety-like behavior and pronounced cognitive impairment in adulthood. These results demonstrated that Paraquat led to the onset of many behavioral changes that stem from the impairment of neuronal developmental processes in prenatally exposed mice.