Assessment of Developmental Milestones in Rodents

Evaluation of developmental milestones and of brain measurements in rats exposed to the pesticide pyriproxyfen in prenatal period

Pyriproxyfen is a pesticide used in Brazil to control the Aedes aegypti mosquito, vector of arboviruses like Zika and dengue. However, this pesticide is structurally similar to retinoic acid, a metabolite of vitamin A that regulates neuronal differentiation and hindbrain development during the embryonic period. Due to the similarity between pyriproxyfen and retinoic acid, studies indicate that this pesticide may have cross-reactivity with retinoid receptors. Thus, pregnant exposure to pyriproxyfen could interfere in the nervous system development of the fetal. In this context, the present study evaluated whether prenatal exposure to pyriproxyfen affects neonatal development and brain structure in rats. Wistar rat pups were divided in three experimental groups: (1) negative control (CT-)-offspring of rats that drink potable water during pregnancy; (2) pyriproxyfen (PIR)-offspring of rats exposed to Sumilarv® prenatally, a pesticide that has pyriproxyfen as active ingredient; and (3) positive control (CT+)-offspring of rats exposed to an excess of vitamin A prenatally. Only vitamin A treated-pregnant showed lower weight gain, but gestation length was similar among pregnant that received potable water, water containing vitamin A and water containing Sumilarv. In relation to the offspring, PIR group exhibits a delayed front-limb suspension response but performed early the negative geotaxis reflex. On the other hand, CT+ group exhibited lower body weight in the 1st postnatal day, delayed audio startle response, but performed early the eyelids opening and hindlimb placing response. A reduction in the maximum brain width was observed both in PIR and CT+ groups, but a reduction in the number of neurons in the M1 cortex was showed only in CT+ group. The number of glial cells in this brain area was similar between the three experimental groups studied. Although prenatal exposure to pyriproxyfen did not alter neonatal milestones in the same way as vitamin A in excess, both substances caused a reduction in the maximum width of the brain, suggesting that this pesticide can produce neurotoxic effects during the embryonic period.

Loss of Elp1 in cerebellar granule cell progenitors models ataxia phenotype of Familial Dysautonomia

Familial Dysautonomia (FD) is an autosomal recessive disorder caused by a splice site mutation in the gene ELP1, which disproportionally affects neurons. While classically characterized by deficits in sensory and autonomic neurons, neuronal defects in the central nervous system have also been described. Although ELP1 expression remains high in the normal developing and adult cerebellum, its role in cerebellar development is unknown. To explore the role of Elp1 in the cerebellum, we knocked out Elp1 in cerebellar granule cell progenitors (GCPs) and examined the outcome on animal behavior and cellular composition. We found that GCP-specific conditional knockout of Elp1 (Elp1cKO) resulted in ataxia by 8 weeks of age. Cellular characterization showed that the animals had smaller cerebella with fewer granule cells. This defect was already apparent as early as 7 days after birth, when Elp1cKO animals also had fewer mitotic GCPs and shorter Purkinje dendrites. Through molecular characterization, we found that loss of Elp1 was associated with an increase in apoptotic cell death and cell stress pathways in GCPs. Our study demonstrates the importance of ELP1 in the developing cerebellum, and suggests that loss of Elp1 in the GC lineage may also play a role in the progressive ataxia phenotypes of FD patients.

Protective role of the ginsenoside Rg1 against methimazole-induced gestational hypothyroidism on reflexive behaviors, conditioned fear and cortical antioxidant levels in mice offspring

Ginsenoside Rg1(Rg1), a monomer of a tetracyclic triterpenoid derivative, possesses diverse medicinal properties attributed to its unique chemical structure and may have beneficial effects on fetal development. This study aimed to investigate the protective effects of prenatal exposure to Rg1 against Methimazole-induced gestational hypothyroidism on reflexive behaviors, conditioned fear, and cortical antioxidant levels in mouse offspring.40 female virgin mice and 12 male NMRI mice were assigned to four groups: group 1 served as the control, group 2 received Methimazole(MMI) at a concentration of 0.02% in their drinking water, group 3 received Rg1(150 mg/kg), and group 4 received both MMI and Rg1.Groups of 2-4 were administered the substances from days 1-9 of gestation. After delivery, pups were selected, and reflexive motor behaviors and conditioned fear were assessed. Additionally, levels of brain tissue catalase(CAT), malondialdehyde(MDA), superoxide dismutase(SOD), and glutathione peroxidase(GPx) levels were measured. Furthermore, postpartum immobility time in the forced swimming test (FST), tail suspension test (TST), and the number of squares crossed in the open field test (OFT)were determined. The results demonstrated that maternal exposure to Rg1 improved ambulation score, hind-limb suspension score, grip strength, front-limb suspension, hind-limb foot angle, negative geotaxis, surface righting, and conditioned fear in hypothyroidism-induced offspring(P<0.05). Rg1 decreased immobility time in the FST, and TST, and increased the number of squares crossed in the OFT in postpartum hypothyroidism-induced mice(P<0.05). Moreover, Rg1 reduced brain tissue MDA levels and increased brain tissue CAT, SOD, and GPx levels in mice and their offspring(P<0.05). These findings indicate that Rg1 mitigated postpartum depression in mice and improved reflexive motor behaviors in their pups.

GABAergic/Glycinergic and Glutamatergic Neurons Mediate Distinct Neurodevelopmental Phenotypes of STXBP1 Encephalopathy

An increasing number of pathogenic variants in presynaptic proteins involved in the synaptic vesicle cycle are being discovered in neurodevelopmental disorders. The clinical features of these synaptic vesicle cycle disorders are diverse, but the most prevalent phenotypes include intellectual disability, epilepsy, movement disorders, cerebral visual impairment, and psychiatric symptoms ( Verhage and Sørensen, 2020; Bonnycastle et al., 2021; John et al., 2021; Melland et al., 2021). Among this growing list of synaptic vesicle cycle disorders, the most frequent is STXBP1 encephalopathy caused by de novo heterozygous pathogenic variants in syntaxin-binding protein 1 (STXBP1, also known as MUNC18-1; Verhage and Sørensen, 2020; John et al., 2021). STXBP1 is an essential protein for presynaptic neurotransmitter release. Its haploinsufficiency is the main disease mechanism and impairs both excitatory and inhibitory neurotransmitter release. However, the disease pathogenesis and cellular origins of the broad spectrum of neurological phenotypes are poorly understood. Here we generate cell type-specific Stxbp1 haploinsufficient male and female mice and show that Stxbp1 haploinsufficiency in GABAergic/glycinergic neurons causes developmental delay, epilepsy, and motor, cognitive, and psychiatric deficits, recapitulating majority of the phenotypes observed in the constitutive Stxbp1 haploinsufficient mice and STXBP1 encephalopathy. In contrast, Stxbp1 haploinsufficiency in glutamatergic neurons results in a small subset of cognitive and seizure phenotypes distinct from those caused by Stxbp1 haploinsufficiency in GABAergic/glycinergic neurons. Thus, the contrasting roles of excitatory and inhibitory signaling reveal GABAergic/glycinergic dysfunction as a key disease mechanism of STXBP1 encephalopathy and suggest the possibility to selectively modulate disease phenotypes by targeting specific neurotransmitter systems.

Long-lasting developmental effects in rat offspring after maternal exposure to acetamiprid in the drinking water during gestation

Neonicotinoids (NNTs) are a class of insecticides proposed to be safe for pest control in urban, suburban, and agricultural applications. However, little is known about their developmental effects after repeated low-dose exposures during gestation. Here, we tested a dose considered subthreshold for maternal toxicity in rats (6 mg/kg/day) by assessing several morphological, biochemical, and neurobehavioral features in preterm fetuses and developing pups after maternal administration of the NTT acetamiprid (ACP) dissolved in the drinking water during gestational days (GD) 2-19. The exploratory evaluation included monitoring maternal body weight gain, fetal viability, body weight and sex ratio, cephalic length, neonatal body weight and sex ratio, metabolic enzymes in the placenta, maternal blood and fetal liver, and anogenital distance and surface righting response during infancy. We also used the circling training test to study the integrity of the associative-spatial-motor response in adolescence. Results showed no consistent findings indicating maternal, reproductive or developmental toxicity. However, we found ACP effects on maternal body weight gain, placental butyrylcholinesterase activity, and neurobehavioral responses, suggestive of a mild toxic action. Thus, our study showed a trend for developmental susceptibility at a dose so far considered subtoxic. Although the ACP concentration in environmental samples of surface water and groundwater has been mostly reported to be much lower than that used in our study, our results suggest that the ACP point of departure used in current guidelines aimed to prevent developmental effects may need to be verified by complementary sensitive multiple-endpoint testing in the offspring.

Suppression of progesterone by influenza A virus mediates adverse maternal and fetal outcomes in mice

Influenza A virus infection during pregnancy can cause adverse maternal and fetal outcomes but the mechanism responsible remains elusive. Infection of outbred mice with 2009 H1N1 at embryonic day (E) 10 resulted in significant maternal morbidity, placental tissue damage and inflammation, fetal growth restriction, and developmental delays that lasted through weaning. Restriction of pulmonary virus replication was not inhibited during pregnancy, but infected dams had suppressed circulating and placental progesterone (P4) concentrations that were caused by H1N1-induced upregulation of pulmonary cyclooxygenase (COX)-1-, but not COX-2-, dependent synthesis and secretion of prostaglandin (PG) F2α. Treatment with 17-α-hydroxyprogesterone caproate (17-OHPC), a synthetic progestin that is safe to use in pregnancy, ameliorated the adverse maternal and fetal outcomes from H1N1 infection and prevented placental cell death and inflammation. These findings highlight the therapeutic potential of progestin treatments for influenza during pregnancy.IMPORTANCEPregnant individuals are at risk of severe outcomes from both seasonal and pandemic influenza A viruses. Influenza infection during pregnancy is associated with adverse fetal outcomes at birth and adverse consequences for offspring into adulthood. When outbred dams, with semi-allogenic fetuses, were infected with 2009 H1N1, in addition to pulmonary virus replication, lung damage, and inflammation, the placenta showed evidence of transient cell death and inflammation that was mediated by increased activity along the arachidonic acid pathway leading to suppression of circulating progesterone. Placental damage and suppressed progesterone were associated with detrimental effects on perinatal growth and developmental delays in offspring. Treatment of H1N1-infected pregnant mice with 17-OHPC, a synthetic progestin treatment that is safe to use in pregnancy, prevented placental damage and inflammation and adverse fetal outcomes. This novel therapeutic option for the treatment of influenza during pregnancy should be explored clinically.

MicroRNA-124 negatively regulates STAT3 to alleviate hypoxic-ischemic brain damage by inhibiting oxidative stress

MicroRNA-124 (miR-124) is implicated in various neurological diseases; however, its significance in hypoxic-ischaemic brain damage (HIBD) remains unclear. This study aimed to elucidate the underlying pathophysiological mechanisms of miR-124 in HIBD. In our study performed on oxygen-glucose deprivation followed by reperfusion (OGD)/R-induced primary cortical neurons, a substantial reduction in miR-124 was observed. Furthermore, the upregulation of miR-124 significantly mitigated oxidative stress, apoptosis, and mitochondrial impairment. We demonstrated that miR-124 interacts with the signal transducer and activator of transcription 3 (STAT3) to exert its biological function using the dual-luciferase reporter gene assay. As the duration of OGD increased, miR-124 exhibited a negative correlation with STAT3. STAT3 overexpression notably attenuated the protective effects of miR-124 mimics, while knockdown of STAT3 reversed the adverse effects of the miR-124 inhibitor. Subsequently, we conducted an HIBD model in rats. In vivo experiments, miR-124 overexpression attenuated cerebral infarction volume, cerebral edema, apoptosis, oxidative stress, and improved neurological function recovery in HIBD rats. In summary, the neuroprotective effects of the miR-124/STAT3 axis were confirmed in the HIBD model. MiR-124 may serve as a potential biomarker with significant therapeutic implications for HIBD.

Resveratrol alleviates perinatal methylmercury-induced neurobehavioral impairments by modulating the gut microbiota composition and neurotransmitter disturbances

Methylmercury (MeHg), a potent neurotoxic substance, causes adverse health outcomes by modulating metabolites through altered gut microbiota patterns. Among the many metabolites, neurotransmitters play a particularly important role in the nervous system and behavior. Resveratrol (RSV) has been investigated as an antiaging, antioxidant, anti-inflammatory, and neuroprotective agent. The current study evaluated that RSV is protective of neurodevelopmental toxicity induced by MeHg and further explored the underlying mechanisms. Sprague-Dawley rats were treated with 1.2 mg/kg/d of MeHg, and the effects were evaluated after supplementation with RSV (20 mg/kg/d). The results indicated that MeHg had adverse effects on early neurodevelopmental indicators in the experimental group offspring as compared to control pups. Interestingly, RSV significantly improved the MeHg-induced delays in the neurobehavioral reflexes and reduced the total mercury (THg) concentration in the colons of the offspring rats. In agreement, RSV administration improved the gut microbiota diversity and structure by increasing the abundance of probiotics and upregulating the expression of tight junction proteins. It also ameliorated the MeHg-induced abnormalities in the expression profiles of neurotransmitters. Furthermore, eight key bacteria that were strongly linked with the neurotransmitters and neuroreflex parameters were identified. Taken together, these results demonstrate that RSV treatment effectively reduces the occurrence of neurodevelopmental toxicity caused by perinatal MeHg exposure by modulating the intestinal flora and neurotransmitter metabolism. These findings provide a new therapeutic approach for treating MeHg-induced neurotoxicity. The cover image is based on the Research Article Resveratrol alleviates perinatal methylmercury-induced neurobehavioral impairments by modulating the gut microbiota composition and neurotransmitter disturbances by Fang Chen et al., https://doi.org/10.1002/tox.23973.

Lipopolysaccharide impairs neurodevelopment and induces changes in astroglial reactivity, antioxidant defenses and bioenergetics in the cerebral cortex of neonatal rats

Neonates have an immature immune system, which increases their vulnerability to infectious agents and inflammatory insults. The administration of the immunostimulatory agent lipopolysaccharide (LPS) has been shown to induce the expression of pro-inflammatory cytokines and cause behavior alterations in rodents at different ages. However, the effects of LPS administration during the neonatal period and its consequences during immune system maturation remain to be elucidated. We showed here that a single intraperitoneal administration of LPS in rats on postnatal day (PND) 7 caused early and variable alterations in TNF-α, S100B and GFAP levels in the cerebral cortex, CSF and serum of the animals, indicating long-term induction of neuroinflammation and astroglial reactivity. However, on PND 21, only GFAP levels were increased by LPS. Additionally, LPS induced oxidative stress and altered energy metabolism enzymes in the cerebral cortex on PND 21, and caused neurodevelopment impairment over time. These data suggest that neuroinflammation induction during the neonatal period induces glial reactivity, oxidative stress and bioenergetic disruption that may lead to neurodevelopment impairment and cognitive deficit in adult life.

Altered Developmental Trajectory in Male and Female Rats in a Prenatal Valproic Acid Exposure Model of Autism Spectrum Disorder

Early motor and sensory developmental delays precede Autism Spectrum Disorder (ASD) diagnosis and may serve as early indicators of ASD. The literature on sensorimotor development in animal models is sparse, male centered, and has mixed findings. We characterized early development in a prenatal valproic acid (VPA) model of ASD and found sex-specific developmental delays in VPA rats. We created a developmental composite score combining 15 test readouts, yielding a reliable gestalt measure spanning physical, sensory, and motor development, that effectively discriminated between VPA and control groups. Considering the heterogeneity in ASD phenotype, the developmental composite offers a robust metric that can enable comparison across different animal models of ASD and can serve as an outcome measure for early intervention studies.

Mbnl2 loss alters novel context processing and impairs object recognition memory

Patients with myotonic dystrophy type I (DM1) demonstrate visuospatial dysfunction and impaired performance in tasks requiring recognition or memory of figures and objects. In DM1, CUG expansion RNAs inactivate the muscleblind-like (MBNL) proteins. We show that constitutive Mbnl2 inactivation in Mbnl2ΔE2/ΔE2 mice selectively impairs object recognition memory in the novel object recognition test. When exploring the context of a novel arena in which the objects are later encountered, the Mbnl2ΔE2/ΔE2 dorsal hippocampus responds with a lack of enrichment for learning and memory-related pathways, mounting instead transcriptome alterations predicted to impair growth and neuron viability. In Mbnl2ΔE2/ΔE2 mice, saturation effects may prevent deployment of a functionally relevant transcriptome response during novel context exploration. Post-novel context exploration alterations in genes implicated in tauopathy and dementia are observed in the Mbnl2ΔE2/ΔE2 dorsal hippocampus. Thus, MBNL2 inactivation in patients with DM1 may alter novel context processing in the dorsal hippocampus and impair object recognition memory.

L-2-Hydroxyglutaric Acid Administration to Neonatal Rats Elicits Marked Neurochemical Alterations and Long-Term Neurobehavioral Disabilities Mediated by Oxidative Stress

L-2-Hydroxyglutaric aciduria (L-2-HGA) is an inherited neurometabolic disorder caused by deficient activity of L-2-hydroxyglutarate dehydrogenase. L-2-Hydroxyglutaric acid (L-2-HG) accumulation in the brain and biological fluids is the biochemical hallmark of this disease. Patients present exclusively neurological symptoms and brain abnormalities, particularly in the cerebral cortex, basal ganglia, and cerebellum. Since the pathogenesis of this disorder is still poorly established, we investigated the short-lived effects of an intracerebroventricular injection of L-2-HG to neonatal rats on redox homeostasis in the cerebellum, which is mostly affected in this disorder. We also determined immunohistochemical landmarks of neuronal viability (NeuN), astrogliosis (S100B and GFAP), microglia activation (Iba1), and myelination (MBP and CNPase) in the cerebral cortex and striatum following L-2-HG administration. Finally, the neuromotor development and cognitive abilities were examined. L-2-HG elicited oxidative stress in the cerebellum 6 h after its injection, which was verified by increased reactive oxygen species production, lipid oxidative damage, and altered antioxidant defenses (decreased concentrations of reduced glutathione and increased glutathione peroxidase and superoxide dismutase activities). L-2-HG also decreased the content of NeuN, MBP, and CNPase, and increased S100B, GFAP, and Iba1 in the cerebral cortex and striatum at postnatal days 15 and 75, implying long-standing neuronal loss, demyelination, astrocyte reactivity, and increased inflammatory response, respectively. Finally, L-2-HG administration caused a delay in neuromotor development and a deficit of cognition in adult animals. Importantly, the antioxidant melatonin prevented L-2-HG-induced deleterious neurochemical, immunohistochemical, and behavioral effects, indicating that oxidative stress may be central to the pathogenesis of brain damage in L-2-HGA.

The loop diuretic torasemide but not azosemide potentiates the anti-seizure and disease-modifying effects of midazolam in a rat model of birth asphyxia

Loop diuretics such as furosemide and bumetanide, which act by inhibiting the Na-K-2Cl cotransporter NKCC2 at the thick ascending limb of the loop of Henle, have been shown to exert anti-seizure effects. However, the exact mechanism of this effect is not known. For bumetanide, it has been suggested that inhibition of the NKCC isoform NKCC1 in the membrane of brain neurons may be involved; however, NKCC1 is expressed by virtually all cell types in the brain, which makes any specific targeting of neuronal NKCC1 by bumetanide impossible. In addition, bumetanide only poorly penetrates the brain. We have previously shown that loop diuretics azosemide and torasemide also potently inhibit NKCC1. In contrast to bumetanide and furosemide, azosemide and torasemide lack a carboxylic group, which should allow them to better penetrate through biomembranes by passive diffusion. Because of the urgent medical need to develop new treatments for neonatal seizures and their adverse outcome, we evaluated the effects of azosemide and torasemide, administered alone or in combination with phenobarbital or midazolam, in a rat model of birth asphyxia and neonatal seizures. Neither diuretic suppressed the seizures when administered alone but torasemide potentiated the anti-seizure effect of midazolam. Brain levels of torasemide were below those needed to inhibit NKCC1. In addition to suppressing seizures, the combination of torasemide and midazolam, but not midazolam alone, prevented the cognitive impairment of the post-asphyxial rats at 3 months after asphyxia. Furthermore, aberrant mossy fiber sprouting in the hippocampus was more effectively prevented by the combination. We assume that either an effect on NKCC1 at the blood-brain barrier and/or cells in the periphery or the NKCC2-mediated diuretic effect of torasemide are involved in the present findings. Our data suggest that torasemide may be a useful option for improving the treatment of neonatal seizures and their adverse outcome.

Sensorimotor development of male and female rats subjected to neonatal anoxia

Neonatal hypoxic-ischemic encephalopathy (HIE) is one of the most important reasons for morbidity and mortality in term-born infants. HIE impacts early somatic, neurological, and motor development including social. To illustrate the damages in the sensorimotor system, an adapted and validated model of neonatal anoxia is used. This study evaluated the sex differences in Wistar rats, neurological reflex, and motor development at the suckling period. Short- and long-term impairments associated with sex differences were observed. In general, anoxic males were more affected in comparison to their control group and to anoxic females. Long-lasting effects of the injury in adolescent rats predominately affected males. Similar to previous studies, we also found a decrease in the number of the substantia nigra cells in both sexes, compared to their control. So far, the results indicate that HIE caused neurobehavioral alterations and asymmetrical motor behavior with brain damage, possibly related to cognitive impairments previously observed at adolescence. These alterations may represent a useful endpoint for studying the efficacy of potential strategies that may improve the developmental consequences of a perinatal asphyxia insult in humans.

Therapeutic hypothermia for the treatment of neonatal hypoxia-ischemia: sex-dependent modulation of reactive astrogliosis

Therapeutic hypothermia (TH) is the standard treatment for neonatal hypoxia-ischemia (HI) with a time window limited up to 6 h post injury. However, influence of sexual dimorphism in the therapeutic window for TH has not yet been elucidated in animal models of HI. Therefore, the aim of this study was to investigate the most effective time window to start TH in male and female rats submitted to neonatal HI. Wistar rats (P7) were divided into the following groups: NAÏVE and SHAM (control groups), HI (submitted to HI) and TH (submitted to HI and TH; 32ºC for 5 h). TH was started at 2 h (TH-2 h group), 4 h (TH-4 h group), or 6 h (TH-6 h group) after HI. At P14, animals were subjected to behavioural tests, volume of lesion and reactive astrogliosis assessments. Male and female rats from the TH-2 h group showed reduction in the latency of behavioral tests, and decrease in volume of lesion and intensity of GFAP immunofluorescence. TH-2 h females also showed reduction of degenerative cells and morphological changes in astrocytes. Interestingly, females from the TH-6 h group showed an increase in volume of lesion and in number of degenerative hippocampal cells, associated with worse behavioral performance. Together, these results indicate that TH neuroprotection is time- and sex-dependent. Moreover, TH started later (6 h) can worsen volume of brain lesion in females. These data indicate the need to develop specific therapeutic protocols for each sex and reinforce the importance of early onset of the hypothermic treatment.

Histone Deacetylase 3 Inhibitor Alleviates Cerebellar Defects in Perinatal Hypothyroid Mice by Stimulating Histone Acetylation and Transcription at Thyroid Hormone-Responsive Gene Loci

Perinatal hypothyroidism impairs cerebellar organogenesis and results in motor coordination defects. The thyroid hormone receptor binds to corepressor complexes containing histone deacetylase (HDAC) 3 in the absence of ligands and acts as a transcriptional repressor. Although histone acetylation status is strongly correlated with transcriptional regulation, its role in cerebellar development remains largely unknown. We aimed to study whether the cerebellar developmental defects induced by perinatal hypothyroidism can be rescued by treatment with a specific HDAC3 inhibitor, RGFP966. Motor coordination was analyzed using three behavioral tests. The cerebella were subjected to RT-qPCR and chromatin immunoprecipitation assays for acetylated histone H3. The treatment with RGFP966 partially reversed the cerebellar morphological defects in perinatal hypothyroid mice. These findings were associated with the alleviation of motor coordination defects in these mice. In addition, the RGFP966 administration increased the mRNA levels of cerebellar thyroid hormone-responsive genes. These increases were accompanied by augmented histone acetylation status at these gene loci. These findings indicate that HDAC3 plays an important role in the cerebellar developmental defects induced by perinatal hypothyroidism. The HDAC3 inhibitor might serve as a novel therapeutic agent for hypothyroidism-induced cerebellar defects by acetylating histone tails and stimulating transcription at thyroid hormone-responsive gene loci.

Neuromotor Development in the Shank3 Mouse Model of Autism Spectrum Disorder

Although autism spectrum disorder (ASD) is mainly characterized by developmental delay in social and communication skills, it has been shown that neuromotor deficits are an early component of ASD. The neuromotor development of B6.129-Shank3tm2Gfng/J (Shank3B−/−) mice as an animal model of autism has not been analyzed yet. The aim of this study was to compare the early neuromotor development of Shank3B−/− to wild-type mice. The mice underwent a multitude of neurodevelopmental tests and observations from postnatal day 1 (PND = 1) to weaning. Shank3B−/− mice opened their eyes later than their wild-type litter mates (p < 0.01). Shank3B−/− mice were also slower in the negative geotaxis test from PND = 13 to PND = 16 (p < 0.001) in both sexes. The results of this study indicate neurodevelopmental deficits in Shank3B−/− mice. The test is partially dependent on truncal motor control, and these lines of evidence suggest a phenotype of developmental hypotonia, which corresponds with the phenotypes seen in patients with Phelan-McDermid Syndrome. There was no observable effect of sex in any of the tests. There were no observed differences in upper and lower incisor eruption, ear unfolding, air righting, surface righting and ear twitch reflexes. Further studies should prove whether the delay in neuromotor development is linked to social or communication deficits, and thus, whether it may serve as an early indicator of autistic-like phenotype in mice.

Early Life Exposure to Tumor Necrosis Factor Induces Precocious Sensorimotor Reflexes Acquisition and Increases Locomotor Activity During Mouse Postnatal Development

Inflammation appears as a cardinal mediator of the deleterious effect of early life stress exposure on neurodevelopment. More generally, immune activation during the perinatal period, and most importantly elevations of pro-inflammatory cytokines levels could contribute to psychopathology and neurological deficits later in life. Cytokines are also required for normal brain function in homeostatic conditions and play a role in neurodevelopmental processes. Despite these latter studies, whether pro-inflammatory cytokines such as Tumor Necrosis Factor (TNF) impact neurodevelopmental trajectories and behavior during the immediate postnatal period remains to be elucidated. To address this issue, we have injected mouse pups daily with recombinant TNF from postnatal day (P)1 to P5. This yielded a robust increase in peripheral and central TNF at P5, and also an increase of additional pro-inflammatory cytokines. Compared to control pups injected with saline, mice injected with TNF acquired the righting and the acoustic startle reflexes more rapidly and exhibited increased locomotor activity 2 weeks after birth. Our results extend previous work restricted to adult behaviors and support the notion that cytokines, and notably TNF, modulate early neurodevelopmental trajectories.

Quantification of Behavioral Deficits in Developing Mice With Dystonic Behaviors

Converging evidence from structural imaging studies in patients, the function of dystonia-causing genes, and the comorbidity of neuronal and behavioral defects all suggest that pediatric-onset dystonia is a neurodevelopmental disorder. However, to fully appreciate the contribution of altered development to dystonia, a mechanistic understanding of how networks become dysfunctional is required for early-onset dystonia. One current hurdle is that many dystonia animal models are ideally suited for studying adult phenotypes, as the neurodevelopmental features can be subtle or are complicated by broad developmental deficits. Furthermore, most assays that are used to measure dystonia are not suited for developing postnatal mice. Here, we characterize the early-onset dystonia in Ptf1a ^Cre ;Vglut2 ^fl/fl mice, which is caused by the absence of neurotransmission from inferior olive neurons onto cerebellar Purkinje cells. We investigate motor control with two paradigms that examine how altered neural function impacts key neurodevelopmental milestones seen in postnatal pups (postnatal day 7-11). We find that Ptf1a ^Cre ;Vglut2 ^fl/fl mice have poor performance on the negative geotaxis assay and the surface righting reflex. Interestingly, we also find that Ptf1a ^Cre ;Vglut2 ^fl/fl mice make fewer ultrasonic calls when socially isolated from their nests. Ultrasonic calls are often impaired in rodent models of autism spectrum disorders, a condition that can be comorbid with dystonia. Together, we show that these assays can serve as useful quantitative tools for investigating how neural dysfunction during development influences neonatal behaviors in a dystonia mouse model. Our data implicate a shared cerebellar circuit mechanism underlying dystonia-related motor signs and social impairments in mice.

Constitutive deficiency of the neurogenic hippocampal modulator AP2γ promotes anxiety-like behavior and cumulative memory deficits in mice from juvenile to adult periods

The transcription factor activating protein two gamma (AP2γ) is an important regulator of neurogenesis both during embryonic development as well as in the postnatal brain, but its role for neurophysiology and behavior at distinct postnatal periods is still unclear. In this work, we explored the neurogenic, behavioral, and functional impact of a constitutive and heterozygous AP2γ deletion in mice from early postnatal development until adulthood. AP2γ deficiency promotes downregulation of hippocampal glutamatergic neurogenesis, altering the ontogeny of emotional and memory behaviors associated with hippocampus formation. The impairments induced by AP2γ constitutive deletion since early development leads to an anxious-like phenotype and memory impairments as early as the juvenile phase. These behavioral impairments either persist from the juvenile phase to adulthood or emerge in adult mice with deficits in behavioral flexibility and object location recognition. Collectively, we observed a progressive and cumulative impact of constitutive AP2γ deficiency on the hippocampal glutamatergic neurogenic process, as well as alterations on limbic-cortical connectivity, together with functional behavioral impairments. The results herein presented demonstrate the modulatory role exerted by the AP2γ transcription factor and the relevance of hippocampal neurogenesis in the development of emotional states and memory processes.

Developmental and Reproductive Outcomes in Male Rats Exposed to Triclosan: Two-Generation Study

Triclosan (TCS) is a phenolic compound with broad-spectrum antimicrobial action that has been incorporated into a variety of personal care products and other industry segments such as toys, textiles, and plastics. Due to its widespread use, TCS and its derivatives have been detected in several environmental compartments, with potential bioaccumulation and persistence. Indeed, some studies have demonstrated that TCS may act as a potential endocrine disruptor for the reproductive system. In the current study, we are reporting on the results obtained for male rats after a two-generation reproduction toxicity study conducted with TCS. Female and male Wistar rats were treated daily by gavage with TCS at doses of 0.8, 2.4, and 8.0 mg/kg/day or corn oil (control group) over 10 weeks (F0) and over 14 weeks (F1) before mating and then throughout mating, until weaning F2 generations, respectively. TCS exposure decreased sperm viability and motility of F1 rats at the dose of 2.4 mg/kg. The effects of TCS on sperm quality may be related to the exposure window, which includes the programming of reproductive cells that occurs during fetal/neonatal development.

SHIRPA as a Neurological Screening Battery in Mice

The SmithKline, Harwell, Imperial College, Royal Hospital, Phenotype Assessment (SHIRPA) is a rapid battery of tests comprising 42 measurements of motor activity, coordination, postural control, muscle tone, autonomic functions, and emotional reactivity, as well as reflexes dependent on visual, auditory, and tactile modalities. Individual scores in SHIRPA are sensitive in detecting phenotypes of several experimental models of neural disease, especially cerebellar degeneration and Alzheimer disease, and combined subscores have been useful in estimating the impact of vascular anomalies and exposure to infectious agents. In cerebellar degeneration, weak forelimb grip, impaired wire maneuver and air righting, and negative geotaxis appear as prevalent features. Most of the measures in the battery are susceptible to change after gene modifications or physiological alterations. SHIRPA can be used both in adult mice and mice in the preweaning period to screen for sensorimotor function and emotional reactivity, not selective attention or memory. © 2021 Wiley Periodicals LLC Basic Protocol: Step-by-step procedure for SHIRPA.

Lactobacillus reuteri in its biofilm state promotes neurodevelopment after experimental necrotizing enterocolitis in rats

Necrotizing enterocolitis (NEC) is a devastating disease affecting premature newborns with no known cure. Up to half of survivors subsequently exhibit cognitive impairment and neurodevelopmental defects. We created a novel probiotics delivery system in which the probiotic Lactobacillus reuteri (Lr) was induced to form a biofilm [Lr (biofilm)] by incubation with dextranomer microspheres loaded with maltose (Lr-DM-maltose). We have previously demonstrated that a single dose of the probiotic Lr administered in its biofilm state significantly reduces the incidence of NEC and decreases inflammatory cytokine production in an animal model of the disease. The aim of our current study was to determine whether a single dose of the probiotic Lr administered in its biofilm state protects the brain after experimental NEC. We found that rat pups exposed to NEC reached developmental milestones significantly slower than breast fed pups, with mild improvement with Lr (biofilm) treatment. Exposure to NEC had a negative effect on cognitive behavior, which was prevented by Lr (biofilm) treatment. Lr administration also reduced anxiety-like behavior in NEC-exposed rats. The behavioral effects of NEC were associated with increased numbers of activated microglia, decreased myelin basic protein (MBP), and decreased neurotrophic gene expression, which were prevented by administration of Lr (biofilm). Our data indicate early enteral treatment with Lr in its biofilm state prevented the deleterious effects of NEC on developmental impairments.

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Early treatment with Lr in its biofilm state improves cognitive function in pups that survive experimental NEC.

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Lr in its biofilm state reduces microglia activation and MBP loss, and maintains memory and learning-related gene expression.

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Administration of Lr in its biofilm state protects the brain, as well as intestines, during experimental NEC.

Trajectories of Mother-Infant Communication: An Experiential Measure of the Impacts of Early Life Adversity

Caretaking stability in the early life environment supports neurobehavioral development, while instability and neglect constitute adverse environments that can alter maturational processes. Research in humans suggests that different types of early life adversity (ELA) can have differential effects on caretaker relationships and later cognitive and social development; however, identifying mechanistic underpinnings will require animal models with translational validity. Two common rodent models, maternal separation (MS) and limited bedding (LB), influence the mother-infant relationship during a critical window of development. We hypothesized that these paradigms may affect the development of communication strategies on the part of the pup. Ultrasonic vocalizations (USVs) are a care-eliciting mechanism and ethologically relevant response to stressors in the rat pup. USV emission rates and acoustic parameters change throughout early development, presenting the opportunity to define developmental milestones in USVs that would reflect neurobehavioral aberrations if disrupted. This study investigated the effects of MS or LB on the dam-pup relationship by quantifying pup USVs, maternal behavior, and the relationship between the two. First, we used a generalized additive model approach to establish typical developmental trajectories of USV acoustic properties and determine windows of change in MS or LB rearing. Additionally, we quantified maternal behaviors and the predictability of maternal care sequences using an entropy rate calculation. MS and LB each shifted the developmental trajectories of USV acoustic parameters and call types in a sex-specific manner. MS more often impacted male USVs, while LB impacted female USVs. MS dams spent more time passive nursing, and LB dams spent more time on the nest. The predictability of maternal care was associated with the rate of USV emissions exclusively in females. Taken together, findings demonstrate sex- and model-specific effects of rearing environments on a novel developmental trajectory involving the mother-infant relationship, facilitating the translation of animal ELA paradigms to assess later-life consequences.

On the Digital Psychopharmacology of Valproic Acid in Mice

Antiepileptic drugs (AEDs) require daily ingestion for maximal seizure prophylaxis. Adverse psychiatric consequences of AEDs present as: (i) reversible changes in mood, anxiety, anger and/or irritability that often necessitate drug discontinuation, and (ii) autism and/or cognitive/psychomotor delays following fetal exposure. Technical advances in quantifying naturalistic rodent behaviors may provide sensitive preclinical estimates of AED psychiatric tolerability and neuropsychiatric teratogenicity. In this study, we applied instrumented home-cage monitoring to assess how valproic acid (VPA, dissolved in sweetened drinking water) alters home-cage behavior in adult C57BL/6J mice and in the adult offspring of VPA-exposed breeder pairs. Through a pup open field assay, we also examined how prenatal VPA exposure impacts early spontaneous exploratory behavior. At 500-600 mg/kg/d, chronic VPA produced hyperphagia and increased wheel-running without impacting sleep, activity and measures of risk aversion. When applied to breeder pairs of mice throughout gestation, VPA prolonged the latency to viable litters without affecting litter size. Two-weeks old VPA-exposed pups displayed open field hypoactivity without alterations in thigmotaxis. As adults, prenatal VPA-exposed mice displayed active state fragmentation, hypophagia and increased wheel running, together with subtle alterations in home-cage dyadic behavior. Together, these data illustrate how automated home-cage assessments of spontaneous behavior capture an ethologically centered psychopharmacological profile of enterally administered VPA that is aligned with human clinical experience. By characterizing the effects of pangestational VPA exposure, we discover novel murine expressions of pervasive neurodevelopment. Incorporating such rigorous assessments of psychological tolerability may inform the design of future AEDs with improved neuropsychiatric safety profiles, both for patients and their offspring.

Firing activity of locus coeruleus noradrenergic neurons decreases in necdin-deficient mice, an animal model of Prader-Willi syndrome

BACKGROUND

Prader-Willi syndrome (PWS) is a neurodevelopmental disorder characterized by multiple respiratory, cognitive, endocrine, and behavioral symptoms, such as central apnea, intellectual disabilities, exaggerated stress responses, and temper tantrums. The locus coeruleus noradrenergic system (LC-NE) modulates a diverse range of behaviors, including arousal, learning, pain modulation, and stress-induced negative affective states, which are possibly correlated with the pathogenesis of PWS phenotypes. Therefore, we evaluated the LC-NE neuronal activity of necdin-deficient mice, an animal model of PWS.

METHODS

Heterozygous necdin-deficient mice (B6.Cg-Ndntm1ky) were bred from wild-type (WT) females to generate WT (+m/+p) and heterozygotes (+m/-p) animals, which were examined of LC-NE neuronal activity, developmental reflexes, and plethysmography.

RESULTS

On slice electrophysiology, LC-NE neurons of Ndntm1ky mice with necdin deficiency showed significantly decreased spontaneous activities and impaired excitability, which was mediated by enhanced A-type voltage-dependent potassium currents. Ndntm1ky mice also exhibited the neonatal phenotypes of PWS, such as hypotonia and blunt respiratory responses to hypercapnia.

CONCLUSIONS

LC-NE neuronal firing activity decreased in necdin-deficient mice, suggesting that LC, the primary source of norepinephrine in the central nervous system, is possibly involved in PWS pathogenesis.

Post-weaning infant-to-mother bonding in nutritionally independent female mice

Infant-parent attachment is highly selective and continues beyond essential care in primates, most prominently in humans, and the quality of this attachment crucially determines cognitive and emotional development of the infant. Altricial rodent species such as mice (Mus musculus) display mutual recognition and communal nursing in wild and laboratory environments, but parental bonding beyond the nursing period has not been reported. We presently demonstrated that socially and nutritionally independent mice still prefer to interact selectively with their mother dam. Furthermore, we observed gender differences in the mother-infant relationship, and showed disruption of this relationship in haploinsufficient Nbea+/- mice, a putative autism model with neuroendocrine dysregulation. To our knowledge, this is the first observation of murine infant-to-mother bonding beyond the nursing period.

Human gestational N-methyl-d-aspartate receptor autoantibodies impair neonatal murine brain function

OBJECTIVE

Maternal autoantibodies are a risk factor for impaired brain development in offspring. Antibodies (ABs) against the NR1 (GluN1) subunit of the N-methyl-d-aspartate receptor (NMDAR) are among the most frequently diagnosed anti-neuronal surface ABs, yet little is known about effects on fetal development during pregnancy.

METHODS

We established a murine model of in utero exposure to human recombinant NR1 and isotype-matched nonreactive control ABs. Pregnant C57BL/6J mice were intraperitoneally injected on embryonic days 13 and 17 each with 240μg of human monoclonal ABs. Offspring were investigated for acute and chronic effects on NMDAR function, brain development, and behavior.

RESULTS

Transferred NR1 ABs enriched in the fetus and bound to synaptic structures in the fetal brain. Density of NMDAR was considerably reduced (up to -49.2%) and electrophysiological properties were altered, reflected by decreased amplitudes of spontaneous excitatory postsynaptic currents in young neonates (-34.4%). NR1 AB-treated animals displayed increased early postnatal mortality (+27.2%), impaired neurodevelopmental reflexes, altered blood pH, and reduced bodyweight. During adolescence and adulthood, animals showed hyperactivity (+27.8% median activity over 14 days), lower anxiety, and impaired sensorimotor gating. NR1 ABs caused long-lasting neuropathological effects also in aged mice (10 months), such as reduced volumes of cerebellum, midbrain, and brainstem.

INTERPRETATION

The data collectively support a model in which asymptomatic mothers can harbor low-level pathogenic human NR1 ABs that are diaplacentally transferred, causing neurotoxic effects on neonatal development. Thus, AB-mediated network changes may represent a potentially treatable neurodevelopmental congenital brain disorder contributing to lifelong neuropsychiatric morbidity in affected children. ANN NEUROL 2019;86:656-670.

Does Age Interfere With Gadolinium Toxicity and Presence in Brain and Bone Tissues?: A Comparative Gadoterate Versus Gadodiamide Study in Juvenile and Adult Rats

OBJECTIVES

The main objective of the study was to assess the effect of age on target tissue total gadolinium (Gd) retention after repeated administration of gadodiamide (linear) or gadoterate (macrocyclic) Gd-based contrast agent (GBCA) in rats. The secondary objective was to assess the potential developmental and long-term consequences of GBCA administration during neonatal and juvenile periods.

MATERIALS AND METHODS

A total of 20 equivalent human clinical doses (cumulated dose, 12 mmol Gd/kg) of either gadoterate or gadodiamide were administered concurrently by the intravenous route to healthy adult and juvenile rats. Saline was administered to juvenile rats forming the control group. In juvenile rats, the doses were administered from postnatal day 12, that is, once the blood-brain barrier is functional as in humans after birth. The tests were conducted on 5 juvenile rats per sex and per group and on 3 adult animals per sex and per group. T1-weighted magnetic resonance imaging of the cerebellum was performed at 4.7 T during both the treatment and treatment-free periods. Behavioral tests were performed in juvenile rats. Rats were euthanatized at 11 to 12 weeks (ie, approximately 3 months) after the last administration. Total Gd concentrations were measured in plasma, skin, bone, and brain by inductively coupled plasma mass spectrometry. Cerebellum samples from the juvenile rats were characterized by histopathological examination (including immunohistochemistry for glial fibrillary acidic protein or GFAP, and CD68). Lipofuscin pigments were also studied by fluorescence microscopy. All tests were performed blindly on randomized animals.

RESULTS

Transient skin lesions were observed in juvenile rats (5/5 females and 2/4 males) and not in adult rats having received gadodiamide. Persisting (up to completion of the study) T1 hyperintensity in the deep cerebellar nuclei (DCNs) was observed only in gadodiamide-treated rats. Quantitatively, a slightly higher progressive increase in the DCN/brain stem ratio was observed in adult rats compared with juvenile rats, whereas no difference was noted visually. In all tissues, total Gd concentrations were higher (10- to 30-fold higher) in the gadodiamide-treated groups than in the gadoterate groups. No age-related differences were observed except in bone marrow where total Gd concentrations in gadodiamide-treated juvenile rats were higher than those measured in adults and similar to those measured in cortical bone tissue. No significant treatment-related effects were observed in histopathological findings or in development, behavior, and biochemistry parameters. However, in the elevated plus maze test, a trend toward an anxiogenic effect was observed in the gadodiamide group compared with other groups (nonsignificant). Moreover, in the balance beam test, a high number of trials were excluded in the gadodiamide group because rats (mainly males) did not completely cross the beam, which may also reflect an anxiogenic effect.

CONCLUSIONS

No T1 hyperintensity was observed in the DCN after administration of the macrocyclic GBCA gadoterate regardless of age as opposed to administration of the linear GBCA gadodiamide. Repeated administration of gadodiamide in neonatal and juvenile rats resulted in similar total Gd retention in the skin, brain, and bone to that in adult rats with sex having no effect, whereas Gd distribution in bone marrow was influenced by age. Further studies are required to assess the form of the retained Gd and to investigate the potential risks associated with Gd retention in bone marrow in juvenile animals treated with gadodiamide. Regardless of age, total Gd concentration in the brain and bone was 10- to 30-fold higher after administration of gadodiamide compared with gadoterate.

Gene-environment interactions in antisocial behavior are mediated by early-life 5-HT2A receptor activation

The ontogeny of antisocial behavior (ASB) is rooted in complex gene-environment (G×E) interactions. The best-characterized of these interplays occurs between: a) low-activity alleles of the gene encoding monoamine oxidase A (MAOA), the main serotonin-degrading enzyme; and b) child maltreatment. The purpose of this study was to develop the first animal model of this G×E interaction, to help understand the neurobiological mechanisms of ASB and identify novel targets for its therapy. Maoa hypomorphic transgenic mice were exposed to an early-life stress regimen consisting of maternal separation and daily intraperitoneal saline injections and were then compared with their wild-type and non-stressed controls for ASB-related neurobehavioral phenotypes. Maoa hypomorphic mice subjected to stress from postnatal day (PND) 1 through 7 - but not during the second postnatal week - developed overt aggression, social deficits and abnormal stress responses from the fourth week onwards. On PND 8, these mice exhibited low resting heart rate - a well-established premorbid sign of ASB - and a significant and selective up-regulation of serotonin 5-HT_2A receptors in the prefrontal cortex. Notably, both aggression and neonatal bradycardia were rescued by the 5-HT₂ receptor antagonist ketanserin (1-3 mg kg^-1, IP), as well as the selective 5-HT_2A receptor blocker MDL-100,907 (volinanserin, 0.1-0.3 mg kg^-1, IP) throughout the first postnatal week. These findings provide the first evidence of a molecular basis of G×E interactions in ASB and point to early-life 5-HT_2A receptor activation as a key mechanism for the ontogeny of this condition. This article is part of the Special Issue entitled 'The neuropharmacology of social behavior: from bench to bedside'.

Gestational folic acid supplementation does not affects the maternal behavior and the early development of rats submitted to neonatal hypoxia-ischemia but the high supplementation impairs the dam's memory and the Na+, K+ - ATPase activity in the pup's hippocampus

Folic acid (FA) is a B-complex vitamin important to the development of the fetus, being supplemented during pregnancy. Our recent findings showed that gestation supplementation (normal and excess doses) prevented the cognitive deficits and BDNF imbalance in adult rats that were submitted to neonatal hypoxia-ischemia (HI). To better understand this protective effect, the present study aimed to evaluate whether FA supplementation could be related to (1) maternal behavior, memory and Na⁺, K⁺ - ATPase activity in the hippocampus of the dams; (2) on somatic growth, early neurobehavioral development and Na⁺, K⁺ - ATPase activity in the hippocampus of the offspring; and (3) the effects of this supplementation in pups submitted to neonatal HI. Pregnant Wistar rats were divided into three groups, according to the diet they received during gestation: standard diet (SD), supplemented with 2 mg/kg of FA (FA2 - normal dose) and supplemented with 20 mg/kg of FA (FA20 -excessive dose). At the 7^th PND pups were submitted to the Levine-Vannucci model of HI. During weaning the maternal behavior, the somatic growth and the neurobehavior development of pups were assessed. After weaning, the memory of the dams (by the Ox-maze task) and the Na⁺, K⁺ - ATPase activity in the hippocampus of both dams and offspring were evaluated. Considering the dams (1), both doses of FA did not alter the maternal behavior or the Na⁺, K⁺ - ATPase activity in the hippocampus, but a memory deficit was observed in the high FA-supplemented mothers. Considering the offspring (2), both FA doses did not affect the somatic growth or the neurobehavior development, but the FA20 pups had a decreased Na⁺, K⁺ - ATPase activity in the hippocampus. The FA supplementation did not change the parameters evaluated in the HI rats (3) and did not prevent the decreased Na⁺, K⁺ - ATPase activity in the hippocampus of the HI pups. These results indicate that normal FA supplementation dose does not influence the maternal behavior and memory and does not impact on the offspring early development in rats. Further studies are needed to confirm the effects of the high FA supplementation dose in the dams' memory and in the Na⁺, K⁺ - ATPase activity in the hippocampus of the offspring.

Behavioral Phenotyping of an Improved Mouse Model of Phelan-McDermid Syndrome with a Complete Deletion of the Shank3 Gene

Phelan–McDermid syndrome (PMS) is a rare genetic disorder in which one copy of the SHANK3 gene is missing or mutated, leading to a global developmental delay, intellectual disability (ID), and autism. Multiple intragenic promoters and alternatively spliced exons are responsible for the formation of numerous isoforms. Many genetically-modified mouse models of PMS have been generated but most disrupt only some of the isoforms. In contrast, the vast majority of known SHANK3 mutations found in patients involve deletions that disrupt all isoforms. Here, we report the production and thorough behavioral characterization of a new mouse model in which all Shank3 isoforms are disrupted. Domains and tasks examined in adults included measures of general health, neurological reflexes, motor abilities, sensory reactivity, social behavior, repetitive behaviors, cognition and behavioral inflexibility, and anxiety. Our mice are more severely affected than previously published models. While the deficits were typically more pronounced in homozygotes, an intermediate phenotype was observed for heterozygotes in many paradigms. As in other Shank3 mouse models, stereotypies, including increased grooming, were observed. Additionally, sensory alterations were detected in both neonatal and adult mice, and motor behavior was strongly altered, especially in the open field and rotarod locomotor tests. While social behaviors measured with the three-chambered social approach and male-female interaction tests were not strongly impacted, Shank3-deficient mice displayed a strong escape behavior and avoidance of inanimate objects in novel object recognition, repetitive novel object contact, marble burying, and nest building tasks, indicating increased novelty-induced anxiety. Similarly, increased freezing was observed during fear conditioning training and amygdala-dependent cued retrieval. Finally, deficits were observed in both initial training and reversal in the Barnes maze and in contextual fear testing, which are memory tasks involving hippocampal-prefrontal circuits. In contrast, working memory in the Y-maze spontaneous alternation test was not altered. This new mouse model of PMS, engineered to most closely represent human mutations, recapitulates core symptoms of PMS providing improvements for both construct and face validity, compared to previous models.

A practical blueprint to systematically study life-long health consequences of novel medically assisted reproductive treatments

In medicine, safety and efficacy are the two pillars on which the implementation of novel treatments rest. To protect the patient from unnecessary or unsafe treatments, usually, a stringent path of (pre) clinical testing is followed before a treatment is introduced into routine patient care. However, in reproductive medicine several techniques have been clinically introduced without elaborate preclinical studies. Moreover, novel reproductive techniques may harbor safety risks not only for the patients undergoing treatment, but also for the offspring conceived through these techniques. If preclinical (animal) studies were performed, efficacy and functionality the upper hand. When a new medically assisted reproduction (MAR) treatment was proven effective (i.e. if it resulted in live birth) the treatment was often rapidly implemented in the clinic. For IVF, the first study on the long-term health of IVF children was published a decade after its clinical implementation. In more recent years, prospective follow-up studies have been conducted that provided the opportunity to study the health of large groups of children derived from different reproductive techniques. Although such studies have indicated differences between children conceived through MAR and children conceived naturally, results are often difficult to interpret due to the observational nature of these studies (and the associated risk of confounding factors, e.g. subfertility of the parents), differences in definitions of clinical outcome measures, lack of uniformity in assessment protocols and heterogeneity of the underlying reasons for fertility treatment. With more novel MARs waiting at the horizon, there is a need for a framework on how to assess safety of novel reproductive techniques in a preclinical (animal) setting before they are clinically implemented. In this article, we provide a blueprint for preclinical testing of safety and health of offspring generated by novel MARs using a mouse model involving an array of tests that comprise the entire lifespan. We urge scientists to perform the proposed extensive preclinical tests for novel reproductive techniques with the goal to acquire knowledge on efficacy and the possible health effects of to-be implemented reproductive techniques to safeguard quality of novel MARs.

Poly-arginine R18 and R18D (D-enantiomer) peptides reduce infarct volume and improves behavioural outcomes following perinatal hypoxic-ischaemic encephalopathy in the P7 rat

We examined the neuroprotective efficacy of the poly-arginine peptide R18 and its D-enantiomer R18D in a perinatal hypoxic-ischaemic (HI) model in P7 Sprague-Dawley rats. R18 and R18D peptides were administered intraperitoneally at doses of 30, 100, 300 or 1000 nmol/kg immediately after HI (8% O₂/92%N₂ for 2.5 h). The previously characterised neuroprotective JNKI-1-TATD peptide at a dose of 1000 nmol/kg was used as a control. Infarct volume and behavioural outcomes were measured 48 h after HI. For the R18 and R18D doses examined, total infarct volume was reduced by 25.93% to 43.80% (P = 0.038 to < 0.001). By comparison, the JNKI-1-TATD reduced lesion volume by 25.27% (P = 0.073). Moreover, R18 and R18D treatment resulted in significant improvements in behavioural outcomes, while with JNKI-1-TATD there was a trend towards improvement. As an insight into the likely mechanism underlying the effects of R18, R18D and JNKI-1-TATD, the peptides were added to cortical neuronal cultures exposed to glutamic acid excitotoxicity, resulting in up to 89, 100 and 71% neuroprotection, respectively, and a dose dependent inhibition of neuronal calcium influx. The study further confirms the neuroprotective properties of poly-arginine peptides, and suggests a potential therapeutic role for R18 and R18D in the treatment of HIE.

Early-onset behavioral and neurochemical deficits in the genetic mouse model of phenylketonuria

Phenylketonuria (PKU) is one of the most common human inborn errors of metabolism, caused by phenylalanine hydroxylase deficiency, leading to high phenylalanine and low tyrosine levels in blood and brain causing profound cognitive disability, if untreated. Since 1960, population is screened for hyperphenylalaninemia shortly after birth and submitted to early treatment in order to prevent the major manifestations of the disease. However, the dietetic regimen (phenylalanine free diet) is difficult to maintain, and despite the recommendation to a strict and lifelong compliance, up to 60% of adolescents partially or totally abandons the treatment. The development and the study of new treatments continue to be sought, taking advantage of preclinical models, the most used of which is the PAH^enu2 (BTBR ENU2), the genetic murine model of PKU. To date, adult behavioral and neurochemical alterations have been mainly investigated in ENU2 mice, whereas there are no clear indications about the onset of these deficiencies. Here we investigated and report, for the first time, a comprehensive behavioral and neurochemical assay of the developing ENU2 mice. Overall, our findings demonstrate that ENU2 mice are significantly smaller than WT until pnd 24, present a significant delay in the acquisition of tested developmental reflexes, impaired communicative, motor and social skills, and have early reduced biogenic amine levels in several brain areas. Our results extend the understanding of behavioral and cerebral abnormalities in PKU mice, providing instruments to an early preclinical evaluation of the effects of new treatments.

Distinct alterations in motor & reward seeking behavior are dependent on the gestational age of exposure to LPS-induced maternal immune activation

The dopaminergic system is involved in motivation, reward and the associated motor activities. Mesodiencephalic dopaminergic neurons in the ventral tegmental area (VTA) regulate motivation and reward, whereas those in the substantia nigra (SN) are essential for motor control. Defective VTA dopaminergic transmission has been implicated in schizophrenia, drug addiction and depression whereas dopaminergic neurons in the SN are lost in Parkinson's disease. Maternal immune activation (MIA) leading to in utero inflammation has been proposed to be a risk factor for these disorders, yet it is unclear how this stimulus can lead to the diverse disturbances in dopaminergic-driven behaviors that emerge at different stages of life in affected offspring. Here we report that gestational age is a critical determinant of the subsequent alterations in dopaminergic-driven behavior in rat offspring exposed to lipopolysaccharide (LPS)-induced MIA. Behavioral analysis revealed that MIA on gestational day 16 but not gestational day 12 resulted in biphasic impairments in motor behavior. Specifically, motor impairments were evident in early life, which were resolved by adolescence, but subsequently re-emerged in adulthood. In contrast, reward seeking behaviors were altered in offspring exposed MIA on gestational day 12. These changes were not due to a loss of dopaminergic neurons per se in the postnatal period, suggesting that they reflect functional changes in dopaminergic systems. This highlights that gestational age may be a key determinant of how MIA leads to distinct alterations in dopaminergic-driven behavior across the lifespan of affected offspring.

Survival and growth of C57BL/6J mice lacking the BK channel, Kcnma1: lower adult body weight occurs together with higher body fat

Big conductance potassium (BK) channels contribute to K⁺ flow and electrical behavior in many cell types. Mice made null for the gene (Kcnma1) producing the BK channel (BK^KO) exhibit numerous deficits in physiological functions. Breeding mice lacking a single allele of Kcnma1 (C57BL/6J background) had litter sizes of approximately eight pups. For the period of maternal care (P0–P21), pup deaths peaked at P1 with a second less severe interval of death peaking near P13. Early deaths were twice as likely during a 20‐month period of building construction compared with the quiescent period after cessation of construction. Births during construction were not consistent with Mendelian predictions indicating the likelihood of a specific disadvantage induced by this environmental stressor. Later BK^KO pup deaths (~P13) also were more numerous than Mendelian expectations. After weaning, weight gain was slower for BK^KO mice compared with wild‐type littermates: 5 g less for male BK^KO mice and 4 g less for female BK^KO mice. Body composition determined by quantitative magnetic resonance indicated a higher fat proportion for wild‐type female mice compared with males, as well as a higher hydration ratio. Both male and female BK^KO mice showed higher fat proportions than wild‐type, with female BK^KO mice exhibiting greater variation. Together, these results indicate that BK^KO mice suffered disadvantages that lead to prenatal and perinatal death. A metabolic difference likely related to glucose handling led to the smaller body size and distinct composition for BK^KO mice, suggesting a diversion of energy supplies from growth to fat storage.

Dietary choline levels modify the effects of prenatal alcohol exposure in rats

Prenatal alcohol exposure can cause a range of physical and behavioral alterations; however, the outcome among children exposed to alcohol during pregnancy varies widely. Some of this variation may be due to nutritional factors. Indeed, higher rates of fetal alcohol spectrum disorders (FASD) are observed in countries where malnutrition is prevalent. Epidemiological studies have shown that many pregnant women throughout the world may not be consuming adequate levels of choline, an essential nutrient critical for brain development, and a methyl donor. In this study, we examined the influence of dietary choline deficiency on the severity of fetal alcohol effects. Pregnant Sprague-Dawley rats were randomly assigned to receive diets containing 40, 70, or 100% recommended choline levels. A group from each diet condition was exposed to ethanol (6.0g/kg/day) from gestational day 5 to 20 via intubation. Pair-fed and ad lib lab chow control groups were also included. Physical and behavioral development was measured in the offspring. Prenatal alcohol exposure delayed motor development, and 40% choline altered performance on the cliff avoidance task, independent of one another. However, the combination of low choline and prenatal alcohol produced the most severe impairments in development. Subjects exposed to ethanol and fed the 40% choline diet exhibited delayed eye openings, significantly fewer successes in hindlimb coordination, and were significantly overactive compared to all other groups. These data suggest that suboptimal intake of a single nutrient can exacerbate some of ethanol's teratogenic effects, a finding with important implications for the prevention of FASD.

A Battery of Motor Tests in a Neonatal Mouse Model of Cerebral Palsy

As the sheer number of transgenic mice strains grow and rodent models of pediatric disease increase, there is an expanding need for a comprehensive, standardized battery of neonatal mouse motor tests. These tests can validate injury or disease models, determine treatment efficacy and/or assess motor behaviors in new transgenic strains. This paper presents a series of neonatal motor tests to evaluate general motor function, including ambulation, hindlimb foot angle, surface righting, negative geotaxis, front- and hindlimb suspension, grasping reflex, four limb grip strength and cliff aversion. Mice between the ages of post-natal day 2 to 14 can be used. In addition, these tests can be used for a wide range of neurological and neuromuscular pathologies, including cerebral palsy, hypoxic-ischemic encephalopathy, traumatic brain injury, spinal cord injury, neurodegenerative diseases, and neuromuscular disorders. These tests can also be used to determine the effects of pharmacological agents, as well as other types of therapeutic interventions. In this paper, motor deficits were evaluated in a novel neonatal mouse model of cerebral palsy that combines hypoxia, ischemia and inflammation. Forty-eight hours after injury, five tests out of the nine showed significant motor deficits: ambulation, hindlimb angle, hindlimb suspension, four limb grip strength, and grasping reflex. These tests revealed weakness in the hindlimbs, as well as fine motor skills such as grasping, which are similar to the motor deficits seen in human cerebral palsy patients.

Transient cerebellar alterations during development prior to obvious motor phenotype in a mouse model of spinocerebellar ataxia type 6

KEY POINTS

Spinocerebellar ataxia type 6 (SCA6) is a midlife-onset neurodegenerative disease caused by a CACNA1A mutation; CACNA1A is also implicated in cerebellar development. We have previously shown that when disease symptoms are present in midlife in SCA6^84Q/84Q mice, cerebellar Purkinje cells spike with reduced rate and precision. In contrast, we find that during postnatal development (P10-13), SCA6^84Q/84Q Purkinje cells spike with elevated rate and precision. Although surplus climbing fibres are linked to ataxia in other mouse models, we found surplus climbing fibre inputs on developing (P10-13) SCA6^84Q/84Q Purkinje cells when motor deficits were not detected. Developmental alterations were transient and were no longer observed in weanling (P21-24) SCA6^84Q/84Q Purkinje cells. Our results suggest that changes in the developing cerebellar circuit can occur without detectable motor abnormalities, and that changes in cerebellar development may not necessarily persist into adulthood.

ABSTRACT

Although some neurodegenerative diseases are caused by mutations in genes that are known to regulate neuronal development, surprisingly, patients may not present disease symptoms until adulthood. Spinocerebellar ataxia type 6 (SCA6) is one such midlife-onset disorder in which the mutated gene, CACNA1A, is implicated in cerebellar development. We wondered whether changes were observed in the developing cerebellum in SCA6 prior to the detection of motor deficits. To address this question, we used a transgenic mouse with a hyper-expanded triplet repeat (SCA6^84Q/84Q ) that displays late-onset motor deficits at 7 months, and measured cerebellar Purkinje cell synaptic and intrinsic properties during postnatal development. We found that firing rate and precision were enhanced during postnatal development in P10-13 SCA6^84Q/84Q Purkinje cells, and observed surplus multiple climbing fibre innervation without changes in inhibitory input or dendritic structure during development. Although excess multiple climbing fibre innervation has been associated with ataxic symptoms in several adult transgenic mice, we observed no detectable changes in cerebellar-related motor behaviour in developing SCA6^84Q/84Q mice. Interestingly, we found that developmental alterations were transient, as both Purkinje cell firing properties and climbing fibre innervation from weanling-aged (P21-24) SCA6^84Q/84Q mice were indistinguishable from litter-matched control mice. Our results demonstrate that significant alterations in neuronal circuit development may be observed without any detectable behavioural read-out, and that early changes in brain development may not necessarily persist into adulthood in midlife-onset diseases.

Developmental delay in motor skill acquisition in Niemann-Pick C1 mice reveals abnormal cerebellar morphogenesis

Niemann-Pick type C1 (NPC1) disease is a lysosomal storage disorder caused by defective intracellular trafficking of exogenous cholesterol. Purkinje cell (PC) degeneration is the main sign of cerebellar dysfunction in both NPC1 patients and animal models. It has been recently shown that a significant decrease in Sonic hedgehog (Shh) expression reduces the proliferative potential of granule neuron precursors in the developing cerebellum of Npc1^−/− mice. Pursuing the hypothesis that this developmental defect translates into functional impairments, we have assayed Npc1-deficient pups belonging to the milder mutant mouse strain Npc1^nmf164 for sensorimotor development from postnatal day (PN) 3 to PN21. Npc1^nmf164/ Npc1^nmf164 pups displayed a 2.5-day delay in the acquisition of complex motor abilities compared to wild-type (wt) littermates, in agreement with the significant disorganization of cerebellar cortex cytoarchitecture observed between PN11 and PN15. Compared to wt, Npc1^nmf164 homozygous mice exhibited a poorer morphological differentiation of Bergmann glia (BG), as indicated by thicker radial shafts and less elaborate reticular pattern of lateral processes. Also BG functional development was defective, as indicated by the significant reduction in GLAST and Glutamine synthetase expression. A reduced VGluT2 and GAD65 expression also indicated an overall derangement of the glutamatergic/GABAergic stimulation that PCs receive by climbing/parallel fibers and basket/stellate cells, respectively. Lastly, Npc1-deficiency also affected oligodendrocyte differentiation as indicated by the strong reduction of myelin basic protein. Two sequential 2-hydroxypropyl-β-cyclodextrin administrations at PN4 and PN7 counteract these defects, partially preventing functional impairment of BG and fully restoring the normal patterns of glutamatergic/GABAergic stimulation to PCs.

These findings indicate that in Npc1^nmf164 homozygous mice the derangement of synaptic connectivity and dysmyelination during cerebellar morphogenesis largely anticipate motor deficits that are typically observed during adulthood.

Functional Role of BDNF Production from Unique Promoters in Aggression and Serotonin Signaling

Brain-derived neurotrophic factor (BDNF) regulates diverse biological functions ranging from neuronal survival and differentiation during development to synaptic plasticity and cognitive behavior in the adult. BDNF disruption in both rodents and humans is associated with neurobehavioral alterations and psychiatric disorders. A unique feature of Bdnf transcription is regulation by nine individual promoters, which drive expression of variants that encode an identical protein. It is hypothesized that this unique genomic structure may provide flexibility that allows different factors to regulate BDNF signaling in distinct cell types and circuits. This has led to the suggestion that isoforms may regulate specific BDNF-dependent functions; however, little scientific support for this idea exists. We generated four novel mutant mouse lines in which BDNF production from one of the four major promoters (I, II, IV, or VI) is selectively disrupted (Bdnf-e1, -e2, -e4, and -e6 mice) and used a comprehensive comparator approach to determine whether different Bdnf transcripts are associated with specific BDNF-dependent molecular, cellular, and behavioral phenotypes. Bdnf-e1 and -e2 mutant males displayed heightened aggression accompanied by convergent expression changes in specific genes associated with serotonin signaling. In contrast, BDNF-e4 and -e6 mutants were not aggressive but displayed impairments associated with GABAergic gene expression. Moreover, quantifications of BDNF protein in the hypothalamus, prefrontal cortex, and hippocampus revealed that individual Bdnf transcripts make differential, region-specific contributions to total BDNF levels. The results highlight the biological significance of alternative Bdnf transcripts and provide evidence that individual isoforms serve distinct molecular and behavioral functions.

Intravenous Prenatal Nicotine Exposure Alters METH-Induced Hyperactivity, Conditioned Hyperactivity, and BDNF in Adult Rat Offspring

In the USA, approximately 15% of women smoke tobacco cigarettes during pregnancy. In utero tobacco smoke exposure produces somatic growth deficits like intrauterine growth restriction and low birth weight in offspring, but it can also negatively influence neurodevelopmental outcomes in later stages of life, such as an increased incidence of obesity and drug abuse. Animal models demonstrate that prenatal nicotine (PN) alters the development of the mesocorticolimbic system, which is important for organizing goal-directed behavior. In the present study, we determined whether intravenous (IV) PN altered the initiation and/or expression of methamphetamine (METH)-induced locomotor sensitization as a measure of mesocorticolimbic function in adult rat offspring. We also determined whether PN and/or METH exposure altered protein levels of BDNF (brain-derived neurotrophic factor) in the nucleus accumbens, the dorsal striatum, and the prefrontal cortex of adult offspring. BDNF was of interest because of its role in the development and maintenance of the mesocorticolimbic pathway and its ability to modulate neural processes that contribute to drug abuse, such as sensitization of the dopamine system. Dams were injected with IV nicotine (0.05 mg/kg/injection) or saline, 3×/day on gestational days 8-21. Testing was conducted when offspring reached adulthood (around postnatal day 90). Following 3 once daily habituation sessions the animals received a saline injection and baseline locomotor activity was measured. PN and prenatal saline (PS)-exposed offspring then received 10 once daily injections of METH (0.3 mg/kg) to induce locomotor sensitization. The animals received a METH injection (0.3 mg/kg) to assess the expression of sensitization following a 14-day period of no injections. A day later, all animals were injected with saline and conditioned hyperactivity was assessed. Brain tissue was harvested 24 h later. PN animals habituated more slowly to the activity chambers compared to PS controls. PN rats treated with METH showed significant enhancement of locomotor behavior compared to PS rats following acute and repeated injections; however, PN did not produce differential initiation or expression of behavioral sensitization. METH produced conditioned hyperactivity, and PN rats exhibited a greater conditioned response of hyperactivity relative to controls. PN and METH exposure produced changes in BDNF protein levels in all three regions, and complex interactions were observed between these two factors. Logistic regression revealed that BDNF protein levels, throughout the mesocorticolimbic system, significantly predicted the difference in the conditioned hyperactive response of the animals: both correlations were significant, but the predicted relationship between BDNF and context-elicited activity was stronger in the PN (r = 0.67) compared to the PS rats (r = 0.42). These findings indicate that low-dose PN exposure produces long-term changes in activity and enhanced sensitivity to the locomotor effects of METH. The enhanced METH-induced contextual conditioning shown by the PN animals suggests that offspring of in utero tobacco smoke exposure have greater susceptibility to learn about drug-related conditional stimuli, such as the context. The PN-induced alterations in mesocorticolimbic BDNF protein lend further support for the hypothesis that maternal smoking during pregnancy produces alterations in neuronal plasticity that contribute to drug abuse vulnerability. The current findings demonstrate that these changes are persistent into adulthood.

Endothelial LRP1 transports amyloid-β(1-42) across the blood-brain barrier

According to the neurovascular hypothesis, impairment of low-density lipoprotein receptor-related protein-1 (LRP1) in brain capillaries of the blood-brain barrier (BBB) contributes to neurotoxic amyloid-β (Aβ) brain accumulation and drives Alzheimer's disease (AD) pathology. However, due to conflicting reports on the involvement of LRP1 in Aβ transport and the expression of LRP1 in brain endothelium, the role of LRP1 at the BBB is uncertain. As global Lrp1 deletion in mice is lethal, appropriate models to study the function of LRP1 are lacking. Moreover, the relevance of systemic Aβ clearance to AD pathology remains unclear, as no BBB-specific knockout models have been available. Here, we developed transgenic mouse strains that allow for tamoxifen-inducible deletion of Lrp1 specifically within brain endothelial cells (Slco1c1-CreER(T2) Lrp1(fl/fl) mice) and used these mice to accurately evaluate LRP1-mediated Aβ BBB clearance in vivo. Selective deletion of Lrp1 in the brain endothelium of C57BL/6 mice strongly reduced brain efflux of injected [125I] Aβ(1-42). Additionally, in the 5xFAD mouse model of AD, brain endothelial-specific Lrp1 deletion reduced plasma Aβ levels and elevated soluble brain Aβ, leading to aggravated spatial learning and memory deficits, thus emphasizing the importance of systemic Aβ elimination via the BBB. Together, our results suggest that receptor-mediated Aβ BBB clearance may be a potential target for treatment and prevention of Aβ brain accumulation in AD.

Treatment during a vulnerable developmental period rescues a genetic epilepsy

The nervous system is vulnerable to perturbations during specific developmental periods. Insults during such susceptible time windows can have long-term consequences, including the development of neurological diseases such as epilepsy. Here we report that a pharmacological intervention timed during a vulnerable neonatal period of cortical development prevents pathology in a genetic epilepsy model. By using mice with dysfunctional Kv7 voltage-gated K(+) channels, which are mutated in human neonatal epilepsy syndromes, we demonstrate the safety and efficacy of the sodium-potassium-chloride cotransporter NKCC1 antagonist bumetanide, which was administered during the first two postnatal weeks. In Kv7 current-deficient mice, which normally display epilepsy, hyperactivity and stereotypies as adults, transient bumetanide treatment normalized neonatal in vivo cortical network and hippocampal neuronal activity, prevented structural damage in the hippocampus and restored wild-type adult behavioral phenotypes. Furthermore, bumetanide treatment did not adversely affect control mice. These results suggest that in individuals with disease susceptibility, timing prophylactically safe interventions to specific windows during development may prevent or arrest disease progression.

Neurobehavioral Alterations in a Genetic Murine Model of Feingold Syndrome 2

Feingold syndrome (FS) is an autosomal dominant disorder characterized by microcephaly, short stature, digital anomalies, esophageal/duodenal atresia, facial dysmorphism, and various learning disabilities. Heterozygous deletion of the miR-17-92 cluster is responsible for a subset of FS (Feingold syndrome type 2, FS2), and the developmental abnormalities that characterize this disorder are partially recapitulated in mice that harbor a heterozygous deletion of this cluster (miR-17-92∆/+ mice). Although Feingold patients develop a wide array of learning disabilities, no scientific description of learning/cognitive disabilities, intellectual deficiency, and brain alterations have been described in humans and animal models of FS2. The aim of this study was to draw a behavioral profile, during development and in adulthood, of miR-17-92∆/+ mice, a genetic mouse model of FS2. Moreover, dopamine, norepinephrine and serotonin tissue levels in the medial prefrontal cortex (mpFC), and Hippocampus (Hip) of miR-17-92∆/+ mice were analyzed.Our data showed decreased body growth and reduced vocalization during development. Moreover, selective deficits in spatial ability, social novelty recognition and memory span were evident in adult miR-17-92∆/+ mice compared with healthy controls (WT). Finally, we found altered dopamine as well as serotonin tissue levels, in the mpFC and Hip, respectively, of miR-17-92∆/+ in comparison with WT mice, thus suggesting a possible link between cognitive deficits and altered brain neurotransmission.

A critical period for postnatal adaptive plasticity in a model of motor axon miswiring

The correct wiring of neuronal circuits is of crucial importance for precise neuromuscular functionality. Therefore, guidance cues provide tight spatiotemporal control of axon growth and guidance. Mice lacking the guidance cue Semaphorin 3F (Sema3F) display very specific axon wiring deficits of motor neurons in the medial aspect of the lateral motor column (LMCm). While these deficits have been investigated extensively during embryonic development, it remained unclear how Sema3F mutant mice cope with these errors postnatally. We therefore investigated whether these animals provide a suitable model for the exploration of adaptive plasticity in a system of miswired neuronal circuitry. We show that the embryonically developed wiring deficits in Sema3F mutants persist until adulthood. As a consequence, these mutants display impairments in motor coordination that improve during normal postnatal development, but never reach wildtype levels. These improvements in motor coordination were boosted to wildtype levels by housing the animals in an enriched environment starting at birth. In contrast, a delayed start of enriched environment housing, at 4 weeks after birth, did not similarly affect motor performance of Sema3F mutants. These results, which are corroborated by neuroanatomical analyses, suggest a critical period for adaptive plasticity in neuromuscular circuitry. Interestingly, the formation of perineuronal nets, which are known to close the critical period for plastic changes in other systems, was not altered between the different housing groups. However, we found significant changes in the number of excitatory synapses on limb innervating motor neurons. Thus, we propose that during the early postnatal phase, when perineuronal nets have not yet been formed around spinal motor neurons, housing in enriched environment conditions induces adaptive plasticity in the motor system by the formation of additional synaptic contacts, in order to compensate for coordination deficits.

IV prenatal nicotine exposure increases the reinforcing efficacy of methamphetamine in adult rat offspring

BACKGROUND

Maternal smoking during pregnancy is correlated with increased substance use in offspring. Research using rodent models shows that gestational nicotine exposure produces enduring alterations in the neurodevelopment of motivational systems, and that rats prenatally treated with nicotine have altered motivation for drug reinforcement on fixed-ratio (FR) schedules of reinforcement.

OBJECTIVE

The present study investigated methamphetamine (METH) self-administration in adult offspring prenatally exposed to intravenous (IV) nicotine or saline using a progressive-ratio (PR) schedule of reinforcement.

METHODS

Pregnant rats were administered IV prenatal saline (PS) or nicotine (PN; 0.05mg/kg/infusion), 3×/day during gestational days 8-21. At postnatal day 70, offspring acquired a lever-press response for sucrose (26%, w/v; FR1-3). Rats were trained with METH (0.05mg/kg/infusion), and following stable FR responding, animals were tested using a progressive-ratio (PR) schedule for three different doses of METH (0.005, 0.025, and 0.05mg/kg/infusion).

RESULTS

METH infusion, active lever presses, and the ratio breakpoint are reported. PN-exposed animals exhibited more METH-maintained responding than PS controls, according to a dose×prenatal treatment interaction (e.g., infusions). PN rats self-administered more METH infusions between the range of 0.025 and 0.05, but not for the 0.005mg/kg/infusion dose.

CONCLUSIONS

IV PN-exposure produced enhanced motivation to self-administer METH. These findings indicate that pregnant women who smoke tobacco may impart neurobiological changes in offspring's motivational systems that render them increasingly vulnerable to drug abuse during adulthood.