Neonatal oxytocin gives the tempo of social and feeding behaviors

The nonapeptide oxytocin (OT) is a master regulator of the social brain in early infancy, adolescence, and adult life. Here, we review the postnatal dynamic development of OT-system as well as early-life OT functions that are essential for shaping social behaviors. We specifically address the role of OT in neonates, focusing on its role in modulating/adapting sensory input and feeding behavior; both processes are involved in the establishing mother-infant bond, a crucial event for structuring all future social interactions. In patients and rodent models of Prader-Willi and Schaaf-Yang syndromes, two neurodevelopmental diseases characterized by autism-related features, sensory impairments, and feeding difficulties in early infancy are linked to an alteration of OT-system. Successful preclinical studies in mice and a phase I/II clinical trial in Prader-Willi babies constitute a proof of concept that OT-treatment in early life not only improves suckling deficit but has also a positive long-term effect on learning and social behavior. We propose that in early postnatal life, OT plays a pivotal role in stimulating and coordinating the maturation of neuronal networks controlling feeding behavior and the first social interactions. Consequently, OT therapy might be considered to improve feeding behavior and, all over the life, social cognition, and learning capabilities.

Oxytocin administration in neonates shapes hippocampal circuitry and restores social behavior in a mouse model of autism

Oxytocin is an important regulator of the social brain. In some animal models of autism, notably in Magel2^tm1.1Mus-deficient mice, peripheral administration of oxytocin in infancy improves social behaviors until adulthood. However, neither the mechanisms responsible for social deficits nor the mechanisms by which such oxytocin administration has long-term effects are known. Here, we aimed to clarify these oxytocin-dependent mechanisms, focusing on social memory performance. Using in situ hybridization (RNAscope), we have established that Magel2 and oxytocin receptor are co-expressed in the dentate gyrus and CA2/CA3 hippocampal regions involved in the circuitry underlying social memory. Then, we have shown that Magel2^tm1.1Mus-deficient mice, evaluated in a three-chamber test, present a deficit in social memory. Next, in hippocampus, we conducted neuroanatomical and functional studies using immunostaining, oxytocin-binding experiments, ex vivo electrophysiological recordings, calcium imaging and biochemical studies. We demonstrated: an increase of the GABAergic activity of CA3-pyramidal cells associated with an increase in the quantity of oxytocin receptors and of somatostatin interneurons in both DG and CA2/CA3 regions. We also revealed a delay in the GABAergic development sequence in Magel2^tm1.1Mus-deficient pups, linked to phosphorylation modifications of KCC2. Above all, we demonstrated the positive effects of subcutaneous administration of oxytocin in the mutant neonates, restoring hippocampal alterations and social memory at adulthood. Although clinical trials are debated, this study highlights the mechanisms by which peripheral oxytocin administration in neonates impacts the brain and demonstrates the therapeutic value of oxytocin to treat infants with autism spectrum disorders.

An Early Postnatal Oxytocin Treatment Prevents Social and Learning Deficits in Adult Mice Deficient for Magel2, a Gene Involved in Prader-Willi Syndrome and Autism

BACKGROUND

Mutations of MAGEL2 have been reported in patients presenting with autism, and loss of MAGEL2 is also associated with Prader-Willi syndrome, a neurodevelopmental genetic disorder. This study aimed to determine the behavioral phenotype of Magel2-deficient adult mice, to characterize the central oxytocin (OT) system of these mutant mice, and to test the curative effect of a peripheral OT treatment just after birth.

METHODS

We assessed the social and cognitive behavior of Magel2-deficient mice, analyzed the OT system of mutant mice treated or not by a postnatal administration of OT, and determined the effect of this treatment on the brain.

RESULTS

Magel2 inactivation induces a deficit in social recognition and social interaction and a reduced learning ability in adult male mice. In these mice, we reveal anatomical and functional modifications of the OT system and show that these defects change from birth to adulthood. Daily administration of OT in the first postnatal week was sufficient to prevent deficits in social behavior and learning abilities in adult mutant male mice. We show that this OT treatment partly restores a normal OT system. Thus, we report that an alteration of the OT system around birth has long-term consequences on behavior and on cognition. Importantly, an acute OT treatment of Magel2-deficient pups has a curative effect.

CONCLUSIONS

Our study reveals that OT plays a crucial role in setting social behaviors during a period just after birth. An early OT treatment in this critical period could be a novel therapeutic approach for the treatment of neurodevelopmental disorders such as Prader-Willi syndrome and autism.

Acute neuromuscular adaptation at the spinal level following middle cerebral artery occlusion-reperfusion in the rat

The purpose of the study was to highlight the acute motor reflex adaptation and to deepen functional deficits following a middle cerebral artery occlusion-reperfusion (MCAO-r). Thirty-six Sprague-Dawley rats were included in this study. The middle cerebral artery occlusion (MCAO; 120 min) was performed on 16 rats studied at 1 and 7 days, respectively (MCAO-D1 and MCAO-D7, n = 8 for each group). The other animals were divided into 3 groups: SHAM-D1 (n = 6), SHAM-D7 (n = 6) and Control (n = 8). Rats performed 4 behavioral tests (the elevated body swing test, the beam balance test, the ladder-climbing test and the forelimb grip force) before the surgery and daily after MCAO-r. H-reflex on triceps brachii was measured before and after isometric exercise. Infarction size and cerebral edema were respectively assessed by histological (Cresyl violet) and MRI measurements at the same time points than H-reflex recordings. Animals with cerebral ischemia showed persistent functional deficits during the first week post-MCAO-r. H-reflex was not decreased in response to isometric exercise one day after the cerebral ischemia contrary to the other groups. The motor reflex regulation was recovered 7 days post-MCAO-r. This result reflects an acute sensorimotor adaptation at the spinal level after MCAO-r.

Natural breaking of the maternal silence at the mouse and human imprinted Prader-Willi locus: A whisper with functional consequences

Genomic imprinting is a normal process of epigenetic regulation leading some autosomal genes to be expressed from one parental allele only, the other parental allele being silenced. The reasons why this mechanism has been selected throughout evolution are not clear; however, expression dosage is critical for imprinted genes. There is a paradox between the fact that genomic imprinting is a robust mechanism controlling the expression of specific genes and the fact that this mechanism is based on epigenetic regulation that, per se, should present some flexibility. The robustness has been well studied, revealing the epigenetic modifications at the imprinted locus, but the flexibility has been poorly investigated.

 

Prader-Willi syndrome is the best-studied disease involving imprinted genes caused by the absence of expression of paternally inherited alleles of genes located in the human 15q11-q13 region. Until now, the silencing of the maternally inherited alleles was like a dogma. Rieusset et al. showed that in absence of the paternal Ndn allele, in Ndn +m/-p mice, the maternal Ndn allele is expressed at an extremely low level with a high degree of non-genetic heterogeneity. In about 50% of these mutant mice, this stochastic expression reduces birth lethality and severity of the breathing deficiency, correlated with a reduction in the loss of serotonergic neurons. Furthermore, using several mouse models, they reveal a competition between non-imprinted Ndn promoters, which results in monoallelic (paternal or maternal) Ndn expression, suggesting that Ndn monoallelic expression occurs in the absence of imprinting regulation. Importantly, specific expression of the maternal NDN allele is also detected in post-mortem brain samples of PWS individuals. Here, similar expression of the Magel2 maternal allele is reported in Magel2 +m/-p mice, suggesting that this loss of imprinting can be extended to other PWS genes. These data reveal an unexpected epigenetic flexibility of PWS imprinted genes that could be exploited to reactivate the functional but dormant maternal alleles in PWS.

Stochastic loss of silencing of the imprinted Ndn/NDN allele, in a mouse model and humans with prader-willi syndrome, has functional consequences

Genomic imprinting is a process that causes genes to be expressed from one allele only according to parental origin, the other allele being silent. Diseases can arise when the normally active alleles are not expressed. In this context, low level of expression of the normally silent alleles has been considered as genetic noise although such expression has never been further studied. Prader-Willi Syndrome (PWS) is a neurodevelopmental disease involving imprinted genes, including NDN, which are only expressed from the paternally inherited allele, with the maternally inherited allele silent. We present the first in-depth study of the low expression of a normally silent imprinted allele, in pathological context. Using a variety of qualitative and quantitative approaches and comparing wild-type, heterozygous and homozygous mice deleted for Ndn, we show that, in absence of the paternal Ndn allele, the maternal Ndn allele is expressed at an extremely low level with a high degree of non-genetic heterogeneity. The level of this expression is sex-dependent and shows transgenerational epigenetic inheritance. In about 50% of mutant mice, this expression reduces birth lethality and severity of the breathing deficiency, correlated with a reduction in the loss of serotonergic neurons. In wild-type brains, the maternal Ndn allele is never expressed. However, using several mouse models, we reveal a competition between non-imprinted Ndn promoters which results in monoallelic (paternal or maternal) Ndn expression, suggesting that Ndn allelic exclusion occurs in the absence of imprinting regulation. Importantly, specific expression of the maternal NDN allele is also detected in post-mortem brain samples of PWS individuals. Our data reveal an unexpected epigenetic flexibility of PWS imprinted genes that could be exploited to reactivate the functional but dormant maternal alleles in PWS. Overall our results reveal high non-genetic heterogeneity between genetically identical individuals that might underlie the variability of the phenotype.

Nasal OEC transplantation promotes respiratory recovery in a subchronic rat model of cervical spinal cord contusion

Engraftment of nasal olfactory ensheathing cells (OEC) is considered as a promising therapeutic strategy for spinal cord repair and one clinical trial has already been initiated. However, while the vast majority of fundamental studies were focused on the recovery of locomotor function, the efficiency of this cellular tool for repairing respiratory motor dysfunction, which affects more than half of paraplegic/tetraplegic patients, remains unknown. Using a rat model that mimics the mechanisms encountered after a cervical contusion that induces a persistent hemi-diaphragmatic paralysis, we assessed the therapeutic efficiency of a delayed transplantation (2 weeks post-contusion) of nasal OECs within the injured spinal cord. Functional recovery was quantified with respiratory behavior tests, diaphragmatic electromyography and neuro-electrophysiological recording of the phrenic motoneurons while axogenesis was evaluated using immunohistochemistry. We show that 3 months post-transplantation, nasal OECs improve i) breathing movements, ii) activities of the ipsilateral diaphragm and corresponding phrenic nerve, and iii) axonal sprouting in the injury site. We also demonstrate that this functional partial recovery is mediated by the restoration of ipsilateral supraspinal command. Our study brings further evidence that olfactory ensheathing cells could have clinical application especially in tetraplegic patients with impaired breathing movements. This article is part of a Special Issue entitled: Understanding olfactory ensheathing glia and their prospect for nervous system repair.

An olfactory receptor pseudogene whose function emerged in humans: a case study in the evolution of structure-function in GPCRs

Human olfactory receptor, hOR17-210, is identified as a pseudogene in the human genome. Experimental data has shown however, that the gene product of frame-shifted, cloned hOR17-210 cDNA was able to bind an odorant-binding protein and is narrowly tuned for excitation by cyclic ketones. Supported by experimental results, we used the bioinformatics methods of sequence analysis (genome-wide and pair-wise), computational protein modeling and docking, to show that functionality in this receptor is retained due to sequence-structure features not previously observed in mammalian ORs. This receptor does not possess the first two transmembrane helical domains (of seven typically seen in GPCRs). It however, possesses an additional TM that has not been observed in other human olfactory receptors. By incorporating these novel structural features, we created two putative models for this receptor. We also docked odor ligands that were experimentally shown to bind hOR17-210. We show how and why structural modifications of OR17-210 do not hinder this receptor's functionality. Our studies reveal that novel gene rearrangements that result in sequence and structural diversity may have a bearing on OR and GPCR function and evolution.

An olfactory receptor pseudogene whose function emerged in humans: a case study in the evolution of structure-function in GPCRs

Human olfactory receptor, hOR17-210, is identified as a pseudogene in the human genome. Experimental data has shown however, that the gene product of frame-shifted, cloned hOR17-210 cDNA was able to bind an odorant-binding protein and is narrowly tuned for excitation by cyclic ketones. Supported by experimental results, we used the bioinformatics methods of sequence analysis (genome-wide and pair-wise), computational protein modeling and docking, to show that functionality in this receptor is retained due to sequence-structure features not previously observed in mammalian ORs. This receptor does not possess the first two transmembrane helical domains (of seven typically seen in GPCRs). It however, possesses an additional TM that has not been observed in other human olfactory receptors. By incorporating these novel structural features, we created two putative models for this receptor. We also docked odor ligands that were experimentally shown to bind hOR17-210. We show how and why structural modifications of OR17-210 do not hinder this receptor's functionality. Our studies reveal that novel gene rearrangements that result in sequence and structural diversity may have a bearing on OR and GPCR function and evolution.

Downregulation of uncoupling protein-3 in vivo is linked to changes in muscle mitochondrial energy metabolism as a result of capsiate administration

Although it has been suggested that the skeletal muscle mitochondrial uncoupling protein-3 (UCP3) is involved in regulating energy expenditure, its role is still poorly understood. In the present study, we aimed at investigating noninvasively, using magnetic resonance techniques, metabolic changes occurring in exercising muscle as a result of capsiate treatment, which has been previously linked to UCP3 upregulation. We showed that capsiate ingestion strongly reduced UCP3 gene expression in rat gastrocnemius muscle. This large underexpression was accompanied by a significant increase in the rate of mitochondrial ATP production and phosphocreatine level both at rest and during muscle stimulation. Similarly, the stimulation-induced ATP fall and ADP accumulation were significantly less after capsiate administration than in untreated rats. The larger oxidative ATP production rate could not be explained by a proportional decrease in the anaerobic component, i.e., glycolysis and phosphocreatine breakdown. In addition, the mechanical performance was not affected by capsiate administration. Finally, the plasma free fatty acid (FFA) level increased in capsiate-treated rats, whereas no significant change was observed after muscle stimulation in the control group. Considering the corresponding enhanced UCP3 mRNA expression occurring in the control group after muscle stimulation, one can suggest that changes in FFA level and UCP3 mRNA expression are not mechanistically correlated. Overall, we have shown that capsiate administration induced a UCP3 downregulation coupled with an increased mitochondrial ATP synthesis, whereas the muscle force-generating capacity was unchanged. This suggests that a decrease in muscle efficiency and/or additional noncontractile ATP-consuming mechanisms result from UCP3 downregulation.

Identification of odorant receptors from the Alpine marmot (Marmota marmota)

Alpine Marmots (Marmota marmota) are a good model to study intraspecific chemical communication among mammals. This species has been subjected to several behavioural and biochemical studies regarding both their scent-marking behaviour by cheek-rubbing, and the chemical composition of their glandular secretions. However, no molecular study has been undertaken until today on proteins from the olfactory epithelium possibly implicated in chemical perception. In this study, we identified, to our knowledge for the first time, some olfatory receptors from this wild rodent. Starting with olfactory epithelium of an Alpine Marmot, and by mean of reverse transcriptase polymerase chain reaction technique (RT-PCR), we isolated fourteen partial sequences that exhibited a high degree of homology (45-92%) with olfactory receptors from other vertebrates. Conserved identities and structural features clearly defined these Alpine Marmot sequences as members of the seven transmembrane domain olfactory receptors. All sequences were observed as belonging to known olfactory receptor families and were classified into ten subfamilies of the tetrapods OR class. Finally, Northern blot analysis revealed specific expression of these sequences in the Alpine Marmot olfactory epithelium tissue.

Isolation of putative olfactory receptor sequences from pig nasal epithelium

Binding to olfactory receptors is the first step in odorant and pheromonal recognition and discrimination. These receptors constitute one of the most important, although poorly known, families of neuronal receptors. In this study we used degenerated oligonucleotides and a RT-PCR approach to selectively amplify olfactory receptors in the nasal epithelium of the domestic pig Sus scrofa. Several combinations of oligonucleotide were tested and allowed the isolation of eleven different partial sequences belonging to the seven transmembrane olfactory receptor family. These receptors formed a separate family within the seven transmembrane receptor superfamily in pigs. Using the criteria of Ben Arie et al. [Ben-Arie N., Lancet D., Taylor C., Khen M., Walker N., Ledbetter DH., Carrozzo R., Patel K., Sheer D., Lehrah H. and North M., Hum. Mol. Genet., 3 (1994) 229-235], the 11 receptors described here can be classified into three known families and seven subfamilies (one known and six new).

[Vertebral fracture caused by electric cardioversion]

A case of vertebral fracture following DC shock for ventricular fibrillation is reported. After a short review of the complications of this procedure the case is described and compared with two other cases known in literature. We conclude that, although this complication is uncommon, it must be kept in mind owing to its potential severity.