Prenatal Restraint Stress (PRS) in rats is a validated model of early stress resulting in permanent behavioral and neurobiological outcomes. Although sexual dimorphism in the effects of PRS has been hypothesized for more than 30 years, few studies in this long period have directly addressed the issue. Our group has uncovered a pronounced gender difference in the effects of PRS (stress delivered to the mothers 3 times per day during the last 10 days of pregnancy) on anxiety, spatial learning, and a series of neurobiological parameters classically associated with hippocampus-dependent behaviors. Adult male rats subjected to PRS (“PRS rats”) showed increased anxiety-like behavior in the elevated plus maze (EPM), a reduction in the survival of newborn cells in the dentate gyrus, a reduction in the activity of mGlu1/5 metabotropic glutamate receptors in the ventral hippocampus, and an increase in the levels of brain-derived neurotrophic factor (BDNF) and pro-BDNF in the hippocampus. In contrast, female PRS rats displayed reduced anxiety in the EPM, improved learning in the Morris water maze, an increase in the activity of mGlu1/5 receptors in the ventral and dorsal hippocampus, and no changes in hippocampal neurogenesis or BDNF levels. The direction of the changes in neurogenesis, BDNF levels and mGlu receptor function in PRS animals was not consistent with the behavioral changes, suggesting that PRS perturbs the interdependency of these particular parameters and their relation to hippocampus-dependent behavior. Our data suggest that the epigenetic changes in hippocampal neuroplasticity induced by early environmental challenges are critically sex-dependent and that the behavioral outcome may diverge in males and females.

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Breastmilk contains bioactive molecules essential for brain and cognitive development. While sialylated human milk oligosaccharides (HMOs) have been implicated in phenotypic programming, their selective role and underlying mechanisms remained elusive. Here, we investigated the long-term consequences of a selective lactational deprivation of a specific sialylated HMO in mice. We capitalized on a knock-out (KO) mouse model (B6.129-St6gal1tm2Jxm/J) lacking the gene responsible for the synthesis of sialyl(alpha2,6)lactose (6′SL), one of the two sources of sialic acid (Neu5Ac) to the lactating offspring. Neu5Ac is involved in the formation of brain structures sustaining cognition. To deprive lactating offspring of 6′SL, we cross-fostered newborn wild-type (WT) pups to KO dams, which provide 6′SL-deficient milk. To test whether lactational 6′SL deprivation affects cognitive capabilities in adulthood, we assessed attention, perseveration, and memory. To detail the associated endophenotypes, we investigated hippocampal electrophysiology, plasma metabolomics, and gut microbiota composition. To investigate the underlying molecular mechanisms, we assessed gene expression (at eye-opening and in adulthood) in two brain regions mediating executive functions and memory (hippocampus and prefrontal cortex, PFC). Compared to control mice, WT offspring deprived of 6′SL during lactation exhibited consistent alterations in all cognitive functions addressed, hippocampal electrophysiology, and in pathways regulating the serotonergic system (identified through gut microbiota and plasma metabolomics). These were associated with a site- (PFC) and time-specific (eye-opening) reduced expression of genes involved in central nervous system development. Our data suggest that 6′SL in maternal milk adjusts cognitive development through a short-term upregulation of genes modulating neuronal patterning in the PFC.

Rett syndrome (RTT) is a rare neurodevelopmental disorder, characterized by severe behavioral and physiological symptoms. Mutations in the methyl CpG binding protein 2 gene (MECP2) cause more than 95% of classic cases, and currently there is no cure for this devastating disorder. Recently we have demonstrated that specific behavioral and brain molecular alterations can be rescued in MeCP2-308 male mice, a RTT mouse model, by pharmacological stimulation of the brain serotonin receptor 7 (5-HT7R). This member of the serotonin receptor family—crucially involved in the regulation of brain structural plasticity and cognitive processes—can be stimulated by systemic repeated treatment with LP-211, a brain-penetrant selective 5-HT7R agonist. The present study extends previous findings by demonstrating that the LP-211 treatment (0.25 mg/kg, once per day for 7 days) rescues RTT-related phenotypic alterations, motor coordination (Dowel test), spatial reference memory (Barnes maze test) and synaptic plasticity (hippocampal long-term-potentiation) in MeCP2-308 heterozygous female mice, the genetic and hormonal milieu that resembles that of RTT patients. LP-211 also restores the activation of the ribosomal protein (rp) S6, the downstream target of mTOR and S6 kinase, in the hippocampus of RTT female mice. Notably, the beneficial effects on neurobehavioral and molecular parameters of a seven-day long treatment with LP-211 were evident up to 2 months after the last injection, thus suggesting long-lasting effects on RTT-related impairments. Taken together with our previous study, these results provide compelling preclinical evidence of the potential therapeutic value for RTT of a pharmacological approach targeting the brain 5-HT7R.

Abbreviations used: 4-AP, 4-aminopyridine; A 1 R, adenosine A 1 receptor; A 2A R, adenosine A 2A receptor; ACSF, artificial CSF; CB 1 R, cannabinoid CB 1 receptor; DPCPX, 8-Cyclopentyl-1,3-dipropylxanthine; FP, field potential; mGlu 5 R, metabotropic glutamate receptor 5; MSNs, medium spiny neurons; PKA, protein kinase A. AbstractAn interaction between adenosine A 2A receptors (A 2A Rs) and cannabinoid CB 1 receptors (CB 1 Rs) has been consistently reported to occur in the striatum, although the precise mechanisms are not completely understood. As both receptors control striatal glutamatergic transmission, we now probed the putative interaction between pre-synaptic CB 1 R and A 2A R in the striatum. In extracellular field potentials recordings in corticostriatal slices from Wistar rats, A 2A R activation by CGS21680 inhibited CB 1 R-mediated effects (depression of synaptic response and increase in paired-pulse facilitation). Moreover, in superfused rat striatal nerve terminals, A 2A R activation prevented, while A 2A R inhibition facilitated, the CB 1 R-mediated inhibition of 4-aminopyridine-evoked glutamate release. In summary, the present study provides converging neurochemical and electrophysiological support for the occurrence of a tight control of CB 1 R function by A 2A Rs in glutamatergic terminals of the striatum. In view of the key role of glutamate to trigger the recruitment of striatal circuits, this pre-synaptic interaction between CB 1 R and A 2A R may be of relevance for the pathogenesis and the treatment of neuropsychiatric disorders affecting the basal ganglia.

Abbreviations used: ACSF, artificial cerebrospinal fluid; AG, arachidonoylglycerol; CB 1 R, type 1 cannabinoid receptor; CHPG, (RS)-2-chloro-5-hydroxyphenylglycine; FPs, field potentials; Fura-2AM, Fura-2 acetoxymethyl ester; LDH, lactate dehydrogenase; mGlu 5 R, metabotropic glutamate 5 Receptor; MPEP, 2-methyl-6-(phenylethynyl)pyridine hydrochloride; PPF, paired-pulse facilitation; PPS, paired-pulse stimulation; st-A 2A R KO mice, striatum-specific A 2A R knockout mice; WT, wild-type. AbstractAdenosine A 2A , cannabinoid CB 1 and metabotropic glutamate 5 (mGlu 5 ) receptors are all highly expressed in the striatum. The aim of the present work was to investigate whether, and by which mechanisms, the above receptors interact in the regulation of striatal synaptic transmission. By extracellular field potentials (FPs) recordings in corticostriatal slices, we demonstrated that the ability of the selective type 1 cannabinoid receptor (CB 1 R) agonist WIN55,212-2 to depress synaptic transmission was prevented by the pharmacological blockade or the genetic inactivation of A 2A Rs. Such a permissive effect of A 2A Rs towards CB 1 Rs does not seem to occur pre-synaptically as the ability of WIN55,212-2 to increase the R2/R1 ratio under a protocol of paired-pulse stimulation was not modified by ZM241385. Furthermore, the effects of WIN55,212-2 were reduced in slices from mice lacking post-synaptic striatal A 2A Rs. The selective mGlu 5 R agonist (RS)-2-chloro-5-hydroxyphenylglycine (CHPG) potentiated the synaptic effects of WIN55,212-2, and such a potentiation was abolished by A 2A R blockade. Unlike the synaptic effects, the ability of WIN55,212-2 to prevent NMDA-induced toxicity was not influenced by ZM241385. Altogether, these results show that the state of activation of A 2A Rs regulates the synaptic effects of CB 1 Rs and that A 2A Rs may control CB 1 effects also indirectly, namely through mGlu 5 Rs. Keywords: adenosine A 2A , cannabinoid CB 1 , metabotropic glutamate 5, paired-pulse stimulation, permissive effect, synaptic transmission.

Adenosine A 2A receptors (A 2A Rs) and cannabinoid CB 1 receptors (CB 1 Rs) are highly expressed in the striatum, where they functionally interact and form A 2A /CB 1 heteroreceptor complexes. We investigated the effects of CB 1 R stimulation in a transgenic rat strain over-expressing A 2A Rs under the control of the neural-specific enolase promoter (NSEA 2A rats) and in age-matched wild-type (WT) animals. The effects of the CB 1 R agonist WIN 55,212-2 (WIN) were significantly lower in NSEA 2A rats than in WT animals, as demonstrated by i) electrophysiological recordings of synaptic transmission in corticostriatal slices; ii) the measurement of glutamate outflow from striatal synaptosomes and iii) in vivo experiments on locomotor activity. Moreover, while the effects of WIN were modulated by both A 2A R agonist (CGS 21680) and antagonists (ZM 241385, KW-6002 and SCH-442416) in WT animals, the A 2A R antagonists failed to influence WIN-mediated effects in NSEA 2A rats. The present results demonstrate that in rats with genetic neuronal overexpression of A 2A Rs, the effects mediated by CB 1 R activation in the striatum are significantly reduced, suggesting a change in the stoichiometry of A 2A and CB 1 receptors and providing a strategy to dissect the involvement of A 2A R forming or not forming heteromers in the modulation of striatal functions. These findings add additional evidence for the existence of an interaction between striatal A 2A Rs and CB 1 Rs, playing a fundamental role in the regulation of striatal functions.

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