Altered Expression and In Vivo Activity of mGlu5 Variant a Receptors in the Striatum of BTBR Mice: Novel Insights Into the Pathophysiology of Adult Idiopathic Forms of Autism Spectrum Disorders.

BACKGROUND: mGlu5 metabotropic glutamate receptors are considered as candidate drug targets in the treatment of "monogenic" forms of autism spectrum disorders (ASD), such as Fragile- X syndrome (FXS). However, despite promising preclinical data, clinical trials using mGlu5 receptor antagonists to treat FXS showed no beneficial effects. OBJECTIVE: Here, we studied the expression and function of mGlu5 receptors in the striatum of adult BTBR mice, which model idiopathic forms of ASD, and behavioral phenotype. METHODS: Behavioral tests were associated with biochemistry analysis including qPCR and western blot for mRNA and protein expression. In vivo analysis of polyphosphoinositides hydrolysis was performed to study the mGlu5-mediated intracellular signaling in the striatum of adult BTBR mice under basal conditions and after MTEP exposure. RESULTS: Expression of mGlu5 receptors and mGlu5 receptor-mediated polyphosphoinositides hydrolysis were considerably high in the striatum of BTBR mice, sensitive to MTEP treatment. Changes in the expression of genes encoding for proteins involved in excitatory and inhibitory neurotransmission and synaptic plasticity, including Fmr1, Dlg4, Shank3, Brd4, bdnf-exon IX, Mef2c, and Arc, GriA2, Glun1, Nr2A, and Grm1, Grm2, GriA1, and Gad1 were also found. Behaviorally, BTBR mice showed high repetitive stereotypical behaviors, including self-grooming and deficits in social interactions. Acute or repeated injections with MTEP reversed the stereotyped behavior and the social interaction deficit. Similar effects were observed with the NMDA receptor blockers MK-801 or ketamine. CONCLUSION: These findings support a pivotal role of mGlu5 receptor abnormal expression and function in idiopathic ASD adult forms and unveil novel potential targets for therapy.

N-Phthalyl-l-Tryptophan (RG108), like Clozapine (CLO), Induces Chromatin Remodeling in Brains of Prenatally Stressed Mice.

Schizophrenia (SZ), schizoaffective (SZA), and bipolar (BP) disorder are neurodevelopmental psychopathological conditions related, in part, to genetic load and, in part, to environmentally induced epigenetic dysregulation of chromatin structure and function in neocortical GABAergic, glutamatergic, and monoaminergic neurons. To test the above hypothesis, we targeted our scientific efforts on identifying whether the molecular epigenetic signature of postmortem brains of patients with SZ, SZA, and BP disorder are also present in the brains of adult mice born from dams prenatally restraint stressed (PRS) during gestation. The brains of PRS mice, which are similar to the brains of patients with SZ and BP disorder, show an ∼2-fold increased binding of DNMT1 to psychiatric candidate promoters (glutamic acid decarboxylase 67, Reelin, and brain-derived neurotrophic factor), leading to their hypermethylation, reduced expression, as well as the behavioral endophenotypes reminiscent of those observed in the above psychiatric disorders. To establish whether clozapine (CLO) produces its behavioral and molecular action through a causal involvement of DNA methylation/demethylation processes, we compared the epigenetic action of CLO with that of the DNMT1 competitive inhibitor N-phthalyl-l-tryptophan (RG108). The intracerebroventricular injection of RG108 (20 nmol/day per 5 days), similar to the systemic administration of CLO, corrects the altered behavioral and molecular endophenotypes that are typical of PRS mice. These results are consistent with an epigenetic etiology underlying the behavioral endophenotypic profile in PRS mice. Further, it suggests that PRS mice may be useful in the preclinical screening of antipsychotic drugs acting to correct altered epigenetic mechanisms.

Combined effect of gestational stress and postpartum stress on maternal care in rats.

Variations in maternal care in the rat influence the development of individual differences in behavioral and endocrine responses to stress. This study aimed to examine the interaction between intragastric intubation during late gestation and postpartum stress, induced by pup separation, on maternal behavior and on dams' emotional state and HPA axis function. Rats received intragastric intubation of water on days 12-20 of gestation or remained untreated in their home cage (naïve dams). Pup separation was used as a model of postpartum stress. The procedure consisted of a daily separation of the dam from its litter for 3h from PND 3 until PND 15. Pup separation was carried out in both naïve and intubated dams. The behavioral results indicate that the association of these two stressors significantly decreased arched-back nursing (ABN) and licking and grooming (LG), behaviors considered important parameters to discriminate the high quality of maternal care. Moreover, dams that received both stressors displayed less nest building and blanket nursing behaviors; no effect on the frequency of passive and total nursing was recorded. The analysis of single effects on ABN and LG, revealed that dams that underwent gestational stress induced by intragastric intubation displayed less LG, but ABN was overall unchanged. On the contrary, pup separation stress significantly increased ABN and LG upon reunion of naïve dams with their pups. Treatments per se or the association of both induced modest changes in plasma levels of allopregnanolone and corticosterone that likely did not influence maternal care. These data show that the association of a mild stress during gestation with an unfavorable experience after parturition had a significant impact on maternal care. This effect seems independent from HPA axis activation or from changes in emotional state; further studies would be necessary to ascertain the neural changes that could contribute to altered maternal behavior in stressed mothers. Moreover, these results suggest that the use of intragastric intubation during gestation would interfere with measures of drug-induced changes in maternal behavior and likely their consequences on the offspring.

Isolation Rearing Reduces Neuronal Excitability in Dentate Gyrus Granule Cells of Adolescent C57BL/6J Mice: Role of GABAergic Tonic Currents and Neurosteroids.

Early-life exposure to stress, by impacting on a brain still under development, is considered a critical factor for the increased vulnerability to psychiatric disorders and abuse of psychotropic substances during adulthood. As previously reported, rearing C57BL/6J weanling mice in social isolation (SI) from their peers for several weeks, a model of prolonged stress, is associated with a decreased plasma and brain levels of neuroactive steroids such as 3α,5α-THP, with a parallel up-regulation of extrasynaptic GABAA receptors (GABAAR) in dentate gyrus (DG) granule cells compared to group-housed (GH) mice. In the present study, together with the SI-induced decrease in plasma concentration of both progesterone and 3α,5α-THP, and an increase in THIP-stimulated GABAergic tonic currents, patch-clamp analysis of DG granule cells revealed a significant decrease in membrane input resistance and action potential (AP) firing rate, in SI compared to GH mice, suggesting that SI exerts an inhibitory action on neuronal excitability of these neurons. Voltage-clamp recordings of glutamatergic spontaneous excitatory postsynaptic currents (sEPSCs) revealed a SI-associated decrease in frequency as well as a shift from paired-pulse (PP) depression to PP facilitation (PPF) of evoked EPSCs, indicative of a reduced probability of glutamate release. Daily administration of progesterone during isolation reverted the changes in plasma 3α,5α-THP as well as in GABAergic tonic currents and neuronal excitability caused by SI, but it had only a limited effect on the changes in the probability of presynaptic glutamate release. Overall, the results obtained in this work, together with those previously published, indicate that exposure of mice to SI during adolescence reduces neuronal excitability of DG granule cells, an effect that may be linked to the increased GABAergic tonic currents as a consequence of the sustained decrease in plasma and hippocampal levels of neurosteroids. All these changes may be consistent with cognitive deficits observed in animals exposed to such type of prolonged stress.

Enhanced Glutamatergic Synaptic Plasticity in the Hippocampal CA1 Field of Food-Restricted Rats: Involvement of CB1 Receptors.

The endogenous endocannabinoid system has a crucial role in regulating appetite and feeding behavior in mammals, as well as working memory and reward mechanisms. In order to elucidate the possible role of cannabinoid type-1 receptors (CB1Rs) in the regulation of hippocampal plasticity in animals exposed to food restriction (FR), we limited the availability of food to a 2-h daily period for 3 weeks in Sprague-Dawley rats. FR rats showed a higher long-term potentiation at hippocampal CA1 excitatory synapses with a parallel increase in glutamate release when compared with animals fed ad libitum. FR rats showed a significant increase in the long-term spatial memory determined by Barnes maze. FR was also associated with a decreased inhibitory effect of the CB1R agonist win55,212-2 on glutamatergic field excitatory postsynaptic potentials, together with a decrease in hippocampal CB1R protein expression. In addition, hippocampal brain-derived neurotrophic factor protein levels and mushroom dendritic spine density were significantly enhanced in FR rats. Altogether, our data suggest that alterations of hippocampal CB1R expression and function in FR rats are associated with dendritic spine remodeling and functional potentiation of CA1 excitatory synapses, and these findings are consistent with increasing evidence supporting the idea that FR may improve cognitive functions.