Conference Agenda

Prenatal infections can increase the risk of developing psychiatric disorders in the offspring. The two-hit hypothesis of schizophrenia postulated that maternal immune activation (MIA) could act as a prime and, later on in life, a second hit could exacerbate latent abnormalities. Thus, we previously tested in a MIA model of schizophrenia whether a second hit during adolescence could exacerbate the dysfunctions observed in adulthood. Hence, we treated adolescent rats with Δ9-Tetrahydrocannabinol (THC), the main psychoactive compound in cannabis. Unexpectedly, THC treatment did not exacerbate the dysfunctions observed in adult rats but attenuated them. These results prompted us to focus our attention on the complex interplay between the endocannabinoid system and the dopamine system and their entangled neurodevelopmental trajectories. Here, we tested, in a rat model of prenatal immune challenge by the viral mimic polyriboinosinic–polyribocytidilic acid, whether MIA affects the endocannabinoid system and endocannabinoid-mediated modulation of dopamine functions. Experiments were performed during adolescence to assess i) the behavioral endophenotype; ii) the locomotor activity in response to THC; iii) the properties of ventral tegmental area (VTA) dopamine neurons in vivo and their response to THC; iv) the endocannabinoid-mediated synaptic plasticity in VTA dopamine neurons; v) the expression of cannabinoid receptors and enzymes involved in endocannabinoid metabolism in mesolimbic structures and vi) MIA-induced neuroinflammatory scenario. We revealed that MIA offspring displayed an altered locomotor activity in response to THC, a higher bursting activity of VTA dopamine neurons and a lack of response to cumulative doses of THC. Consistently, MIA offspring showed an enhanced 2-arachidonoylglycerol-mediated synaptic plasticity and decreased monoacylglycerol lipase activity. Moreover, they displayed latent inflammation and persistent microglia activity. In conclusion, we unveiled neurobiological mechanisms whereby inflammation caused by MIA influences the proper development of endocannabinoid signaling that negatively impacts the dopamine system, eventually leading to psychotic-like symptoms in adulthood.

Cannabis Sativa is one of the most commonly used illicit drug worldwide and its legalization in different countries as well as its misperception as a harmless substance has determined an increase of consumption also among pregnant and breastfeeding women. Evidence suggests how its use may represent a major potential risk of developing psychosis throughout the lifespan and alterations in the epigenome could underlie Cannabis transcriptional and behavioral driven effects. According to the neurodevelopmental hypothesis and the well documented dysregulation of the endocannabinoid and dopaminergic systems in psychosis, here we evaluated the expression of the genes of these two systems and its transcriptional regulation through DNA methylation in brain regions of peri- and pre-natal rats exposed to the Δ⁹-tetrahydrocannabinol (THC), the main psychoactive component of Cannabis. Rats were sacrificed at different time points: perinatal THC rats at adulthood while prenatal THC rats in early or late adolescence. We observed a significant increase in Cnr1, coding for type 1 cannabinoid receptor, and Drd2, coding for dopamine D2 receptor, mRNAs levels selectively in the prefrontal cortex (PFC) of perinatal THC rats with a consistent reduction of Drd2 DNA methylation in the average of the 6 CpG sites investigated. Drd2 gene expression resulted increased also in the PFC of prenatal rats sacrificed at late adolescence with a consistent reduction of DNA methylation at CpG 2 while a significant increase of Cnr1 mRNA levels was only observed in the Ventral Tegmental Area (VTA). Prenatal THC rats sacrificed in early adolescence showed a significant increase in mRNA expression levels within the PFC of Mgll, coding for 2-arachydonoylglycerol degrading enzyme Monoacylglycerol lipase, with no changes in DNA Methylation. Thus, our data confirm the relevant role of Drd2 gene regulation on the effects evoked by pre-and peri- natal THC in particular in adult and late adolescent rats.

Based on the strong clinical evidence for an association between the use of valproic acid (VPA) during pregnancy and the increased risk to develop autism in newborns, exposure to VPA in rodents has become a widely used and recognized model to study the neurobiological mechanisms underlying the development of autism spectrum disorder (ASD). In particular, gestational VPA exposure in rats leads to the development of autism-like behaviors in the offspring, including reduced sociability and preference for social novelty, the appearance of stereotyped behaviors, impairment in several domains of learning and memory, altered pain sensitivity. These phenotypes are present both in male and female offspring, being however more intense in the male counterpart. Of note, among the neurochemical alterations associated with ASD-like behaviors in the model, changes in the endocannabinoid system, altered glia activity, reduced synaptic spine density as well as impaired spine maturation have been found. Namely, prenatal VPA exposure increased CB1 receptor, FAAH and MAGL levels, enhanced GFAP, CD11b, and TNFα levels and triggered microglia activation restricted to the hippocampus. In addition, in the same brain region, we observed reduced spine density and immature spine morphology. More recently, upregulated matrix metalloproteinases (MMP)-2 and MMP-9 activity was also reported in the hippocampus of rats prenatally exposed to VPA, together with a significant down-regulation of the expression of CX3CR1 receptors on microglia cells, and preliminary evidence suggests that inhibition of MMP-2 and MMP-9 proteolytic activity could represent a promising approach to relieve ASD symptoms. These data refer to the male offspring; however, given that the male-to-female ratio for autism is slightly narrowing, analysis in females is needed and preliminary data are unveiling sex-differences in the neurobiological correlates of the ASD-like phenotype triggered by prenatal VPA exposure.

During postnatal development, sensory experiences shape neural connections and individuals acquire memory of these sensory cues. Among the variety of sensory stimuli at which newborn mice are exposed during development, paternal ultrasound vocalizations (USVs) play an important role in forming memories of conspecifics that are recalled in adulthood females to influence mate choice. However, how paternal USVs influence the functional development of cortical auditory circuits is unknown. We performed in vivo two-photon functional imaging of layer 2/3 (L2/3) neurons in the primary auditory areas of anaesthetized mice at different postnatal ages, in animals raised with or without their father. P0 mice were injected in the auditory cortex with adeno-associated viral vectors expressing GCaMP7 and spontaneous activity was characterized at three developmental time windows: i) P8-P11: when the external auditory canal is closed; ii) P12-P14: when the onset of hearing occurs; iii) P15-P21: during the critical period for hearing. At P8-P11, L2/3 neurons show spontaneous synchronous transients. From hearing onset, a switch from synchronous to asynchronous activity occurs and, at the end of the critical period, most cells display asynchronous largely decorrelated neuronal activity. Interestingly, during the critical period, animals raised in the absence of their father showed significantly more correlated activity compared to those raised in the presence of the father. We finally analyzed neuronal responses evoked by pure tones and USVs during the critical window to assess the effect of postnatal father exposure for sound representation. Overall, our results demonstrate that the transition from synchronized to decorrelated activity follows the progress of hearing and suggest a role of father exposure during the postnatal development in the maturation of neuronal circuits in the primary auditory areas.