Giovanni Carriero

Abstract Multimodal astrocyte–neuron communications govern brain circuitry assembly and function 1 . For example, through rapid glutamate release, astrocytes can control excitability, plasticity and synchronous activity 2,3 of synaptic networks, while also contributing to their dysregulation in neuropsychiatric conditions 4–7 . For astrocytes to communicate through fast focal glutamate release, they should possess an apparatus for Ca 2+ -dependent exocytosis similar to neurons 8–10 . However, the existence of this mechanism has been questioned 11–13 owing to inconsistent data 14–17 and a lack of direct supporting evidence. Here we revisited the astrocyte glutamate exocytosis hypothesis by considering the emerging molecular heterogeneity of astrocytes 18–21 and using molecular, bioinformatic and imaging approaches, together with cell-specific genetic tools that interfere with glutamate exocytosis in vivo. By analysing existing single-cell RNA-sequencing databases and our patch-seq data, we identified nine molecularly distinct clusters of hippocampal astrocytes, among which we found a notable subpopulation that selectively expressed synaptic-like glutamate-release machinery and localized to discrete hippocampal sites. Using GluSnFR-based glutamate imaging 22 in situ and in vivo, we identified a corresponding astrocyte subgroup that responds reliably to astrocyte-selective stimulations with subsecond glutamate release events at spatially precise hotspots, which were suppressed by astrocyte-targeted deletion of vesicular glutamate transporter 1 (VGLUT1). Furthermore, deletion of this transporter or its isoform VGLUT2 revealed specific contributions of glutamatergic astrocytes in cortico-hippocampal and nigrostriatal circuits during normal behaviour and pathological processes. By uncovering this atypical subpopulation of specialized astrocytes in the adult brain, we provide insights into the complex roles of astrocytes in central nervous system (CNS) physiology and diseases, and identify a potential therapeutic target.

PURPOSE: Dravet syndrome (DS) is caused by dominant mutations of the SCN1A gene, encoding the NaV 1.1 sodium channel α subunit. Gene targeted mouse models of DS mutations replicate patients' phenotype and show reduced γ-aminobutyric acid (GABA)ergic inhibition. However, little is known on the properties of network hyperexcitability and on properties of seizure generation in these models. In fact, seizures have been studied thus far with surface electroencephalography (EEG), which did not show if specific brain regions are particularly involved. We have investigated hyperexcitability and epileptiform activities generated in neuronal networks of a mouse model of DS. METHODS: We have studied heterozygous NaV 1.1 knock-out mice performing field potential recordings in combined hippocampal/cortical slices in vitro and video/depth electrode intracerebral recordings in vivo during hyperthermia-induced seizures. KEY FINDINGS: In slices, we have disclosed specific signs of hyperexcitability of hippocampal circuits in both the pre-epileptic and epileptic periods, and a specific epileptiform activity was generated in the hippocampus upon application of the convulsant 4-aminopyridine in the epileptic period. During in vivo hyperthermia-induced seizures, we have observed selective hippocampal activity in early preictal phases and pronounced hippocampal activity in the ictal phase. SIGNIFICANCE: We have identified specific epileptiform activities and signs of network hyperexcitability, and disclosed the important role of the hippocampus in seizure generation in this model. These activities may be potentially used as targets for screenings of antiepileptic approaches.

Since health-related quality of life (HRQL) measures are numerous, comparisons have been suggested. To compare three HRQL measures: SF6D, HUI3 and EQ5D. Three questionnaires (SF36, HUI3, EQ5D) were administered to 1,011 patients attending 16 general practices in two Italian cities. Information about patients’ gender, age, education, marital status, smoking, body mass index (BMI) and chronic diseases (hypertension, diabetes, cardiovascular and musculoskeletal diseases) were also collected. Questionnaires scores were calculated using the appropriate algorithms; in particular SF6D scores were obtained from SF36 items. Agreement and correlation between questionnaires scores were investigated using Bland and Altman method and Spearman coefficient. The influence of socio-demographic and morbidity indicators on scores was analysed using the nonparametric quantile regression. The Spearman coefficient was about 0.6 for all questionnaires. The 95% limits of agreement of the scores were approximately from −0.5 to 0.3 except for SF6D and EQ5D when they were from −0.4 to 0.2. The measures were influenced by socio-demographic and clinical variables in a similar way, especially SF6D (the index obtained from SF36) and EQ5D, which appeared to be influenced by the same pattern of factors, including gender, chronic diseases, smoking and BMI. Overall, the agreement between questionnaires scores was quite low, whilst the correlation level was good. Questionnaire scores were influenced by socio-demographic and clinical variables in a similar way, especially SF6D and EQ5D. Therefore, the descriptive capacity of SF6D and EQ5D was found to be similar.

We have generated an experimental 'double-hit' model of chronic epilepsy to recapitulate the co-existence of abnormal cortical structure and frequently recurrent seizures as observed in human focal cortical dysplasia. We induced cortical malformations by exposing rats prenatally to methylazoxymethanol acetate and triggered status epilepticus and recurrent seizures in adult methylazoxymethanol acetate rats with pilocarpine. We studied the course of epilepsy and the long-term morphologic and molecular changes induced by the occurrence of status epilepticus and subsequent chronic epilepsy in the malformed methylazoxymethanol acetate exposed brain. Behavioural and electroencephalographic analyses showed that methylazoxymethanol acetate pilocarpine rats develop more severe epilepsy than naïve rats. Morphologic and molecular analyses demonstrated that status epilepticus and subsequent seizures, but not pilocarpine treatment per se, was capable of affecting both cortical architectural and N-methyl-D-aspartate receptor abnormalities induced by methylazoxymethanol acetate. In particular, cortical thickness was further decreased and N-methyl-D-aspartate regulatory subunits were recruited at the postsynaptic membrane. In addition, methylazoxymethanol acetate pilocarpine rats showed abnormally large cortical pyramidal neurons with neurofilament over-expression. These neurons bear similarities to the hypertrophic/dysmorphic pyramidal neurons observed in acquired human focal cortical dysplasia. These data show that status epilepticus sets in motion a pathological process capable of significantly changing the cellular and molecular features of pre-existing experimental cortical malformations. They suggest that seizure recurrence in human focal cortical dysplasia might be an additional factor in establishing a pathological circuitry that favours chronic neuronal hyperexcitability.

Summary Purpose: Models of temporal lobe epilepsy are commonly utilized to study focal epileptogenesis and ictogenesis. The criteria that define animal models representative of human mesial temporal lobe may vary in different laboratories. We describe herein a focal epilepsy model of mesial temporal (hippocampal) origin that relies on the analysis of interictal and ictal electroencephalography (EEG) patterns and on their correlation with seizure symptoms and neuropathologic findings. The study is based on guinea pigs, a species seldom utilized to develop chronic epilepsy models. Methods: Young adult guinea pigs were bilaterally implanted under isoflurane anesthesia with epidural electrodes over somatosensory cortex and depth electrodes in CA1 hippocampal region. A stainless steel guide cannula was positioned unilaterally in the right dorsal hippocampus to inject 1 μl of 0.9% NaCl solution containing 1 μg kainic acid (KA). One week after surgery, continuous 24 h/day video‐EEG monitoring was performed 48 h before and every other week after KA injection, for no <1 month. EEG data were recorded wide‐band at 2 kHz. After video‐EEG monitoring, brains were analyzed for thionine and Timm staining and glial fibrillary acid protein (GFAP) immunostaining. Key Findings: Unilateral injection of KA in dorsal hippocampus of guinea pigs induces an acute nonconvulsive status epilepticus (SE) that terminates within 24 h (n = 22). Chronic seizures with very mild motor signs (undetectable without EEG monitoring) and highly variable recurrence patterns appear in 45.5% (10 of 22) KA‐treated animals, with variable delays from the initial SE. In these animals interictal events, CA1 cell loss, gliosis, and altered Timm staining pattern were observed. The induction of a chronic condition did not correlate with the duration of the nonconvulsive acute SE, but correlated with the extension and quality of neuropathologic damage. Significance: We demonstrate that a model of hippocampal (mesial temporal lobe) epilepsy can be developed in the guinea pig by intrahippocampal injection of KA. Seizure events in this model show little behavioral signs and may be overlooked without extensive video‐EEG monitoring. The establishment of a chronic epileptic condition correlates with the extension of the hippocampal damage (mainly cell loss and gliosis) and not with the intensity of the initial SE.