Opposing effects of the purinergic P2X7 receptor on seizures in neurons and microglia in male mice.

BACKGROUND: The purinergic ATP-gated P2X7 receptor (P2X7R) is increasingly recognized to contribute to pathological neuroinflammation and brain hyperexcitability. P2X7R expression has been shown to be increased in the brain, including both microglia and neurons, in experimental models of epilepsy and patients. To date, the cell type-specific downstream effects of P2X7Rs during seizures remain, however, incompletely understood. METHODS: Effects of P2X7R signaling on seizures and epilepsy were analyzed in induced seizure models using male mice including the kainic acid model of status epilepticus and pentylenetetrazole model and in male and female mice in a genetic model of Dravet syndrome. RNA sequencing was used to analyze P2X7R downstream signaling during seizures. To investigate the cell type-specific role of the P2X7R during seizures and epilepsy, we generated mice lacking exon 2 of the P2rx7 gene in either microglia (P2rx7:Cx3cr1-Cre) or neurons (P2rx7:Thy-1-Cre). To investigate the protective potential of overexpressing P2X7R in GABAergic interneurons, P2X7Rs were overexpressed using adeno-associated virus transduction under the mDlx promoter. RESULTS: RNA sequencing of hippocampal tissue from wild-type and P2X7R knock-out mice identified both glial and neuronal genes, in particular genes involved in GABAergic signaling, under the control of the P2X7R following seizures. Mice with deleted P2rx7 in microglia displayed less severe acute seizures and developed a milder form of epilepsy, and microglia displayed an anti-inflammatory molecular profile. In contrast, mice lacking P2rx7 in neurons showed a more severe seizure phenotype when compared to epileptic wild-type mice. Analysis of single-cell expression data revealed that human P2RX7 expression is elevated in the hippocampus of patients with temporal lobe epilepsy in excitatory and inhibitory neurons. Functional studies determined that GABAergic interneurons display increased responses to P2X7R activation in experimental epilepsy. Finally, we show that viral transduction of P2X7R in GABAergic interneurons protects against evoked and spontaneous seizures in experimental temporal lobe epilepsy and in mice lacking Scn1a, a model of Dravet syndrome. CONCLUSIONS: Our results suggest a dual and opposing action of P2X7R in epilepsy and suggest P2X7R overexpression in GABAergic interneurons as a novel therapeutic strategy for acquired and, possibly, genetic forms of epilepsy.

A systems approach delivers a functional microRNA catalog and expanded targets for seizure suppression in temporal lobe epilepsy.

Temporal lobe epilepsy is the most common drug-resistant form of epilepsy in adults. The reorganization of neural networks and the gene expression landscape underlying pathophysiologic network behavior in brain structures such as the hippocampus has been suggested to be controlled, in part, by microRNAs. To systematically assess their significance, we sequenced Argonaute-loaded microRNAs to define functionally engaged microRNAs in the hippocampus of three different animal models in two species and at six time points between the initial precipitating insult through to the establishment of chronic epilepsy. We then selected commonly up-regulated microRNAs for a functional in vivo therapeutic screen using oligonucleotide inhibitors. Argonaute sequencing generated 1.44 billion small RNA reads of which up to 82% were microRNAs, with over 400 unique microRNAs detected per model. Approximately half of the detected microRNAs were dysregulated in each epilepsy model. We prioritized commonly up-regulated microRNAs that were fully conserved in humans and designed custom antisense oligonucleotides for these candidate targets. Antiseizure phenotypes were observed upon knockdown of miR-10a-5p, miR-21a-5p, and miR-142a-5p and electrophysiological analyses indicated broad safety of this approach. Combined inhibition of these three microRNAs reduced spontaneous seizures in epileptic mice. Proteomic data, RNA sequencing, and pathway analysis on predicted and validated targets of these microRNAs implicated derepressed TGF-ß signaling as a shared seizure-modifying mechanism. Correspondingly, inhibition of TGF-ß signaling occluded the antiseizure effects of the antagomirs. Together, these results identify shared, dysregulated, and functionally active microRNAs during the pathogenesis of epilepsy which represent therapeutic antiseizure targets.

Evaluation of prenatal calabash chalk geophagy on the developing brain of Wistar rats.

Calabash chalk (CaC) is an aluminium silicate hydroxide compound with heavy metal constituents, making it a potential neurotoxicant. Pregnant women often consume CaC as an antiemetic, which may interfere with the normal development of the foetal brain. Here, we evaluated the effects of CaC administration in pregnant rats on the brain of the offspring. Wistar rat dams were assigned to one of three groups: control, 200 mg/kg and 800 mg/kg of a CaC suspension. Administrations lasted 14 days (gestation days 7-20). On day 14, 5-bromo-2'-deoxyuridine (BrdU) was administered and dams were allowed to term. Behavioural tests were performed on different days as the pups matured, and they were sacrificed on post-natal days 30 and 60. Brains were processed for histology and Western blotting. Results showed no significant differences in surface righting reflex, cliff avoidance, negative geotaxis and open-field activity. No hippocampal and somatosensory cortical cytoarchitectonic alterations and no significant signs of glial fibrillary acidic protein (GFAP) activation were observed. Neuronal nuclei counts showed variability in the somatosensory cortex and hippocampus of the CaC group. BrdU-positive cells were significantly lower in the 200 mg/kg group and higher in the 800 mg/kg group. Doublecortin-X-positive cells were not different in all the CaC groups. Astrocytes and microglia Western blotting quantification confirmed no significant increase in pup glial cells in adulthood. Prenatal consumption of CaC at indicated dosages may not be deleterious to the developing brain, especially after cessation of exposure and during maturation of the animal. However, the differences in neuronal and glial populations may be due to their ability to cope with CaC.

Enhancement of GABA(A)-current run-down in the hippocampus occurs at the first spontaneous seizure in a model of temporal lobe epilepsy.

Refractory temporal lobe epilepsy (TLE) is associated with a dysfunction of inhibitory signaling mediated by GABA(A) receptors. In particular, the use-dependent decrease (run-down) of the currents (I(GABA)) evoked by the repetitive activation of GABA(A) receptors is markedly enhanced in hippocampal and cortical neurons of TLE patients. Understanding the role of I(GABA) run-down in the disease, and its mechanisms, may allow development of medical alternatives to surgical resection, but such mechanistic insights are difficult to pursue in surgical human tissue. Therefore, we have used an animal model (pilocarpine-treated rats) to identify when and where the increase in I(GABA) run-down occurs in the natural history of epilepsy. We found: (i) that the increased run-down occurs in the hippocampus at the time of the first spontaneous seizure (i.e., when the diagnosis of epilepsy is made), and then extends to the neocortex and remains constant in the course of the disease; (ii) that the phenomenon is strictly correlated with the occurrence of spontaneous seizures, because it is not observed in animals that do not become epileptic. Furthermore, initial exploration of the molecular mechanism disclosed a relative increase in alpha4-, relative to alpha1-containing GABA(A) receptors, occurring at the same time when the increased run-down appears, suggesting that alterations in the molecular composition of the GABA receptors may be responsible for the occurrence of the increased run-down. These observations disclose research opportunities in the field of epileptogenesis that may lead to a better understanding of the mechanism whereby a previously normal tissue becomes epileptic.

Finding a better drug for epilepsy: antiinflammatory targets.

This monograph summarizes one of the sessions of the XI Workshop on Neurobiology of Epilepsy (WONOEP), and provides a critical review of the current state of the field. Speakers and discussants focused on several broad topics: (1) the coexistence of inflammatory processes encompassing several distinct signal-transduction pathways with the epileptogenic process; (2) evidence for the contribution of specific inflammatory molecules and processes to the onset and progression of epilepsy, as well as to epilepsy-related morbidities including depression; (3) the complexity and intricate cross-talk of the pathways involved in inflammation, and the discrete, often opposite roles of a given mediator in neurons versus other cell types. These complexities highlight the challenges confronting the field as it aims to define inflammatory molecules as promising targets for epilepsy prevention and treatment.

Localized delivery of fibroblast growth factor-2 and brain-derived neurotrophic factor reduces spontaneous seizures in an epilepsy model.

A loss of neurons is observed in the hippocampus of many patients with epilepsies of temporal lobe origin. It has been hypothesized that damage limitation or repair, for example using neurotrophic factors (NTFs), may prevent the transformation of a normal tissue into epileptic (epileptogenesis). Here, we used viral vectors to locally supplement two NTFs, fibroblast growth factor-2 (FGF-2) and brain-derived neurotrophic factor (BDNF), when epileptogenic damage was already in place. These vectors were first characterized in vitro, where they increased proliferation of neural progenitors and favored their differentiation into neurons, and they were then tested in a model of status epilepticus-induced neurodegeneration and epileptogenesis. When injected in a lesioned hippocampus, FGF-2/BDNF expressing vectors increased neuronogenesis, embanked neuronal damage, and reduced epileptogenesis. It is concluded that reduction of damage reduces epileptogenesis and that supplementing specific NTFs in lesion areas represents a new approach to the therapy of neuronal damage and of its consequences.

Modulation of peripheral cytotoxic cells and ictogenesis in a model of seizures.

PURPOSE: A link between seizure susceptibility, blood-brain barrier (BBB) failure, and the activation of peripheral white blood cells has been recently proposed. However, the molecular players involved in this cascade of events are unknown. We tested the hypothesis that immunosupression by splenectomy or lack of perforin, a downstream factor of natural killer (NK) and cytotoxic T cells, could reduce seizure onset. METHODS: Pilocarpine was used to induce seizures in adult rats wild-type and perforin-deficient mice. Splenectomy was performed prior to pilocarpine injection. Seizure onset was evaluated by electroencephalography (EEG) and joint time-frequency analysis. Spleens from control and pilocarpine-treated groups were analyzed for anatomical changes and CD3+ cell content. BBB damage was assessed by measuring albumin parenchymal extravasation. Fluorescence-activated cell sorting (FACS) analysis was performed on spleen and brain tissue of wild-type and perforin-deficient mice treated, or not, with pilocarpine. KEY FINDINGS: Splenectomy significantly reduced seizure-associated mortality. Histologic analysis of the spleens exposed to pilocarpine revealed altered white and red pulp anatomy and an increase in CD3+ T cells. Onset of status epilepticus (SE) and mortality were significantly decreased in perforin-deficient mice. Pilocarpine significantly increased spleen NK 1.1 and CD8+ cell percentage; in contrast, the brain inflammatory cell profile remained unchanged at the time of pilocarpine SE. BBB damage was reduced in the perforin-deficient pilocarpine-treated mice. SIGNIFICANCE: Immunosuppressant maneuvers such as splenectomy or lack of perforin decrease the onset or the severity of pilocarpine SE. Our results suggest that cytotoxic lymphocytes, and specifically the cytolytic factor perforin, may be key molecular players involved in the axis between peripheral intravascular inflammation and seizures.

Localized overexpression of FGF-2 and BDNF in hippocampus reduces mossy fiber sprouting and spontaneous seizures up to 4 weeks after pilocarpine-induced status epilepticus.

PURPOSE: We have recently reported that viral vector-mediated supplementation of fibroblast growth factor-2 (FGF-2) and brain-derived neurotrophic factor (BDNF) in a lesioned, epileptogenic rat hippocampus limits neuronal damage, favors neurogenesis, and reduces spontaneous recurrent seizures. To test if this treatment can also prevent hippocampal circuit reorganization, we examined here its effect on mossy fiber sprouting, the best studied form of axonal plasticity in epilepsy. METHODS: A herpes-based vector expressing FGF-2 and BDNF was injected into the rat hippocampus 3 days after an epileptogenic insult (pilocarpine-induced status epilepticus). Continuous video-electroencephalography (EEG) monitoring was initiated 7 days after status epilepticus, and animals were sacrificed at 28 days for analysis of cell loss (measured using NeuN immunofluorescence) and mossy fiber sprouting (measured using dynorphin A immunohistochemistry). KEY FINDINGS: The vector expressing FGF-2 and BDNF decreased both mossy fiber sprouting and the frequency and severity of spontaneous seizures. The effect on sprouting correlated strictly with the cell loss in the terminal fields of physiologic mossy fiber innervation (mossy cells in the dentate gyrus hilus and CA3 pyramidal neurons). SIGNIFICANCE: These data suggest that the supplementation of FGF-2 and BDNF in an epileptogenic hippocampus may prevent epileptogenesis by decreasing neuronal loss and mossy fiber sprouting, that is, reducing some forms of circuit reorganization.

Hippocampal FGF-2 and BDNF overexpression attenuates epileptogenesis-associated neuroinflammation and reduces spontaneous recurrent seizures.

Under certain experimental conditions, neurotrophic factors may reduce epileptogenesis. We have previously reported that local, intrahippocampal supplementation of fibroblast growth factor-2 (FGF-2) and brain-derived neurotrophic factor (BDNF) increases neurogenesis, reduces neuronal loss, and reduces the occurrence of spontaneous seizures in a model of damage-associated epilepsy. Here, we asked if these possibly anti-epileptogenic effects might involve anti-inflammatory mechanisms. Thus, we used a Herpes-based vector to supplement FGF-2 and BDNF in rat hippocampus after pilocarpine-induced status epilepticus that established an epileptogenic lesion. This model causes intense neuroinflammation, especially in the phase that precedes the occurrence of spontaneous seizures. The supplementation of FGF-2 and BDNF attenuated various parameters of inflammation, including astrocytosis, microcytosis and IL-1ß expression. The effect appeared to be most prominent on IL-1ß, whose expression was almost completely prevented. Further studies will be needed to elucidate the molecular mechanism(s) for these effects, and for that on IL-1ß in particular. Nonetheless, the concept that neurotrophic factors affect neuroinflammation in vivo may be highly relevant for the understanding of the epileptogenic process.

Different patterns of neuronal activation and neurodegeneration in the thalamus and cortex of epilepsy-resistant Proechimys rats versus Wistar rats after pilocarpine-induced protracted seizures.

PURPOSE: To analyze cellular mechanisms of limbic-seizure suppression, the response to pilocarpine-induced seizures was investigated in cortex and thalamus, comparing epilepsy-resistant rats Proechimys guyannensis with Wistar rats. METHODS: Fos immunoreactivity revealing neuronal activation, and degenerating neurons labeled by Fluoro-Jade B (FJB) histochemistry were analyzed on the first day after onset of seizures lasting 3 h. Subpopulations of gamma-aminobutyric acid (GABA)ergic cells were characterized with double Fos-parvalbumin immunohistochemistry. RESULTS: In both cortex and thalamus, degenerating neurons were much fewer in Proechimys than Wistar rats. Fos persisted at high levels at 24 h only in the Proechimys thalamus and cortex, especially in layer VI where corticothalamic neurons reside. In the parietal cortex, about 50% of parvalbumin-containing interneurons at 8 h, and 10-20% at 24 h, were Fos-positive in Wistar rats, but in Proechimys, Fos was expressed in almost all parvalbumin-containing interneurons at 8 h and dropped at 24 h. Fos positivity in cingulate cortex interneurons was similar in both species. In the Wistar rat thalamus, Fos was induced in medial and midline nuclei up to 8 h, when <30% of reticular nucleus cells were Fos-positive, and then decreased, with no relationship with cell loss, evaluated in Nissl-stained sections. In Proechimys, almost all reticular nucleus neurons were Fos-positive at 24 h. DISCUSSION: At variance with laboratory rats, pilocarpine-induced protracted seizures elicit in Proechimys limited neuronal death, and marked and long-lasting Fos induction in excitatory and inhibitory cortical and thalamic cell subsets. The findings implicate intrathalamic and intracortical regulation, and circuits linking thalamus and cortex in limbic seizure suppression leading to epilepsy resistance.

Pulsed-arterial-spin-labeling perfusion 3T MRI following single seizure: a first case report study.

A 41-year-old woman with focal epilepsy was analyzed immediately and 1 week post-ictally using pulsed-arterial-spin-labeling perfusion 3T MRI, a non-invasive method. Seizure-associated blood flow alterations were characterized by increased ictal perfusion in the occipito-parietal right cortex, and hypoperfusion in the same location 1 week later. These results indicate that non-invasive perfusion MRI can be used routinely to detect vascular alterations in epilepsy, and possibly to identify the location of the seizure focus.

Ongoing Electroencephalographic Activity Associated with Cortical Arousal in Transgenic PDAPP Mice (hAPP V717F).

BACKGROUND: It has been shown that theta (6-10 Hz) and delta (1-6 Hz) ongoing electroencephalographic (EEG) rhythms revealed variations in the cortical arousal in C57 Wild Type (WT) mice during cage exploration (active condition) compared to awake quiet behavior (passive condition; IMI PharmaCog project, www.pharmacog.eu). OBJECTIVE: The objective was to test if these EEG rhythms might be abnormal in old PDAPP mice modeling Alzheimer's disease (AD) with a hAPP Indiana V717F mutation (They show abnormal neural transmission, cognitive deficits, and brain accumulation of Aß1-42). METHODS: Ongoing EEG rhythms were recorded by a frontoparietal bipolar channel in 15 PDAPP and 23 WT C57 male mice (mean age of 22.8 months ±0.4 and 0.3 standard error, respectively). EEG absolute power (density) was calculated. Frequency and amplitude of individual delta and theta frequency (IDF and ITF) peaks were considered during passive and active states in the wakefulness. RESULTS: Compared with the WT group, the PDAPP group showed higher frequency of the IDF during the passive condition and lower frequency of the ITF during the active state. Furthermore, the WT but not PDAPP group showed significant changes in the frontoparietal EEG power (IDF, ITF) during active over passive state. CONCLUSION: PDAPP mice were characterized by less changes in the brain arousal during an active state as revealed by frontoparietal EEG rhythms. Future studies will have to cross-validate the present results on large animal groups, clarify the neurophysiological underpinning of the effect, and test if the disease modifying drugs against AD amyloidosis normalize those candiate EEG biomarkers in PDAPP mice.

Assessment of cerebral blood volume in schizophrenia: A magnetic resonance imaging study.

Brain atrophy has consistently been observed in schizophrenia, representing a 'gross' evidence of anatomical abnormalities. Reduced cerebral blood volume (CBV) may accompany brain size decrement in schizophrenia, as suggested by prior small SPECT studies. In this study, we non-invasively investigated the hemisphere CBV in a large sample of patients suffering from schizophrenia with perfusion-weighted imaging (PWI). PWI images were obtained, following intravenous injection of paramagnetic contrast agent (Gadolinium-DTPA), for 54 DSM-IV patients with schizophrenia (mean age+/-SD=39.19+/-12.20 years; 34 males, 20 females) and 24 normal controls (mean age+/-SD=44.63+/-10.43 years; 9 males, 15 females) with a 1.5T Siemens magnet using an echo-planar sequence (TR=2160 ms, TE=47 ms, slice thickness=5mm). The contrast of enhancement (CE), a semi-quantitative parameter inversely estimating the CBV, were calculated pixel by pixel as the ratio of the maximum signal intensity drop during the passage of contrast agent (Sm) by the baseline pre-bolus signal intensity (So) (CE=Sm/Sox100) for right and left hemisphere on two axial images. Specifically, higher CE values correspond to lower CBV and viceversa Compared to normal controls, patients with schizophrenia had significantly higher bilateral hemisphere CE values (p=0.02) and inverse CE laterality index (p=0.02). This study showed abnormally reduced and inverse hemisphere CBV in a large population of patients with schizophrenia. Hypothetically, chronic low CBV may sustain neural hypoactivation and concomitant increase of free radicals, ultimately resulting in neuronal loss and cognitive impairments. Thus, altered intracranial hemodynamics may accompany brain atrophy and cognitive deficits, being a crucial factor in the pathophysiology of schizophrenia.

Axon-like processes in type III cells of taste organs.

Type III cells of the taste organs are widely considered to be chemoreceptors. The present study was performed on the frog taste disk and describes an axon-like process in type III cells, which often contains a bundle of densely-packed parallel microfilaments. These processes pass through the basal membrane of the gustatory epithelium, running into the lamina propria (transbasal membrane processes, tBMPs). In their intraepithelial tract, tBMPs contain dense-cored vesicles revealing their origin from type III cells. Type III cells showing both classic nonrigid processes (with vesicles and nerve contacts) and tBMPs are present. The connective tract of a tBMP usually contains dense-cored vesicles only in its proximal portion. In some cases, the connective tract of tBMPs is almost perpendicular to the basal lamina. In other cases, it runs parallel to and below the basal lamina. Some tBMPs contact nerve fibers running in the subepithelial connective tissue; the contact area is rather wide but evident synapse-like junctions were never detected. Contacts between tBMPs and nerve fibers innervating basal cells are also found. In conclusion, the data demonstrate the existence of epithelial cells resembling primitive neurons that display an apical dendrite and axon-like basal processes. Until now, it was not considered possible that epithelial receptor cells extend processes out of the epithelium.

Sub-chronic nicotine-induced changes in regional cerebral blood volume and transversal relaxation time patterns in the rat: a magnetic resonance study.

This preliminary study describes magnetic resonance imaging (MRI) data on the effects of sub-chronic nicotine administration in rats. Nicotine 0.4 mg/kg s.c. free base was given once a day for 4 days to Wistar adult male rats. On day 5, anaesthetized subjects were observed using an MRI tomography system. Regional cerebral blood volume (rCBV) and transversal relaxation time (T2) MRI parameters were measured. Nicotine treatment increased T2 values, with a significant effect in the cingulate cortex. A trend to increase was also observed in the prefrontal cortex and nucleus accumbens. Similarly, the effect of nicotine on rCBV was a significant increase in values compared to saline treatment. Post hoc analysis showed a significant effect of nicotine in the prefrontal cortex, cingulate cortex, mediodorsal thalamus and lateral posterior thalamus. This study showed for the first time that sub-chronic nicotine administration can induce changes in MRI pattern which are (i) similar to human MRI studies, and (ii) common to those described for markers of neuronal metabolic activation in corticolimbic brain regions known to be involved in nicotine dependence.

Regional cerebral blood volume (rCBV) and trasversal relaxation time (T2) mapping of the rat limbic system during pre-puberal and adult age.

We analyzed modifications in transversal relaxation time (T2) and regional cerebral blood volume (rCBV) in two areas of the limbic system, i.e., olfactory bulb (OB) and amygdala (AMY), in pre-puberty and post-puberty female rats. The aim of this work was to extend the knowledge about physiological modifications of these MRI parameters at different developmental phases. No significant difference was observed in T2 values of the OB between the two groups (pre-puberty: T2 = 86.92 +/- 8.57 ms, post-puberty: T2 = 88.11 +/- 13.06 ms; mean +/- S.D.). On the contrary T2 values of the AMY were significantly different (P = 0.0001) between the two groups (pre-puberty 76.08 +/- 3.2, post-puberty 81.77 +/- 11.77 ms). rCBV values of OB were significantly different (P = 0.0025) between pre-puberty (0.38 +/- 0.12 a.u.) and post-puberty female rats (0.15 +/- 0.09 a.u.). A significant decrease in rCBV (P = 5.1 x 10(-13)) between pre-puberty and post-puberty females (pre-puberty: 0.36 +/- 0.12, post-puberty: 0.07 +/- 0.05 a.u.) was also observed in the AMY. These findings suggest that in the limbic system, microvascular plasticity parallels neuronal maturation and indicate the importance of an appropriate baseline study in experiments dealing with the limbic system performed at different time-points.

Fos induction in cortical interneurons during spontaneous wakefulness of rats in a familiar or enriched environment.

It has been repeatedly reported that Fos is spontaneously induced in several brain structures, including the cerebral cortex, during wakefulness. To ascertain whether cortical interneurons are involved in this state-dependent oscillation of gene regulation, we combined Fos immunocytochemistry with immunostaining of either parvalbumin or calbindin, known markers of cortical interneurons. Immunopositive neurons were examined in the sensorimotor and cingulate cortex. In rats perfused in basal conditions, a minor proportion (around 8%) of Fos-immunoreactive neurons in the parietal cortex were also parvalbumin- or calbindin-immunoreactive; these double immunostained cells accounted for 13% of the parvalbumin- and 34% of the calbindin-labeled neurons. Colocalization of Fos with either calcium-binding protein was instead not observed in the cingulate cortex. In rats stimulated by novel environmental cues during the period of wakefulness preceding perfusion, Fos-positive neurons increased markedly relative to unstimulated animals, and involved the majority of the calbindin- or parvalbumin-labeled cell populations (60-75% and over 95%, respectively). In the neuronal populations in which Fos was induced by exposure to the enriched environment, the proportion of calbindin- and parvalbumin-labeled cells was larger than in the unstimulated cases, and the increment was statistically significant in the cingulate cortex. The results demonstrate that Fos induction occurring in the cortex during undisturbed wakefulness in a familiar environment involves a minor proportion of interneurons. Furthermore, the findings indicate that the addition of novel environmental stimuli results in an increase of Fos-expressing neurons whose recruitment, at least in the cingulate cortex, involves a higher proportion of interneurons than of projection neurons.

Cortical development and focal cortical dysplasia.

A brief survey of cortical development is presented, focusing on neuronal migration and its alterations. Corticogenesis is achieved through ordered temporospatial steps, via the formation of transient structures, and successive waves of cell proliferation and migration (followed by cell differentiation and maturation), and apoptotic cell death. The appearance of the proliferative ventricular zone and marginal zone, and of the superficial primordial plexiform layer, is followed by the formation of the prospective layer I, of the subplate, whose neurons are destined to die, and of the cortical plate that will give rise to layers II-VI. Cells arising in the ventricular zone migrate radially using radial glia as a scaffold, and are destined to form pyramidal cells. Cortical interneurons are mainly generated in the ganglionic eminence and migrate along axonal substrates following tangential routes. Disorders of this complex process lead to a wide range of alterations, and focal derangements of cortical organization have been grouped under the term focal cortical dysplasia (FCD). As the result of a neuropathological revision of FCD cases with intractable epilepsy, a novel classification comprising three subgroups of FCD has been introduced, and is supported by electroclinical and neuroimaging data, as well as by the postsurgical outcome of patients: i). architectural dysplasia, characterized by altered cortical lamination; ii). cytoarchitectural dysplasia, with the occurrence of giant neurons besides cortical dyslamination; iii). Taylor-type cortical dysplasia, in which altered cortical lamination is consistently associated with the occurrence of giant, dysmorphic and ectopic neurons, and frequently with the so-called balloon cells.

Manganese-enhanced magnetic resonance imaging investigation of the interferon-α model of depression in rats.

Therapeutic effects of interferon-α (IFN-α) are known to be associated with CNS toxicity in humans, and in particular with depression symptoms. Animal models of IFN-α-induced depression (sickness behaviour) have been developed in rodents using various preparations, dosing schedules or routes of administrations. In this work, Manganese Enhanced MRI (MEMRI) has been applied to investigate an experimental model of sickness behaviour induced by administration of IFN-α in rats. IFN-α (3.10(5) U/kg), or vehicle, was daily administered i.p., for 7days in rats (n=20 IFN-α treated and n=20 controls). After treatment, animals were assigned to behavioural (n=10 treated, n=10 control) or MRI (n=10 treated and n=10 control) studies. Animals assigned to the MRI study received two repeated i.p. injections of MnCl2, before image acquisition. Images were acquired at 4.7T using T1 mapping for determination of Mn concentration in brain. After co-registration of T1 maps to a digital brain atlas, differences between brains of treated and untreated animals were assessed pixel-to-pixel by statistical analysis. Behavioural tests showed alterations in freezing and struggling parameters, as expected in an experimental model of sickness behaviour. MRI showed a well defined brain region, mainly contained in the visual cortex, in which Mn uptake was significantly lower in treated than in control animals, indicating probably altered functionality. No significant difference was detected in other brain regions. In addition, a statistically significant decrease in the volume of the pituitary gland, paralleled by a slight increase in its Mn content, was detected in treated animals. MEMRI provides both morphological and functional information in the brain of small laboratory animals and can constitute a valuable tool in the investigation of experimental models of psychiatric diseases.