Javier Gilabert-Juan

Chronic stress induces changes in the structure of interneurons and in the expression of molecules related to neuronal structural plasticity and inhibitory neurotransmission in the amygdala of adult mice.

Chronic stress in experimental animals, one of the most accepted models of chronic anxiety and depression, induces structural remodeling of principal neurons in the amygdala and increases its excitation by reducing inhibitory tone. These changes may be mediated by the polysialylated form of the neural cell adhesion molecule (PSA-NCAM), a molecule related to neuronal structural plasticity and expressed by interneurons in the adult CNS, which is downregulated in the amygdala after chronic stress. We have analyzed the amygdala of adult mice after 21 days of restraint stress, studying with qRT-PCR the expression of genes related to general and inhibitory neurotransmission, and of PSA synthesizing enzymes. The expression of GAD67, synaptophysin and PSA-NCAM was also studied in specific amygdaloid nuclei using immunohistochemistry. We also analyzed dendritic arborization and spine density, and cell activity, monitoring c-Fos expression, in amygdaloid interneurons. At the mRNA level, the expression of GAD67 and of St8SiaII was significantly reduced. At the protein level there was an overall reduction in the expression of GAD67, synaptophysin and PSA-NCAM, but significant changes were only detected in specific amygdaloid regions. Chronic stress did not affect dendritic spine density, but reduced dendritic arborization in interneurons of the lateral and basolateral amygdala. These results indicate that chronic stress modulates inhibitory neurotransmission in the amygdala by regulating the expression of molecules involved in this process and by promoting the structural remodeling of interneurons. The addition of PSA to NCAM by St8SiaII may be involved in these changes.

The Polysialylated Form of the Neural Cell Adhesion Molecule (PSA-NCAM) Is Expressed in a Subpopulation of Mature Cortical Interneurons Characterized by Reduced Structural Features and Connectivity

Principal neurons in the adult cerebral cortex undergo synaptic, dendritic, and spine remodeling in response to different stimuli, and several reports have demonstrated that the polysialylated form of the neural cell adhesion molecule (PSA-NCAM) participates in these plastic processes. However, there is only limited information on the expression of this molecule on interneurons and on its role in the structural plasticity of these cells. We have found that PSA-NCAM is expressed in mature interneurons widely distributed in all the extension of the cerebral cortex and have excluded the expression of this molecule in most principal cells. Although PSA-NCAM expression is generally considered a marker of immature neurons, birth-dating analyses reveal that these interneurons do not have an adult or perinatal origin and that they are generated during embryonic development. PSA-NCAM expressing interneurons show reduced density of perisomatic and peridendritic puncta expressing different synaptic markers and receive less perisomatic synapses, when compared with interneurons lacking this molecule. Moreover, they have reduced dendritic arborization and spine density. These data indicate that PSA-NCAM expression is important for the connectivity of interneurons in the adult cerebral cortex and that its regulation may play an important role in the structural plasticity of inhibitory networks.

Alterations in the expression of PSA-NCAM and synaptic proteins in the dorsolateral prefrontal cortex of psychiatric disorder patients.

Alterations in the structure and physiology of the prefrontal cortex (PFC) have been found in different psychiatric disorders and some of them involve inhibitory networks, especially in schizophrenia and major depression. Changes in the structure of these networks may be mediated by the polysialylated neural cell adhesion molecule (PSA-NCAM), a molecule related to neuronal structural plasticity, expressed in the PFC exclusively by interneurons. Different studies have found that PSA-NCAM expression in the hippocampus and the amygdala is altered in schizophrenia, major depression and animal models of these disorders, in parallel to changes in the expression of molecules related to inhibitory neurotransmission and synaptic plasticity. We have analyzed post-mortem sections of the dorsolateral PFC from the Stanley Neuropathology Consortium, which includes controls, schizophrenia, bipolar and major depression patients, to check whether similar alterations occur. PSA-NCAM was found in neuronal somata and neuropil puncta, many of which corresponded to interneurons. PSA-NCAM expression was only reduced significantly in schizophrenic patients, in parallel to a decrease in glutamic acid-decarboxylase-67 (GAD67) and to an increased expression of vesicular glutamate transporter 1 (VGLUT1) in the white matter. Depressed patients showed significant decreases in synaptophysin (SYN) and VGLUT1 expression. Whereas in bipolar patients, decreases in VGLUT1 expression have also been found, together with a reduction of GAD67. These results indicate that the expression of synaptic proteins is altered in the PFC of patients suffering from these disorders and that, particularly in schizophrenia, abnormal PSA-NCAM and GAD67 expression may underlie the alterations observed in inhibitory neurotransmission.

Expression of PSA-NCAM and synaptic proteins in the amygdala of psychiatric disorder patients

Neuroimaging has revealed structural abnormalities in the amygdala of different psychiatric disorders. The polysialylated neural cell adhesion molecule (PSA-NCAM), a molecule related to neuronal structural plasticity, which expression is altered in schizophrenia, major depression and in animal models of these disorders, may participate in these changes. However, PSA-NCAM has not been studied in the human amygdala. To know whether its expression and that of presynaptic markers, was affected in psychiatric disorders, we have analyzed post-mortem sections from the Stanley Neuropathology Consortium, which includes controls, schizophrenia, bipolar and major depression patients. PSA-NCAM was expressed in neuronal somata and neuropil puncta, many of which corresponded to interneurons. Depressed patients showed decreases in PSA-NCAM expression in the basolateral and basomedial amygdala; synaptophysin and GAD67 were also decreased, while VGLUT-1 was increased, in different nuclei. Increases in PSA-NCAM expression were found in the lateral nucleus of bipolar patients; synaptophysin and GAD67 were reduced, and VGLUT-1 increased, in their basolateral and lateral nuclei. The expression of synaptophysin and GAD67 was downregulated in the basolateral nucleus of schizophrenics. These results indicate that inhibitory and excitatory amygdaloid circuits are affected in these disorders and that abnormal PSA-NCAM expression in depressive and bipolar patients may underlie these alterations.

Post-weaning social isolation rearing influences the expression of molecules related to inhibitory neurotransmission and structural plasticity in the amygdala of adult rats

Several lines of evidence indicate that alterations in the structure of neural circuits and inhibitory neurotransmission underlie the physiopathogenesis of schizophrenia. Most of the studies on these parameters have been focused on cortical regions and, despite the crucial role of the amygdala in this psychiatric disorder, there is less information on this region. In order to expand this knowledge, we have studied the expression of molecules related to inhibitory neurotransmission and structural plasticity in rats subjected to post-weaning isolation rearing, an animal model that reproduces several core symptoms of schizophrenia. We have analyzed, using qRT-PCR and immunohistochemistry, the expression of synaptophysin, GAD65, GAD67, the neural cell adhesion molecule (NCAM), its polysialylated form (PSA-NCAM) and its synthesizing enzymes (St8siaII and St8SiaIV). Isolation-reared rats showed significant increases in the expression of GAD67 protein in the centromedial, medial and basolateral amygdaloid nuclei, but no significant changes in GAD65 or synaptophysin expression were found in these regions. The expression of PSA-NCAM and NCAM was significantly increased in the basolateral and medial nuclei respectively. Our results indicate that isolation-rearing influences positively inhibitory neurotransmission and neuronal structural plasticity in the amygdala, probably through PSA-NCAM. These findings are in contrast to reports describing decreased expression of molecules related to inhibitory neurotransmission in the amygdala of schizophrenic patients. Consequently, although the social isolation rearing model can reproduce some of the behavioral traits of schizophrenics it may fail to reproduce some of the neurobiological features of this disorder, particularly in the amygdala.

Altered Distribution of Hippocampal Interneurons in the Murine Down Syndrome Model Ts65Dn

Down Syndrome, with an incidence of one in 800 live births, is the most common genetic alteration producing intellectual disability. We have used the Ts65Dn model, that mimics some of the alterations observed in Down Syndrome. This genetic alteration induces an imbalance between excitation and inhibition that has been suggested as responsible for the cognitive impairment present in this syndrome. The hippocampus has a crucial role in memory processing and is an important area to analyze this imbalance. In this report we have analysed, in the hippocampus of Ts65Dn mice, the expression of synaptic markers: synaptophysin, vesicular glutamate transporter-1 and isoform 67 of the glutamic acid decarboxylase; and of different subtypes of inhibitory neurons (Calbindin D-28k, parvalbumin, calretinin, NPY, CCK, VIP and somatostatin). We have observed alterations in the inhibitory neuropil in the hippocampus of Ts65Dn mice. There was an excess of inhibitory puncta and a reduction of the excitatory ones. In agreement with this observation, we have observed an increase in the number of inhibitory neurons in CA1 and CA3, mainly interneurons expressing calbindin, calretinin, NPY and VIP, whereas parvalbumin cell numbers were not affected. These alterations in the number of interneurons, but especially the alterations in the proportion of the different types, may influence the normal function of inhibitory circuits and underlie the cognitive deficits observed in DS.

Reduced interneuronal dendritic arborization in CA1 but not in CA3 region of mice subjected to chronic mild stress

Chronic stress induces dendritic atrophy and decreases spine density in excitatory hippocampal neurons, although there is also ample evidence indicating that the GABAergic system is altered in the hippocampus after this aversive experience. Chronic stress causes dendritic remodeling both in excitatory neurons and interneurons in the medial prefrontal cortex and the amygdala.

Sex-specific association of the ST8SIAII gene with schizophrenia in a Spanish population

We investigated the association between ST8SIAII and schizophrenia in a sample of Spanish origin. We found that the G allele (P=0.044) and the AG genotype (P=0.040) of rs3759916 were associated in females. The ACAG haplotype (rs3759914, rs3759915, rs3759916 and rs2305561) was associated in males (P=0.028).

Semaphorin and plexin gene expression is altered in the prefrontal cortex of schizophrenia patients with and without auditory hallucinations.

Auditory hallucinations (AH) are clinical hallmarks of schizophrenia, however little is known about molecular genetics of these symptoms. In this study, gene expression profiling of postmortem brain samples from prefrontal cortex of schizophrenic patients without AH (SNA), patients with AH (SA) and control subjects were compared. Genome-wide expression analysis was conducted using samples of three individuals of each group and the Affymetrix GeneChip Human-Gene 1.0 ST-Array. This analysis identified the Axon Guidance pathway as one of the most differentially expressed network among SNA, SA and CNT. To confirm the transcriptome results, mRNA level quantification of seventeen genes involved in this pathway was performed in a larger sample. PLXNB1, SEMA3A, SEMA4D and SEM6C were upregulated in SNA or SA patients compared to controls. PLXNA1 and SEMA3D showed down-regulation in their expression in the patients samples, but differences remained statistically significant between the SNA patients and controls. Differences between SNA and SA were found in PLXNB1 expression which is decreased in SA patients. This study strengthens the contribution of brain plasticity in pathophysiology of schizophrenia and shows that non-hallucinatory patients present more alterations in frontal regions than patients with hallucinations concerning neural plasticity.

Altered expression of neuropeptides in the primary somatosensory cortex of the Down syndrome model Ts65Dn

Down syndrome is the most common genetic disorder associated with mental retardation. Subjects and mice models for Down syndrome (such as Ts65Dn) show defects in the formation of neuronal networks in both the hippocampus and the cerebral cortex. The principal neurons display alterations in the morphology, density and distribution of dendritic spines in the cortex as well as in the hippocampus. Several evidences point to the possibility that the atrophy observed in principal neurons could be mediated by changes in their inhibitory inputs and, in fact, an imbalance between excitation and inhibition has been observed in Ts65Dn mice in these regions, which are crucial for learning and information processing. These animals have an increased density of interneurons in the primary somatosensory cortex, especially of those expressing calretinin and calbindin D-28k. Here, we have analysed the expression and distribution of several neuropeptides in the primary somatosensory cortex of Ts65Dn mice in order to investigate whether these subpopulations of interneurons are affected. We have observed an increase in the total density of somatostatin expressing interneurons and of those expressing VIP in layer IV in Ts65Dn mice. The typology of the somatostatin and VIP interneurons was unaltered as attested by the pattern of co-expression with other markers. Somatostatin immunoreactive neurons co-express mainly D-28k calbindin and VIP expressing interneurons maintain its pattern of co-expression with calcium binding proteins. These alterations, in case they were also present in subjects with Down syndrome, could be related to their impairment in cognitive profile and could be involved in the neurological defects observed in this disorder.