Early chronic fasudil treatment rescues hippocampal alterations in the Ts65Dn model for down syndrome.

Down syndrome (DS) is the most common genetic disorder associated with intellectual disability. To study this syndrome, several mouse models have been developed. Among the most common is the Ts65Dn model, which mimics most of the alterations observed in DS. Ts65Dn mice, as humans with DS, show defects in the structure, density, and distribution of dendritic spines in the cerebral cortex and hippocampus. Fasudil is a potent inhibitor of the RhoA kinase pathway, which is involved in the formation and stabilization of dendritic spines. Our study analysed the effect of early chronic fasudil treatment on the alterations observed in the hippocampus of the Ts65Dn model. We observed that treating Ts65Dn mice with fasudil induced an increase in neural plasticity in the hippocampus: there was an increment in the expression of PSA-NCAM and BDNF, in the dendritic branching and spine density of granule neurons, as well as in cell proliferation and neurogenesis in the subgranular zone. Finally, the treatment reduced the unbalance between excitation and inhibition present in this model. Overall, early chronic treatment with fasudil increases cell plasticity and eliminates differences with euploid animals.

Phenotype and Distribution of Immature Neurons in the Human Cerebral Cortex Layer II.

This work provides evidence of the presence of immature neurons in the human brain, specifically in the layer II of the cerebral cortex. Using surgical samples from epileptic patients and post-mortem tissue, we have found cells with different levels of dendritic complexity (type I and type II cells) expressing DCX and PSA-NCAM and lacking expression of the mature neuronal marker NeuN. These immature cells belonged to the excitatory lineage, as demonstrated both by the expression of CUX1, CTIP2, and TBR1 transcription factors and by the lack of the inhibitory marker GAD67. The type II cells had some puncta expressing inhibitory and excitatory synaptic markers apposed to their perisomatic and peridendritic regions and ultrastructural analysis suggest the presence of synaptic contacts. These cells did not present glial cell markers, although astroglial and microglial processes were found in close apposition to their somata and dendrites, particularly on type I cells. Our findings confirm the presence of immature neurons in several regions of the cerebral cortex of humans of different ages and define their lineage. The presence of some mature features in some of these cells suggests the possibility of a progressively integration as excitatory neurons, as described in the olfactory cortex of rodents.

Piriform cortex alterations in the Ts65Dn model for down syndrome.

The piriform cortex is involved in olfactory information processing, that is altered in Down Syndrome. Moreover, piriform cortex has a crucial involvement in epilepsy generation and is one of the first regions affected in Alzheimer's Disease, both maladies being prevalent among Down Syndrome individuals. In this work, we studied the alterations in neuronal morphology, synaptology and structural plasticity in the piriform cortex of the Ts65Dn mouse model, which is the most used model for the study of this syndrome and mimics some of their alterations. We have observed that Ts65Dn piriform cortex displays: a reduction in dendritic arborisation, a higher density of inhibitory synapses (GAD67), a lower density of excitatory synapses (vGLUT1) and a higher density of inhibitory postsynaptic puncta (gephyrin). Under electron microscopy the excitatory presynaptic and postsynaptic elements were larger in trisomic mice than in controls. Similar results were obtained using confocal microscopy. There were less immature neurons in piriform cortex layer II in addition to a reduction in the expression of PSA-NCAM in the neuropil that subsequently can reflect impairment in structural plasticity. These data support the idea of an impaired environment with altered ratio of inhibition and excitation that involves a reduction in plasticity and dendritic atrophy, providing a possible substrate for the olfactory processing impairment observed in DS individuals.

Morphological alterations in the hippocampus of the Ts65Dn mouse model for Down Syndrome correlate with structural plasticity markers.

Down syndrome (DS) is the most common chromosomal aneuploidy. Although trisomy on chromosome 21 can display variable phenotypes, there is a common feature among all DS individuals: the presence of intellectual disability. This condition is partially attributed to abnormalities found in the hippocampus of individuals with DS and in the murine model for DS, Ts65Dn. To check if all hippocampal areas were equally affected in 4-5 month adult Ts65Dn mice, we analysed the morphology of dentate gyrus granule cells and cornu ammonis pyramidal neurons using Sholl method on Golgi-Cox impregnated neurons. Structural plasticity has been analysed using immunohistochemistry for plasticity molecules followed by densitometric analysis (Brain Derived Neurotrophic Factor (BDNF), Polysialylated form of the Neural Cell Adhesion Molecule (PSA-NCAM) and the Growth Associated Protein 43 (GAP43)). We observed an impairment in the dendritic arborisation of granule cells, but not in the pyramidal neurons in the Ts65Dn mice. When we analysed the expression of molecules related to structural plasticity in trisomic mouse hippocampus, we observed a reduction in the expression of BDNF and PSA-NCAM, and an increment in the expression of GAP43. These alterations were restricted to the regions related to dentate granule cells suggesting an interrelation. Therefore the impairment in dendritic arborisation and molecular plasticity is not a general feature of all Down syndrome principal neurons. Pharmacological manipulations of the levels of plasticity molecules could provide a way to restore granule cell morphology and function.

Effects of Chronic Dopamine D2R Agonist Treatment and Polysialic Acid Depletion on Dendritic Spine Density and Excitatory Neurotransmission in the mPFC of Adult Rats.

Dopamine D2 receptors (D2R) in the medial prefrontal cortex (mPFC) are key players in the etiology and therapeutics of schizophrenia. The overactivation of these receptors contributes to mPFC dysfunction. Chronic treatment with D2R agonists modifies the expression of molecules implicated in neuronal structural plasticity, synaptic function, and inhibitory neurotransmission, which are also altered in schizophrenia. These changes are dependent on the expression of the polysialylated form of the neural cell adhesion molecule (PSA-NCAM), a plasticity-related molecule, but nothing is known about the effects of D2R and PSA-NCAM on excitatory neurotransmission and the structure of mPFC pyramidal neurons, two additional features affected in schizophrenia. To evaluate these parameters, we have chronically treated adult rats with PPHT (a D2R agonist) after enzymatic removal of PSA with Endo-N. Both treatments decreased spine density in apical dendrites of pyramidal neurons without affecting their inhibitory innervation. Endo-N also reduced the expression of vesicular glutamate transporter-1. These results indicate that D2R and PSA-NCAM are important players in the regulation of the structural plasticity of mPFC excitatory neurons. This is relevant to our understanding of the neurobiological basis of schizophrenia, in which structural alterations of pyramidal neurons and altered expression of D2R and PSA-NCAM have been found.

The dendritic spines of interneurons are dynamic structures influenced by PSA-NCAM expression.

Excitatory neurons undergo dendritic spine remodeling in response to different stimuli. However, there is scarce information about this type of plasticity in interneurons. The polysialylated form of the neural cell adhesion molecule (PSA-NCAM) is a good candidate to mediate this plasticity as it participates in neuronal remodeling and is expressed by some mature cortical interneurons, which have reduced dendritic arborization, spine density, and synaptic input. To study the connectivity of the dendritic spines of interneurons and the influence of PSA-NCAM on their dynamics, we have analyzed these structures in a subpopulation of fluorescent spiny interneurons in the hippocampus of glutamic acid decarboxylase-enhanced green fluorescent protein transgenic mice. Our results show that these spines receive excitatory synapses. The depletion of PSA in vivo using the enzyme Endo-Neuraminidase-N (Endo-N) increases spine density when analyzed 2 days after, but decreases it 7 days after. The dendritic spine turnover was also analyzed in real time using organotypic hippocampal cultures: 24 h after the addition of EndoN, we observed an increase in the apparition rate of spines. These results indicate that dendritic spines are important structures in the control of the synaptic input of hippocampal interneurons and suggest that PSA-NCAM is relevant in the regulation of their morphology and connectivity.

Cells expressing markers of immature neurons in the amygdala of adult humans.

The polysialylated form of the neuronal cell adhesion molecule (PSA-NCAM) is expressed by immature neurons in the amygdala of adult mammals, including non-human primates. In a recent report we have also described the presence of PSA-NCAM-expressing cells in the amygdala of adult humans. Although many of these cells have been classified as mature interneurons, some of them lacked mature neuronal markers, suggesting the presence of immature neurons. We have studied, using immunohistochemistry, the existence and distribution of these immature neurons using post mortem material. We have also analysed the presence of proliferating cells and the association between immature neurons and specialised astrocytes. These parameters have also been studied for comparative purposes in the amygdalae of cats and squirrel monkeys. Our results demonstrate that cells coexpressing doublecortin and PSA-NCAM, but lacking neuronal nuclear antigen expression, were present in the amygdala of adult humans. These cells were organised in elongated clusters, which were located between the white matter of the dorsal hippocampus and the basolateral amygdaloid nucleus. These clusters were not associated with astroglial specialised structures. No cells expressing the proliferative marker Ki67 were observed in the amygdaloid parenchyma, although some of them were found in the vicinity of the lateral ventricle. Immature neurons were also present in the amygdala of squirrel monkeys and cats. These cells also appeared clustered in monkeys, although not as organised as in humans. In cats these cells are scarce, appear isolated and most of the PSA-NCAM-expressing structures corresponded to processes apparently originating from the paleocortical layer II.

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.

Chronic fluoxetine treatment in middle-aged rats induces changes in the expression of plasticity-related molecules and in neurogenesis.

BACKGROUND: Antidepressants promote neuronal structural plasticity in young-adult rodents, but little is known of their effects on older animals. The polysialylated form of the neural cell adhesion molecule (PSA-NCAM) may mediate these structural changes through its anti-adhesive properties. PSA-NCAM is expressed in immature neurons and in a subpopulation of mature interneurons and its expression is modulated by antidepressants in the telencephalon of young-adult rodents. RESULTS: We have analyzed the effects of 14 days of fluoxetine treatment on the density of puncta expressing PSA-NCAM and different presynaptic markers in the medial prefrontal cortex, hippocampus and amygdala of middle-aged (8 months old) rats. The density of puncta expressing PSA-NCAM increased in the dorsal cingulate cortex, as well as in different hippocampal and amygdaloid regions. In these later regions there were also increases in the density of puncta expressing glutamic acid decarboxylase 65/67 (GAD6), synaptophysin (SYN), PSA-NCAM/SYN and PSA-NCAM/GAD6, but a decrease of those expressing vesicular glutamate transporter 1 (VGluT1). Since there is controversy on the effects of antidepressants on neurogenesis during aging, we analyzed the number of proliferating cells expressing Ki67 and that of immature neurons expressing doublecortin or PSA-NCAM. No significant changes were found in the subgranular zone, but the number of proliferating cells decreased in the subventricular zone. CONCLUSIONS: These results indicate that the effects of fluoxetine in middle-aged rats are different to those previously described in young-adult animals, being more restricted in the mPFC and even following an opposite direction in the amygdala or the subventricular zone.

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.

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.

Polysialic acid is required for dopamine D2 receptor-mediated plasticity involving inhibitory circuits of the rat medial prefrontal cortex.

Decreased expression of dopamine D2 receptors (D2R), dysfunction of inhibitory neurotransmission and impairments in the structure and connectivity of neurons in the medial prefrontal cortex (mPFC) are involved in the pathogenesis of schizophrenia and major depression, but the relationship between these changes remains unclear. The polysialylated form of the neural cell adhesion molecule (PSA-NCAM), a plasticity-related molecule, may serve as a link. This molecule is expressed in cortical interneurons and dopamine, via D2R, modulates its expression in parallel to that of proteins related to synapses and inhibitory neurotransmission, suggesting that D2R-targeted antipsychotics/antidepressants may act by affecting the plasticity of mPFC inhibitory circuits. To understand the role of PSA-NCAM in this plasticity, rats were chronically treated with a D2R agonist (PPHT) after cortical PSA depletion. PPHT-induced increases in GAD67 and synaptophysin (SYN) neuropil expression were blocked when PSA was previously removed, indicating a role for PSA-NCAM in this plasticity. The number of PSA-NCAM expressing interneuron somata also increased after PPHT treatment, but the percentages of these cells belonging to different interneuronal subpopulations did not change. Cortical pyramidal neurons did not express PSA-NCAM, but puncta co-expressing this molecule and parvalbumin could be found surrounding their somata. PPHT treatment increased the number of PSA-NCAM and parvalbumin expressing perisomatic puncta, but decreased the percentage of parvalbumin puncta that co-expressed SYN. PSA depletion did not block these effects on the perisomatic region, but increased further the number of parvalbumin expressing puncta and increased the percentage of puncta co-expressing SYN and parvalbumin, suggesting that the polysialylation of NCAM may regulate perisomatic inhibition of mPFC principal neurons. Summarizing, the present results indicate that dopamine acting on D2R influences structural plasticity of mPFC interneurons and point to PSA-NCAM as a key player in this remodeling.

Differential evolution of PSA-NCAM expression during aging of the rat telencephalon.

Changes in the ability of neuronal networks to undergo structural remodeling may be involved in the age-associated cognitive decline. The polysialylated form of the neural cell adhesion molecule (PSA-NCAM) declines dramatically during postnatal development, but persists in several regions of the young-adult rat telencephalon, where it participates, through its anti-adhesive properties, in neuronal structural plasticity. However, PSA-NCAM expression during aging has only been studied in the dentate gyrus and the piriform cortex layer II, where it is strongly downregulated in adult (middle-aged) individuals. Using immunohistochemistry, we have observed that in most of the telencephalic areas studied the number of PSA-NCAM expressing cells and the intensity of PSA-NCAM expression in the neuropil remains stable during aging. Old rats only show decreases in the number of PSA-NCAM expressing cells in the lateral amygdala and retrosplenial cortex, and in neuropil expression of stratum lucidum. Given the role of PSA-NCAM in neuronal plasticity, the present results indicate that, even during aging, many regions of the CNS may display neurite, spine or synaptic remodeling.

Dopamine acting through D2 receptors modulates the expression of PSA-NCAM, a molecule related to neuronal structural plasticity, in the medial prefrontal cortex of adult rats.

A "neuroplastic" hypothesis proposes that changes in neuronal structural plasticity may underlie the aetiology of depression and the action of antidepressants. The medial prefrontal cortex (mPFC) is affected by this disorder and shows an intense expression of the polysialylated form of the neural cell adhesion molecule (PSA-NCAM), a plasticity-associated molecule, which is expressed mainly in interneurons. The monoamines serotonin, dopamine and noradrenaline are the principal targets of antidepressant action. Pharmacological manipulation of serotonin levels regulates synaptophysin and PSA-NCAM expression in the adult mPFC. However, the involvement of structural plasticity on the antidepressant effects of dopamine has not been well explored yet. Using immunohistochemistry, we have studied the relationship between dopaminergic fibers and PSA-NCAM expressing neurons in the mPFC and the expression of D2 receptors. In order to evaluate the effects of dopamine in neuronal structural plasticity and on inhibitory neurotransmission, we have analyzed the expression of synaptophysin, PSA-NCAM and GAD67 in the mPFC after cortical dopamine depletion with 6-OHDA and after chronic treatments with the D2 receptor antagonist haloperidol or the D2 receptor agonist PPHT. Many dopaminergic fibers were observed in close apposition to PSA-NCAM expressing neurons and 76% of these cells co-expressed D2 receptor. Both haloperidol treatment and 6-OHDA injection reduced significantly PSA-NCAM, synaptophysin and GAD67 expression in the mPFC. Conversely, PPHT treatment increased the expression of these molecules. Our results give support to the "neuroplastic" hypothesis of depression, suggesting that dopamine acting on D2 receptors may modulate neuronal structural plasticity and inhibitory neurotransmission through changes in PSA-NCAM expression.

A population of prenatally generated cells in the rat paleocortex maintains an immature neuronal phenotype into adulthood.

New neurons in the adult brain transiently express molecules related to neuronal development, such as the polysialylated form of neural cell adhesion molecule, or doublecortin (DCX). These molecules are also expressed by a cell population in the rat paleocortex layer II, whose origin, phenotype, and function are not clearly understood. We have classified most of these cells as a new cell type termed tangled cell. Some cells with the morphology of semilunar-pyramidal transitional neurons were also found among this population, as well as some scarce cells resembling semilunar, pyramidal. and fusiform neurons. We have found that none of these cells in layer II express markers of glial cells, mature, inhibitory, or principal neurons. They appear to be in a prolonged immature state, confirmed by the coexpression of DCX, TOAD/Ulip/CRMP-4, A3 subunit of the cyclic nucleotide-gated channel, or phosphorylated cyclic adenosine monophosphate response element-binding protein. Moreover, most of them lack synaptic contacts, are covered by astroglial lamellae, and fail to express cellular activity markers, such as c-Fos or Arc, and N-methyl-d-aspartate or glucocorticoid receptors. We have found that none of these cells appear to be generated during adulthood or early youth and that most of them have been generated during embryonic development, mainly in E15.5.

PSA-NCAM expression in the human prefrontal cortex.

The prefrontal cortex (PFC) of adult rodents is capable of undergoing neuronal remodeling and neuroimaging studies in humans have revealed that the structure of this region also appears affected in different psychiatric disorders. However, the cellular mechanisms underlying this plasticity are still unclear. The polysialylated form of the neural cell adhesion molecule (PSA-NCAM) may mediate these structural changes through its anti-adhesive properties. PSA-NCAM participates in neurite outgrowth and synaptogenesis and changes in its expression occur parallel to neuronal remodeling in certain regions of the adult brain. PSA-NCAM is expressed in the hippocampus and temporal cortex of adult humans, but it has not been studied in the PFC. Employing immunohistochemistry on sections from the rostromedial superior frontal gyrus we have found that PSA-NCAM is expressed in the human PFC neuropil following a laminated pattern and in a subpopulation of mature neurons, which lack doublecortin expression. Most of these cells have been identified as interneurons expressing calbindin. The expression of PSA-NCAM in the human PFC is similar to that of rodents. Since this molecule has been linked to the neuronal remodeling found in experimental models of depression, it may also participate in the structural plasticity described in the PFC of depressed patients.

Chronic fluoxetine treatment increases the expression of PSA-NCAM in the medial prefrontal cortex.

Recent hypotheses suggest that changes in neuronal structure and connectivity may underlie the etiology of depression. The medial prefrontal cortex (mPFC) is affected by depression and shows neuronal remodeling during adulthood. This plasticity may be mediated by the polysialylated form of the neural cell adhesion molecule (PSA-NCAM), which is intensely expressed in the adult mPFC. As the expression of PSA-NCAM is increased by serotonin in other cerebral regions, antidepressants acting on serotonin reuptake may influence PSA-NCAM expression and thus counteract the effects of depression by modulating neuronal structural plasticity. Using immunohistochemistry, we have studied the relationship between serotoninergic fibers and PSA-NCAM expressing neurons in the adult rat mPFC and the expression of serotonin receptors in these cells. The effects of fluoxetine treatment for 14 days on mPFC PSA-NCAM expression have also been analyzed. Although serotoninergic fibers usually do not contact PSA-NCAM immunoreactive neurons, most of these cells express 5-HT3 receptors. In general, chronic fluoxetine treatment induces significant increases in the number of PSA-NCAM immunoreactive neurons and in neuropil immunostaining and coadministration of the 5-HT3 antagonist ondansetron blocks the effects of fluoxetine on PSA-NCAM expression. These results indicate that fluoxetine, acting through 5-HT3 receptors, can modulate PSA-NCAM expression in the mPFC. This modulation may mediate the structural plasticity of this cortical region and opens new perspectives on the study of the molecular bases of depression.

Neural overexcitation and implication of NMDA and AMPA receptors in a mouse model of temporal lobe epilepsy implying zinc chelation.

PURPOSE: Zinc chelation with diethyldithiocarbamate (DEDTC) during nondamaging kainic acid administration enhances excitotoxicity to the level of cell damage. The objective of this work was to study the developing of the lesion in this model of temporal lobe epilepsy and the implications of the different types of glutamate receptors. METHODS: The antagonist of the N-methyl-D-aspartate (NMDA) receptor MK-801, and the antagonist of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor GYKI52466, were used concomitantly with intraperitoneal administration of kainic acid (15 mg/kg) followed by DEDTC (150 mg/kg) in mouse. The animals were killed at different times from 4 h to 7 days. Fos proteins were used as markers of cell overexcitation; heat-shock protein 72 (HSP72) as marker of cell stress. RESULTS: Neither kainic acid nor DEDTC alone, at the doses used, led to cell loss, HSP72 expression, or permanent Fos protein induction. When combined, the hilus and cornu ammonis were damaged; principal cells in these areas coexpressed c-Fos and HSP72, with the exception of CA2; interneurons did not express HSP72 in any area. MK-801 completely abolished damage and HSP72 expression from the hippocampus. GYKI52466 blocked CA1 damage and HSP72 expression in the CA1 but not in the CA3. CONCLUSIONS: Synaptic zinc increases the tolerance of hippocampus to overexcitation. All the areas that are fated to die are determined simultaneously; the damage in the CA1 is not an extension of the damage in the CA3. Damage of the CA3 is dependent on kainate and NMDA receptors, whereas the damage of the CA1 depends on AMPA and NMDA receptors.

Chelation of synaptic zinc induces overexcitation in the hilar mossy cells of the rat hippocampus.

Complete removal of synaptic zinc by the chelator dietyldithiocarbamate (DEDTC; 500 mg/kg i.p.) in rat was followed by convulsive behaviour including wet dog shakes alternating immobility. Histological analysis 1 day after DEDTC administration detected expression of heat shock protein in the hippocampus restricted to hilar cells. These cells colocalize the marker for neurons and the glutamate receptor GluR2/3 showing that they are excitatory neurons. Additionally, they projected to the contralateral dentate gyrus. Therefore, they correspond to hilar mossy cells. These data show that the synaptic zinc has a role in normal hippocampus avoiding overexcitation, that would impair functionality even in absence of pathological or exoexcitotoxic phenomena.

VIP-containing deep short-axon cells of the olfactory bulb innervate interneurons different from granule cells.

This study investigates the targets of the population of vasoactive intestinal polypeptide (VIP)-containing deep short-axon cells of the rat olfactory bulb (OB), combining single- and double-immunocytochemical approaches under light and electron microscopy. It has been assumed that deep short-axon cells innervate granule cells in the mammalian OB, but their synaptic connectivity has not been demonstrated to date. Our results indicate that, instead of the accepted scheme of the bulbar circuitry, VIP-containing deep short-axon cells are gamma-aminobutyric acid (GABA)ergic interneurons specialized in the selective innervation of other GABAergic deep short-axon cells. Their axons contact with the perisomatic region and the dendritic portions of subsets of deep short-axon cells that contain VIP, calbindin D-28k and neuropeptide Y. Electron microscopy reveals axo-somatic and axo-dendritic symmetrical synapses from VIP-containing boutons. Taken altogether, our data show that the VIP-containing deep short-axon cells of the rat OB form an interneuronal network that modulates the function of other interneurons different from granule cells. They might be involved indirectly in the inhibition or disinhibition of principal cells or might participate in the generation of oscillatory activity and in the synchronization of populations of interneurons and, then, of principal cells. Present data demonstrate that modulation of the OB by local circuits is more complex than the simple inhibition from periglomerular cells and granule cells, and remark the importance of considering the contribution of other classes of GABAergic interneurons different from periglomerular cells and granule cells to the bulbar circuitry.