De novo expression of parvalbumin in ependymal cells in response to brain injury promotes ependymal remodeling and wound repair

The calcium-binding protein parvalbumin (PV) hallmarks subpopulations of interneurons in the murine brain. We serendipitously observed the de novo expression of PV in ependymal cells of the lateral ventricle wall following in vivo lesioning and brain slicing for the preparation of organotypic hippocampal slice cultures (OHSCs). In OHSCs, de novo PV-expression begins shortly after the onset of culturing, and the number of ependymal cells implicated in this process increases with time. PV-immunopositive ependymal cells aggregate and form compact cell clusters, which are characterized by lumen-formation and beating cilia. Scratches inflicted on such clusters with a sharp knife are rapidly closed. Exposure of OHSCs to NF-КB-inhibitors and to antioxidants reduces PV-expression in ependymal cells, thereby implicating injury-induced inflammation in this process. Indeed, in vivo stab injury enhances PV-expression in ependymal cells adjacent to the lesion, whereas neuraminidase denudation is without effect. PV-knock-out mice manifest an impaired wound-healing response to in vivo injury, and a reduced scratch-wound reparation capacity in OHSCs. Whole-transcriptome analysis of ependymal-cell clusters in OHSCs revealed down-regulation of genes involved in cytoskeletal rearrangement, cell motility and cell adhesion in PV-knock out mice as compared with wild-type mice. Our data indicate that the injury-triggered up-regulation of PV-expression is mediated by inflammatory cytokines, and promotes the motility and adhesion of ependymal cells, thereby contributing to leakage closure by the re-establishment of a continuous ependymal layer

The ventrolateral hypothalamic area and the parvafox nucleus: Role in the expression of (positive) emotions?

The lateral hypothalamus has been long suspected of triggering the expression of positive emotions, because stimulations of its tuberal portion provoke bursts of laughter. Electrophysiological studies in various species have indeed confirmed that the lateral hypothalamus contributes to reward mechanisms. However, only the rudiments of the neural circuit underlying the expression of positive emotions are known. The prefrontal cortex, the lateral hypothalamus, and the periaqueductal gray matter (PAG) are involved in these circuits; so, too, are the brainstem nuclei that control the laryngeal muscles and subserve mimicry, as well as the cardiovascular and respiratory systems. The implicated populations of hypothalamic neurons have not been defined either anatomically or molecularly. One promising candidate is the novel parvafox nucleus, which we recently described, in the murine medial forebrain bundle (mfb), which specifically expresses parvalbumin and Foxb1. With the molecularly defined parvafox nucleus as a centerpiece, the inputs from the prefrontal cortex and the projections to the PAG and brainstem can be studied with precision. By drawing on genetic approaches, it will be possible to manipulate the circuitry selectively with spatial and temporal exactitude and to evaluate the concomitant autonomic changes. These data will serve as a basis for imaging studies in humans using various paradigms to provoke the expression of positive emotions. In conclusion, studies of the hypothalamic parvafox nucleus will reveal whether this entity represents the fulcrum for positive emotions, as is the amygdala for fear and the insula for disgust

The Foxb1‐expressing neurons of the ventrolateral hypothalamic parvafox nucleus project to defensive circuits

The parvafox nucleus is an elongated structure that is lodged within the ventrolateral hypothalamus and lies along the optic tract. It comprises axially located parvalbumin (Parv)-positive neurons and a peripheral cuff of Foxb1-expressing ones. In the present study, injections of Cre-dependent adenoviral constructs were targeted to the ventrolateral hypothalamus of Foxb1/Cre mice to label specifically and map the efferent connections of the Foxb1-expressing subpopulation of neurons of the parvafox nucleus. These neurons project more widely than do the Parv-positive ones and implicate a part of the axons known to emanate from the lateral hypothalamus. High labeling densities were found in the dorsolateral and the upper lateral portion of the periaqueductal gray (PAG), the Su3 and PV2 nuclei of the ventrolateral PAG, the cuneiform nucleus, the mesencephalic reticular formation, and the superior colliculus. Intermediate densities of terminals were encountered in the septum, bed nucleus of the stria terminalis, substantia innominata, various thalamic and hypothalamic nuclei, pedunculopontine nucleus, Barrington's nucleus, retrofacial nucleus, and retroambigual nucleus. Scattered terminals were observed in the olfactory bulbs, the prefrontal cortex and the lamina X of the cervical spinal cord. Because the terminals were demonstrated to express the glutamate transporter VGlut2, the projections are presumed to be excitatory. A common denominator of the main target sites of the Foxb1-positive axons of the parvafox nucleus appears to be an involvement in the defensive reactions to life-threatening situations. The hypothalamic parvafox nucleus may contribute to the autonomic manifestations that accompany the expression of emotions

Parvalbumin-neurons of the ventrolateral hypothalamic parvafox nucleus receive a glycinergic input: a gene-microarray study

The ventrolateral hypothalamic parvafox (formerly called PV1-Foxb1) nucleus is an anatomical entity of recent discovery and unknown function. With a view to gaining an insight into its putative functional role(s), we conducted a gene-microarray analysis and, armed with the forthcoming data, controlled the results with the Allen databases and the murine BrainStars (B*) database. The parvafox nucleus was specifically sampled by laser-capture microdissection and the transcriptome was subjected to a microarray analysis on Affymetrix chips. Eighty-two relevant genes were found to be potentially more expressed in this brain region than in either the cerebral cortex or the hippocampus. When the expression patterns of these genes were counterchecked in the Allen-Database of in-situ hybridizations and in the B*-microarray database, their localization in the parvafox region was confirmed for thirteen. For nine novel genes, which are particularly interesting because of their possible involvement in neuromodulation, the expression was verified by quantitative real time-PCR. Of particular functional importance may be the occurrence of glycine receptors, the presence of which indicates that the activity of the parvafox nucleus is under ascending inhibitory control

Birthdate of parvalbumin-neurons in the Parvafox-nucleus of the lateral hypothalamus

The Parvafox-nucleus in the lateral hypothalamus is characterized by the presence of two distinct neural populations, the Parvalbumin (Parv) and the Foxb1-expressing ones. Foxb1-neurons are born at day 10 in the subventricular zone of the mouse mammillary region. It would be interesting to know if the subpopulation of Parv- neurons develop independently at different times and then meet the Foxb1- expressing neurons in the lateral hypothalamus, their final settling place. The aim of this study was to define the period of birth of the Parv-positive neurons using an in-vivo Bromodeoxyuridine-based method in rats. Parv-neurons are generated from embryonic day 10 to day 13, with a peak at day 12. Thus, it appears that the birthdates of the two subpopulations in these two species is similar, perhaps suggesting that they are born from the same neuroepithelial region

Coaxiality of Foxb1- and parvalbumin-expressing neurons in the lateral hypothalamic PV1-nucleus

In the ventrolateral hypothalamus, the PV1-nucleus is defined by its population of parvalbumin-expressing neurons. During embryogenesis, the ventrolateral hypothalamus is colonized also by Foxb1-expressing neurons. In adult Foxb1-EGFP mice, many immunofluorescent neurons were found within the region that is occupied by the PV1-nucleus. They formed a cloud around the axial cord of the parvalbumin-immunopositive cells, which they greatly outnumber (3:1). Only a small proportion of the neurons in the PV1-nucleus co-expressed both parvalbumin and Foxb1. In the light of these findings, a redesignation of this lateral hypothalamic structure as the PV1-Foxb1 nucleus would more accurately reflect its specific biochemical properties

The EF-hand Ca²⁺-binding protein super-family: A genome-wide analysis of gene expression patterns in the adult mouse brain

In mice, 249 putative members of the superfamily of EF-hand domain Ca²⁺-binding proteins, manifesting great diversity in structure, cellular localization and functions have been identified. Three members in particular, namely, calbindin-D28K, calretinin and parvalbumin, are widely used as markers for specific neuronal subpopulations in different regions of the brain. The aim of the present study was to compile a comprehensive atlas of the gene-expression profiles of the entire EF-hand gene superfamily in the murine brain. This was achieved by a meticulous examination of the in-situ hybridization images in the Allen Brain Atlas database. Topographically, our analysis focused on the olfactory bulb, cerebral cortex (barrel cortex in the primary somatosensory area), basal ganglia, hippocampus, amygdala, thalamus, hypothalamus, cerebellum, midbrain, pons and medulla, and on clearly identifiable sub-structures within each of these areas. The expression profiles of four family-members, namely hippocalcin-like 4, neurocalcin-δ, plastin 3 and tescalcin, that have not been hitherto reported, at either the mRNA (in-situ-hybridization) or the protein (immunohistochemical) levels, are now presented for the first time. The fruit of our analysis is a document in which the gene-expression profiles of all members of the EF-hand family genes are compared, and in which future possible neuronal markers for specific cells/brain areas are identified. The assembled information could afford functional clues to investigators, conducive to further experimental pursuit

Insular cortex activity and the evocation of laughter

The insular cortex is fundamentally involved in the processing of interoceptive information. It has been postulated that the integrative monitoring of the bodily responses to environmental stimuli is crucial for the recognition and experience of emotions. Because emotional arousal is known to be closely coupled to functions of the anterior insula, we suspected laughter to be associated primarily with neuronal activity in this region. An anatomically constrained re-analysis of our imaging data pertaining to ticklish laughter, to inhibited ticklish laughter, and to voluntary laughter revealed regional differences in the levels of neuronal activity in the posterior and mid-/anterior portions of the insula. Ticklish laughter was associated specifically with right ventral anterior insular activity, which was not detected under the other two conditions. Hence, apparently, only laughter that is evoked as an emotional response bears the signature of autonomic arousal in the insular cortex

Parvalbumin-expressing ependymal cells in rostral lateral ventricle wall adhesions contribute to aging-related ventricle stenosis in mice

Aging-associated ependymal-cell pathologies can manifest as ventricular gliosis, ventricle enlargement, or ventricle stenosis. Ventricle stenosis and fusion of the lateral ventricle (LV) walls is associated with a massive decline of the proliferative capacities of the stem cell niche in the affected subventricular zone (SVZ) in aging mice. We examined the brains of adult C57BL/6 mice and found that ependymal cells located in the adhesions of the medial and lateral walls of the rostral LVs upregulated parvalbumin (PV) and displayed reactive phenotype, similarly to injury-reactive ependymal cells. However, PV+ ependymal cells in the LV-wall adhesions, unlike injury-reactive ones, did not express glial fibrillary acidic protein. S100B+/PV+ ependymal cells found in younger mice diminished in the LV-wall adhesions throughout aging. We found that periventricular PV-immunofluorescence showed positive correlation to the grade of LV stenosis in nonaged mice (10-month-old) PV-knock out (PV-KO) mice. This suggests an involvement of PV+ ependymal cells in aging-associated ventricle stenosis. Additionally, we observed a time-shift in microglial activation in the LV-wall adhesions between age-grouped PV- KO and wild-type mice, suggesting a delay in microglial activation when PV is absent from ependymal cells. Our findings implicate that compromised ependymal cells of the adhering ependymal layers upregulate PV and display phenotype shift to “reactive” ependymal cells in aging-related ventricle stenosis; moreover, they also contribute to the progression of LV-wall fusion associated with a decline of the affected SVZ-stem cell niche in aged mice

Reduction in 50-kHz call-numbers and suppression of tickling-associated positive affective behaviour after lesioning of the lateral hypothalamic parvafox nucleus in rats

The parvafox nucleus is located ventrolaterally in the lateral hypothalamic area (LHA). Its core and shell are composed of neurons expressing the calcium-binding protein parvalbumin (PV) and the transcription factor Foxb1, respectively. Given the known functions of the LHA and that the parvafox nucleus receives afferents from the lateral orbitofrontal cortex and projects to the periaqueductal gray matter, a functional role of this entity in the expression of positive emotions has been postulated.The purpose of the present study was to ascertain whether the deletion of neurons in the parvafox nucleus influenced the tickling-induced 50-kHz calls, which are thought to reflect positive affective states, in rats. To this end, tickling of the animals (heterospecific play) was combined with intracerebral injections of the excitotoxin kainic acid into the parvafox nucleus.The most pronounced surgery-associated reduction in 50-kHz call-numbers was observed in the group of rats in which, on the basis of PV-immunoreactive-cell counts in the parvafox nucleus, bilateral lesions had been successfully produced. Two other parameters that were implemented to quantify positive affective behaviour, namely, an approach towards and a following of the hand of the tickling experimenter, were likewise most markedly suppressed in the group of rats with bilaterally successful lesions. Furthermore, positive correlations were found between each of the investigated parameters. Our data afford evidence that the parvafox nucleus plays a role in the production of 50-kHz calls in rats, and, more generally, in the expression of positive emotions