Gene expression analysis in the parvalbumin-immunoreactive PV1 nucleus of the mouse lateral hypothalamus

Neuronostatin regulates neuronal function and energetic metabolism in Alzheimer's disease in a GPR107-dependent manner

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease, which is characterized by the accumulation and aggregation of amyloid in brain. Neuronostatin (NST) is an endogenous peptide hormone that participates in many fundamental neuronal processes. However, the metabolism and function of NST in neurons of AD mice are not known. In this study, by combining the structural analyses, primary cultures, knockout cells, and various assessments, the behavior, histopathology, brain-wide expression and cellular signaling pathways in the APP/PS1 mice were investigated. It was found that NST directly bound to GPR107, which was primarily expressed in neurons. NST modulated the neuronal survivability and neurite outgrowth induced by Aβ via GPR107 in neurons. Intracerebroventricular (i.c.v.) administration of NST attenuated learning and memory abilities, reduced the synaptic protein levels of hippocampus, but improved amyloid plaques in the cortex and hippocampus of APP/PS1 mice. NST modulated glucose metabolism of hypothalamus-hippocampus-cortex axis in APP/PS1 mice and decreased ATP levels via the regulation of reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) in response to Aβ, suppressed energetic metabolism, and mitochondrial function in neurons via GPR107/protein kinase A (PKA) signaling pathway. In summary, our findings suggest that NST regulates neuronal function and brain energetic metabolism in AD mice via the GPR107/PKA signaling pathway, which can be a promising target for the treatment of AD.

Chemo- and optogenetic activation of hypothalamic Foxb1-expressing neurons and their terminal endings in the rostral-dorsolateral PAG leads to tachypnea, bradycardia, and immobility

Foxb1 -expressing neurons occur in the dorsal premammillary nucleus (PMd) and further rostrally in the parvafox nucleus, a longitudinal cluster of neurons in the lateral hypothalamus of rodents. The descending projection of these Foxb1+ neurons end in the dorsolateral part of the periaqueductal gray (dlPAG). The functional role of the Foxb1+ neuronal subpopulation in the PMd and the parvafox nucleus remains elusive. In this study, the activity of the Foxb1+ neurons and of their terminal endings in the dlPAG in mice was selectively altered by employing chemo- and optogenetic tools. Our results show that in whole-body barometric plethysmography, hM3Dq-mediated, global Foxb1+ neuron excitation activates respiration. Time-resolved optogenetic gain-of-function manipulation of the terminal endings of Foxb1+ neurons in the rostral third of the dlPAG leads to abrupt immobility and bradycardia. Chemogenetic activation of Foxb1+ cell bodies and ChR2-mediated excitation of their axonal endings in the dlPAG led to a phenotypical presentation congruent with a 'freezing-like' situation during innate defensive behavior.

Intersectional mapping of multi-transmitter neurons and other cell types in the brain

Recent developments in intersectional strategies have greatly advanced our ability to precisely target brain cell types based on unique co-expression patterns. To accelerate the application of intersectional genetics, we perform a brain-wide characterization of 13 Flp and tTA mouse driver lines and selected seven for further analysis based on expression of vesicular neurotransmitter transporters. Using selective Cre driver lines, we created more than 10 Cre/tTA combinational lines for cell type targeting and circuit analysis. We then used VGLUT-Cre/VGAT-Flp combinational lines to identify and map 30 brain regions containing neurons that co-express vesicular glutamate and gamma-aminobutyric acid (GABA) transporters, followed by tracing their projections with intersectional viral vectors. Focusing on the lateral habenula (LHb) as a target, we identified glutamatergic, GABAergic, or co-glutamatergic/GABAergic innervations from ∼40 brain regions. These data provide an important resource for the future application of intersectional strategies and expand our understanding of the neuronal subtypes in the brain.

The PV2 cluster of parvalbumin neurons in the murine periaqueductal gray: connections and gene expression

The PV2 (Celio 1990), a cluster of parvalbumin-positive neurons located in the ventromedial region of the distal periaqueductal gray (PAG) has not been previously described as its own entity, leading us to study its extent, connections, and gene expression. It is an oval, bilateral, elongated cluster composed of approximately 475 parvalbumin-expressing neurons in a single mouse hemisphere. In its anterior portion it impinges upon the paratrochlear nucleus (Par4) and in its distal portion it is harbored in the posterodorsal raphe nucleus (PDR). It is known to receive inputs from the orbitofrontal cortex and from the parvafox nucleus in the ventrolateral hypothalamus. Using anterograde tracing methods in parvalbumin-Cre mice, the main projections of the PV2 cluster innervate the supraoculomotor periaqueductal gray (Su3) of the PAG, the parvafox nucleus of the lateral hypothalamus, the gemini nuclei of the posterior hypothalamus, the septal regions, and the diagonal band in the forebrain, as well as various nuclei within the reticular formation in the midbrain and brainstem. Within the brainstem, projections were discrete, but involved areas implicated in autonomic control. The PV2 cluster expressed various peptides and receptors, including the receptor for Adcyap1, a peptide secreted by one of its main afferences, namely, the parvafox nucleus. The expression of GAD1 and GAD2 in the region of the PV2, the presence of Vgat-1 in a subpopulation of PV2-neurons as well as the coexistence of GAD67 immunoreactivity with parvalbumin in terminal endings indicates the inhibitory nature of a subpopulation of PV2-neurons. The PV2 cluster may be part of a feedback controlling the activity of the hypothalamic parvafox and the Su3 nuclei in the periaqueductal gray.

Quercetin ameliorates glutamate toxicity-induced neuronal cell death by controlling calcium-binding protein parvalbumin

Background

Glutamate is the main excitatory neurotransmitter. Excessive glutamate causes excitatory toxicity and increases intracellular calcium, leading to neuronal death. Parvalbumin is a calcium-binding protein that regulates calcium homeostasis. Quercetin is a polyphenol found in plant and has neuroprotective effects against neurodegenerative diseases.

Objectives

We investigated whether quercetin regulates apoptosis by modulating parvalbumin expression in glutamate induced neuronal damage.

Methods

Glutamate was treated in hippocampal-derived cell line, and quercetin or vehicle was treated 1 h before glutamate exposure. Cells were collected for experimental procedure 24 h after glutamate treatment and intracellular calcium concentration and parvalbumin expression were examined. Parvalbumin small interfering RNA (siRNA) transfection was performed to detect the relation between parvalbumin and apoptosis.

Results

Glutamate reduced cell viability and increased intracellular calcium concentration, while quercetin preserved calcium concentration and neuronal damage. Moreover, glutamate reduced parvalbumin expression and quercetin alleviated this reduction. Glutamate increased caspase-3 expression, and quercetin attenuated this increase in both parvalbumin siRNA transfected and non-transfected cells. The alleviative effect of quercetin was statistically significant in non-transfected cells. Moreover, glutamate decreased bcl-2 and increased bax expressions, while quercetin alleviated these changes. The alleviative effect of quercetin in bcl-2 family protein expression was more remarkable in non-transfected cells.

Conclusions

These results demonstrate that parvalbumin contributes to the maintainace of intracellular calcium concentration and the prevention of apoptosis, and quercetin modulates parvalbumin expression in glutamate-exposed cells. Thus, these findings suggest that quercetin performs neuroprotective function against glutamate toxicity by regulating parvalbumin expression.

Quercetin attenuates the reduction of parvalbumin in middle cerebral artery occlusion animal model

Background

Calcium is a critical factor involved in modulation of essential cellular functions. Parvalbumin is a calcium buffering protein that regulates intracellular calcium concentrations. It prevents rises in calcium concentrations and inhibits apoptotic processes during ischemic injury. Quercetin exerts potent antioxidant and anti-apoptotic effects during brain ischemia. We investigated whether quercetin can regulate parvalbumin expression in cerebral ischemia and glutamate toxicity-induced neuronal cell death. Adult male rats were treated with vehicle or quercetin (10 mg/kg) 30 min prior to middle cerebral artery occlusion (MCAO) and cerebral cortical tissues were collected 24 h after MCAO. We used various techniques including Western blot, reverse transcription-PCR, and immunohistochemical staining to elucidate the changes of parvalbumin expression.

Results

Quercetin ameliorated MCAO-induced neurological deficits and behavioral changes. Moreover, quercetin prevented MCAO-induced a decrease in parvalbumin expression.

Conclusions

These findings suggest that quercetin exerts a neuroprotective effect through regulation of parvalbumin expression.

Gene expression analysis in the mouse brainstem identifies Cart and Nesfatin as neuropeptides coexpressed in the Calbindin-positive neurons of the Nucleus papilio

Study Objectives: The brainstem contains several neuronal populations, heterogeneous in terms of neurotransmitter/neuropeptide content, which are important for controlling various aspects of the rapid eye movement (REM) phase of sleep. Among these populations are the Calbindin (Calb)-immunoreactive NP^Calb neurons, located in the Nucleus papilio, within the dorsal paragigantocellular nucleus (DPGi), and recently shown to control eye movement during the REM phase of sleep. Methods: We performed in-depth data mining of the in situ hybridization data collected at the Allen Brain Atlas, in order to identify potentially interesting genes expressed in this brainstem nucleus. Our attention focused on genes encoding neuropeptides, including Cart (Cocaine and Amphetamine Regulated Transcripts) and Nesfatin 1. Results: While nesfatin 1 appeared ubiquitously expressed in this Calb-positive neuronal population, Cart was coexpressed in only a subset of these glutamatergic NP^Calb neurons. Furthermore, an REM sleep deprivation and rebound assay performed with mice revealed that the Cart-positive neuronal population within the DPGi was activated during REM sleep (as measured by c-fos immunoreactivity), suggesting a role of this neuropeptide in regulating some aspects of REM sleep. Conclusions: The assembled information could afford functional clues to investigators, conducive to further experimental pursuits.

Glutamatergic fast-spiking parvalbumin neurons in the lateral hypothalamus: Electrophysiological properties to behavior

Throughout the central nervous system, neurons expressing the calcium-binding protein parvalbumin have been typically classified as GABAergic with fast-spiking characteristics. However, new methods that allow systematic characterization of the cytoarchitectural organization, connectivity, activity patterns, neurotransmitter nature, and function of genetically-distinct cell types have revealed populations of parvalbumin-positive neurons that are glutamatergic. Remarkably, such findings challenge longstanding concepts that fast-spiking neurons are exclusively GABAergic, suggesting conservation of the fast-spiking phenotype across at least two neurotransmitter systems. This review focuses on the recent advancements that have begun to reveal the functional roles of lateral hypothalamic parvalbumin-positive neurons in regulating behaviors essential for survival.

Lateral hypothalamic fast-spiking parvalbumin neurons modulate nociception through connections in the periaqueductal gray area

A pivotal role of the lateral hypothalamus (LH) in regulating appetitive and reward-related behaviors has been evident for decades. However, the contributions of LH circuits to other survival behaviors have been less explored. Here we examine how lateral hypothalamic neurons that express the calcium-binding protein parvalbumin (PVALB; LH^PV neurons), a small cluster of neurons within the LH glutamatergic circuitry, modulate nociception in mice. We find that photostimulation of LH^PV neurons suppresses nociception to an acute, noxious thermal stimulus, whereas photoinhibition potentiates thermal nociception. Moreover, we demonstrate that LH^PV axons form functional excitatory synapses on neurons in the ventrolateral periaqueductal gray (vlPAG), and photostimulation of these axons mediates antinociception to both thermal and chemical visceral noxious stimuli. Interestingly, this antinociceptive effect appears to occur independently of opioidergic mechanisms, as antagonism of μ-opioid receptors with systemically-administered naltrexone does not abolish the antinociception evoked by activation of this LH^PV→vlPAG pathway. This study directly implicates LH^PV neurons in modulating nociception, thus expanding the repertoire of survival behaviors regulated by LH circuits.

The Ventral Tegmental Area has calbindin neurons with the capability to co-release glutamate and dopamine into the nucleus accumbens

The ventral tegmental area (VTA) has three major classes of neurons: dopaminergic (expressing tyrosine hydroxylase; TH), GABAergic (expressing vesicular GABA transporter; VGaT) and glutamatergic (expressing vesicular glutamate transporter 2; VGluT2). While VTA dopaminergic and GABAergic neurons have been further characterized by expression of calcium-binding proteins (calbindin, CB; calretinin, CR or parvalbumin, PV), it is unclear whether these proteins are expressed in rat VTA glutamatergic neurons. Here, by a combination of in situ hybridization (for VGluT2 mRNA detection) and immunohistochemistry (for CB-, CR- or PV-detection), we found that among the total population of VGluT2 neurons, 30% coexpressed CB, 3% coexpressed PV and <1% coexpressed CR. Given that some VGluT2 neurons coexpress TH or VGaT, we examined whether these neurons coexpress CB, and found that about 20% of VGluT2-CB neurons coexpressed TH and about 13% coexpressed VGaT. Because VTA TH-CB neurons are known to target the nucleus accumbens (nAcc), we determined whether VGluT2-CB-TH neurons innervate nAcc, and found that about 80% of VGluT2-CB neurons innervating the nAcc shell coexpressed TH. In summary, (a) CB, PV and CR are detected in subpopulations of VTA-VGluT2 neurons; (b) CB is the main calcium-binding protein present in VTA-VGluT2 neurons; (c) one-third of VTA-VGluT2 neurons coexpress CB; (d) some VTA-VGluT2-CB neurons have the capability to co-release dopamine or GABA, and (e) a subpopulation of VTA glutamatergic-dopaminergic neurons innervates nAcc shell. These findings further provide evidence for molecular diversity among VTA-VGluT2 neurons, neurons that may play a role in specific circuitry and behaviours.

The orbitofrontal cortex projects to the parvafox nucleus of the ventrolateral hypothalamus and to its targets in the ventromedial periaqueductal grey matter

Although connections between the orbitofrontal cortex (OFC)-the seat of high cognitive functions-the lateral hypothalamus and the periaqueductal grey (PAG) have been recognized in the past, the precise targets of the descending fibres have not been identified. In the present study, viral tracer-transport experiments revealed neurons of the lateral (LO) and the ventrolateral (VLO) OFC (homologous to part of Area 13 in primates) to project to a circumscribed region in the ventrolateral hypothalamus, namely, the horizontally oriented, cylindrical parvalbumin- and Foxb1-expressing (parvafox) nucleus. The fine collaterals stem from coarse axons in the internal capsule and form excitatory synapses specifically with neurons of the parvafox nucleus, avoiding the rest of the hypothalamus. In its further caudal course, this contingent of LO/VLO-axons projects collaterals to the Su3- and the PV2 nuclei, which lie ventral to the aqueduct in the (PAG), where the terminals fields overlap those deriving from the parvafox nucleus itself. The targeting of the parvafox nucleus by the LO/VLO-projections, and the overlapping of their terminal fields within the PAG, suggest that the two cerebral sites interact closely. An involvement of this LO/VLO-driven circuit in the somatic manifestation of behavioural events is conceivable.

Eliminating the VGlut2-Dependent Glutamatergic Transmission of Parvalbumin-Expressing Neurons Leads to Deficits in Locomotion and Vocalization, Decreased Pain Sensitivity, and Increased Dominance

The calcium-binding protein parvalbumin (PV) is a recognized marker of short-axon GABA-ergic neurons in the cortex and the hippocampus. However in addition, PV is expressed by excitatory, glutamatergic neurons in various areas of the brain and spinal cord. Depending on the location of these neurons, loading of their synaptic vesicles with glutamate is mediated by either of three vesicular glutamate transporters (VGlut): VGlut1, VGlut2, or VGlut3. Driven by our interest in one of these glutamatergic/PV-expressing cell clusters-the lateral hypothalamic parvafox nucleus-we investigated the functions of this population of neurons by the selective deletion of VGlut2 expression in PV-expressing cells according to the Cre/Lox-approach. PV-Cre;VGlut2-Lox mutant mice are phenotypically characterized by deficits in locomotion and vocalization, by a decreased thermal nociception, and by an increased social dominance. We conducted a search of the Allen Brain Atlas for regions that might co-express the genes encoding PV and VGlut2, and that might thus contribute to the manifestation of the observed phenotypes. Our survey revealed several structures that could contribute to the deficits in locomotion and vocalization, such as the red, the subthalamic and the deep cerebellar nuclei. It also disclosed that a shift in the balance of afferental glutamatergic neurotransmission to the periaqueductal gray matter might be accountable for the decrease in sensitivity to pain and for the increase in social dominance. As a whole, this study broadens the state of knowledge about PV-expressing excitatory neurons.

Electrophysiological properties and projections of lateral hypothalamic parvalbumin positive neurons

Cracking the cytoarchitectural organization, activity patterns, and neurotransmitter nature of genetically-distinct cell types in the lateral hypothalamus (LH) is fundamental to develop a mechanistic understanding of how activity dynamics within this brain region are generated and operate together through synaptic connections to regulate circuit function. However, the precise mechanisms through which LH circuits orchestrate such dynamics have remained elusive due to the heterogeneity of the intermingled and functionally distinct cell types in this brain region. Here we reveal that a cell type in the mouse LH identified by the expression of the calcium-binding protein parvalbumin (PVALB; LHPV) is fast-spiking, releases the excitatory neurotransmitter glutamate, and sends long range projections throughout the brain. Thus, our findings challenge long-standing concepts that define neurons with a fast-spiking phenotype as exclusively GABAergic. Furthermore, we provide for the first time a detailed characterization of the electrophysiological properties of these neurons. Our work identifies LHPV neurons as a novel functional component within the LH glutamatergic circuitry.

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.

Modification of tooth development by heat shock protein 60

Although several heat shock proteins have been investigated in relation to tooth development, no available information is available about the spatial and temporal expression pattern of heat shock protein 60 (Hsp 60). To characterize Hsp 60 expression in the structures of the developing tooth germ, we used Western blotting, immunohistochemistry and in situ hybridization. Hsp 60 was present in high amounts in the inner and outer enamel epithelia, enamel knot (EK) and stratum intermedium (SI). Hsp 60 also appeared in odontoblasts beginning in the bell stage. To obtain data on the possible effect of Hsp 60 on isolated lower incisors from mice, we performed in vitro culturing. To investigate the effect of exogenous Hsp 60 on the cell cycle during culturing, we used the 5-bromo-2-deoxyuridine (BrdU) incorporation test on dental cells. Exogenously administered Hsp 60 caused bluntness at the apical part of the 16.5-day-old tooth germs, but it did not influence the proliferation rate of dental cells. We identified the expression of Hsp 60 in the developing tooth germ, which was present in high concentrations in the inner and outer enamel epithelia, EK, SI and odontoblasts. High concentration of exogenous Hsp 60 can cause abnormal morphology of the tooth germ, but it did not influence the proliferation rate of the dental cells. Our results suggest that increased levels of Hsp 60 may cause abnormalities in the morphological development of the tooth germ and support the data on the significance of Hsp during the developmental processes.

TLR signalling can modify the mineralization of tooth germ

OBJECTIVE

The aim of this work is to investigate the possible role of Toll-like receptor 4 (TLR4) during the development of mouse tooth germ. TLR4 is well known to inhibit mineralization and cause inflammation in mature odontoblasts and dental pulp cells. However, unlike these pathological functions of TLR4, little is known about the developmental function(s) of TLR4 during tooth development.

MATERIALS AND METHODS

TLR4 expression was studied via Western blot in developing lower mouse incisors from E13.5 to E18.5. To generate functional data about the effects of TLR4, a specific agonist (LPS) was applied to the medium of in vitro tooth germ cultures, followed by Western blot, histochemical staining, ELISA assay, in situ hybridization and RT-qPCR.

RESULTS

Increased accumulation of biotin-labelled LPS was detected in the enamel organ and in preodontoblasts. LPS treatment induced degradation of the inhibitor molecule (IκB) of the NF-κB signalling pathway. However, no morphological alterations were detected in cultured tissue after LPS addition at the applied dosage. Activation of TLR4 inhibited the mineralization of enamel and dentin, as demonstrated by alizarin red staining and as decreased levels of collagen type X. mRNA expression of ameloblastin was elevated after LPS administration.

CONCLUSION

These results demonstrate that TLR4 may decrease the mineralization of hard tissues of the tooth germ and may trigger the maturation of ameloblasts; it can give valuable information to understand better congenital tooth abnormalities.

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.

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.

Lateral hypothalamic thyrotropin-releasing hormone neurons: distribution and relationship to histochemically defined cell populations in the rat

The lateral hypothalamic area (LHA) constitutes a large component of the hypothalamus, and has been implicated in several aspects of motivated behavior. The LHA is of particular relevance to behavioral state control and the maintenance of arousal. Due to the cellular heterogeneity of this region, however, only some subpopulations of LHA cells have been properly anatomically characterized. Here, we have focused on cells expressing thyrotropin-releasing hormone (TRH), a peptide found in the LHA that has been implicated as a promoter of arousal. Immunofluorescence and in situ hybridization were used to map the LHA TRH population in the rat, and cells were observed to form a large ventral cluster that extended throughout almost the entire rostro-caudal axis of the hypothalamus. Almost no examples of coexistence were seen when sections were double-stained for TRH and markers of other LHA populations, including the peptides hypocretin/orexin, melanin-concentrating hormone and neurotensin. In the juxtaparaventricular area, however, a discrete group of TRH-immunoreactive cells were also stained with antisera against enkephalin and urocortin 3. Innervation from the metabolically sensitive hypothalamic arcuate nucleus was investigated by double-staining for peptide markers of the two centrally projecting groups of arcuate neurons, agouti gene-related peptide and α-melanocyte-stimulating hormone, respectively; both populations of terminals were observed forming close appositions on TRH cells in the LHA. The present study indicates that TRH-expressing cells form a unique population in the LHA that may serve as a link between metabolic signals and the generation of arousal.

Thrombospondin 4 deficiency in mouse impairs neuronal migration in the early postnatal and adult brain

In the post-natal rodent brain, neuronal precursors originating from the sub-ventricular zone (SVZ) migrate over a long distance along the rostral migratory stream (RMS) to eventually integrate the olfactory bulb neuronal circuitry. In order to identify new genes specifically expressed in the RMS, we have screened the Allen Brain Atlas Database. We focused our attention on Thrombospondin 4 (Thbs4), one of the 5 members of the Thrombospondin family of large, multidomain, extracellular matrix proteins. In post-natal and adult brain Thbs4 mRNA and protein are specifically expressed in the neurogenic regions, including the SVZ and along the entire RMS. RMS cells expressing Thbs4 are GFAP (Glial Fibrillary Acidic Protein) positive astrocytes. Histological analysis in both wild-type and Thbs4 knock-out mice revealed no major abnormality in the general morphology of these neurogenic regions. Nevertheless, immunostaining for doublecortin demonstrates that in Thbs4-KO, migration of newly formed neurons along the RMS is somehow impaired, with several neurons migrating out of the RMS. This is further supported by a Bromodeoxyuridine-based in vivo approach showing a decrease in the number of newly born neuronal precursors reaching the olfactory bulb, while proliferation in the SVZ is not affected compared to wild-type, both in young animals (P15) and in adults (8 to 12 weeks of age). Corroborating this observation, the number of Parvalbumin- and Calbindin-immunoreactive interneurons in the olfactory bulb is also reduced in Thbs4-KO. Together, these observations support a role for the astrocyte-secreted protein Thbs4 in the migration of newly form neurons within the RMS to the olfactory bulb.

Discharge properties of neurons recorded in the parvalbumin-positive (PV1) nucleus of the rat lateral hypothalamus

This study reports for the first time the extracellular activity recorded, in anesthetized rats, from cells located in an identified cluster of parvalbumin (PV)-positive neurons of the lateral hypothalamus forming the PV1-nucleus. Random-like firing characterized the majority (21/30) of the cells, termed regular cells, with a median firing rate of 1.7 spikes/s, Fano factor equal to 1, and evenly distributed along the rostro-caudal axis. Four cells exhibiting an oscillatory activity in the range 1.6-2.1Hz were observed only in the posterior part of the PV1-nucleus. The asynchronous activity of PV1 neurons is likely to produce a "network-driven" effect on their main target within the periaqueductal gray matter. The hypothesis is raised that background random-like firing of PV1-nucleus is associated with functional network activity likely to contribute dynamic information related to condition transitions of awareness and non-conscious perception.

Efferent connections of the parvalbumin-positive (PV1) nucleus in the lateral hypothalamus of rodents

A solitary cluster of parvalbumin-positive neurons--the PV1 nucleus--has been observed in the lateral hypothalamus of rodents. In the present study, we mapped the efferent connections of the PV1 nucleus using nonspecific antero- and retrograde tracers in rats, and chemoselective, Cre-dependent viral constructs in parvalbumin-Cre mice. In both species, the PV1 nucleus was found to project mainly to the periaqueductal grey matter (PAG), predominantly ipsilaterally. Indirectly in rats and directly in mice, a discrete, longitudinally oriented cylindrical column of terminal fields (PV1-CTF) was identified ventrolateral to the aqueduct on the edge of the PAG. The PV1-CTF is particularly dense in the rostral portion, which is located in the supraoculomotor nucleus (Su3). It is spatially interrupted over a short stretch at the level of the trochlear nucleus and abuts caudally on a second parvalbumin-positive (PV2) nucleus. The rostral and the caudal portions of the PV1-CTF consist of axonal endings, which stem from neurons scattered throughout the PV1 nucleus. Topographically, the longitudinal orientation of the PV1-CTF accords with that of the likewise longitudinally oriented functional modules of the PAG, but overlaps none of them. Minor terminal fields were identified in a crescentic column of the lateral PAG, as well as in the Edinger-Westphal, the lateral habenular, and the laterodorsal tegmental nuclei. So far, no obvious functions have been attributed to this small, circumscribed column ventrolateral to the aqueduct, the prime target of the PV1 nucleus.

Expression of the calcium binding proteins Necab-1,-2 and -3 in the adult mouse hippocampus and dentate gyrus

The family of EF-hand calcium binding proteins is composed of more than 250 members. In search for other neuronal markers, we studied the expression pattern of Necab-1, -2 and -3 in the Ammons horn of adult mice at the gene- and protein levels using in-situ hybridization and immunohistochemistry. The genes for the three Necab's were expressed in specific, non-overlapping areas of the hippocampus. A minority of the Necab-positive interneurons were GABA-ergic, and they virtually never coexpressed one of the classical calcium binding proteins (calretinin, calbindin D-28k and parvalbumin). Necab's are promising new neuronal markers in the brain.

Ginkgo biloba extract (EGb 761) prevents the ischemic brain injury-induced decrease in parvalbumin expression

Ginkgo biloba extract (EGb 761) exerts a neuroprotective effect against ischemic brain injury through an anti-apoptotic mechanism. Parvalbumin is a calcium buffering protein that plays an important role in modulating intracellular calcium concentration and regulating apoptotic cell death. The aim of this study was to investigate whether EGb 761 affects parvalbumin expression in cerebral ischemic injury. Adult male Sprague-Dawley rats were treated with vehicle or EGb 761 (100 mg/kg) prior to middle cerebral artery occlusion (MCAO) and cerebral cortex tissues were collected 24 h after MCAO. A proteomic approach revealed a reduction in parvalbumin expression in the vehicle-treated animals, whereas EGb 761 pretreatment attenuates the ischemic injury-induced decrease in parvalbumin expression. RT-PCR and Western blot analyses clearly confirmed the fact that EGb 761 prevents the injury-induced decrease in parvalbumin. Moreover, the results of immunohistochemical staining showed that the number of parvalbumin-positive cells was lower in vehicle-treated animals than in sham-operated animals, and EGb 761 averted this decrease. Thus, these results suggest that the maintenance of parvalbumin expression is associated with the neuroprotective function of EGb 761 against neuronal damage induced by ischemia.

Exploration of the neural correlates of ticklish laughter by functional magnetic resonance imaging

The burst of laughter that is evoked by tickling is a primitive form of vocalization. It evolves during an early phase of postnatal life and appears to be independent of higher cortical circuits. Clinicopathological observations have led to suspicions that the hypothalamus is directly involved in the production of laughter. In this functional magnetic resonance imaging investigation, healthy participants were 1) tickled on the sole of the right foot with permission to laugh, 2) tickled but asked to stifle laughter, and 3) requested to laugh voluntarily. Tickling that was accompanied by involuntary laughter activated regions in the lateral hypothalamus, parietal operculum, amygdala, and right cerebellum to a consistently greater degree than did the 2 other conditions. Activation of the periaqueductal gray matter was observed during voluntary and involuntary laughter but not when laughter was inhibited. The present findings indicate that hypothalamic activity plays a crucial role in evoking ticklish laughter in healthy individuals. The hypothalamus promotes innate behavioral reactions to stimuli and sends projections to the periaqueductal gray matter, which is itself an important integrative center for the control of vocalization. A comparison of our findings with published data relating to humorous laughter revealed the involvement of a common set of subcortical centers.