Several studies have proposed that brain glutamate signaling abnormalities and glial pathology play a role in the etiology of major depressive disorder (MDD). These conclusions were primarily drawn from postmortem studies in which forebrain brain regions were examined. The locus coeruleus is the primary source of extensive noradrenergic innervation of the forebrain and as such exerts a powerful regulatory role over cognitive and affective functions, which are dysregulated in MDD. Furthermore, altered noradrenergic neurotransmission is associated with depressive symptoms and is thought to play a role in the pathophysiology of MDD. In the present study we used laser-capture microdissection to selectively harvest locus coeruleus (LC) tissue from postmortem brains of MDD patients, patients with bipolar disorder (BPD), and from psychiatrically-normal subjects. Using microarray technology we examined global patterns of gene expression. Differential mRNA expression of select candidate genes was then interrogated using quantitative real-time PCR and in situ hybridization. Our findings reveal multiple signaling pathway alterations in the LC of MDD, but not BPD subjects. These include glutamate signaling genes SLC1A2, SLC1A3, GLUL, growth factor genes FGFR3 and TrkB, and several genes exclusively expressed in astroglia. Our data extend previous findings of altered glutamate, astroglial and growth factor functions in MDD for the first time to the brainstem. These findings indicate that such alterations: 1) are unique to MDD and distinguishable from BPD, and 2) affect multiple brain regions, suggesting a whole-brain dysregulation of such functions.

In humans, temporal lobe epilepsy (TLE) is often associated with Ammon's horn sclerosis (AHS) characterized by hippocampal cell death, gliosis and granule cell dispersion (GCD) in the dentate gyrus. Granule cells surviving TLE have been proposed to be hyperexcitable and to play an important role in seizure generation. However, it is unclear whether this applies to conditions of AHS. We studied granule cells using the intrahippocampal kainate injection mouse model of TLE, brain slice patch-clamp recordings, morphological reconstructions and immunocytochemistry. With progressing AHS and GCD, 'epileptic' granule cells of the injected hippocampus displayed a decreased input resistance, a decreased membrane time constant and an increased rheobase. The resting leak conductance was doubled in epileptic granule cells and roughly 70-80% of this difference were sensitive to K + replacement. Of the increased K + leak, about 50% were sensitive to 1 mm Ba 2+ . Approximately 20-30% of the pathological leak was mediated by a bicuculline-sensitive GABA A conductance. Epileptic granule cells had strongly enlarged inwardly rectifying currents with a low micromolar Ba 2+ IC 50 , reminiscent of classic inward rectifier K + channels (Irk/Kir2). Indeed, protein expression of Kir2 subunits (Kir2.1, Kir2.2, Kir2.3, Kir2.4) was upregulated in epileptic granule cells. Immunolabelling for two-pore weak inward rectifier K + channels (Twik1/K2P1.1, Twik2/K2P6.1) was also increased. We conclude that the excitability of granule cells in the sclerotic focus of TLE is reduced due to an increased resting conductance mainly due to upregulated K + channel expression. These results point to a local adaptive mechanism that could counterbalance hyperexcitability in epilepsy.

The lateral habenular complex (LHb) is a bilateral epithalamic brain structure involved in the modulation of ascending monoamine systems in response to afferents from limbic regions and basal ganglia. The LHb is implicated in various biological functions, such as reward, sleep-wake cycle, feeding, pain processing, and memory formation. The modulatory role of the LHb is partially assumed by putative spontaneously active LHb neurons projecting to the dopaminergic ventral tegmental area (VTA) and to the serotonergic median (MnR) and dorsal raphe nuclei (DR). All four nuclei form a complex and coordinated network to evoke appropriate responses to reward-related stimuli. At present it is not known whether individual LHb neurons project to only one or to more than one monoaminergic nucleus. To answer this question, we made dual injections of two different retrograde tracers into the rat VTA and either DR or MnR. Tracers were visualized by immunohistochemistry. In coronal sections, the different retrogradly labeled habenular neurons were quantified and assigned to the corresponding habenular subnuclei. Our results show that 1) the distribution of neurons in the LHb projecting to the three monoamine nuclei is similar and exhibits a great overlap, 2) the vast majority of LHb projection neurons target one monoaminergic nucleus only, and 3) very few, heterogeneously distributed LHb neurons project to both dopaminergic and serotonergic nuclei. These results imply that the LHb forms both separate and interconnected circuits with each monoaminergic nucleus, permitting the LHb to modulate its output to different monoamine systems either independently or jointly.

Lesion volume measurements with magnetic resonance imaging are widely used to assess outcome in rodent models of stroke. In this study, we improved a mathematical framework to correct lesion size for edema which is based on manual delineation of the lesion and hemispheres. Furthermore, a novel MATLAB toolbox to register mouse brain MR images to the Allen brain atlas is presented. Its capability to calculate edema-corrected lesion size was compared to the manual approach. Automated image registration performed equally well in in a mouse middle cerebral artery occlusion model (Pearson r ¼ 0.976, p ¼ 2.265e-11). Information encapsulated in the registration was used to generate maps of edema induced tissue volume changes. These showed discrepancies to simplified tissue models underlying the manual approach. The presented techniques provide biologically more meaningful, voxel-wise biomarkers of vasogenic edema after stroke.

In vertebrates the "anti-reward-system" mainly is represented by the habenula and its medial (MHb) and especially lateral (LHb) complexes. Considerable knowledge has accumulated concerning subnuclear structures and connectivities of MHb and LHb subnuclei. The present investigation aimed to obtain novel information, whether MHb or LHb or their subnuclei display field-characteristic gene products, which may shed light on biological functions of these areas. Unfortunately this was not the case. Microarray analysis of mRNAs in microdissected habenular and thalamic control areas yielded expression values of 17,745 RNAs representing protein-coding genes, to which annotated gene names could be assigned. High relative values of genes with known expression in MHb, LHb or thalamus in the corresponding areas indicated a high precision of the microdissection procedure. Note that the present report emphasizes differences between and not absolute expression values in the selected regions. The present investigation disclosed that the LHb genetically is much closer related to the thalamus as compared to the MHb. The results presented here focuse on gene transcripts related to major transmitter systems, catecholamines and neuropeptides. Quite surprisingly, our data indicate potentially inhibitory effects of acetylcholine and glutamate in the habenula. In addition, the absence of the K-Cl co-transporter 2 supports a largely excitatory role of GABAergic transmission especially in the MHb. Furthermore, several G-protein related receptors (Gpr83, Gpr139, Gpr149, Gpr151, Gpr158) and many neuropeptides related to feeding are differentially expressed in the habenular region, indicating that its involvement in the regulation of food consumption and energy expenditure may have been underestimated so far.

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Orexin and melanin-concentrating hormone (MCH) have been implicated in mediating a variety of different behaviors. These include sleep and wakefulness, locomotion, ingestive behaviors, and fight-or-flight response, as well as anxiety- and panic-like behaviors in rodents. Despite such diversity, all these processes require coordinated recruitment of the autonomic and somatomotor efferents. We have previously mapped the locations of presympathetic-premotor neurons (PSPMNs) in the rat brain. These putative dual-function neurons send trans-synaptic projections to somatomotor and sympathetic targets and likely participate in somatomotor-sympathetic integration. A significant portion of these neurons is found within the dorsomedial (DMH) and lateral hypothalamus (LH), areas of the brain that contain MCH- and orexin- synthesizing neurons in the central nervous system. Thus, we hypothesized that hypothalamic PSPMNs utilize MCH or orexin as their neurotransmitter. To test this hypothesis, we identified PSPMNs by using recombinant strains of the pseudorabies virus (PRV) for trans-synaptic tract tracing. PRV-152, a strain that expresses enhanced green fluorescent protein, was injected into sympathectomized gastrocnemius muscle, whereas PRV-BaBlu, which expresses beta-galactosidase, was injected into the adrenal gland in the same animals. By using immunofluorescent methods, we determined whether co-infected neurons express MCH or orexin. Our findings demonstrate that PSPMNs synthesizing either MCH or orexin are present within LH, where they form two separate populations. PSPMNs located around the fornix express orexin, whereas those located around the cerebral peduncle are more likely to express MCH. These two clusters of PSPMNs within LH likely play distinct functional roles in autonomic homeostasis and stress coping mechanisms.

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