Neuronal Activity Promotes Glioma Growth through Neuroligin-3 Secretion.

Active neurons exert a mitogenic effect on normal neural precursor and oligodendroglial precursor cells, the putative cellular origins of high-grade glioma (HGG). By using optogenetic control of cortical neuronal activity in a patient-derived pediatric glioblastoma xenograft model, we demonstrate that active neurons similarly promote HGG proliferation and growth in vivo. Conditioned medium from optogenetically stimulated cortical slices promoted proliferation of pediatric and adult patient-derived HGG cultures, indicating secretion of activity-regulated mitogen(s). The synaptic protein neuroligin-3 (NLGN3) was identified as the leading candidate mitogen, and soluble NLGN3 was sufficient and necessary to promote robust HGG cell proliferation. NLGN3 induced PI3K-mTOR pathway activity and feedforward expression of NLGN3 in glioma cells. NLGN3 expression levels in human HGG negatively correlated with patient overall survival. These findings indicate the important role of active neurons in the brain tumor microenvironment and identify secreted NLGN3 as an unexpected mechanism promoting neuronal activity-regulated cancer growth.

Transsynaptic cerebellin 4-neogenin 1 signaling mediates LTP in the mouse dentate gyrus.

Five decades ago, long-term potentiation (LTP) of synaptic transmission was discovered at entorhinal cortex→dentate gyrus (EC→DG) synapses, but the molecular determinants of EC→DG LTP remain largely unknown. Here, we show that the presynaptic neurexin­ligand cerebellin-4 (Cbln4) is highly expressed in the entorhinal cortex and essential for LTP at EC→DG synapses, but dispensable for basal synaptic transmission at these synapses. Cbln4, when bound to cell-surface neurexins, forms transcellular complexes by interacting with postsynaptic DCC (deleted in colorectal cancer) or neogenin-1. DCC and neogenin-1 act as netrin and repulsive guidance molecule-a (RGMa) receptors that mediate axon guidance in the developing brain, but their binding to Cbln4 raised the possibility that they might additionally function in the mature brain as postsynaptic receptors for presynaptic neurexin/Cbln4 complexes, and that as such receptors, DCC or neogenin-1 might mediate EC→DG LTP that depends on Cbln4. Indeed, we observed that neogenin-1, but not DCC, is abundantly expressed in dentate gyrus granule cells, and that postsynaptic neogenin-1 deletions in dentate granule cells blocked EC→DG LTP, but again did not affect basal synaptic transmission similar to the presynaptic Cbln4 deletions. Thus, binding of presynaptic Cbln4 to postsynaptic neogenin-1 renders EC→DG synapses competent for LTP, but is not required for establishing these synapses or for otherwise enabling their function.

Cerebellin-2 regulates a serotonergic dorsal raphe circuit that controls compulsive behaviors.

Cerebellin-1 (Cbln1) and cerebellin-2 (Cbln2) are secreted glycoproteins that are expressed in distinct subsets of neurons throughout the brain. Cbln1 and Cbln2 simultaneously bind to presynaptic neurexins and postsynaptic GluD1 and GluD2, thereby forming trans-synaptic adhesion complexes. Genetic associations link cerebellins, neurexins and GluD's to neuropsychiatric disorders involving compulsive behaviors, such as Tourette syndrome, attention-deficit hyperactivity disorder (ADHD), and obsessive-compulsive disorder (OCD). Extensive evidence implicates dysfunction of serotonergic signaling in these neuropsychiatric disorders. Here, we report that constitutive Cbln2 KO mice, but not Cbln1 KO mice, display robust compulsive behaviors, including stereotypic pattern running, marble burying, explosive jumping, and excessive nest building, and exhibit decreased brain serotonin levels. Strikingly, treatment of Cbln2 KO mice with the serotonin precursor 5-hydroxytryptophan or the serotonin reuptake-inhibitor fluoxetine alleviated compulsive behaviors. Conditional deletion of Cbln2 both from dorsal raphe neurons and from presynaptic neurons synapsing onto dorsal raphe neurons reproduced the compulsive behaviors of Cbln2 KO mice. Finally, injection of recombinant Cbln2 protein into the dorsal raphe of Cbln2 KO mice largely reversed their compulsive behaviors. Taken together, our results show that Cbln2 controls compulsive behaviors by regulating serotonergic circuits in the dorsal raphe.

Cbln2 and Cbln4 are expressed in distinct medial habenula-interpeduncular projections and contribute to different behavioral outputs.

Cerebellins are important neurexin ligands that remain incompletely understood. Two critical questions in particular remain unanswered: do different cerebellins perform distinct functions, and do these functions act in the initial establishment of synapses or in rendering nascent synapses capable of normal synaptic transmission? Here we show that in mice, Cbln2 and Cbln4 are expressed in the medial habenula (MHb) nucleus in different types of neurons that project to distinct target neurons in the interpeduncular nucleus. Conditional genetic deletion of Cbln2 in the MHb impaired synaptic transmission at Cbln2+ synapses in the interpeduncular neurons within 3 wk, but decreased synapse numbers only after 3 mo, suggesting a functional, but not a structural, requirement for Cbln2 in synapses formed by Cbln2-expressing neurons. In contrast, genetic deletions of Cbln4 in the MHb had no major effect on synaptic transmission or synapse numbers in interpeduncular target neurons. Nevertheless, MHb ablation of both Cbln2 and Cbln4 significantly impaired behavioral responses in mice, but affected different types of behaviors. Specifically, Cbln2 MHb deletions decreased spatial learning, as measured in the water T-maze, whereas Cbln4 MHb deletions increased anxiety levels, as monitored in the open field test and elevated plus maze. Thus, Cbln2 and Cbln4 are expressed in distinct MHb neurons that contribute to different behaviors.

A critical role for the PAR-1/MARK-tau axis in mediating the toxic effects of Aß on synapses and dendritic spines.

Alzheimer's disease (AD) is the most common neurodegenerative disease and the leading cause of dementia in the elderly. Accumulating evidence supports soluble amyloid-ß (Aß) oligomers as the leading candidate for the causative agent in AD and synapses as the primary site of Aß oligomer action. However, the molecular and cellular mechanisms by which Aß oligomers cause synaptic dysfunction and cognitive impairments remain poorly understood. Using primary cultures of rat hippocampal neurons as a model system, we show that the partitioning defective-1 (PAR-1)/microtubule affinity-regulating kinase (MARK) family kinases act as critical mediators of Aß toxicity on synapses and dendritic spines. Overexpression of MARK4 led to tau hyperphosphorylation, reduced expression of synaptic markers, and loss of dendritic spines and synapses, phenotypes also observed after Aß treatment. Importantly, expression of a non-phosphorylatable form of tau with the PAR-1/MARK site mutated blocked the synaptic toxicity induced by MARK4 overexpression or Aß treatment. To probe the involvement of endogenous MARK kinases in mediating the synaptic toxicity of Aß, we employed a peptide inhibitor capable of effectively and specifically inhibiting the activities of all PAR-1/MARK family members. This inhibitor abrogated the toxic effects of Aß oligomers on dendritic spines and synapses as assayed at the morphological and electrophysiological levels. Our results reveal a critical role for PAR-1/MARK kinases in AD pathogenesis and suggest PAR-1/MARK inhibitors as potential therapeutics for AD and possibly other tauopathies where aberrant tau hyperphosphorylation is involved.

A specific class of interneuron mediates inhibitory plasticity in the lateral amygdala.

The lateral amygdala (LA) plays a key role in emotional learning and is the main site for sensory input into the amygdala. Within the LA, pyramidal neurons comprise the major cell population with plasticity of inputs to these neurons thought to underlie fear learning. Pyramidal neuron activity is tightly controlled by local interneurons, and GABAergic modulation strongly influences amygdala-dependent learning. Synaptic inputs to some interneurons in the LA can also undergo synaptic plasticity, but the identity of these cells and the mechanisms that underlie this plasticity are not known. Here we show that long-term potentiation (LTP) in LA interneurons is restricted to a specific type of interneuron that is defined by the lack of expression of synaptic NR2B subunits. We find that LTP is only present at cortical inputs to these cells and is initiated by calcium influx via calcium-permeable AMPA receptors. LTP is maintained by trafficking of GluR2-lacking AMPA receptors that require an interaction with SAP97 and the actin cytoskeleton. Our results define a novel population of interneurons in the LA that control principal neuron excitability by feed-forward inhibition of cortical origin. This selective enhanced inhibition may contribute to reducing the activity of principal neurons engaged during extinction of conditioned fear.

Diversity of interneurons in the lateral and basal amygdala.

The basolateral amygdala (BLA) is a temporal lobe structure that contributes to a host of behaviors. In particular, it is a central player in learning about aversive events and thus assigning emotional valence to sensory events. It is a cortical-like structure and contains glutamatergic pyramidal neurons and GABAergic interneurons. It is divided into the lateral (LA) and basal (BA) nuclei that have distinct cell types and connections. Interneurons in the BLA are a heterogenous population, some of which have been implicated in specific functional roles. Here we use optogenetics and slice electrophysiology to investigate the innervation, postsynaptic receptor stoichiometry, and plasticity of excitatory inputs onto interneurons within the BLA. Interneurons were divided into six groups based on their discharge properties, each of which received input from the auditory thalamus (AT) and auditory cortex (AC). Auditory innervation was concentrated in the LA, and optogenetic stimulation evoked robust synaptic responses in nearly all interneurons, drove many cells to threshold, and evoked disynaptic inhibition in most interneurons. Auditory input to the BA was sparse, innervated fewer interneurons, and evoked smaller synaptic responses. Biophysically, the subunit composition and distribution of AMPAR and NMDAR also differed between the two nuclei, with fewer BA IN expressing calcium permeable AMPAR, and a higher proportion expressing GluN2B-containing NMDAR. Finally, unlike LA interneurons, LTP could not be induced in the BA. These findings show that interneurons in the LA and BA are physiologically distinct populations and suggest they may have differing roles during associative learning.

Modulation of excitation on parvalbumin interneurons by neuroligin-3 regulates the hippocampal network.

Hippocampal network activity is generated by a complex interplay between excitatory pyramidal cells and inhibitory interneurons. Although much is known about the molecular properties of excitatory synapses on pyramidal cells, comparatively little is known about excitatory synapses on interneurons. Here we show that conditional deletion of the postsynaptic cell adhesion molecule neuroligin-3 in parvalbumin interneurons causes a decrease in NMDA-receptor-mediated postsynaptic currents and an increase in presynaptic glutamate release probability by selectively impairing the inhibition of glutamate release by presynaptic Group III metabotropic glutamate receptors. As a result, the neuroligin-3 deletion altered network activity by reducing gamma oscillations and sharp wave ripples, changes associated with a decrease in extinction of contextual fear memories. These results demonstrate that neuroligin-3 specifies the properties of excitatory synapses on parvalbumin-containing interneurons by a retrograde trans-synaptic mechanism and suggest a molecular pathway whereby neuroligin-3 mutations contribute to neuropsychiatric disorders.

Gating of social reward by oxytocin in the ventral tegmental area.

The reward generated by social interactions is critical for promoting prosocial behaviors. Here we present evidence that oxytocin (OXT) release in the ventral tegmental area (VTA), a key node of the brain's reward circuitry, is necessary to elicit social reward. During social interactions, activity in paraventricular nucleus (PVN) OXT neurons increased. Direct activation of these neurons in the PVN or their terminals in the VTA enhanced prosocial behaviors. Conversely, inhibition of PVN OXT axon terminals in the VTA decreased social interactions. OXT increased excitatory drive onto reward-specific VTA dopamine (DA) neurons. These results demonstrate that OXT promotes prosocial behavior through direct effects on VTA DA neurons, thus providing mechanistic insight into how social interactions can generate rewarding experiences.

A class III histidine kinase acts as a novel virulence factor in Botrytis cinerea.

Filamentous ascomycetes contain large numbers of histidine kinases (HK) that belong to eleven classes. Members of class III from different species were previously shown to be involved in osmoregulation and resistance to dicarboximide and phenylpyrrole fungicides. We have inactivated the gene encoding the single group III HK, BOS1, in the economically important plant pathogen Botrytis cinerea. BOS1 inactivation had pleiotropic effects on the fungus. Besides the expected osmosensitivity and resistance to fungicides, null mutants presented additional characteristics indicating that BOS1 is necessary for normal macroconidiation and full virulence. On standard culture media, null mutants very rarely formed conidiophores and those few conidiophores failed to produce conidia. This defect could be partially restored with 1 M sorbitol, suggesting that another BOS1-independent signal cascade may be involved in macroconidiation. The mutants were not found to be hypersensitive to various oxidative stresses but were more resistant to menadione. Finally, pathogenicity tests showed that bos1-null mutants were significantly reduced in the ability to infect host plants. Appressorium morphogenesis was not altered; however, in planta growth was severely reduced. To our knowledge, this is the first class III HK characterized as a pathogenicity factor in a plant-pathogenic ascomycete.

Chronic pain. Decreased motivation during chronic pain requires long-term depression in the nucleus accumbens.

Several symptoms associated with chronic pain, including fatigue and depression, are characterized by reduced motivation to initiate or complete goal-directed tasks. However, it is unknown whether maladaptive modifications in neural circuits that regulate motivation occur during chronic pain. Here, we demonstrate that the decreased motivation elicited in mice by two different models of chronic pain requires a galanin receptor 1-triggered depression of excitatory synaptic transmission in indirect pathway nucleus accumbens medium spiny neurons. These results demonstrate a previously unknown pathological adaption in a key node of motivational neural circuitry that is required for one of the major sequela of chronic pain states and syndromes.

Postsynaptic complexin controls AMPA receptor exocytosis during LTP.

Long-term potentiation (LTP) is a compelling synaptic correlate of learning and memory. LTP induction requires NMDA receptor (NMDAR) activation, which triggers SNARE-dependent exocytosis of AMPA receptors (AMPARs). However, the molecular mechanisms mediating AMPAR exocytosis induced by NMDAR activation remain largely unknown. Here, we show that complexin, a protein that regulates neurotransmitter release via binding to SNARE complexes, is essential for AMPAR exocytosis during LTP but not for the constitutive AMPAR exocytosis that maintains basal synaptic strength. The regulated postsynaptic AMPAR exocytosis during LTP requires binding of complexin to SNARE complexes. In hippocampal neurons, presynaptic complexin acts together with synaptotagmin-1 to mediate neurotransmitter release. However, postsynaptic synaptotagmin-1 is not required for complexin-dependent AMPAR exocytosis during LTP. These results suggest a complexin-dependent molecular mechanism for regulating AMPAR delivery to synapses, a mechanism that is surprisingly similar to presynaptic exocytosis but controlled by regulators other than synaptotagmin-1.

Interneurons in the basolateral amygdala.

The amygdala is a temporal lobe structure that is the center of emotion processing in the mammalian brain. Recent interest in the amygdala arises from its role in processing fear and the relationship of fear to human anxiety. The amygdaloid complex is divided into a number of subnuclei that have extensive intra and extra nuclear connections. In this review we discuss recent findings on the physiology and plasticity of inputs to interneurons in the basolateral amygdala, the primary input station. These interneurons are a heterogeneous group of cells that can be separated on immunohistochemical and electrophysiological grounds. Glutamatergic inputs to these interneurons form diverse types of excitatory synapses. This diversity is manifest in both the subunit composition of the underlying NMDA receptors as well as their ability to show plasticity. We discuss these differences and their relationship to fear learning. This article is part of a Special Issue entitled 'Synaptic Plasticity & Interneurons'.

Phylogenetic analysis of Pinguicula (Lentibulariaceae): chloroplast DNA sequences and morphology support several geographically distinct radiations.

The genus Pinguicula is one of the three genera of the carnivorous Lentibulariaceae, comprising approximately 80 species. Phylogeny inference using nucleotide sequences of the chloroplast gene matK and the trnK group II intron, as well as a set of 32 morphological characters revealed five well-supported, major lineages within the genus. These lineages largely reflect radiations in clearly defined geographic regions, whereas most previously recognized sections of the genus are shown to be para- or polyphyletic. A species-rich Mexican-Central American-Caribbean clade has the Eurasian P. alpina and an East Asian clade as successive sisters. All three are characterized by a production of flower buds on winter-resting plants, a specific corolla hair structure and a very large corolla lower central lobe. Another diverse clade is composed of species with primarily European distribution including the widespread type species P. vulgaris. For this clade, vegetative reproduction during dormancy is synapomorphic. Species native to SE North America and the South American Andes and a group of Mediterranean and NE Atlantic coast species together appear in a fifth well-supported clade, that is characterized by a tropical-type growth habit. It is the only clade that has reached temperate zones of the southern hemisphere.