GABAB receptors are the G protein-coupled receptors for the main inhibitory neurotransmitter in the brain, gamma-aminobutyric acid (GABA). Molecular diversity in the GABAB system arises from the GABAB1a and GABAB1b subunit isoforms that solely differ in their ectodomains by a pair of sushi repeats that is unique to GABAB1a. Using a combined genetic, physiological, and morphological approach, we now demonstrate that GABAB1 isoforms localize to distinct synaptic sites and convey separate functions in vivo. At hippocampal CA3-to-CA1 synapses, GABAB1a assembles heteroreceptors inhibiting glutamate release, while predominantly GABAB1b mediates postsynaptic inhibition. Electron microscopy reveals a synaptic distribution of GABAB1 isoforms that agrees with the observed functional differences. Transfected CA3 neurons selectively express GABAB1a in distal axons, suggesting that the sushi repeats, a conserved protein interaction motif, specify heteroreceptor localization. The constitutive absence of GABAB1a but not GABAB1b results in impaired synaptic plasticity and hippocampus-dependent memory, emphasizing molecular differences in synaptic GABAB functions.

Despite the importance of the aberrant polymerization of A␤ in the early pathogenic cascade of Alzheimer's disease, little is known about the induction of A␤ aggregation in vivo. Here we show that induction of cerebral ␤-amyloidosis can be achieved in many different brain areas of APP23 transgenic mice through the injection of dilute A␤-containing brain extracts. Once the amyloidogenic process has been exogenously induced, the nature of the induced A␤-deposition is determined by the brain region of the host. Because these observations are reminiscent of a prion-like mechanism, we then investigated whether cerebral ␤-amyloidosis also can be induced by peripheral and systemic inoculations or by the intracerebral implantation of stainless steel wires previously coated with minute amounts of A␤-containing brain extract. Results reveal that oral, intravenous, intraocular, and intranasal inoculations yielded no detectable induction of cerebral ␤-amyloidosis in APP23 transgenic mice. In contrast, transmission of cerebral ␤-amyloidosis through the A␤-contaminated steel wires was demonstrated. Notably, plasma sterilization, but not boiling of the wires before implantation, prevented the induction of ␤-amyloidosis. Our results suggest that minute amounts of A␤-containing brain material in direct contact with the CNS can induce cerebral ␤-amyloidosis, but that systemic cellular mechanisms of prion uptake and transport to the CNS may not apply to A␤.Alzheimer's disease ͉ amyloid ͉ prion ͉ sterilization ͉ transmission

BackgroundAlzheimer’s disease (AD) is the most common form of dementia, the number of affected individuals is rising, with significant impacts for healthcare systems. Current symptomatic treatments delay, but do not halt, disease progression. Genetic evidence points to aggregation and deposition of amyloid-β (Aβ) in the brain being causal for the neurodegeneration and dementia typical of AD. Approaches to target Aβ via inhibition of γ-secretase or passive antibody therapy have not yet resulted in substantial clinical benefits. Inhibition of BACE1 (β-secretase) has proven a challenging concept, but recent BACE1inhibitors can enter the brain sufficiently well to lower Aβ. However, failures with the first clinical BACE1 inhibitors have highlighted the need to generate compounds with appropriate efficacy and safety profiles, since long treatment periods are expected to be necessary in humans.ResultsTreatment with NB-360, a potent and brain penetrable BACE-1 inhibitor can completely block the progression of Aβ deposition in the brains of APP transgenic mice, a model for amyloid pathology. We furthermore show that almost complete reduction of Aβ was achieved also in rats and in dogs, suggesting that these findings are translational across species and can be extrapolated to humans. Amyloid pathology may be an initial step in a complex pathological cascade; therefore we investigated the effect of BACE-1 inhibition on neuroinflammation, a prominent downstream feature of the disease. NB-360 stopped accumulation of activated inflammatory cells in the brains of APP transgenic mice. Upon chronic treatment of APP transgenic mice, patches of grey hairs appeared.ConclusionsIn a rapidly developing field, the data on NB-360 broaden the chemical space and expand knowledge on the properties that are needed to make a BACE-1 inhibitor potent and safe enough for long-term use in patients. Due to its excellent brain penetration, reasonable oral doses of NB-360 were sufficient to completely block amyloid-β deposition in an APP transgenic mouse model. Data across species suggest similar treatment effects can possibly be achieved in humans. The reduced neuroinflammation upon amyloid reduction by NB-360 treatment supports the notion that targeting amyloid-β pathology can have beneficial downstream effects on the progression of Alzheimer’s disease.

SignificanceSpider venom is a rich source of peptides, many targeting ion channels. We assessed a venom peptide, Hm1a, as a potential targeted therapy for Dravet syndrome, the genetic epilepsy linked to a mutation in the gene encoding the sodium channel alpha subunit NaV1.1. Cell-based assays showed Hm1a was selective for hNaV1.1 over other sodium and potassium channels. Utilizing a mouse model of Dravet syndrome, Hm1a restored inhibitory neuron function and significantly reduced seizures and mortality in heterozygote mice. Evidence from the structure of Hm1a and modeling suggest Hm1a interacts with NaV1.1 inactivation domains, providing a structural correlate of the functional mechanisms. This proof-of-concept study provides a promising strategy for future drug development in genetic epilepsy and other neurogenetic disorders.

Depression is a growing pandemic in developed societies. The use of inbred mouse strains in pre-clinical psychiatric research has proven to be a valuable resource. Firstly, they provide the background for genetic manipulations that aid in the discovery of molecular pathways that may be involved in major depression. Further, inbred mouse strains are also being used in the determination of genetic and environmental influences that may pre-dispose or trigger depression-related behavior. This review aims to highlight the utility of inbred mouse strains in depression research, while providing an overview of the current state of research into behavioral differences between strains in paradigms commonly used in the field. Neurochemical differences that may underlie strain differences are examined, and some caveats and cautions associated with the use of inbred strains are highlighted.

Immunization against amyloid-β (Aβ) can reduce amyloid accumulation in vivo and is considered a potential therapeutic approach for Alzheimer's disease. However, it has been associated with meningoencephalitis thought to be mediated by inflammatory T-cells. With the aim of producing an immunogenic vaccine without this side effect, we designed CAD106 comprising Aβ1-6 coupled to the virus-like particle Qβ. Immunization with this vaccine did not activate Aβ-specific T-cells. In APP transgenic mice, CAD106 induced efficacious Aβ antibody titers of different IgG subclasses mainly recognizing the Aβ3-6 epitope. CAD106 reduced brain amyloid accumulation in two APP transgenic mouse lines. Plaque number was a more sensitive readout than plaque area, followed by Aβ42 and Aβ40 levels. Studies with very strong overall amyloid reduction showed an increase in vascular Aβ, which atypically was nonfibrillar. The efficacy of Aβ immunotherapy depended on the Aβ levels and thus differed between animal models, brain regions, and stage of amyloid deposition. Therefore, animal studies may not quantitatively predict the effect in human Alzheimer's disease. Our studies provided no evidence for increased microhemorrhages or inflammatory reactions in amyloid-containing brain. In rhesus monkeys, CAD106 induced a similar antibody response as in mice. The antibodies stained amyloid deposits on tissue sections of mouse and human brain but did not label cellular structures containing APP. They reacted with Aβ monomers and oligomers and blocked Aβ toxicity in cell culture. We conclude that CAD106 immunization is suited to interfere with Aβ aggregation and its downstream detrimental effects.

Formation and extinction of aversive memories in the mammalian brain are insufficiently understood at the cellular and molecular levels. Using the novel metabotropic glutamate receptor 7 (mGluR7) agonist AMN082, we demonstrate that mGluR7 activation facilitates the extinction of aversive memories in two different amygdala-dependent tasks. Conversely, mGluR7 knockdown using short interfering RNA attenuated the extinction of learned aversion. mGluR7 activation also blocked the acquisition of Pavlovian fear learning and its electrophysiological correlate long-term potentiation in the amygdala. The finding that mGluR7 critically regulates extinction, in addition to acquisition of aversive memories, demonstrates that this receptor may be relevant for the manifestation and treatment of anxiety disorders.

Dual orexin receptor (OXR) antagonists (DORAs) such as almorexant, 1 (SB-649868), or suvorexant have shown promise for the treatment of insomnias and sleep disorders in several recent clinical trials in volunteers and primary insomnia patients. The relative contribution of antagonism of OX1R and OX2R for sleep induction is still a matter of debate. We therefore initiated a drug discovery project with the aim of creating both OX2R selective antagonists and DORAs. Here we report that the OX2R selective antagonist 26 induced sleep in mice primarily by increasing NREM sleep, whereas the DORA suvorexant induced sleep largely by increasing REM sleep. Thus, OX2R selective antagonists may also be beneficial for the treatment of insomnia.