Stereotaxic Adeno-associated Virus Injection and Cannula Implantation in the Dorsal Raphe Nucleus of Mice.

Optogenetic methods are now widespread in neuroscience research. Here we present a detailed surgical procedure to inject adeno-associated viruses and implant optic fiber cannulas in the dorsal raphe nucleus (DRN) of living mice. Combined with transgenic mouse lines, this protocol allows specific targeting of serotonin-producing neurons in the brain. It includes fixing a mouse in a stereotaxic frame, performing a craniotomy, virus injection and fiber implantation. Animals can be later used in behavioral experiments, combined with optogenetic manipulations (Dugué et al., 2014; Correia et al., 2017) or monitoring of neuronal activity (Matias et al., 2017). The described procedure is a fundamental step in both optogenetic and fiber photometry experiments of deep brain areas. It is optimized for serotonin neurons in the DRN, but it can be applied to any other cell type and brain region. When using transgenic mouse lines that express functionally relevant levels of optogenetic tools or reporter lines, the virus injection step can be skipped and the protocol is reduced to the cannula implantation procedure.

Transient inhibition and long-term facilitation of locomotion by phasic optogenetic activation of serotonin neurons.

Serotonin (5-HT) is associated with mood and motivation but the function of endogenous 5-HT remains controversial. Here, we studied the impact of phasic optogenetic activation of 5-HT neurons in mice over time scales from seconds to weeks. We found that activating dorsal raphe nucleus (DRN) 5-HT neurons induced a strong suppression of spontaneous locomotor behavior in the open field with rapid kinetics (onset ≤1 s). Inhibition of locomotion was independent of measures of anxiety or motor impairment and could be overcome by strong motivational drive. Repetitive place-contingent pairing of activation caused neither place preference nor aversion. However, repeated 15 min daily stimulation caused a persistent increase in spontaneous locomotion to emerge over three weeks. These results show that 5-HT transients have strong and opposing short and long-term effects on motor behavior that appear to arise from effects on the underlying factors that motivate actions.

Bonsai: an event-based framework for processing and controlling data streams.

The design of modern scientific experiments requires the control and monitoring of many different data streams. However, the serial execution of programming instructions in a computer makes it a challenge to develop software that can deal with the asynchronous, parallel nature of scientific data. Here we present Bonsai, a modular, high-performance, open-source visual programming framework for the acquisition and online processing of data streams. We describe Bonsai's core principles and architecture and demonstrate how it allows for the rapid and flexible prototyping of integrated experimental designs in neuroscience. We specifically highlight some applications that require the combination of many different hardware and software components, including video tracking of behavior, electrophysiology and closed-loop control of stimulation.

Optogenetic recruitment of dorsal raphe serotonergic neurons acutely decreases mechanosensory responsivity in behaving mice.

The inhibition of sensory responsivity is considered a core serotonin function, yet this hypothesis lacks direct support due to methodological obstacles. We adapted an optogenetic approach to induce acute, robust and specific firing of dorsal raphe serotonergic neurons. In vitro, the responsiveness of individual dorsal raphe serotonergic neurons to trains of light pulses varied with frequency and intensity as well as between cells, and the photostimulation protocol was therefore adjusted to maximize their overall output rate. In vivo, the photoactivation of dorsal raphe serotonergic neurons gave rise to a prominent light-evoked field response that displayed some sensitivity to a 5-HT1A agonist, consistent with autoreceptor inhibition of raphe neurons. In behaving mice, the photostimulation of dorsal raphe serotonergic neurons produced a rapid and reversible decrease in the animals' responses to plantar stimulation, providing a new level of evidence that serotonin gates sensory-driven responses.

Dissecting the conserved NPxxY motif of the M3 muscarinic acetylcholine receptor: critical role of Asp-7.49 for receptor signaling and multiprotein complex formation.

Acetylcholine challenge produces M(3) muscarinic acetylcholine receptor activation and accessory/scaffold proteins recruitment into a signalsome complex. The dynamics of such a complex is not well understood but a conserved NPxxY motif located within transmembrane 7 and juxtamembrane helix 8 of the receptor was found to modulate G protein activation. Here by means of receptor mutagenesis we unravel the role of the conserved M(3) muscarinic acetylcholine receptor NPxxY motif on ligand binding, signaling and multiprotein complex formation. Interestingly, while a N7.49D receptor mutant showed normal ligand binding properties a N7.49A mutant had reduced antagonist binding and increased affinity for carbachol. Also, besides this last mutant was able to physically couple to Gα(q/11) after carbachol challenge it was neither capable to activate phospholipase C nor phospholipase D. On the other hand, we demonstrated that the Asn-7.49 is important for the interaction between M(3)R and ARF1 and also for the formation of the ARF/Rho/ß Î³ signaling complex, a complex that might determine the rapid activation and desensitization of PLD. Overall, these results indicate that the NPxxY motif of the M(3) muscarinic acetylcholine receptor acts as key conformational switch for receptor signaling and multiprotein complex formation.

Muscarinic receptor family interacting proteins: role in receptor function.

G protein-coupled receptors constitute one of the most important families of membrane receptors through which cells respond to extracellular stimuli. Receptors of this superfamily likely function as signal transduction complexes. The identification and analysis of their components provide new insights into a better understanding of these receptors' function and regulation. We used tandem-affinity purification and mass spectrometry as a systematic approach to characterize multiprotein complexes in the acetylcholine muscarinic receptor subfamily. To overcome the limitations associated with membrane protein receptor solubilization with detergents, we developed a strategy in which receptors are co-expressed with a cytoplasmic minigene construct, encoding the third intracellular loop and the C-terminal tail tagged to the tandem-affinity-cassette of each receptor subtype. Numerous protein complexes were identified, including many new interactions in various signalling pathways. Systematic identification data set together with protein interactions reported in the literature revealed a high degree of connectivity. These allow the proposal, for the first time, of an outline of the muscarinic interactome as a network of protein complexes and a context for a more reasoned and informed approach to drug discovery and muscarinic receptor subtype specificities.

Impaired M(3) muscarinic acetylcholine receptor signal transduction through blockade of binding of multiple proteins to its third intracellular loop.

Several motifs found in the third intracellular loop of the M(3) muscarinic receptor are critical for G protein activation and scaffold protein interaction. However, how multiprotein complexes form is not fully understood. A minigene encoding the third intracellular loop of the M(3) muscarinic receptor was constructed to explore whether peptides from this intracellular region could act as inhibitors of the muscarinic multiprotein complex formation and signaling. We found that this construct, when co-expressed with the M(3) receptor, has the ability to act as a competitive antagonist of G protein receptors and receptor-scaffold/accessory proteins. Transient transfection of human embryonic kidney-293 cells with DNA encoding the human M(3) and M(5) receptor subtypes results in a carbachol-dependent increase of inositol phosphate. Co-expression of the M(3) third cytoplasmic loop minigene dramatically reduces both carbachol-mediated G protein activation and inositol phosphate accumulation. Minigene expression also abrogates activation of M(3) and M(5) receptor mitogen-activated protein kinases pathway. Furthermore, minigene expression led to reduced AKT activation. These data, together with results of co-immunoprecipitation of different scaffold and kinase proteins, provide experimental evidence for the role for the third cytoplasmic loop of the human M(3) muscarinic receptor in G-protein activation and multiprotein complex formation.