We combined local photolysis of caged compounds with fluorescence imaging to visualize molecular diffusion within dendrites of cerebellar Purkinje cells. Diffusion of a volume marker, fluorescein ...dextran, within spiny dendrites was remarkably slow in comparison to its diffusion in smooth dendrites. Computer simulations indicate that this retardation is due to a transient trapping of molecules within dendritic spines, yielding anomalous diffusion. We considered the influence of spine trapping on the diffusion of calcium ions (Ca2+) and inositol-1,4,5-triphospate (IP3), two synaptic second messengers. Diffusion of IP3 was strongly influenced by the presence of dendritic spines, while Ca2+ was removed so rapidly that it could not diffuse far enough to be trapped. We conclude that an important function of dendritic spines may be to trap chemical signals and thereby create slowed anomalous diffusion within dendrites.
Regulation of organ size is essential in animal development, and Hippo (Hpo) signaling is a major conserved mechanism for controlling organ growth. In Drosophila, Hpo and Warts kinases are core ...components of this pathway and function as tumor suppressors by inhibiting Yorkie (Yki). Expanded (Ex) is a regulator of the Hpo activity, but how they are linked is unknown. Here, we show that Schip1, a Drosophila homolog of the mammalian Schwannomin interacting protein 1 (SCHIP1), provides a link between Ex and Hpo. Ex is required for apical localization of Schip1 in imaginal discs. Schip1 is necessary for promoting membrane localization and phosphorylation of Hpo by recruiting the Hpo kinase Tao-1. Taking these findings together, we conclude that Schip1 directly links Ex to Hpo signaling by recruiting Tao-1. This study provides insights into the mechanism of Tao-1 regulation and a potential growth control function for SCHIP1 in mammals.
•Schip1 controls Hippo signaling to suppress organ growth in Drosophila•Schip1 forms a complex with Expanded for Hippo localization•Schip1 directly promotes Tao-1 activity for Hippo phosphorylation•Schip1 links Expanded and Tao-1 to activate Hippo, hence suppressing Yorkie
The Hippo signaling pathway is a major conserved mechanism that controls organ growth in Drosophila and mammals. Here, Chung et al. show that the Drosophila protein Schip1 acts as a linker between Expanded and Tao-1 to control Hippo activity.
Luminopsins are fusion proteins of luciferase and opsin that allow interrogation of neuronal circuits at different temporal and spatial resolutions by choosing either extrinsic physical or intrinsic ...biological light for its activation. Building on previous development of fusions of wild-type Gaussia luciferase with channelrhodopsin, here we expanded the utility of luminopsins by fusing bright Gaussia luciferase variants with either channelrhodopsin to excite neurons (luminescent opsin, LMO) or a proton pump to inhibit neurons (inhibitory LMO, iLMO). These improved LMOs could reliably activate or silence neurons in vitro and in vivo. Expression of the improved LMO in hippocampal circuits not only enabled mapping of synaptic activation of CA1 neurons with fine spatiotemporal resolution but also could drive rhythmic circuit excitation over a large spatiotemporal scale. Furthermore, virus-mediated expression of either LMO or iLMO in the substantia nigra in vivo produced not only the expected bidirectional control of single unit activity but also opposing effects on circling behavior in response to systemic injection of a luciferase substrate. Thus, although preserving the ability to be activated by external light sources, LMOs expand the use of optogenetics by making the same opsins accessible to noninvasive, chemogenetic control, thereby allowing the same probe to manipulate neuronal activity over a range of spatial and temporal scales.
Sleep spindles are rhythmic patterns of neuronal activity generated within the thalamocortical circuit. Although spindles have been hypothesized to protect sleep by reducing the influence of external ...stimuli, it remains to be confirmed experimentally whether there is a direct relationship between sleep spindles and the stability of sleep. We have addressed this issue by using in vivo photostimulation of the thalamic reticular nucleus of mice to generate spindle oscillations that are structurally and functionally similar to spontaneous sleep spindles. Such optogenetic generation of sleep spindles increased the duration of non-rapid eye movement (NREM) sleep. Furthermore, the density of sleep spindles was correlated with the amount of NREM sleep. These findings establish a causal relationship between sleep spindles and the stability of NREM sleep, strongly supporting a role for the thalamocortical circuit in sleep regulation.
Lower urinary tract (LUT) function is controlled by the central nervous system, including higher-order cognitive brain regions. The anterior cingulate cortex (ACC) is one of these regions, but the ...role of its activity in LUT function remains poorly understood. In the present study, we conducted optogenetic experiments to manipulate neural activity in mouse ACC while monitoring bladder pressure to elucidate how the activity of ACC regulates LUT function. Selective optogenetic stimulation of excitatory neurons in ACC induced a sharp increase in bladder pressure, whereas activation of inhibitory neurons in ACC prolonged the interval between bladder contractions. Pharmacological manipulation of ACC also altered bladder contractions, consistent with those observed in optogenetic experiments. Optogenetic mapping of the cortical area responsible for eliciting the increase in bladder pressure revealed that stimulation to ACC showed more potent effects than the neighboring motor cortical areas. These results suggest that ACC plays a crucial role in initiating the bladder pressure change and the micturition reflex. Thus, the balance between excitation and inhibition in ACC may regulate the reflex bidirectionally.
Here we summarize the evidence from two "giant" presynaptic terminals-the squid giant synapse and the mammalian calyx of Held-supporting the involvement of nanodomain calcium signals in triggering of ...neurotransmitter release. At the squid synapse, there are three main lines of experimental evidence for nanodomain signaling. First, changing the size of the unitary calcium channel current by altering external calcium concentration causes a non-linear change in transmitter release, while changing the number of open channels by broadening the presynaptic action potential causes a linear change in release. Second, low-affinity calcium indicators, calcium chelators, and uncaging of calcium all suggest that presynaptic calcium concentrations are as high as hundreds of micromolar, which is more compatible with a nanodomain type of calcium signal. Finally, neurotransmitter release is much less affected by the slow calcium chelator, ethylene glycol tetraacetic acid (EGTA), in comparison to the rapid chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA). Similarly, as the calyx of Held synapse matures, EGTA becomes less effective in attenuating transmitter release while the number of calcium channels required to trigger a single fusion event declines. This suggests a developmental transformation of microdomain to nanodomain coupling between calcium channels and transmitter release. Calcium imaging and uncaging experiments, in combination with simulations of calcium diffusion, indicate the peak calcium concentration seen by presynaptic calcium sensors reaches at least tens of micromolar at the calyx of Held. Taken together, data from these provide a compelling argument that nanodomain calcium signaling gates very rapid transmitter release.
The striatum is predominantly composed of medium spiny projection neurons, with the remaining neurons consisting of several types of interneurons. Among the interneurons are a group of cells that ...express tyrosine hydroxylase (TH). Although the intrinsic electrical properties of these TH-expressing interneurons have been characterized, there is no agreement on the number of TH-expressing cell types and their electrical properties. Here, we have used transgenic mice in which YFP-tagged channelrhodopsin-2 (ChR2) was expressed in potential TH-expressing cells in a Cre-dependent manner. We found that the YFP
neurons in the striatum were heterogeneous in their intrinsic electrical properties; unbiased clustering indicated that there are three main neuronal subtypes. One population of neurons had aspiny dendrites with high-frequency action potential (AP) firing and plateau potentials, resembling the TH interneurons (THIN) described previously. A second, very small population of labeled neurons resembled medium-sized spiny neurons (MSN). The third population of neurons had dendrites with an intermediate density of spines, showed substantial AP adaptation and generated prolonged spikes. This type of striatal neuron has not been previously identified in the adult mouse and we have named it the Frequency-Adapting Neuron with Spines (FANS). Because of their distinctive properties, FANS may play a unique role in striatal information processing.
The function of a feedback inhibitory circuit between cerebellar Purkinje cells and molecular layer interneurons (MLIs) was defined by combining optogenetics, neuronal activity recordings both in ...cerebellar slices and in vivo, and computational modeling. Purkinje cells inhibit a subset of MLIs in the inner third of the molecular layer. This inhibition is non-reciprocal, short-range (less than 200 μm) and is based on convergence of one to two Purkinje cells onto MLIs. During learning-related eyelid movements in vivo, the activity of a subset of MLIs progressively increases as Purkinje cell activity decreases, with Purkinje cells usually leading the MLIs. Computer simulations indicate that these relationships are best explained by the feedback circuit from Purkinje cells to MLIs and that this feedback circuit plays a central role in making cerebellar learning efficient.
During murine development, this form of social learning underpins intergenerational transmission of food choices between adult mice and pups, allowing weanlings who are exploring their food options ...to learn vicariously about safe foods (and avoid eating poisoned foods) that their elders have experienced (Silverman et al., 2010). ...in both human and murine species, knowledge transmission through social interaction with adult caregivers plays a vital role in shaping the developing youngling's understanding of the world and how to interact successfully with it. ...perceptual stimuli that are delivered during a high-excitability phase of neural oscillations are more likely to be detected and encoded than stimuli that arrive at a low-excitability, inhibitory phase (Busch et al., 2009; Mathewson et al., 2009). Conversely, if the balls are fired randomly without reference to the phase of the turning wheel, then many balls will hit the blades and bounce out and only a few will pass through by chance. ...synchronisation is the key to transmitting all the information (balls) from the sender (machine) safely through to the receiver (wheel), where the timing of ball firing and wheel rotation represent the neuronal oscillation patterns of the sender and receiver, respectively. (Right) Conversely, if the balls are fired randomly without reference to the phase of the turning wheel, then many balls will hit the blades and bounce out and only a few will pass through by chance. ...synchronisation permits all the information (balls) to be safely transmitted from the sender (machine) to the receiver (wheel), where the timing of ball firing and wheel rotation represent the neuronal oscillation patterns of the information sender (blue solid line) and the information receiver (red dotted line), respectively.
The claustrum is a thin sheet of neurons that is densely connected to many cortical regions and has been implicated in numerous high-order brain functions. Such brain functions arise from brain ...states that are influenced by neuromodulatory pathways from the cholinergic basal forebrain, dopaminergic substantia nigra and ventral tegmental area, and serotonergic raphe. Recent revelations that the claustrum receives dense input from these structures have inspired investigation of state-dependent control of the claustrum. Here, we review neuromodulation in the claustrum-from anatomical connectivity to behavioral manipulations-to inform future analyses of claustral function.
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