Synaptic modifications in the medial prefrontal cortex in susceptibility and resilience to stress

When facing stress, most individuals are resilient whereas others are prone to developing mood disorders. The brain mechanisms underlying such divergent behavioral responses remain unclear. Here we used the learned helplessness procedure in mice to examine the role of the medial prefrontal cortex (mPFC), a brain region highly implicated in both clinical and animal models of depression, in adaptive and maladaptive behavioral responses to stress. We found that uncontrollable and inescapable stress induced behavioral state-dependent changes in the excitatory synapses onto a subset of mPFC neurons: those that were activated during behavioral responses as indicated by their expression of the activity reporter c-Fos. Whereas synaptic potentiation was linked to learned helplessness, a depression-like behavior, synaptic weakening, was associated with resilience to stress. Notably, enhancing the activity of mPFC neurons using a chemical-genetic method was sufficient to convert the resilient behavior into helplessness. Our results provide direct evidence that mPFC dysfunction is linked to maladaptive behavioral responses to stress, and suggest that enhanced excitatory synaptic drive onto mPFC neurons may underlie the previously reported hyperactivity of this brain region in depression

Genetic Approaches to Reveal the Connectivity of Adult-Born Neurons

Much has been learned about the environmental and molecular factors that influence the division, migration, and programmed cell death of adult-born neurons in the mammalian brain. However, detailed knowledge of the mechanisms that govern the formation and maintenance of functional circuit connectivity via adult neurogenesis remains elusive. Recent advances in genetic technologies now afford the ability to precisely target discrete brain tissues, neuronal subtypes, and even single neurons for vital reporter expression and controlled activity manipulations. Here, I review current viral tracing methods, heterologous receptor expression systems, and optogenetic technologies that hold promise toward elucidating the wiring diagrams and circuit properties of adult-born neurons

Optogenetics: Molecular and Optical Tools for Controlling Life with Light

Optogenetic tools are genetically-encoded reagents that, when targeted to specific brain cells, enable their activity to be controlled by light. These tools are having broad impact on science, and may serve clinical roles as well. 150-word Biography: Ed Boyden is Associate Professor of Biological Engineering and Brain and Cognitive Sciences, at the MIT Media Lab and the MIT McGovern Institute. He leads the Synthetic Neurobiology Group, which develops tools for analyzing and engineering the circuits of the brain. These technologies, created often in interdisciplinary collaborations, include 'optogenetic' tools, which enable the activation and silencing of neural circuit elements with light, 3-D microfabricated neural interfaces, and robotic methods for performing single-cell analyses in living brain. He has received the NIH Director's New Innovator Award, the Society for Neuroscience Research Award for Innovation in Neuroscience, the Paul Allen Distinguished Investigator Award, the Perl/UNC prize, the A. F. Harvey Prize, the Grete Lundbeck “Brain” Prize, amongst other recognitions. He has contributed to over 300 peer-reviewed papers, current or pending patents, and articles, and has given over 200 invited talks on his work

Two-way communication with neural networks in vivo using focused light

Neuronal networks process information in a distributed, spatially heterogeneous manner that transcends the layout of electrodes. In contrast, directed and steerable light offers the potential to engage specific cells on demand. We present a unified framework for adapting microscopes to use light for simultaneous in vivo stimulation and recording of cells at fine spatiotemporal resolutions. We use straightforward optics to lock onto networks in vivo, to steer light to activate circuit elements and to simultaneously record from other cells. We then actualize this 'free' augmentation on both an 'open' two-photon microscope and a leading commercial one. By following this protocol, setup of the system takes a few days, and the result is a noninvasive interface to brain dynamics based on directed light, at a network resolution that was not previously possible and which will further improve with the rapid advance in development of optical reporters and effectors. This protocol is for physiologists who are competent with computers and wish to extend hardware and software to interface more fluidly with neuronal networks.National Institutes of Health (U.S.) (Postdoctoral Fellowship)Simons Foundation (Postdoctoral Fellowship)National Institutes of Health (U.S.) (Predoctoral Fellowship)National Institutes of Health (U.S.)Simons Foundatio

AgRP Neurons Are Not Indispensable for Body Weight Maintenance in Adult Mice

In addition to their role in promoting feeding and obesity development, hypothalamic arcuate agouti-related protein/neuropeptide Y (AgRP/NPY) neurons are widely perceived to be indispensable for maintaining normal feeding and body weight in adults, and consistently, acute inhibition of AgRP neurons is known to reduce short-term food intake. Here, we adopted complementary methods to achieve nearly complete ablation of arcuate AgRP/NPY neurons in adult mice and report that lesioning arcuate AgRP/NPY neurons in adult mice causes no apparent alterations in ad libitum feeding or body weight. Consistent with previous studies, loss of AgRP/NPY neurons blunts fasting refeeding. Thus, our studies show that AgRP/NPY neurons are not required for maintaining ad libitum feeding or body weight homeostasis in adult mice

Co-Transmitting Interneurons in the Mouse Olfactory Bulb Regulate Olfactory Detection and Discrimination

Co-transmission of multiple neurotransmitters from a single neuron increases the complexity of signaling information within defined neuronal circuits. Superficial short-axon cells in the olfactory bulb release both dopamine and γ-aminobutyric acid (GABA), yet the specific targets of these neurotransmitters and their respective roles in olfaction have remained unknown. Here, we implement intersectional genetics in mice to selectively block GABA or dopamine release from superficial short-axon cells to identify their distinct cellular targets, impact on circuit function, and behavioral contribution of each neurotransmitter toward olfactory behaviors. We provide functional and anatomical evidence for divergent superficial short-axon cell signaling onto downstream neurons to shape patterns of mitral cell firing that contribute to olfactory-related behaviors

An Excitatory Projection from the Basal Forebrain to the Ventral Tegmental Area That Underlies Anorexia-Like Phenotypes

Maladaptation in balancing internal energy needs and external threat cues may result in eating disorders. However, brain mechanisms underlying such maladaptations remain elusive. Here, we identified that the basal forebrain (BF) sends glutamatergic projections to glutamatergic neurons in the ventral tegmental area (VTA) in mice. Glutamatergic neurons in both regions displayed correlated responses to various stressors. Notably, in vivo manipulation of BF terminals in the VTA revealed that the glutamatergic BF → VTA circuit reduces appetite, increases locomotion, and elicits avoidance. Consistently, activation of VTA glutamatergic neurons reduced body weight, blunted food motivation, and caused hyperactivity with behavioral signs of anxiety, all hallmarks of typical anorexia symptoms. Importantly, activation of BF glutamatergic terminals in the VTA reduced dopamine release in the nucleus accumbens. Collectively, our results point to overactivation of the glutamatergic BF → VTA circuit as a potential cause of anorexia-like phenotypes involving reduced dopamine release

The Melanocortin Action Is Biased Toward Protection from Weight Loss in Mice

The melanocortin action is well perceived for its ability to regulate body weight bidirectionally with its gain of function reducing body weight and loss of function promoting obesity. However, this notion cannot explain the difficulty in identifying effective therapeutics toward treating general obesity via activation of the melanocortin action. Here, we provide evidence that altered melanocortin action is only able to cause one-directional obesity development. We demonstrate that chronic inhibition of arcuate neurons expressing proopiomelanocortin (POMC) or paraventricular hypothalamic neurons expressing melanocortin receptor 4 (MC4R) causes massive obesity. However, chronic activation of these neuronal populations failed to reduce body weight. Furthermore, gain of function of the melanocortin action through overexpression of MC4R, POMC or its derived peptides had little effect on obesity prevention or reversal. These results reveal a bias of the melanocortin action towards protection of weight loss and provide a neural basis behind the well-known, but mechanistically ill-defined, predisposition to obesity development

Olfactory Deficit and Gastrointestinal Dysfunction Precede Motor Abnormalities in Alpha-Synuclein G51D Knock-In Mice

Many Parkinson’s disease (PD) models overexpress α-Synuclein using heterologous promoters, which is adequate to demonstrate that excessive α-Synuclein is toxic but not ideal for learning the precise ontogeny of the disease pathogenesis, specifically where the disease starts and how it progresses. To answer these questions, it is beneficial to generate a mouse model expressing a disease-causing mutation under the endogenous promoter. Here, we generated three Snca knock-in mice. Among them, homozygous SncaG51D mice develop motor deficits by 9 mo of age. These mice exhibit olfactory and gastrointestinal abnormalities by 6 mo. They lose dopaminergic neurons and have reduced dopamine at 18 mo, respectively. Their spatiotemporal pattern of phosphorylated alpha-Synuclein and progression of symptoms parallel those of human PD

The Melanocortin Action Is Biased Toward Protection From Weight Loss in Mice

The melanocortin action is well perceived for its ability to regulate body weight bidirectionally with its gain of function reducing body weight and loss of function promoting obesity. However, this notion cannot explain the difficulty in identifying effective therapeutics toward treating general obesity via activation of the melanocortin action. Here, we provide evidence that altered melanocortin action is only able to cause one-directional obesity development. We demonstrate that chronic inhibition of arcuate neurons expressing proopiomelanocortin (POMC) or paraventricular hypothalamic neurons expressing melanocortin receptor 4 (MC4R) causes massive obesity. However, chronic activation of these neuronal populations failed to reduce body weight. Furthermore, gain of function of the melanocortin action through overexpression of MC4R, POMC or its derived peptides had little effect on obesity prevention or reversal. These results reveal a bias of the melanocortin action towards protection of weight loss and provide a neural basis behind the well-known, but mechanistically ill-defined, predisposition to obesity development