The locus coeruleus (LC) is a seemingly singular and compact neuromodulatory nucleus that is a prominent component of disparate theories of brain function due to its broad noradrenergic projections ...throughout the CNS. As a diffuse neuromodulatory system, noradrenaline affects learning and decision making, control of sleep and wakefulness, sensory salience including pain, and the physiology of correlated forebrain activity (ensembles and networks) and brain hemodynamic responses. However, our understanding of the LC is undergoing a dramatic shift due to the application of state-of-the-art methods that reveal a nucleus of many modules that provide targeted neuromodulation. Here, we review the evidence supporting a modular LC based on multiple levels of observation (developmental, genetic, molecular, anatomical, and neurophysiological). We suggest that the concept of the LC as a singular nucleus and, alongside it, the role of the LC in diverse theories of brain function must be reconsidered.
Brain serotonin neurons are heterogeneous and can be distinguished by several anatomical and physiological characteristics. Toward resolving this heterogeneity into classes of functional relevance, ...subtypes of mature serotonin neurons were previously identified based on gene expression differences initiated during development in different rhombomeric (r) segments of the hindbrain. This redefinition of mature serotonin neuron subtypes based on the criteria of genetic lineage, along with the enabling genetic fate mapping tools, now allows various functional properties, such as axonal projections, to be allocated onto these identified subtypes. Furthermore, our approach uniquely enables interconnections between the different serotonin neuron subtypes to be determined; this is especially relevant because serotonin neuron activity is regulated by several feedback mechanisms. We used intersectional and subtractive genetic fate mapping tools to generate three independent lines of mice in which serotonin neurons arising in different rhombomeric segments, either r1, r2 or both r3 and r5, were uniquely distinguished from all other serotonin neurons by their expression of enhanced green fluorescent protein. Each of these subgroups of serotonergic neurons had a unique combination of forebrain projection targets. Typically more than one subgroup innervated an individual target area. Unique patterns of interconnections between the different groups of serotonin neurons were also observed and these pathways could subserve feedback regulatory circuits. Overall, the current findings suggest that activation of subsets of serotonin neurons could result in topographic serotonin release in the forebrain coupled with feedback inhibition of serotonin neurons with alternative projection targets.
Brain serotonin neurons are heterogeneous and can be distinguished by several anatomical and physiological characteristics. Toward resolving this heterogeneity into classes of functional relevance, subtypes of mature serotonin neurons were previously identified based on gene expression differences initiated during development in different rhombomeric (r) segments of the hindbrain.
Millions of students in the US and Mexico begin their educations in one country and find themselves trying to integrate into the school system of the other. As global migration increases, their ...numbers are expected to grow and more and more teachers will find these transnational students in their classrooms. The goal of "The Students We Share" is to prepare educators for this present and future reality. While the US has been developing English as a Second Language programs for decades, Mexican schools do not offer such programs in Spanish and neither the US nor Mexico has prepared its teachers to address the educational, social-psychological, or other personal needs of transnational students. Teachers know little about the circumstances of transnational students' lives or histories and have little to no knowledge of the school systems of the country from which they or their family come. As such, they are fundamentally unprepared to equitably educate the "students we share," who often fall through the cracks and end their educations prematurely. Written by both Mexican and US pioneers in the field, chapters in this volume aim to prepare educators on both sides of the US-Mexico border to better understand the circumstances, strengths, and needs of the transnational students we teach. With recommendations for policymakers, administrators, teacher educators, teachers, and researchers in both countries, "The Students We Share" shows how preparing teachers is our shared responsibility and opportunity. It describes policies, classroom practices, and norms of both systems, as well as examples of ongoing partnerships across borders to prepare the teachers we need for our shared students to thrive. Forward written by Linda Darling-Hammond.
Investigating the developmental, structural and functional complexity of mammalian tissues and organs depends on identifying and gaining experimental access to diverse cell populations. Here, we ...describe a set of recombinase-responsive fluorescent indicator alleles in mice that significantly extends our ability to uncover cellular diversity by exploiting the intrinsic genetic signatures that uniquely define cell types. Using a recombinase-based intersectional strategy, these new alleles uniquely permit non-invasive labeling of cells defined by the overlap of up to three distinct gene expression domains. In response to different combinations of Cre, Flp and Dre recombinases, they express eGFP and/or tdTomato to allow the visualization of full cellular morphology. Here, we demonstrate the value of these features through a proof-of-principle analysis of the central noradrenergic system. We label previously inaccessible subpopulations of noradrenergic neurons to reveal details of their three-dimensional architecture and axon projection profiles. These new indicator alleles will provide experimental access to cell populations at unprecedented resolution, facilitating analysis of their developmental origin and anatomical, molecular and physiological properties.
Hippocampal oscillations arise from coordinated activity among distinct populations of neurons and are associated with cognitive functions. Much progress has been made toward identifying the ...contribution of specific neuronal populations in hippocampal oscillations, but less is known about the role of hippocampal area CA2, which is thought to support social memory. Furthermore, the little evidence on the role of CA2 in oscillations has yielded conflicting conclusions. Therefore, we sought to identify the contribution of CA2 to oscillations using a controlled experimental system. We used excitatory and inhibitory DREADDs to manipulate CA2 neuronal activity and studied resulting hippocampal-prefrontal cortical network oscillations. We found that modification of CA2 activity bidirectionally regulated hippocampal and prefrontal cortical low-gamma oscillations and inversely modulated hippocampal ripple oscillations in mice. These findings support a role for CA2 in low-gamma generation and ripple modulation within the hippocampus and underscore the importance of CA2 in extrahippocampal oscillations.
Chemogenetic technologies, including the mutated human Gq-coupled M3 muscarinic receptor (hM3Dq), have greatly facilitated our ability to directly link changes in cellular activity to altered ...physiology and behavior. Here, we extend the hM3Dq toolkit with recombinase-responsive mouse lines that permit hM3Dq expression in virtually any cell type. These alleles encode a fusion protein designed to increase effective expression levels by concentrating hM3Dq to the cell body and dendrites. To illustrate their broad utility, we targeted three different genetically defined cell populations: noradrenergic neurons of the compact, bilateral locus coeruleus and two dispersed populations, Camk2a+ neurons and GFAP+ glia. In all three populations, we observed reproducible expression and confirmed that activation of hM3Dq is sufficient to dose-dependently evoke phenotypic changes, without extreme phenotypes associated with hM3Dq overexpression. These alleles offer the ability to non-invasively control activity of diverse cell types to uncover their function and dysfunction at any developmental stage.
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•Recombinase-responsive mice express hM3Dq DREADD for induction of cellular activity•Targeting of hM3Dq to cell body and dendrites increases effective expression levels•mCherry fusion permits visualization of hM3Dq+ cells in vivo•Dose-dependent activation of hM3Dq drives behavioral and physiological changes
Sciolino et al. develop Cre- and Flp/Cre-responsive mouse lines for non-invasive expression of hM3Dq in genetically defined cells. A targeted fusion protein is designed to increase effective expression level, enabling dose-dependent induction of cellular activity in diverse cell types.
Accumulating evidence indicates that disruption of galanin signaling is associated with neuropsychiatric disease, but the precise functions of this neuropeptide remain largely unresolved due to lack ...of tools for experimentally disrupting its transmission in a cell type-specific manner. To examine the function of galanin in the noradrenergic system, we generated and crossed two novel knock-in mouse lines to create animals lacking galanin specifically in noradrenergic neurons (
Gal
cKO–Dbh
). We observed reduced levels of galanin peptide in pons, hippocampus, and prefrontal cortex of
Gal
cKO–Dbh
mice, indicating that noradrenergic neurons are a significant source of galanin to those brain regions, while midbrain and hypothalamic galanin levels were comparable to littermate controls. In these same brain regions, we observed no change in levels of norepinephrine or its major metabolite at baseline or after an acute stressor, suggesting that loss of galanin does not affect noradrenergic synthesis or turnover.
Gal
cKO–Dbh
mice had normal performance in tests of depression, learning, and motor-related behavior, but had an altered response in some anxiety-related tasks. Specifically,
Gal
cKO–Dbh
mice showed increased marble and shock probe burying and had a reduced latency to eat in a novel environment, indicative of a more proactive coping strategy. Together, these findings indicate that noradrenergic neurons provide a significant source of galanin to discrete brain areas, and noradrenergic-specific galanin opposes adaptive coping responses.
The brainstem nucleus locus coeruleus (LC) sends projections to the forebrain, brainstem, cerebellum and spinal cord and is a source of the neurotransmitter norepinephrine (NE) in these areas. For ...more than 50 years, LC was considered to be homogeneous in structure and function such that NE would be released uniformly and act simultaneously on the cells and circuits that receive LC projections. However, recent studies have provided evidence that LC is modular in design, with segregated output channels and the potential for differential release and action of NE in its projection fields. These new findings have prompted a radical shift in our thinking about LC operations and demand revision of theoretical constructs regarding impact of the LC-NE system on behavioral outcomes in health and disease. Within this context, a major gap in our knowledge is the relationship between the LC-NE system and CNS motor control centers. While we know much about the organization of the LC-NE system with respect to sensory and cognitive circuitries and the impact of LC output on sensory guided behaviors and executive function, much less is known about the role of the LC-NE pathway in motor network operations and movement control. As a starting point for closing this gap in understanding, we propose using an intersectional recombinase-based viral-genetic strategy TrAC (Tracing Axon Collaterals) as well as established
ex vivo
electrophysiological assays to characterize efferent connectivity and physiological attributes of mouse LC-motor network projection neurons. The novel hypothesis to be tested is that LC cells with projections to CNS motor centers are scattered throughout the rostral-caudal extent of the nucleus but collectively display a common set of electrophysiological properties. Additionally, we expect to find these LC projection neurons maintain an organized network of axon collaterals capable of supporting selective, synchronous release of NE in motor circuitries for the purpose of coordinately regulating operations across networks that are responsible for balance and movement dynamics. Investigation of this hypothesis will advance our knowledge of the role of the LC-NE system in motor control and provide a basis for treating movement disorders resulting from disease, injury, or normal aging.
Central noradrenergic neurons, collectively defined by synthesis of the neurotransmitter norepinephrine, are a diverse collection of cells in the hindbrain, differing in their anatomy, physiological ...and behavioral functions, and susceptibility to disease and environmental insult. To investigate the developmental basis of this heterogeneity, we have used an intersectional genetic fate mapping strategy in mice to study the dorsoventral origins of the
-derived locus coeruleus (LC) complex which encompasses virtually all of the anatomically defined LC proper, as well as a portion of the A7 and subcoeruleus (SubC) noradrenergic nuclei. We show that the noradrenergic neurons of the LC complex originate in two different territories of the
expression domain in the embryonic hindbrain. Consistent with prior studies, we confirm that the majority of the LC proper arises from the alar plate, the dorsal domain of the neural tube, as defined by expression of
. In addition, our analysis shows that a large proportion of the
-derived A7 and SubC nuclei also originate in the
-defined alar plate. Surprisingly, however, we identify a smaller subpopulation of the LC complex that arises from outside the
expression domain. We characterize the distribution of these neurons within the LC complex, their cell morphology, and their axonal projection pattern. Compared to the broader LC complex, the newly identified
-negative noradrenergic subpopulation has very sparse projections to thalamic nuclei, suggestive of distinct functions. This developmental genetic analysis opens new avenues of investigation into the functional diversity of the LC complex.
Cholecystokinin-expressing GABAergic (CCK-GABA) neurons are perisomatic inhibitory cells that have been argued to regulate emotion and sculpt the network oscillations associated with cognition. ...However, no study has selectively manipulated CCK-GABA neuron activity during behavior in freely-moving animals. To explore the behavioral effects of activating CCK-GABA neurons on emotion and cognition, we utilized a novel intersectional genetic mouse model coupled with a chemogenetic approach. Specifically, we generated triple transgenic
(CCK-GABA/hM3Dq) mice that expressed the synthetic excitatory hM3Dq receptor in CCK-GABA neurons. Results showed that clozapine-N-oxide (CNO)-mediated activation of CCK-GABA neurons did not alter open field (OF) or tail suspension (TS) performance and only slightly increased anxiety in the elevated plus maze (EPM). Although CNO treatment had only modestly affected emotional behavior, it significantly enhanced multiple cognitive and memory behaviors including social recognition, contextual fear conditioning, contextual discrimination, object recognition, and problem-solving in the puzzle box. Collectively, these findings suggest that systemic activation of CCK-GABA neurons minimally affects emotion but significantly enhances cognition and memory. Our results imply that CCK-GABA neurons are more functionally diverse than originally expected and could serve as a potential therapeutic target for the treatment of cognitive/memory disorders.
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