Connections of the superior colliculus to shoulder muscles of the rat: a dual tracing study

Acetylcholine Neurons Become Cholinergic during Three Time Windows in the Developing Mouse Brain

Acetylcholine (ACh) neurons in the central nervous system are required for the coordination of neural network activity during higher brain functions, such as attention, learning, and memory, as well as locomotion. Disturbed cholinergic signaling has been described in many neurodevelopmental and neurodegenerative disorders. Furthermore, cotransmission of other signaling molecules, such as glutamate and GABA, with ACh has been associated with essential roles in brain function or disease. However, it is unknown when ACh neurons become cholinergic during development. Thus, understanding the timeline of how the cholinergic system develops and becomes active in the healthy brain is a crucial part of understanding brain development. To study this, we used transgenic mice to selectively label ACh neurons with tdTomato. We imaged serial sectioned brains and generated whole-brain reconstructions at different time points during pre- and postnatal development. We found three crucial time windows-two in the prenatal and one in the postnatal brain-during which most ACh neuron populations become cholinergic in the brain. We also found that cholinergic gene expression is initiated in cortical ACh interneurons, while the cerebral cortex is innervated by cholinergic projection neurons from the basal forebrain. Taken together, we show that ACh neuron populations are present and become cholinergic before postnatal day 12, which is the onset of major sensory processes, such as hearing and vision. We conclude that the birth of ACh neurons and initiation of cholinergic gene expression are temporally separated during development but highly coordinated by brain anatomical structure.

Multimodal integration and modulation of visual and somatosensory inputs on the corticospinal excitability

OBJECTIVE

Corticospinal excitability may be affected by various sensory inputs under physiological conditions. In this study, we aimed to investigate the corticospinal excitability by using multimodal conditioning paradigms of combined somatosensory electrical and visual stimulation to understand the sensory-motor integration.

METHODS

We examined motor evoked potentials (MEP) obtained by using transcranial magnetic stimulation (TMS) that were conditioned by using a single goggle-light-emitting diode (LED) stimulation, peripheral nerve electrical stimulation (short latency afferent inhibition protocol), or a combination of both (goggle-LED+electrical stimulation) at different interstimulus intervals (ISIs) in 14 healthy volunteers.

RESULTS

We found MEP inhibition at ISIs of 50-60 ms using the conditioned goggle-LED stimulation. The combined goggle-LED stimulation at a 60 ms ISI resulted in an additional inhibition to the electrical stimulation.

CONCLUSIONS

Visual inputs cause significant modulatory effects on the corticospinal excitability. Combined visual and somatosensory stimuli integrate probably via different neural circuits and/or interneuron populations. To our knowledge, multimodal integration of visual and somatosensory inputs by using TMS-short latency inhibition protocol have been evaluated via electrophysiological methods for the first time in this study.

Contrasting walking styles map to discrete neural substrates in the mouse brainstem

Walking is a slow gait which is particularly adaptable to meet internal or external needs and is prone to maladaptive alterations that lead to gait disorders. Alterations can affect speed, but also style (the way one walks). While slowed speed may signify the presence of a problem, style represents the hallmark essential for clinical classification of gait disorders. However, it has been challenging to objectively capture key stylistic features while uncovering neural substrates driving these features. Here we revealed brainstem hotspots that drive strikingly different walking styles by employing an unbiased mapping assay that combines quantitative walking signatures with focal, cell type specific activation. We found that activation of inhibitory neurons that mapped to the ventromedial caudal pons induced slow motion-like style. Activation of excitatory neurons that mapped to the ventromedial upper medulla induced shuffle-like style. Contrasting shifts in walking signatures distinguished these styles. Activation of inhibitory and excitatory neurons outside these territories or of serotonergic neurons modulated walking speed, but without walking signature shifts. Consistent with their contrasting modulatory actions, hotspots for slow-motion and shuffle-like gaits preferentially innervated different substrates. These findings lay the basis for new avenues to study mechanisms underlying (mal)adaptive walking styles and gait disorders.

Graphical abstract

The Collicular-Pulvinar-Amygdala Axis and Adult-Onset Idiopathic Focal Dystonias

Adult-onset idiopathic focal dystonias (AOIFD) are the most common type of dystonia. It has varied expression including multiple motor (depending on body part affected) and non-motor symptoms (psychiatric, cognitive and sensory). The motor symptoms are usually the main reason for presentation and are most often treated with botulinum toxin. However, non-motor symptoms are the main predictors of quality of life and should be addressed appropriately, as well as treating the motor disorder. Rather than considering AOIFD as a movement disorder, a syndromic approach should be taken, one that accommodates all the symptoms. Dysfunction of the collicular-pulvinar-amygdala axis, with the superior colliculus as a central node, can explain the diverse expression of this syndrome.

The brain-body disconnect: A somatic sensory basis for trauma-related disorders

Although the manifestation of trauma in the body is a phenomenon well-endorsed by clinicians and traumatized individuals, the neurobiological underpinnings of this manifestation remain unclear. The notion of somatic sensory processing, which encompasses vestibular and somatosensory processing and relates to the sensory systems concerned with how the physical body exists in and relates to physical space, is introduced as a major contributor to overall regulatory, social-emotional, and self-referential functioning. From a phylogenetically and ontogenetically informed perspective, trauma-related symptomology is conceptualized to be grounded in brainstem-level somatic sensory processing dysfunction and its cascading influences on physiological arousal modulation, affect regulation, and higher-order capacities. Lastly, we introduce a novel hierarchical model bridging somatic sensory processes with limbic and neocortical mechanisms regulating an individual's emotional experience and sense of a relational, agentive self. This model provides a working framework for the neurobiologically informed assessment and treatment of trauma-related conditions from a somatic sensory processing perspective.

The connectome from the cerebral cortex to skeletal muscle using viral transneuronal tracers: a review

Connectomics has developed from an initial observation under an electron microscope to the present well-known medical imaging research approach. The emergence of the most popular transneuronal tracers has further advanced connectomics research. Researchers use the virus trans-nerve tracing method to trace the whole brain, mark the brain nerve circuit and nerve connection structure, and construct a complete nerve conduction pathway. This review assesses current methods of studying cortical to muscle connections using viral neuronal tracers and demonstrates their application in disease diagnosis and prognosis.

Basal Ganglia Circuits for Action Specification

Behavior is readily classified into patterns of movements with inferred common goals-actions. Goals may be discrete; movements are continuous. Through the careful study of isolated movements in laboratory settings, or via introspection, it has become clear that animals can exhibit exquisite graded specification to their movements. Moreover, graded control can be as fundamental to success as the selection of which action to perform under many naturalistic scenarios: a predator adjusting its speed to intercept moving prey, or a tool-user exerting the perfect amount of force to complete a delicate task. The basal ganglia are a collection of nuclei in vertebrates that extend from the forebrain (telencephalon) to the midbrain (mesencephalon), constituting a major descending extrapyramidal pathway for control over midbrain and brainstem premotor structures. Here we discuss how this pathway contributes to the continuous specification of movements that endows our voluntary actions with vigor and grace.

'Building a perfect body': control of vertebrate organogenesis by PBX-dependent regulatory networks

Pbx genes encode transcription factors that belong to the TALE (three-amino-acid loop extension) superclass of homeodomain proteins. We have witnessed a surge in information about the roles of this gene family as leading actors in the transcriptional control of development. PBX proteins represent a clear example of how transcription factors can regulate developmental processes by combinatorial properties, acting within multimeric complexes to implement activation or repression of transcription depending on their interaction partners. Here, we revisit long-emphasized functions of PBX transcription factors as cofactors for HOX proteins, major architects of the body plan. We further discuss new knowledge on roles of PBX proteins in different developmental contexts as upstream regulators of Hox genes-as factors that interact with non-HOX proteins and can work independently of HOX-as well as potential pioneer factors. Committed to building a perfect body, PBX proteins govern regulatory networks that direct essential morphogenetic processes and organogenesis in vertebrate development. Perturbations of PBX-dependent networks can cause human congenital disease and cancer.

Noninvasive Ultrasonic Drug Uncaging Maps Whole-Brain Functional Networks

Being able to noninvasively modulate brain activity, where and when an experimenter desires, with an immediate path toward human translation is a long-standing goal for neuroscience. To enable robust perturbation of brain activity while leveraging the ability of focused ultrasound to deliver energy to any point of the brain noninvasively, we have developed biocompatible and clinically translatable nanoparticles that allow ultrasound-induced uncaging of neuromodulatory drugs. Utilizing the anesthetic propofol, together with electrophysiological and imaging assays, we show that the neuromodulatory effect of ultrasonic drug uncaging is limited spatially and temporally by the size of the ultrasound focus, the sonication timing, and the pharmacokinetics of the uncaged drug. Moreover, we see secondary effects in brain regions anatomically distinct from and functionally connected to the sonicated region, indicating that ultrasonic drug uncaging could noninvasively map the changes in functional network connectivity associated with pharmacologic action at a particular brain target.

A Proposed Circuit Computation in Basal Ganglia: History-Dependent Gain

In this Scientific Perspectives we first review the recent advances in our understanding of the functional architecture of basal ganglia circuits. Then we argue that these data can best be explained by a model in which basal ganglia act to control the gain of movement kinematics to shape performance based on prior experience, which we refer to as a history-dependent gain computation. Finally, we discuss how insights from the history-dependent gain model might translate from the bench to the bedside, primarily the implications for the design of adaptive deep brain stimulation. Thus, we explicate the key empirical and conceptual support for a normative, computational model with substantial explanatory power for the broad role of basal ganglia circuits in health and disease. © 2018 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Deletion of pseudorabies virus US2 gene enhances viral titers in a porcine cerebral cortex primary culture system

Pseudorabies virus (PRV) is a neurotropic virus with the ability to infect peripheral sensory ganglia. The transport of PRV from the peripheral to the central nervous system can cause lethal encephalitis in young piglets. However, the pathogenicity of PRV in the cerebral cortex remains poorly understood. In the present study, we developed a porcine cerebral cortex primary culture system (PCCS) using cerebral cortex tissue dissected from a 3-day-old piglet to investigate the pathogenicity of wild-type (WT) and US2 deleted (ΔUS2) PRV in the CNS in vitro. Immunofluorescence assays revealed cell bodies and neurites as the cellular locations infected by PRV. Growth kinetic analysis showed a persistent increase in WT and ΔUS2 viral titers in PCCS from 4 to 24 h post infection (hpi), thus indicating that US2 deletion did not disrupt viral growth. However, the mean plaque size was significantly higher in ΔUS2 PRV than in WT PRV in infected Vero cells. The viral titers and DNA levels of ΔUS2 PRV were significantly higher at 8 hpi than at 4 hpi, whereas those of WT showed no significant difference between the two time points in PCCS. Morphological investigation revealed induction of massive amounts of bouton-like swellings (varicosities) along the axon shaft in both WT and ΔUS2 PRV-infected neurons in the PCCS. Our data suggest that PRV US2 gene deletion enhances viral titers in PCCS but does not affect the varicosities induced by the viral infection.

Arm movements induced by electrical microstimulation in the superior colliculus of the macaque monkey

Neuronal activity in the deep layers of the macaque (Macaca mulatta) superior colliculus (SC) and the underlying reticular formation is correlated with the initiation and execution of arm movements (Werner, 1993). Although the correlation of this activity with EMGs of proximal arm muscles is as strong as in motor cortex (Werner et al., 1997a; Stuphorn et al., 1999), little is known about the influence of electrical microstimulation in the SC on the initiation and trajectories of arm movements. Our experiments on three macaque monkeys clearly show that arm movements can be elicited by electrical microstimulation in the deep layers of the lateral SC and underlying reticular formation. The most extensively trained monkey, M1, extended his arm toward the screen in front of him more or less stereotypically upon electrical SC stimulation. In two other monkeys, M2 and M3, a larger repertoire of arm movements were elicited, categorized into three movement types, and compared before (M3) and after (M2 and M3) training: twitch (56% vs. 62%), lift (6% vs. 5%), and extend (37% vs. 32%), respectively. Therefore, arm movements induced by electrical stimulation in the monkey SC represent a further component of the functional repertoire of the SC using its impact on motoneurons in the spinal cord, probably via premotor neurons in the brainstem, as well as on structures involved in executing more complex movements such as target-directed reaching. Therefore, the macaque SC could be involved directly in the initiation, execution, and amendment of arm and hand movements.