Afferent Connections Research Articles

Trigeminal cervical complex: A neural network affecting the head and neck

ObjectivesTo introduce the trigeminal cervical complex (TCC) as a comprehensive framework for understanding the anatomical and functional scope of the afferences and efferences of the trigeminal nerve and explaining common otolaryngologic symptoms, including head and neck myofascial pain syndrome. Additionally, it explores how the bidirectional transmission of neurotransmitters contributes to the sensitization of the TCC and motor nuclei. MethodsThe study was conducted as a narrative review. The authors performed a comprehensive search of multiple databases, including Medline/OVID, Embase, Scopus, and PubMed, covering publications from inception until August 2023. Both keywords and medical subject headings related to the TCC were utilized in the search. Information from 66 studies was extracted based on predetermined inclusion and exclusion criteria. ResultsThis review discusses the multiple afferent connections from cranial nerves, specifically VII, IX, X, and XI, to the TCC, and their respective efferent pathways. These connections may explain various clinical manifestations in the head and neck that cannot be attributed to other medical conditions. Additionally, the review highlights the dual sensory and motor nature of cranial nerves, emphasizing the bidirectional transmission of neurotransmitters in head and neck areas, which leads to the sensitization of both the TCC and motor nuclei innervating the cervicofacial muscles. ConclusionThe authors hypothesize that the central and peripheral sensitization and the intricate connections of the TCC can elucidate the pathophysiology of conditions such as otalgia, tinnitus, hearing loss, vertigo, headache, cervicogenic dizziness, bruxism, and other symptoms affecting the head and neck.

Mapping of afferent and efferent connections of phenylethanolamine N-methyltransferase-expressing neurons in the nucleus tractus solitarii.

Phenylethanolamine N-methyltransferase (PNMT)-expressing neurons in the nucleus tractus solitarii (NTS) contribute to the regulation of autonomic functions. However, the neural circuits linking these neurons to other brain regions remain unclear. This study aims to investigate the connectivity mechanisms of the PNMT-expressing neurons in the NTS (NTSPNMT neurons). The methodologies employed in this study included a modified rabies virus-based retrograde neural tracing technique, conventional viral anterograde tracing, and immunohistochemical staining procedures. A total of 43 upstream nuclei projecting to NTSPNMT neurons were identified, spanning several key brain regions including the medulla oblongata, pons, midbrain, cerebellum, diencephalon, and telencephalon. Notably, dense projections to the NTSPNMT neurons were observed from the central amygdaloid nucleus, paraventricular nucleus of the hypothalamus, area postrema, and the gigantocellular reticular nucleus. In contrast, the ventrolateral medulla, lateral parabrachial nucleus, and lateral hypothalamic area were identified as the primary destinations for axon terminals originating from NTSPNMT neurons. Additionally, reciprocal projections were evident among 21 nuclei, primarily situated within the medulla oblongata. Our research findings demonstrate that NTSPNMT neurons form extensive connections with numerous nuclei, emphasizing their essential role in the homeostatic regulation of vital autonomic functions.

Genetically defined nucleus incertus neurons differ in connectivity and function.

The nucleus incertus (NI), a conserved hindbrain structure implicated in the stress response, arousal, and memory, is a major site for production of the neuropeptide relaxin-3. On the basis of goosecoid homeobox 2 (gsc2) expression, we identified a neuronal cluster that lies adjacent to relaxin 3a (rln3a) neurons in the zebrafish analogue of the NI. To delineate the characteristics of the gsc2 and rln3a NI neurons, we used CRISPR/Cas9 targeted integration to drive gene expression specifically in each neuronal group, and found that they differ in their efferent and afferent connectivity, spontaneous activity, and functional properties. gsc2 and rln3a NI neurons have widely divergent projection patterns and innervate distinct subregions of the midbrain interpeduncular nucleus (IPN). Whereas gsc2 neurons are activated more robustly by electric shock, rln3a neurons exhibit spontaneous fluctuations in calcium signaling and regulate locomotor activity. Our findings define heterogeneous neurons in the NI and provide new tools to probe its diverse functions.

Medial superior olive in the rat: Anatomy, sources of input and axonal projections

Although rats and mice are among the preferred animal models for investigating many characteristics of auditory function, they are rarely used to study an essential aspect of binaural hearing: the ability of animals to localize the sources of low-frequency sounds by detecting the interaural time difference (ITD), that is the difference in the time at which the sound arrives at each ear. In mammals, ITDs are mostly encoded in the medial superior olive (MSO), one of the main nuclei of the superior olivary complex (SOC). Because of their small heads and high frequency hearing range, rats and mice are often considered unable to use ITDs for sound localization. Moreover, their MSO is frequently viewed as too small or insignificant compared to that of mammals that use ITDs to localize sounds, including cats and gerbils. However, recent research has demonstrated remarkable similarities between most morphological and physiological features of mouse MSO neurons and those of MSO neurons of mammals that use ITDs. In this context, we have analyzed the structure and neural afferent and efferent connections of the rat MSO, which had never been studied by injecting neuroanatomical tracers into the nucleus.The rat MSO spans the SOC longitudinally. It is relatively small caudally, but grows rostrally into a well-developed column of stacked bipolar neurons. By placing small, precise injections of the bidirectional tracer biotinylated dextran amine (BDA) into the MSO, we show that this nucleus is innervated mainly by the most ventral and rostral spherical bushy cells of the anteroventral cochlear nucleus of both sides, and by the most ventrolateral principal neurons of the ipsilateral medial nucleus of the trapezoid body. The same experiments reveal that the MSO densely innervates the most dorsolateral region of the central nucleus of the inferior colliculus, the central region of the dorsal nucleus of the lateral lemniscus, and the most lateral region of the intermediate nucleus of the lateral lemniscus of its own side. Therefore, the MSO is selectively innervated by, and sends projections to, neurons that process low-frequency sounds. The structural and hodological features of the rat MSO are notably similar to those of the MSO of cats and gerbils. While these similarities raise the question of what functions other than ITD coding the MSO performs, they also suggest that the rat MSO is an appropriate model for future MSO-centered research.

Ventral amygdalofugal pathway as an integrated surgically important network: microsurgical anatomy and segmentation based on fiber dissection.

The ventral amygdalofugal pathway (VAFP) provides afferent and efferent connections to the amygdala and spans along some of the frequently traversed intra-axial surgical corridors as a dominant fiber bundle. This study aimed to reveal the frequently overlooked VAFP fibers by examining their courses and connections to the basal forebrain, septal region, hypothalamus, thalamus, tegmentum, and brainstem. Ten postmortem human brains were used to display the characteristics of the VAFP, and fiber dissection results were compared with those of tractography. From anterior to posterior, the VAFP was separated into 5 different portions: 1) amygdala-substantia innominata; 2) amygdaloseptal (diagonal band of Broca); 3) amygdalo-thalamic; 4) amygdalo-hypothalamic, intermingling with the medial forebrain bundle and extending to the bed nucleus of stria terminalis; and 5) amygdalotegmental. The results of fiber dissections were confirmed with findings obtained from diffusion tensor tractography. This study supports the concept that interconnected forebrain, diencephalic, mesencephalic, and brainstem connections of the VAFP form an integrated surgically important network. The fiber dissection findings also provide the neuroanatomical basis for VAFP segmentation, which may help neurosurgeons better appreciate the complex microsurgical anatomy of the amygdalar connections. Amygdala-substantia innominata and amygdalotegmental connections are demonstrated for the first time and clarified within the structure of the VAFP.

Abstract TP86: Stroke-Impaired Proprioception Limits Motor Recovery With BCI-FES Device

Introduction: Non-invasive brain-computer interface (BCI) therapy with contingent (i.e., closed-loop) functional electrical stimulation (FES) shows efficacy improving motor function. However, it is not well understood why some stroke survivors respond better to closed-looped BCI-FES intervention than others. Contingent BCI-FES intervention drives neuroplastic change toward adaptive functional connectivity in stroke-impaired sensorimotor brain areas by enriching the afferent feedback environment. The interruption of afferent-efferent feedback circuits is a neural correlate of long-term acquired disability and intactness of functional connections predicts recovery capacity. Studies suggest that proprioception is essential for motor learning and performance. Therefore, we hypothesize that proprioceptive intactness is essential for recovery of motor performance when using a BCI-FES. Methods: Participants with upper extremity motor loss resulting from stroke (n=35) completed up to 30 hours of closed-loop BCI-FES. Results: Change in ARAT scores over the course of the control period were compared to ARAT change scores over the intervention period at a one-month follow up assessment. On average, participants in the intervention realized greater change in ARAT (M = 2.11, SD = 4.68) than during the control phase (M = 0.294, SD = 3.53). An independent-samples t-test indicated this difference, 1.82, 95%CI [-4.17, 0.534], was not statistically significant, t (40.901) = -1.56, p = 0.126. Preliminary results indicate that Proprioceptive sensory loss has a greater limiting effect on recovery than cutaneous somatosensory loss. Discussion: Rehabilitating motor capacity after stroke depends on the intactness of sensorimotor neural circuits. If afference signals are missing or degraded due to stroke, motor recovery is poor. When the stroke spares afferent connectivity to the peripheral muscles, the sensorimotor cortex can leverage plasticity-based motor rehab strategies such as BCI-FES. Conclusion: Intactness of sensorimotor circuits is related to baseline severity of motor impairment as well as recovery of motor function. Efficacious prescription of BCI-FES intervention is best suited for patients with stroke-spared proprioception.

Impaired effective functional connectivity in the social preference of children with autism spectrum disorder.

The medial prefrontal cortex (mPFC), amygdala (Amyg), and nucleus accumbens (NAc) have been identified as critical players in the social preference of individuals with ASD. However, the specific pathophysiological mechanisms underlying this role requires further clarification. In the current study, we applied Granger Causality Analysis (GCA) to investigate the neural connectivity of these three brain regions of interest (ROIs) in patients with ASD, aiming to elucidate their associations with clinical features of the disorder. Resting-state functional magnetic resonance imaging (rs-fMRI) data were acquired from the ABIDE II database, which included 37 patients with ASD and 50 typically developing (TD) controls. The mPFC, Amyg, and NAc were defined as ROIs, and the differences in fractional amplitude of low-frequency fluctuations (fALFF) within the ROIs between the ASD and TD groups were computed. Subsequently, we employed GCA to investigate the bidirectional effective connectivity between the ROIs and the rest of the brain. Finally, we explored whether this effective connectivity was associated with the social responsiveness scale (SRS) scores of children with ASD. The fALFF values in the ROIs were reduced in children with ASD when compared to the TD group. In terms of the efferent connectivity from the ROIs to the whole brain, the ASD group exhibited increased connectivity in the right cingulate gyrus and decreased connectivity in the right superior temporal gyrus. Regarding the afferent connectivity from the whole brain to the ROIs, the ASD group displayed increased connectivity in the right globus pallidus and decreased connectivity in the right cerebellar Crus 1 area and left cingulate gyrus. Additionally, we demonstrated a positive correlation between effective connectivity derived from GCA and SRS scores. Impairments in social preference ASD children is linked to impaired effective connectivity in brain regions associated with social cognition, emotional responses, social rewards, and social decision-making. This finding further reveals the potential neuropathological mechanisms underlying ASD.

Neural connections of the torus semicircularis in the adult Zebrafish.

The torus semicircularis (TS) of teleosts is a key midbrain center of the lateral line and acoustic sensory systems. To characterize the TS in adult zebrafish, we studied their connections using the carbocyanine tracers applied to the TS and to other related nuclei and tracts. Two main TS nuclei, central and ventrolateral, were differentiable by their afferent connections. From central TS, (TSc) numerous toropetal cells were labeled bilaterally in several primary octaval nuclei (anterior, magnocellular, descending, and posterior octaval nuclei), in the secondary octaval nucleus, in the caudal octavolateralis nucleus, and in the perilemniscular region. In the midbrain, numerous toropetal cells were labeled in the contralateral TSc. In the diencephalon, toropetal cells labeled from the TSc were observed ipsilaterally in the medial prethalamic nucleus and the periventricular posterior tubercle nucleus. TSc toropetal neurons were also labeled bilaterally in the hypothalamic anterior tuberal nucleus (ATN) and ipsilaterally in the parvicellular preoptic nucleus but not in the telencephalon. Tracer application to the medial octavolateralis nucleus revealed contralateral projections to the ventrolateral TS (TSvl), whereas tracer application to the secondary octaval nucleus labeled fibers bilaterally in TSc and neurons in rostral TSc. The TSc sends ascending fibers to the ipsilateral lateral preglomerular region that, in turn, projects to the pallium. Application of DiI to the optic tectum labeled cells and fibers in the TSvl, whereas application of DiI to the ATN labeled cells and fibers in the TSc. These results reveal that the TSvl and TSc are mainly related with the mechanosensory lateral line and acoustic centers, respectively, and that they show different higher order connections.

Whole-brain inputs and outputs of Phox2b and GABAergic neurons in the nucleus tractus solitarii.

The nucleus tractus solitarii (NTS) plays a critical role in the homeostatic regulation of respiration, blood pressure, sodium consumption and metabolic processes. Despite their significance, the circuitry mechanisms facilitating these diverse physiological functions remain incompletely understood. In this study, we present a whole-brain mapping of both the afferent and efferent connections of Phox2b-expressing and GABAergic neurons within the NTS. Our findings reveal that these neuronal populations not only receive monosynaptic inputs primarily from the medulla oblongata, pons, midbrain, supra-midbrain and cortical areas, but also mutually project their axons to these same locales. Moreover, intense monosynaptic inputs are received from the central amygdala, the paraventricular nucleus of the hypothalamus, the parasubthalamic nucleus and the intermediate reticular nucleus, along with brainstem nuclei explicitly engaged in respiratory regulation. In contrast, both neuronal groups extensively innervate brainstem nuclei associated with respiratory functions, although their projections to regions above the midbrain are comparatively limited. These anatomical findings provide a foundational platform for delineating an anatomical framework essential for dissecting the specific functional mechanisms of these circuits.

In Humans, Insulo-striate Structural Connectivity is Largely Biased Toward Either Striosome-like or Matrix-like Striatal Compartments.

The insula is an integral component of sensory, motor, limbic, and executive functions, and insular dysfunction is associated with numerous human neuropsychiatric disorders. Insular efferents project widely, but insulo-striate projections are especially numerous. The targets of these insulo-striate projections are organized into tissue compartments, the striosome and matrix. These striatal compartments have distinct embryologic origins, afferent and efferent connectivity, dopamine pharmacology, and susceptibility to injury. Striosome and matrix appear to occupy separate sets of cortico-striato-thalamo-cortical loops, so a bias in insulo-striate projections toward one compartment may also embed an insular subregion in distinct regulatory and functional networks. Compartment-specific mapping of insulo-striate structural connectivity is sparse; the insular subregions are largely unmapped for compartment-specific projections. In 100 healthy adults, diffusion tractography was utilized to map and quantify structural connectivity between 19 structurally-defined insular subregions and each striatal compartment. Insulo-striate streamlines that reached striosome-like and matrix-like voxels were concentrated in distinct insular zones (striosome: rostro- and caudoventral; matrix: caudodorsal) and followed different paths to reach the striatum. Though tractography was generated independently in each hemisphere, the spatial distribution and relative bias of striosome-like and matrix-like streamlines were highly similar in the left and right insula. 16 insular subregions were significantly biased toward 1 compartment: 7 toward striosome-like voxels and 9 toward matrix-like voxels. Striosome-favoring bundles had significantly higher streamline density, especially from rostroventral insular subregions. The biases in insulo-striate structural connectivity that were identified mirrored the compartment-specific biases identified in prior studies that utilized injected tract tracers, cytoarchitecture, or functional MRI. Segregating insulo-striate structural connectivity through either striosome or matrix may be an anatomic substrate for functional specialization among the insular subregions.

Afferent and efferent connections of the secondary general visceral sensory nucleus in goldfish.

The secondary general visceral sensory nucleus (SVN) receives ascending fibers from the commissural nucleus of Cajal (NCC), or the primary general visceral sensoru in the medulla oblongata of teleosts. However, the full set of fiber connections of the SVN have been studied only in the Nile tilapia. We have investigated the connections of the SVN in goldfish by tracer injection experiments to the nucleus. We paid special attention to the possible presence of spinal afferents, since the spinal cord projects to the lateral parabrachial nucleus, or the presumed homologue of SVN, in mammals. We found that the SVN indeed receives spinal projections. Spinal terminals were restricted to a region ventrolaterally adjacent to the terminal zone of NCC fibers, suggesting that the SVN can be subdivided into two subnuclei: the commissural nucleus-recipient (SVNc) and spinal-recipient (SVNsp) subnuclei. Tracer injections to the SVNc and SVNsp as well as reciprocal injections to the diencephalon revealed that both subnuclei project directly to diencephalic structures, such as the posterior thalamic nucleus and nucleus of lateral recess, although diencephalic projections of the SVNsp were rather sparse. The SVNsp appears to send fibers to more wide-spread targets in the preoptic area than the SVNc does. The SVNc projects to the telencephalon, while the SVNsp sends scarce or possibly no fibers to the telencephalon. Another notable difference was that the SVNsp gives rise to massive projections to the dorsal diencephalon (ventromedial thalamic, central posterior thalamic, and periventricular posterior tubercular nuclei). These differential connections of the subnuclei may reflect discrete functional significances of the general visceral sensory information mediated by the medulla oblongata and spinal cord.

Organization of thalamocortical structural covariance and a corresponding 3D atlas of the mouse thalamus

For information from sensory organs to be processed by the brain, it is usually passed to appropriate areas of the cerebral cortex. Almost all of this information passes through the thalamus, a relay structure that reciprocally connects to the vast majority of the cortex. The thalamus facilitates this information transfer through a set of thalamocortical connections that vary in cellular structure, molecular profiles, innervation patterns, and firing rates. Additionally, corticothalamic connections allow for intracortical information transfer through the thalamus. These efferent and afferent connections between the thalamus and cortex have been the focus of many studies, and the importance of cortical connectivity in defining thalamus anatomy is demonstrated by multiple studies that parcellate the thalamus based on cortical connectivity profiles.Here, we examine correlated morphological variation between the thalamus and cortex, or thalamocortical structural covariance. For each voxel in the thalamus as a seed, we construct a cortical structural covariance map that represents correlated cortical volume variation, and examine whether high structural covariance is observed in cortical areas that are functionally relevant to the seed. Then, using these cortical structural covariance maps as features, we subdivide the thalamus into six non-overlapping regions (clusters of voxels), and assess whether cortical structural covariance is associated with cortical connectivity that specifically originates from these regions.We show that cortical structural covariance is high in areas of the cortex that are functionally related to the seed voxel, cortical structural covariance varies along cortical depth, and sharp transitions in cortical structural covariance profiles are observed when varying seed locations in the thalamus. Subdividing the thalamus based on structural covariance, we additionally demonstrate that the six thalamic clusters of voxels stratify cortical structural covariance along the dorsal–ventral, medial–lateral, and anterior–posterior axes. These cluster-associated structural covariance patterns are prominently detected in cortical regions innervated by fibers projecting out of their related thalamic subdivisions.Together, these results advance our understanding of how the thalamus and the cortex couple in their volumes. Our results indicate that these volume correlations reflect functional organization and structural connectivity, and further provides a novel segmentation of the mouse thalamus that can be used to examine thalamic structural variation and thalamocortical structural covariation in disease models.

Concept: Electrical Cardiac Stimulation is Detected by the Cardiac Autonomic Nervous System with Possible Effects on the Vasovagal Reflex

Abstract A novel concept is described concerning the possible effect of right ventricular pacing stimulation being detected by the cardiac autonomic nervous system and through its afferent neuronal connection to the central autonomic nervous system (spinal cord) causing reversal or attenuation of the vasovagal reflex. This could be a direct effect of electrical stimulation or may occur by the known adverse consequences on ventricular synchrony induced by stimulation which could be right ventricular site and timing in the evolution of the vasovagal reflex dependent.

A brain model of altered self-appraisal in social anxiety disorder

The brain’s default mode network has a central role in the processing of information concerning oneself. Dysfunction in this self-referential processing represents a key component of multiple mental health conditions, particularly social anxiety disorder (SAD). This case-control study aimed to clarify alterations to network dynamics present during self-appraisal in SAD participants. A total of 38 adolescents and young adults with SAD and 72 healthy control participants underwent a self-referential processing fMRI task. The task involved two primary conditions of interest: direct self-appraisal (thinking about oneself) and reflected self-appraisal (thinking about how others might think about oneself). Dynamic causal modeling and parametric empirical Bayes were then used to explore differences in the effective connectivity of the default mode network between groups. We observed connectivity differences between SAD and healthy control participants in the reflected self-appraisal but not the direct self-appraisal condition. Specifically, SAD participants exhibited greater excitatory connectivity from the posterior cingulate cortex (PCC) to medial prefrontal cortex (MPFC) and greater inhibitory connectivity from the inferior parietal lobule (IPL) to MPFC. In contrast, SAD participants exhibited reduced intrinsic connectivity in the absence of task modulation. This was illustrated by reduced excitatory connectivity from the PCC to MPFC and reduced inhibitory connectivity from the IPL to MPFC. As such, participants with SAD showed changes to afferent connections to the MPFC which occurred during both reflected self-appraisal as well as intrinsically. The presence of connectivity differences in reflected and not direct self-appraisal is consistent with the characteristic fear of negative social evaluation that is experienced by people with SAD.

Abstract 17051: Oxytocin Receptor in the Spinal Neuraxial Modulation of Ventricular Excitability

Introduction: Cardiac sympathoexcitation is a major contributor to the pathogenesis of ventricular tachyarrhymias (VTs) during ischemia reperfusion (I/R) and chronic myocardial infarction (MI). Afferent network connections in the intermediolateral cell column (IML) and dorsal horn (DH) control sympathetic output to the heart. Our team reported spinal cord stimulation (SCS), decreased cardiac sympathoexcitation and reduced VTs during ischemia. Oxytocin (OXT) is a known neuromodulator; however, whether OXT signaling can modulate the cardiospinal neural network is unknown. Hypothesis: SCS neuromodulation is reducing sympathoexcitation and VTs through OXT signaling pathways. Methods: Two models of cardiac ischemia were used in Yorkshire domestic swine. In acute I/R, a suture was placed around the left anterior descending (LAD) coronary artery, after sternotomy. Chronic infarction (MI) was created by accessing the femoral with fluoroscopy guidance. Polystyrene microspheres (1ml) were injected via a 3mm angioplasty balloon catheter to the LAD. Animals then recovered post-MI for 6-8wk. SCS treatment was delivered through a four-pole lead which was inserted in the epidural space (T1-T4)(50Hz, 0.4ms pulse duration). T2-T4 spinal cord was collected postmortem for molecular analysis. Fluorescence in situ hybridization (FISH) protocol for RNAscope Fluorescent v2 Assay (ACD) was followed. Cell counts represented as 3 puncta or more centered around DAPI. Results: We report that OXT receptor positive cells significantly decreased as a result of I/R and MI (p<0.001, two-way ANOVA n=4-5 animals, average of 2-3 slices per animal). Within the DH the majority of OXT positive cells were inhibitory GABAergic neurons. Within the IML, a majority of the cells regulated by I/R and MI were microglia, and both an inhibitory and excitatory population contributed to the onset of ischemia. SCS treatment after I/R and MI resulted in the recovery of this OXT receptor cell population. Conclusions: By evaluating the role of OXT in reducing cardiac sympathoexcitation at the level of the spinal cord, we provide new insights into optimizing current neuromodulation approaches and developing new pharmacologic therapies.

Mapping mesoscale connectivity within the human hippocampus

The connectivity of the hippocampus is essential to its functions. To gain a whole system view of intrahippocampal connectivity, ex vivo mesoscale (100 μm isotropic resolution) multi-shell diffusion MRI (11.7T) and tractography were performed on entire post-mortem human right hippocampi. Volumetric measurements indicated that the head region was largest followed by the body and tail regions. A unique anatomical organization in the head region reflected a complex organization of the granule cell layer (GCL) of the dentate gyrus. Tractography revealed the volumetric distribution of the perforant path, including both the tri-synaptic and temporoammonic pathways, as well as other well-established canonical connections, such as Schaffer collaterals. Visualization of the perforant path provided a means to verify the borders between the pro-subiculum and CA1, as well as between CA1/CA2. A specific angularity of different layers of fibers in the alveus was evident across the whole sample and allowed a separation of afferent and efferent connections based on their origin (i.e. entorhinal cortex) or destination (i.e. fimbria) using a cluster analysis of streamlines. Non-canonical translamellar connections running along the anterior-posterior axis were also discerned in the hilus. In line with “dentations” of the GCL, mossy fibers were bunching together in the sagittal plane revealing a unique lamellar organization and connections between these. In the head region, mossy fibers projected to the origin of the fimbria, which was distinct from the body and tail region. Mesoscale tractography provides an unprecedented systems view of intrahippocampal connections that underpin cognitive and emotional processing.

Anatomical Connectivity of the Intercalated Cells of the Amygdala.

The intercalated cells of the amygdala (ITCs) are a fundamental processing structure in the amygdala that remain relatively understudied. They are phylogenetically conserved from insectivores through primates, inhibitory, and project to several of the main processing and output stations of the amygdala and basal forebrain. Through these connections, the ITCs are best known for their role in conditioned fear, where they are required for fear extinction learning and recall. Prior work on ITC connectivity is limited, and thus holistic characterization of their afferent and efferent connectivity in a genetically defined manner is incomplete. The ITCs express the FoxP2 transcription factor, affording genetic access to these neurons for viral input-output mapping. To fully characterize the anatomic connectivity of the ITCs, we used cre-dependent viral strategies in FoxP2-cre mice to reveal the projections of the main (mITC), caudal (cITC), and lateral (lITC) clusters along with their presynaptic sources of innervation. Broadly, the results confirm many known pathways, reveal previously unknown ones, and demonstrate important novel insights about each nucleus's unique connectivity profile and relative distributions. We show that the ITCs receive information from a wide range of cortical, subcortical, basal, amygdalar, hippocampal, and thalamic structures, and project broadly to areas of the basal forebrain, hypothalamus, and entire extent of the amygdala. The results provide a comprehensive map of their connectivity and suggest that the ITCs could potentially influence a broad range of behaviors by integrating information from a wide array of sources throughout the brain.

Oncomodulin regulates spontaneous calcium signalling and maturation of afferent innervation in cochlear outer hair cells.

Cochlear outer hair cells (OHCs) are responsible for the exquisite frequency selectivity and sensitivity of mammalian hearing. During development, the maturation of OHC afferent connectivity is refined by coordinated spontaneous Ca2+ activity in both sensory and non-sensory cells. Calcium signalling in neonatal OHCs can be modulated by oncomodulin (OCM, β-parvalbumin), an EF-hand calcium-binding protein. Here, we investigated whether OCM regulates OHC spontaneous Ca2+ activity and afferent connectivity during development. Using a genetically encoded Ca2+ sensor (GCaMP6s) expressed in OHCs in wild-type (Ocm+/+ ) and Ocm knockout (Ocm-/- ) littermates, we found increased spontaneous Ca2+ activity and upregulation of purinergic receptors in OHCs from Ocm-/- cochlea immediately following birth. The afferent synaptic maturation of OHCs was delayed in the absence of OCM, leading to an increased number of ribbon synapses and afferent fibres on Ocm-/- OHCs before hearing onset. We propose that OCM regulates the spontaneous Ca2+ signalling in the developing cochlea and the maturation of OHC afferent innervation. KEY POINTS: Cochlear outer hair cells (OHCs) exhibit spontaneous Ca2+ activity during a narrow period of neonatal development. OHC afferent maturation and connectivity requires spontaneous Ca2+ activity. Oncomodulin (OCM, β-parvalbumin), an EF-hand calcium-binding protein, modulates Ca2+ signals in immature OHCs. Using transgenic mice that endogenously expressed a Ca2+ sensor, GCaMP6s, we found increased spontaneous Ca2+ activity and upregulated purinergic receptors in Ocm-/- OHCs. The maturation of afferent synapses in Ocm-/- OHCs was also delayed, leading to an upregulation of ribbon synapses and afferent fibres in Ocm-/- OHCs before hearing onset. We propose that OCM plays an important role in modulating Ca2+ activity, expression of Ca2+ channels and afferent innervation in developing OHCs.

Structure-function dynamics of engineered, modular neuronal networks with controllable afferent-efferent connectivity

Objective. Microfluidic devices interfaced with microelectrode arrays have in recent years emerged as powerful platforms for studying and manipulating in vitro neuronal networks at the micro- and mesoscale. By segregating neuronal populations using microchannels only permissible to axons, neuronal networks can be designed to mimic the highly organized, modular topology of neuronal assemblies in the brain. However, little is known about how the underlying topological features of such engineered neuronal networks contribute to their functional profile. To start addressing this question, a key parameter is control of afferent or efferent connectivity within the network. Approach. In this study, we show that a microfluidic device featuring axon guiding channels with geometrical constraints inspired by a Tesla valve effectively promotes unidirectional axonal outgrowth between neuronal nodes, thereby enabling us to control afferent connectivity. Main results. Our results moreover indicate that these networks exhibit a more efficient network organization with higher modularity compared to single nodal controls. We verified this by applying designer viral tools to fluorescently label the neurons to visualize the structure of the networks, combined with extracellular electrophysiological recordings using embedded nanoporous microelectrodes to study the functional dynamics of these networks during maturation. We furthermore show that electrical stimulations of the networks induce signals selectively transmitted in a feedforward fashion between the neuronal populations. Significance. A key advantage with our microdevice is the ability to longitudinally study and manipulate both the structure and function of neuronal networks with high accuracy. This model system has the potential to provide novel insights into the development, topological organization, and neuroplasticity mechanisms of neuronal assemblies at the micro- and mesoscale in healthy and perturbed conditions.

Functional and structural synaptic remodeling mechanisms underlying somatotopic organization and reorganization in the thalamus

The somatosensory system organizes the topographic representation of body maps, termed somatotopy, at all levels of an ascending hierarchy. Postnatal maturation of somatotopy establishes optimal somatosensation, whereas deafferentation in adults reorganizes somatotopy, which underlies pathological somatosensation, such as phantom pain and complex regional pain syndrome. Here, we focus on the mouse whisker somatosensory thalamus to study how sensory experience shapes the fine topography of afferent connectivity during the critical period and what mechanisms remodel it and drive a large-scale somatotopic reorganization after peripheral nerve injury. We will review our findings that, following peripheral nerve injury in adults, lemniscal afferent synapses onto thalamic neurons are remodeled back to immature configuration, as if the critical period reopens. The remodeling process is initiated with local activation of microglia in the brainstem somatosensory nucleus downstream to injured nerves and heterosynaptically controlled by input from GABAergic and cortical neurons to thalamic neurons. These fruits of thalamic studies complement well-studied cortical mechanisms of somatotopic organization and reorganization and unveil potential intervention points in treating pathological somatosensation.