Biology subjects

Dougherty, K. J.

Publications and source records attributed to Dougherty, K. J..

10 recordsLinked to original sources

bioRxiv2026

Long-term Connectivity between Spinal Cord Tissue Transplants and the Injured Phrenic Motor Network

Restoring vital motor functions after spinal cord injury (SCI) remains a central challenge in neuroscience and regenerative medicine. Cervical SCI can cause life-threatening respiratory deficits by damaging the phrenic motor network that controls the diaphragm. Cellular transplantation offers a viable means to improve function by providing new neurons that can relay supraspinal drive to denervated spinal phrenic networks, yet the long-term stability of transplants is poorly defined. Here, we examine donor-host neuronal synaptic connectivity in a respiratory model of cervical SCI, 1-year post-transplantation in adult rats. Embryonically-derived spinal cord tissue was transplanted into the lesion cavity one-week post-SCI, and transplant integration and diaphragm function were assessed at 1-month and 1-year post-transplantation. At 1-month, transplant-recipients exhibited significantly greater diaphragm output than injured, vehicle control animals. The extent of recovery at 1-year, however, was significantly less, coinciding with anatomical changes in graft neuronal density and donor-host connectivity, revealed by transneuronal tracing (pseudorabies virus). These results demonstrate that embryonic spinal cord transplants can improve phrenic motor activity after cervical SCI, but that long-term efficacy may be limited by reduced donor-host connectivity. Significance StatementCell transplantation can repair injured spinal cord circuits, but whether donor-host connections persist long term remains unclear. Using a rat model of cervical spinal cord injury, we show that embryonic spinal cord transplants improve diaphragm activity and integrate with the injured phrenic motor network at early time points, but these benefits decline by 1 year after transplantation. This loss of functional recovery is accompanied by reduced transneuronal labeling of donor neurons and changes in graft tissue composition. These results provide important proof of principle that transplant-host connectivity can be evaluated over extended survival times and identify long-term stability of donor-host integration as a critical challenge for achieving durable respiratory repair after spinal cord injury.

neuroscience↗

bioRxiv2025

Lumbar spinal Shox2 interneurons receive monosynaptic excitatory input from the lateral paragigantocellular nucleus in the adult mouse

Locomotor output in vertebrates is generated in the spinal cord but is initiated and controlled by descending projections from supraspinal structures. Spinal interneurons involved in locomotion have been revealed through manipulation of genetically identified interneurons in transgenic mouse lines. Lumbar spinal interneurons expressing the transcription factor Shox2 include putative locomotor rhythm generating neurons in mice. The direct connection between supraspinal and lumbar spinal locomotor-related interneurons is comprised of reticulospinal neurons which are thought to directly provide drive to spinal rhythm generating interneurons that receive descending input and convert it to a rhythmic output. Excitatory neurons in the lateral paragigantocellular nucleus (LPGi) within the medulla have been shown to provide this descending drive in the context of forward locomotor initiation. However, a direct connection between excitatory LPGi neurons and identified spinal rhythm generating neurons has yet to be demonstrated. Here, we performed viral tracing and electrophysiological recordings to test for direct connections between the LPGi and lumbar Shox2 interneurons in adult mice. Using both monosynaptic-restricted transsynaptic rabies and anterograde AAV tracing, we show that excitatory neurons from the LPGi make direct putative excitatory synaptic contacts onto lumbar spinal Shox2 interneurons. A monosynaptic connection was confirmed via recordings of excitatory postsynaptic potentials in Shox2 interneurons in lumbar spinal slices evoked by optogenetic activation of LPGi terminals. These results demonstrate that at least a subset of lumbar spinal Shox2 interneurons receive monosynaptic excitatory input from the LPGi in the medulla, a connection which may provide the substrate for the initiation of locomotion.

neuroscience↗

bioRxiv2024

Postnatal maturation of serotonergic modulation of spinal RORβ interneurons in the medial deep dorsal horn

Proprioceptive input is essential for coordinated locomotion and this input must be properly gated to ensure smooth and effective movement. Presynaptic inhibition mediated by GABAergic interneurons provides regulation of sensory afferent feedback. Serotonin not only promotes locomotion, but also modulates feedback from sensory afferents, both directly and indirectly, potentially by acting on the GABAergic interneurons that mediate presynaptic inhibition. Developmental disruptions in presynaptic inhibition can produce deficits in sensorimotor processing. Importantly, both presynaptic inhibition of proprioceptive afferents and serotonergic innervation of the spinal cord become mature and functional after the first postnatal week. However, little is known about the serotonergic receptors involved in the modulation of interneurons mediating presynaptic inhibition and when developmentally their actions mature. Here, we used whole-cell patch clamp recordings in lumbar spinal slices from neonatal and juvenile mice to assess the intrinsic properties and serotonergic modulation of deep dorsal horn GABAergic ROR{beta} interneurons previously shown to mediate presynaptic inhibition of proprioceptive afferents. ROR{beta} interneurons from juvenile cords displayed more mature membrane properties. Further, serotonin increased the excitability of ROR{beta} interneurons via actions at 5-HT2A, 5-HT2B/2C, and 5-HT7 receptors in juvenile but not early neonatal spinal cords. Our findings indicate that deep dorsal horn ROR{beta} interneurons undergo postnatal maturation in both their intrinsic excitability and ability to respond to serotonin, concurrent with the maturation of serotonergic innervation of the dorsal horn. This information can prompt future targeted studies testing relationships between impairments of serotonergic development, proprioceptive processing disorders, and presynaptic inhibition mediated by ROR{beta} interneurons.

neuroscience↗

bioRxiv2024

Properties of rhythmogenic currents in spinal Shox2 interneurons across postnatal development

Locomotor behaviors are performed by organisms throughout life, despite developmental changes in cellular properties, neural connectivity, and biomechanics. The basic rhythmic activity in the central nervous system that underlies locomotion is thought to be generated via a complex balance between network and intrinsic cellular properties. Within mature mammalian spinal locomotor circuitry, we have yet to determine which properties of spinal interneurons (INs) are critical to rhythmogenesis and how they change during development. Here, we combined whole cell patch clamp recordings, immunohistochemistry, and RNAscope targeting lumbar Shox2 INs in mice, which are known to be involved in locomotor rhythm generation. We focused on the properties of putatively rhythmogenic ionic currents and the expression of corresponding ion channels across postnatal time points in mice. We show that subsets of Shox2 INs display voltage-sensitive conductances, in addition to respective ion channels, which may contribute to or shape rhythmic bursting. Persistent inward currents, M-type potassium currents, slow afterhyperpolarization, and T-type calcium currents are enhanced with age. In contrast, the hyperpolarization-activated and A-type potassium currents were either found with low prevalence in subsets of neonatal, juvenile, and adult Shox2 INs or did not developmentally change. We show that Shox2 INs become more electrophysiologically diverse by juvenile and adult ages, when locomotor behavior is weight-bearing. These results suggest a developmental shift in the magnitude of rhythmogenic ionic currents and the expression of corresponding ion channels that may be important for mature, weight-bearing locomotor behavior.

neuroscience↗

bioRxiv2024

A distinct down state assembly in retrosplenial cortex during slow-wave sleep

Understanding the intricate mechanisms underlying slow-wave sleep (SWS) is crucial for deciphering the brains role in memory consolidation and cognitive functions. It is well-established that cortical delta oscillations (0.5-4 Hz) coordinate communications among various cortical, hippocampal, and thalamic regions during SWS. These delta oscillations have periods of Up and Down states, with the latter previously thought to represent complete cortical silence; however, new evidence suggests that Down states serve important functions for information exchange during memory consolidation. The retrosplenial cortex (RSC) stands out for its pivotal role in memory consolidation due to its extensive connectivity with memory-associated regions, although it remains unclear how RSC neurons engage in delta-associated consolidation processes. Here, we employed multi-channel in vivo electrophysiology to study RSC neuronal activity in freely behaving mice during natural SWS. We discovered that the RSC contains a discrete assembly of putative excitatory neurons ([~]20%) that initiated firing at SWS Down states and reached maximal firing at the Down-to-Up transitions. Therefore, we termed these RSC neurons the Down state assembly (DSA), and the remaining RSC excitatory neurons as non-DSA. Compared to non-DSA, DSA neurons exhibit a higher firing rate, larger cell body size, and no connectivity with nearby RSC neurons. Subsequently, we investigated RSC neuronal activity during a contextual fear conditioning paradigm and found that both DSA and non-DSA neurons exhibited increased firing activity during post-training sleep compared to pre-training sleep, indicating their roles in memory consolidation. Lastly, optogenetics combined with electrophysiology revealed that memory-associated inputs differentially innervated RSC excitatory neurons. Collectively, these findings provide insight on distinct RSC neuronal subpopulation activity in sleep and memory consolidation.

neuroscience↗

bioRxiv2024

Covert actions of epidural stimulation on spinal locomotor circuits

Spinal circuitry produces the rhythm and patterning of locomotion. However, both descending and sensory inputs are required to initiate and adapt locomotion to the environment. Spinal cord injury (SCI) disrupts descending controls of the spinal cord, producing paralysis. Epidural stimulation (ES) is a promising clinical therapy for motor control recovery and is capable of reactivating the lumbar spinal locomotor networks, yet little is known about the effects of ES on locomotor neurons. Previously, we found that both sensory afferent pathways and serotonin exert mixed excitatory and inhibitory actions on lumbar interneurons involved in the generation of the locomotor rhythm, identified by the transcription factor Shox2. However, after chronic complete SCI, sensory afferent inputs to Shox2 interneurons become almost exclusively excitatory and Shox2 interneurons are supersensitive to serotonin. Here, we investigated the effects of ES on these SCI-induced changes. Inhibitory input from sensory pathways to Shox2 interneurons was maintained and serotonin supersensitivity was not observed in SCI mice that received daily sub-motor threshold ES. Interestingly, the effects of ES were maintained for at least three weeks after the ES was discontinued. In contrast, the effects of ES were not observed in Shox2 interneurons from mice that received ES after the establishment of the SCI-induced changes. Our results demonstrate mechanistic actions of ES at the level of identified spinal locomotor circuit neurons and the effectiveness of early treatment with ES on preservation of spinal locomotor circuitry after SCI, suggesting possible therapeutic benefits prior to the onset of motor rehabilitation.

neuroscience↗

bioRxiv2024

Activity of spinal RORβ neurons is related to functional improvements following combination treatment after complete SCI

Various strategies targeting spinal locomotor circuitry have been associated with functional improvements after spinal cord injury (SCI). However, the neuronal populations mediating beneficial effects remain largely unknown. In a mouse model of complete SCI, virally-delivered BDNF (AAV-BDNF) activates hindlimb stepping and causes hyperreflexia, whereas sub-motor threshold epidural stimulation (ES) reduced BDNF-induced hyperreflexia. Given their role in gating proprioceptive afferents and potential convergence point of BDNF and ES, we hypothesized that an enhanced excitability of inhibitory ROR{beta} neurons would be associated with locomotor improvements. Ex vivo spinal slice recordings revealed that the excitability of ROR{beta} neurons was decreased in mice with poor locomotor function after SCI, but was similar between the uninjured and best stepping SCI groups. Further, chemogenetic excitation of ROR{beta} neurons reduced BDNF-induced hyperreflexia and improved stepping, similar to ES. Our findings identify inhibitory ROR{beta} neurons as a target population to limit hyperreflexia and enhance locomotor function after SCI.

neuroscience↗

bioRxiv2021

The role of V3 neurons in speed-dependent interlimb coordination during locomotion in mice

Speed-dependent interlimb coordination allows animals to maintain stable locomotion under different circumstances. We have previously demonstrated that a subset of spinal V3 neurons contributes to stable locomotion by mediating mutual excitation between left and right lumbar rhythm generators (RGs). Here, we expanded our investigation to the V3 neurons involved in ascending long propriospinal interactions (aLPNs). Using retrograde tracing, we revealed a subpopulation of lumbar V3 aLPNs with contralateral cervical projections. V3OFF mice, in which all V3 neurons were silenced, had a significantly reduced maximal locomotor speed, were unable to move using stable trot, gallop, or bound, and predominantly used lateral-sequence walk. To understand the functional roles of V3 aLPNs, we adapted our previous model of spinal circuitry controlling quadrupedal locomotion (Danner et al., 2017), by incorporating diagonal V3 aLPNs mediating inputs from each lumbar RG to the contralateral cervical RG. The updated model reproduces our experimental results and suggests that locally projecting V3 neurons, mediating left-right interactions within lumbar and cervical cords, promote left-right synchronization necessary for gallop and bound, whereas the V3 aLPNs promote synchronization between diagonal fore and hind RGs necessary for trot. The model proposes the organization of spinal circuits available for future experimental testing.

neuroscience↗

bioRxiv2020

Neural interactions in developing rhythmogenic spinal networks: Insights from computational modeling

The mechanisms involved in generation of rhythmic locomotor activity in the mammalian spinal cord remain poorly understood. These mechanisms supposedly rely on both intrinsic properties of constituting neurons and interactions between them. A subset of Shox2 neurons was found to contribute to generation of spinal locomotor activity, but the possible cellular basis for rhythmic bursting in these neurons remains unknown. Ha and Dougherty (2018) recently revealed the presence of bidirectional electrical coupling between Shox2 neurons in neonatal spinal cords, which can be critically involved in neuronal synchronization and generation of populational bursting. Gap junctional connections found between functionally-related Shox2 interneurons decrease with age, possibly being replaced by increasing interactions through chemical synapses. Here, we developed a computational model of a heterogeneous population of neurons sparsely connected by electrical or/and chemical synapses and investigated the dependence of frequency of populational bursting on the type and strength of neuronal interconnections. The model proposes a mechanistic explanation for emergence of a synchronized rhythmic activity in the neuronal population and provides insights into the mechanisms of the locomotor rhythm generation.

bioinformatics↗

bioRxiv2020

PEDF-Rpsa-Itga6 signaling regulates cortical neuronal morphogenesis

Neuromorphological defects underlie neurodevelopmental disorders and functional defects. We identified a function for ribosomal protein SA (Rpsa) in regulating neuromorphogenesis using in utero electroporation to knockdown Rpsa, which results in apical dendrite misorientation, fewer/shorter extensions with decreased arborization, and decreased spine density with altered spine morphology. We investigated Rpsas ligand, pigment epithelium-derived factor (PEDF), and interacting partner on the plasma membrane, Integrin subunit 6 (Itga6). Rpsa, PEDF, and Itga6 knockdown cause similar phenotypes, with Rpsa and Itga6 overexpression rescuing morphological defects in PEDF deficient neurons in vivo. Additionally, Itga6 overexpression increases and stabilizes Rpsa expression on the plasma membrane by preventing ubiquitination of Rpsa. GCaMP6s was used to functionally analyze Rpsa knockdown via ex vivo calcium imaging. Rpsa deficient neurons showed less fluctuation in fluorescence intensity, suggesting defective sub-threshold calcium signaling. Our study identifies a role for PEDF-Rpsa-Itga6 signaling in neuromorphogenesis, thus implicating these molecules in the etiology of neurodevelopmental disorders and identifying them as potential therapeutic candidates.

neuroscience↗