Biology subjects

Hachisuka, J.

Publications and source records attributed to Hachisuka, J..

7 recordsLinked to original sources

bioRxiv2026

A neuronal pathway for the supraspinal relay of warm and cool sensation

Cutaneous thermosensation is a fundamental sense allowing discrimination of external temperature changes and driving adaptive responses essential for survival and well-being. This sensory process begins with the activation of peripheral thermoreceptors, which encode the quality and intensity of thermal stimuli into neuronal activity that is further integrated by spinal cord circuits and relayed to supraspinal centres through the anterolateral tract (ALT). While classical experiments identified thermal responsive ALT neurons in the superficial spinal dorsal horn, the functional logic of innocuous temperature relay remains poorly understood. We show that, in mice, the majority of Phox2a-lineage lamina I ALT are selectively tuned to innocuous warming or cooling, and receive direct inputs from peripheral thermoreceptors. Their genetic ablation, chemogenetic or optogenetic manipulation impaired temperature discrimination. Our findings contrast with the previous finding that the majority of ALT neurons being mechano- and thermo-nociceptive and provide novel evidence for the existence of a large ensemble of genetically defined warming- and cooling- responsive ALT neurons. The large representation of innocuous temperature in supraspinal-relaying ALT neurons indicates substantial spinal amplification of thermal information and underscores the importance of innocuous thermosensation in the ascending sensory pathway.

neuroscience↗

bioRxiv2025

Characterisation of cold-selective lamina I spinal projection neurons

Skin cooling is detected by primary afferents that express the Trpm8 channel, but how this information is conveyed to the brain remains poorly understood. We have previously identified a population of lamina I projection neurons belonging to the anterolateral system (ALS) that receive numerous contacts from Trpm8-expressing primary afferents. Here, using a semi-intact somatosensory preparation, we provide evidence that these cells correspond to the cold-selective ALS neurons identified in previous physiological studies. We also confirm the presence of synapses from Trpm8 afferents onto these cells at the ultrastructural level and with optogenetics. Based on our previous transcriptomic findings, we identify calbindin as a molecular marker, and show that this can be used to target the cold-selective ALS neurons for anterograde tracing studies. We provide evidence that they project to brain regions that have been implicated in thermosensation: the rostralmost part of the lateral parabrachial area, the caudal part of the periaqueductal grey matter, and the posterior triangular and ventral posterolateral nuclei of the thalamus. Our findings provide important insights into the organisation of neuronal circuits that underlie thermoregulation and the perception of cold stimuli applied to the skin.

neuroscience↗

bioRxiv2024

Anatomical characterisation of somatostatin-expressing neurons belonging to the anterolateral system

Anterolateral system (ALS) spinal projection neurons are essential for pain perception. However, these cells are heterogeneous, and there has been extensive debate about the roles of ALS populations in the different pain dimensions. We recently performed single-nucleus RNA sequencing on a developmentally-defined subset of ALS neurons, and identified 5 transcriptomic populations. One of these, ALS4, consists of cells that express Sst, the gene coding for somatostatin, and we reported that these were located in the lateral part of lamina V. Here we use a SstCre mouse line to characterise these cells and define their axonal projections. We find that their axons ascend mainly on the ipsilateral side, giving off collaterals throughout their course in the spinal cord. They target various brainstem nuclei, including the parabrachial internal lateral nucleus, and the posterior triangular and medial dorsal thalamic nuclei. We also show that in the L4 segment Sst is expressed by [~]75% of ALS neurons in lateral lamina V and that there are around 120 Sst-positive lateral lamina V cells on each side. Our findings indicate that this is a relatively large population, and based on projection targets we conclude that they are likely to contribute to the affective-motivational dimension of pain.

neuroscience↗

bioRxiv2023

Deep sequencing of Phox2a nuclei reveals five classes of anterolateral system neurons

The anterolateral system (ALS) is a major ascending pathway from the spinal cord that projects to multiple brain areas and underlies the perception of pain, itch and skin temperature. Despite its importance, our understanding of this system has been hampered by the considerable functional and molecular diversity of its constituent cells. Here we use fluorescence-activated cell sorting to isolate ALS neurons belonging to the Phox2a-lineage for single-nucleus RNA sequencing. We reveal five distinct clusters of ALS neurons (ALS1-5) and document their laminar distribution in the spinal cord using in situ hybridization. We identify 3 clusters of neurons located predominantly in laminae I-III of the dorsal horn (ALS1-3) and two clusters with cell bodies located in deeper laminae (ALS4 & ALS5). Our findings reveal the transcriptional logic that underlies ALS neuronal diversity in the adult mouse and uncover the molecular identity of two previously identified classes of projection neurons. We also show that these molecular signatures can be used to target groups of ALS neurons using retrograde viral tracing. Overall, our findings provide a valuable resource for studying somatosensory biology and targeting subclasses of ALS neurons. Significance StatementThe anterolateral system (ALS) is a major ascending pathway from the spinal cord that underlies perception of pain, itch and skin temperature. It is therefore an important target for the development of new treatments for chronic pain. Our understanding of this system has been hampered by the considerable diversity of its constituent cells. Here we dissect the complex heterogeneity of these cells by using high-resolution RNA sequencing. We reveal five distinct types of ALS neurons, which are differentially distributed within the spinal cord, and probably represent functional populations. Our data provide novel insights into the molecular architecture of the ALS, and will be important for future studies to define the roles of different ALS cell types in sensory processing.

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bioRxiv2021

Population Imaging of Central Sensitization

Capsaicin applied locally to the skin causes central sensitization that results in allodynia, a state in which pain is elicited by innocuous stimuli. Here, we used two-photon calcium imaging of neurons in the dorsal spinal cord to visualize central sensitization across excitatory interneurons and spinal projection neurons. To distinguish among excitatory neuron subtypes, we developed CICADA, a cell profiling approach that leverages the expression of distinct Gq-coupled receptors. We then identified capsaicin-responsive and capsaicin-sensitized neuronal populations. Capsaicin-sensitized neurons showed emergent responses to low threshold input and increased receptive field sizes consistent with the psychophysical phenomenon that allodynia is observed across an extended secondary zone. Finally, we identified spinal projection neurons that showed a shift in tuning toward low threshold input. These experiments provide a population-level view of central sensitization and a framework with which to model somatosensory integration in the dorsal horn. HighlightWarwick et al. use two-photon calcium imaging coupled with pharmacological profiling to identify neuronal populations in the spinal dorsal horn that mediate capsaicin-induced central sensitization.

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bioRxiv2020

Optogenetic evaluation of the ability of different cutaneous C-fiber afferents to evoke aversive behaviors

Most cutaneous C-fibers, including both peptidergic and non-peptidergic subtypes are presumed to be nociceptors and respond to noxious input in a graded manner. However, mechanically sensitive, non-peptidergic C-fibers also respond to mechanical input in the innocuous range, and so the degree to which they contribute to nociception remains unclear. To address this gap, we investigated the function of non-peptidergic afferents using the MrgprdCre allele. In real time place aversion studies, we found that low frequency optogenetic activation of MrgrpdCre lineage neurons was not aversive in naive mice, but became aversive after spared nerve injury (SNI). To address the underlying mechanisms of this allodynia, we recorded from lamina I spinoparabrachial (SPB) neurons using the semi-intact ex vivo preparation. Following SNI, innocuous brushing of the skin gave rise to abnormal activity in lamina I SPB neurons, consisting of an increase in the proportion of recorded neurons that responded with excitatory post synaptic potentials or action potentials. This increase was likely due, at least in part, to an increase in the proportion of lamina I (LI) SPB neurons that received input upon optogenetic activation of MrgprdCre lineage neurons. Intriguingly, in SPB neurons there was a significant increase in the EPSC latency from MrgprdCre lineage input following SNI, consistent with the possibility that the greater activation post SNI could be due to the recruitment of a new polysynaptic circuit. Together, our findings suggest MrgprdCre lineage neurons can provide mechanical input to the dorsal horn that is non-noxious before injury but becomes noxious afterwards due the engagement of a previously silent polysynaptic circuit in the dorsal horn.

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bioRxiv2019

A labeled-line for cold from the periphery to the parabrachial nucleus

Spinal projection neurons are a major pathway through which somatic stimuli are conveyed to the brain. However, the manner in which this information is coded is poorly understood. Here, we report the identification of a modality-selective spinoparabrachial (SPB) neuron subtype with unique properties. Specifically, we find that cold-selective SPB neurons are differentiated by selective afferent input, reduced neuropeptide sensitivity, distinct physiological properties, small soma size, and low basal drive. In addition, optogenetic experiments reveal that cold-selective SPB neurons are distinctive with respect to their connectivity, with little to no input from either Pdyn or Nos1 inhibitory interneurons. Together, these data define a neural substrate supporting a labeled-line for cold from the periphery to the brain.

neuroscience↗