Biology subjects

Wildner, H.

Publications and source records attributed to Wildner, H..

6 recordsLinked to original sources

bioRxiv2026

Peripheral nerve injury reallocates primary afferent input through spinal parvalbumin microcircuits

Complex neural functions rely on finely tuned circuits in which the recruitment of local interneurons gates the flow of information, determining whether an input is relayed, amplified, or suppressed. Somatosensory information, such as touch or pain, is processed through such complex circuits in the dorsal horn of the spinal cord. There, local inhibitory interneurons play a key role in the proper segregation of touch and pain inputs. After nerve injury-evoked neuropathic pain, loss of inhibition impairs the function of these circuits, resulting in mechanical allodynia, where innocuous touch is perceived as painful. Disinhibition can be attributed to pruning of inhibitory synapses, reduced intrinsic excitability of inhibitory neurons, or weakened excitatory drive from primary afferents. Yet the complexity of the excitatory drive onto inhibitory neurons, and its potential modification after nerve injury, remains largely unexplored. Here we examined the nature of the synaptic drive from low-threshold A{beta} mechanoreceptors (A{beta}-LTMRs) onto parvalbumin-expressing interneurons (PVNs), and how this recruitment is affected by nerve injury. A{beta}-LTMR stimulation evoked excitatory responses in a subset of PVNs, which is expected given the exclusively excitatory nature of primary afferent inputs. However, an unexpected subset of PVNs displayed inhibitory responses, suggesting the recruitment of a feedforward inhibitory circuit. We reconciled these observations by showing that A{beta}-LTMRs engaged PVNs through both direct excitation and feedforward inhibition, which are differentially distributed between the inhibitory (iPVN) and excitatory (ePVN) subpopulation. Indeed, our results show that under naive conditions, A{beta} input preferentially recruited iPVNs, while ePVNs were predominantly suppressed by A{beta}-driven feedforward inhibition mediated by a previously unrecognized Complexin-1 (Cplx1)-expressing inhibitory interneuron. After peripheral nerve injury, this balance becomes functionally redistributed. A{beta}-to-iPVN transmission showed increased failure rates and impaired temporal precision, whereas A{beta} drive onto ePVNs shifted from inhibition toward excitation. Notably, these functional changes occurred despite preserved afferent connectivity, synapse density, and spontaneous synaptic events, indicating that the dynamic reallocation of circuit recruitment occurs in the absence of structural changes. To test the behavioral consequences of these two populations, we used chemogenetic approaches and found that iPVNs suppress, whereas ePVNs promote, mechanical hypersensitivity. Together, these findings show that nerve injury functionally reallocates primary afferent drive away from inhibitory and toward excitatory spinal PVNs, establishing functional reallocation of afferent input as a mechanism of spinal disinhibition and a key determinant of mechanical allodynia.

neuroscience↗

bioRxiv2023

Calretinin-expressing islet cells: a source of pre- and post-synaptic inhibition of non-peptidergic nociceptor input to the mouse spinal cord

Unmyelinated non-peptidergic nociceptors (NP afferents) arborise in lamina II of the spinal cord and receive GABAergic axoaxonic synapses, which mediate presynaptic inhibition. However, until now the source of this axoaxonic synaptic input was not known. Here we provide evidence that it originates from a population of inhibitory calretinin-expressing interneurons (iCRs), which correspond to lamina II islet cells. The NP afferents can be assigned to 3 functionally distinct classes (NP1-3). NP1 afferents have been implicated in pathological pain states, while NP2 and NP3 afferents also function as pruritoceptors. Our findings suggest that all 3 of these afferent types innervate iCRs and receive axoaxonic synapses from them, providing feedback inhibition of NP input. The iCRs also form axodendritic synapses, and their targets include cells that are themselves innervated by the NP afferents, thus allowing for feedforward inhibition. The iCRs are therefore ideally placed to control the input from non-peptidergic nociceptors and pruritoceptors to other dorsal horn neurons, and thus represent a potential therapeutic target for the treatment of chronic pain and itch.

neuroscience↗

bioRxiv2023

Descending GABAergic Neurons of the RVM That Mediate Widespread Bilateral Antinociception

SummaryNeurons projecting from the rostral ventromedial medulla (RVM) to the spinal dorsal horn are critical elements of endogenous pain control systems. Here, we describe a GABA/glycinergic pathway that predominantly innervates the superficial dorsal horn. Anatomical and optogenetic tracing of these neurons from a single unilateral site of the lumbar spinal cord indicated that these neurons give rise to a dense bilateral innervation of the spinal cord along its entire rostrocaudal axis. Chemogenetic activation of these neurons caused a bilateral and widespread reduction in heat, cold, and mechanical sensitivity, while their silencing with tetanus toxin induced allodynia and spontaneous pain-like aversive behaviors. Consistent with a continuous role in the prevention of spontaneous pain, many descending RVM GABAergic neurons were found to be tonically active. This pathway may therefore be relevant for widespread conditioned analgesia, while its dysfunction may underlie chronic widespread pain syndromes.

neuroscience↗

bioRxiv2022

Targeted Anatomical and Functional Identification of Antinociceptive and Pronociceptive Serotonergic Neurons that project to the Superficial Dorsal Horn

Spinally-projecting serotonergic neurons play a key role in controlling pain sensitivity and can either increase or decrease nociception depending on physiological context. It is currently unknown how serotonergic neurons mediate these opposing effects. Utilizing virus-based strategies, we identified two anatomically separated populations of serotonergic hindbrain neurons located in the lateral paragigantocellularis (LPGi) and the medial hindbrain, which respectively innervate the superficial and deep spinal dorsal horn and have contrasting effects on sensory perception. Our tracing experiments revealed that serotonergic neurons of the LPGi were much more susceptible to transduction with spinally injected AAV2retro vectors than medial hindbrain serotonergic neurons. Taking advantage of this difference, we employed intersectional chemogenetic approaches to demonstrate that activation of the LPGi serotonergic projections decreases thermal sensitivity, whereas activation of medial serotonergic neurons increases sensitivity to mechanical von Frey stimulation. Together these results suggest that there are functionally distinct classes of serotonergic hindbrain neurons that differ in their anatomical location in the hindbrain, their postsynaptic targets in the spinal cord, and their impact on nociceptive sensitivity. The LPGi neurons that give rise to rather global and bilateral projections throughout the rostrocaudal extent of the spinal cord appear to be ideally posed to contribute to widespread systemic pain control.

neuroscience↗

bioRxiv2020

In-depth characterization of layer 5 output neurons of the primary somatosensory cortex innervating the mouse dorsal spinal cord

Neuronal circuits of the spinal dorsal horn integrate sensory information from the periphery with inhibitory and facilitating input from higher CNS areas. Most previous work focused on projections descending from the hindbrain. Less is known about inputs descending from the cerebral cortex. Here, we identified cholecystokinin (CCK) positive layer 5 pyramidal neurons of the primary somatosensory cortex (CCK+ S1-CST neurons) as a major source of input to the spinal dorsal horn. We combined intersectional genetics and virus-mediated gene transfer to characterize CCK+ S1-CST neurons and to define their presynaptic input and postsynaptic target neurons. We found that S1-CST neurons constitute a heterogeneous population that can be subdivided into distinct molecular subgroups. Rabies-based retrograde tracing revealed monosynaptic input from layer 2/3 pyramidal neurons, from parvalbumin (PV) positive cortical interneurons, and from thalamic relay neurons in the ventral posterolateral nucleus. WGA-based anterograde tracing identified postsynaptic target neurons in dorsal horn laminae III and IV. About 60% of these neurons were inhibitory and about 60% of all spinal target neurons expressed the transcription factor c-Maf. The heterogeneous nature of both S1-CST neurons and their spinal targets suggest complex roles in the fine-tuning of sensory processing.

neuroscience↗

bioRxiv2020

Neuron Type-Specific Translatomes in Spinal Cords of Naive and Neuropathic Mice

The spinal dorsal horn harbors a sophisticated and heterogeneous network of excitatory and inhibitory neurons that process peripheral signals encoding different sensory modalities. Although it has long been recognized that this network is crucial both for the separation and the integration of sensory signals of different modalities, the molecular identity of the underlying neurons and signaling mechanisms are still only partially understood. Here, we have used the translating ribosome affinity purification (TRAP) technique to map the translatomes of excitatory glutamatergic (VGLUT2+) and inhibitory GABA and/or glycinergic (VGAT+ or Gad67+) neurons of the mouse spinal cord. Our analyses demonstrate that inhibitory and excitatory neurons are primarily set apart by the expression of genes encoding transcription factors or genes related to the production, release or re-uptake of their principal neurotransmitters (glutamate, GABA or glycine). Subsequent gene ontology (GO) term analyses revealed that neuropeptide signaling-related GO terms were highly enriched in the excitatory population. Eleven neuropeptide genes displayed largely non-overlapping expression patterns closely adhering to the laminar and hence also functional organization of the spinal cord grey matter, suggesting that they may serve as major determinants of modality-specific processing. Since this modality-specific processing of sensory input is severely compromised in chronic, especially neuropathic, pain, we also investigated whether peripheral nerve damage changes the neuron typespecific translatome. In summary, our results suggest that neuropeptides contribute to modalityspecific sensory processing in the spinal cord but also indicate that altered sensory encoding in neuropathic pain states occurs independent of major translatome changes in the spinal neurons.

neuroscience↗