Biology subjects

Hughes, D. I.

Publications and source records attributed to Hughes, D. I..

6 recordsLinked to original sources

bioRxiv2026

Discovery of the Honeycomb Synapse in Spinal Motor Circuits

The structural and molecular diversity of synapses in the nervous system contributes to the specialisation of neural circuits underlying diverse behaviours. We have discovered a morphologically distinct postsynaptic specialisation in the mammalian spinal cord. We have named this the Honeycomb Synapse based on its elaborate postsynaptic nanostructure, comprising rings formed of ~6 scaffolding protein domains that create multiple perforations throughout the large postsynaptic domain. Analysis of the organisation of other synaptic proteins reveals that Honeycomb Synapses harbour mixed signalling properties structurally facilitated by a postsynaptic scaffold matrix supporting chemical transmission, with gap junction proteins occupying some of the perforations. We reveal anatomical diversity in the presence of Honeycomb Synapses on populations of -motoneurons across the lumbar spinal cord in mice from approximately 2 weeks of age through to adulthood. The Honeycomb Synapse was found to be a subtype of synapse within the Ia afferent monosynaptic stretch reflex circuit. Finally, we have identified that Honeycomb Synapses are highly vulnerable to degeneration in two different genetically engineered mouse models of Amyotrophic Lateral Sclerosis (ALS), contributing to monosynaptic stretch reflex circuit dysfunction. These findings suggest that synaptic diversity within circuits may confer selective vulnerability to distinct synaptic subclasses.

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

Neuropeptide Y-expressing dorsal horn inhibitory interneurons gate spinal pain and itch signalling

Somatosensory information is processed by a complex network of interneurons in the spinal dorsal horn. It has been reported that inhibitory interneurons that express neuropeptide Y (NPY), either permanently or during development, suppress mechanical itch, with no effect on pain. Here we investigate the role of interneurons that continue to express NPY (NPY-INs) in adulthood. We find that chemogenetic activation of NPY-INs reduces behaviours associated with acute pain and pruritogen-evoked itch, whereas silencing them causes exaggerated itch responses that depend on cells expressing the gastrin-releasing peptide receptor. As predicted by our previous studies, silencing of another population of inhibitory interneurons (those expressing dynorphin) also increases itch, but to a lesser extent. Importantly, NPY- IN activation also reduces behavioural signs of inflammatory and neuropathic pain. These results demonstrate that NPY-INs gate pain and itch transmission at the spinal level, and therefore represent a potential treatment target for pathological pain and itch.

neuroscience↗

bioRxiv2020

Three neurotransmitters regulate diverse inhibitory and excitatory Parvalbumin interneuron circuits in the dorsal horn

Parvalbumin-expressing interneurons (PVINs) in the spinal dorsal horn are found primarily in laminae II inner and III. Inhibitory PVINs (iPVINs) play an important in segregating innocuous tactile input from pain-processing circuits, achieved through presynaptic inhibition of myelinated low-threshold mechanoreceptors and postsynaptic inhibition of distinct spinal circuits. By comparison, relatively little is known of the role of excitatory PVINs (ePVINs) in sensory processing. Here we use neuroanatomical and optogenetic approaches to show that ePVINs comprise a larger proportion of the PVIN population than previously reported, and that both ePVIN and iPVIN populations form synaptic connections amongst (and between) themselves. We find that these cells contribute to neuronal networks that influence activity within several functionally distinct circuits, and that aberrant activity of ePVINs under pathological conditions contributes to the development of mechanical hypersensitivity.

neuroscience↗

bioRxiv2020

Chemogenetic analysis of how receptors for short chain fatty acids regulate the gut-brain axis

The gut-brain axis allows bi-directional communication between the enteric and central nervous systems. Short chain fatty acids (SCFAs) generated by the gut microbiota are important regulators of this interface. However, defining mechanisms by which SCFAs do so has been challenging because, amongst various roles, they co-activate both of a pair of closely related and poorly characterized G protein-coupled receptors, FFA2 and FFA3. Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) can provide an important approach in defining receptor-specific functions. By screening a library of carboxylate-containing small molecules we identified 4-methoxy-3-methyl-benzoic acid (MOMBA) as a specific agonist of a DREADD variant of FFA2 which is not activated by SCFAs. Using mice engineered to replace FFA2 with this FFA2-DREADD, whilst retaining FFA3 expression, combinations of MOMBA and the now FFA3 receptor selective SCFAs defined key, but distinct, roles of FFA2 and FFA3 in each of gut transit time, secretion of entero-endocrine hormones, and communication from the gut to each of autonomic and somatic sensory ganglion cells and the spinal cord. These studies map mechanisms and signalling pathways by which each of FFA2 and FFA3 act to link the gut and the brain and provide both animal models and novel tool compounds to further explore this interface.

pharmacology and toxicology↗

bioRxiv2019

Calretinin positive neurons form an excitatory amplifier network in the spinal cord dorsal horn

The passage of nociceptive information is relayed through the spinal cord dorsal horn, a critical area in sensory processing. The neuronal circuits in this region that underpin sensory perception must be clarified to better understand how dysfunction can lead to pathological pain. This study used an optogenetic approach to selectively activate neurons that contain the calcium-binding protein calretinin (CR). We show that CR+ interneurons form an interconnected network that can initiate and sustain enhanced excitatory signaling, and directly relays signals to lamina I projection neurons. In vivo photoactivation of CR+ interneurons resulted in a significant nocifensive behavior that was morphine sensitive and cause a conditioned place aversion. Furthermore, halorhodopsin-mediated inhibition of CR+ interneurons elevated sensory thresholds. These results suggest that neuronal circuits in the superficial dorsal horn that involve excitatory CR+ neurons are important for the generation and amplification of pain, and identify these interneurons as a future analgesic target.

neuroscience↗