Biology subjects

Greenhill, S. D.

Publications and source records attributed to Greenhill, S. D..

4 recordsLinked to original sources

bioRxiv2025

Nanoporous Microelectrodes for Neural Electrophysiology Recordings in Organotypic Culture

Organotypic cultures, specifically brain slices, have been used in neuroscience studies for many years to prolong the lifetime of the biological tissue outside of the host organism. However, the cultures must be kept in a sterile environment, maintaining supply of gas/nutrients for tissue survival and physiological relevance. Electrophysiological recordings from cultured tissue are challenging as the conventional approaches implicate a compromise on biological stability or environmental integrity. In this article, a novel approach has been used to design and print nanoporous microelectrodes on culture wells enabling in situ recording of electrophysiological neural activities. Optimized ink formulations are developed for conductive nanocarbon microelectrodes, and furthermore, fluoropolymer (polytetrafluoroethylene-based AF2400) ink has been inkjet printed for the first time acting as an insulator layer for microelectrodes. To keep the biocompatible nanoporous structure of culture wells, the microelectrodes have been printed on the bottom of the culture cells and only small connector pads have been produced on top of the culture membrane. Neural activity has been recorded by such a microelectrode structure for rodent brain slices cultured for three weeks. Furthermore, aerosol jet printing has been used for printing of nanocarbon microelectrodes allowing to produce much smaller size features compared to the inkjet printing.

neuroscience↗

bioRxiv2024

A GABA-A receptor response to CBD following status epilepticus in the medial entorhinal cortex of the rat

Cannabidiol is a non-psychoactive phytocannabinoid that has been implicated as a potential therapeutic in numerous neurological diseases. Perhaps the most widespread therapeutic use of CBD has been in the form of Epidiolex, which is used to treat seizures associated with Lennox-Gastaut syndrome, Dravet syndrome and tuberous sclerosis. Whilst the effectiveness of CBD in seizure reduction is clear, its mechanism of action is complex, and reflects the wide range of pharmacodynamic targets that includes receptors, ion channels and enzymes. This study investigated the effects of action of cannabidiol (CBD) on GABAergic transmission in layer II of the medial entorhinal cortex in animals that had previously undergone a period of status epilepticus (SE). Spontaneous post-synaptic currents were recorded from medial entorhinal cortex layer II pyramidal cells in animals 1-7 after SE and in age matched controls as well as in tissue resected from children with temporal lobe epilepsy (TLE). CBD enhanced GABAAR-mediated inhibition by increasing decay times and inhibitory charge transfer across the postsynaptic membrane in status epilepticus (SE) but did not alter GABAergic transmission in age-matched control rats. The SE-induced effects of CBD were blocked by ligands acting as inverse agonists at the benzodiazepine site of the GABAAR receptor and the effects of CBD were additive to low-doses of benzodiazepine and barbiturate agonists, consistent with allosteric actions on the GABAAR. Similar effects were observed in both SE rat and human layer II neurons. Overall, these data suggest CBD may act as a positive allosteric modulator (PAM) at postsynaptic GABAARs and this action appears to develop following SE. Key pointsO_LICBD increases inhibition only post status epilepticus. C_LIO_LIThis effect is blocked by benzodiazepine site inverse agonists C_LIO_LICBD is additive to low-dose zolpidem, suggesting an allosteric effect on the GABAAR C_LIO_LICBD was similarly effective in ex vivo human epileptic tissue C_LIO_LIThese results suggest CBD is a positive allosteric modulator at the GABAAR C_LI

neuroscience↗

bioRxiv2024

High-bandwidth, low-profile, long-term wireless EEG telemetry allows for optogenetic entrainment of natural cortical oscillations in freely-moving rats

Recording of whole-brain or multi-unit neuronal activity in the rodent brain is a powerful and widely used technique in neuroscience research. However, the acquisition of data from freely-moving animals is subject to a range of compromises. If a high bandwidth of data digitisation is needed, animals will either need to be tethered to the acquisition system or any telemetry used will have a short working battery life. For freely-moving experiments, especially those requiring careful behavioural measurements, such tethers and/or headstages incorporating e.g. optogenetic stimulation systems may prove to be confounding or limiting in the experiments which may be performed. Here we present the re[fi]nement and deployment of a wirelessly-charged, self-contained EEG telemeter at high data bandwidths (2kHz) with integrated optogenetic stimulator (473nm) and fully subcutaneous [fi]bre routing and implantation. This approach has allowed for rats to be recorded long-term (6 months) without requiring device explants, charging or maintenance, with an outward appearance identical to an unimplanted rodent. We have demonstrated the use of this system to stimulate cortical networks at a range of frequencies in freely-moving and acutely-anaesthetised rats allowing for the boosting or entrainment of physiological oscillations at will.

neuroscience↗

bioRxiv2020

In vitro characterisation and neurosteroid treatment of an N-Methyl-D-Aspartate receptor antibody-mediated seizure model

Seizures are a prominent feature in N-Methyl-D-Aspartate receptor antibody (NMDAR-Ab) encephalitis, a distinct neuro-immunological disorder in which specific human autoantibodies bind and crosslink the surface of NMDAR proteins thereby causing internalization and a state of NMDAR hypofunction. To further understand ictogenesis in this disorder, and to test a novel treatment compound, we developed an NMDAR-Ab mediated rat seizure model that displays spontaneous epileptiform activity in vivo and in vitro. Using a combination of electrophysiological and dynamic causal modelling techniques we show that, contrary to expectation, reduction of synaptic excitatory, but not inhibitory, neurotransmission underlies the ictal events through alterations in the dynamical behaviour of microcircuits in brain tissue. Moreover, in vitro application of an NMDAR-specific neurosteroid, pregnenolone sulfate, that upregulates NMDARs, reduced established ictal activity. This proof-of-concept study highlights the complexity of circuit disturbances that may lead to seizures and the potential use of receptor-specific treatments in antibody-mediated seizures and epilepsy.

neuroscience↗