Multi-electrode Array services at NDimension are currently based around three rigs: (i) 4 x MCS MEA1060-Up-BC, (ii) 2 x MCS MEA2100-2×60, and (iii) twin array MED64 systems, each with accompanying mini-bioincubators, heated perfusion systems and other peripherals (NB high-density CMOS-based and multi-well formats are also planned in the near future). This technology facilitates parallel multi-preparation recordings from brain or spinal cord slices (or other excitable tissues) or distributed neuronal networks and organoids. Thus, a set of experimental compounds can be rapidly evaluated, and/or studied over much longer timescales.

Changes in macroscopic spatiotemporal dynamics within native rodent- or hiPSC-derived ‘healthy’ and ‘patient-derived’ neuronal network cultures grown on our MEAs reveal useful ‘state’ data, such as the degree of network ‘maturity’, intrinsic excitability, its position on a ‘healthy’ to ‘diseased’ ‘signature’ spectrum, and the effects of challenge with experimental compounds. Metrics include array-wide spike detection rate (AWSDR), spiking synchrony/cooperativity, oscillatory activity, the occurrence of ‘network bursts’ and burst structure/shape statistics (burst envelope profiles).

The MEA recording of local field potentials (LFPs) in acute or long-term cultured brain and spinal cord slices (including ex-vivo human), aids the investigation of both baseline synaptic function and models of synaptic plasticity in regions or pathways relevant to particular disease models: i/o analysis, paired-pulse facilitation (PPF) and paired-pulse depression (PPD) of field EPSPs (fEPSPs), long-term potentiation (LTP) and long-term depression (LTD) elicited by specific electrical stimulation patterns or chemical induction.

Episodes of pathological hypersynchrony and hyperexcitability are features common to epilepsy and neuropathic pain and are elegantly modelled using MEA techniques. Spontaneous ‘population spikes’, ‘sharp-waves’, and disease-specific features, such as spike-and-wave discharges, inter-ictal spikes, pathological high-frequency oscillations (pHFOs) and ictal seizures can all be clearly defined and form major components of our relevant in vitro drug assays.

‘Region-specific’ effects can be clearly defined within tissue slices, for example, layer-specific activities can be resolved within stratified structures such as hippocampus, cortex, olfactory bulb, spinal cord or cerebellum using current sink/source density analysis (CSDA) (chronotopograms).

Other MEA-based models include sleep/wake cycles and other circadian activity, information processing, storage, and retrieval mechanisms and neural-glial interactions.

In order to study ion channel and receptor pharmacology in detail as part of the drug discovery process, whole-cell patch clamp recording techniques (current/voltage) may be used in the same brain regions and neuronal culture preparations (and other excitable cell types) as the MEA platforms.

Notably, DRG sensory neuron cultures are available as preclinical drug assays for pain, especially for compounds specifically developed to target neuropathic pain syndromes such as hyperalgesia and allodynia. Spiral ganglion neurons are also used in studies of sensorineural hearing loss, and of potential new drugs and technologies to mitigate this pathology.

Standard Patch Clamp Protocols include analysis of: (i) Membrane Properties: Resting membrane potential (RMP; Vm); input resistance (Rm); membrane capacitance (Cm); access resistance; voltage ‘sag’ (V_sag); (ii) Currents: Peak inward Na⁺ current; peak steady-state K⁺ current; Ca²⁺ and Cl^– channel physiology; hyperpolarization-activated cation current (Ih)/’pacemaker’ activity (V_sag-associated); (iii) Spontaneous Action Potential (AP) Discharge: Firing rates; firing patterns (inc. burst analysis); (iv) Electrically-evoked Single APs (membrane excitability): AP threshold (at Rheobase); AP amplitude; AP half-width (at Rheobase); AP risetime/decay time (at Rheobase); AP latency (at Rheobase); AP after hyperpolarizing potentials (sAHPs and fAHPs); (v) Repetitive Firing Properties: Firing rate; 1^st-2^nd interspike interval (ISI); maximum ISI; accomodation/adaptation; maximum # of spikes; burst analysis; (vi) Miniature Spontaneous Excitatory( mEPSC) and Inhibitory (mIPSC) Post-synaptic Currents: Amplitude (quantal size); area-under-the-curve (charge transfer); rise time (kinetics of channel activation); decay time (kinetics of channel inactivation); frequency (presynaptic release characteristics); (vii) Synaptic transmission/synaptic plasticity: Evoked excitatory (evEPSC) and inhibitory (evIPSC) postsynaptic currents: Amplitude (synaptic strength); area-under-the-curve (charge transfer pA.ms); rise time (kinetics of channel activation); decay time (kinetics of channel inactivation); paired-pulse ratio of evEPSCs.

Target Categories: These assays are designed to examine the effects of test molecules on a wide range of targets, including voltage-gated ion channels (e.g., NaV and CaV families); ligand-gated ion channels (e.g., AMPA, NMDA, GABA_A, nAChRs, P2x receptors), G protein-coupled receptors (GPCRs) (e.g. muscarinic mAChRs, 5-HT receptors, mGluRs, GABA_B receptors, adrenoceptors, dopamine receptors), and electrogenic transporters (e.g., sodium- and chloride-dependent glycine transporter1 – GlyT1). Electrotonic (gap junction) function and ephaptic effects (in conjunction with MEA) can also be studied.

NDimension offers an expanding service in retinal electrophysiology, using rodent and donated human retinal explants and hiPSC-derived retinal organoids for pharmacological- and regenerative medicine-based pre-clinical studies aimed at combating retinal degenerative disorders such as macular degeneration and retinitis pigmentosa, retinal pigment epithelium (RPE) dysfunction and retinal synaptic abnormalities.

Using special versions of our mini-bioincubators, MEAs and photic stimulators, we have developed capabilities in long-term cultured retinal assays. These arrangements allow the recording of in vitro, light-stimulated slow wave mini-electroretinogram (mERG) signals. The initial -ve -going response (not always clearly visible) is called the ‘a-wave’, which is generated by the closure of rod or cone light-gated channels, leading to hyperpolarization of the photoreceptor. The +ve- going ‘b-wave’ trace that follows the ‘a-wave’ is produced by the depolarization of bipolar cells, which are postsynaptic to the photoreceptors. Other signals specific to the RPE and to other retinal cell types can also be observed and assayed. In addition, action potentials generated by different classes of retinal ganglion cells (RGCs) are routinely recorded concurrently with the mERGs, either driven by photoreceptor activation, or expressed by melanopsin-containing, intrinsically photosensitive RGCs.

These electrophysiological recordings can be conducted for protracted periods under either light- or dark-adapted conditions while maintaining sterility. The responses to light pulses of different colour (red, green, blue, cyan and two different white ‘colour temperatures’), intensity, duration or temporal patterning are usually run in two separate preparations in parallel, for instance, ‘control’ versus compound or other ‘treatment’ conditions. More advanced forms of photic stimulation are also currently under development.