Dr. hab. Anna Błasiak, Professor at the Jagiellonian University, and Dr. Aleksandra Trenk utilize Multi-Electrode Array (MEA) recordings—a powerful technique for studying neuronal activity and the effects of neuroactive substances in brain slices. This method enables simultaneous monitoring of signals from multiple neurons, offering valuable insights into neural network function, synaptic transmission, and the mechanisms underlying neurological disorders.

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1.   Why use this method?

Multi-Electrode Array (MEA) recordings are a powerful non-invasive electrophysiological technique that enable the real-time recording of neuronal activity from multiple sites simultaneously. MEAs are suitable for recording both single-cell action potentials and network-level field potentials with high temporal resolution. Moreover, MEAs are perfectly suitable for studying the modulatory potential of neuropeptides like oxytocin or relaxin-3 on neuronal circuits. Its ability to maintain viable tissue ex vivo, combined with stimulation capabilities and compatibility with pharmacological interventions, makes it ideal for studying brain slice physiology, receptor pharmacology, and intracellular signaling pathways.

2.  What you’ll need

Tissue & Reagents:

• Acute brain slices (example: rat ventral hippocampus)
• Artificial cerebrospinal fluid (ACSF)
• Neuroactive compounds (example: oxytocin, relaxin-3, RXFP3 agonist – A2)
• Synaptic blockers (example: CNQX, DL-AP5, Gabazine)

MEA System & Accessories:

• Perforated MEA chips (for improved tissue perfusion and viability)
• MEA headstage and interface board
• Computer with acquisition and analysis software
• Drug application system with perfusion and syringe control

Equipment:

• Vibratome (for slicing brain tissue)
• Incubation chamber (for slice recovery at 32–35°C)
• Temperature controller and oxygenation systems
• Pipettes, tubing, and sterile tools

Software:

• Real-time acquisition software (for spike and field potential detection)
• KiloSort or other spike sorting tools
• Data analysis and data visualization tools (example: MatLab, Python)

3. Step-by-step instructions

A. Slice Preparation

1. Dissect brain quickly and immerse in ice-cold, oxygenated ACSF
2. Slice 200 to 400 μm thick sections using a vibratome
3. Recover slices in warm ACSF for at least 30 minutes before use

B. MEA Recording Setup

1. Place slice onto the MEA chip and secure using suction and perfusion
2. Maintain temperature and oxygenation during the experiment
3. Record baseline neuronal activity

C. Pharmacological Protocol

1. Apply neuroactive compounds (example of oxytocin alone, or with relaxin-3)
2. Record multi-unit activity and single-unit responses
3. Use synaptic blockers to distinguish direct vs. indirect drug effects
4. Apply channel blockers (example of XE-991 for KCNQ) to investigate ionic mechanisms

D. Spike Detection & Sorting

1. Filter signals to isolate action potentials or field potentials
2. Perform spike sorting using automated tools like KiloSort
3. Refine spike data manually (PCA, waveform, and autocorrelogram analysis)

4. Practical tips

• Use perforated MEAs for optimal tissue contact and long recordings
• Normalize electrode coverage and spacing depending on target region
• Include control conditions (ACSF only, drug alone, drug + blocker)
• Use real-time visualization to assess quality of signal and response dynamics
• Validate drug specificity with known agonists/antagonists

5.  Critical appraisal & implications for future research

MEA technology offers an unparalleled combination of spatial and temporal resolution to study dynamic brain activity under pharmacological manipulation. It has confirmed the ventral hippocampus as a functional hub integrating oxytocin-mediated social signaling and stress-related signals via relaxin-3. The integration appears to be modulated by shared intracellular pathways involving KCNQ channels.

Although slice-based MEA studies lack full in vivo connectivity, they provide highly reproducible, region-specific insights into neuronal responses. Future directions should include integrating MEA with optogenetics, expanding high-density electrode arrays, and applying this technology to organoids and human tissue slices. Combining MEA with advanced biosensors and genetically defined cell types will further deepen our understanding of circuit-level neuropharmacology.

This protocol is licensed under a Creative Commons Attribution-NonCommercial (CC BY-NC) license, allowing sharing and adaptation for non-commercial purposes with proper attribution.