The importance of electrode positions – Electrophysiological recordings from acute hippocampus slices of 3-months and 1-year-old male mice in the CA1 region
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1
University of Osnabrück, Neurobiology, Germany
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2
University of Osnabrück, Neurobiology, Germany
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3
University of Osnabrück, Neurobiology, Germany
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4
University of Osnabrück, Neurobiology, Germany
The functional connectivity-map of neuronal circuits in relation to their normal physiology and pathological alterations has long been intensely studied by diverse electrophysiological approaches. Among the various brain regions the hippocampus has become the most established experimental paradigm for studying cellular and molecular mechanisms underlying learning and memory formation. It has well-described internal fiber pathways that are organized essentially in one plane, which grants the ability to maintain the pattern of synaptic connections even within a tissue slice. Furthermore, the clearly layered structure provides relevant advantages regarding collection and interpretation of electrophysiological data. More than four decades ago Andersen and colleagues (1971) detected marked differences in the outputs originating from distinct layers of the hippocampus by field potential recordings. Specifically, in the stratum radiatum where the apical dendritic arbors of the pyramidal cells are positioned excitatory postsynaptic potentials (fEPSPs) are elicited by synaptically induced current movements, while in the stratum pyramidale where the cell bodies of the respective neurons are aligned synchronous action potentials generate population spikes (PS). In the past several studies have been performed involving electrophysiological recordings in the synaptic pathway between CA3 and CA1 pyramidal cells of the hippocampus. However, precise information about the position of stimulating or recording electrodes in one of the hippocampal layers is lacking in many reports making cross-comparison difficult. Therefore, re-visiting the issue of how electrophysiological parameters are affected by the electrode position in correlation to the hippocampal layers is of high importance.
Here we used planar titanium nitride microelectrode array (MEA) with electrodes that are 30 µm in diameter and 200 µm apart to obtain spatially distinct recordings from the stratum radiatum and stratum pyramidale of acute mouse hippocampal slices. The electrode positions were confirmed by cryostat sectioning, staining and digital superposition of the respective slices. Recordings involved input-output (IO) test, paired pulse facilitation (PPF) and theta-burst induced LTP. Input/output (I/O) tests were performed by delivering a series of increasing stimulus intensities ranging from 250 mV to 3000 mV at a time interval of 1 min. Paired pulse facilitation tests were done by delivering a pair of stimuli of the same intensity but variable interstimulus intervals ranging from 20 ms to 200 ms. LTP was induced by 1 train of theta burst (5 bursts of 4 pulses at 100Hz with 200 ms interval). To gain information if age is potentially influencing the signals elicited from the two strata, slices from 3-months-old and 1-year-old male mice were comparatively analyzed.
We observed significant differences between the two strata mainly in the IO test and during LTP recordings. In particular, there was a significantly increased response from the stratum pyramidale in comparison to the stratum radiatum, when higher input voltages (2.5V and 3V) were applied in the I/O test. Furthermore, there was a significant increase in the responses from the stratum pyramidale compared to those from the stratum radiatum during the first 10 min of potentiation and also during the last 10 min of LTP recordings. These differences were evident in both age groups. Notably, age-related differences were present only in the stratum pyramidale, where young animals were showing significantly higher potentiation as well as maintenance of the LTP signal after theta-burst stimulation. PPF appears to be less sensitive in correlation to the layer from where the recordings were obtained.
The results presented here thus emphasize the necessity of a careful separation of data collected from different electrode positions, since mixed data sets might blur potential alterations between different experimental conditions.
References
Andersen P, Bliss TV, Skrede KK. Unit analysis of hippocampal polulation spikes. Exp Brain Res. 1971;13(2):208-21.
Keywords:
electrophysiological recordings,
microelectrode array,
acute hippocampus slices,
Stratum radiatum,
stratum pyramidale
Conference:
MEA Meeting 2018 | 11th International Meeting on Substrate Integrated Microelectrode Arrays, Reutlingen, Germany, 4 Jul - 6 Jul, 2018.
Presentation Type:
Poster Presentation
Topic:
Neural Networks
Citation:
Monteiro Abreu
ND,
Jeserich
G,
Brandt
R and
Bakota
L
(2019). The importance of electrode positions – Electrophysiological recordings from acute hippocampus slices of 3-months and 1-year-old male mice in the CA1 region.
Conference Abstract:
MEA Meeting 2018 | 11th International Meeting on Substrate Integrated Microelectrode Arrays.
doi: 10.3389/conf.fncel.2018.38.00099
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Received:
17 Mar 2018;
Published Online:
17 Jan 2019.
*
Correspondence:
Dr. Lidia Bakota, University of Osnabrück, Neurobiology, Osnabrück, Germany, lidia.bakota@biologie.uni-osnabrueck.de