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A reliable method for intracranial electrode implantation and chronic electrical stimulation in the mouse brain.

Jeffrey M, Lang M, Gane J, Wu C, Burnham WM, Zhang L - BMC Neurosci (2013)

Bottom Line: A daily stimulation protocol was used to induce electrographic discharges and motor seizures.Electrographic discharges and motor seizures were successfully induced via hippocampal electrical kindling.Importantly, no animal encountered infection in the implanted area or a loss of implanted electrodes after 4-6 months of repetitive stimulation/recording.

View Article: PubMed Central - HTML - PubMed

Affiliation: Toronto Western Research Institute, University Health Network, Toronto, Ontario, Canada.

ABSTRACT

Background: Electrical stimulation of brain structures has been widely used in rodent models for kindling or modeling deep brain stimulation used clinically. This requires surgical implantation of intracranial electrodes and subsequent chronic stimulation in individual animals for several weeks. Anchoring screws and dental acrylic have long been used to secure implanted intracranial electrodes in rats. However, such an approach is limited when carried out in mouse models as the thin mouse skull may not be strong enough to accommodate the anchoring screws. We describe here a screw-free, glue-based method for implanting bipolar stimulating electrodes in the mouse brain and validate this method in a mouse model of hippocampal electrical kindling.

Methods: Male C57 black mice (initial ages of 6-8 months) were used in the present experiments. Bipolar electrodes were implanted bilaterally in the hippocampal CA3 area for electrical stimulation and electroencephalographic recordings. The electrodes were secured onto the skull via glue and dental acrylic but without anchoring screws. A daily stimulation protocol was used to induce electrographic discharges and motor seizures. The locations of implanted electrodes were verified by hippocampal electrographic activities and later histological assessments.

Results: Using the glue-based implantation method, we implanted bilateral bipolar electrodes in 25 mice. Electrographic discharges and motor seizures were successfully induced via hippocampal electrical kindling. Importantly, no animal encountered infection in the implanted area or a loss of implanted electrodes after 4-6 months of repetitive stimulation/recording.

Conclusion: We suggest that the glue-based, screw-free method is reliable for chronic brain stimulation and high-quality electroencephalographic recordings in mice. The technical aspects described this study may help future studies in mouse models.

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Related in: MedlinePlus

Electrophysiological verifications of implanted electrodes. A, representative field potentials collected from a mouse at the beginning the kindling procedure (gray) and after reaching a fully kindled state (black). These field potentials were evoked by unilateral hippocampal CA3 stimulation (arrowed) and recorded from the contralateral CA3 area. Each illustrated trace was averaged from 5 consecutive responses. The artifact of the stimulation is indicated (arrow). B, the amplitudes of CA3 field potentials measured from 5 animals pre-kindling (gray) and after kindled (black). *, initial vs. kindled responses; p < 0.05, paired t test. C, interictal-like hippocampal spikes (arrowed) recorded from a kindled animal. D, incidences of hippocampal spikes measured pre-kindling and after fully kindled. *, p = 0.013, paired t-test, n = 7. E-F, representative spectral plots were generated from EEG signals that were recorded from an animal (G) pre-kindling (E) and after fully kindled (F). The spectral plots were generated from EEG segments of 30-second or 5-second during wake immobile (black) or exploratory (gray) behavior. Power was normalized to the peak of the delta band (0.5-4 Hz). G, representative EEG traces collected from the same animal after fully kindled. H, peak frequencies of hippocampal theta rhythms (5–12 Hz) and delta irregular activities (0.5-4 Hz) were measured from 7 animals. The peak frequencies of hippocampal theta and delta activities were not significantly altered in kindled animal relative to pre-kindling measurements (p = 0.723 and p = 0.524, paired test).
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Figure 2: Electrophysiological verifications of implanted electrodes. A, representative field potentials collected from a mouse at the beginning the kindling procedure (gray) and after reaching a fully kindled state (black). These field potentials were evoked by unilateral hippocampal CA3 stimulation (arrowed) and recorded from the contralateral CA3 area. Each illustrated trace was averaged from 5 consecutive responses. The artifact of the stimulation is indicated (arrow). B, the amplitudes of CA3 field potentials measured from 5 animals pre-kindling (gray) and after kindled (black). *, initial vs. kindled responses; p < 0.05, paired t test. C, interictal-like hippocampal spikes (arrowed) recorded from a kindled animal. D, incidences of hippocampal spikes measured pre-kindling and after fully kindled. *, p = 0.013, paired t-test, n = 7. E-F, representative spectral plots were generated from EEG signals that were recorded from an animal (G) pre-kindling (E) and after fully kindled (F). The spectral plots were generated from EEG segments of 30-second or 5-second during wake immobile (black) or exploratory (gray) behavior. Power was normalized to the peak of the delta band (0.5-4 Hz). G, representative EEG traces collected from the same animal after fully kindled. H, peak frequencies of hippocampal theta rhythms (5–12 Hz) and delta irregular activities (0.5-4 Hz) were measured from 7 animals. The peak frequencies of hippocampal theta and delta activities were not significantly altered in kindled animal relative to pre-kindling measurements (p = 0.723 and p = 0.524, paired test).

Mentions: The locations of implanted electrodes were initially verified by in vivo electrographic activities and later, histological assessments. In response to a single stimulation of the unilateral CA3 area, synaptic field potentials were reliably recorded from the contralateral CA3 area (Figure 2A). The amplitudes of these field potentials increased with strong stimuli and reached a near plateau level at the stimulation intensity of ≥100 μA (Figure 2B). No animals showed epileptic responses (such as long-lasting multi-spike waveforms) following a single stimulation. In addition, the animals exhibited hippocampal “physiological” activities similar to those we and others have previously observed in mice [15-20,22]. Specifically, CA3 recordings revealed rhythmic activities in the theta band (5–12 Hz) while the animals moved/explored local environments and irregular activities in the delta band (0.5-4 Hz) during immobility or sleep (Figure 2E-H). The peak frequencies of hippocampal theta and delta activities were not significantly changed in kindled animals (n = 7 mice; Figure 2H). As bilateral hippocampi are strongly interconnected via ventral and dorsal hippocampal fissures and the CA3 area is critical for the generation of hippocampal EEG rhythms and epileptiform activities [23], the above data provide electrographic evidence for accurately implanted CA3 electrodes.


A reliable method for intracranial electrode implantation and chronic electrical stimulation in the mouse brain.

Jeffrey M, Lang M, Gane J, Wu C, Burnham WM, Zhang L - BMC Neurosci (2013)

Electrophysiological verifications of implanted electrodes. A, representative field potentials collected from a mouse at the beginning the kindling procedure (gray) and after reaching a fully kindled state (black). These field potentials were evoked by unilateral hippocampal CA3 stimulation (arrowed) and recorded from the contralateral CA3 area. Each illustrated trace was averaged from 5 consecutive responses. The artifact of the stimulation is indicated (arrow). B, the amplitudes of CA3 field potentials measured from 5 animals pre-kindling (gray) and after kindled (black). *, initial vs. kindled responses; p < 0.05, paired t test. C, interictal-like hippocampal spikes (arrowed) recorded from a kindled animal. D, incidences of hippocampal spikes measured pre-kindling and after fully kindled. *, p = 0.013, paired t-test, n = 7. E-F, representative spectral plots were generated from EEG signals that were recorded from an animal (G) pre-kindling (E) and after fully kindled (F). The spectral plots were generated from EEG segments of 30-second or 5-second during wake immobile (black) or exploratory (gray) behavior. Power was normalized to the peak of the delta band (0.5-4 Hz). G, representative EEG traces collected from the same animal after fully kindled. H, peak frequencies of hippocampal theta rhythms (5–12 Hz) and delta irregular activities (0.5-4 Hz) were measured from 7 animals. The peak frequencies of hippocampal theta and delta activities were not significantly altered in kindled animal relative to pre-kindling measurements (p = 0.723 and p = 0.524, paired test).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC3750568&req=5

Figure 2: Electrophysiological verifications of implanted electrodes. A, representative field potentials collected from a mouse at the beginning the kindling procedure (gray) and after reaching a fully kindled state (black). These field potentials were evoked by unilateral hippocampal CA3 stimulation (arrowed) and recorded from the contralateral CA3 area. Each illustrated trace was averaged from 5 consecutive responses. The artifact of the stimulation is indicated (arrow). B, the amplitudes of CA3 field potentials measured from 5 animals pre-kindling (gray) and after kindled (black). *, initial vs. kindled responses; p < 0.05, paired t test. C, interictal-like hippocampal spikes (arrowed) recorded from a kindled animal. D, incidences of hippocampal spikes measured pre-kindling and after fully kindled. *, p = 0.013, paired t-test, n = 7. E-F, representative spectral plots were generated from EEG signals that were recorded from an animal (G) pre-kindling (E) and after fully kindled (F). The spectral plots were generated from EEG segments of 30-second or 5-second during wake immobile (black) or exploratory (gray) behavior. Power was normalized to the peak of the delta band (0.5-4 Hz). G, representative EEG traces collected from the same animal after fully kindled. H, peak frequencies of hippocampal theta rhythms (5–12 Hz) and delta irregular activities (0.5-4 Hz) were measured from 7 animals. The peak frequencies of hippocampal theta and delta activities were not significantly altered in kindled animal relative to pre-kindling measurements (p = 0.723 and p = 0.524, paired test).
Mentions: The locations of implanted electrodes were initially verified by in vivo electrographic activities and later, histological assessments. In response to a single stimulation of the unilateral CA3 area, synaptic field potentials were reliably recorded from the contralateral CA3 area (Figure 2A). The amplitudes of these field potentials increased with strong stimuli and reached a near plateau level at the stimulation intensity of ≥100 μA (Figure 2B). No animals showed epileptic responses (such as long-lasting multi-spike waveforms) following a single stimulation. In addition, the animals exhibited hippocampal “physiological” activities similar to those we and others have previously observed in mice [15-20,22]. Specifically, CA3 recordings revealed rhythmic activities in the theta band (5–12 Hz) while the animals moved/explored local environments and irregular activities in the delta band (0.5-4 Hz) during immobility or sleep (Figure 2E-H). The peak frequencies of hippocampal theta and delta activities were not significantly changed in kindled animals (n = 7 mice; Figure 2H). As bilateral hippocampi are strongly interconnected via ventral and dorsal hippocampal fissures and the CA3 area is critical for the generation of hippocampal EEG rhythms and epileptiform activities [23], the above data provide electrographic evidence for accurately implanted CA3 electrodes.

Bottom Line: A daily stimulation protocol was used to induce electrographic discharges and motor seizures.Electrographic discharges and motor seizures were successfully induced via hippocampal electrical kindling.Importantly, no animal encountered infection in the implanted area or a loss of implanted electrodes after 4-6 months of repetitive stimulation/recording.

View Article: PubMed Central - HTML - PubMed

Affiliation: Toronto Western Research Institute, University Health Network, Toronto, Ontario, Canada.

ABSTRACT

Background: Electrical stimulation of brain structures has been widely used in rodent models for kindling or modeling deep brain stimulation used clinically. This requires surgical implantation of intracranial electrodes and subsequent chronic stimulation in individual animals for several weeks. Anchoring screws and dental acrylic have long been used to secure implanted intracranial electrodes in rats. However, such an approach is limited when carried out in mouse models as the thin mouse skull may not be strong enough to accommodate the anchoring screws. We describe here a screw-free, glue-based method for implanting bipolar stimulating electrodes in the mouse brain and validate this method in a mouse model of hippocampal electrical kindling.

Methods: Male C57 black mice (initial ages of 6-8 months) were used in the present experiments. Bipolar electrodes were implanted bilaterally in the hippocampal CA3 area for electrical stimulation and electroencephalographic recordings. The electrodes were secured onto the skull via glue and dental acrylic but without anchoring screws. A daily stimulation protocol was used to induce electrographic discharges and motor seizures. The locations of implanted electrodes were verified by hippocampal electrographic activities and later histological assessments.

Results: Using the glue-based implantation method, we implanted bilateral bipolar electrodes in 25 mice. Electrographic discharges and motor seizures were successfully induced via hippocampal electrical kindling. Importantly, no animal encountered infection in the implanted area or a loss of implanted electrodes after 4-6 months of repetitive stimulation/recording.

Conclusion: We suggest that the glue-based, screw-free method is reliable for chronic brain stimulation and high-quality electroencephalographic recordings in mice. The technical aspects described this study may help future studies in mouse models.

Show MeSH
Related in: MedlinePlus