Memantine Improves Recovery After Spreading Depolarization in Brain Slices and can be Considered for Future Clinical Trials

Abstract

Background: Spreading depolarization (SD) has been identified as a key mediator of secondary lesion progression after acute brain injuries, and clinical studies are beginning to pharmacologically target SDs. Although initial work has focused on the N-Methyl-D-aspartate receptor antagonist ketamine, there is also interest in alternatives that may be better tolerated. We recently showed that ketamine can inhibit mechanisms linked to deleterious consequences of SD in brain slices. The present study tested the hypothesis that memantine improves recovery of brain slices after SD and explored the effects of memantine in a clinical case targeting SD.

Methods: For mechanistic studies, electrophysiological and optical recordings were made from hippocampal area CA1 in acutely prepared brain slices from mice. SDs were initiated by localized microinjection of K⁺ in conditions of either normal or reduced metabolic substrate availability. Memantine effects were assessed from intrinsic optical signals and extracellular potential recordings. For the clinical report, a subdural strip electrode was used for continuous electrocorticographic recording after the surgical evacuation of a chronic subdural hematoma.

Results: In brain slice studies, memantine (10-300 µM) did not prevent the initiation of SD, but impaired SD propagation rate and recovery from SD. Memantine reduced direct current (DC) shift duration and improved recovery of synaptic potentials after SD. In brain slices with reduced metabolic substrate availability, memantine reduced the evidence of structural disruption after the passage of SD. In our clinical case, memantine did not noticeably immediately suppress SD; however, it was associated with a significant reduction of SD duration and a reduction in the electrocorticographic (ECoG) suppression that occurs after SD. SD was completely suppressed, with improvement in neurological examination with the addition of a brief course of ketamine.

Conclusions: These data extend recent work showing that N-Methyl-D-aspartate receptor antagonists can improve recovery from SD. These results suggest that memantine could be considered for future clinical trials targeting SD, and in some cases as an adjunct or alternative to ketamine.

Keywords: Brain injury; Cortical spreading depression; Excitotoxin; Kemantine; Ketamine; NMDA receptors; Subdural hematoma.

Figure 1:

Effect of memantine on SD propagation rate. A: Representative images demonstrating electrode placements (KCl, Rec.) and changes in transmitted light during SD propagation in control (top panel) and in memantine (below, 3rd SD in mem) within the same slice. Arrowheads indicate the wavefront of SD, scale bar = 250μm. B: Summary data showing SD propagation rates during successive SD stimulations from three separate sets of experiments. Left: effect of acute memantine wash in (n = 6) on SD rate, filled symbols are values measured from the preparation shown in A. *** P<0.001 compared to the second control SD. Middle: slower propagation rates during the first SD following extended memantine exposure (≥ 3h, n = 5). Right: faster SD propagation could be observed following extensive memantine wash out (n = 6). **P<0.01 third SD in memantine compared to wash out.

Figure 2:

Memantine reduces SD duration. A. Example traces demonstrating the effect of memantine on DC shift duration during successive SDs in a single slice. Return to a biphasic waveform could be achieved following memantine wash out. Arrowheads indicate SD onset and double lines represent 15 minute intervals between successive SDs. B: Summary data showing effect on DC duration during acute memantine exposure (left, n = 10), following extended memantine treatment (middle, ≥ 3h, n = 6), and after memantine wash out (right, n = 6). Filled symbols show DC durations from the same preparation shown in A. **P<0.01, ***P<0.005,****P<0.0001 compared to second control SD; *P<0.05 third SD in memantine compared to wash out.

Figure 3:

Memantine accelerates recovery of postsynaptic potentials after SD. A: Left panel shows a representative time course of EPSP amplitude recovery after SD in control and then in memantine within the same slice. Mean data of 6 preparations (right) demonstrates that acute memantine exposure reduces the duration of synaptic depression after SD. B: Shorter DC durations during the third SD in memantine were associated with accelerated recovery of postsynaptic potentials compared to the control SD in the same slice. *** P<0.001

Figure 4:

Memantine protects against IOS decreases after SD in vulnerable brain slices. A: Left hand panel shows the arrangement of KCl and recording electrodes in transmitted light images from representative slices in the three experimental conditions: control, vulnerable, and vulnerable + memantine (>2h). Solid white boxes show the regions of interest (ROIs) positioned in CA1 stratum radiatum and used for analyses; s.r.: stratum radiatum, s.p.: stratum pyramidale, scale bar = 250μm. The white dotted box outlines the imaging area shown in subsequent panels demonstrating changes in intrinsic optical signals (IOS, light transmittance) at baseline (during KCl microinjection), during SD propagation (arrowheads), and at the 10-minute time point after SD. Right hand inset panels show transmitted light images of each slice 10 minutes post SD. In control recording conditions (top row) SD led to a persistent IOS increase in stratum radiatum regions, consistent with full recovery in these nominally healthy conditions. In contrast, in the vulnerable conditions (middle row) there was persistent decrease IOS after SD, characteristic of lack of recovery. Pre-exposure to memantine (bottom row) prevented the decrease in IOS signal, consistent with improved recovery of SD in these metabolically compromised conditions. B: Average IOS traces (left; from n = 27 preparations) extracted from regions in CA1 (ROIs in stratum radiatum shown in A) during experiments shown in A. Summary data (right) confirm substantial decreases in CA1 light transmittance 10 minutes after passage of the SD wavefront in vulnerable slices (red symbols, n = 8) compared to control conditions (black symbols n = 8) with prevention by memantine pretreatment (>2h, white symbols, n = 11). ****P<0.0001

Figure 5:

Clinical management of patient with recurrent SD after chronic subdural hematoma evacuation. A: axial non-contrast CT scans demonstrating a large isodense/ mixed density chronic subdural hematoma (left panel, white arrow and outline). The center panel shows the result of the initial drainage with a small amount of residual blood product but improved mass effect (arrow, outline). The right panel demonstrates further decrease in residual volume after the second surgery with electrode placement. The inset shows the position of the electrode strip (white dots) on the lateral CT scout film. All these occurred prior to SD recordings. B: time course of neurological examination (Glasgow coma scale[GCS]),_SD frequency, and memantine and ketamine use during >100 hours of ECoG monitoring. Note that the GCS progressively deteriorated with recurrent SD and improved after cessation of SD. Overall rate of SD did not immediately decrease after memantine administration, but were completely abolished after initiation of ketamine. After ketamine was discontinued, memantine was continued with only one isolated SD during the monitoring period. C, D: Box plots of C) DC duration and D) Depression duration before and after memantine administration in this subject. E: Example SD from this subject. This SD is from the single electrode where the events were most prominent. The top trace is the raw DC (direct current) trace, the bottom is the same data with 0.5–50Hz band pass filter to display the high frequency data only. Note the depression of the high frequency activity lasting ~10 minutes.