Direct Current Shifts Research Articles

Scalp recorded direct current potential shifts associated with quenching thirst in humans

As an indicator of cortical excitability, direct current (DC) potentials were recorded from thirsted subjects before, during and after drinking 400 ml of water. Self-rated thirst was distinctly reduced after drinking. Compared with control conditions in which the subjects remained thirsty, during drinking a widespread negative potential shift occurred averaging over −70 μV at Cz. At the transition from the consumatory phase to the postconsumption phase, a slow positive potential shift commenced that was most pronounced over the anterior cortex (averaging over +40 μV at Fz) and persisted for more than 3 min after drinking. Control conditions excluded muscle activity, ocular movements, and changes in body fluid and serum osmolality as possible non-neuronal sources of the DC-potential changes. The sequence of negative and positive potential shifts associated with drinking indicates a coordinate regulation of cortical excitability that may facilitate consumatory behavior and its context-dependent encoding into memory.

Hypoxia- and hypercapnia-induced DC potential shifts in rat at the scalp and the skull are opposite in polarity to those at the cerebral cortex

In anaesthetized and artificially ventilated rats DC (direct current) potential shifts induced by hypoxia or hypercapnia for 10 min were monitored at the surface of the skin, of the skull and of the cerebral cortex. Hypoxia was induced by decreasing the inspiratory O 2 content from 20 to 10 or to 6% O 2 in N 2. Hypercapnia was induced by applying gas mixtures with CO 2 contents from 0 to 5, 10, 20 or 30% CO 2 in O 2. DC potentials were recorded with non-polarizing electrodes filled with 150 mM NaCl solution. Hypercapnia evoked a negative DC shift (1.2–1.9 mV) epicranially and a large positive DC deflection (8.8–17.1 mV) epidurally. In contrast, hypoxia elicited a positive DC shift in skull recordings with a negative DC shift (2.6–3.1 mV) overshooting the baseline during recovery. DC shifts at the skin were positive, but smaller in amplitude (up to 3.1 mV). At the surface of the dura hypoxic DC shifts were negative and smaller (1.5–2.2 mV) than at the skull. The results show that a negative DC shift induced by hypercapnia recorded non-invasively from the skin or the skull is not always reflecting an increased cortical activation state and, vice versa, a positive DC shift does not always reflect a decreased state of neuronal activation. The electrogenesis of gas content-induced potentials could be due to the electrochemical diffusion of ions through the selective permeability barrier between the blood and tissue compartment. These observations are relevant for any application of non-invasive DC electroencephalography in the human cortex.

Interactions Between Hypothermia and the Latency to Ischemic Depolarization: Implications for Neuroprotection

BART, ROBERT D.; TAKAOKA, SEIJI; PEARLSTEIN, ROBERT D.; DEXTER, FRANKLIN; WARNER, DAVID S.Author Information

Expression of c- fos, junB, c- jun, MKP-1 AND hsp72 following traumatic neocortical lesions in rats—relation to spreading depression

The effects of a traumatic neocortical lesion on c- fos, junB, c- jun, MKP-1 and hsp72 expression were examined by in situ hybridization and immunocytochemistry 1–6 h following transcranial cold injury. The direct current potential was recorded in the injury-remote cortex to evaluate the role of transient direct current shifts, i.e. spreading depressions, in gene expression. In 14 out of 21 injured rats, spreading depression-like depolarizations of the direct current potential were noticed, which were accompanied by a transient decrease in electroencephalographic activity and increase in laser Doppler flow. In seven injured animals, no spontaneous direct current deflections were seen. In animals without spreading depressions, only a short-lasting response of c- fos, junB, c- jun and MKP-1 messenger RNAs as well as c-Fos protein was bilaterally found in the piriform cortex, and—with ipsilateral dominance—the dentate gyrus and hippocampal CA3/4 fields at 1 h after lesioning. In injured animals with spreading depressions however, a strong elevation was seen in layers II–IV and VI of the injury-remote ipsilateral cerebral cortex, which persisted over as long as 6 h. Messenger RNA levels for c- fos, junB and MKP-1 were closely related to the time interval between the last direct current deflection and the end of experiment. Levels were highest shortly after transient direct current shifts, and decreased thereafter mono-exponentially with half-lives of 48, 75 and 58 min for c- fos, junB and MKP-1 messenger RNAs, respectively. In 6 h animals with spreading depressions, hsp72 messenger RNA was slightly elevated in layer II of the injury-remote cortex, but Hsp72 was not increased. The present results demonstrate that spreading depression is the most prominent factor influencing the trauma-related gene response in the lesion-remote cortical tissue.

Perception of species-specific vocalizations in rats : role of the cholinergic septo-hippocampal pathway and aging

The effect of a chemical lesion of the cholinergic septo-hippocampal pathway induced by ethylcholine aziridinium (AF64A) on brain potentials evoked by species-specific vocalization containing informations of high biological relevance was studied in young adult (10 months) and aged (24 months) rats by means of neocortical electroencephalographic recordings. In control rats, the perception of a rats vocalization in a life endangering situation (lasting 0.8 s) initiated an evoked potential followed by a late positive slow wave (LPSW)-complex and a direct current shift with a duration of up to 16 s. Four months after treatment with AF64A (2 nmol into each of the lateral ventricles), the main negative component of the initial acoustic evoked potential (peak latency of about 60 ms after stimulus onset) was reduced (P = 0.04) both in young adult and aged rats. Further changes included a decrease of the late positive wave amplitude in young adult rats (P = 0.001) and a shorter duration of the LPSW-complex in aged rats (P = 0.03). AF64A induced also changes in specific components revealed by Principle Component Analysis, but only in the group of young rats. A decrease in the slow wave component (factor 1, 3000–4000 ms after stimulus onset ; P = 0.02) was observed. Age per se affected the late positive potential shifts as indicated by a shorter latency of the late positive wave (P = 0.03).A detailed analysis of the major neurotransmitter markers proved an almost exclusive reduction of the activity of choline acetyltransferase in the ventral and dorsal hippocampus (up to 60%), which was equal in young adult and aged rats. The irreversible loss in choline acetyltransferase activity, which was restricted to the hippocampus, was associated by a slight reduction in serotonergic function.The present data suggest that the complex cognitive and emotional processes initiated by species-specific vocalization appear to be affected by aging. Furthermore, as a consequence of a cholinergic deficit in the hippocampus, the integration processes essential for the recognition of the biological meaning of a species-specific vocalization are considerably disturbed. These findings provide an experimental basis for studying disturbances in the perceptual response to stimuli of high emotional value in patients with hypocholinergic function as in Alzheimers disease.

Magnetic resonance imaging assessment of cerebral hemodynamics during spreading depression in rats.

High-speed magnetic resonance imaging was used to perform simultaneous measurements of relative cerebral blood volume (rCBV) and water diffusion changes during spreading depression (SD) induced by cortical potassium chloride application. Rats were fitted epidurally with a rubber chamber. Potassium chloride was perfused through the chamber until SD was indicated by a negative direct current (DC) potential shift. Magnetic resonance imaging scans used echo planar diffusion and T2-weighted images. Iron dextran was injected as a blood pool contrast agent to make subsequent changes in T2 (or T2*) directly proportional to changes in CBV. Multislice maps of apparent diffusion coefficient (ADC) and rCBV were generated with 6- to 16-second time resolution, which revealed transient ADC and rCBV changes propagating over the cortex after potassium chloride application. Transient ADC declines appeared simultaneously with the DC shift, whereas rCBV increase followed with a delay of 16.4+/-14.9 seconds. Prolonged rCBV decrease was observed after the initial increase during the SD in half of the animals. The delayed rCBV response after the ADC change supports the observation of increased energy demand because of repolarization. Simultaneous DC potential recording and ADC measurements in corresponding sites of the cortex indicate that transient ADC decreases during SD reflect water shifts associated with cell depolarization.

Nitric oxide scavenging by hemoglobin or nitric oxide synthase inhibition by N-nitro-L-arginine induces cortical spreading ischemia when K+ is increased in the subarachnoid space.

We investigated the combined effect of increased brain topical K+ concentration and reduction of the nitric oxide (NO.) level caused by nitric oxide scavenging or nitric oxide synthase (NOS) inhibition on regional cerebral blood flow and subarachnoid direct current (DC) potential. Using thiopental-anesthetized male Wistar rats with a closed cranial window preparation, brain topical superfusion of a combination of the NO. scavenger hemoglobin (Hb; 2 mmol/L) and increased K+ concentration in the artificial cerebrospinal fluid ([K+]ACSF) at 35 mmol/L led to sudden spontaneous transient ischemic events with a decrease of CBF to 14+/-7% (n=4) compared with the baseline (100%). The ischemic events lasted for 53+/-17 minutes and were associated with a negative subarachnoid DC shift of -7.3+/-0.6 mV of 49+/-12 minutes' duration. The combination of the NOS inhibitor N-nitro-L-arginine (L-NA, 1 mmol/L) with [K+]ACSF at 35 mmol/L caused similar spontaneous transient ischemic events in 13 rats. When cortical spreading depression was induced by KCl at a 5-mm distance, a typical cortical spreading hyperemia (CSH) and negative DC shift were measured at the closed cranial window during brain topical superfusion with either physiologic artificial CSF (n=5), or artificial CSF containing increased [K+]ACSF at 20 mmol/L (n=4), [K+]ACSF at 3 mmol/L combined with L-NA (n=10), [K+]ACSF at 10 mmol/L combined with L-NA (five of six animals) or [K+]ACSF at 3 mmol/L combined with Hb (three of four animals). Cortical spreading depression induced longlasting transient ischemia instead of CSH, when brain was superfused with either [K+]ACSF at 20 mmol/L combined with Hb (CBF decrease to 20+/-20% duration 25+/-21 minutes, n=4), or [K+]ACSF at 20 mmol/L combined with L-NA (n=19). Transient ischemia induced by NOS inhibition and [K],ACSF at 20 mmol/L propagated at a speed of 3.4+/-0.6 mm/min, indicating cortical spreading ischemia (CSI). Although CSH did not change oxygen free radical production, as measured on-line by in vivo lucigenin-enhanced chemiluminescence, CSI resulted in the typical radical production pattern of ischemia and reperfusion suggestive of brain damage (n=4). Nimodipine (2 microg/kg body weight/min intravenously) transformed CSI back to CSH (n=4). Vehicle had no effect on CSI (n=4). Our data suggest that the combination of decreased NO. levels and increased subarachnoid K+ levels induces spreading depression with acute ischemic CBF response. Thus, a disturbed coupling of metabolism and CBF can cause ischemia. We speculate that CSI may be related to delayed ischemic deficits after subarachnoid hemorrhage, a clinical condition in which the release of Hb and K+ from erythrocytes creates a microenvironment similar to the one investigated here.

The effects of 17β-estradiol on ischemia-induced neuronal damage in the gerbil hippocampus

The effects of 17β-estradiol, a potent estrogen, on ischemia-induced neuronal damage, membrane depolarization and changes in intracellular Ca 2+ concentration were studied in gerbil hippocampi. The histological outcome evaluated seven days after 3 min of transient forebrain ischemia in hippocampal CA1 pyramidal cells was improved by high doses of 17β-estradiol (30 μg, i.c.v. and 4 mg/kg, i.p.), whereas low doses of 17β-estradiol (3 and 10 μg, i.c.v.) showed no protective effect. Administration of 17β-estradiol did not affect the changes in the direct current potential shift in ischemia in the hippocampal CA1 area at any dosage. A hypoxia-induced intracellular Ca 2+ increase was evaluated by in vitro microfluorometry in gerbil hippocampal slices. Pretreatment of 17β-estradiol (4 mg/kg, injected i.p. 1 h before decapitation) suppressed the increase in the intracellular concentration of Ca 2+ due to the in vitro hypoxia, affecting both the onset of the increase and the extent. The in vitro hypoxia in the Ca 2+-free condition induced an elevation of the intracellular concentration of Ca 2+, although the increase was gradual. Pretreatment of 17β-estradiol (4 mg/kg, i.p.) also inhibited this elevation. These findings imply that high doses of 17β-estradiol protect the neurons from ischemia by inhibiting the release of Ca 2+ from the intracellular Ca 2+ stores, as well as by inhibiting the influx of Ca 2+ from the extracellular space.

Neuroprotective effect of sumatriptan, a 5-HT 1D receptor agonist, in focal cerebral ischemia of rat brain

The effect of the 5-HT(1D) receptor agonist sumatriptan on the volume of ischemic injury was studied in rats subjected to permanent middle cerebral artery (MCA) occlusion. Sumatriptan (2 mg/kg) was administered intravenously 5 minutes after MCA occlusion and the ischemic injury volume was determined 3 hours after MCA occlusion using regional adenosine-5'-triphosphate imaging. In addition, electroencephalographic activity, direct current (DC) potential and cortical blood flow (CBF) was monitored throughout the experiment. In untreated animals, MCA occlusion resulted in a decline in penumbral CBF to 43.3%+/-7.6% of control, 21 spreading depression (SD)-like DC shifts with an average integrated depolarization negativity of 320.2+/-297.4 (mVxmin) and an ATP depletion volume of 61.8+/-22.9 mm(3) (mean+/-SD). Three hours after MCA occlusion in sumatriptan-treated animals, penumbral CBF recovered to 63.5%+/-12.6% of control (P<.05), only 13 SD-like shifts were detected (P<.05) with a significantly reduced integrated depolarization negativity of 104.7+/-98.4 (mVxmin) (P<.05), and the volume of ATP depletion decreased to 16.6+/-12.3 mm(3) (P<.01). However, no significant neuroprotective effect was observed for the caudate nucleus (untreated, 19.7+/-16.5 mm(3); treated, 7.9+/-8.5 mm(3)). The reduction in the volume of ischemic injury in sumatriptantreated animals is explained by both the improvement of blood flow and the inhibition of SD-like shifts leading to an amelioration of the misrelationship between the depolarization-related energy demand and flow-dependent substrate delivery.

Reappraisal of the effect of electrode property on recording slow potentials

Subdural electrodes made of stainless steel, which were believed to be unsuitable for recording slow potentials, can still record Bereitschaftspotential (BP) (Neshige, R., Lüders, H. and Shibasaki, H. Recording of movement-related potentials from scalp and cortex in man. Brain, 1988, 11: 719–736) and ictal direct current (DC) shifts (Ikeda, A., Terada, K., Mikuni, N., Burgess, R.C., Comair, Y., Taki, W., Hamano, T., Kimura, J., Lüders, H.O. and Shibasaki, H. Subdural recording of ictal DC shifts in neocortical seizures in humans. Epilepsia, 1996b, 37: 662–674) sufficiently. In this study, therefore, the effects of different kinds of metals on slow potential recordings were reevaluated. First, slow electro-oculograms (EOGs) were recorded with 3 different levels of input impedance (200 M Ω, 470 k Ω and 10 k Ω) of a DC amplifier by using surface electrodes made of silver (Ag), silver/silver chloride (Ag/AgCl) and stainless steel. Secondly, BP was recorded by using the above electrodes with a long time constant of 3 s and with a fixed input impedance of 100 M Ω. As a result: (1) slow EOGs were equally recorded with the input impedance of 200 M Ω and 470 k Ω regardless of the kind of metals used, although stainless steel electrodes caused baseline fluctuation, (2) low input impedance of 10 k Ω allowed only the Ag/AgCl electrode to record slow EOGs without any decay, and (3) electrodes made of stainless steel could record BP as efficiently as the other two types of electrode with high input impedance. In conclusion, electrodes with a large surface area contact such as cup electrodes and an amplifier with a large input impedance, electrodes made of Ag, and even of stainless steel, can record slow potentials reasonably well.

Dose-dependent effects of tetraethylammonium on circling spreading depressions in chicken retina.

The K+-channel blocker tetraethylammonium (TEA) was applied to study its effects in self-sustaining, circling spreading depression in the chicken retina (RSD). Extracellular K+ (Ke+ activities and the direct-current (DC) signal were recorded using double-barrelled microelectrodes. Superfusion of TEA-concentrations of 10 to 250 microM for 4 to 7 min reduced the RSD-associated DC amplitude (by 9 to 45%) and the maximum of the K+ concentration (by 9 to 34%) in a dose-dependent manner. Propagation velocity of the RSD was lowered by 24%. At concentrations higher than 250 microM TEA (0.5 to 10 mM), the propagation was slowed by more than 60%, after which the RSD disappeared. Recovery upon reperfusion with Ringer was immediate. These observations illustrate: 1) TEA affects the Ke+ changes during RSD at very low concentrations. 2) The reduced Ke+ transients are accompanied by a reduction of the DC shifts. 3) These changes of the electrical properties of the RSDs are paralleled by a reduction of the propagation velocity. 4) The effects of TEA are reversible. 5) The changes of these parameters occur dose-dependently. These data suggest a close relationship between the amplitudes of the ionic/electric changes during RSDs and the mechanisms of propagation.

Profiles of cortical tissue depolarization in cat focal cerebral ischemia in relation to calcium ion homeostasis and nitric oxide production.

Cortical depolarization was investigated in a topographic gradient of ischemic density after 1-hour transient middle cerebral artery occlusion in halothane-anesthetized cats. A laser Doppler flow probe, an ion-selective microelectrode, and a nitric oxide (NO) electrode measured regional CBF (rCBF), direct current (DC) potential, extracellular Ca2+ concentration ([Ca2+]o), and NO concentration in ectosylvian and suprasylvian gyri of nine animals. Recordings revealed 12 of 18 sites with persistent negative shifts of the DC potential, severe rCBF reduction, and a drop of [Ca2+]o characteristic for core regions of focal ischemia. Among these sites, two types were distinguished by further analysis. In Type 1 (n = 5), rapid, negative DC shifts resembled anoxic depolarization as described for complete global ischemia. In this type, ischemia was most severe (8.9 +/- 2.5% of control rCBF), [Ca2+]o dropped fast and deepest (0.48 +/- 0.20 mmol/L), and NO concentration increased transiently (36.1 +/- 24.0 nmol/L at 2.5 minutes), and decreased thereafter. In Type 2 (n = 7), the DC potential fell gradually over the first half of the ischemic episode, rCBF and [Ca2+]o reductions were smaller than in Type 1 (16.2 +/- 8.2%; 0.77 +/- 0.41 mmol/L), and NO increased continuously during ischemia (53.1 +/- 60.4 nmol/L at 60 minutes) suggesting that in this type NO most likely exerts its diverse actions on ischemia-threatened tissue. In the remaining six recording sites, a third type (Type 3) attributable to the ischemic periphery was characterized by minimal DC shifts, mild ischemia (37.2 +/- 13.3%), nonsignificant alterations of [Ca2+]o, but decreased NO concentrations during middle cerebral artery occlusion. Reperfusion returned the various parameters to baseline levels within 1 hour, the recovery of [Ca2+]o and NO concentration being delayed in Type 1. An NO synthase inhibitor (N(G)-nitro-L-arginine, 50 mg/kg intravenously; four animals) abolished NO elevation during ischemia. In conclusion, even in the core of focal cerebral ischemia and reperfusion, different ischemic densities produce different types of cortical tissue manifesting distinctive chronological profiles of depolarization, Ca2+ influx, and NO synthesis.

Glycine antagonism does not block ischemic spontaneous depolarization in the rat.

This study examined the effect of glycine recognition site antagonism (ACEA 1021) on the incidence of spontaneous depolarizations in the penumbra of a focal ischemic lesion. Rats were administered either vehicle (n = 7), ACEA 1021 (n = 7) or dizocilpine (n = 5) and then underwent 90 min middle cerebral artery occlusion. The cortical direct current (DC) potential was recorded. During ischemia, 7 +/- 3 DC shifts occurred in the vehicle group. ACEA 1021 did not reduce this frequency (7 +/- 2 DC shifts) although dizocilpine did (1 +/- 1 DC shifts; p = 0.02). The previously demonstrated neuroprotective property of ACEA 1021 during focal cerebral ischemia cannot be attributed to reduction of spontaneous depolarization in the ischemic penumbra.

Blood flow dependent duration of cortical depolarizations in the periphery of focal ischemia of rat brain

Cortical depolarizations in the periphery of focal ischemia result in metabolic disturbances which contribute to the progression of the ischemic injury. In this experimental study, therefore, it was examined whether the duration of peri-infarct depolarizations, which reflects the severity of a metabolic mismatch, is determined by the level of residual blood flow in the periphery of focal ischemia. After occlusion of the middle cerebral artery for 3 h, the depolarization time of direct current (DC) shifts was 2.5±0.7 min at flow rates ranging from 60–100% of control increasing discretely to 3.5±3.2 (ns) min when flow values varied from 40–59%. At flow values below 40% of control, however, depolarization time of peri-infarct DC shifts increased significantly to 25.3±22.5 min ( P<0.05). These findings suggest that at critical flow levels, repetitive penumbral depolarizations cause a severe disturbance of cell ion homeostasis due to transient intervals of impaired energy metabolism which explains the gradual expansion of the evolving brain infarct.

Histaminergic H2 action protects hippocampal CA1 neurons by prolonging the onset of the anoxic depolarization in gerbils.

The central histaminergic action on ischemia-induced neuronal damage was examined by evaluating the histological outcome and the direct current (DC) potential shift in the hippocampal CA1 region in gerbils. An intracerebroventricular administration of histamine (10-100 nmol) improved the delayed ischemic damage in hippocampal CA1 pyramidal cells produced by 3 min of transient forebrain ischemia. A high dose (75 nmol) of mepyramine, an H1 antagonist, aggravated ischemia-induced neuronal damage, but not a low dose (0.75 nmol). Administration of cimetidine (4 nmol) and ranitidine (3 nmol), H2 antagonists, aggravated the neuronal damage. An injection of histamine (100 nmol) prolonged the onset time of the ischemia-induced sudden shift in the extracellular DC potential (anoxic depolarization; AD) to 133% of that in control animals. Administration of mepyramine (75 nmol) did not markedly change the AD, whereas injections of cimetidine (40 nmol) and ranitidine (3 nmol) reduced the onset latency to 47 and 45%, respectively. These findings suggest that the central H2 action serves to protect neurons by delaying the onset of AD in gerbils.

Hypothermia reduces the propensity of cortical tissue to propagate direct current depolarizations in the rat

Both spreading depression (SD) and spontaneous cortical ischemic depolarizations are known to be sensitive to brain temperature. What is unknown is whether this temperature effect is caused by altered sensitivity of cortical tissue to the initiating stimulus or is attributable to an altered ability of cortex to propagate the depolarization wave. To address this, halothane anesthetized rats underwent surface heating/cooling to produce pericranial temperatures of 33°C, 38°C, or 40°C. Spreading depression was first initiated by electrocortical stimulation and then by topical application of KCl. The electrical threshold for SD and the time to direct current shift onset after KCl administration were unaffected by temperature. In contrast, the ability of cortical tissue to propagate the SD wave was temperature dependent. Decreasing temperature from 40°C to 33°C was associated with a slowing of the rate of propagation by 25–30% while the duration of the propagated direct current (DC) shifts was increased by 80% regardless of the initiating stimulus. After elicitation of persistent local DC shift with KCl, the interval between initial waves of SD was progressively increased as temperature was decreased. For either method of stimulation, once SD was initiated, the amplitude of the waveform was temperature independent. These results confirm the importance of temperature regulation in procedures examining SD in vivo. Further, temperature effects on SD reflect propensity of the tissue to propagate depolarization waves although ability of cortex to depolarize in direct response to the stimulus does not undergo substantive change.

Scalp-recorded direct current potential shifts induced by hypocapnia and hypercapnia in humans

Shifts in scalp-recorded direct current (DC) potential were studied in relation to the changes in end-tidal partial CO 2 (PA co 2) or O 2 (PA o 2) of the expired gas either during hyperventilation (HV), hypoventilation (HYPO) or inhalation of high CO 2 content air during HV or HYPO in 10 healthy subjects. The DC potential was obtained through a chopper stabilized type of DC amplifier from Cz referred to linked earlobes. Each session was comprised of 3 min control, 3 min experimental and 5 min recovery periods. HV induced a negative shift of the DC potential of 765.5 ± 203.0 μV (mean ± SEM). Inhalation of 6% CO 2 air during HYPO induced a positive shift of the DC potential of 280.6 ± 62.8 μV (mean ± SEM). The magnitude of the DC potential shifts was linearly dependent on the changes in the end-tidal PA co 2 ( r = 0.78, P < 0.0001). There was no change in the cephalic inter-electrodes impedance during each experimental session. The results suggest that the scalp-recorded DC potentials reflect the changes in cortical excitability associated with the PA co 2 level.

Subdural Recording of Ictal DC Shifts in Neocortical Seizures in Humans

Invasive ictal EEG recording is often necessary to delineate epileptogenic areas in patients with intractable partial epilepsy, but even intracranial ictal recordings often reveal ill-defined onset zones in neocortical epilepsy. We studied the physiologic significance of ictal direct current (DC) potentials recorded intracranially in human epilepsy. We made intracranial ictal EEG recordings in three patients with intractable partial seizures arising from frontal, lateral temporal, and parietal neocortical areas by using closely spaced subdural electrodes (platinum in two patients and stainless steel in one patient) with both standard (1.5 Hz) and open (0.016 Hz) low-frequency filter (LFF) settings. The initial ictal pattern was localized to two to nine subdural electrodes and characterized by very low voltage and high-frequency rhythmic activity ("electrodecremental pattern"). A slow-rising negative potential (DC potential) was seen in a slightly more restricted area (two to six electrodes) and occurred 1-10 s before the initial ictal EEG discharges in two patients. These results agree with those of previous studies of ictal DC shifts in animals and suggest that ictal DC shifts may be helpful in delineating the epileptogenic area more precisely in human epilepsy.

Induction of Spreading Depression in the Ischemic Hemisphere following Experimental Middle Cerebral Artery Occlusion: Effect on Infarct Morphology

This study was undertaken to test whether transient depolarizations occurring in periinfarct regions are important in contributing to infarct spread and maturation. Following middle cerebral artery (MCA) occlusion we stimulated the ischemic penumbra with recurrent waves of spreading depression (SD) and correlated the histopathological changes with the electrophysiological recordings. Halothane-anesthetized, artificially ventilated Sprague-Dawley rats underwent repetitive stimulation of SD in intact brain (Group 1; n = 8) or photothrombotic MCA occlusion coupled with ipsilateral common carotid artery occlusion (Groups 2 and 3, n = 9 each). The electroencephalogram and direct current (DC) potential were recorded for 3 h in the parietal cortex, which represented the periinffarct border zone in ischemic rats. In Group 2, only spontaneously occurring negative DC shifts occurred; in Group 3, the (nonischemic) frontal pole of the ischemic hemisphere was electrically stimulated to increase the frequency of periinfarct DC shifts. Animals underwent perfusion-fixation 24 h later, and volumes of complete infarction and scattered neuronal injury ("incomplete infarction") were assessed on stained coronal sections by quantitative planimetry. Electrical induction of SD in Group 1 did not cause morphological injury. During the initial 3 h following MCA occlusion, the number of spontaneous periinfarct depolarization in Group 2 (7.0 +/- 1.5 DC shifts) was doubled in Group 3 by frontal current application (13.4 +/- 2.7 DC shifts; p < 0.001). The duration as well as the integrated negative amplitude of DC shifts over time were significantly greater in Group 3 than in Group 2 rats (duration, 5.7 +/- 3.8 vs. 4.1 +/- 2.5 min; p < 0.05). Histopathological examination disclosed well-defined areas of pannecrosis surrounded by a cortical rim exhibiting selectively damaged acidophilic neurons and astrocytic swelling in otherwise normal-appearing brain. Induction of SD in the ischemic hemisphere led to a significant increase in the volume of incomplete infarction (19.0 +/- 6.1 mm3 in Group 3 vs. 10.3 +/- 5.1 mm3 in Group 2; p < 0.01) and of total ischemic injury (100.7 +/- 41.0 mm3 in Group 3 vs. 66.5 +/- 24.7 mm3 in Group 2; p < 0.05). The integrated magnitude of DC negativity per experiment correlated significantly with the volume of total ischemic injury (r = 0.780, p < 0.0001). Thus, induction of SD in the ischemic hemisphere accentuated the development of scattered neuronal injury and increased the volume of total ischemic injury. This observation may be explained by the fact that with limited perfusion reserve, periinfarct depolarization are associated with episodic energy failure in the acute ischemic penumbra.

Neurobehavioral consequences of induced spreading depression following photothrombotic middle cerebral artery occlusion

In a model of experimental focal cerebral ischemia, we have recently reported a strong correlation between the magnitude of ischemic depolarizations in the peri-infarct borderzone and the extent of histological injury. In the present study, we assessed the neurobehavioral consequences of spontaneously occurring and induced ischemic depolarizations in rats following middle cerebral artery (MCA) occlusion, as well as the effects of induced spreading depression (SD) in intact animals. Halothane-anesthetized, artificially ventilated Sprague-Dawley rats underwent photothrombotic MCA occlusion coupled with ipsilateral common carotid artery (CCA) occlusion. The electroencephalogram and direct current (DC) potential were recorded in the parietal infarct borderzone-corresponding to the cortical forelimb area-for 3 h following MCA occlusion. Group 1 rats ( n = 9) received MCA/CCA occlusion, and the spontaneously occurring negative DC shifts were recorded in the ischemic borderzone. In Group 2 animals ( n = 9), the (non-ischemic) frontal pole of the ipsilateral hemisphere was electrically stimulated in order to double the frequency of peri-infarct DC shifts occurring over the initial 3 h postocclusion. Group 3 consisted of intact rats ( n = 3) in which SD was repeatedly evoked in the frontal pole. Four animals served as sham-operated controls. A battery of sensorimotor behavioral tests, consisting of beam balance, postural reflex and elicited forelimb placing, was applied in a blinded fashion. Sham controls and animals of Groups 1 and 2 were tested 24 h after surgery, and Group 3 rats were tested 2, 6 and 24 h after generation of SDs. A cumulative neurobehavioral index, ranging from 0 to 144, was calculated by adding the individual test results. Brains were perfusion-fixed 24 h following surgery for calculation of volumes of infarction and scattered neuronal injury. Functional outcome at 24 h was significantly worse in Group 2 animals (spontaneous plus induced ischemic depolarizations) (neurobehavior index 43 ± 19, mean ± S.D.) compared to Group 1 rats, in which only spontaneous depolarizations occurred (neurobehavior index 24 ± 19, P < 0.05). The cumulative neurobehavioral index of Group 1 and 2 animals correlated positively with the volume of total ischemic injury ( r = 0.765, P < 0.001) and with the frequency of ischemic depolarizations ( r = 0.474, P < 0.05). Correlations between severe forelimb placing deficits and severe degrees of histological injury (necrosis or ischemic cell change) in the corresponding primary sensorimotor cortical region FR1 were significant in these rats. Group 3 rats showed severe neurobehavioral deficits at 2 and 6 h following SD stimulation (index 57 ± 1 and 39 ± 1, respectively) but returned to normal at 24 h (4 ± 0). The findings indicate that cortical spreading depression is accompanied by transient neurobehavioral deterioration and that SD in the ischemic hemisphere of animals subjected to MCA occlusion worsened functional outcome 24 h after surgery.