Brain networks involved in generalized periodic discharges (GPD) in post-anoxic-ischemic encephalopathy

AIM

Generalized periodic discharge (GPD) is an EEG pattern of poor neurological outcome, frequently observed in comatose patients after cardiac arrest. The aim of our study was to identify the neuronal network generating ≤2.5 Hz GPD using EEG source localization and connectivity analysis.

METHODS

We analyzed 40 comatose adult patients with anoxic-ischemic encephalopathy, who had 19 channel-EEG recording. We computed electric source analysis based on distributed inverse solution (LAURA) and we estimated cortical activity in 82 atlas-based cortical brain regions. We applied directed connectivity analysis (Partial Directed Coherence) on these sources to estimate the main drivers.

RESULTS

Source analysis suggested that the GPD are generated in the cortex of the limbic system in the majority of patients (87.5%). Connectivity analysis revealed main drivers located in thalamus and hippocampus for the large majority of patients (80%), together with important activation also in amygdala (70%).

CONCLUSIONS

We hypothesize that the anoxic-ischemic dysfunction, leading to hyperactivity of the thalamo-cortical (limbic presumably) circuit, can result in an oscillatory thalamic activity capable of inducing periodic cortical (limbic, mostly medial-temporal and orbitofrontal) discharges, similarly to the case of generalized rhythmic spike-wave discharge in convulsive or non-convulsive status epilepticus.

Effect of hypocapnia on extracellular glutamate and glycine concentrations during the periischemic period in rabbit hippocampus

Glutamate (GLU) is a neurotransmitter. Massive release of GLU and glycine (GLY) into the brain's extracellular space may be triggered by ischemia, and may result in acute neuronal lysis or delayed neuronal death. The aim of this study was to evaluate the possible relationship between hyperventilation and the level of GLU and GLY during brain ischemia. Rabbits were anesthetized with halothane and oxygen. Group 1 was allowed to hyperventilate (PaCO2 25-35 mmHg). PaCO2 was maintained throughout the study. Group 2 was a normal control group that maintained normocapnia. Two global cerebral ischemic episodes were produced. Microdialysate was collected during the periischemic and reperfusion periods from the dorsal hippocampus. GLU and GLY concentrations were determined using high-performance liquid chromatography. In the control group, GLU and GLY were significantly elevated during each episode of ischemia; these levels returned to baseline within 10 minutes after reperfusion. In contrast, in the hyperventilation group GLU and GLY concentrations increased during ischemia, but they were not statistically significant. Two way ANOVA for the periischemic periods (t = 15,80; p = 0.06) revealed lower GLU values for the hyperventilated animals. A similar analysis for periischemic GLY concentrations revealed significantly lower values in the hyperventilated group (t = 10,15,75,80: p = 0.03) as compared to normal controls. We were able to demonstrate that hypocapnia during periischemic period lowered extracellular GLU and GLY concentrations. These results can explain a part of the protective action of hypocapnia during cerebral ischemia.

Early prediction of individual outcome after cardiopulmonary resuscitation

Prediction of individual outcome after cardiopulmonary resuscitation is of major medical, ethical, and socioeconomic interest but uncertain. We studied the early predictive potency of evoked potential recording after cardiac arrest in 66 resuscitated patients who returned to spontaneous circulation but were unconscious and mechanically ventilated. Detailed long-latency and short-latency sensory evoked potentials were recorded and neurological evaluations were done 4-48 h after admission to intensive care. In all 17 patients with favourable outcome (cerebral performance categories 1 and 2) the cortical evoked potential N70 peak, a reliable measure of cortical function, was detected between 74 and 116 ms. In 49 patients with bad outcome (categories 4 and 5) the N70 peak was absent in 35 or found with a delay between 121 and 171 ms in 14 (p < 0.05 vs favourable outcome). Thus the predictive ability was 100% with cutoff of 118 ms. To confirm reproducibility and validity, repeated tracings, and linked-earlobe referenced techniques were done and gave similar results. Early recording of long-latency evoked potentials after cardiopulmonary resuscitation is highly predictive of outcome.

Changes in extracellular concentrations of glutamate, aspartate, glycine, dopamine, serotonin, and dopamine metabolites after transient global ischemia in the rabbit brain

Although considerable evidence supports a role for excitatory amino acids in the pathogenesis of ischemic neuronal injury, few in vivo studies have examined the effect of increasing durations of ischemia on the extracellular concentrations of these agents. Recently, other neurotransmitters (e.g., glycine and dopamine) have been implicated in the mechanism of ischemic neuronal injury. Accordingly, this study was undertaken to examine the patterns of changes of extracellular glutamate, aspartate, glycine concentrations in the hippocampus, and dopamine, serotonin, and dopamine metabolites in the caudate nucleus with varying durations (5, 10, or 15 minutes) of transient global cerebral ischemia as evidence to support their pathogenetic roles. Microdialysis was used to sample the brain's extracellular space before, during, and after the ischemic period. Glutamate and aspartate concentrations in the dialysate increased from baseline by 1-, 5-, and 13-fold and by 4-, 9-, and 31-fold, respectively, for the three ischemic durations. The concentrations returned to baseline rapidly after reperfusion. The peak concentrations of glutamate and aspartate were significantly higher with increasing ischemic duration. Dopamine concentrations increased by approximately 700-fold in response to all three ischemic durations and returned to baseline within 10 min of reperfusion. Glycine, in contrast, increased during ischemia by a mean of 4-fold, but remained elevated throughout the 80-min period of reperfusion. The final concentrations of glycine were significantly higher than baseline levels (p = 0.0002, Mann-Whitney test). That glutamate and aspartate concentrations in the hippocampus co-vary with the duration of global ischemia is taken as supportive evidence of their pathogenetic role in ischemic neuronal injury.(ABSTRACT TRUNCATED AT 250 WORDS)