Temporal course of gene expression during motor memory formation in primary motor cortex of rats.

Motor learning is associated with plastic reorganization of neural networks in primary motor cortex (M1) that depends on changes in gene expression. Here, we investigate the temporal profile of these changes during motor memory formation in response to a skilled reaching task in rats. mRNA-levels were measured 1h, 7h and 24h after the end of a training session using microarray technique. To assure learning specificity, trained animals were compared to a control group. In response to motor learning, genes are sequentially regulated with high time-point specificity and a shift from initial suppression to later activation. The majority of regulated genes can be linked to learning-related plasticity. In the gene-expression cascade following motor learning, three different steps can be defined: (1) an initial suppression of genes influencing gene transcription. (2) Expression of genes that support translation of mRNA in defined compartments. (3) Expression of genes that immediately mediates plastic changes. Gene expression peaks after 24h - this is a much slower time-course when compared to hippocampus-dependent learning, where peaks of gene-expression can be observed 6-12h after training ended.

Neurologic prognosis and withdrawal of life support after resuscitation from cardiac arrest.

OBJECTIVE: To study the impact of neurologic prognostication on the decision to withdraw life-sustaining therapies (LST) in comatose patients resuscitated after cardiac arrest. METHODS: The authors prospectively studied a consecutive series of post-resuscitation comatose patients referred for neurologic prognostication at a single center for 4 years. For most patients, neurologic prognostication was not sought due to early death or rapid return to consciousness. Prognostication was based on Glasgow Coma Score (GCS) and Brainstem Reflex Score (BRS), with EEG and cortical evoked potentials (CEP), which were graded as benign, uncertain, and malignant. The outcomes were as follows: survivors (Group S), brain or cardiac death (Group D), and death from withdrawal of life sustaining therapy (Group W). In Group W, the time interval to withdrawal of LST was analyzed by EEG and CEP grades. RESULTS: Of 58 patients studied, 10 were in Group S, 8 in Group D, and 40 in Group W. Initial median GCS and BRS was similar for all groups with significant improvement noted in Group S, but not in Group D or Group W. In Group W, CEP grade correlated with the median duration of continued therapy before a decision to withdraw LST: 7 days for benign CEP, 2 days for uncertain CEP, and 1 day for malignant CEP, p = 0.0004. CONCLUSION: In patients with poor neurologic recovery early after resuscitation from cardiac arrest, physicians appear to use the cortical evoked potential grade to estimate prognosis. Cortical evoked potential grade correlated with the waiting time until life sustaining therapies were withdrawn after no improvement in neurologic examination was seen.