Spinal neuronal activation during locomotor-like activity enabled by epidural stimulation and 5-hydroxytryptamine agonists in spinal rats.

UNLABELLED: The neural networks that generate stepping in complete spinal adult rats remain poorly defined. To address this problem, we used c-fos (an activity-dependent marker) to identify active interneurons and motoneurons in the lumbar spinal cord of adult spinal rats during a 30-min bout of bipedal stepping. Spinal rats were either step trained (30 min/day, 3 days/week, for 7.5 weeks) or not step trained. Stepping was enabled by epidural stimulation and the administration of the serotonergic agonists quipazine and 8-OHDPAT. A third group of spinal rats served as untreated (no stimulation, drugs, or stepping) controls. The numbers of activated cholinergic central canal cluster cells and partition neurons were higher in both step-trained and nontrained rats than in untreated rats and were higher in nontrained than in step-trained rats. The latter finding suggests that daily treatment with epidural stimulation plus serotonergic agonist treatment without step training enhances the excitability of a broader cholinergic interneuronal population than does step training. The numbers of activated interneurons in laminae II-VI of lumbar cross-sections were higher in both step-trained and nontrained rats than in untreated rats, and they were highest in step-trained rats. This finding suggests that this population of interneurons is responsive to epidural stimulation plus serotonergic treatment and that load-bearing induced when stepping has an additive effect. The numbers of activated motoneurons of all size categories were higher in the step-trained group than in the other two groups, reflecting a strong effect of loading on motoneuron recruitment. In general, these results indicate that the spinal networks for locomotion are similar with and without brain input. SIGNIFICANCE: We identified neurons within the spinal cord networks that are activated during assisted stepping in paraplegic rats. We stimulated the spinal cord and administered a drug to help the rats step. One group was trained to step and another was not trained. We observed a lower percentage of activated neurons in specific spinal cord regions in trained rats than in nontrained rats after a 1-hr stepping bout, suggesting that step training reduces activation of some types of spinal neurons. This observation indicates that training makes the spinal networks more efficient and suggests a "learning" phenomenon in the spinal cord without any brain input.

Prognosis of Low-Risk Young Women Presenting to the Emergency Department With Chest Pain.

Identification of patients at low risk presenting to the emergency department with chest pain is a continuing challenge. We examined a cohort of low-risk women with negative cardiac injury markers, electrocardiogram with normal results, and clinical stability. We hypothesized that these patients can be safely and accurately managed in a chest pain unit (CPU), may not require predischarge cardiac testing, and have an excellent short-term prognosis. The primary end point was major cardiovascular events during index admission or follow-up. Mean age of the 403 women was 42 ± 4.3 years (30 to 50 years). No patient had a cardiovascular event in the CPU, and none of the 321 patients followed for 6 months had a late cardiovascular event. Most (211, 52%) did not receive predischarge cardiac testing. The remaining 192 patients (48%) had predischarge exercise treadmill test, stress imaging, or cardiac catheterization. Of those patients who underwent treadmill testing, almost 90% had no exercise-induced chest pain and approximately 50% had functional capacity 8 to 14 METs. In addition, 166 patients (41%) were discharged from the CPU after <2 hours and 21% (n = 86) within 2 to 8 hours. In conclusion, this group of low-risk women was safely and accurately managed in the CPU and discharged promptly. There were no cardiac events on index admission or 6-month follow-up, and in most patients, predischarge cardiac testing was unnecessary.