Calcium, network activity, and the role of NMDA channels in synaptic plasticity in vitro.

Functionally effective neuronal circuits are constructed through a competitive process that requires patterned neuronal activity elicited by structured input from the environment. To explore the mechanisms of this activity-dependent synaptic restructuring, we have developed an in vitro preparation of mouse spinal cord neurons maintained in a 3-chambered cell-culture system. Sensory afferents that received chronic electrical stimulation for 3-5 d developed stronger synaptic connections than unstimulated afferents converging onto the same postsynaptic spinal cord neuron. Exposure to 100 microM DL-2-amino-5-phosphonovaleric acid (APV), an antagonist of the NMDA channel, during the stimulation period prevented the competitive advantage associated with electric stimulation. However, when APV was applied with a higher concentration of calcium (3 mM), activity-dependent synaptic plasticity was no longer inhibited by the NMDA receptor antagonist. This reversal of APV block of the plasticity was not impaired by reducing transmitter release with 3 mM magnesium (in addition to 3 mM calcium and APV). A suppressant effect of APV on spontaneous activity was observed, which was attributed to loss of the NMDA component of the EPSP. Activity-dependent plasticity was also blocked if spontaneous activity was suppressed with dilute tetrodotoxin (TTX; 5-10 nM), a dosage that reduces excitability of neurons but is insufficient to block sodium-dependent action potentials. These experiments bring into question how NMDA channel activation is involved in the processes of synaptic remodeling during development. The data suggest that postsynaptic activity is required for synaptic remodeling, but this activity need not involve NMDA receptor activation specifically for activity-evoked synaptic plasticity. Instead, the mechanism for plasticity appears to operate through calcium-dependent processes in general.     

Invasive hemodynamic monitoring in children

Invasive monitoring is an important aspect of the care of the infant or child with multisystem organ dysfunction or severe acute respiratory failure. The indications for these procedures in children vary little from current recommendations for adults. The size, anatomy, physiologic responses, and pathophysiologic processes in children frequently require modifications in the placement and maintenance of these lines, and in the interpretation of the data. The literature suggests that although the absolute numbers may vary, broad therapeutic goals may be identified and treated in pediatric patients as in older patients.     

Clerkship directors' perceptions of the impact of HCFA documentation guidelines.

PURPOSE: Chart notes are used to support billing codes under the evaluation and management guidelines of the Health Care Financing Administration (HCFA), in addition to serving as a record of the visit. To better understand the effect of the HCFA documentation guidelines, the authors collected data on how the guidelines affect participation by university- and community-based faculty in clinical education programs. METHOD: In 2000, the authors sent six copies of their questionnaire to the associate deans of the 125 U.S. medical schools and requested they distribute them to all core clerkship directors. The questionnaire consisted of multiple-choice and short-answer questions regarding documentation of medical visits, participation of community-based faculty, understanding of HCFA documentation guidelines, and effects on education programs. RESULTS: The response rate was about 50%. Most of the 379 clerkship directors who responded (77%) stated they were aware the HCFA documentation guidelines include specifications regarding the role medical students can play and documentation of medical visits, and 64% indicated they were concerned the guidelines would affect their educational programs. Concerns included the loss of student independence and active participation in the patient care environment (37), time constraints and the changing balance between education and service (16), loss of faculty and decreased morale (11), and decreased quality of care for patients (7). CONCLUSION: Leaders of medical education must work to modify these guidelines to protect the quality of patients' care, while maximizing students' educational opportunity and participation.     

Oral and subcutaneous sumatriptan in the acute treatment of migraine: an open randomized cress-over study

In an open, randomized cross-over study in 124 patients, we compared the efficacy, safety and patient preference of oral and subcutaneous sum triptan in the acute treatment of migraine. Patients were treated for 3 attacks or 3 months and then crossed over. Primary clinical efficacy was defined as a reduction in headache severity on a four-point self-rating scale from severe (3) or moderate (2) to mild (1) or none (0), or mild (1) to none (0). Efficacy was evaluated 2 h after the administration of subcutaneous and 4h after the administration of oral sumatriptan. Subcutaneous sumatriptan was significantly more effective than oral sumatriptan in relieving headache (over all three attacks 78% vs 61% improvement), improving clinical disability (55% vs 41 % improvement) and relieving nausea (69% vs 53%), vomiting (72% vs 32%) and phono- or photophobia (67% vs 49%). Median time to recurrence was shorter after subcutaneous (12.5 h) than after oral sumatriptan (18 h); the number of patients experiencing a recurrence was similar Patients reported more adverse events after subcutaneous sumatriptan (1.32 per attack) than after the oral form (0.85 per attack), but all adverse events were mild to moderate in intensity and of short duration. Patient opinion was more often positive after subcutaneous sumatriptan. These results may be useful in counselling patients to choose between the available marketed formulations of sumatriptan.     

An improved method of flexible endoscopic creation of tracheoesophageal fistula for voice restoration

We present improvements of a previously reported method of tracheoesophageal puncture for voice restoration in postlaryngectomy patients. Our method utilizes a flexible endoscope to enable the tracheoesophageal puncture to be made under direct visualization using only local anesthesia and intravenous sedation. After 3 days, the created tracheoesophageal fistula tract is mature enough to allow placement of a voice prosthesis in the office. This allows the entire procedure to be performed in an outpatient setting with minimal risk. Received: 24 October 1996/Accepted: 24 January 1997     

超细β-磷酸三钙/聚-L-乳酸复合材料的制备与骨折内固定器的加工

目的：制备分散性良好的超细β-磷酸三钙(β-TCP)／聚-L-乳酸(PLLA)复合材料及新型可吸收骨折内固定器。方法：通过研磨方法制备β-TCP超细粒子，用一缩二乙二醇作分散剂研磨β-TCP后，再将β-TCP与PLLA超声混合，制得复合材料，经注塑加工制成可吸收骨钉，并采用扫描电镜等方法进行表征。结果与结论：用一缩二乙二醇作分散剂研磨β-TCP后再经超声混合，可以使β-TCP超细粒子在复合材料中分散均匀，粒子大小仅为300nm左右，β-TCP与PLlA基体之间结合良好。超细β-TCP／PLLA复合材料可加工成可吸收骨钉，弯曲强度达到100MPa左右，完全满足松质骨内固定的要求。