Artificial Synapse: Spatiotemporal Heterogeneities in Dopamine Electrochemistry at a Carbon Fiber Ultramicroelectrode.

An artificial synapse is developed that mimics ultramicroelectrode (UME) amperometric detection of single cell exocytosis. It comprises the nanopipette of a scanning ion conductance microscope (SICM), which delivers rapid pulses of neurotransmitter (dopamine) locally and on demand at >1000 defined locations of a carbon fiber (CF) UME in each experiment. Analysis of the resulting UME current-space-time data reveals spatiotemporal heterogeneous electrode activity on the nanoscale and submillisecond time scale for dopamine electrooxidation at typical UME detection potentials. Through complementary surface charge mapping and finite element method (FEM) simulations, these previously unseen variations in electrochemical activity are related to heterogeneities in the surface chemistry of the CF UME.

Maximal venous outflow velocity: an index for iliac vein obstruction.

Leg swelling is a common cause for vascular surgical evaluation, and iliocaval obstruction due to May-Thurner syndrome (MTS) can be difficult to diagnose. Physical examination and planar radiographic imaging give anatomic information but may miss the fundamental pathophysiology of MTS. Similarly, duplex ultrasonographic examination of the legs gives little information about central impedance of venous return above the inguinal ligament. We have modified the technique of duplex ultrasonography to evaluate the flow characteristics of the leg after tourniquet-induced venous engorgement, with the objective of revealing iliocaval obstruction characteristic of MTS. Twelve patients with signs and symptoms of MTS were compared with healthy control subjects for duplex-derived maximal venous outflow velocity (MVOV) after tourniquet-induced venous engorgement of the leg. The data for healthy control subjects were obtained from a previous study of asymptomatic volunteers using the same MVOV maneuvers. The tourniquet-induced venous engorgement mimics that caused during vigorous exercise. A right-to-left ratio of MVOV was generated for patient comparisons. Patients with clinical evidence of MTS had a mean right-to-left MVOV ratio of 2.0, asymptomatic control subjects had a mean ratio of 1.3, and MTS patients who had undergone endovascular treatment had a poststent mean ratio of 1.2 (P = 0.011). Interestingly, computed tomography and magnetic resonance imaging results, when available, were interpreted as positive in only 53% of the patients with MTS according to both our MVOV criteria and confirmatory venography. After intervention, the right-to-left MVOV ratio in the MTS patients was found to be reduced similar to asymptomatic control subjects, indicating a relief of central venous obstruction by stenting the compressive MTS anatomy. Duplex-derived MVOV measurements are helpful for detection of iliocaval venous obstruction, such as MTS. Right-to-left MVOV ratios and postengorgement spectral analysis are helpful adjuncts to duplex imaging for leg swelling. The MVOV maneuvers are well tolerated by patients and yields physiological data regarding central venous obstruction that computed tomography and magnetic resonance imaging fail to detect.

Endocrine response after gamma knife-based stereotactic radiosurgery for secretory pituitary adenoma.

PURPOSE: To examine treatment outcomes of Gamma Knife-based stereotactic radiosurgery (GK-based SRS) for secretory pituitary adenomas. MATERIALS AND METHODS: 25 patients were treated with GK-based SRS for secretory pituitary adenomas with >or=12 months of follow-up. RESULTS: For prolactinomas, 2 of 4 patients (50%) showed normalization of serum prolactin at a mean time of 18 months. One of 4 had a >or=50% decrease but still abnormal prolactin levels. For adrenocorticotrophic hormone-secreting tumors, 6 of 12 patients (50%) showed normalization of their endocrine levels at a median of 10 months. An additional 2 (17%) had a >or=50% decrease. For growth hormone-secreting tumors, 4 of 9 patients (44%) showed normalization of endocrine levels at a median time of 30 months. Two patients (22%) had >or=50% lower but abnormal endocrine levels. CONCLUSION: GK-based SRS provides a reasonable rate of endocrine normalization of secretory pituitary adenoma. The time to endocrine response is shorter than reported for fractionated external beam radiotherapy. There is a low risk of optic neuropathy.

Acromegaly caused by a growth hormone-releasing hormone-secreting carcinoid tumor: case report.

OBJECTIVE AND IMPORTANCE: We describe a patient with acromegaly and pituitary hyperplasia secondary to a growth hormone-releasing hormone-secreting gastrointestinal carcinoid tumor. This case report illustrates the importance of including this rare clinical syndrome in the differential diagnosis of acromegaly for patients with suspected or known neuroendocrine tumors. CLINICAL PRESENTATION: A 19-year-old, Asian-American, male patient with a 2-year history of a nonresectable, metastatic, intestinal carcinoid tumor presented with complaints of headaches, arthralgias, sweats, and changing features. The examination revealed a young subject with acromegalic features, without visual field deficits. Magnetic resonance imaging revealed a diffuse sellar mass that extended suprasellarly to compress the optic chiasm. Endocrinological studies demonstrated a growth hormone level of more than 100 ng/ml and an inappropriately elevated growth hormone-releasing hormone level. INTERVENTION: The patient underwent transsphenoidal resection of the pituitary mass for diagnostic and decompressive purposes. The pathological examination revealed pituitary hyperplasia, without evidence of an adenoma. Therapy with long-acting repeatable octreotide (Sandostatin LAR; Novartis AG, Basel, Switzerland) was initiated postoperatively, to further control the acromegaly and carcinoid tumor. The soft-tissue swelling resolved, and the patient remained free of headaches, arthralgias, and sweats at the 6-month follow-up examination. CONCLUSION: Ectopic acromegaly is a rare syndrome that must be recognized by neurosurgeons because its treatment differs from that of classic pituitary acromegaly. We describe a patient for whom this syndrome was documented with magnetic resonance imaging, endocrinological testing, and pathological examinations.