[Effects of snow removal on soil labile nitrogen in a subalpine spruce forest of western Sichuan, China]. / 雪被去除对川西亚高山云杉林土壤活性氮的影响.

Warming-induced decrease in seasonal snow cover has a great potential to affect soil nitrogen cycle in alpine cold forest ecosystems. In this study, a wooden-shelter method was used to remove the snow accumulation. Soil nitrogen pools and mineralization rates in the snow removal and control plots were measured synchronously in three critical periods (early snow cover, deep snow cover and snow cover melting) in a subalpine spruce forest of western Sichuan, China. Seasonal snow cover kept soil from cold air temperature. Snow removal decreased average and minimum soil temperatures (5 cm) by 0.33 and 1.17 ℃, respectively. In addition, snow removal caused a positive effect on soil frost depth and freeze-thaw cycle. There was a significant dynamic in soil labile nitrogen pool among different periods. Snow removal on average increased NH4+-N, NO3--N and dissolved organic nitrogen (DON) contents by 38.6%, 23.5% and 57.3%, respectively, over the winter. Moreover, snow removal increased soil net nitrification and mineralization rates in the snow co-ver melting period. Overall, warming-induced decrease in snow cover could stimulate winter soil nitrogen cycle of subalpine forests.

Topographic variations of the optic chiasm and the pituitary stalk: a morphometric study based on midsagittal T2-weighted MR images.

PURPOSE: This study was conducted to characterize topographic variations of the optic chiasm (OC) and the pituitary stalk (PS) in situ based on MR images. METHODS: Normal T2-weighted midsagittal MR images were obtained in 157 children and 323 adults. The height of OC (PC) and the inclination angle of PS (PS-AP angle) were measured in each case. All chiasms were classified into prefixed, normal and postfixed types, and low, medium and high types, respectively. All stalks were performed classification (prefixed, centered and postfixed PS) and grading (Grade 1-3 according to the relationship between PS and the dorsum sellae), respectively. RESULTS: PC averaged 4.33 ± 1.59 mm. Adults had a greater PC (P = 0.023) than children. There were 80 (16.7 %) prefixed, 354 (73.8 %) normal and 46 (9.6 %) postfixed chiasms, and 112 (23.3 %), 295 (61.5 %) and 73 (15.2 %) cases with low, medium and high OC, respectively. High OC was more frequent in adults than in children (P = 0.001). The mean PS-AP angle of the whole group was 59.47 ± 8.62º. Children had a greater PS-AP angle than adults (P = 0.012). Adults had a greater percentage of postfixed (P = 0.000) and grade 3 (P = 0.000) PS than children, whereas centered (P = 0.002) and grade 1 (P = 0.001) PS were more prevalent in children than in adults. CONCLUSIONS: The classifications of OC and PS based on MR images reflect the topographic variations of their real position in vivo. It would be helpful to identify and characterize the anomalies involving OC and PS and understand the anatomical and physiological influence in pathological situations.

Stereotactic neurosurgical technique and electrophysiological study in ablating the ventromedial shell of the nucleus accumbens.

OBJECTIVE: To describe in as much detail as possible the method for ablating the ventromedial shell of the nucleus accumbens (NAc) and investigate the efficacy and safety of the ablation treatment. METHODS: Sixty-five patients with drug addictions received operations within the time frame from 2004 to 2009. The ablation targets were located in the bilateral medial posterior inferior shell of the NAc. Intraoperative electrophysiological monitoring was performed. RESULTS: Tissue impedance in the shell of the NAc varied from 185 to 355 Ω. When stimulated with a low frequency (2 Hz) and a voltage above 3 V, 57 out of 65 (87.7%) patients experienced slight throbbing sensations. During the lesion procedure, fever was detected on the head and face of 59 patients (90.8%), the heart rate decreased in 19 cases (29.2%), and restlessness, irritability and hyperalgia were noted for all patients. Among the 65 patients, 52 (80%) no longer experienced a psychological craving for the drug. CONCLUSIONS: The shell of the NAc may be a promising surgical target for psychosurgery. Electrophysiological recordings revealed that the shell is indeed an appropriate structure.

[Proton magnetic resonance spectroscopic imaging of the hippocampus in schizophrenia patients before and after surgery].

OBJECTIVE: To explore the features of proton magnetic resonance spectroscopy (1H-MRS) of the hippocampus in schizophrenia patients before and after stereotactic neurosurgery. METHODS: 1H-MRS was performed to determine NAA/Cr and CHO/Cr ratios on the bilateral hippocampal regions before and after stereotactic neurosurgery in 20 schizophrenia patients, with 20 healthy individuals as the controls. RESULTS: The NAA/Cr ratio in the hippocampal regions was significantly lower and the CHO/Cr ratio significantly higher in schizophrenia patients before the surgery than in the healthy controls (P<0.01). The NAA/Cr and CHO/Cr ratios in the hippocampal regions underwent no significant changes in the patients after the surgeries (P>0.05). CONCLUSION: Neuronal and cell membrane metabolism impairment is present in the hippocampus of schizophrenia patients, and stereotactic neurosurgery does not produce obvious adverse effects on the cell membrane metabolism in the hippocampus of the patients.

[Radiation-induced rat cerebral neuron apoptosis].

OBJECTIVE: To explore the correlation between X-ray-induced rat cerebral neuron apoptosis and radiation doses. METHODS: In a controlled experiment, the rats in the experimental group received X-ray radiation at different doses (2, 4, 6 and 8 Gy), and the apoptotic cerebral neurons were counted after in situ end-labeling and immunohistochemical staining. RESULTS: X-ray radiation induced apoptosis of rat cerebral neurons, and the apoptotic rate varied with the radiation doses. Significant difference in the apoptotic rate was noted before and after radiation (P<0.0001), and between different radiation dose groups (P<0.005). The apoptotic rate differed significantly at different time points after the radiation. CONCLUSION: Low or medium doses of X-ray is able to induce rat cerebral neuron apoptosis depending on the radiation doses and following a definable time course.

[Ultrastructural features of cultured rat cortical astrocytes with stretch-induced injury].

OBJECTIVE: To investigate the changes of ultrastructural features of cultured rat cortical astrocytes after stretch-induced injury. METHODS: Rat cortical astrocytes isolated from 1- to 2-day-old rats were cultured till confluency, and then plated in tissue culture wells with flexible silastic bottom after purification. A computer-controlled device was used to produce stretch-induced injury in the astrocytes with the imposed pressure of 50, 150, and 250 kPa respectively, followed by observation of the ultrastructural changes in the astrocytes with light and electron microscopy. RESULTS: Obvious ultrastructural destruction of the astrocytes occurred when the imposed stretch pressure was 50 kPa, and scanning electron microscopy demonstrated increased intercellular space and laceration of the cell body and its processes. Transmission electron microscopy revealed mitochondria swelling 1 h after stretch-induced injury and 6 h after the injury, vacuolar degeneration of the mitochondria occurred. Increased stretch pressure caused further decrease in the amount of glial filaments and densification of astrocytes. CONCLUSIONS: Stress, even at a relatively small scale, can cause disruption of intercellular juncture and ultrastructural change of the cultured astrocyte, which may be related with extensive brain edema after traumatic brain injury.

Radiosurgical treatment of intractable epilepsy with low radiation dose.

OBJECTIVE: To localize the epileptic foci with positron emission tomography (PET), and study the principles of target definition and method to determine the optimal range of exposure in radiosurgery for intractable epilepsy. METHODS: This study included 176 patients with intractable epilepsy, who received linear accelerator radiosurgery after (18)F-FDG PET for epileptic foci localization. The patients were divided according to different peripheral doses used in the treatment into Group A in which radiation dose of 9 to 11 Gy was used, Group B with 11 to 13 Gy and Group C with exposure to over 13 Gy. Follow-up study was conducted in all the patients for a period ranging from 3 to 16 months, during which the frequency of seizure after treatment was recorded to evaluate the therapeutic effect. RESULTS: The seizure frequency significantly decreased after radiosurgical treatment in all the groups, but between the groups, the decrement evinced no significant difference. According to Wieser's classification of the effect after operation, 46.9% cases belonged to grade I to II and 41.5% to grade III to IV. Obvious complications were not observed, nor did disability or mortality occurred in these cases. CONCLUSIONS: Stereotactic radiosurgery with low radiation dose under the guidance of PET provides a safe, effective and minimally invasive surgical approach for patients with intractable epilepsy, and peripheral radiation doses of 9 to 11 Gy for the epileptic foci localized by PET is sufficient to ensure good clinical outcome.