Effects of nitric oxide on the prefrontal cortex in stressed rats

BACKGROUND： Nitric oxide （NO） exhibits both protective and detrimental effects in the central nervous system. OBJECTIVE： To investigate the effect of NO on the prefrontal cortex in neonatal stressed rats. DESIGN, TIME AND SETTING： A randomized, controlled, animal study was performed at the Anatomical Department of Iran University of Medical Sciences from May 2007 to August 2008. MATERIALS; Forty-eight male, Wistar rats were obtained from Pasteur＇s Institute, Tehran, Iran. METHODS： Rat stress models were established by immobilization and randomly received intraperitoneal injection of 2 mL physiological saline, L-arginine （200 mg/kg） as a NO precursor, N（G）-nitro-L-arginine methyl ester （20 mg/kg）, or subcutaneous injection of 7-nitroindazole （25 mg/kg） as a NO synthase inhibitor. MAIN OUTCOME MEASURES： After the rats were treated for 4 weeks, the frontal cortex was harvested for histological observation and NO detection. RESULTS： Subcutaneous administration of N（G）-nitro-L-arginine methyl ester or 7-nitroindazole resulted in significantly lower prefrontal cortex thickness and NO production compared with subcutaneous administration of L-arginine （P 〈 0.05）. Prefrontal cortex thickness significantly increased in rats following L-arginine treatment, compared with physiological saline intervention （P 〈 0.05）. CONCLUSION： NO exhibited protective effects on the prefrontal cortex of stressed rats.

The worldwide allometric relationship in anatomical structures for plant roots

The cortex(i.e.,absorptive tissue)and stele(transportive vascular tissue)are fundamental to the function of plant roots.Unraveling how these anatomical structures are assembled in absorptive roots is essential for our understanding of plant ecology,physiology,and plant responses to global environmental changes.In this review,we first compile a large data set on anatomical traits in absorptive roots,including cortex thickness and stele radius,across 698 observations and 512 species.Using this data set,we reveal a common root allometry in absorptive root structures,i.e.,cortex thickness increases much faster than stele radius with increasing root diameter(hereafter,root allometry).Root allometry is further validated within and across plant growth forms(woody,grass,and liana species),mycorrhiza types(arbuscular mycorrhiza,ectomycorrhiza,and orchid mycorrhizas),phylogenetic gradients(from ferns to Orchidaceae),and environmental change scenarios(e.g.,elevation of atmospheric CO_(2)concentration and nitrogen fertilization).These findings indicate that root allometry is common in plants.Importantly,root allometry varies greatly across species.We then summarize recent research on the mechanisms of root allometry and potential issues regarding these mechanisms.We further discuss ecological and evolutionary implications of root allometry.Finally,we propose several important research directions that should be pursued regarding root allometry.

Altered relationship between thickness and intrinsic activity amplitude in generalized tonic–clonic seizures

A thinner cortex has higher potential for binding GABA receptor A which is associated with larger amplitudes of intrinsic brain activity(i BA). However, the relationship between cortical thickness and i BA is unknown in intact and epileptic brains. To this end, we investigated the relationship between cortical thickness measured by highresolution MRI and surface-based i BA derived from resting-state functional MRI in normal controls(n = 82) andpatients with generalized tonic–clonic seizures(GTCS)only(n = 82). We demonstrated that the spatial distribution of cortical thickness negatively correlated with surface-based i BA amplitude at both whole-brain and within independent brain functional networks. In GTCS patients,spatial coupling between thickness and i BA amplitude decreased in the default mode, dorsal attention, and somatomotor networks. In addition, the vertex-wise acrosssubject thickness–i BA amplitude correspondence altered in the frontal and temporal lobes as well as in the precuneus in GTCS patients. The relationship between these two modalities can serve as a brain-based marker for detecting epileptogenic changes.