Effects of L-arginine and N~ω-nitro-L-arginine methylester on learning and memory and α7 nAChR expression in the prefrontal cortex and hippocampus of rats

Nitric oxide （NO） is a novel type of neurotransmitter that is closely associated with synaptic plasticity, learning and memory. In the present study, we assessed the effects of Larginine and NnitroL arginine methylester （LNAME, a nitric oxide synthase inhibitor） on learning and memory. Rats were assigned to three groups receiving intracerebroventricular injections of LArg （the NO precursor）, LNAME, or 0.9% NaCI （control）, once daily for seven con secutive days. Twelve hours after the last injection, they underwent an electric shockpaired Y maze test. Twentyfour hours later, the rats＇ memory of the safe illuminated arm was tested. After that, the levels of NO and a7 nicotinic acetylcholine receptor （a7 nAChR） in the prefrontal cortex and hippocampus were assessed using an NO assay kit, and immunohistochemistry and Western blots, respectively. We found that, compared to controls, LArgtreated rats received fewer foot shocks and made fewer errors to reach the learning criterion, and made fewer errors during the memorytesting session. In contrast, LNAMEtreated rats received more foot shocks and made more errors than controls to reach the learning criterion, and made more errors during the memorytesting session. In parallel, NO content in the prefrontal cortex and hippocampus was higher in LArgtreated rats and lower inLNAME rats, compared to controls. Similarly, （]7 nAChR immunoreactivity and protein expression in the prefrontal cortex and hippocampus were higher in LArgtreated rats and lower in LNAME rats, compared to controls. These results suggest that the modulation of NO content in the brain correlates with a7 nAChR distribution and expression in the prefrontal cortex and hippocampus, as well as with learning and memory performance in the Ymaze.

Ultrafast laser-scanning time-stretch imaging at visible wavelengths

Optical time-stretch imaging enables the continuous capture of non-repetitive events in real time at a line-scan rate of tens of MHz—a distinct advantage for the ultrafast dynamics monitoring and high-throughput screening that are widely needed in biological microscopy.However,its potential is limited by the technical challenge of achieving significant pulse stretching(that is,high temporal dispersion)and low optical loss,which are the critical factors influencing imaging quality,in the visible spectrum demanded in many of these applications.We present a new pulse-stretching technique,termed free-space angular-chirpenhanced delay(FACED),with three distinguishing features absent in the prevailing dispersive-fiber-based implementations:(1)it generates substantial,reconfigurable temporal dispersion in free space(41 ns nm^(−1))with low intrinsic loss(o6 dB)at visible wavelengths;(2)its wavelength-invariant pulse-stretching operation introduces a new paradigm in time-stretch imaging,which can now be implemented both with and without spectral encoding;and(3)pulse stretching in FACED inherently provides an ultrafast all-optical laser-beam scanning mechanism at a line-scan rate of tens of MHz.Using FACED,we demonstrate not only ultrafast laser-scanning time-stretch imaging with superior bright-field image quality compared with previous work but also,for the first time,MHz fluorescence and colorized time-stretch microscopy.Our results show that this technique could enable a wider scope of applications in high-speed and high-throughput biological microscopy that were once out of reach.