Label-free chemical contrast is highly desirable in biomedical imaging. Spontaneous Raman microscopy provides specific vibrational signatures of chemical bonds, but is often hindered by low sensitivity. Here we report a three-dimensional multiphoton vibrational imaging technique based on stimulated Raman scattering (SRS). The sensitivity of SRS imaging is significantly greater than that of spontaneous Raman microscopy, which is achieved by implementing high-frequency (megahertz) phase-sensitive detection. SRS microscopy has a major advantage over previous coherent Raman techniques in that it offers background-free and readily interpretable chemical contrast. We show a variety of biomedical applications, such as differentiating distributions of omega-3 fatty acids and saturated lipids in living cells, imaging of brain and skin tissues based on intrinsic lipid contrast, and monitoring drug delivery through the epidermis.

Docosahexaenoic acid (DHA), an n-3 long chain polyunsaturated fatty acid (LC-PUFA), highly enriched in the central nervous system, is critical for brain development and function. It has been shown that DHA deficiency impairs cognitive performance whereas DHA supplementation improves the condition. However, the mechanisms underlying the role of DHA in brain development and function remain to be elucidated. By using transgenic fat-1 mice rich in endogenous n-3 PUFA, we show that increased brain DHA significantly enhances hippocampal neurogenesis shown by an increased number of proliferating neurons and neuritogenesis, evidenced by increased density of dendritic spines of CA1 pyramidal neurons in the hippocampus. Concurrently, fat-1 mice exhibit a better spatial learning performance in the Morris water maze compared with control WT littermates. In vitro experiments further demonstrate that DHA promotes differentiation and neurite outgrowth of neuronal cells derived from mouse ES cells and increases the proliferation of cells undergoing differentiation into neuronal lineages from the ES cells. These results together provide direct evidence for a promoting effect of DHA on neurogenesis and neuritogenesis and suggest that this effect may be a mechanism underlying its beneficial effect on behavioral performance.cognitive function ͉ omega-3 fatty acids ͉ transgenic fat-1 mice ͉ neural stem cells D ocosahexaenoic acid (22:6n-3, DHA) is an omega-3 (n-3) long chain polyunsaturated fatty acid (LC-PUFA) that is highly enriched in the central nervous system, particularly in the synaptosomal membrane, synaptic vesicles, growth cones, and the retina photoreceptors (1). DHA serves not only as a building block for neural development, but also as a functional molecule to maintain proper fluidity of neuronal membranes and modulate neurochemical, gene expression, and memory processes (2). Clinical evidence indicates that term infants given formula supplemented with either DHA plus arachidonic acid or DHA alone have substantially better visual acuity (3) and improved cognitive ability (4). Animal studies revealed that deficiency of DHA resulted in a poorer performance on cognitive and behavioral tests whereas supplementation with DHA led to recovery of learning and memory-related performance (5). Furthermore, neurodegeneration and neuropsychiatric disorders are related to a low level of DHA, and supplementation with DHA ameliorated the symptoms (6). These studies suggest that DHA plays a key role in the development and function of the central nervous system. However, the mechanisms underlying the effects of DHA on brain development and function remain to be elucidated.The dentate gyrus (DG) has been an intensively investigated area of the hippocampus because DG is one of the few brain regions where neurogenesis takes place throughout the life span of mammals and where new memories are formed (7). In addition, DG is critical for normal cognitive function, and dysfunctions in this region are linked to diverse clinical conditions (e.g.,...

The development of cardiac hypertrophy in response to increased hemodynamic load and neurohormonal stress is initially a compensatory response that may eventually lead to ventricular dilation and heart failure. Regulator of G protein signaling 5 (Rgs5) is a negative regulator of G protein-mediated signaling by inactivating Gα(q) and Gα(i), which mediate actions of most known vasoconstrictors. Previous studies have demonstrated that Rgs5 expresses among various cell types within mature heart and showed high levels of Rgs5 mRNA in monkey and human heart tissue by Northern blot analysis. However, the critical role of Rgs5 on cardiac remodeling remains unclear. To specifically determine the role of Rgs5 in pathological cardiac remodeling, we used transgenic mice with cardiac-specific overexpression of human Rgs5 gene and Rgs5 −/− mice. Our results demonstrated that the transgenic mice were resistant to cardiac hypertrophy and fibrosis through inhibition of MEK-ERK1/2 signaling, whereas the Rgs5 −/− mice displayed the opposite phenotype in response to pressure overload. These studies indicate that Rgs5 protein is a crucial component of the signaling pathway involved in cardiac remodeling and heart failure.