Rapid and local autoregulation of cerebrovascular blood flow: a deep-brain imaging study in the mouse.

The brain obtains energy by keeping the cerebral blood flow constant against unexpected changes in systemic blood pressure. Although this homeostatic mechanism is widely known as cerebrovascular autoregulation, it is not understood how widely and how robustly it works in the brain. Using a needle-like objective lens designed for deep-tissue imaging, we quantified the degree of autoregulation in the mouse hippocampus with single-capillary resolution. On average, hippocampal blood flow exhibited autoregulation over a comparatively broad range of arterial blood pressure and did not significantly respond to pressure changes induced by the pharmacological activation of autonomic nervous system receptors, whereas peripheral tissues showed linear blood flow changes. At the level of individual capillaries, however, about 40% of hippocampal capillaries did not undergo rapid autoregulation. This heterogeneity suggests the presence of a local baroreflex system to implement cerebral autoregulation.

In vivo imaging of the dendritic arbors of layer V pyramidal cells in the cerebral cortex using a laser scanning microscope with a stick-type objective lens.

In the field of neuroscience, low-invasive in vivo imaging would be a very useful method of monitoring the morphological dynamics of intact neurons in living animals. At present, there are two widely used in vivo imaging methods; one is the two-photon microscope method, and the other is the fiber optics method. However, these methods are not suitable for the in vivo imaging of deeper subcortical structures. In our study, we have developed a novel method for the in vivo imaging of pyramidal neurons in layer V of the cerebral cortex, utilizing a MicroLSM system and a stick-type objective lens that can be directly inserted into the target tissue. By using this method, we succeeded in obtaining clear images of pyramidal neurons in layer V of the cerebral cortex under a low-invasive condition. The MicroLSM system is a useful and versatile in vivo imaging system that will be applicable not only to the brain but also to other organs.