[Fluorescence microscopy for brain activity imaging: one-photon microscopy and its application to pharmacological research].

The development of genetically-encoded fluorescent probes for the detection of intracellular calcium ions and various neurotransmitters has progressed significantly in recent years, and there is a growing need for techniques that rapidly and efficiently image these signals in the living brain for pharmacological studies of the central nervous system. In this article, we discuss one-photon fluorescence microscopy techniques used for brain activity imaging, particularly wide-field imaging and head-mounted miniaturized microscopy, and introduce their basic principles, recent advances, and applications in pharmacological research. Wide-field calcium imaging is suitable for mesoscopic observation of cortical activity during behavioral tasks in head-fixed awake mice, while head-mounted miniaturized microscopes can be attached to the animal's head to image brain activity associated with naturalistic behaviors such as social behavior and sleep. One-photon microscopy allows for the development of a simple and cost-effective imaging system using an affordable excitation light source such as a light-emitting diode. Its excitation light illuminates the entire field of view simultaneously, making it easy to perform high-speed imaging using a high-sensitivity camera. In contrast, the short wavelength of the excitation light limits the field of observation to areas on or near the brain surface due to its strong light scattering. Moreover, the out-of-focus fluorescence makes it difficult to obtain images with a high signal-to-noise ratio and spatial resolution. The use of one-photon microscopy in brain activity imaging has been limited compared to two-photon microscopy, but its advantages have recently been revisited. Therefore, this technique is expected to become a useful method for pharmacologists to visualize the activity of the living brain.

Nicotine promotes angiogenesis in mouse brain after intracerebral hemorrhage.

Here we examined the effect of nicotine on angiogenesis in the brain after intracerebral hemorrhage (ICH), as angiogenesis is considered to provide beneficial effects on brain tissues during recovery from injury after stroke. Nicotine was administered to C57BL/6 mice suffering from collagenase-induced ICH in the striatum, either by inclusion in drinking water or by daily intraperitoneal injection. Nicotine administration by both routes enhanced angiogenesis within the hematoma-affected regions, as revealed by increased CD31-immunopositive area at 7 and 14 d after ICH. Double immunofluorescence histochemistry against CD31 and proliferating cell nuclear antigen revealed that nicotine increased the number of newly generated vascular endothelial cells within the hematoma. In spite of enhanced angiogenesis, nicotine did not worsen vascular permeability after ICH, as assessed by Evans Blue extravasation. These effects of nicotine were accompanied by an increased number of surviving neurons in the hematoma at 7 d after ICH. Unexpectedly, nicotine did not increase expression of vascular endothelial growth factor mRNA in the brain and did not enhance recruitment of endothelial progenitor cells from the bone marrow. These results suggest that nicotine enhances angiogenesis in the brain after ICH, via mechanisms distinct from those involved in its action on angiogenesis in peripheral tissues.

Laquinimod and 3,3'-diindolylemethane alleviate neuropathological events and neurological deficits in a mouse model of intracerebral hemorrhage.

We examined the effects of compounds shown to activate aryl hydrocarbon receptor (AhR) signaling on a mouse model of intracerebral hemorrhage (ICH). Daily oral administration of laquinimod (25 mg/kg) or 3,3'-diindolylmethane (250 mg/kg) from 3 h after ICH induction improved motor functions, prevented the decrease of neurons within the hematoma, and attenuated activation of microglia/macrophages and astrocytes in the perihematomal region as well as infiltration of neutrophils into the hematoma. Elevated expression of AhR was detected in microglia and neutrophils, and both drugs inhibited upregulation of interleukin-6 and CXCL1. These results propose AhR as a therapeutic target for ICH.

A Nurr1 agonist amodiaquine attenuates inflammatory events and neurological deficits in a mouse model of intracerebral hemorrhage.

Inflammatory responses are considered to play pivotal roles in the pathogenesis of intracerebral hemorrhage (ICH). Here we show that a nuclear receptor Nurr1 (NR4A2) was expressed prominently in microglia/macrophages and astrocytes in the perihematomal region in the striatum of mice after ICH. Daily administration of a Nurr1 agonist amodiaquine (40 mg/kg, i.p.) from 3 h after ICH induction diminished perihematomal activation of microglia/macrophages and astrocytes. Amodiaquine also suppressed ICH-induced mRNA expression of IL-1ß, CCL2 and CXCL2, and ameliorated motor dysfunction of mice. These results suggest that Nurr1 serves a novel target for ICH therapy.