What has intrinsic signal optical imaging taught us about NGF-induced rapid plasticity in adult cortex and its relationship to the cholinergic system?

Current trends in intraoperative optical imaging for functional brain mapping and delineation of lesions of language cortex

Resection of a cerebral arteriovenous malformation (AVM), epileptic focus, or glioma, ideally has a prerequisite of microscopic delineation of the lesion borders in relation to the normal gray and white matter that mediate critical functions. Currently, Wada testing and functional magnetic resonance imaging (fMRI) are used for preoperative mapping of critical function, whereas electrical stimulation mapping (ESM) is used for intraoperative mapping. For lesion delineation, MRI and positron emission tomography (PET) are used preoperatively, whereas microscopy and histological sectioning are used intraoperatively. However, for lesions near eloquent cortex, these imaging techniques may lack sufficient resolution to define the relationship between the lesion and language function, and thus not accurately determine which patients will benefit from neurosurgical resection of the lesion without iatrogenic aphasia. Optical techniques such as intraoperative optical imaging of intrinsic signals (iOIS) show great promise for the precise functional mapping of cortices, as well as delineation of the borders of AVMs, epileptic foci, and gliomas. Here we first review the physiology of neuroimaging, and then progress towards the validation and justification of using intraoperative optical techniques, especially in relation to neurosurgical planning of resection AVMs, epileptic foci, and gliomas near or in eloquent cortex. We conclude with a short description of potential novel intraoperative optical techniques.

In situ measurements of brain tissue hemoglobin saturation and blood volume by reflectance spectrophotometry in the visible spectrum

Before the development of near-infrared spectroscopy (NIRS) for monitoring of hemoglobin and cytochromes in situ, the Jobsis laboratory designed a visible light reflectance spectrophotometer. The method was not as useful for cytochrome oxidase measurements, which stimulated the search for a better method that culminated in NIRS. Visible light reflectance spectrophotomery was, however, usefully applied in several experimental applications, such as the study of brain capillary hemoglobin saturation during changes in inspired gas mixtures in awake and anesthetized animals, and to record transient increases in total hemoglobin (blood volume) after local neuronal activation by direct cortical electrical stimulation, demonstrating a response that is fundamental to functional magnetic resonance imaging blood oxygen level-dependent methods. A third application of the instrumentation was for brain capillary red cell mean transit time analysis, estimated by recording the passage of a red cell-free bolus through the cerebral cortical optical monitoring field. Taken together with his previous application of fluorescence detection of nicotinamide adenine dinucleotide, the visible and near-infrared spectroscopy demonstrate that Frans Jobsis was a pioneer in the application of optical techniques to the study of intact organs in situ. These methods have been used to illuminate the basic function of the cerebrovascular and metabolic pathways in both physiological and pathological conditions.

Contrasting and brain region-specific roles of neurogenin2 and mash1 in GABAergic neuron differentiation in vitro

We have cultivated highly uniform populations of neural precursor cells, which retain their region-specific identities, from various rat embryonic brain regions. The roles of the proneural basic-helix-loop-helix (bHLH) factors neurogenin2 (Ngn2) and Mash1 in gamma-aminobutyric acid (GABA) neuron differentiation were explored in the region-specific cultures. Consistent with previous in vivo studies, forced expression of Mash1 promoted GABA neuron formation from the precursors derived from the developing forebrains, whereas Ngn2 displayed an inhibitory role in forebrain GABA neuron differentiation. Functional analyses of mutant bHLH proteins indicated that the helix-loop-helix domains of Mash1 and Ngn2, known as the structures for protein-protein interactions, impart the distinct activities. Intriguingly, the regulatory activities of Mash1 and Ngn2 in GABA neuron differentiation from the hindbrain- and spinal cord-derived precursor cells were completely opposite of those observed in the forebrain-derived cultures: increased GABA neuron yield by Ngn2 and decreased yield by Mash1 were shown in the precursors of those posterior brain regions. No clear difference that depended on dorsal-ventral brain regions was observed in the bHLH-mediated activities. Finally, we demonstrated that Otx2, the expression of which is developmentally confined to the regions anterior to the isthmus, is a factor responsible for the anterior-posterior region-dependent opposite effects of the bHLH proteins.