The present study examined the role of the basal forebrain corticopetal cholinergic projection in the regulation of cortical electroencephalographic activity across sleep/wake states in rats. Selective lesions of this projection were effected by local intraparenchymal infusions of the immunotoxin 192 IgG-saporin. Lesions spared the septo-hippocampal cholinergic system, as well as p75-receptor-bearing noncholinergic neurons in the suprachiasmatic nucleus. Relative to sham-lesioned control animals, rats with lesions of basal forebrain cholinergic neurons displayed a significant reduction in high frequency EEG activity, characterized especially by a reduction in gamma EEG power. Lesions did not significantly alter the overall proportion of sleeping and waking states as defined behaviourally, but the attenuation of high frequency EEG activity was apparent across all stages, including REM-like periods. Results are consistent with the view that the basal forebrain corticopetal cholinergic system exerts a general activational effect on the cortical mantle. Although this system may not be essential for sleep/wake stage-switching, it does impact on the cortical states associated with those stages.

Purpose:To demonstrate the feasibility of mapping cerebral perfusion metrics with BOLD MRI during modulation of pulmonary venous oxygen saturation.Methods: A gas blender with a sequential gas delivery breathing circuit was used to implement rapid isocapnic changes in the partial pressure of oxygen of the arterial blood. Partial pressure of oxygen was initially lowered to a baseline of 40 mmHg. It was then rapidly raised to 95 mmHg for 20 s before rapidly returning to baseline. The induced cerebral changes in deoxyhemoglobin concentration were tracked over time using BOLD MRI in 6 healthy subjects and 1 patient with cerebral steno-occlusive disease. BOLD signal change, contrast-to-noise ratio, and time delay metrics were calculated. Perfusion metrics such as mean transit time, relative cerebral blood volume, and relative cerebral blood flow were calculated using a parametrized method with a mono-exponential residue function. An arterial input function from within the middle cerebral artery was used to scale relative cerebral blood volume and calculate absolute cerebral blood volume and cerebral blood flow. Results:In normal subjects, average gray and white matter were: BOLD change

No abstract

BACKGROUND: The paramagnetic properties of deoxyhemoglobin shorten T2* as do gadolinium based contrast agents. Induction of abrupt changes in arterial deoxyhemoglobin concentration ([dOHb]) can mimic the action of intra-vascular boluses of gadolinium based contrast agents (GBCAs) used for perfusion imaging. AIM: To demonstrate the feasibility of rapidly changing pulmonary venous hemoglobin saturation for generating boluses of blood with altered T2* properties for measuring flow metrics in the systemic circulation. METHODS: A gas blender with a sequential gas delivery breathing circuit and software enabling prospective arterial blood gas targeting was used to implement rapid lung changes in the partial pressure of blood oxygen (PaO2) while maintaining isocapnea. Lung PaO2 was initially lowered to induce a low baseline deoxyhemoglobin concentration [dOHb]. PaO2 was then rapidly raised to normal for 10 seconds and then rapidly lowered to the initial low baseline creating a oxyhemoglobin (OHb) bolus. R2* changes were measured using blood oxygenation dependent (BOLD) MRI signal changes in large arteries and veins as well as in the microcirculation. This enabled generation of the following maps: bolus arrival time delay (TD) cerebral blood volume (CBV), mean transit time (MTT) and cerebral blood flow (CBF). RESULTS: BOLD signal in the middle cerebral artery showed a sharp increase during the OHb bolus transit indicating minimal dispersion confirming effective rapid modulation of pulmonary venous PO2 with reasonable cortical contrast-to-noise ratio of 3. Signals sorted by amplitude of signal changes and arrival times enabled the visualization of major arteries and veins. Contrast to noise ratio was adequate for a single gas challenge to provide most of the contrast, little improved by averaging over the remaining set of challenges. Values of the flow metrics derived from the perfusion maps were within normal ranges from published literature values. CONCLUSION: Non-invasive induction of abrupt changes in OHb saturation can function as a novel non-invasive vascular contrast agent for use in perfusion imaging.

Concussions are associated with a range of cognitive, neuropsychological and behavioral sequelae that, at times, persist beyond typical recovery times and are referred to as postconcussion syndrome (PCS). There is growing support that concussion can disrupt network-based connectivity post-injury. To date, a significant knowledge gap remains regarding the sex-specific impact of concussion on resting state functional connectivity (rs-FC). The aims of this study were to (1) investigate the injury-based rs-FC differences across three large-scale neural networks and (2) explore the sex-specific impact of injury on network-based connectivity. MRI data was collected from a sample of 80 concussed participants who fulfilled the criteria for postconcussion syndrome and 31 control participants who did not have any history of concussion. Connectivity maps between network nodes and brain regions were used to assess connectivity using the Functional Connectivity (CONN) toolbox. Network based statistics showed that concussed participants were significantly different from healthy controls across both salience and fronto-parietal network nodes. More specifically, distinct subnetwork components were identified in the concussed sample, with hyperconnected frontal nodes and hypoconnected posterior nodes across both the salience and fronto-parietal networks, when compared to the healthy controls. Node-to-region analyses showed sex-specific differences across association cortices, however, driven by distinct networks. Sex-specific network-based alterations in rs-FC post concussion need to be examined to better understand the underlying mechanisms and associations to clinical outcomes.