Rafal Janik

Magnetic resonance spectroscopy reveals oral Lactobacillus promotion of increases in brain GABA, N-acetyl aspartate and glutamate

The gut microbiome has been shown to regulate the development and functions of the enteric and central nervous systems. Its involvement in the regulation of behavior has attracted particular attention because of its potential translational importance in clinical disorders, however little is known about the pathways involved. We previously have demonstrated that administration of Lactobacillus rhamnosus (JB-1) to healthy male BALB/c mice, promotes consistent changes in GABA-A and -B receptor sub-types in specific brain regions, accompanied by reductions in anxiety and depression-related behaviors. In the present study, using magnetic resonance spectroscopy (MRS), we quantitatively assessed two clinically validated biomarkers of brain activity and function, glutamate+glutamine (Glx) and total N-acetyl aspartate+N-acetyl aspartyl glutamic acid (tNAA), as well as GABA, the chief brain inhibitory neurotransmitter. Mice received 1×10(9) cfu of JB-1 per day for 4weeks and were subjected to MRS weekly and again 4weeks after cessation of treatment to ascertain temporal changes in these neurometabolites. Baseline concentrations for Glx, tNAA and GABA were equal to 10.4±0.3mM, 8.7±0.1mM, and 1.2±0.1mM, respectively. Delayed increases were first seen for Glx (~10%) and NAA (~37%) at 2weeks which persisted only to the end of treatment. However, Glx was still elevated 4weeks after treatment had ceased. Significantly elevated GABA (~25%) was only seen at 4weeks. These results suggest specific metabolic pathways in our pursuit of mechanisms of action of psychoactive bacteria. They also offer through application of standard clinical neurodiagnostic techniques, translational opportunities to assess biomarkers accompanying behavioral changes induced by alterations in the gut microbiome.

Cerebral microvascular network geometry changes in response to functional stimulation

The cortical microvessels are organized in an intricate, hierarchical, three-dimensional network. Superimposed on this anatomical complexity is the highly complicated signaling that drives the focal blood flow adjustments following a rise in the activity of surrounding neurons. The microvascular response to neuronal activation remains incompletely understood. We developed a custom two photon fluorescence microscopy acquisition and analysis to obtain 3D maps of neuronal activation-induced changes in the geometry of the microvascular network of the primary somatosensory cortex of anesthetized rats. An automated, model-based tracking algorithm was employed to reconstruct the 3D microvascular topology and represent it as a graph. The changes in the geometry of this network were then tracked, over time, in the course of electrical stimulation of the contralateral forepaw. Both dilatory and constrictory responses were observed across the network. Early dilatory and late constrictory responses propagated from deeper to more superficial cortical layers while the response of the vertices that showed initial constriction followed by later dilation spread from cortical surface toward increasing cortical depths. Overall, larger caliber adjustments were observed deeper inside the cortex. This work yields the first characterization of the spatiotemporal pattern of geometric changes on the level of the cortical microvascular network as a whole and provides the basis for bottom-up modeling of the hemodynamically-weighted neuroimaging signals.

Hemodynamic effects of cholinesterase inhibition in mild Alzheimer's disease

To evaluate the spatiotemporal progression of perfusion changes in early stages of Alzheimers disease (AD), we imaged the perfusion response to pharmacological treatment in a group of mild AD patients and contrasted it to the perfusion of age‐, sex‐, and education‐matched healthy volunteers over the same time interval.

Neurovascular unit remodelling in the subacute stage of stroke recovery

Abstract Brain plasticity following focal cerebral ischaemia has been observed in both stroke survivors and in preclinical models of stroke. Endogenous neurovascular adaptation is at present incompletely understood yet its potentiation may improve long‐term functional outcome. We employed longitudinal MRI, intracranial array electrophysiology, Montoya Staircase testing, and immunofluorescence to examine function of brain vessels, neurons, and glia in addition to forelimb skilled reaching during the subacute stage of ischemic injury progression. Focal ischemic stroke (˜100 mm3 or ˜20% of the total brain volume) was induced in adult Sprague‐Dawley rats via direct injection of endothelin‐1 (ET‐1) into the right sensori‐motor cortex, producing sustained impairment in left forelimb reaching ability. Resting perfusion and vascular reactivity to hypercapnia in the peri‐lesional cortex were elevated by approximately 60% and 80% respectively seven days following stroke. At the same time, the normal topological pattern of local field potential (LFP) responses to peripheral somatosensory stimulation was abolished and the average power of spontaneous LFP activity attenuated by approximately 50% relative to the contra‐lesional cortex, suggesting initial response attenuation within the peri‐infarct zone. By 21 days after stroke, perilesional blood flow resolved, but peri‐lesional vascular reactivity remained elevated. Concomitantly, the LFP response amplitudes increased with distance from the site of ET‐1 injection, suggesting functional remodelling from the core of the lesion to its periphery. This notion was further buttressed by the lateralization of spontaneous neuronal activity: by day 21, the average ipsi‐lesional power of spontaneous LFP activity was almost twice that of the contra‐lesional cortex. Over the observation period, the peri‐lesional cortex exhibited increased vascular density, along with neuronal loss, astrocytic activation, and recruitment and activation of microglia and macrophages, with neuronal loss and inflammation extending beyond the peri‐lesional cortex. These findings highlight the complex relationship between neurophysiological state and behaviour and provide evidence of highly dynamic functional changes in the peri‐infarct zone weeks following the ischemic insult, suggesting an extended temporal window for therapeutic interventions.

Differences in iron and manganese concentration may confound the measurement of myelin from R1 and R2 relaxation rates in studies of dysmyelination

A model of dysmyelination, the Long Evans Shaker (les) rat, was used to study the contribution of myelin to MR tissue properties in white matter. A large region of white matter was identified in the deep cerebellum and was used for measurements of the MR relaxation rate constants, R1 = 1/T1 and R2 = 1/T2, at 7 T. In this study, R1 of the les deep cerebellar white matter was found to be 0.55 ± 0.08 s –1 and R2 was found to be 15 ± 1 s–1, revealing significantly lower R1 and R2 in les white matter relative to wild‐type (wt: R1 = 0.69 ± 0.05 s–1 and R2 = 18 ± 1 s–1). These deviated from the expected ΔR1 and ΔR2 values, given a complete lack of myelin in the les white matter, derived from the literature using values of myelin relaxivity, and we suspect that metals could play a significant role. The absolute concentrations of the paramagnetic transition metals iron (Fe) and manganese (Mn) were measured by a micro‐synchrotron radiation X‐ray fluorescence (μSRXRF) technique, with significantly greater Fe and Mn in les white matter than in wt (in units of μg [metal]/g [wet weight tissue]: les: Fe concentration,19 ± 1; Mn concentration, 0.71 ± 0.04; wt: Fe concentration,10 ± 1; Mn concentration, 0.47 ± 0.04). These changes in Fe and Mn could explain the deviations in R1 and R2 from the expected values in white matter. Although it was found that the influence of myelin still dominates R1 and R2 in wt rats, there were non‐negligible changes in the contribution of the metals to relaxation. Although there are already problems with the estimation of myelin from R1 and R2 changes in disease models with pathology that also affects the relaxation rate constants, this study points to a specific pitfall in the estimation of changes in myelin in diseases or models with disrupted concentrations of paramagnetic transition metals. Copyright

Reduced Cerebrovascular Reactivity and Increased Resting Cerebral Perfusion in Rats Exposed to a Cafeteria Diet

To better understand the effects of a diet high in fat, sugar, and sodium on cerebrovascular function, Sprague Dawley rats were chronically exposed to a Cafeteria diet. Resting cerebral perfusion and cerebrovascular reactivity was quantified using continuous arterial spin labeling (CASL) magnetic resonance imaging (MRI). In addition, structural changes to the cerebrovasculature and susceptibility to ischemic lesion were examined. Compared to control animals fed standard chow (SD), Cafeteria diet (CAF) rats exhibited increased resting brain perfusion in the hippocampus and reduced cerebrovascular reactivity in response to 10% inspired CO2 challenges in both the hippocampus and the neocortex. CAF rats switched to chow for one month (SWT) exhibited improved resting perfusion in the hippocampus as well as improved cerebrovascular reactivity in the neocortex. However, the diet switch did not correct cerebrovascular reactivity in the hippocampus. These changes were not accompanied by alterations in the structural integrity of the cerebral microvasculature, examined using rat endothelial cell antigen-1 (RECA-1) and immunoglobulin G (IgG) immunostaining. Also, the extent of tissue damage induced by endothelin-1 injection into sensorimotor cortex was not affected by the Cafeteria diet. These results demonstrate that short-term consumption of an ultra-processed diet reduces cerebrovascular reactivity. This effect persists after dietary normalization despite recovery of peripheral symptomatology.

Modulation of the peri‐infarct neurogliovascular function by delayed COX‐1 inhibition

Stroke is the leading cause of adult disability worldwide. The absence of more effective interventions in the chronic stage—that most patients stand to benefit from—reflects uncertainty surrounding mechanisms that govern recovery. The present work investigated the effects of a novel treatment (selective cyclooxygenase‐1, COX‐1, inhibition) in a model of focal ischemia.