Connectome dysfunction in patients at clinical high risk for psychosis and modulation by oxytocin

Abnormalities in functional brain networks (functional connectome) are increasingly implicated in people at Clinical High Risk for Psychosis (CHR-P). Intranasal oxytocin, a potential novel treatment for the CHR-P state, modulates network topology in healthy individuals. However, its connectomic effects in people at CHR-P remain unknown. Forty-seven men (30 CHR-P and 17 healthy controls) received acute challenges of both intranasal oxytocin 40 IU and placebo in two parallel randomised, double-blind, placebo-controlled cross-over studies which had similar but not identical designs. Multi-echo resting-state fMRI data was acquired at approximately 1 h post-dosing. Using a graph theoretical approach, the effects of group (CHR-P vs healthy control), treatment (oxytocin vs placebo) and respective interactions were tested on graph metrics describing the topology of the functional connectome. Group effects were observed in 12 regions (all p  < 0.05) most localised to the frontoparietal network. Treatment effects were found in 7 regions (all p  < 0.05) predominantly within the ventral attention network. Our major finding was that many effects of oxytocin on network topology differ across CHR-P and healthy individuals, with significant interaction effects observed in numerous subcortical regions strongly implicated in psychosis onset, such as the thalamus, pallidum and nucleus accumbens, and cortical regions which localised primarily to the default mode network (12 regions, all p  < 0.05). Collectively, our findings provide new insights on aberrant functional brain network organisation associated with psychosis risk and demonstrate, for the first time, that oxytocin modulates network topology in brain regions implicated in the pathophysiology of psychosis in a clinical status (CHR-P vs healthy control) specific manner. [Abstract copyright: © 2024. The Author(s).

Frontal GABA Levels Change during Working Memory

Functional neuroimaging metrics are thought to reflect changes in neurotransmitter flux, but changes in neurotransmitter levels have not been demonstrated in humans during a cognitive task, and the relationship between neurotransmitter dynamics and hemodynamic activity during cognition has not yet been established. We evaluate the concentration of the major inhibitory (GABA) and excitatory (glutamate + glutamine: Glx) neurotransmitters and the cerebral perfusion at rest and during a prolonged delayed match-to-sample working memory task. Resting GABA levels in the dorsolateral prefrontal cortex correlated positively with the resting perfusion and inversely with the change in perfusion during the task. Further, only GABA increased significantly during the first working memory run and then decreased continuously across subsequent task runs. The decrease of GABA over time was paralleled by a trend towards decreased reaction times and higher task accuracy. These results demonstrate a link between neurotransmitter dynamics and hemodynamic activity during working memory, indicating that functional neuroimaging metrics depend on the balance of excitation and inhibition required for cognitive processing

Photoluminiscence response of nanocrystalline GaAs thin films grown by R.F. magnetron sputtering in the blue-violet region

Using the transmission electron microscopy (TEM) photographs we were able to obtain the mean grain sizes in GaAs nanocrystalline films grown by the r.f. sputtering deposition technique, which were in the range between about 17 and 19 Å. The photoacoustic (PA) technique was used to measure the absorption spectra in these films. In the spectra obtained by PA spectroscopy it was possible to distinguish clearly the bands due to transitions between quantized levels. From these PA measurements and the photoluminescence emission in the films it was possible to observe a high blue shift of the absorption edge, due to the quantum confinement effects. We have for explain the behavior of shift of the absorption edge with the nanocrystals size the parabolic bands mode

Actividad fotocatalítica con luz visible de películas de TiO2 crecidas por R.F sputtering reactivo

El TiO2 es un semiconductor de energía de banda prohibida ancha con propiedades fotocatalíti-cas bien conocidas, las cuales tienen enorme potencial en procesos de control de contaminación de la fase líquida y gaseosa bajo la irradiación de luz ultravioleta. Dicha potencialidad aumentaría si el proceso fotocatalítico se pudiera dar con la presencia de luz visible. En este trabajo se reporta el crecimiento de películas delgadas de TiO2 usando sputtering reactivo de radio frecuencia (r.f.), variando la presión par-cial (O2/Ar/N) de N, con el fin de incorporar un bajo contenido de este en las mismas. La disminución del ancho de banda de energía prohibida de las películas con el contenido de N, fue obtenida usando un es-pectrofotómetro UV-Vis. La actividad fotocatalítica fue evaluada por la decoloración de una solución de azul de metileno en agua, en la cual fue inmersa cada película expuesta a la radiación de luz blanca pro-veniente de una lámpara de Xenón. La eficiencia de las películas bajo la acción de luz visible fue caracte-rizada midiendo con espectrofotómetro, la solución luego del proceso

Areas of cerebral blood flow changes on arterial spin labelling with the use of symmetric template during nitroglycerin triggered cluster headache attacks

BACKGROUND: Cluster headache is a rare, strictly unilateral, severe episodic primary headache disorder. Due to the unpredictable and episodic nature of the attacks, nitroglycerin has been used to trigger attacks for research purposes to further our understanding of cluster headache pathophysiology. OBJECTIVES: We aimed to identify regions of significant cerebral blood flow (CBF) changes during nitroglycerin triggered cluster headache attacks, using MRI with arterial spin labelling (ASL). METHODS: Thirty-three subjects aged 18–60 years with episodic and chronic cluster headache were recruited and attended an open clinical screening visit without scanning to receive an intravenous nitroglycerin infusion (0.5 μg/kg/min over 20 min). Those for whom nitroglycerin successfully triggered a cluster headache attack, were invited to attend two subsequent scanning visits. They received either single-blinded intravenous nitroglycerin (0.5 μg/kg/min) or an equivalent volume of single-blinded intravenous 0.9% sodium chloride over a 20-minute infusion. Whole-brain CBF maps were acquired using a 3 Tesla MRI scanner pre-infusion and post-infusion. As cluster headache is a rare condition and purely unilateral disorder, an analysis strategy to ensure all the image data corresponded to symptomatology in the same hemisphere, without losing coherence across the group, was adopted. This consisted of spatially normalising all CBF maps to a standard symmetric reference template before flipping the images about the anterior-posterior axis for those CBF maps of subjects who experienced their headache in the right hemisphere. This procedure has been employed in previous studies and generated a group data set with expected features on the left hemisphere only. RESULTS: Twenty-two subjects successfully responded to the nitroglycerin infusion and experienced triggered cluster headache attacks. A total of 20 subjects completed the placebo scanning visit, 20 completed the nitroglycerin scanning visit, and 18 subjects had completed both the nitroglycerin and placebo scanning visits. In a whole-brain analysis, we identified regions of significantly elevated CBF in the medial frontal gyrus, superior frontal gyrus, inferior frontal gyrus and cingulate gyrus, ipsilateral to attack side, in CBF maps acquired during cluster headache attack; compared with data from the placebo session. We also identified significantly reduced CBF in the precuneus, cuneus, superior parietal lobe and occipital lobe contralateral to the attack side. Of particular interest to this field of investigation, both the hypothalamus and ipsilateral ventral pons showed higher CBF in a separate region of interest analysis. CONCLUSION: Our data demonstrate that severe cluster headache leads to significant increases in regional cerebral perfusion, likely to reflect changes in neuronal activity in several regions of the brain, including the hypothalamus and the ventral pons. These data contribute to our understanding of cluster headache pathophysiology; and suggest that non-invasive ASL technology may be valuable in future mechanistic studies of this debilitating condition