D Zaldivar

Dopamine-Induced Dissociation of BOLD and Neural Activity in Macaque Visual Cortex

Neuromodulators determine how neural circuits process information during cognitive states such as wakefulness, attention, learning, and memory. fMRI can provide insight into their function and dynamics, but their exact effect on BOLD responses remains unclear, limiting our ability to interpret the effects of changes in behavioral state using fMRI. Here, we investigated the effects of dopamine (DA) injections on neural responses and haemodynamic signals in macaque primary visual cortex (V1) using fMRI (7T) and intracortical electrophysiology. Aside from DAs involvement in diseases such as Parkinsons and schizophrenia, it also plays a role in visual perception. We mimicked DAergic neuromodulation by systemic injection of L-DOPA and Carbidopa (LDC) or by local application of DA in V1 and found that systemic application of LDC increased the signal-to-noise ratio (SNR) and amplitude of the visually evoked neural responses in V1. However, visually induced BOLD responses decreased, whereas cerebral blood flow (CBF) responses increased. This dissociation of BOLD and CBF suggests that dopamine increases energy metabolism by a disproportionate amount relative to the CBF response, causing the reduced BOLD response. Local application of DA in V1 had no effect on neural activity, suggesting that the dopaminergic effects are mediated by long-range interactions. The combination of BOLD-based and CBF-based fMRI can provide a signature of dopaminergic neuromodulation, indicating that the application of multimodal methods can improve our ability to distinguish sensory processing from neuromodulatory effects.

Pharmacological preconditioning by diazoxide downregulates cardiac L-type Ca2+ channels

BACKGROUND AND PURPOSE Pharmacological preconditioning (PPC) with mitochondrial ATP‐sensitive K+ (mitoKATP) channel openers such as diazoxide, leads to cardioprotection against ischaemia. However, effects on Ca2+ homeostasis during PPC, particularly changes in Ca2+ channel activity, are poorly understood. We investigated the effects of PPC on cardiac L‐type Ca2+ channels.

In vivo characterization of the downfield part of 1H MR spectra of human brain at 9.4T: Magnetization exchange with water and relation to conventionally determined metabolite content

To perform exchange‐rate measurements on the in vivo human brain downfield spectrum (5–10 ppm) at 9.4 T and to compare the variation in concentrations of the downfield resonances and of known upfield metabolites to determine potential peak labels.