Tyrosine-free amino acid mixtures reduce physiologically-evoked release of dopamine in a selective and activity-dependent manner.

Depletion of the catecholamine precursor tyrosine using tyrosine-free amino acid mixtures is an important tool in neuropsychological studies, and often considered dopamine selective on the basis of neuropharmacological studies. However, little is known of the effects of tyrosine depletion when catecholamine neurons are activated physiologically. Here we investigated the effect of tyrosine-free amino acid mixtures on catecholamine release evoked in vivo using a stimulation paradigm aimed to approximate the phasic firing pattern of these neurons that accompanies cognitive and behavioural change.

Magnetic resonance imaging in late-life depression: vascular and glucocorticoid cascade hypotheses.

Background: Late-life depression is a common and heterogeneous illness, associated with structural abnormalities in both grey and white matter.

Aims: To examine the relationship between age at onset and magnetic resonance imaging (MRI) measures of grey and white matter to establish whether they support particular hypotheses regarding the anatomy and aetiology of network disruption in late-life depression.

Method: We studied 36 participants with late-life depression.

Magnetic resonance imaging in late-life depression: multimodal examination of network disruption.

Context: Disruption of frontal-subcortical and limbic networks is hypothesized to have a key role in late-life depression (LLD) and can be examined using magnetic resonance imaging (MRI) techniques. Gray matter can be examined using T1-weighted MRI, white matter using T2-weighted MRI and diffusion tensor imaging, and functional connectivity in resting-state networks using functional MRI. Although independent MRI studies have supported gray and white matter abnormalities in frontosubcortical and limbic networks and increased functional connectivity in the default-mode network in depression, no study has concurrently examined gray matter, white matter, and functional connectivity.

Emotional bias and waking salivary cortisol in relatives of patients with major depression.

Background: Biases in the processing of emotional information have been shown to be abnormal in subjects with major depression, both during an episode and after full recovery. However, it is unclear whether these biases are a cause or an effect of the depression. This study set out to explore whether such biases represent a vulnerability factor for depression by looking at unaffected first-degree relatives of those with major depressive disorder.

Effect of acute tyrosine depletion in using a branched chain amino-acid mixture on dopamine neurotransmission in the rat brain.

Central dopamine function is reduced by decreasing the availability of the catecholamine precursor, tyrosine, using a tyrosine-free amino acid mixture containing multiple large neutral as well as branched chain amino-acids, which compete with tyrosine for uptake into the brain. Current mixtures are cumbersome to make and administer, and unpalatable to patients and volunteers. Here, we investigate whether individual or limited amino-acid combinations could reduce brain tyrosine levels and hence dopamine function.

Fos immunocytochemical studies on the neuroanatomical sites of action of acute tyrosine depletion in the rat brain.

Rationale: Acute depletion of brain tyrosine using a tyrosine-free amino acid mixture offers a nutritional approach to reduce central catecholamine function. Recent preclinical data suggest that tyrosine-free amino acid mixtures may have region-specific effects through targeting dopamine neurones.

Objectives: Here we used fos immunocytochemistry to examine the neuroanatomical sites of action of a tyrosine-free amino acid mixture administered either alone or combined with amphetamine.

Tyrosine-free amino acid mixture attenuates amphetamine-induced displacement of [11C]raclopride in striatum in vivo: a rat PET study.

Previous neurochemical and behavioural studies show that tyrosine depletion using a nutritionally balanced tyrosine-free amino acid mixture attenuates the dopamine-releasing and psychostimulant properties of amphetamine. Here we investigate the effect of a tyrosine-free amino acid mixture on striatal binding of [(11)C]raclopride, and amphetamine-induced [(11)C]raclopride displacement, using positron emission tomography in the rat. Rats were scanned for 60 min after an i.