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Rovelli V, Longo N. Phenylketonuria and the brain. Mol Genet Metab 2023; 139:107583. [PMID: 37105048 DOI: 10.1016/j.ymgme.2023.107583] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/22/2022] [Revised: 04/14/2023] [Accepted: 04/14/2023] [Indexed: 04/29/2023]
Abstract
Classic phenylketonuria (PKU) is caused by defective activity of phenylalanine hydroxylase (PAH), the enzyme that coverts phenylalanine (Phe) to tyrosine. Toxic accumulation of phenylalanine and its metabolites, left untreated, affects brain development and function depending on the timing of exposure to elevated levels. The specific mechanisms of Phe-induced brain damage are not completely understood, but they correlate to phenylalanine levels and on the stage of brain growth. During fetal life, high levels of phenylalanine such as those seen in maternal PKU can result in microcephaly, neuronal loss and corpus callosum hypoplasia. Elevated phenylalanine levels during the first few years of life can cause acquired microcephaly, severe cognitive impairment and epilepsy, likely due to the impairment of synaptogenesis. During late childhood, elevated phenylalanine can cause alterations in neurological functioning, leading to ADHD, speech delay and mild IQ reduction. In adolescents and adults, executive function and mood are affected, with some of the abnormalities reversed by better control of phenylalanine levels. Altered brain myelination can be present at this stage. In this article, we review the current knowledge about the consequences of high phenylalanine levels in PKU patients and animal models through different stages of brain development and its effect on cognitive, behavioural and neuropsychological function.
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Affiliation(s)
- Valentina Rovelli
- Clinical Department of Pediatrics, University of Milan, ASST Santi Paolo e Carlo, San Paolo Hospital, Milan, Italy.
| | - Nicola Longo
- Division of Medical Genetics, Department of Pediatrics, University of Utah, Salt Lake City, UT, USA
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Acute depletion of dopamine precursors in the human brain: effects on functional connectivity and alcohol attentional bias. Neuropsychopharmacology 2021; 46:1421-1431. [PMID: 33727642 PMCID: PMC8209208 DOI: 10.1038/s41386-021-00993-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/02/2020] [Revised: 02/20/2021] [Accepted: 02/23/2021] [Indexed: 02/07/2023]
Abstract
Individuals who abuse alcohol often show exaggerated attentional bias (AB) towards alcohol-related cues, which is thought to reflect reward conditioning processes. Rodent studies indicate that dopaminergic pathways play a key role in conditioned responses to reward- and alcohol-associated cues. However, investigation of the dopaminergic circuitry mediating this process in humans remains limited. We hypothesized that depletion of central dopamine levels in adult alcohol drinkers would attenuate AB and that these effects would be mediated by altered function in frontolimbic circuitry. Thirty-four male participants (22-38 years, including both social and heavy drinkers) underwent a two-session, placebo-controlled, double-blind dopamine precursor depletion procedure. At each visit, participants consumed either a balanced amino acid (control) beverage or an amino acid beverage lacking dopamine precursors (order counterbalanced), underwent resting-state fMRI, and completed behavioral testing on three AB tasks: an alcohol dot-probe task, an alcohol attentional blink task, and a task measuring AB to a reward-conditioned cue. Dopamine depletion significantly diminished AB in each behavioral task, with larger effects among subjects reporting higher levels of binge drinking. The depletion procedure significantly decreased resting-state functional connectivity among ventral tegmental area, striatum, amygdala, and prefrontal regions. Beverage-related AB decreases were mediated by decreases in functional connectivity between the fronto-insular cortex and striatum and, for alcohol AB only, between anterior cingulate cortex and amygdala. The results support a substantial role for dopamine in AB, and suggest specific dopamine-modulated functional connections between frontal, limbic, striatal, and brainstem regions mediate general reward AB versus alcohol AB.
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Shnitko TA, Taylor SC, Stringfield SJ, Zandy SL, Cofresí RU, Doherty JM, Lynch WB, Boettiger CA, Gonzales RA, Robinson DL. Acute phenylalanine/tyrosine depletion of phasic dopamine in the rat brain. Psychopharmacology (Berl) 2016; 233:2045-2054. [PMID: 26944052 PMCID: PMC4864125 DOI: 10.1007/s00213-016-4259-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/13/2015] [Accepted: 02/17/2016] [Indexed: 12/26/2022]
Abstract
RATIONALE Dopamine plays a critical role in striatal and cortical function, and depletion of the dopamine precursors phenylalanine and tyrosine is used in humans to temporarily reduce dopamine and probe the role of dopamine in behavior. This method has been shown to alter addiction-related behaviors and cognitive functioning presumably by reducing dopamine transmission, but it is unclear what specific aspects of dopamine transmission are altered. OBJECTIVES We performed this study to confirm that administration of an amino acid mixture omitting phenylalanine and tyrosine (Phe/Tyr[-]) reduces tyrosine tissue content in the prefrontal cortex (PFC) and nucleus accumbens (NAc), and to test the hypothesis that Phe/Tyr[-] administration reduces phasic dopamine release in the NAc. METHODS Rats were injected with a Phe/Tyr[-] amino acid mixture, a control amino acid mixture, or saline. High-performance liquid chromatography was used to determine the concentration of tyrosine, dopamine, or norepinephrine in tissue punches from the PFC and ventral striatum. In a separate group of rats, phasic dopamine release was measured with fast-scan cyclic voltammetry in the NAc core after injection with either the Phe/Tyr[-] mixture or the control amino acid solution. RESULTS Phe/Tyr[-] reduced tyrosine content in the PFC and NAc, but dopamine and norepinephrine tissue content were not reduced. Moreover, Phe/Tyr[-] decreased the frequency of dopamine transients, but not their amplitude, in freely moving rats. CONCLUSIONS These results indicate that depletion of tyrosine via Phe/Tyr[-] decreases phasic dopamine transmission, providing insight into the mechanism by which this method modifies dopamine-dependent behaviors in human imaging studies.
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Affiliation(s)
- Tatiana A. Shnitko
- Bowles Center for Alcohol Studies, University of North Carolina, Chapel Hill, NC, USA
| | - Sarah C. Taylor
- Bowles Center for Alcohol Studies, University of North Carolina, Chapel Hill, NC, USA
| | - Sierra J. Stringfield
- Bowles Center for Alcohol Studies, University of North Carolina, Chapel Hill, NC, USA,Neurobiology Curriculum, University of North Carolina, Chapel Hill, NC, USA
| | - Shannon L. Zandy
- Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA
| | - Roberto U. Cofresí
- Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA
| | - James M. Doherty
- Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA
| | - William B. Lynch
- Bowles Center for Alcohol Studies, University of North Carolina, Chapel Hill, NC, USA
| | - Charlotte A. Boettiger
- Bowles Center for Alcohol Studies, University of North Carolina, Chapel Hill, NC, USA,Neurobiology Curriculum, University of North Carolina, Chapel Hill, NC, USA,Department of Psychology and Neuroscience, University of North Carolina, Chapel Hill, NC, USA
| | - Rueben A. Gonzales
- Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA
| | - Donita L. Robinson
- Bowles Center for Alcohol Studies, University of North Carolina, Chapel Hill, NC, USA,Neurobiology Curriculum, University of North Carolina, Chapel Hill, NC, USA,Department of Psychiatry, University of North Carolina, Chapel Hill, NC, USA
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