Research Notes: Dopamine

J Neurosci Res. 2007 Apr 23.
Metabolic interactions between glutamatergic and dopaminergic neurotransmitter systems are mediated through D(1) dopamine receptors.
Rodrigues TB, Granado N, Ortiz O, Cerdan S, Moratalla R.
Instituto de Investigaciones Biomedicas "Alberto Sols," C.S.I.C./U.A.M., Madrid, Spain.

Interactions between the dopaminergic and glutamatergic neurotransmission systems were investigated in the adult brain of wild-type (WT) and transgenic mice lacking the dopamine D(1) or D(2) receptor subtypes. Activity of the glutamine cycle was evaluated by using (13)C NMR spectroscopy, and striatal activity was assessed by c-Fos expression and motor coordination. Brain extracts from (1,2-(13)C(2)) acetate-infused mice were prepared and analyzed by (13)C NMR to determine the incorporation of the label into the C4 and C5 carbons of glutamate and glutamine. D(1)R(-/-) mice showed a significantly higher concentration of cerebral (4,5-(13)C(2)) glutamine, consistent with an increased activity of the glutamate-glutamine cycle and of glutamatergic neurotransmission. Conversely, D(2)R(-/-) mice did not show any significant changes in (4,5-(13)C(2)) glutamate or (4,5-(13)C(2)) glutamine, suggesting that alterations in glutamine metabolism are mediated through D(1) receptors. This was confirmed with D(1)R(-/-) and WT mice treated with reserpine, a dopamine-depleting drug, or with reserpine followed by L-DOPA, a dopamine precursor. Exposure to reserpine increased (4,5-(13)C(2)) glutamine in WT to levels similar to those found in untreated D(1)R(-/-) mice. These values were the same as those reached in the reserpine-treated D(1)R(-/-) mice. Treatment of WT animals with L-DOPA returned (4,5-(13)C(2)) glutamine levels to normal, but this was not verified in D(1)R(-/-) animals. Reserpine impaired motor coordination and decreased c-Fos expression, whereas L-DOPA restored both variables to normal values in WT but not in D(1)R(-/-). Together, our results reveal novel neurometabolic interactions between glutamatergic and dopaminergic systems that are mediated through the D(1), but not the D(2), dopamine receptor subtype.

Biol Psychiatry. 1998 Dec 15.
Cerebrospinal fluid monoamines in Prader-Willi syndrome.
Akefeldt A, Ekman R, Gillberg C, Mansson JE.
Department of Child and Adolescent Psychiatry, University of Goteborg, Molndal.

Background: The behavioral phenotype of Prader-Willi syndrome (PWS) suggests hypothalamic dysfunction and altered neurotransmitter regulation. The purpose of this study was to examine whether there was any difference in the concentrations of monoamine metabolites in the cerebrospinal fluid (CSF) in PWS and non-PWS comparison cases. Methods: The concentration of monoamine metabolites in CSF was determined in 13 children and adolescents with PWS diagnosed on clinical and genetic criteria. The concentrations were compared with those from 56 comparison cases in healthy and other contrast groups. Results: The concentrations of dopamine and particularly serotonin metabolites were increased in the PWS group. The differences were most prominent for 5-hydroxyindoleacetic acid [the main serotonin metabolite]. The increased concentrations were found in all PWS cases independently of age, body mass index, and level of mental retardation. Conclusions: The findings implicate dysfunction of the serotonergic system and possibly also of the dopamine system in PWS individuals, and might help inform future psychopharmacologic studies.

Eur Child Adolesc Psychiatry. 1998 Sep.
Is monoamine oxidase activity elevated in Prader-Willi syndrome?
Akefeldt A, Mansson JE.
Department of Child and Adolescent Psychiatry, Goteborg University, Annedals Clinics, Sweden.

The platelet contents of monoamine oxidase (MAO-B) were analyzed in 17 children and young adults with Prader-Willi syndrome and 18 non-PWS comparison cases. MAO-B activity was significantly higher in the former group, suggesting monoamine dysfunction in Prader-Willi syndrome.

[Note: MOA-B is an enzyme that catalyzes the inactivation or breakdown of monoamines such as the neurotransmitter dopamine and phenethylamines.]