Byron C. Jones

The nature and identification of quantitative trait loci: a community’s view

This white paper by eighty members of the Complex Trait Consortium presents a communitys view on the approaches and statistical analyses that are needed for the identification of genetic loci that determine quantitative traits. Quantitative trait loci (QTLs) can be identified in several ways, but is there a definitive test of whether a candidate locus actually corresponds to a specific QTL?

Iron Deficiency Decreases dopamine D1 and D2 receptors in rat brain

Iron deficiency (ID) in early life is known to alter neurological development and functioning, but data regarding specific effects on dopamine biology are lacking. The objective of this study was to determine the extent of functional alterations in dopamine receptors in two dopaminergic tracts in young, growing, iron-deficient rats. Forty male and 40 female weanling Sprague-Dawley rats were fed either an iron-deficient (ID) diet or control (CN) diet for 6 weeks. ID decreased densities of D(1) and D(2) receptors in the caudate-putamen and decreased D(2) receptor densities in the nucleus accumbens. There were no apparent effects of ID on the affinities for the ligands in either receptor in several brain regions. In situ hybridization studies for both dopamine receptors revealed no significant effect of ID on mRNA expression for either receptor. Iron-deficient rats had a significantly higher ED(50) for raclopride-induced hypolocomotion in male and female rats compared to control rats of each sex. The loss of iron in the striatum due to dietary ID was significantly correlated with the decrease in D(2) receptor density; however, this relationship was not apparent in other brain regions. These experiments thus demonstrate abnormal dopamine receptor density and functioning in several brain regions that are related to brain regional iron loss. Importantly, the impact of ID on dopamine was more pronounced in males than females, demonstrating sex-related different sensitivities to nutrient deprivation.

Altered monamine metabolism in caudate-putamen of iron-deficient rats

The effect of iron deficiency on brain monoamine metabolism using in vivo microdialysis techniques has not been previously reported. We, therefore, examined the monoamines, dopamine and norepinephrine, and their metabolites at steady state by in vivo microdialysis in rat brain caudate-putamen in 11-week-old iron-deficient anemic (hemoglobin < 7 g/dl) and control rats (Hb > 14 g/dl). Caudate-putamen dopamine (DA), dihydroxyphenyl acetic acid (DOPAC), and homovanillic acid (HVA) concentrations were increased by 53%, 57%, and 30% (p < 0.001), respectively, in iron-deficient rats in samples collected over a 4-h period. While diminished numbers of D2 receptors have been previously reported, the present findings suggest an additional defect in monoamine uptake and catabolism.

Iron deficiency: differential effects on monoamine transporters.

Abstract In this study, we extend previous work on iron deficiency and dopamine (DA) transporters to include an examination of central serotonin (5-HT) and noradrenergic (NE) transporters. Rats were fed either iron deficient (ID) or iron adequate (CN) diets from weaning until adulthood. In males, an additional group of iron deficient animals (IR) were given iron supplementation. DA, 5-HT, and NE transporter binding was done in situ on thin sections. ID males, but not females, decreased DA transporter binding in the nucleus accumbens, caudate putamen and substantia nigra by 20–40%. ID males also had a 20–30% reduction in 5-HT transporter binding in several areas (nucleus accumbens, olfactory tubercle, colliculus) while in ID females there was 15–25% increased serotonin transporter binding in the olfactory tubercle, zona incerta, anteroventral thalamic nucleus and vestibular nucleus. Iron deficiency reduced 3 H-nisoxetine binding to the NE transporter in locus ceruleus and anteroventral thalamic nucleus in males but not females. Only some of the changes observed in DA, serotonin and NE transporter binding were reversible by iron supplementation. These findings show that iron deficiency affects monoamine systems related to homeostasis and in most cases males appear to be more vulnerable than females.

Neurobehavioral analysis of developmental iron deficiency in rats

Iron deficiency (ID) in early life alters the course of behavioral and cognitive development in humans, causing decreased physical activity and responsiveness to the environment. The effects of ID on behavior are similar in rats and hypothesized to be related to ID-related impairments in central dopamine pathways. The objective of this study was to examine the association between brain iron measures of dopamine function, and behavioral measures of activity and reactivity. Male and female weanling rats were fed either an iron deficient diet or control diet for 6 weeks. The iron deficient rats showed significantly decreased activity and increased anxiety-like behaviors. Iron deficient rats also showed significant decrements in brain iron content in the corpus striatum, prefrontal cortex, and midbrain and decreases in dopamine receptors and the transporter in the same areas. Multiple regression analysis showed ventral midbrain iron concentration and dopamine D(1) receptor density to be highly associated with exploration and repeated movements, respectively. In addition, the results showed anxiety-like behaviors to be related to prefrontal cortex dopamine transporter and dopamine D(1) receptor densities. We conclude from these analyses that iron concentration in dopamine containing regions and densities of dopamine receptors and the transporter, are significant predictors of measures of activity and reactivity. These observations also strengthen the argument that the Fe-dopamine link is fundamental to understanding biobehavioral difficulties seen in children with ID anemia.

Quantitative-trait loci analysis of cocaine-related behaviours and neurochemistry

We recently conducted a dose-response study of the effects of cocaine on several activity measures in the panel of BxD/Ty recombinant inbred mice. Animals were tested in an automated activity chamber over 2 days with i.p. saline on day 1 and i.p. cocaine on day 2, at one of four doses, 5, 15, 30 or 45 mg kg(-1). The monitor recorded total distance traveled, nosepokes in a holeboard, repeated movements and time spent by an individual in proximity to the centre of the apparatus. Dose-response curves for locomotor activation, i.e. the difference between cocaine and saline scores, showed that for all strains tested, scores increased 5-30 mg kg(-1). With few exceptions, locomotor activity at 45 mg kg(-1) was not significantly higher than that at 30 mg kg(-1). Repeated movement scores showed patterns similar to locomotor activity and nosepokes tended to be progressively inhibited by increasing doses of cocaine. Recombinant inbred strain mean distributions for all behaviours and at all doses exhibited continuous, rather than discrete variation, thus providing evidence of multiple-gene effects on cocaine-related behaviours. Quantitative trait loci (QTL) analysis pointed to several chromosomal locations associated with variations in cocaine-related behaviours and some are either identical or close to QTL reported by others. In separate groups of animals, densities of dopamine D1, and D2 receptors and dopamine uptake transporters were measured in the medial prefrontal cortex, caudate-putamen, nucleus accumbens and ventral midbrain. In all areas, all measures showed distributions consistent with polygenic influence and were associated with QTL. Of particular interest was our finding of a large segment on chromosome 15, which is related to dopamine receptor densities and cocaine-related behaviours.

CONTRIBUTION OF SEX AND GENETICS TO NEUROENDOCRINE ADAPTATION TO STRESS IN MICE

Male and female C57BL/6 (B6) and DBA/2 (D2) mice were subjected to either acute or 5 days of repeated restraint in ventilated, 50 ml centrifuge tubes. Control animals were not disturbed. The acute restraint animals were killed immediately following 15, 30 or 60 min of restraint and blood collected for corticosterone (CORT) analysis. The results of the acute restraint procedure revealed a strain difference in time to peak CORT in plasma with D2 animals showing an earlier peak. The males of both strains evinced similar maximum response and similar to B6 females; however, the D2 females showed a 2-fold greater CORT response than did the B6 females. Repeated restraint consisted of 5 days of 12 h in the tubes. At the end of 5 days, the animals were weighted and adrenalectomized in preparation for determination of brain corticosteroid receptors. Upon sacrifice, brains, thymus, adrenals and blood were harvested, the last for corticosteroid binding globulin (CBG). Five days of repeated restraint produced body weight loss in both strains, with B6s less affected than D2s. Repeated restraint reduced the mass of the adrenals in the B6s only. Restraint also reduced the mass of the thymus in both strains and sexes, but to a greater extent in the B6s. Plasma CBG densities were also sensitive to restraint, but only in females, showing a restraint-related decrease. Repeated restraint had no effect on hippocampal glucocorticoid or mineralocorticoid receptors; however for the latter, we observed significant strain and sex effects with D2 having higher Bmax than B6 and females having higher Bmax than males. In the pituitary, glucocorticoid receptors (GR) were reduced by repeated restraint in males, but increased in females, especially in the B6. These findings lend preliminary evidence for involvement of sex and genetics as sources of individual differences in bioadaptation to stress.

Iron deficiency alters dopamine uptake and response to L-DOPA injection in Sprague-Dawley rats.

Iron deficiency (ID) disrupts brain dopamine (DA) and norepinephrine (NE) metabolism including functioning of monoamine transporters and receptors. We employed caudate microdialysis and no net flux (NNF) in post‐weaning rats to determine if ID decreased the extraction fraction (Ed). Five micromolar quinpirole, a dopamine D2 receptor agonist, resulted in 80% decrease in extracellular DA and 45% higher Ed in control animals. The D2 agonist had no effect on Ed in ID animals despite a reduction in basal DA. DAT mRNA levels were reduced by 58% with ID, while DAT protein in ventral midbrain and caudate and membrane associated DAT were also reduced by ID. Carbidopa/l‐DOPA was administered to determine if elevated extracellular DA in ID was due to increased release. The DA response to l‐DOPA in ID rats was 50% smaller and delayed, whereas the NE response was threefold higher. The caudate concentration of NE was also elevated in ID. Elevated dopamine‐β‐hydroxylase activity in ID provides a tentative explanation for the increased NE response to l‐DOPA. These experiments provide new evidence that ID results in altered synthesis and functioning of DAT and perhaps suggests some compensatory changes in NE metabolism.

Neurobehavioral genetics : methods and applications

Background and Basic Concepts A History of Behavior Genetics Stephen C. Maxson Developmental Neurobehavioral Genetics: Development as Explanation Gilbert Gottlieb Some Basics: Mendelian Traits, Polygenic Traits and Complex Traits Byron C. Jones An Introduction to Quantitative Principles Wim E. Crusio Methods From QTL Detection to Gene Identification Marie-Pierre Moisan Gene expression Richard A. Radcliffe Bioinformatics of Behavior Elissa J. Chesler Congenic and Consomic Strains Lorraine Flaherty and Valerie Bolivar Animal Resources in Behavioral Neurogenetics Jean-Michel Lassalle Sample Size Requirements for Experiments on Laboratory Animals Douglas Wahlsten Studies in Hominids Neurobehavioral Genetics: The Role of Association Studies in Psychiatric Disorders Nicolas Ramoz and Phillip Gorwood Family and Twin Methods Keith E. Whitfield Gene-environment interactions Byron C. Jones and Leslie C. Jones And Now it Starts to Get Interesting: Gene-gene interactions Yamima Osher Schizophrenia: Study of a Genetically Complex Phenotype Michael Pogue-Geile and Irving Gottesman Genetics of Major Affective Disorders Wade Berrettini Pedigree Analyses and the Study of Chimpanzee (Pan troglodytes): Personality and Subjective Well-Being Alexander Weiss and James E. King The Elusive World of Personality Genes: Cherchez le phenotype Richard P. Ebstein, Rachel Bachner-Melman, Jonathan Benjamin and Robert H. Belmaker Studies in Rodents Aggression: Concepts and Methods Relevant to Genetic Analyses in Mice and Humans Stephen C. Maxson and Andrew Canastar Genetic Analysis of Emotional Behaviors Using Animal Models Andre Ramos and Pierre Mormede Studies in Invertebrates Genetic Analysis of Food Search Behavior in the Fruit Fly (Drosophila melanogaster) Amsale T. Belay and Marla B. Sokolowski Genetic and Molecular Analysis of Drosophila Courtship Behavior Jean-Marc Jallon A New Era for Drosophila Learning and Memory Studies Daniel Comas, Guillaume Isabel, and Thomas Preat Behavioral Genetics in the Nematode Caenorhabditis Elegans Gert Jensen and Laurent Segalat Bridging Neurobiology and Behavior Genetics, Behavior and Brain Dopamine Systems Robert Hitzmann, Shannon McWeeney, and John K. Belknap Natural Genetic Variation of Hippocampal Structures and Behavior Hans-Peter Lipp, Irmgard Amrein, Lutz Slomianka, and David P. Wolfer Expression and Brain Structure: Black Boxes between Genes and Behaviors Jeremy L. Peirce, Robert W. Williams Synaptic Mechanisms Involved in Cognitive Function: Cues From Mental Retardation Genes Guntram Borck, Florence Molinari, Birgit Dreier, Peter Sonderegger and Laurence Colleaux Pharmacology Pharmacogenetics Byron C. Jones Alcohol Psychopharmacogenetics John C. Crabbe

Abnormal rat brain monoamine metabolism in iron deficiency anemia

Iron deficiency in rats produces numerous alterations in brain metabolism as assessed by in vitro techniques. We used a new method of in vivo microdialysis to study the effect of acute iron deficiency anemia on rat brain monoamine metabolism. This method was used to sample extracellular fluid from an implanted microdialysis probe in the caudate putamen from freely moving animals. Method validation experiments showed that steady-state levels of dopamine, norepinephrine, and their metabolites were obtained only after 5 to 7 days of surgical recovery and with prior perfusion of the brain region. Caudate putamen dopamine was significantly increased 30% and 40% in fasted light-exposed and 2-hr-fed dark-exposed iron deficient anemic rats (hemoglobin in vitro demonstrations of down-regulation of dopamine D 2 receptors, they also suggest that uptake and processing of monoamines is significantly perturbed by iron deficiency.