In vitro binding assays using 3H nisoxetine and 3H WIN 35,428 reveal selective effects of gonadectomy and hormone replacement in adult male rats on norepinephrine but not dopamine transporter sites in the cerebral cortex

Abstract

The prefrontal cortices mediate cognitive functions that critically depend on local dopamine levels. In male rats, many prefrontal tasks where performance is disrupted by changes in dopamine signaling are also impaired by gonadectomy, a manipulation that increases cortical dopamine concentration, prefrontal dopamine axon density and possibly extracellular prefrontal dopamine levels as well. Because these actions could be responsible for the impairing effects of gonadectomy on prefrontal function, the question of how they might arise comes to the fore. Accordingly, the present studies asked whether dopamine levels might be increased via a hormone sensitivity of transporter mediated dopamine uptake. Specifically, 3 HWIN 35,428 and 3 Hnisoxetine, ligands selective for the dopamine (DAT)-and norepinephrine transporter (NET) respectively, were used in in vitro binding assays to ask whether gonadectomy altered transporter affinity (Kd) and/or binding site number (Bmax) in prefrontal cortex, sensorimotor cortex and/or caudate. Assays performed on tissues dissected from sham-operated, gonadectomized and gonadectomized rats supplemented with testosterone propionate or estradiol for 4 or 28 days revealed no significant group differences or obvious trends in Kd or Bmax for DAT binding or in measures of Bmax for NET binding. However, affinity constants for 3 Hnisoxetine were found to be significantly higher in sensorimotor and/or prefrontal cortex of rats gonadectomized and gonadectomized and supplemented with estradiol for 4 or 28 days but similar to control in gonadectomized rats given testosterone. Because the NET contributes substantially to extracellular prefrontal dopamine clearance, these androgen-mediated effects could influence prefrontal dopamine levels and might thus be relevant for observed effects of gonadectomy on dopamine-dependent prefrontal behaviors. A hormone sensitivity of the NET could also have bearing on the prefrontal dopamine dysfunction seen in disorders like schizophrenia that disproportionately affect males, whose severity correlates with abnormal testosterone levels, and for which the NET is among suspected sites of pathology.Keywords prefrontal cortex; estrogen; androgen; working memory; schizophrenia; ADHD Corresponding Author: Mary Kritzer, Department of Neurobiology and Behavior, Stony Brook University, Stony Brook, New York 11794-5230, E-mail: mkritzer@notes.cc.sunysb.edu, phone: 631-632-8634, FAX: 631-632-6661. Section, Section Editor: Neuropharmacology, Dr. Yoland Smith Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Auth...

Gonadectomy and hormone replacement exert region- and enzyme isoform-specific effects on monoamine oxidase and catechol-O-methyltransferase activity in prefrontal cortex and neostriatum of adult male rats

“…Further, it is also unlikely that these effects are involved in the gonadectomy-induced upregulation of the prefrontal DA system that has been identified in the same animal model, where enzyme inhibition would be expected in the GDX cohort. The stimulation of COMT-s observed in both cortical and subcortical tissues of the testosterone- and the estradiol-supplemented groups is also at odds with the exclusively androgen-sensitive and prefrontal-selective effects that long-term gonadectomy in adult male rats exerts on mesocortical dopaminergic endpoints (Kritzer et al, 1999; Kritzer, 2000; Meyers and Kritzer, 2009). …”

“…Gonadal hormone influence over the monoamine and indolamine neurotransmitters in forebrain regions of the brain has been shown to include modulation of synthesis (Simerly, 1989; Fink et al, 1996, 1999; Pecins-Thompson et al, 1996; Thanky et al, 2002; Serova et al, 2004; Jeong et al, 2006; Guerra-Araiza et al, 2008), vesicular and/or synaptic release (Ji et al, 2007; Dluzen et al, 2008; Dluzen and McDermott, 2008), the number and/or affinity of the receptors and transporter proteins they interact with (Landry and Di Paolo, 2003; Bhatt and Dluzen, 2005; Le Saux and Di Paolo, 2006; Meyers and Kritzer, 2009), and the second messenger cascades these can activate (Le Saux and Di Paolo, 2005; Mani et al, 2009). It is likely that these actions—and very possibly others, help shape the sex differences and hormone malleability that has been observed for the complex cognitive, mnemonic and affective functions that these neurotransmitter systems support (Cosgrove et al, 2007), and could also have bearing on the sex differences that are also seen in the incidence, symptom severity and efficacy of drug treatment in the devastating forms of mental illness such as schizophrenia and major depression in which these forebrain systems fail (Goodman and Stevenson, 1989; Seeman and Lang, 1990).…”

The Cognition-Enhancing Effects of Psychostimulants Involve Direct Action in the Prefrontal Cortex

“…However, this may involve the fact that the density of DA transporters (DAT) is sparse in the PFC relative to the striatum (44,45), largely consistent with the reduced density of DA innervation of the PFC relative to the striatum (except see, 45). Moreover, the NE transporter (NET) displays a high affinity for DA and plays a prominent role in PFC DA clearance (46–48).…”

“…It is important to note that ‘limited’ DAT density in the PFC (relative to the striatum) does not indicate an absence of functional DAT. Indeed, evidence demonstrates measurable DAT in the medial PFC of rats (44,45). Further, DAT inhibitors are known to elevate extracellular DA levels in this region (43,51,52).…”

Amitraz changes NE, DA and 5-HT biosynthesis and metabolism mediated by alterations in estradiol content in CNS of male rats

“…***Significant difference between brain regions for each amitraz dose (p < 0.001); þþþ p < 0.001, significantly different compared to each amitraz dose. monoaminergic neurotransmitters transporters, which have been shown to be regulated by E 2 (Le Saux and Di Paolo, 2006;Meyers and Kritzer, 2009;Rivera et al, 2009;Yu et al, 2009).…”