Age- and Sex-Specific Plasticity in Dopamine Transporter Function Revealed by Food Restriction and Exercise in a Rat Activity-Based Anorexia Paradigm

Abstract

Eating disorders such as anorexia typically emerge during adolescence, are characterized by engagement in compulsive and detrimental behaviors, and are often comorbid with neuropsychiatric disorders and drug abuse. No effective treatments exist. Moreover, anorexia lacks adolescent animal models, contributing to a poor understanding of underlying age-specific neurophysiological disruptions. To evaluate the contribution of dopaminergic signaling to the emergence of anorexia-related behaviors during the vulnerable adolescent period, we applied an established adult activity-based anorexia (ABA) paradigm (food restriction plus unlimited exercise access for 4 to 5 days) to adult and adolescent rats of both sexes. At the end of the paradigm, measures of plasma volume, blood hormone levels, dopamine transporter (DAT) expression and function, acute cocaine-induced locomotion, and brain water weight were taken. Adolescents were dramatically more affected by the ABA paradigm than adults in all measures. In vivo chronoamperometry and cocaine locomotor responses revealed sex-specific changes in adolescent DAT function after ABA that were independent of DAT expression differences. Hematocrit, insulin, ghrelin, and corticosterone levels did not resemble shifts typically observed in patients with anorexia, though decreases in leptin levels aligned with human reports. These findings are the first to suggest that food restriction in conjunction with excessive exercise sex-dependently and age-specifically modulate DAT functional plasticity during adolescence. The adolescent vulnerability to this relatively short manipulation, combined with blood measures, evidence need for an optimized ageappropriate ABA paradigm with greater face and predictive validity for the study of the pathophysiology and treatment of anorexia. SIGNIFICANCE STATEMENT Adolescent rats exhibit a distinctive, sex-specific plasticity in dopamine transporter function and cocaine response after food restriction and exercise access; this plasticity is both absent in adults and not attributable to changes in dopamine transporter expression levels. These novel findings may help explain sex differences in vulnerability to eating disorders and drug abuse during adolescence. P. France]. Funding sources had no role in the generation, analyses, interpretations, or writing of these results. Interim results from this project have been

High Salt Intake Lowers Behavioral Inhibition

“…Serum corticosterone levels were analyzed using an Enzo (Enzo Life Sciences, Inc., Farmingdale, NY, United States) corticosterone immunosorbent assay (cat. no ADI-900-097) as previously reported (Latsko et al, 2016;Mitchell et al, 2018;Gilman et al, 2019b).…”

“…Trunk blood was collected under brief isoflurane anesthesia, either 2 h following completion of social interaction testing (Experiments 1 and 3) or 18 h after completion of marble burying (Experiment 2; Figure 1). Following previously published procedures (Latsko et al, 2016;Mitchell et al, 2018;Gilman et al, 2019b), blood was allowed to clot at room temperature for 1 h, then spun at 3500 rpm for 1 h at 4 • C. The supernatant was then removed, and this serum was stored at −80 • C until analysis.…”

“…Similar to our previous description of analyzing plasma protein (Gilman et al, 2019b), quantification of serum protein involved pipetting 50 µL of serum onto a calibrated, hand-held manual refractometer (AtagoUSA, Inc., Bellevue, WA, United States) to determine specific gravity (g/100 ml).…”

Animal Models for Anorexia Nervosa—A Systematic Review

“…Gelegen et al described increased dopamine receptor D2 expression in the caudate putamen of ABA mice (Gelegen et al, 2008 ). Gilman et al studied dopamine transporters in ABA and suggest that ABA modulates dopamine transporter functional plasticity during adolescence in a sex-dependent and age-specific manner (Gilman et al, 2019 ).…”

“…Neuroendocrine changes that were described in the ABA model include an increase in α4 GABA receptors in the CA1 hippocampus and amygdala (Aoki et al, 2012;Wable et al, 2014), alterations and decreased cell proliferation in the hippocampus (Chowdhury et al, 2013a) and a reduction in the density of astrocytes and a reduction in the volume of the cerebral cortex and corpus callosum (Frintrop et al, 2018a), which might be completely reversible by refeeding (Frintrop et al, 2019). Other findings were altered endocannabinoid (Casteels et al, 2014), histaminergic (Endou et al, 2001), BDNF (Gelegen et al, 2008;Ho et al, 2016), and dopaminergic (Gelegen et al, 2008;Gilman et al, 2019) transmission. Several studies investigated the effects of medication on ABA where specifically chlorpromazine (Adams et al, 2009), fluoxetine (Altemus et al, 1996), olanzapine (Klenotich et al, 2012), amisulpride (Klenotich et al, 2015), and cis-flupenthixol (Verhagen et al, 2009a) were shown to reduce ABA symptoms and point therefore in future directions of medication trials in anorexia nervosa.…”