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Sex differences in sucrose reinforcement in Long-Evans rats.

ABSTRACT:

Background

There are sex differences in addiction behaviors. To develop a pre-clinical animal model to investigate this, the present study examined sex differences in sucrose taking and seeking using Long-Evans rats.

Methods

Five experiments were conducted using separate groups of subjects. The first two examined sucrose or saccharin preference in two-bottle home cage choice tests. Experiment three assessed sucrose intake in a binge model with sucrose available in home cage bottles. Experiments four and five utilized operant-based procedures. In experiment four rats responded for sucrose on fixed and progressive ratio (FR, PR) schedules of reinforcement over a range of concentrations of sucrose. A final component of experiment four was measuring seeking in the absence of sucrose challenged with the dopamine D1 receptor antagonist SCH23390. Experiment five assessed responding for water on FR and PR schedules of reinforcement.

Results

When accounting for body weight, female rats consumed more sucrose than water; but there was no sex difference in saccharin preference over a range of saccharin concentrations. When accounting for body weight, females consumed more sucrose than males in the binge model, and only females increased binge intake over 14 days of the study. Females responded at higher rates for sucrose under both FR and PR schedules of reinforcement. Females responded at higher rates in extinction (seeking); SCH23390 reduced sucrose seeking of both females and males. Females responded at higher rates for water on FR and PR schedules than males, although rates of responding were low and decreased over sessions.

Conclusions

Across bottle-choice, binge intake, and operant procedures, female Long-Evans rats consumed more sucrose and responded at higher rates for sucrose. Although females also responded more for water, the vigor of responding did not explain the consistent sex difference in sucrose taking and seeking. The sex difference in sucrose taking was also not explained by sweet preference, as there was no sex difference in saccharin preference. These data provide a pre-clinical model to further evaluate sex differences in addiction behaviors and manipulations designed to reduce them.

SUBMITTER: Grimm JW

PROVIDER: S-EPMC8753819 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:To study the molecular mediators of naturally rewarding effects of palatable food we used a model of palatable âsnackingâ (Ulrich-Lai et al., 2007) in which rats are given chronic, brief access to a limited amount of sucrose solution (30%). Single housed, male Long-Evans rats (250g) (n=12 per group) from Harlan Labs (Indianapolis, IN) received normal rat chow (Harlan Teklad) and water ad libitum for the duration of the experiment. After a one-week period of acclimation, rats were randomly assigned to drink treatment groups of either 30% sucrose solution or water. Rats received a 14-day regimen of twice daily (9:30 and 15:30) brief (maximum of 30 minutes) limited (up to 4 mL) access of their assigned drink solution. Drink solutions were delivered via a graduated sipper placed onto the cage top in addition to the existing water bottle and sippers were immediately removed when the animal had consumed 4mL or after the 30-minute access period, whichever occurred first. Drink intake, food intake, and body weight were monitored throughout the experiment to verify that the rats learned to drink sucrose, that they adjusted chow intake for calories consumed from sucrose (~10%), and that there was no effect on body weight gain as is normally seen with this model (Ulrich-Lai et al., 2007). Drink treatment terminated on day 14 and at 8:00 on the morning of day 15, the rats were sacrificed by rapid decapitation. BLA tissue was dissected, RNA extracted, and gene expression changes between water and sucrose groups were accessed by microarray. We used microarray to assess the changes in gene expression in the BLA of rats that have had a history of sucrose snacks (n=12) vs control (n=12). Rats received access (up to 4 mL) to extra bottles containing water (control) or 30% sucrose twice daily for 14 days. Rats had ab lib access to chow and water for the duration of the experiment. Rats were sacrificed the morning of day 15 and the BLA was removed for microarray analysis. Functional cluster analysis was performed on the list of 145 significantly upregulated genes using Ingenuity Pathway Analysis (Ingenuity Systems, Redwood City, CA). See supplementary file at the foot of this record.

Project description:ObjectiveOur laboratory previously published that long-term administration of estradiol (E2) was detrimental to the kidneys of midlife ovariectomized Long Evans rats, contrasting clinical studies in showing that menopausal hormone therapy is associated with decreased albuminuria. However, it is unknown whether this renal benefit was due to estrogen and/or the combination with progestogen. Therefore, the objective of the current study was to determine the impact of medroxyprogesterone (MPA) on E2-mediated renal damage using a rodent model.MethodsFemale Long Evans retired breeders underwent ovariectomy at 11 months of age and were treated for 40 days with subcutaneous E2, E2+MPA or vehicle at doses mimicking that of menopausal hormone therapy (N = 5-7 per group). Systolic blood pressure was measured along with indices of renal damage and function to investigate the impact of MPA on E2-mediated renal outcomes. Renal estrogen receptor alpha and G protein-coupled estrogen receptor transcript copy numbers were measured in all treatment groups through droplet digital PCR.ResultsMiddle-aged female Long Evans rats displayed spontaneous hypertension with similar systolic blood pressures and heart weights between groups. Even though blood pressure was comparable, E2 reduced glomerular filtration rate and increased proteinuria indicating pressure-independent renal damage. Coadministration with MPA prevented E2-induced glomerular filtration rate impairment and proteinuria by promoting renal hypertrophy and preventing renal interstitial fibrosis. Both E2 and E2+MPA reduced renal estrogen receptor alpha (ERα) and increased renal G protein-coupled estrogen receptor mRNA, but neither ERα nor ERß protein was different between groups.ConclusionMPA was protective against E2-induced renal damage and dysfunction in middle-aged female Long Evans rats. Assessing the impact of hormone therapy on renal outcomes may be an important clinical factor when considering treatment options for postmenopausal women.