Norepinephrine uptake sites in the locus coeruleus of rat lines selectively bred for high and low alcohol preference: A quantitative autoradiographicbinding study using [H-3]-tomoxetine

Background: The locus coeruleus (LC) is the largest norepinephrinergic cell group in the central nervous system and contains a high density of norepin ephrine (NE) uptake sites. Alcohol-preferring (AP) rats and high-alcohol-dr inking (HAD) rats are selectively bred for high alcohol preference, whereas alcohol-nonpreferring(NP) rats and low-alcohol-drinking (LAD) rats are bre d for low alcohol preference. However, it is unknown whether NE uptake site s in the LC are associated with alcohol preference in AP and HAD rats when compared with their respective control rats, NP and LAD rats. This study wa s designed to examine this question. Methods: Animals were decapitated and brains were removed, frozen with dry ice powder, and stored in a deep freezer. The LC tissue blocks were cut int o 14 mu cryostat sections, collected on glass slides, and incubated with 0. 6 nM [H-3]-tomoxetine in 50 mM Tris-HCl buffer system. For nonspecific bind ing. 1 mu M desipramine was added to the radioactive ligand. Sections were rinsed, quickly dried, and processed for quantitative autoradiography. In a ddition, galanin content in the LC was also studied. Results: The LC possessed a high density of [H-3]-tomoxetine binding sites. There were fewer tomoxetine binding sites (fmol/mg protein) in the AP rats (433.0 +/- 8.1) than in the NP rats (495.6 +/- 3.7). HAD rats: (386.5 +/- 13.2) also possessed fewer tomoxetine binding sires than LAD rats (458.7 +/ - 10.1). Galanin content in the LC was Similar between AP and NP rats and b etween HAD and LAD rats. Conclusions: Because both AP rats and HAD rats were selectively bred for al cohol preference, the finding of consistently Low levels of [H-3]-tomoxetin e binding in the LC of these two lines of rats with high alcohol preference suggests that down-regulation of NE transporters in the LC of AP and HAD r ats may be associated with alcohol-seeking behavior. A possible involvement of the coerulear NE uptake sites in depression is also discussed. Galanin in the LC may not relate to alcohol preference.