Background: The locus coeruleus (LC) is the largest norepinephrinergic cell group in the central nervous system and contains a high density of norepinephrine (NE) uptake sites. Alcohol-preferring (AP) rats and high-alcohol-drinking (HAD) rats are selectively bred for high alcohol preference, whereas alcohol-nonpreferring (NP) rats and low-alcohol-drinking (LAD) rats are bred for low alcohol preference. However, it is unknown whether NE uptake sites 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 was 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 into 14 micro cryostat sections, collected on glass slides, and incubated with 0.6 nM [3H]-tomoxetine in 50 mM Tris-HCl buffer system. For nonspecific binding, 1 microM desipramine was added to the radioactive ligand. Sections were rinsed, quickly dried, and processed for quantitative autoradiography. In addition, galanin content in the LC was also studied.
Results: The LC possessed a high density of [3H]-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 sites than LAD rats (458.7 +/- 10.1). Galanin content in the LC was similar between AP and NP rats and between HAD and LAD rats.
Conclusions: Because both AP rats and HAD rats were selectively bred for alcohol preference, the finding of consistently low levels of [3H]-tomoxetine 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 rats 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.