Autoradiography of dopamine receptors and dopamine uptake sites in the spontaneously hypertensive rat

We examined the status of dopamine (DA) D1 and D2 receptors by using 3H]SCH 23390 and 3H]spiperone binding, respectively, and DA uptake sites by using 3H]mazindol binding in spontaneously hypertensive rats (SHR) and Sprague-Dawley (SD) rats. SHR showed significantly higher 3H]SCH 23390 and 3H]spiperone binding in the caudate-putamen (CPu), the nucleus accumbens (NAc) and the olfactory tubercle (OT) in comparison to the SD rats. There were no significant differences in 3H]mazindol-labeled DA uptake sites between the two strains. Unilateral 6-hydroxydopamine (6-OHDA) injection into the striatum resulted in more than 90% depletion of DA uptake sites in the CPu in both strains. 6-OHDA-induced DA depletion was associated with significant increases in striatal 3H]spiperone binding which were of similar magnitude in the SD rats (+64.1%) and SHR (+51.3%). There were only small decreases (-5.4%) in D1 receptor binding in the dorsolateral aspect of the CPu in the SHR, whereas there were no changes in striatal D1 receptors in the SD rats. These results indicate that, although the SHR have higher concentrations of both D1 and D2 receptors in the basal ganglia, these receptors are regulated in a fashion similar to DA receptors in SD rats after 6-OHDA-induced striatal DA depletion.