Developmental regulation of alpha 1A-adrenoceptor function in rat brain oligodendrocyte cultures

In this study, we examined the effect of norepinephrine (NE) on phosphatidylinositol-4,5-bisphosphate (PI) hydrolysis in progenitors and differentiated oligodendrocytes. NE caused a time- and concentration-dependent increase in total inositol phosphate (IP(t)) formation. The magnitude of this response increased as oligodendrocytes matured and was accompanied with an increase in alpha(1)-adrenoceptor (alpha(1)-AR) levels. To pharmacologically characterize the alpha(1)-AR subtype mediating PI hydrolysis in 12-day differentiated oligodendrocytes, various selective antagonists were used. Prazosin, the non-selective 1-AR antagonist, blocked NE-mediated IP(t) formation. Similarly, the alpha(1A)-AR selective competitive antagonists, 5-methyl urapidil (5-MU) and WB4104, were potent blockers of NE-mediated IP(t) formation. In contrast, the alpha(1B)- and alpha(1D)-AR antagonist, chloroethylclonidine and the alpha(1D)-AR antagonist, BMY 7378, had no effect. These results suggest that NE-induced PI hydrolysis in differentiated oligodendrocytes was mediated through the alpha(1A)-AR. Furthermore, this response was prevented by EGTA and CdCl(2), suggesting a requirement for extracellular calcium. The presence of alpha(1)-AR subtypes in oligodendrocytes was confirmed by reverse transcriptase coupled polymerase chain reaction and by immunoprecipitation, with subtype specific antibodies. The results indicated that mRNA and protein for the alpha(1A)-, alpha(1B)- and alpha(1D)-AR subtypes were expressed. In conclusion, our findings show that oligodendrocytes express all three alpha(1)-AR subtypes but that only the alpha(1A)-AR was involved in NE-mediated IP(t) formation.