Expression of mRNA and functional alpha1-adrenoceptors that suppress the GIRK conductance in adult rat locus coeruleus neurons

Abstract

1 Locus coeruleus neurons in adult rats express binding sites and mRNA for α1-adrenoceptors even though the depolarizing effect of α1-adrenoceptor agonists on neonatal neurons disappears during development. 2 In this study intracellular microelectrodes were used to record from locus coeruleus neurons in brain slices of adult rats and reverse transcription-polymerase chain reaction (RT-PCR) was used to investigate the mRNA expression of α1- and α2-adrenoceptors in juvenile and adult rats. 3. The α1-adrenoceptor agonist phenylephrine had no effect on the membrane conductance of locus coeruleus neurons (Vhold -60 mV) but decreased the G protein coupled, inward rectifier potassium (GIRK) conductance induced by α2-adrenoceptor or μ-opioid agonists. The GIRK conductance induced by noradrenaline was increased in amplitude when α1-adrenoceptors were blocked with prazosin. 4 RT-PCR of total cellular RNA isolated from microdissected locus coeruleus tissue demonstrated strong mRNA expression of α1a-, α1b and α1d-adrenoceptors in both juvenile and adult rats. However, only mRNA transcripts for the α1b-adrenoceptors were consistently detected in cytoplasmic samples taken from single locus coeruleus neurons of juvenile rats, suggesting that this subtype may be responsible for the physiological effects seen in juvenile rats. 5 Juvenile and adult locus coeruleus tissue expressed mRNA for the α2a- and α2c-adrenoceptors while the α2b-adrenoceptor was only weakly expressed in juveniles and was not detected in adults. 6 The results of this study show that α1-adrenoceptors expressed in adult locus coeruleus neurons function to suppress the GIRK conductance that is activated by μ-opioid and α2-adrenoceptors.