Changes in the expression of a₂-adrenergic receptor subtypes during maturation of neuronal cells from fetal pig superior cervical ganglia

The expression of presynaptic a₂-adrenergic receptor a₂-AR subtypes was investigated in cultured neurons from fetal pig superior cervical ganglion SCG. Cells were incubated with chicken antibodies against a₂A-, a₂B- or a₂C-AR subtypes either alone or together with antibodies against dopamine-b-hydroxylase DbH, a marker for adrenergic neurons or against choline acetyl transferase ChAT, a marker for cholinergic neurons. We found immunoreactivity for all three a₂-AR subtypes in SCG-cells when cultured for 8-11 days. The relative expression of the a₂A-subtype was approximately 1r3 of that of a₂B- and a₂C-AR. Co-localisation of all three a₂-AR subtypes was observed in cells expressing DbH or ChAT. Increasing the potassium concentration in the culture medium increased the expression of DbH and decreased the expression of the a₂A- and a₂C-subtype without altering the expression of the a₂B-subtype. Co-culture of neurons with pig splenocytes enhanced the expression of ChAT and decreased the expression of the a₂B- subtype without altering the expression of a₂A- and a₂C-subtypes. Our results indicate that the three a₂-receptor subtypes are expressed on both noradrenergic and cholinergic nerves. Induction of the noradrenergic phenotype favours the expression of the a₂B-subtype over that of the a₂A- and a₂C-subtype. Conversely, enhancement of the cholinergic phenotype favours the expression of the a₂A- and a₂C-subtypes over that of the a₂B- subtype. Our results suggest that the a₂B-receptor is preferentially associated with noradrenergic nerve endings.