Vol. 288, Issue 3, 1134-1142, March 1999

Alpha-2 Adrenergic Receptor Functional Coupling to G Proteins in Rat Brain During Postnatal Development¹

H. Kevin Happe, David B. Bylund and L. Charles Murrin

Departments of Pharmacology (H.K.H., D.B.B., L.C.M.) and Internal Medicine Neurology Section (L.C.M.), University of Nebraska Medical Center, Omaha, Nebraska

During postnatal development, alpha-2 adrenergic receptors (A2AR) change in both density and distribution. In forebrain, receptor density increases about 4-fold over neonatal levels, reaching adult levels before postnatal day (P) 28, whereas in hindbrain, including cerebellum, there is a decrease in overall receptor density. We examined the coupling of A2AR to G proteins using agonist-stimulated [³⁵S]GTPS binding as a functional assay. In forebrain the A2AR agonist-stimulated [³⁵S]GTPS binding increases rapidly after P7, reaching its highest levels at P21 and then declining slightly to adult levels. This binding increases more slowly than receptor number, suggesting that the appearance of G proteins, rather than the A2AR, determines the developmental appearance of functional A2AR-G protein interactions in forebrain. Basal [³⁵S]GTPS binding and [³⁵S]GTPS binding stimulated by other neurotransmitter receptor systems (GABA-B, mu opiate, and muscarinic) increase with a time course similar to A2AR-stimulated [³⁵S]GTPS binding. In contrast, in hindbrain, A2AR-stimulated [³⁵S]GTPS binding decreases during postnatal development in parallel with the decrease in A2AR levels, whereas [³⁵S]GTPS binding stimulated by other neurotransmitter receptor systems increases in parallel with basal [³⁵S]GTPS binding. Functional receptor-G protein coupling in hindbrain appears to be dependent on the developmental appearance of G proteins for most neurotransmitter systems. However, for A2AR the decrease in receptor density is the overriding factor. These studies 1) demonstrate the functional measurement of A2AR-G protein coupling in native tissue for the first time, 2) demonstrate that A2AR are coupled to G proteins throughout postnatal development, and 3) describe developmental increases and decreases in functional A2AR in brain.