Development of beta-adrenergic receptors and their function in glia-neuron communication in cultured chick brain

The beta-receptors of intact neuronal and glial cells of chick embryonic brain were studied via the specific binding of the beta-antagonist [3H]dihydro-L-alprenolol ( [3H]DHA). Cells were cultivated in either highly homogeneous or mixed populations; the neuronal cells were also grown under the influence of glial conditioned medium (GCM) or 10(-11)-10(-10) M L-norepinephrine or L-isoproterenol. The beta-receptors of both neuronal and glial cells proved to be positively cooperative (n = 2.5) and of high affinity, with a Kdapp of 98 and 44 pM, respectively. The Kdapp value was influenced only slightly by the different culture conditions. The receptor concentration was relatively low in the homogeneous neuronal and glial cultures (Bmax = 6.4 and 3.3 fmol/10(6) cells, respectively). It increased by a factor of 2-3 if development of the neuron-glia contacts in the culture was possible (mixed cultures). GCM and beta-agonists elevated the number of beta-receptors of the neuronal cells approximately 4-fold, even in the absence of glial cells. This receptor-number change was preceded by a well observable morphological differentiation. Both the morphological and the beta-receptor effects of L-norepinephrine were antagonized by L-propranolol. The beta-receptor number increased about 2-fold during a 10-day in vitro development, even in neuron-glia mixed cultures.