Regultion of adrenergic receptors in intraocular hippocampal transplants: Role of Noradrenergic Innervation

Hippocampal tissue transplanted into the anterior chamber of the eye offers a unique system in which development can be studied in the absensce of the noradrenergic innervation. This system was used to determine the extent to which noradrenergic innervation regulates the developement of adrenergic receptors. In addition to examining single denervated transplates, transplants grown with innervation from the superior cervical ganglia of the host rat or from locus coeruleus cotransplants were also examined to determine whether the source of norepinephrine and extent of innervation in oculo regulate the developement and density of adrenergic receptors. In vitro autoradiographic analysis of ligand binding to both α₁‐ and β‐adrenergic receptors. In vitro autoradiographic analysis of ligand binding to both α₁‐and β‐adrenergic receptors with ¹²⁵‐I‐BE2254 and ¹²⁵I‐pindolol, respectively, was used to charcterize aderenergic receptors in the intraocular transplants. Quantitative analysis of the receptors showed and up‐regulation of both α₁‐ and β‐adrenergic receptors in tissue grown in the absence of norepinephrine, but in general there was not a high degree of correlation between norepinephrine content and receptor density. Although high‐performance liquid chromatography (HPLC) analysis of catecholamines revealed higher than normal amounts of norepinephrine in hippocampal transplants innervated by the superior cervical ganglia or a locus coeruleus cotransplant, the density of α₁‐ and βreceptors was quite comparable with values found in the literature for normal adult hippocampus. These results suggest that the relationship between receptor number and density of innervation may differ significantly from what is observed in response to pharmacological manipultion of norepinephrne systems in the adult brain.