Search

beta 1 Integrin-like immunoreactivity was localized in rat brain using a polyclonal antibody raised in rabbit against rat liver beta 1 integrin. One-dimensional immunoblotting of whole rat brain membranes indicated that this antiserum recognized a single molecular species at 116,000 M(r), indicative of rat beta 1 integrins. Specific staining of beta 1 integrin-like immunoreactivity was found in the vascular structures of the brain, including microvessels, the ventricular ependymal cells, and pia mater. The pineal gland stained densely, and diffuse staining was present throughout the gray matter of the brain. This diffuse staining had a patterned appearance in certain structures, such as the apical dendritic field of CA1 in hippocampus, and occasional labeling of astrocytes, verified by labeling with GFAP on adjacent sections, was noted.

The postnatal development of brain alpha 1-adrenergic receptors was studied in the rat brain using in vitro autoradiography. In some regions, such as the globus pallidus, receptor-binding sites were present at birth and increased during the first week but then decreased to very low levels by adulthood. In contrast, other regions such as the olfactory bulb and cerebral cortex exhibited little binding at birth, with a subsequent increase in receptors during the second week of life that persisted into the mature stage. Several regions had an intermediate pattern with significant labelling at birth, an increase in the first few weeks and a smaller decrement in binding sites as adulthood was approached. The data suggested that there were two archetypal development patterns, one of which was potentially related to the arrival of noradrenergic nerve projections (olfactory bulb) and the other of which was determined intrinsically by differentiation (globus pallidus). The two patterns could be distinguished by their sensitivity to alpha-difluoromethylornithine, a drug that inhibits ornithine decarboxylase, leading to a slowing of cellular replication, differentiation and migration. Drug treatment dramatically delayed the developmental fall-off of binding in the globus pallidus such that receptor sites remained in high concentration well past the point at which they disappeared in control animals. In the olfactory bulb, however, alpha-difluoromethylornithine had little or no effect on the ontogeny of receptor binding. These studies provide evidence that alpha 1-adrenergic receptors in various brain regions develop at different rates and with at least two characteristic patterns. Autoradiographic techniques provide important insights into receptor development that cannot be garnered from biochemical methods using isolated membrane preparations.

Much useful information on the localization of alpha 1-adrenergic binding sites has been gained by using tritiated radioligands for in vitro autoradiography. However, the iodinated alpha 1-adrenergic antagonist HEAT [( 2-beta (4-hydroxyphenyl)-ethylaminomethyl)-tetralone], BE 2254), a radioligand with high affinity and specificity, provides autoradiographs with a higher signal to noise ratio. This has allowed us to describe the anatomy of these binding sites in much greater detail than previously possible. Regions showing the highest levels of binding include external plexiform layer of the olfactory bulb, layers Va and Vc of frontoparietal cortex, lateral and central amygdaloid nuclei, thalamus, and inferior olive. Other regions were generally less intensely labeled, with the least evidence of labeling in white matter, such as corpus callosum. Some regions (e.g., hippocampus) had only moderate labeling, but the binding appeared in a discrete pattern that reflected the functional organization of the structure. Although the [125I]-HEAT binding sites were distributed in a pattern similar to that previously reported for [3H]-WB 4101 and [3H]-prazosin, the anatomical detail seen with the iodinated ligand is greater. As a result, an association of alpha 1-adrenergic antagonist binding sites with specific layers in the cortex and with some catecholamine-containing nuclei in the brainstem, such as the locus coeruleus, have been seen for the first time.