Unique Profiles of the al-, a2-, and ,&Adrenergic Receptors in the Developing Cortical Plate and Transient Embryonic Zones of the Rhesus Monkey

Film receptor autoradiography was used to study the distribution of ml-, (r2-, and @-adrenergic receptors in the occipital lobe of developing rhesus monkeys ranging in age from the 65th embryonic day (E65) to adulthood (5 years of age). The study shows that each adrenergic receptor subtype has a unique distribution in the cortical plate and transient embryonic zones of the developing cerebral wall. For example, crl receptors are prominent throughout the proliferative ventricular and subventricular zones while ~7~2 receptors in the same zones form three distinct bands interdigitated with three bands rich in B sites. There are also considerable temporal differences in the emergence of adrenergic receptor subtypes in specific embryonic zones. For instance, the high density of (~1 sites in the germinal zones occurs only in conjunction with intensive proliferative activity. In contrast, ,!3 receptors emerge in these zones after the majority of cortical neurons have been generated. The transient embryonic zones often display higher densities of adrenergic sites than the cortical plate itself. In particular, the subplate zone subjacent to the developing visual cortex contains the highest density of a2-adrenergic sites in the cerebral wall throughout all prenatal ages studies. Finally, the regional differences in the density of @-adrenergic receptors are evident in the subplate zone underlying the prospective striate and extrastriate cortex before such differences emerge in the cortical plate. The early appearance, unique pattern of distribution, and time-dependent changes of adrenergic receptors in the transient embryonic zones suggest their involvement in the regulation of the cortical development. [