CEREBROSPINAL FLUID-CONTACTING NEURONS IN THE PARAVENTRICULAR ORGAN AND IN THE SPINAL-CORD OF THE QUAIL EMBRYO - A FLUORESCENCE-HISTOCHEMICAL STUDY

Although the cerebrospinal fluid-contacting neurons of the avian parav entricular organ exhibit considerable amounts of catecholamines, they show no tyrosine hydroxylase immunoreactivity. In the quail embryo, th e development of these neurons has been studied using the paraformalde yde-glutaraldeyde method for the fluorescence-histochemical localizati on of catecholamines. The timing of the appearance of catecholamine fl uorescence in cerebrospinal fluid-contacting neurons and that in catec holamine-containing neurons of the brainstem have been compared. The f irst neurons displaying catecholamine fluorescence are found within th e locus coeruleus and the nucleus subcoeruleus ventralis on the 5.5th day of incubation. Catecholaminergic neuronal groups of the medulla an d mesencephalon can be identified by embryonic day 7, and fluorescent cerebrospinal fluid-contacting neurons of the hypothalamic paraventric ular organ can be first recognized at the 8th day of incubation. If th e catecholamine content of cerebrospinal fluid-contacting neurons that lack tyrosine hydroxylase depends upon an uptake mechanism, it may be significant that, in fluorescence-histochemical preparations, these n eurons can be identified 1-3 days later than those in which catecholam ines are synthesized and from which catecholamines are released at an earlier developmental stage. Moreover, cerebrospinal fluid-contacting neurons that have previously been shown to be tyrosine-hydroxylase imm unoreactive, and that lie at the spinal-medullary junction display a d ifferent developmental pattern. By fluorescence histochemistry, they c an be detected only by embryonic day 10.5. The chemical, developmental and topographical differences suggest that the catecholamine-containi ng cerebrospinal fluid-contacting elements of the paraventricular orga n and those of the spinal cord represent two different subsets of cere brospinal fluid-contacting neurons whose respective functional roles r emain to be investigated.