Biochemical characterization of [3H]norepinephrine uptake in dissociated brain cell cultures from chick embryos

Autoradiography of high affinity uptake of catecholamines by primary astrocyte cultures

Uptake of D.L-[3H]norepinephrine ([3H]NE) and [3H]dopamine ([3H]DA) by primary astrocyte cultures prepared from neonatal rat brains, which are greater than or equal to 95% glial fibrillary acidic protein (GFAP(+)), was studied by measuring accumulation of tritium label, and localizing such uptake at the cellular level by autoradiography. Uptake of [3H]NE was 95% Na+ dependent at 10(-7) M and 80% Na+ dependent at 7.5 X 10(-7) M [3H]NE. Uptake of [3H]DA at 7.5 X 10(-7) M was 58% Na+ dependent, but total uptake of [3H]DA was greater than uptake of [3H]NE. Autoradiography of cells incubated with 7.5 X 10(-7) M [3H]NE or [3H]DA showed that a high proportion of all the cells in these cultures had a grain density which was clearly above background. When Na+ was omitted from the medium, the temperature was lowered to 4 degrees C, or 10(-7) M desmethylimipramine or 10(-7) M amitryptyline were present, cellular grain density after exposure to both [3H]NE and [3H]DA was greatly reduced, to close to background levels. It also appeared necessary to have inhibitors of both monoamine oxidase (pargyline) and catecholamine-O-methyltransferase (tropolone) present to see clear cellular localization for [3H]DA. In the case of [3H]NE the presence of tropolone alone was adequate to observe cellular localization. These results confirm our previous findings of the existence of a high affinity uptake process for catecholamines in primary astrocyte cultures based on uptake properties, and in the present study also localizes such uptake to the major, astrocytic cell type.

An immunocytochemical study of the development of central serotoninergic neurons in the chick embryo

The development of central serotoninergic neurons in the chick embryo has been investigated immunocytochemically by utilizing an antiserum to serotonin (5-HT). Immunoreactive neurons are first detected in the brainstem on embryonic day 4 (E4, stage 23), days earlier than 5-HT systems have been detected previously by biochemical techniques. The earliest 5-HT-containing cells at E4 appear rostral to the pontine flexure, yet by E5, 5-HT neuronal groups are observed throughout the brainstem from just caudal to the mesencephalic flexure to the cervical flexure. During this and subsequent phases of development, two distinct patterns of cellular migration seem to be involved in the formation of the various 5-HT neuronal groups. One pattern involves a ventral migration of 5-HT cells, which appears dependent upon the directional guidance of midline radial processes (formed by floor plate cells) that extend across the neuroepithelium. The other pattern involves a lateral migration of cells, followed by an aggregation and rearrangement of 5-HT neurons into distinct subgroups or clusters. Through these patterns of migration most components of the 5-HT neuronal system can be recognized as early as E12, with the mature organization of the 5-HT cell groups occurring by E17. One unexpected finding was the comparatively late appearance (between E9 and E12) of 5-HT neurons in the paraventricular organ of the hypothalamus. Thus, in comparison to the initial observation of the majority of brainstem 5-HT neurons at E4 to E5, the hypothalamic 5-HT cells appear after a delay of between 5 and 7 days. Such differences illustrate the fact that neurons sharing a common neurotransmitter phenotype do not necessarily share the same developmental timetable for the expression of that particular phenotype, or they may undergo neurogenesis during considerably different periods of embryogenesis.

Characteristics of norepinephrine uptake in developing peripheral nerve terminals

In the chick the various characteristics of [3H]norepinephrine (NE) uptake do not appear simultaneously during the development of the iris. Na+-dependence and ouabain sensitivity are both first seen at a significant level at 10 days of incubation (d.i.). Na+-dependence achieves its peak value at 14 d.i. and is unchanged at 3 months after hatching (a.h.). Ouabain sensitivity increases after its initial appearance to 14 days a.h. and then slowly declines. Temperature sensitivity develops only at hatching and is modified subsequently. Both desmethylimipramine (DMI) and cocaine inhibition develop at 10 d.i. and follow the same developmental pattern; however, DMI appears to be a more effective inhibitor than cocaine. Metanephrine, an inhibtor of extraneuronal uptake, first inhibits NE uptake to a significant degree at hatching. These changes may be related to changes in membrane structure and metabolic function in the developing neuronal membrane. No evidence of [3H]NE uptake is seen at 7 d.i. After this age the Km values tend to fall into two groups, the first 1.3--1.9 X 10(-5) M, up to one month a.h., the second, 3.5--5.0 X 10(-6) M, after one month a.h. There is a large increase in Vmax from 10 to 14 d.i., a period of rapid growth of sympathetic innervation of the iris. Our study suggests that Na+-dependent uptake is a more reliable and constant index of innervation in development than temperature-dependent uptake. It also indicates that in longitudinal developmental studies it is necessary to determine the characteristrics of the transport process of each stage, as characteristics such as N1+-, drug- and temperature-sensitivity may all have unique developmental profiles.