Biomedical subjects

J Engele

Publications and source records attributed to J Engele.

23 records · Page 2Linked to original sources

PubMed1991

The neurotrophic effects of fibroblast growth factors on dopaminergic neurons in vitro are mediated by mesencephalic glia.

Neurotrophic support is generally believed to result from a direct action of growth factors on developing neurons. However, there is increasing evidence that growth factors can indirectly affect neuronal development by glial-mediated processes. To investigate a possible role of glia in mediating neurotrophic effects on dopaminergic neurons, four purified growth factors were screened for dual effects on the survival and differentiation of dopaminergic neurons and on the proliferation of mesencephalic glial cells in vitro. Dissociated embryonic day 14.5 rat mesencephalon was grown at low cell density without serum, conditions under which both glial growth and neuronal survival are not optimal. Treatment of these cultures with acidic fibroblast growth factor (aFGF) or basic fibroblast growth factor (bFGF) increased the number of surviving tyrosine hydroxylase-immunoreactive (TH-IR) neurons by 90-110% [corrected] at 8 d in vitro in a dose-dependent manner. The effects of these factors were not additive. High-affinity dopamine uptake was increased by bFGF, but not by aFGF. Length of TH-IR neurites was not affected by either aFGF or bFGF. Both growth factors induced proliferation of mesencephalic astrocytes as demonstrated by autoradiographic labeling with 3H-thymidine combined with immunocytochemistry for glial fibrillary acidic protein (GFAP). In contrast, platelet-derived growth factor (PDGF) and interleukin-1 had no effect on the survival or differentiation of dopaminergic neurons or the proliferation of mesencephalic astrocytes. Inhibition of glial proliferation abolished the neurotrophic effects exerted by aFGF or bFGF on dopaminergic neurons. Moreover, conditioned medium derived from mesencephalic glial cultures replated in the virtual absence of neurons also contained neurotrophic activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Different developmental potentials of diencephalic and mesencephalic dopaminergic neurons in vitro.

Morphological and functional differentiation of dopamine (DA) neurons was compared in dissociated cultures from gestational day 14 rat mesencephalon and diencephalon. Numbers of tyrosine hydroxylase-immunoreactive (TH-IR) neurons relative to all neurons were 4 and 1.7 times higher in mesencephalic than in diencephalic cultures at 6 and 13 days in vitro (DIV), respectively. Morphological maturation of diencephalic DA neurons was retarded in comparison to mesencephalic DA neurons. There were gross differences in soma size and length of processes between the two types of DA neurons, the appearance of which was strongly reminiscent of DA cell types described in vivo. Functional maturation of DA neurons was quantified by measuring uptake and Ca2+-dependent K+-stimulated release of [3H]DA per TH-IR neuron. As early as 6 DIV, DA uptake by mesencephalic DA neurons was saturable, was sensitive to benztropine and reserpine, and could be displaced by unlabeled DA. Twenty to 30% of the radioactivity accumulated could be released upon depolarization within a period of 5 min. At 6 DIV, influx of [3H]DA into diencephalic DA neurons was almost insensitive to benztropine, reserpine and unlabeled DA. Even after 13 DIV, diencephalic DA uptake was characterized by a markedly lower initial velocity, a longer time needed to reach saturation, a lower uptake capacity, and a lower sensitivity to benztropine than mesencephalic DA uptake. The releasable pool was very small and did not increase between DIV 6 and 13. The results demonstrate that mesencephalic DA neurons in vitro differentiate considerably faster than diencephalic DA neurons and gain functional competence very early in brain development. Comparison with data on adult nigrostriatal and hypothalamic DA systems suggests that the in vitro differences reflect a fundamental regional diversity of DA neurons.

Animals↗

PubMed1989

Early sexual differentiation of diencephalic dopaminergic neurons of the rat in vitro.

Development of dopaminergic neurons was investigated in dissociated cell cultures raised from the diencephalon of male and female rat fetuses from days 14 and 17 of gestation. Striking differences in morphology and function of male and female dopaminergic neurons were observed. Outgrowth of tyrosine hydroxylase-immunoreactive processes initially proceeded at a faster rate in female than in male cultures. Morphological differences disappeared in cultures of gestational day 17. Irrespective of the age of the cultures and of the length of cultivation, the uptake capacity for (3H)dopamine per immunoreactive neuron was twice as high in female than in male cultures. Treatment of the cultures with sex steroids did not influence morphology, numbers or transmitter uptake of tyrosine hydroxylase-immunoreactive neurons. The results suggest that diencephalic dopaminergic systems exhibit a sexual dimorphism that develops unexpectedly early in ontogeny and is independent of the action of gonadal hormones.

Animals↗

PubMed1989

Sexual differentiation of mesencephalic neurons in vitro: effects of sex and gonadal hormones.

In order to study the influence of gender on the development of transmitter uptake by dopaminergic neurons, dissociated cell cultures were raised separately from male and female midbrains of gestational day 14 rats. It was ascertained by use of specific inhibitors and by autoradiography that the uptake of [3H]dopamine was restricted to neurons immunoreactive for tyrosine hydroxylase and that these neurons have dopaminergic properties. The uptake capacity was higher in male than in female dopaminergic neurons by a factor of 1.5. This sexual dimorphism in dopamine uptake was present in cultures of tissue removed before the perinatal rise of testosterone occurs in males, and was present even in the absence of hormonal additives to the culture medium. It therefore appears to be independent of the presence of gonadal steroids. It occurred likewise in cultures raised with serum-supplemented and serum-free medium, which may indicate that glia are not decisive in generating these differences. In addition, sexual differences were found regarding hormone responsiveness. Whereas testosterone and dihydrotestosterone were ineffective, estradiol was seen to promote dopamine uptake in female but not in male neurons. The results would suggest that mesostriatal and/or mesolimbic dopaminergic systems assume an early role in the development of some sexual dimorphisms of the brain.

Animals↗

PubMed1986

Different developmental schedules of dopaminergic and noradrenergic neurons in dissociation culture of fetal rat midbrain and hindbrain.

The development of dopaminergic and noradrenergic neurons in dissociation cultures of mesencephalon and rhombencephalon obtained from 18-day-old rat fetuses was characterized by their capacity to take up and release catecholamines. In both types of cultures, uptake of [3H]dopamine and [3H]noradrenaline was obtained which could be inhibited by reserpine. Autoradiographic studies demonstrated an almost exclusive neuronal localization of the labeled catecholamines. The transmitters could be released by depolarization with K+ in a Ca2+-dependent manner during the entire cultivation period. In contrast, catecholamine uptake by cultures of neocortex was minimal, could not be inhibited by reserpine, and the accumulated radioactivity could not be released upon depolarization. These points provide evidence for an active accumulation of the exogenous transmitters and for the presence of stimulus-secretion coupling in a distinct population of neurons of both brain stem cultures. Striking differences between the two brain stem cultures concerned their sensitivity to desmethylimipramine and benztropine as well as the time course of the development of the uptake capacity. Desmethylimipramine inhibited the uptake of both catecholamines in rhombencephalic, but not in mesencephalic cultures. The reverse was true for benztropine. It is concluded that cultures of rhombencephalon contain predominantly noradrenergic, and those of mesencephalon dopaminergic cells. Comparison of the uptake behaviour suggested that noradrenergic neurons mature considerably later than dopaminergic neurons. The results show that dissociation cultures of mid- and hindbrain, inspite of their heterogeneous composition, can serve as valuable models for the study of development and function of dopaminergic and noradrenergic neurons, respectively.

Adrenergic Fibers↗