Testosterone propionate (TP) and corticosterone acetate (CA) were administered alone and in combination with T4 to assess the effect on submaxillary gland (SMG) nerve growth factor (NGF) and epidermal growth factor (EGF) concentrations in adult female mice. Mice were treated for 5 or 10 days. SMG NGF, and EGF concentrations were measured by specific RIA techniques. Mean SMG NGF (0.68 +/- 0.08 microgram/mg protein) and EGF (0.58 +/- 0.05 microgram/mg protein) concentrations were similar in control mice. T4 (0.4 microgram/g BW, sc, daily) significantly increased mean SMG NGF and EGF concentrations to 469% and 347%, respectively, of control values after 5 days and to 1190% and 568%, respectively, after 10 days of treatment. TP (25 microgram/g BW, sc, every 2 days) significantly increased mean SMG NGF and EGF concentrations to 734% and 767%, respectively, of control values at 5 days and to 1971% and 1953%, respectively, at 10 days. T4 and TP resulted in no further significant increases in either SMG NGF or EGF concentrations above the levels observed after TP alone. CA (25 microgram/g BW, sc, daily) increased mean SMG NGF, but not EGF, concentrations at both 5 and 10 days. Moreover, T4 and CA appeared to exert an additive effect on NGF. In contrast to the observations in adult female mice, T4 increased mean SMG NGF concentrations to 178% of control levels in adult male mice, but had no significant effect of SMG EGF concentrations. These data indicate that T4 and TP modulate SMG NGF and EGF concentrations in adult female mice. T4, however, appears to have a preferential effect on NGF on both male and female mice, unlike the equal effect on TP on both NGF and EGF. CA, like T4, also appears to increase NGF, but not EGF, concentrations in adult female SMG. The present results suggest separate regulatory mechanisms for T4, TP, and CA on SMG NGF and EGF biosyntheses.

A pure neuronal culture grown in a defined serum-free environment has been developed and characterized. Insulin was the only hormone found to enhance the growth of neurons obtained from embryonic chicken brains during the early proliferative stage, a time when many neurons survived without the addition of any growth factors to the culture. With increasing embryonic age, there was an increase in the number of neurons requiring transferrin. By the time neurons reached a postmitotic state in older brains, they were completely dependent on both insulin and transferrin for survival and growth. Because this culture is free of glial cells and serum, it provides an effective basis for investigating molecular mechanisms underlying neuronal development.Current understanding of neuronal development has progressed slowly due to the complexity of the developing brain, in which astrocytes, oligodendrocytes, neurons, and their precursors interact in an ever-changing chemical environment. This complexity has been a major obstacle to defining the stages and characterizing the biochemical changes through which neurons progress during development. Our approach towards unravelling the developmental process has been to isolate, culture, and study a population composed of a single cell type as it proliferates and differentiates. This investigation defines the requirements for neuronal growth in vitro and the changes occurring in these requirements as the neurons develop in vivo.We have studied 6-to 9-embryonic day (ED) chicken brains because they are composed of a nearly pure population of neuronal cells that during this period progress in vivo from a dividing to a postmitotic state (1-3). The majority of neuronal cultures previously described (4, 5) contain serum. Its ill-defined and variable composition and its ability to promote the proliferation of glial cells, which produce neuronal growth factors (6), have prevented investigators from defining the molecular growth requirements of neurons. The only previous attempt to culture chicken brain cells in a defined medium, after an exposure to serum, did not delineate the factors critical for neuronal survival and, in addition, did not characterize the cell types of the culture (7).In this study, we have investigated the essential growth requirements for pure neuronal populations obtained from embryos of various ages. We found these requirements to change with development. The neuronal cultures were characterized by immunocytochemical and biochemical means and were found to be essentially free of glial cells. This eliminated the possibility of the factors acting on, or via, glial cells and increases the effectiveness of this culture system for studying neuronal development. MATERIALS AND METHODSCell Culture Preparation. Neuronal cultures were prepared from 6-, 7-, 8-, or 9-ED brains. After the brains had been dissected from the chicken embryos and the meninges had been stripped off, the tissue was put in 1:1 mixture of Dulbecco-Vogt modified Eagle's medium and Ham's F-12 medium...

The expanding perinatal use of glucocorticoids entails potentially hazardous effects of these hormones on nervous system development. Neonatal animal experimentation with pharmacological doses of glucocorticoids has revealed immediate effects on brain cell division, differentiation, myelination, and electrophysiological reactions. In addition, delayed (latent) effects include changes in control of circadian periodicity, altered biogenic amine levels, altered response to stress, and changes in ultimate behavior. Thus perinatal hormone therapy during critical periods of brain development is capable of exerting irreversible immediate effects on brain cell division and differentiation, resulting in latent or long-term physiological and behavioral effects.

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