Direct hypertonic stimulation of the rat supraoptic nucleus increases c-fos expressionin glial cells rather than magnocellular neurones

We investigated whether hypertonicity acts directly on supraoptic neurones to activate c-fos expression. Hypertonic artificial cerebrospinal fluid was infused into the supraoptic nucleus (SON) via a microdialysis probe implanted 24 h previously. The rats were decapitated after 90 min for immunohistochemistry with a Fos protein antibody. Direct hypertonic stimulation increased Fos protein expression in glial cells, identified by glial fibrillary acidic protein immunoreactivity, but not in magnocellular neurones. Similarly, with in situ hybridisation c-fos mRNA expression was predominantly seen in glial cells. Fos expression in SON neurones was stimulated by systemic hypertonicity even with a microdialysis probe in the SON, and magnocellular neurones expressed Fos after direct microinjection of cholecystokinin-8S into the SON. Thus, while direct hypertonic stimulation of SON neurones activates secretion of vasopressin and oxytocin, the c-fos gene is not activated, unlike following systemic hypertonic stimulation. This indicates that excitation of neuronal electrical and secretory activity does not necessarily lead to activation of the c-fos gene. Activation of c-fos expression in glial cells by direct hypertonic stimulation may reflect their role in regulating brain extracellular fluid composition. Received: 11 March 1996 / Accepted: 24 July 1996     

Effects of neonatal diethylstilbestrol exposure on c-fos and c-jun protooncogene expression in the mouse uterus

Quantitative and cell-type-specific expression of c-fos and c-jun genes after 17beta-estradiol (E2) stimulation, was investigated in the uteri of neonatally diethylstilbestrol (DES)-exposed and ovariectomized adult mice (neoDES-mice), employing Northern blot analysis, immunohistochemistry and in situ hybridization. The c-fos mRNA level before E2 injection (at baseline) was about 2.2-fold higher in neoDES-mice than in vehicle-treated control mice. In controls, E2 treatment transiently increased c-fos mRNA levels, showing a peak value (15.8-fold relative to the baseline) after 2 hours. In neoDES-mice, c-fos mRNA level reached a peak showing a 2.1-fold increase compared with its baseline value 1 hour after E2 injection. Immunohistochemistry and in situ hybridization revealed that c-fos protein (Fos) and mRNA are induced in the epithelium and vascular endothelium in both groups. Most uterine epithelia of neoDES-mice revealed low sensitivity to the c-fos expression after E2 administration compared with those of vehicle-treated controls, whereas few epithelia showed high c-fos mRNA expression even at baseline. The c-jun mRNA concentration in the neoDES-mice uteri at baseline was 70% of that in vehicle-treated controls. At 1 hour after E2 injection, c-jun mRNA levels increased 1.8-fold in controls and 1.3-fold in the neoDES-mice relative to each baseline value. There were no significant differences in the distribution pattern of c-jun protein (Jun) and mRNA in the uteri of either groups; E2 stimulated c-jun mRNA expression in the stromal and myometrial cells but suppressed it in the epithelial cells, whereas intensity of c-jun immunostaining increased in the three cell types. The permanent changes in the expression of estrogen-regulated protooncogenes, c-fos and c-jun genes, by neonatal DES exposure may be responsible for the wide range of abnormalities in the genital tract of mature animals.     

Stimulus-induced coordinate changes in mRNA abundance in single postsynaptic hippocampal CA1 neurons.

The molecular effects of use-dependent changes in synaptic transmission were studied in individual CA1 pyramidal neurons from rat hippocampal slices. Potentiation of excitatory postsynaptic currents was associated with coordinate changes in the relative abundance of several mRNAs 30 min to 3 hr after stimulation. There was a 300% increase in calcium/calmodulin-dependent protein kinase II mRNA levels concordant with a 50% decrease in protein kinase C beta 1 isoform mRNA. A 2-fold increase in zif-268 mRNA was seen, while increases in c-fos and c-jun mRNA levels were inconsistent, gamma-Aminobutyric acid A receptor beta 1 subunit mRNA levels increased 3-fold. Potentiation-induced changes were prevented by N-methyl-D-aspartate receptor blockade. Changes in mRNA abundance in individual cells, with synaptic and glial interactions intact, combine to produce a molecular fingerprint of a potentiated CA1 neuron.     

Differential effects of forskolin and phobol 12-myristate-13-acetate on the c-fos and c-jun mRNA expression in rat C6 glioma cells

The effects of forskolin (FSK) and phobol 12-myristate-13-acetate (PMA) on c-fos and c-jun mRNA expressions in rat C6 glioma cells were studied. Both FSK and PMA increased the c-fos mRNA level. The C-jun mRNA level was decreased by FSK, whereas it was increased by PMA. The elevated c-fos mRNA level, induced by FSK or PMA, was significantly inhibited by dexamethasone (DEX). In contrast, DEX did not affect the FSK- and PMA-induced response of the c-jun mRNA level. Cycloheximide (CHX) caused a superinduction of the FSK- or PMA-induced c-fos mRNA level. Furthermore, CHX also potentiated the PMA-induced c-jun mRNA level. However, CHX did not affect the FSK-induced down-regulation of the c-jun mRNA level. When C6 glioma cells were incubated with PMA and FSK, the PMA-induced c-jun mRNA level was inhibited by FSK, whereas FSK did not affect the PMA-induced c-fos mRNA level. Our results suggest that the activations of PKA and PKC pathways have different roles in the regulation of the c-jun mRNA expression in rat C6 glioma cells. PKA activation can inhibit induction of the c-jun mRNA expression by PMA. In addition, DEX appears to have a selective inhibitory action against c-fos, but not c-jun, -mRNA expression that is regulated by PKA and PKC. On-going protein synthesis inhibition is required for the superinduction of the c-fos expression that is induced by PMA, or FSK and the PMA-induced c-jun mRNA level.