Light and electron microscopic evidences of the presence of c-fos-like immunoreactivity in the rat adrenal cortex

Ultrastructure of Fos-labeled neurons relating to nociceptive primary afferent and substance P terminals in rat spinal superficial laminae

The presence of Fos-labeled neurons at ultrastructural level was confirmed in the spinal superficial laminae following an injection of formalin into rat hindpaw in the present study. The Fos-like immunoreactive products were found exclusively in regions associated with the euchromatin in the nuclei of Fos-labeled neurons. By the methods used-of anterograde transport of horseradish peroxidase conjugated to wheat-germ agglutinin and immunocytochemistry-it was observed that some Fos-labeled neuronal bodies received synaptic contacts from, or were apposed directly to, small diameter primary afferent terminals in the spinal superficial laminae. By means of double-labeled immunocytochemistry, a direct apposition was often observed and a synaptic relationship was occasionally found between Fos-labeled neuronal bodies and substance P-like immunoreactive terminals.

Nicotine-induced fos-like immunoreactivity in rat sympathetic ganglia and adrenal medulla

The expression of c-fos proteins (Fos) in principal sympathetic neurons and adrenal chromaffin cells was studied immunocytochemically after a single s.c. injection of nicotine (2mg/kg). One and 2 h after injection most of the adrenal chromaffin cells showed nuclear Fos-like immunoreactivity (Fos-IR). In the superior cervical ganglion more than 80% of the neuronal nuclei were Fos-IR 2-5 h after nicotine administration, whereas only 50-60% of the neurons in the hypogastric ganglion were immunoreactive at these time points. The results suggest that nicotinic receptor mediates signal transduction, which induces c-fos expression both in sympathetic neurons and in adrenal chromaffin cells in vivo.

The immediate-early genes c-fos and c-jun are differentially expressed in the rat adrenal gland after capsaicin treatment

In situ hybridization histochemistry was used to study the expression of c-fos and c-jun mRNA in the rat adrenal gland of untreated and capsaicin treated rats. In untreated animals, very low levels of c-fos mRNA were present both in zona fasciculata and reticulata of the adrenal cortex, with no detectable labelling in the zona glomerulosa or adrenal medulla. In contrast, the levels of c-jun mRNA were high in the cortical layers fasciculata and reticulata, again without labelling in the zona glomerulosa or adrenal medulla. After capsaicin (25 mg/kg, s.c.), a rapid increase in both c-fos and c-jun mRNA levels was observed in adrenal medulla. Capsaicin also induced an increase in c-fos mRNA levels in all 3 cortical layers, especially in the zona glomerulosa, whereas only small changes in c-jun mRNA levels were seen in zona fasciculata and reticulata. The present results indicate that c-fos and c-jun mRNA levels are both increased in the adrenal gland after capsaicin treatment, although the time course, magnitude and regional distribution of these increases differed for the two mRNAs.

Circadian rhythm in c-fos-like immunoreactivity in the rat brain

The circadian variation in the expression of Fos protein(s) in the rat brain was studied immunohistochemically. The number of Fos-immunoreactive nuclei was statistically increased in the hippocampus and caudate putamen after the onset of darkness. Unlike the cells of the hippocampus and putamen the cells in the suprachiasmatic nucleus displayed a circadian variation with the lowest values during the nighttime and the highest in the morning. As the circadian rhythm of Fos expression in the normal rat brain may correlate with that reported for ACTH and corticosteroids, the results suggest that the fos gene is involved in mediating physiological activation of specific neuron populations of intact rats.

c-fos protein-like immunoreactivity in cultured human glial cells

The expression of the c-fos protein(s) in cultured glial cells of the human brain and sympathetic ganglia was studied immunocytochemically using an antibody to a synthetic fragment of the c-fos protein (M-peptide). GFAP (glial fibrillary acidic protein) and S-100 antibodies were used as glial cell markers. The c-fos immunoreactivity (c-fos IR) was observed in both brain and peripheral ganglion derived cells maintained 7-22 days in culture. In general, c-fos IR was stronger in small spindle-shaped cells than in large cells. Deprivation of serum for 24 h decreased drastically c-fos IR in both types of cultures. The results demonstrate a serum-dependent expression of c-fos in the human glial cells derived from central and peripheral nervous systems.

Circadian rhythm in c-fos protein expression in the rat adrenal cortex

The circadian variation in the expression of c-fos protein(s) in the adrenal cortex of adult rats was investigated immunocytochemically. The animals were maintained in standard laboratory facilities with a 12:12 h light:dark schedule (07.00-19.00 h) until sacrificed. The number of c-fos immunoreactive (c-fos IR) cells was statistically constant in the zona fasciculata and zona reticulata at 20.00 h and 24.00 h, and 04.00 h, but was decreased to 52% at 08.00 h and to 18% at 12.00 h, respectively, when compared to the 24.00 h value. At 16.00 h, the number of c-fos IR cells was increased again to 63% of the 24.00 h value. In the zona granulosa c-fos IR was observed only at 20.00 h and 24.00 h. Administration of dexamethasone, a potent inhibitor of ACTH release, significantly reduced the number of c-fos IR cells. As the circadian rhythm of c-fos expression in the adrenal cortex correlates to that reported for ACTH secretion from the pituitary, the results suggest that c-fos gene is involved in mediating physiological ACTH-induced responses in the adrenal cortical cells.

Induction of c-fos protein-like immunoreactivity in the rat and hamster pineal gland after the onset of darkness

Induction of c-fos protein (FOS) after the onset of darkness was studied immunocytochemically in the rat and hamster pineal gland. The animals were kept on a 12:12 h light-dark cycle. Before the dark period no FOS staining was seen in either rat or hamster pineal cells. Five hours after the onset of darkness 342 +/- 18 pinealocytes/0.2 mm2 (mean +/- SD) displayed FOS-like immunoreactivity in the hamster pineal gland; in the rat pineal gland only 5 +/- 2 pinealocytes/0.2 mm2 showed a faint staining. Two hours later the density of FOS positive cells was decreased to 60 +/- 11/0.2 mm2 in the hamster but increased to 519 +/- 103/0.2 mm2 in the rat pineal gland. Three hours before the beginning of the light period no FOS positive cells were detected in either animal. Both the rat and hamster pineal gland showed a transient and temporally defined expression of c-fos protein in the middle of the dark period. This may be related to a more active functional state of pinealocytes, which is reflected in a peak of melatonin synthesis during the darkness.