Steroid hormones modify several functions of the nervous system by altering expression of particular genes that are relevant for cell-to-cell communication, neuronal structure, and differentiation. There are many regions of the brain showing structural differences between male and female. These sexual dimorphisms are primarily based on cytological features of the nervous system brought about by the organizational action of sex steroid hormones. Glucocorticoids also have a great influence on neuronal survival and differentiation. First, in this paper the estrogen effect on the phenotypic changes of neurons in the preoptic area in vivo was described, particularly in the neuronal system of methionine-enkephalin and calcitonin gene-related peptide. Second, the tissue culture system for the preoptic area was developed and the estrogen effect on process extension associated with cytoskeletal changes was examined. Third, glucocorticoid suppression of the differentiation of adrenal chromaffin cells and transmitter/neuropeptide plasticity was studied in the dissociated culture system. The results suggest that steroids modulate neurotransmitters and neuropeptides expression along with the alteration of cell structures in a different manner in a tissue-specific pattern.