PLASTICITY OF NO SYNTHASE EXPRESSION IN THE NERVOUS AND ENDOCRINE SYSTEMS

Using immunohistochemistry and in situ hybridization the effect of ner ve injury and of hormones was analysed in sensory and hypothalamic sys tems and in the pituitary gland. After peripheral axotomy a marked inc rease in NOS protein and mRNA levels was observed in dorsal root gangl ia, the trigeminal ganglion and a less dramatic effect in the nodose g anglia. This effect lasted in the dorsal root ganglion neurons for at least 10 weeks. In the hypothalamic magnocellular neurons a transient increase was observed in the paraventricular and supraoptic nuclei. A similar effect was also seen after salt loading. In the anterior pitui tary gland NOS was expressed in gonadotrophs and folliculo-stellate ce lls. Castration markedly increased NOS levels in the anterior lobe, an d this could be counteracted by steroid hormone replacement. Thus, the present results show that the constitutive, neuronal NOS can be drama tically regulated in response to various manipulations, suggesting an important involvement of NO in these situations.