FOS INDUCTION BY NERVE GROWTH-FACTOR IN THE ADULT-RAT BRAIN

The distribution of Fos, the protein product of the immediate early ge ne c-fos, was studied with immunocytochemistry in the adult male rat b rain after nerve growth factor (NGF) administration. NGF was injected in the lateral cerebral ventricle through a previously implanted cannu la. The total number of Fos-immunoreactive (ir) neurons in the brain w as 2-3 times higher after NGF administration than in control animals ( untreated or injected with cytochrome c). With respect to control rats , in the NGF-treated cases Fos-ir cells were more numerous in the ante rior olfactory nucleus, in the medial prefrontal and anterior cingulat e cortices, in the basal forebrain, in the preoptic and ventromedial n uclei of the hypothalamus, as well as anterior hypothalamic area, in t he thalamic midline nuclei, and in some brainstem structures, such as the parabrachial nucleus. The relative quantitative increase of Fos-ir neurons varied in the different structures. In addition, Fos-ir neuro ns were evident after NGF administration in areas devoid of immunoposi tive cells in control animals. These included: frontoparietal and occi pital cortical fields, the hypothalamic arcuate nucleus, and many brai nstem structures, such as the dorsal nucleus of the lateral lemniscus, posterodorsal tegmental, medial and lateral vestibular, ventral cochl ear, and prepositus hypoglossal nuclei. These findings demonstrate tha t the intracerebroventricular administration of NGF can induce c-fos e xpression in neurons in vivo. The distribution of Fos-ir neurons indic ates that NGF can induce activation of functionally and chemically het erogeneous neuronal subsets in the brain.