Changes of NGF level in mouse hypothalamus following intermale aggressive behaviour: biological and immunohistochemical evidence

Nerve growth factor (NGF) immunoreactivity was detected in the hypothalamus of adult male mice. NGF-immunoreactive cell bodies were examined through consecutive brain sections, and it was found that most of the NGF-positive cells were located in the dorsomedial and mediolateral portions of the hypothalamus. Tissue culture bioassays showed that hypothalamic extract elicits neurite outgrowth from both chick sensory ganglia and rat superior cervical ganglia neurons, and that these effects are inhibited by addition of NGF antibodies. Our results also showed that intermale aggressive behaviour induced by 6-8 weeks of social isolation induces an NGF increase in the hypothalamic area, which is not abolished by sialoadenectomy, suggesting that the increased brain NGF is locally synthesized, and does not come from salivary sources. Likewise, the level of NGF in the hypothalamus of adrenalectomized fighting mice increased, although to a much lesser extent, when compared to hypothalamic levels of sham-operated fighting mice. The present results and a recent report showing that aggressive behaviour causes an increase of mRNANGF in hypothalamic areas are discussed in relation to a possible functional role of NGF in these brain structures.