Nerve growth factor brain concentration and stress: changes depend on type of stressor and age

In the relationship between the hippocampus and the hypothalamo-pituitary-adrenocortical axis, trophic and tropic actions of nerve growth factor are involved in parallel with those on the cholinergic nuclei of the basal forebrain. Here, we report the changes produced by stress activation of the hypothalamo-pituitary-adrenocortical axis on hippocampal and basal forebrain nerve growth factor concentrations in 3-month-old male Wistar rats. The stressors used were: restraint; cold exposure; foot-shock; and rotatory platform. Restraint stress tended to reduce nerve growth factor in the hippocampus and reduced it significantly in the basal forebrain. Nerve growth factor levels in the hippocampus were not modified by cold exposure. However, a single unrepeated exposure significantly increased nerve growth factor in the basal forebrain. Both acute and chronic foot-shock reduced nerve growth factor in the hippocampus, leaving the levels in the basal forebrain unmodified. Acute but not chronic rotatory platform reduced nerve growth factor in the hippocampus, while showing a tendency, more pronounced after chronic application, toward an increase in the basal forebrain. Since with aging both activity of the hypothalamus-pituitary-adrenal axis and nerve growth factor trophic and tropic functions change, we studied the effect of restraint and cold stress in the 24-month-old male rat. The variations in nerve growth factor concentrations in the basal forebrain following stress activation are no longer present in the aged rat. The picture that emerges is indicative of a complex relationship between stress and nerve growth factor which is influenced by the kind of stressor and by age. Lack of uniformity in the effects produced by different stressors might reside in different qualitative and/or quantitative degree of involvement of neurotransmitters and/or neurohormones for each of them.