Nerve growth factor receptor-immunoreactive fibres innervate the reticular thalamic nucleus: modulation by nerve growth factor treatment in neonate, adult and aged rats

Terminal arborizations expressing nerve growth factor receptor (NGF‐R) have been detected with immunohistochemistry in the reticular thalamic nucleus of neonate, adult and aged rats. Intracerebroventricular administration of nerve growth factor (NGF) resulted in a dramatic increase in NGF‐R immunoreactivity throughout the lifespan. This effect was paralleled by a concomitant increase in NGF‐R immunopositivity in the neurons of the basal forebrain, which was here demonstrated also in aged animals, thus indicating that the NGF‐R immunoreactivity within the reticular thalamic nucleus derives in all likelihood from cholinergic neuronal cell bodies of the basal forebrain. Our results demonstrate a prominent ability of NGF to up‐regulate its receptors within fibres innervating the reticular thalamic nucleus, and show that this up‐regulation of NGF‐R is maintained throughout the lifetime. Altogether this indicates that the reticular thalamic nucleus may represent a new, important site of action of endogenous NGF or NGF‐like molecules within the brain. In view of the crucial role played by the reticular thalamic nucleus in gating thalamocortical information, the autoregulation of NGF‐R in this structure may have important concomitants in both physiological and pathological conditions.