Nerve growth factor differentially modulates the expression of its receptor within the CNS.

The effect of nerve growth factor on the expression of nerve growth factor receptor in the central nervous system of newborn and adult rats was studied by means of immunohistochemistry with the monoclonal antibody 192-IgG. Both during development and in adulthood, the intracerebroventricular administration of nerve growth factor elicited a pronounced increase of nerve growth factor receptor-like immunoreactivity in the cell bodies and neural processes of the basal forebrain cholinergic nuclei, as compared to cytochrome c-treated rats (controls). A pronounced nerve growth factor-induced increase of nerve growth factor receptor-like immunoreactivity was also observed in central regions innervated by trigeminal and spinal ganglia. A moderate to a marked increase of nerve growth factor receptor-like immunoreactivity was evident in some mesencephalic visual system-related structures and thalamic nuclei expressing nerve growth factor receptor. In contrast, NGF treatment did not induce appreciable modification of nerve growth factor receptor-like immunoreactivity in cerebellar, brainstem, and spinal motor structures of newborn rats. In adult nerve growth factor-treated rats, a decrease of nerve growth factor receptor-like immunoreactivity was detected in the cerebellum, whereas no re-expression of nerve growth factor receptor-like immunoreactivity occurred in the motor structures that had expressed it in the first postnatal week. Finally, nerve growth factor was also found to enhance, in both adult and newborn rats, nerve growth factor receptor-like immunoreactivity associated with ependymal and subependymal cellular elements of the lateral and third ventricles, as well as with the leptomeninges overlying the superior colliculus and supraoptic area. The present results indicate that endogenous nerve growth factor or nerve growth factor-like molecules may play a dynamic role in a variety of cell populations of both the developing and mature mammalian central nervous system. We thus propose the nerve growth factor ability to modulate its receptor in vivo as a novel criterion to define nerve growth factor or nerve growth factor-like molecules, sensitive neuronal, and non-neuronal cells. Whereas this criterion does not intrinsically possess absolute physiological validity, its pharmacological concomitants might be relevant in view of the proposed therapeutical use of this trophic factor.

Rat NGF receptor is recognized by the tumor-associated antigen monoclonal antibody 217c.

The expression of the epitope recognized by the tumor-associated antigen monoclonal antibody 217c increased on cultured rat Schwann cells with time. The same phenomenon has previously been reported for the rat nerve growth factor (NGF) receptor by using monoclonal antibody 192-IgG. The distribution of 217c antibody immunoreactivity closely paralleled that observed for NGF receptors on NGF-primed pheochromocytoma (PC12) cells in culture and a number of central neurons in vivo. Immunoprecipitation of affinity-labeled NGF receptors was used to examine whether these two antibodies shared common or unique antigens. Both the quantitative data and the electrophoretic mobility of the immunoprecipitated 125I-NGF/receptor complex indicate that the antigen recognized by the 217c mAb monoclonal antibody is, in fact, the NGF receptor. Furthermore, binding studies indicated that 192-IgG and 217c recognize different epitopes on the same molecule. The characterization of the 217c antibody should provide a valuable new tool in the study of NGF receptors.

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.

Characterization and calibration of a variable-angle absolute reflectometer.

The instrument described is a newly designed reflectometer. Measurements are made with a polarized light beam as a function of wavelength and angle of incidence. Calibration tests have outlined the possibility of using the instrument for reflectance measurements on mirrors with good reproducibility (0.2%) and accuracy (better than 1%). This has been obtained by the alignment system of the sample and the absolute method used for the determination of its reflectance.

Effects of phosphatidylserine administration of aged-related structural changes in the rat hippocampus and septal complex.

Dendritic spine density of CA1 pyramidal neurons in the hippocampus and morphometric characteristics of the cholinergic neuronal population of the septal complex, were evaluated in young (four months), aged (27 months), and age-matched rats which had received long-term phosphatidylserine (BC-PS) administration (50 mg/kg/die, suspended in the drinking water). In aged rats, spine density decreased significantly by 12.11% in the basal dendrites and by 10.64% in the apical ones, as compared with young controls. In the cholinergic neuronal population of medial septum and diagonal band, aging induced a statistically significant reduction in cell number (-19.6%), in soma area (-18.5%), in cell maximal diameter (-9.2%), and in the area covered by all cholinergic profiles (-33%). By contrast, no significant reductions in the above-mentioned structural parameters were observed in aged BC-PS-treated rats when compared with young animals. The mechanisms underlying the beneficial effects of BC-PS can possibly be ascribed to the pharmacological actions exerted by BC-PS on neuronal membranes, neurotransmission, and/or interaction with NGF.

Evidence for a physiological role of nerve growth factor in the central nervous system of neonatal rats.

Forebrain cholinergic neurons have been shown to respond in vivo to administration of nerve growth factor (NGF) with a prominent and selective increase of choline acetyltransferase (ChAT) activity. This has suggested that NGF can act as a trophic factor for these neurons. To test this hypothesis directly, anti-NGF antibodies (and their Fab fragments) were intracerebroventricularly injected into neonatal rats to neutralize endogenously occurring NGF. The anti-NGF antibody administration produced a decrease of ChAT activity in the hippocampus, septal area, cortex, and striatum of rat pups. This finding was substantiated by a concomitant decrease of immunopositive staining for ChAT in the septal area. These effects indicate that the occurrence of endogenous NGF in the CNS is physiologically relevant for regulating the function of forebrain cholinergic neurons.

NGF Amplifies Expression of NGF Receptor Messenger RNA in Forebrain Cholinergic Neurons of Rats.

In order to study the ligand-mediated regulation of NGF receptors in vivo, we assessed NGF receptor mRNA in the septal area of both neonatal and adult rats following intraventricular NGF administration. In neonatal rats NGF treatment, in comparison with cytochrome c, elicited a pronounced augmentation in the level of NGF receptor mRNA. A similar effect was also observed following continuous intraventricular NGF infusion in young adult rats. In addition, in this latter case, the increase in NGF receptor mRNA was associated with an increase in NGF receptor-related immunoreactivity, most likely associated with the cholinergic neurons, in the septal area. These results show that NGF itself may regulate expression of NGF receptor mRNA and corresponding protein levels in forebrain cholinergic neurons and suggest that NGF effects in the CNS may be mediated by an up-regulation of NGF receptors.

Muscle reinnervation--II. Sprouting, synapse formation and repression.

Extensor digitorum longus muscle is reinnervated by the regenerating neurites at the end-plate region; as soon as the contact is made, the rate of neurite elongation inside the cleft decreases about 1000-fold while interfibre growth and sprout formation proceed unchanged. Polyinnervation reaches the maximum level 7-10 days after reinnervation, then synaptic repression begins. The elimination of redundant innervation takes place when the biophysical properties of the muscle are again normal. There is no sign of either phagocytosis or degeneration, therefore the process of synaptic repression is probably due to retraction, as neurites do when in culture. The role of Schwann cells and nerve sheath in the process of maintenance is suggested.