Developing rat retinal ganglion cells express the functional NGF receptor p140trkA.

The expression and cellular localization of NGF receptors in the developing rat retina were investigated immunocytochemically and biochemically. In in vitro preparations of retinal neurons from neonatal rats the functional NGF receptor p140trkA was immunocytochemically detected on retrogradely labeled retinal ganglion cells (RGCs). In transverse retinal sections p140trk-immunopositive cells were localized exclusively at the level of the RGC layer. Affinity labeling with 125I-NGF, chemical cross-linking, and immunoprecipitation with anti-NGF antibodies revealed the presence of three complexes which migrate on SDS-PAGE at approximately 90, 95, and 150 kDa. The bands at 90 and 95 kDa correspond to the so-called low affinity NGF receptor p75NGFR. Western blotting experiments using anti-TRK antibodies revealed that the slowest migrating band (150 kDa), which is not immunoprecipitated by monoclonal antibodies to p75NGFR, corresponds to p140trkA. The presence of the functional NGF receptor on RGCs provides the molecular explanation for the reported sensitivity of these cells to the biological action of NGF.

Time course, localization and pharmacological modulation of immediate early inducible genes, brain-derived neurotrophic factor and trkB messenger RNAs in the rat brain following photochemical stroke.

A focal, unilateral thrombotic stroke was produced in the rat sensorimotor cortex. The time course of expression and localization of the immediate early inducible genes: c-fos, c-jun, zif268; nerve growth factor, brain-derived neurotrophic factor and the related tyrosine kinase high-affinity receptor (trkB) messenger RNAs were studied by in situ hybridization. The levels of messenger RNAs for c-fos, zif268, brain-derived neurotrophic factor (but not nerve growth factor) and trkB were consistently increased in cortex ipsilaterally to the lesion, while c-jun messenger RNA content was only slightly increased. The brain-derived neurotrophic factor messenger RNA was increased from 2 to 18 h following the stroke, mainly in cells having a normal morphological appearance. The trkB messenger RNA displayed temporal and spatial increases similar to brain-derived neurotrophic factor messenger RNA. The time course and pattern of expression of immediate early inducible gene and trophic factor messenger RNAs did not clearly support a causal relationship between these two families of factors. The observed messenger RNA increases were greatly attenuated by the non-competitive N-methyl-D-aspartate-sensitive glutamate receptor antagonist (+)-5-methyl-10,11-dihydroxy-5H-dibenzo(a,d)cyclohepten-5,10-imine , but substantially unaffected by the non-N-methyl-D-aspartate receptor antagonist 2,3-dihydroxy-6-nitrosulphanoylbenzoquinoxaline. The results suggest a major contribution of N-methyl-D-aspartate-sensitive glutamate receptor activation to the transcriptionally directed events subsequent to stroke. Future studies should clarify the contribution of these processes to either the progression of neuronal degeneration or the establishment of protective compensatory responses.

Effects of nerve growth factor on neuronal plasticity of the kitten visual cortex.

1. The effect of intraventricular administration of nerve growth factor (NGF) by means of a cannula-minipump system was studied in kittens monocularly deprived during the critical period. The ocular dominance of area 17 neurones of NGF-treated and control kittens was determined by conventional extracellular recordings. The soma size of cells in A and A1 laminae of the lateral geniculate nucleus (LGN) was also evaluated in Cresyl Violet preparations. 2. Binocularly responsive neurons were found to be significantly more numerous in NGF-treated than in control kittens. The shrinkage of cells from the deprived LGN laminae normally observed in control kittens was prevented by NGF administration. 3. Following an initial period of monocular deprivation (MD) kittens subsequently treated with NGF showed a substantial recovery of functional binocular connections. 4. These findings indicate that the administration of NGF during the period of deprivation reduces the amblyopic effects of MD, while its administration to kittens with both eyes open following the initial deprivation promotes recovery of the deprived eye. 5. Neurotrophic factors may contribute to the regulation of experience-dependent modifications of synaptic connectivity in the visual cortex.

Glucocorticoids depress activity-dependent expression of BDNF mRNA in hippocampal neurones.

Glucocorticoid hormones are important regulators of brain development and ageing, and can impair the capacity of hippocampal neurones to survive various neurological insults. Here we show that dexamethasone, a synthetic glucocorticoid, prevents activity-dependent increases of brain-derived neurotrophic factor (BDNF) mRNA in cultures of rat hippocampal neurones. In situ hybridization was used to evaluate the levels of BDNF mRNA. Up-regulation of BDNF mRNA triggered by depolarization with high potassium, or exposure to the glutamate receptor agonist kainic acid, resulted both from higher levels of expression in neurones and from new recruitment of cells. These data suggest that the known ability of glucocorticoids to exacerbate neuronal injury following ischaemia and other metabolic insults could be due to antagonism of regulatory mechanisms governing neurotrophin levels in the brain.

Distribution of protein gene product 9.5 (PGP 9.5) in the vertebrate retina: evidence that immunoreactivity is restricted to mammalian horizontal and ganglion cells.

Using light microscopic immunocytochemistry, we have studied the distribution of protein gene product 9.5 (PGP 9.5), a neuron-specific protein first extracted from human brain (Doran et al., '83:J. Neurochem. 40:1542-1547), in the vertebrate retina. Retinas were obtained from frog, chicken, rat, rabbit, cow, cat, dog, and human. No immunoreactivity was observed in frog and only a faint staining was present in chicken. In mammalian retinas, a strong positive reaction was restricted to horizontal and ganglion cells, with minor interspecies variations. Immunostaining was present throughout the cell body and the dendritic tree in horizontal cells. At the level of retinal ganglion cells, immunolabel was particularly abundant in cell bodies and axons forming the optic nerve. Only the main dendrites were stained, the remainder of the dendritic tree giving rise to a diffuse punctate reaction in the inner plexiform layer. In rats, displaced amacrine cells, which are known to contribute largely (40-50%) to the total neuronal population within the ganglion cell layer (Perry, '81: Neuroscience 6:931-944) were not immunoreactive, as demonstrated from (i) analysis of the morphology, cell size and cell density of immunoreactive neurons in wholemounts; (ii) colocalization of retrograde label and PGP 9.5 immunoreactivity in about 80% of ganglion cells after injection of peroxidase into the optic nerve; and (iii) reduction of immunoreactivity in the inner plexiform and ganglion cell layers following optic nerve transection. Western blot analysis of extracts from rabbit retinas indicated that the immunoreactive species is PGP 9.5 or a closely related molecule. Recent studies have demonstrated that PGP 9.5 is a ubiquitin carboxyl-terminal hydrolase (Wilkinson et al., '89:Science 246:670-673). The present results, therefore, suggest that differences in the ubiquitination process exist between retinal neurons.

Photochemical stroke and brain-derived neurotrophic factor (BDNF) mRNA expression.

In situ hybridization and Northern blotting were used to study the expression of brain-derived neurotrophic factor (BDNF) mRNA in the rat brain following photochemical stroke. A focal thrombotic lesion of the sensorimotor cortex was produced by intravenously injecting the light-sensitive dye rose bengal and exposing the skull to a controlled beam of light. Four hours after the light exposure the level of BDNF mRNA was increased in the hippocampus and cortex ipsilateral and perifocal to the lesion. The stroke-induced BDNF mRNA increase was prevented by the non-competitive glutamate receptor blocker dizocilpine (MK-801). The results indicate that the activation of N-methyl-D-aspartate (NMDA)-sensitive glutamate receptors is involved in the stroke-triggered stimulation of BDNF mRNA increase.

Expression of NGF receptor and NGF receptor mRNA in the developing and adult rat retina.

Nerve growth factor (NGF) has been recently found to rescue axotomized retinal ganglion cells (RGCs) of the adult rat from degeneration. Because the trophic effect of NGF involves a receptor-coupling event, the characterization and cellular localization of the NGF receptor (NGFR) in the retina are essential to understanding the possible specific action of NGF in this district of the central nervous system. We report here that the NGFR mRNA is expressed in fetal, neonatal, and adult rat retina. Using monoclonal antibody 192-IgG to immunoprecipitate and immunohistochemically identify NGFR, we also found that the NGFR from the retina has a molecular weight identical to that of the NGFR from PC12 cells. The NGFR is localized on RGCs and Müller cells. Finally, following ligation of the optic nerve, NGFR-immunopositive material was found to accumulate both distal and proximal to the site of ligation, suggesting that RGC axons anterogradely and retrogradely transport the NGFR. These data raise the possibility that NGF may play a specific role in rat RGCs.