Nerve growth factor in the primate central nervous system: regional distribution and ontogeny

[Expression of IFN-γ, IL-1α, NGF-β and TNF-α during the development of cerebellar cortex of Western Anhui white goose]

The strep avidin-biotin-peroxidase complex (SABC) immunohistochemical methods were applied to investigate the localization and semi-quantitative distribution of IFN-γ, IL-1α, NGF-β and TNF-α-immunoreactive cells in the cerebellar cortex of Western Anhui white goose at embryonic day 13, 19, 24, 28 (E13, E19, E24, E28) and postnatal day 7, 15 (P7, P15). The possible roles of IFN-γ,IL-1α,NGF-β and TNF-α in the development of cerebellar cortex were discussed. The results indicated that in the external granular layer, there were IFN-γ and TNF-α positive cells at E13, E19, E24, E28, P7, IL-1α positive cells at E13, E19, E24, E28 and NGF-β positive cells at E13, E19 , E24. The expression levels of these four cytokines all reached peaks at E19 of the six tested periods in this study. In the Purkinje cell layer, there were IFN-γ, IL-1α and TNF-α positive cells at E13, E19, E24, E28, P7, P15 and NGF-β positive cells at E13, E19, E24, E28, P7. In the internal granular layer, there were IFN-γ positive cells at E13, E19, E24, E28, P7, P15, IL-1α and TNF-α positive cells at E13, E19, E24, E28, P7 and NGF-β positive cells at E13, E19, E24, E28. These results showed that E19 might be the "critical stage"in the cerebellar cortex development of Western Anhui white goose. IFN-γ, IL-1α and TNF-α might be synthesized by cerebellar cortex itself, and NGF-β could be transported from regions which project to Purkinje cells. IFN-γ may interfer the transfer of granular cells, and NGF-β may have neurotrophic functions that are beneficial to the growth and development of Purkinje cells.

Heterogeneity of the developmental patterns of neurotrophin protein levels among neocortical areas of macaque monkeys

Based on morphological and physiological characteristics, the mammalian neocortex is divided into various neocortical areas and its diversity is prominent in the primates including humans. These neocortical areas are constructed during development, but the details of the developmental events remain unclear, especially at the molecular level. We measured the mRNA and protein levels of neurotrophins in various neocortical areas of developing rhesus monkeys. The expression patterns of both the neurotrophin-3 (NT-3) mRNA and the protein showed area differences. In the sensory and motor areas, NT-3 mRNA and protein levels had started to decline by a week after birth. In contrast, the levels declined after the third postnatal week in the association neocortical areas. The level of brain-derived neurotrophic factor (BDNF) protein changed in an area-dependent manner during development, but that of mRNA did not. The decline of the BDNF protein level started earlier in the sensory and motor neocortical areas than in the association neocortical areas, suggesting that sensory and motor neocortical areas develop earlier than the association areas in terms of the developmental changes in neurotrophins.

Differential expression patterns of TrkB ligands in the macaque monkey brain

We measured the concentrations of brain-derived neurotrophic factor (BDNF) and neurotrophin-4 (NT-4) in the brains of mature and developing macaque monkeys. In the adult macaque brain, the highest level of BDNF was found in the hippocampus. Comparisons between cortical regions showed higher levels of BDNF in the prefrontal, temporal, and parietal association cortices than elsewhere. In contrast, NT-4 levels were 3-30 times lower than those of BDNF. During development, the contents of BDNF and NT-4 protein in cerebral cortices were highest at the postnatal second month and at embryonic day 140, respectively. These results suggest that the two TrkB ligands, BDNF and NT-4, may be differently regulated and might play separate roles in monkey cortical development.

NGF treatment potentiates c-fos expression in the rat nucleus basalis upon excitotoxic lesion with quisqualic acid

The induction of the c-fos gene in the rat brain by NGF was studied in a model of acute cholinergic hypofunction, i.e., the lesion of the nucleus basalis magnocellularis (NBM) with quisqualic acid. Choline acetyltransferase and Fos immunoreactivity (IR) in the NBM were analyzed at different times after the excitotoxic lesion. NGF treatment induced a potentiation of Fos expression 4 and 24 h after lesion. The possibility is discussed that c-fos induction is one of the early mechanisms of the neuroprotective action of NGF.

Transplant of Schwann cells allows normal development of the visual cortex of dark-reared rats

Visual experience is necessary for the correct development of the visual cortex. Dark-rearing from birth affects normal maturation of the functional properties of mammalian visual cortex: cortical cells show rapid habituation to repeated stimulation, decreased orientation selectivity, and enlarged receptive fields. Spatial resolution and response latency are also impaired. Recent experiments have demonstrated that visual deprivation reduces the expression of neurotrophins in the visual cortex. We formulated the hypothesis that visual experience drives the maturation of functional properties of the visual cortex by regulating cortical levels of neurotrophins. If this hypothesis is correct, exogenous supply of neurotrophins during dark-rearing from birth should prevent, or at least ameliorate, the effects of a lack of visual experience. Since Schwann cells are efficient biological minipumps of neurotrophic factors, we transplanted 1.0 or 1.5 x 10(6) Schwann cells or infused vehicle solution as a control into the lateral ventricles of 13 day old rats reared in total darkness from birth until the end of the critical period (postnatal day 45). Single-cell responses and visual-evoked potentials were recorded from the binocular zone of the primary visual cortex of each group. We found that in Schwann cell-transplanted animals all parameters tested were significantly improved upon those of dark-reared control rats and were in the range of normal adult values. Thus, Schwann cell transplant contributed to the normal development of visual response properties in the visual cortex, compensating for a complete absence of visual experience.

Role of neurotrophins in synapse development and plasticity

Neurotrophic factors are traditionally viewed as secretory proteins that regulate long-term survival and differentiation of neurons. The role of neurotrophic factors in the structural integrity of the nervous system makes them attractive candidates as therapeutic agents for neurodegenerative diseases. However, the fact that expression of many neurotrophic factors in the central nervous system is rapidly enhanced by neuronal activity suggests a new role for these factors in activity-dependent processes, such as synaptic development and plasticity. A series of recent studies has provided strong evidence for this novel function of neurotrophic factors. The neurotrophin family of proteins has been shown to acutely potentiate synaptic transmission at the neuromuscular junction and in the brain. These factors are also involved in the maturation of the neuromuscular synapses and in the development of synapses in the visual system. Gene targeting and physiological experiments demonstrate that brain-derived neurotrophic factor (BDNF) plays an important role in long-term potentiation (LTP), a cellular model for learning and memory. These findings have brought together two hotly pursued areas of neuroscience, namely, the function of neurotrophic factors and the mechanisms for synaptic plasticity. Continuous studies in this new field will help understand how synapses develop and function in the brain, and may have significant implications in treating learning disorders in both children and adults.

Neurotrophins and the primate central nervous system: a minireview

The central nervous system (CNS) of primates is more complex than the CNS of other mammals. Details of the development and aging of the primate CNS have recently been revealed by various neurobiological techniques. It has become clear that the primate CNS has unique characteristics, for example, the capacity for the overproduction and elimination of fibers and synapses. Some differences have also been found in the distribution of and changes with development in levels of various neuroactive substances. Recent discoveries of a variety of neurotrophins in the mammalian CNS have led to research on the neurobiology of these molecules in the primate CNS. The distribution of and changes with development in levels of nerve growth factor (NGF) in the primate CNS are closely correlated with the cholinergic system of the basal forebrain. The administration of NGF into the monkey brain prevents the degeneration of the cholinergic neurons of the basal forebrain after axotomy, a result that suggests that neurotrophins might be very valuable agents for the future treatment of neurological diseases, such as Alzheimer's and Parkinson's diseases.

NT-4-mediated rescue of lateral geniculate neurons from effects of monocular deprivation

Altering the balance of activity between the two eyes during the critical period for visual-system development profoundly affects competitive interactions among neurons in the lateral geniculate nucleus and primary visual cortex. Neurons in the lateral geniculate nucleus that are deprived of activity by closing or silencing one eye atrophy as a result of competition with non-deprived neurons for some critical factor(s) presumed to be present in the cortex. Based on their actions in the developing visual system, neurotrophins are attractive candidates for such factors. We tested whether neurotrophins mediate intracortical competition of afferents from the lateral geniculate nucleus by using monocular deprivation and a new method for highly localized, in vivo delivery of neurotrophins. This method allowed unambiguous identification of neurons that were exposed to neurotrophin. Here we report that only one neurotrophin, the TrkB ligand NT-4, rescued neurons in the lateral geniculate nucleus from the dystrophic effects of monocular deprivation.

Involvement of nerve growth factor in visual cortex plasticity

The physiological role of nerve growth factor (NGF), the prototype member of the neurotrophin family, has been widely studied. NGF has been shown to promote survival, sprouting and differentiation of sympathetic ganglion cells and sensory neurons in the peripheral nervous system; it has also been shown to support survival and regeneration of cholinergic neurons in the central nervous system. Recent evidence indicates that NGF is also involved in the neuronal plasticity of the visual cortex. Exogenous supplies of NGF have been shown to interfere with normal processes underlying activity- and age-dependent synaptic modifications in both developing and adult visual cortex. In parallel to these physiological effects, numerous neuronal markers in the visual cortex have been found to be influenced by NGF. Several proposals have been introduced to explain the physiological role of NGF in visual cortex plasticity. Although the mechanisms underlying NGF effects in the visual cortex are still under active investigation, current evidence implies that NGF, and perhaps other neurotrophins as well, may be useful for preventing or correcting inappropriate or anomalous connections in the visual cortex, and thus for treating visual dysfunctions such as amblyopia and strabismus.

Inhibition of ocular dominance column formation by infusion of NT-4/5 or BDNF

During the development of the visual system of higher mammals, axons from the lateral geniculate nucleus (LGN) become segregated into eye-specific patches (the ocular dominance columns) within their target, layer 4 of the primary visual cortex. This occurs as a consequence of activity-dependent synaptic competition between axons representing the two eyes. The possibility that this competition could be mediated through neurotrophin-receptor interactions was tested. Infusion of neurotrophin-4/5 (NT-4/5) or brain-derived neurotrophic factor (BDNF) into cat primary visual cortex inhibited column formation within the immediate vicinity of the infusion site but not elsewhere in the visual cortex. Infusion of nerve growth factor, neurotrophin 3 (NT-3), or vehicle solution did not affect column formation. These observations implicate TrkB, the common receptor for BDNF and NT-4/5, in the segregation of LGN axons into ocular dominance columns in layer 4. Moreover, they suggest that in addition to their better known roles in the prevention of cell death, neurotrophins may also mediate the activity-dependent control of axonal branching during development of the central nervous system.

Nerve growth factor (NGF) uptake and transport following injection in the developing rat visual cortex

Recent investigations have shown that cortical nerve growth factor (NGF) infusions during the critical period inhibit ocular-dominance plasticity in the binocular portion of the rat visual cortex. The mechanisms underlying the effects of NGF on visual cortical plasticity are still unclear. To investigate whether during normal development intracortical and/or extracortical cells possess uptake/transport mechanisms for the neurotrophin, we injected 125I-NGF into the occipital cortex of rats at different postnatal ages. Within the cortex, only a few labelled cells were observed. These cells were confined to the vicinity of the injection site and their number depended on the animal's age at the time of injection. Labelled cells were absent at postnatal day (PD) 10 but could be detected between PD 14 and PD 18. They then decreased in number over the following period and were not detected in adult animals. Outside the cortex, neurons of the lateral geniculate nucleus (LGN) were not observed to take up and retrogradely transport NGF at any age after birth. In contrast, retrogradely labelled neurons were found in the basal forebrain. Labelled cells were first observed here at PD 14 and then increased in number until reaching the adult pattern. Our results show that intrinsic and extrinsic neurons are labelled following intracortical injections of iodinated NGF. In both neuronal populations, the uptake and transport of NGF is present over a period corresponding to the critical period for visual cortical plasticity. These findings suggest that NGF may play a role, both intra and extracortically, in plasticity phenomena.

Monoclonal antibodies to nerve growth factor affect the postnatal development of the visual system

Exogenous supply of nerve growth factor (NGF) prevents the effects of monocular deprivation. This suggests that visual afferents may be competing for an endogenous neurotrophic factor, related to NGF, whose production by postsynaptic cells depends on the activity of afferent fibers. To test the hypothesis that endogenous NGF may play a role in the functional and anatomical development of the rat geniculo cortical system, the physiological action of NGF in the rat visual system was antagonized by using two independent monoclonal antibodies which neutralize NGF (alpha D11 and 4C8). To provide a continuous supply of antibodies during the period of visual cortical plasticity, alpha D11 or 4C8 antibody-producing hybridoma cells were implanted in the lateral ventricle of rats at postnatal day 15. This resulted in dramatic alterations of two of the most important parameters characterizing the functional development of the visual system, namely, visual acuity and binocularity of cortical neurons and in shrinkage of cells in the lateral geniculate nucleus. This demonstrates that the action of endogenous NGF is necessary for the normal functional and anatomical development of the geniculocortical system.

Fos induction by nerve growth factor in the adult rat brain

The distribution of Fos, the protein product of the immediate early gene c-fos, was studied with immunocytochemistry in the adult male rat brain after nerve growth factor (NGF) administration. NGF was injected in the lateral cerebral ventricle through a previously implanted cannula. The total number of Fos-immunoreactive (ir) neurons in the brain was 2-3 times higher after NGF administration than in control animals (untreated or injected with cytochrome c). With respect to control rats, in the NGF-treated cases Fos-ir cells were more numerous in the anterior olfactory nucleus, in the medial prefrontal and anterior cingulate cortices, in the basal forebrain, in the preoptic and ventromedial nuclei of the hypothalamus, as well as anterior hypothalamic area, in the thalamic midline nuclei, and in some brainstem structures, such as the parabrachial nucleus. The relative quantitative increase of Fos-ir neurons varied in the different structures. In addition, Fos-ir neurons were evident after NGF administration in areas devoid of immunopositive cells in control animals. These included: frontoparietal and occipital cortical fields, the hypothalamic arcuate nucleus, and many brainstem structures, such as the dorsal nucleus of the lateral lemniscus, posterodorsal tegmental, medial and lateral vestibular, ventral cochlear, and prepositus hypoglossal nuclei. These findings demonstrate that the intracerebroventricular administration of NGF can induce c-fos expression in neurons in vivo. The distribution of Fos-ir neurons indicates that NGF can induce activation of functionally and chemically heterogeneous neuronal subsets in the brain.

Expression of the gene for nerve growth factor (NGF) in the monkey central nervous system

The expression of the gene for nerve growth factor (NGF) was examined in the central nervous system of adult and fetal monkeys. In adults, the highest level of NGF mRNA was found in the hippocampus and relatively high levels were observed in the cerebral cortices and thalamus. NGF mRNA was also detected in the cerebellum and the caudate nucleus. In the spinal cord, there was no evidence of the mRNA. The levels of NGF mRNA were closely correlated with those of NGF. At embryonic day 140 (E140), levels of NGF mRNA in the visual cortex and cerebellum were three times higher than those at the adult stage. Our previous study on the ontogeny of NGF (Hayashi, M. et al., Neuroscience, 36 (1990) 683-689) showed that the level of NGF in the visual cortex at E140 is the same as that at adult stage. Thus, at the fetal stage, NGF may be actively transported from the cerebral cortex to other regions of the brain, such as the basal forebrain area. By contrast, the levels of NGF and NGF mRNA in the cerebellum were almost the same at the adult and fetal stages, suggesting that NGF, which is synthesized in the cerebellum, may be taken up locally by cerebellar cells.

Low-affinity p75 nerve growth factor receptor expression in the embryonic monkey telencephalon: timing and localization in diverse cellular elements

Monoclonal antibodies against the low-affinity (p75) subunit of the human nerve growth factor receptor have been used to determine the temporal appearance of this receptor and to identify the associated cellular elements in the developing occipital cortex of rhesus monkeys. Adult and fetal brains from embryos at embryonic days 45-121 were used. This embryonic time span includes periods of active neurogenesis, cell migration and initial formation of axonal connections in the cerebral cortex. The first immunolabeling in the developing cerebral wall was seen between embryonic days 56 and 64. The labeling was present in the transient subplate neurons, a small number of axonal processes and pericytes associated with blood vessels. By birth, labeled neurons of the subplate zone disappeared, but immunolabeled axonal processes could now be seen in large numbers in the cortex. These findings are consistent with the role of nerve growth factor in the coordination of cortical differentiation, but not with the initiation of neuronal proliferation, since the emergence of nerve growth factor receptor-labeled elements in the cortex occurs two to three weeks after the onset of neurogenesis in this species. Further, the diverse cellular elements labeled in the fetal cerebrum with the antibodies to the low-affinity nerve growth factor receptor suggests that a receptor or receptors associated with growth factor signaling for more than one growth factor family are recognized by these antibodies. Differential timing in the expression of families of growth factor receptors may be one mechanism by which developing neurons in the cerebral cortex could respond to the different signals which guide such processes as synaptogenesis and morphogenesis.

Monocular deprivation effects in the rat visual cortex and lateral geniculate nucleus are prevented by nerve growth factor (NGF). II. Lateral geniculate nucleus

In the preceding paper (Berardi et al. Proc. R. Soc. Lond. B 251, 17 (1993)), it has been shown that nerve growth factor (NGF) prevents the functional and anatomical alterations induced by monocular deprivation (MD) at the level of the visual cortex. Here we report that an exogenous supply of NGF prevents the shrinkage of neurons in the deprived laminae of lateral geniculate nucleus (LGN). The soma size distribution for the deprived ipsilateral laminae of MD rats is shifted towards smaller sizes (mean percentage of shrinkage with respect to the ipsilateral undeprived lamina = 21%, s.d. = 2%). As in other mammals, MD affects LGN relay neurons and spares LGN neurons projecting to the monocular portion of primary visual cortex. In NGF-treated animals we found that the soma size distributions for the deprived and undeprived ipsilateral laminae extensively overlap. The results of the two papers show that an exogenous supply of NGF prevents MD effects at both levels, visual cortex and LGN, and suggest a role for NGF in the plasticity of the geniculo-cortical pathway.

Exogenous supply of nerve growth factor prevents the effects of strabismus in the rat

It has recently been reported that exogenous supply of nerve growth factor prevents the effects of monocular deprivation both in rats and in cats. Here we have extended these experiments to the case of strabismus. Repeated intraventricular injections of nerve growth factor were performed in rats made surgically strabismic early in the critical period. At the end of the critical period the ocular dominance distribution of visual cortical neurons was assessed in strabismic untreated, strabismic nerve growth factor-treated and strabismic Cytochrome C-treated (control) rats by means of extracellular recordings. We found that in rats surgical strabismus causes a consistent loss of binocular neurons. By contrast the treatment with nerve growth factor maintains the normal ocular dominance distribution of neurons in the primary visual cortex. We conclude that nerve growth factor exogenously supplied prevents the effects induced by surgical strabismus in rats and suggest that nerve growth factor has a role in visual cortical plasticity.

Nerve growth factor receptor-immunoreactive neurons within the developing human cortex

A monoclonal antibody recognizing the p75 receptor for nerve growth factor (NGF) was used to assess the immunohistochemical expression of NGF receptors within the developing human neo-, limbic, and paralimbic cortices as well as the hippocampal complex. Between embryonic weeks 16 and 26, a transient population of neurons located within the upper and lower subplate zones of the neo-, limbic, and paralimbic cortices expressed the receptor for NGF. In contrast, NGF receptor-immunoreactive neurons were only observed in the upper subplate zone of the entorhinal cortex at embryonic week 40 (term), a staining pattern not observed in a 5-year-old specimen. The expression of NGF receptor-immunoreactive neurons within the upper subplate zone between embryonic weeks 16 and 40 was characterized by a dense band of immunoreactive neurons and neuropil. These neurons were bipolar with basal and apically directed neurites. NGF receptor-immunoreactive neurons were also scattered throughout the lower subplate zone and underlying white matter between embryonic weeks 19 and 26. These neurons were multipolar, with less apically directed neurites. NGF receptor-immunoreactive subplate neurons displayed a topographic distribution with the heaviest concentration found within limbic and paralimbic cortices as well as association neocortex. In contrast, light to moderate NGF receptor-immunoreactivity was seen in sensory-motor cortex. Within the hippocampal complex, only a few lightly stained NGF receptor-immunoreactive neurons were seen within the fimbria, hilar region of the dentate gyrus, and subiculum. The expression of NGF receptor-immunoreactivity increased within the subplate zone of the pre- and parasubiculum culminating in intense entorhinal cortex staining. As the entorhinal cortex merged with the developing inferior temporal association cortex, there was a marked reduction in staining intensity. In contrast to those in the subplate zone, neurons within the germinal zone and cortical plate were NGF receptor immunonegative at all times examined. The presence of NGF receptors in the subplate zone suggests that neurotrophins such as NGF play an important role in the transient viability of these neurons as well as in the guidance of cortical afferent inputs into topographically organized regions of the cerebral cortex.

Nerve growth factor prevents the amblyopic effects of monocular deprivation

Monocular deprivation early in life causes dramatic changes in the functional organization of mammalian visual cortex and severe reduction in visual acuity and contrast sensitivity of the deprived eye. We tested whether or not these changes could be from competition between the afferents from the two eyes for a target-derived neurotrophic factor. Rats monocularly deprived during early postnatal development were treated with repetitive intraventricular injections or topical administration of nerve growth factor. The effects of monocular deprivation were then assessed electrophysiologically. In untreated animals visual acuity and contrast sensitivity of the deprived eye were strongly reduced, whereas in nerve growth factor-treated animals these parameters were normal.

Nerve growth factor receptor immunoreactivity in the new world monkey (Cebus apella) and human cerebellum

The present study used the NGFR-5 monoclonal antibody raised against human nerve growth factor receptor (NGFR) to determine the extent of NGFR immunoreactivity within the embryonic and young adult Cebus apella cerebellum as well as the human cerebellum. Immunohistochemically processed tissue revealed NGFR expressing Purkinje cell somata, axons, and dendrites, the latter being observed within the molecular layer of both adult species. Within all regions of the cerebellum we observed both darkly and lightly immunostained Purkinje cells. The proximal axons of these cells, which were visualized for short distances within the granular cell layer, appeared to contain bulbous aggregates of reaction product. In sagittal sections, the full extent of the Purkinje cell dendritic tree was observed in the more lightly stained portions of the cerebellum. In situ hybridization experiments revealed NGFR mRNA within Purkinje cells in a pattern similar to that seen with immunohistochemistry. The distribution of NGFR immunoreactivity within the cerebellum exhibits a general topographic organization with the heaviest and most consistent staining occurring within the archi- and neocerebellum and weaker staining within the paleocerebellum. In fetal Cebus monkey cerebellum obtained at gestational day 50 and 70, NGFR immunoreactivity was observed as a band composed of developing Purkinje cell neurites. These profiles were seen in the paleo- and neocerebellum, but not the archicerebellum. The present investigation is the first demonstration of NGFR immunoreactive profiles in the adult monkey and human cerebellum. These findings suggest that nerve growth factor may influence locomotor and vestibular behaviors that are mediated by cerebellar circuity. The precise mode of action for the NGF/NGFR system within the cerebellum remains to be determined.