NGF receptor immunoreactivity in aged rat brain

Efficacy of leukemia inhibitory factor as a therapeutic for permanent large vessel stroke differs among aged male and female rats

Preclinical studies using rodent models of stroke have had difficulty in translating their results to human patients. One possible factor behind this inability is the lack of studies utilizing aged rodents of both sexes. Previously, this lab showed that leukemia inhibitory factor (LIF) promoted recovery after stroke through antioxidant enzyme upregulation. This study examined whether LIF promotes neuroprotection in aged rats of both sexes. LIF did not reduce tissue damage in aged animals, but LIF-treated female rats showed partial motor skill recovery. The LIF receptor (LIFR) showed membrane localization in young male and aged rats of both sexes after stroke. Although LIF increased neuronal LIFR expression in vitro, it did not increase LIFR in the aged brain. Levels of LIFR protein in brain tissue were significantly downregulated between young males and aged males/females at 72 h after stroke. These results demonstrated that low LIFR expression reduces the neuroprotective efficacy of LIF in aged rodents of both sexes. Furthermore, the ability of LIF to promote motor improvement is dependent upon sex in aged rodents.

Age-dependent alterations in nerve growth factor (NGF)-related proteins, sortilin, and learning and memory in rats

The objective of this study was to evaluate the effects of aging on the performance of specific memory-related tasks in rats as well as to determine the levels of several nerve growth factor (NGF)-related proteins in relevant brain regions. The results indicated age-related impairments in spatial learning in a water maze task as well as deficits in recognition memory in a Spontaneous Novel Object Recognition task. In the prefrontal cortex and hippocampus, aged rats (compared to young controls) had elevated levels of the proneurotrophin, proNGF (+1.8-1.9 fold), p75(NTR) receptors (+1.6-1.8 fold) and sortilin (+1.8-2.1 fold), and decreased levels of mature NGF (-36 to 44%), and phospho-TrkA receptors (-45 to 49%). The results of this study support the argument that NGF signaling is altered in the aging brain, and that such alterations may contribute to an age-related decline in cognitive function. These results may also help to identify specific components of the NGF-signaling pathway that could serve as targets for novel drug discovery and development for age-related disorders of cognition (e.g., Alzheimer's disease).

Long-term treadmill exposure protects against age-related neurodegenerative change in the rat hippocampus

The potential of exercise or environmental enrichment to prevent or reverse age-related cognitive decline in rats has been widely investigated. The data suggest that the efficacy of these interventions as neuroprotectants may depend upon the duration and nature of the protocols and age of onset. Investigations of the mechanisms underlying these neuroprotective strategies indicate a potential role for the neurotrophin family of proteins, including nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). In this study, we have assessed the effects of 8 months of forced exercise, begun in middle-age, on the expression of long-term potentiation (LTP) and on spatial learning in the Morris water maze in aged Wistar rats. We also assessed these measures in a cage control group and in a group of rats exposed to the stationary treadmill for the same duration as the exercised rats. Our data confirm an age-related decline in expression of LTP and in spatial learning concomitant with decreased expression of NGF and BDNF mRNA in dentate gyrus (DG). The age-related impairments in both plasticity and growth factor expression were prevented in the long-term exercised group and, surprisingly, the treadmill control group. Given the extensive handling that the treadmill control group received and their regular exposure to an environment outside the home cage, this group can be considered to have experienced environmentally enriched conditions when compared with the cage control group. Significant correlations were observed between both learning and LTP and the expression of NGF and BDNF mRNA in the dentate gyrus. We conclude that decreased expression of NGF and BDNF in the dentate gyrus of aged rats is associated with impaired LTP and spatial learning. We suggest that the reversal of these age-related impairments by enrichment and exercise may be linked with prevention of the age-related decline in expression of these growth factors and, furthermore, that enrichment is as efficacious as exercise in preventing this age-related decline.

Nerve growth factor concentration in human saliva

OBJECTIVE

The aims of this study were to measure the normal concentration of nerve growth factor (NGF) in healthy human saliva and to investigate the effects of age and gender differences on saliva NGF level.

MATERIALS AND METHODS

Resting whole, stimulated parotid, and stimulated submandibular/sublingual saliva were collected from 127 healthy volunteers with ages ranging from 20 to 81 years. The saliva NGF concentration was measured by enzyme immunoassay.

RESULTS AND CONCLUSIONS

The mean concentrations of NGF were 901.4 +/- 75.6 pg ml(-1) in resting whole saliva, 885.9 +/- 79.9 pg ml(-1) in stimulated parotid saliva, and 1066.1 +/- 88.1 pg ml(-1) in stimulated submandibular/sublingual saliva. The stimulated submandibular saliva showed lower NGF concentrations with increasing age (rho = -0.296, P = 0.001). The NGF concentrations of resting whole saliva (P = 0.025) and stimulated parotid saliva (P = 0.005) were significantly higher in women than men. The NGF concentration of stimulated submandibular saliva was significantly higher than stimulated parotid saliva (P = 0.005) and significantly correlated with stimulated parotid saliva NGF level (rho = -0.244, P = 0.008). We found measurable concentrations of NGF in all three sources of saliva; the concentration was affected by the source for the stimulated parotid and submandibular saliva, age for stimulated submandibular saliva, and gender difference for resting whole saliva and stimulated parotid saliva.

Modulation of presbycusis: current status and future directions

Literature and ideas are reviewed concerning the modulation of presbycusis - the influence of variables that can alter the severity and/or time course of presbycusis or counteract its negative aspects. Eleven topics are identified: variables related to biological aging; genetics; noise-induced hearing loss; moderately augmented acoustic environment; neural plasticity and the central auditory system; neural plasticity and hearing aids; socioeconomic and cultural barriers to hearing aid use; lifestyle (diet, exercise, etc.); medical variables; pharmaceutical interventions for presbycusis, and cognitive variables. It is concluded that the field of otogerontology will best be served by a comprehensive, integrative interaction among basic researchers and clinical scientists who will continue to learn how the auditory problems associated with presbycusis can be intentionally modulated in beneficial ways.

Effect of age on cerebral venous circulation disturbances in the rat

OBJECT

Mild cerebral venous circulation disturbances (CVCDs) in aged patients are frequently known to cause unexpectedly severe postoperative complications in neurosurgical practice. The object of the present study was to determine whether there are age-related differences involved in vulnerability to CVCDs.

METHODS

Thirty-eight male Wistar rats were used. A single cortical vein with a 100-microm diameter was occluded photochemically by using rose bengal dye and fiberoptic illumination in young (Group Y, 19 animals aged 10-14 weeks) and aged (Group A, seven animals aged 80-100 weeks) rats. Five young and seven aged animals served as sham-operated controls. Regional cerebral blood flow (rCBF) was determined from local CBF, which was measured at 25 (5 x 5) identical locations, with the occluded vein located central to the scanning field, by using a laser Doppler scanning technique every 15 minutes for 90 minutes after venous occlusion. The cerebral venous flow pattern was examined using fluorescence angiography until 90 minutes after occlusion. Histological specimens were examined 24 hours after occlusion. In Group Y, rCBF did not change significantly after venous occlusion. However, in Group A, rCBF decreased rapidly beginning 15 minutes after occlusion. Significant intergroup differences were observed 30, 60, and 90 minutes after occlusion. Venous flow arrest, which resulted in venous infarct, was observed on angiography 90 minutes after occlusion in two (10.5%) of 19 young and six (85.7%) of seven aged rats. The venous thrombus in Group A rats was significantly larger than that in Group Y rats 90 minutes after occlusion. Venous infarction was seen in all aged rats (100%) and in six young rats (31.6%); the infarct size, expressed as a percentage of the size of the ipsilateral hemisphere, was significantly larger in aged rats than in young rats.

CONCLUSIONS

This study demonstrated an age-related increase in the rate and size of venous infarct following vein occlusion, suggesting that the greater vulnerability to CVCDs in the aged brain might be attributed to early and extensive hypoperfusion of circumscribed brain areas drained by the occluded vein. The larger thrombus formation in aged animals indicates that a shift in the thrombogenetic/thrombolytic equilibrium is responsible for the observed effect.

Immunohistochemical and neurochemical correlates of learning deficits in aged rats

This study examined whether cholinergic and monoaminergic dysfunctions in the brain could be related to spatial learning capabilities in 26-month-old, as compared to three-month-old, Long-Evans female rats. Performances were evaluated in the water maze task and used to constitute subgroups with a cluster analysis statistical procedure. In the first experiment (histological approach), the first cluster contained young rats and aged unimpaired rats, the second one aged rats with moderate impairment and the third one aged rats with severe impairment. Aged rats showed a reduced number of choline acetyltransferase- and p75(NTR)-positive neurons in the nucleus basalis magnocellularis, and choline acetyltransferase-positive neurons in the striatum. In the second experiment (neurochemical approach), the three clusters comprised young rats, aged rats with moderate impairment and aged rats with severe impairment. Alterations related to aging consisted of reduced concentration of acetylcholine, norepinephrine and serotonin in the striatum, serotonin in the occipital cortex, dopamine and norepinephrine in the dorsal hippocampus, and norepinephrine in the ventral hippocampus. In the first experiment, there were significant correlations between water maze performance and the number of; (i) choline acetyltransferase- and p75(NTR)-positive neurons in the nucleus basalis magnocellularis; (ii) choline acetyltransferase-positive neurons in the striatum and; (iii) p75(NTR)-positive neurons in the medial septum. In the second experiment, water maze performance was correlated with the concentration of; (i) acetylcholine and serotonin in the striatum; (ii) serotonin and norepinephrine in the dorsal hippocampus; (iii) norepinephrine in the frontoparietal cortex and; (iv) with other functional markers such as the 5-hydroxyindoleacetic acid/serotonin ratio in the striatum, 3,4-dihydroxyphenylacetic acid/dopamine ratio in the dorsal hippocampus, 5-hydroxyindoleacetic acid/serotonin and homovanillic acid/dopamine ratios in the frontoparietal cortex, and 3,4-dihydroxyphenylacetic acid/dopamine ratio in the occipital cortex. The results indicate that cognitive deficits related to aging might involve concomitant alterations of various neurochemical systems in several brain regions such as the striatum, the hippocampus or the cortex. It also seems that these alterations occur in a complex way which, in addition to the loss of cholinergic neurons in the basal forebrain, affects dopaminergic, noradrenergic and serotonergic processes.

Deficits in nerve growth factor release and tyrosine receptor kinase phosphorylation are associated with age-related impairment in long-term potentiation in the dentate gyrus

Previous findings have indicated that nerve growth factor may play a role in the expression of long-term potentiation in perforant path-granule cell synapses and that nerve growth factor treatment restores the ability of aged rats to sustain long-term potentiation. In this study, we have attempted to analyse the changes which occur in nerve growth factor release and tyrosine receptor kinase phosphorylation following tetanization in tissue prepared from dentate gyrus of young rats, as well as aged rats which did or did not sustain long-term potentiation. We report that KCl-stimulated nerve growth factor release was significantly increased in slices of the dentate gyrus or whole hippocampus, but not in synaptosomes prepared from the dentate gyrus. KCl-induced nerve growth factor release was also significantly enhanced in slices prepared from tetanized, compared with untetanized, tissue obtained from young rats and aged rats which sustained long-term potentiation; this response was absent in tissue prepared from aged rats which failed to sustain long-term potentiation, perhaps due to the enhanced basal nerve growth factor release observed in this tissue. Tetanization increased tyrosine receptor kinase phosphorylation in the dentate gyrus of young rats and aged rats which sustained long-term potentiation. In parallel with the changes in nerve growth factor release, tyrosine receptor kinase phosphorylation was markedly increased in untetanized tissue, which may contribute to the lack of effect in tetanized tissue prepared from aged rats which failed to sustain long-term potentiation. We observed that nerve growth factor concentration and tyrosine receptor kinase expression were decreased in aged, compared with young, rats. The data suggest that deficits in nerve growth factor release and subsequent signalling may contribute to age-related deficits in long-term potentiation.

Effect of physical training on the age-related changes of acetylcholinesterase-positive fibers in the hippocampal formation and parietal cortex in the C57BL/6J mouse

We investigated the effect of a moderate amount of prolonged physical training initiated at 3 months of age on the age-related changes of the hippocampal and cortical cholinergic fibers. A total of 80 male C57BL/6J mice were divided into five groups which were trained (including adult and old trained, AT and OT), sedentary (adult and old sedentary, AS and OS) and young (Y). From 3 months old, the mice of the trained groups were treated with a voluntary running wheel for 1 h each day, 5 days per week. AT had been trained up to 13-month-old whereas OT up to 24 months old. At the same time, the mice of the sedentary groups were put in immobilized wheels. We set the criterion for effective training in the trained mice such that the heart-to-body weight ratio should be at least 2 S.D. above the mean in the age-matched groups. Using AChE histochemistry and stereology, the AChE-positive fibers were analyzed quantitatively in the molecular layers in CA1, CA3 and the dentate gyrus of the hippocampal formation, and in III, V layers in the motor and somatosensory cortex. Comparison of Y, AS and OS (3, 13 and 24 months of age) showed minimum AChE-positive fiber density in the hippocampal formation and the cortex in OS (P < 0.01). After 10 and 21 months of running, the AChE-positive fibers in all regions examined in the trained groups were significantly increased compared to their age-matched controls (P < 0.05 or 0.01). In the hippocampal formation, the increase was about 17% in AT and 23% in OT, whereas, in the cortex, it was 13% in AT and 22% in OT. These results indicated that a moderate amount of prolonged physical training could modify the age-related loss of cholinergic fibers in the hippocampal formation and cortex, furthermore the modified loss of cholinergic fibers might be associated with the regeneration of hippocampal and cortical cholinergic fibers stimulated by chronic running.

Neuronal precursors of the adult rat subependymal zone persist into senescence, with no decline in spatial extent or response to BDNF

The adult mammalian brain continues to harbor ependymal/subependymal zone (SZ) precursor cells, which can give rise to neurons in vitro. In adult rats, explants of the rostral 6-7 mm of the SZ give rise to neurons in vitro, and over this entire expanse, neuronal survival is supported specifically by brain-derived neurotrophic factor (BDNF). We asked whether either the (a) spatial distribution, (b) abundance, or (c) BDNF responsiveness of the neuronal precursor population was affected by age. Explants of three rostrocaudally defined regions were taken from both young and old rats (3 and 20 months old, respectively), and cultured in 2% fetal bovine serum-containing media with or without added BDNF (20 ng/ml). The extent of neuronal production by these explants varied only minimally with their level of derivation, such that substantial outgrowth was observed at each level tested. Neuronal outgrowth was marginally higher and more rapid in achieving its maximal extent in the 3-month-old rats compared with their aged counterparts, but neuronal outgrowth was robust at each age tested. The duration of survival of SZ-derived neurons did not differ between the young and old rats. At both ages, BDNF supported the survival of these new adult neurons. The extent of BDNF's influence was independent of both the age of the donor rat and the rostrocaudal level at which the parent SZ explant was taken. Thus, the neuronal precursors of the rat brain persist into senescence; the size of the precursor pool attenuates minimally with age, and its spatial extent remains constant. The neurons generated from these precursors can respond to BDNF throughout life.

Age-dependent effect of AF64A on cholinergic activity in the septo-hippocampal pathway of the rat brain: decreased responsiveness in aged rats

Our previous studies have demonstrated that intracerebroventricular (icv) administration of low doses of ethylcholine mustard aziridinium (AF64A), up to 1.0 nmol/side, induces a reversible cholinergic deficit in the hippocampus, paralleled by a compensatory transient increase in choline acetyltransferase (ChAT) activity in the septum [El Tamer, A., Corey, J., Wülfert, E. and Hanin, I., Neuropharmacology, 31 (1992) 397-402]. In the present study we have addressed the question as to whether this effect might differ in old rats. AF64A (0.5 nmol/side) icv administered to three groups of rats aged 4, 12 and 22 months, respectively, induced a reduction of ChAT activity in the hippocampus to the same extent (-26%, -30.6% and -29.6%; P < 0.01) by 7 days post-icv injection. Acetylcholinesterase (AChE) was decreased to a similar extent in the 4 and 12 month old rats (-22% and -29%; P < 0.01), respectively, but remained unchanged in the 22 month old group. Whereas AChE activity remained unchanged in the septum in all three groups of rats, ChAT activity was increased significantly (+20% and +20.8%; P < 0.05 versus corresponding control group) in the 4 and 12 month old groups, respectively. No change in ChAT activity was measured in the septum of the 22 months old group. By 14 days post-icv injection of AF64A, ChAT and AChE activities were back to normal in all three groups and in both brain regions studied. These results demonstrate that a difference in AF64A's effect does exist between the 22 month old group and the youngest group. This might reflect a possible age-dependent change in the ability of the cholinergic system to respond to the cholinotoxicity of AF64A, as well as in the potential of the cell bodies, at the septal level, to respond to such an insult by a compensatory mechanism such as increasing ChAT activity.

A reproducible model of middle cerebral infarcts, compatible with long-term survival, in aged rats

BACKGROUND AND PURPOSE

Stroke is a disease associated with aging, but experimental stroke studies are generally done in young male animals. Because there are numerous differences associated with aging, such as an altered immune system and altered neurochemistry, that could affect the outcome of these experiments, a model of reproducible cerebral infarction in aged rats is needed.

METHODS

We attempted to produce middle cerebral artery (MCA) infarcts in aged (22 months of age) rats using two standard methods. A nylon suture with a heat-induced bulb was passed through the external carotid artery in seven animals, with an attempt to place the tip at the origin of the MCA. The MCA was ligated through a craniotomy just proximal to the internal cerebral vein in 14 rats. Survival potential was tested by attempting 2-week survival in four rats and 2-month survival in one rat.

RESULTS

The suture model failed to produce MCA infarcts, even when the bulb of the suture was properly placed in the MCA. The intracranial MCA occlusion resulted in reproducible MCA infarcts. There were no deaths, including the animals allowed to survive 2 weeks and 2 months.

CONCLUSIONS

We conclude that reproducible MCA infarcts can be produced in aged rats by craniotomy and that these lesions may be compatible with long-term survival. This should be a useful technique for studying therapeutic interventions and rehabilitation strategies in an animal model that immunologically and neurochemically more closely resembles humans at risk for stroke.

GM1 and NGF synergism on choline acetyltransferase and choline uptake in aged brain

In the brain of aged rats high affinity choline uptake (HAChU) of the striatum, hippocampus, and frontal cortex is lower than in young rats, while choline acetyltransferase (ChAT) activity is lower in striatum and frontal cortex. Infusion into the lateral cerebral ventricle with nerve growth factor (NGF) enhances the low values of these cholinergic markers in a dose- and region-dependent manner. GM1 ganglioside infused into the lateral ventricle, at a dose that is ineffective alone, together with NGF synergistically enhances the effect of NGF on ChAT and HAChU activities in the brain of aged animals. The pharmacology of this GM1/NGF synergism suggests potentiation of response.

Age-related decrease of nerve growth factor-like immunoreactivity in the basal forebrain of senescence-accelerated mice

The senescence-accelerated mouse P10 (SAMP10) is a murine model of accelerated senescence characterized by the deterioration of learning and memory with advancing age. In the present study, we examined the distribution of nerve growth factor (NGF) immunohistochemically in SAMP10 mice and its control strain, SAMR1. In both strains, NGF-like immunoreactivity (NGF-IR) was observed in neurons throughout the entire forebrain and in glial cells in a particular location. In aged SAMP10 mice, each layer of the cerebral cortex retained its NGF-IR, although the thickness of the cortical mantle was markedly decreased in comparison with younger animals. There was an age-related decline in NGF-IR in the substantia innominata of SAMP10 mice at the age of 10 months, when compared to 2-month-old SAMP10. These results indicate age-related decrease of NGF in the basal forebrain in SAMP10 mice.

Axonal atrophy in aging is associated with a decline in neurofilament gene expression

Neurofilaments (Nfs) are major determinants of axonal caliber. Nf transcript levels increase during development and maturation, and are associated with an increase in Nf protein, Nf numbers, and caliber of axons. With aging there is axonal atrophy. In this study we asked whether the axonal atrophy of aging was associated with a decline in Nf transcript expression, Nf protein levels, and Nf numbers. Expression of transcripts for the three Nf subunits was evaluated in dorsal root ganglia (DRG) of Fischer-344 rats aged 3-32 months by Northern and in situ hybridization. There was an approximately 50% decrease in Nf subunit mRNA levels in DRG of aged (> 23 months) as compared to young and mature (3 and 12 months) rats, whereas expression of another neuronal mRNA, GAP-43, showed no decline. Western analysis showed a corresponding decrease in Nf subunit proteins and no decline in GAP-43. Morphometric analysis showed a 50% decrease in Nf numbers within axons. The decrease in Nf gene expression and Nf numbers was accompanied by a decrease in cross-sectional area and circularity of all myelinated fibers, with the largest fibers showing the most marked changes, and a shrinkage in the perikaryal area of large neurons. Furthermore, we found a concomitant decrease in the expression of transcripts for the nerve growth factor receptors trkA and p75 with aging. Although the mechanisms leading to the decrease in Nf gene expression with aging are not known, a decrease in the availability of growth factors, or the neuron's ability to respond to them, may play a role in this process.

Limited responses of neuronal mRNAs to unilateral lesions of the rat entorhinal cortex

Following unilateral electrolytic lesioning of the rat entorhinal cortex, we assessed changes in messenger RNA (mRNA) levels for four neuron-associated proteins, GAP-43, SCG10, 68 kDa neurofilament (NF68), and alpha 1-tubulin that encode proteins of importance to synaptic remodelling. The mRNA levels for GAP-43 and SCG10 were reduced in the septal nuclei, while those of SCG10 and alpha 1-tubulin were elevated in the hippocampus; at most, the changes ranged from -40% to +50% of controls. Changes in NF68 mRNA levels were not significant. Correlations were found between mRNA for SCG10 and both GAP-43 and NF68. In view of these modest changes in most mRNA levels examined, we suggest that post-translational regulation may also be important in responses to injury.

The pedunculopontine tegmental nucleus: a role in cognitive processes?

The cholinergic pedunculopontine tegmental nucleus, located in the brainstem and part of the reticular formation, has been traditionally linked to motor function, arousal and sleep. Its anatomical connections, however, raise the possibility that the pedunculopontine tegmental nucleus is also involved in other aspects of behaviour such as motivation, attention and mnemonic processes. This is of obvious importance, since the pedunculopontine tegmental nucleus undergoes degeneration in human neurodegenerative disorders also characterized by attentional and/or mnemonic deficits. Moreover, recent behavioural animal work suggests that cognitive processes may be represented in the pedunculopontine tegmental nucleus. The difficulty that faces research in this area, however is the possible influence of cognition by other processes, such as arousal state, motivation and motor function. Nevertheless, by reviewing the literature, the pedunculopontine tegmental nucleus seems to be involved in attentional and possibly also in learning processes. These processes could be mediated by influencing cortical function via the thalamus, basal forebrain and basal ganglia. The involvement of the pedunculopontine tegmental nucleus in mechanisms of memory, however, seems to be rather unlikely.

Nerve growth factor and Alzheimer's disease

Nerve growth factor (NGF) is a well-characterized protein that exerts pharmacological effects on a group of cholinergic neurons known to atrophy in Alzheimer's disease (AD). Considerable evidence from animal studies suggests that NGF may be useful in reversing, halting, or at least slowing the progression of AD-related cholinergic basal forebrain atrophy, perhaps even attenuating the cognitive deficit associated with the disorder. However, many questions remain concerning the role of NGF in AD. Levels of the low-affinity receptor for NGF appear to be at least stable in AD basal forebrain, and the recent finding of AD-related increases in cortical NGF brings into question whether endogenous NGF levels are related to the observed cholinergic atrophy and whether additional NGF will be useful in treating this disorder. Evidence regarding the localization of NGF within the central nervous system and its presumed role in maintaining basal forebrain cholinergic neurons is summarized, followed by a synopsis of the relevant aspects of AD neuropathology. The available data regarding levels of NGF and its receptor in the AD brain, as well as potential roles for NGF in the pathogenesis and treatment of AD, are also reviewed. NGF and its low affinity receptor are abundantly present within the AD brain, although this does not rule out an NGF-related mechanism in the degeneration of basal forebrain neurons, nor does it eliminate the possibility that exogenous NGF may be successfully used to treat AD. Further studies of the degree and distribution of NGF within the human brain in normal aging and in AD, and of the possible relationship between target NGF levels and the status of basal forebrain neurons in vivo, are necessary before engaging in clinical trials.

Age-dependent changes in gp75LNGFR (low-affinity nerve growth factor receptor) immunoreactivity in the rat cerebellar cortex

The expression of gp75LNGFR (low-affinity receptor of the nerve growth factor (NGF) family of neurotrophins) immunoreactivity was studied in the cerebellar cortex of male Wistar rats of 3 months (young), 12 months (adult) and 24 months of age using immunohistochemical techniques and a monoclonal antibody against rat-gp75LNGFR. The percentage of Purkinje neurons displaying gp75LNGFR immunoreactivity (IR), and the intensity of gp75LNGFR IR in the cytoplasm of Purkinje and granule neurons, and in the neuropil of molecular layer of the cerebellar cortex were determined by quantitative image analysis and microdensitometry. The number of Purkinje neurons displaying gp75LNGFR IR and the intensity of gp75LNGFRIR in the cytoplasm of Purkinje neurons was significantly higher in rats of 12 months of age in comparison with 24- and 3-month-old rats. No significant changes were observed in the intensity of gp75LNGFRIR in the granule neuron layer of young, adult and old rats. In the molecular layer, the highest gp75LNGFRIR was found in young animals. It was reduced as a function of age. The present results show that changes in gp75LNGFRIR observed as a function of age affect to a different extent the three layers of the rat cerebellar cortex.

NGF can induce a 'young' pattern of reinnervation in transplanted cerebral blood vessels from ageing rats

Peripheral target tissues can determine age-related changes in their density and pattern of innervation. We have shown previously that middle cerebral arteries from young and old rats transplanted in oculo in young hosts become reinnervated with a density and pattern of innervation that is typical of the age of the donor, i.e., the density of reinnervation on old transplants is 50% lower than on young transplants. The alterations in the target tissues responsible for their decreased innervation in old age are still unknown. We have investigated the possibility that increasing the availability of nerve growth factor (NGF) might restore the pattern and density of perivascular nerves on old blood vessels to levels of innervation typical of young tissues. Old middle cerebral transplants were therefore treated with NGF or vehicle by three weekly transscleral injections. NGF treatment markedly increased the reinnervation of old transplants, restoring the density and pattern of innervation to one characteristic of young animals. NGF produced an equivalent increase in nerve growth on young and old transplants, thus confirming that the receptivity of old blood vessels to reinnervation is not impaired. Control experiments were performed by treating transplants with saline, bovine serum albumin, or cytochrome c. Unexpectedly, bovine serum albumin was shown to promote axonal growth, although to a lesser extent and with a different pattern than NGF.

Nerve growth factor receptor immunoreactivity in the cerebellar cortex of aged rats: effect of choline alfoscerate treatment

The rat cerebellar cortex represents an interesting animal model for the analysis of age-dependent changes in brain microanatomy and function. Moreover, the cerebellar cortex contains detectable amounts of nerve growth factor (NGF) and express NGF receptors, which are sensitive to aging. Previous studies of our group have shown that treatment with choline alfoscerate (alpha-glyceryl-phosphorylcholine) countered the loss of nerve cells and fibers occurring with age in the cerebellar cortex. The present study was designed to assess whether treatment for 6 months with a daily dose of 100 mg/kg of choline alfoscerate has any effect on the expression of NGF receptor immunoreactivity in male Wistar rats of 24 months of age. Twelve-month-old rats were used as an adult reference group. NGF receptor immunoreactivity which was developed in the 3 layers of the cerebellar cortex in adult rats was decreased in the neuropil of the molecular layer and in the cytoplasm of Purkinje neurons of rats of 24 months. The number of NGF receptor immunoreactive Purkinje neurons was also lower in the oldest age group, whereas the NGF receptor immunoreactivity in the cytoplasm of granule neurons was unchanged. Treatment with choline alfoscerate increased NGF receptor immunoreactivity in the molecular layer and in the cytoplasm of Purkinje neurons as well as the number of immunoreactive Purkinje neurons but was without effect on NGF receptor immunoreactivity in the granule neurons. These results suggest that choline alfoscerate treatment may increase the expression of NGF receptors in the rat cerebellar cortex.

BDNF and trkB mRNA expression in the hippocampal formation of aging rats

Quantitative in situ hybridization and northern blot analysis techniques were used to determine the topographical distribution and levels of mRNA coding for brain-derived neurotrophic factor (BDNF) and the tyrosine receptor kinase (trkB) mRNA in the hippocampal formation of two strains of male rat during aging. Age did not change the prevalence or regional distribution patterns of BDNF or trkB mRNA in the hippocampal formation throughout the lifespan of male Sprague-Dawley rats. There also were no significant differences in the prevalence or topographical distribution patterns of trkB mRNA transcripts during aging. Northern blot analysis of hippocampal RNA from male Fischer 344 confirmed that neither BDNF mRNA nor trkB mRNA levels changed with age. These findings suggest that age-related neurodegenerative changes, including the atrophy of the cholinergic septo-hippocampal pathway, are not the result of changes in hippocampal BDNF or trkB mRNA expression. Moreover, the prevalence and distribution of synaptosomal-associated protein 25 (SNAP-25), a neuron-specific protein located in synaptic terminals and a putative marker of synaptic integrity, did not change with age. These findings indicate that altered hippocampal synaptic plasticity which occurs in the aged rat brain is not a reflection of changes in the expression of BDNF or trkB receptor mRNA.

Effect of chronic ethanol on the septohippocampal system: a role for neurotrophic factors?

The mechanisms by which chronic ethanol exposure produces neuronal damage have not been established. Potentially ethanol may reduce normal neurotrophic influences necessary for neuronal survival, growth, and function. We hypothesized that chronic ethanol exposure might produce a decrease in the synthesis, availability, upregulation, delivery, and/or the biological activity of normally occurring neurotrophic factors, or may alter the capacity of target neurons to respond to these factors. The available evidence leading to this hypothesis and supporting data from our laboratory are discussed.

Stimulation of nerve growth factor receptors in PC12 by acetyl-L-carnitine

Acetyl-L-carnitine (ALCAR) prevents some deficits associated with aging in the central nervous system (CNS), such as the aged-related reduction of nerve growth factor (NGF) binding. The aim of this study was to ascertain whether ALCAR could affect the expression of an NGF receptor (p75NGFR). Treatment of PC12 cells with ALCAR increased equilibrium binding of 125I-NGF. ALCAR treatment also increased the amount of immunoprecipitable p75NGFR from PC12 cells. Lastly, the level of p75NGFR messenger RNA (mRNA) in PC12 was increased following ALCAR treatment. These results are in agreement with the hypothesis that there is a direct action of ALCAR on p75NGFR expression in aged rodent CNS.

Culture of dorsal root ganglion neurons from aged rats: effects of acetyl-L-carnitine and NGF

In vitro neuronal preparations are used to study the action mechanism of substances which are active in normal and pathological brain aging. One major concern with in vitro assays is that the use of embryonic or adult neurons may hamper an appreciation of the relevance of these substances on aged nervous tissue. In the present study for the first time cultures of aged dorsal root ganglia from 24-months-old rats were maintained in vitro up to 2 weeks. This model was used to investigate the neurotrophic/neuroprotective action of nerve growth factor and acetyl-L-carnitine. A large population of aged dorsal root ganglia neurons was responsive to nerve growth factor (100 ng/ml). Nerve growth factor induced an increase of initial rate of axonal regeneration and influenced the survival time of these neurons. Acetyl-L-carnitine (250 microM) did not affect the axonal regeneration but substantially attenuated the rate of neuronal mortality. A significant difference was evident between the acetyl-L-carnitine-treated and the untreated neurons from the first cell counting (day 3 in culture). After 2 weeks the number of aged neurons treated with acetyl-L-carnitine was almost double that of the controls. The effects of acetyl-L-carnitine on aged DRG neurons potentially explain the positive effects in clinical and in vivo experimental studies.

Hippocampal nerve growth factor levels are related to spatial learning ability in aged rats

Brain nerve growth factor (NGF) was determined in two groups of aged rats: 'good' and 'poor' performers. The animals were selected out of a population of 40 aged rats (26-28 months old) trained in a spatial learning task. Animals performing well in the test had significantly higher NGF in the hippocampus when compared to 'poor' performers. No differences in the levels of NGF were found in the cortex, septum and cerebellum. The results implicate hippocampal NGF in cognitive functioning of aged rats, and suggests that the forebrain cholinergic neuronal atrophy which has been observed in cognitively impaired aged rats may be due to reduced availability of target-derived NGF.

Progressive decline in spatial learning and integrity of forebrain cholinergic neurons in rats during aging

Rats distributed over five different age groups, 3, 12, 18, 24 and 30 months of age, were screened for their spatial learning and memory ability in the Morris water maze, and the degree of place navigational impairments was correlated with morphological changes in the four major forebrain cholinergic cell groups (medial septum, MS; vertical limb of the diagonal band of Broca, VDB; nucleus basalis magnocellularis, NBM; and striatum) using choline acetyltransferase (ChAT) and nerve growth factor receptor (NGFr) histochemistry. Impaired place navigation developed progressively with age, such that 8% of the 12-month-old rats, 45% of the 18-month-old, 53% of the 24-month-old, and over 90% of the 30-month-old rats were behaviorally impaired. Significant reductions in the number of ChAT/NGFr-positive cell bodies, amounting to between 19 and 45%, were observed in all four cell groups, and the remaining cells were reduced in size (6-24% reduction in cross-sectional area in the oldest age groups). Although the morphological changes were less severe and tended to develop later than the behavioral impairments, there was overall a significant correlation between water maze performance and ChAT/NGFr-positive cell counts, and to a lesser degree also cell size in all four cell groups. These changes were also highly correlated with age. The highest correlations were seen in MS, VDB and NBM, which are known to play a role in spatial memory performance in young rats. The results indicate that degenerative and/or atrophic changes in the forebrain cholinergic system and decline in spatial learning ability are parallel processes during aging. Although the magnitude of the morphological changes does not appear to be substantial enough, by itself, to explain the severe spatial learning impairments that develop in the oldest animals, the present data are consistent with the view that impaired function in the forebrain cholinergic system can contribute to age-dependent cognitive decline in rodents.

Embolic stroke in aged rats

BACKGROUND AND PURPOSE

Although stroke is a disorder associated with aging, experimental studies of stroke are conducted in young adult (2-4-month-old) animals (rat life span, 27-29 months). To determine whether histopathologic changes caused by cerebral infarction would be altered in aged animals, we produced embolic cerebral infarction in 17 aged (23-24-month-old) and 16 young (2-4-month-old) rats.

METHODS

The right common carotid artery was irradiated with a laser (632 nm, 200 mW/cm2, 15-20 minutes) after the intravenous injection of the photosensitizing dye Photofrin II (12.5 mg/kg). This produces a nonocclusive platelet thrombus that spontaneously embolizes to the brain. Animals were killed 4 days later.

RESULTS

Analysis was done on 142 infarcts, 68 in aged rats and 74 in young rats. Hypercellularity, with infiltration of macrophages, was more common within small infarcts (less than 1 mm) in young than in aged rats (p = 0.002), and hypertrophy of astroglial fibers surrounding the infarcts was more prominent in young rats. Larger infarcts (greater than or equal to 1 mm) were often hypocellular, with a trend toward more macrophages in the periphery of the infarcts in young than in old animals (p = 0.170).

CONCLUSIONS

The infiltration of macrophages into cerebral infarcts and the hypertrophy of astroglial fibrils surrounding these infarcts are reduced in the aged rat. These age-related differences emphasize the importance of using appropriately aged animals in experimental models of stroke.

Normal beta-NGF content in Alzheimer's disease cerebral cortex and hippocampus

Nerve growth factor (beta-NGF) is known to have beneficial effects on cholinergic cell survival and to function both in vivo and in vitro. It has been speculated that this protein, or the lack of it, may be involved in the aetiology of Alzheimer's disease (AD). We describe the measurement of beta-NGF content in 4 regions of the cerebral cortex and the hippocampus in AD brain compared with brain tissue from age-matched normal subjects using a sensitive sandwich immunoassay (ELISA). There was no difference in beta-NGF content in any region examined in AD compared with normal values despite the marked loss of cortical cholinergic function.

In vivo acetylcholine release as measured by microdialysis is unaltered in the hippocampus of cognitively impaired aged rats with degenerative changes in the basal forebrain

Acetylcholine (ACh) release was studied in awake, freely moving animals using in vivo microdialysis in the hippocampus of young (3-month-old) and aged (24-month-old) female Sprague-Dawley rats. Two groups of aged rats were selected on basis of their spatial learning performance in the Morris water maze: non-impaired aged rats which performed as well as the young control animals, and impaired aged rats which learnt the task very poorly. Baseline ACh overflow (in the presence of 5 microM neostigmine) was 1.9 +/- 0.3 +/- pmol/15 min in the young animals and 1.6 +/- 0.4 pmol/15 min in both the impaired and the non-impaired aged rats; these levels did not differ from each other. Depolarization by KCl (100 mM) or muscarinic receptor blockade by atropine (3 microM) added to the perfusion fluid produced dramatic, 4-6-fold, increases in ACh overflow that was similar in magnitude in both the young and the aged impaired and non-impaired rats. Behavioral activation by either handling or electrical stimulation of the lateral habenula produced 2-3-fold increases in extracellular ACh-levels in the hippocampus similarly in all three groups. The results indicate that hippocampal ACh release is maintained in aged rats that exhibit severe spatial learning and memory impairments and that the septo-hippocampal cholinergic system retains its capacity to increase its ACh release in response to both K(+)-induced depolarization and behavioral activation in the aged rat.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Acetyl-L-carnitine enhances the response of PC12 cells to nerve growth factor

We have demonstrated that treatment of rat pheochromocytoma (PC12) cells with acetyl-L-carnitine (ALCAR) stimulates the synthesis of nerve growth factor receptors (NGFR). ALCAR has also been reported to prevent some age-related impairments of the central nervous system (CNS). In particular, ALCAR reduces the loss of NGFR in the hippocampus and basal forebrain of aged rodents. On these bases, a study on the effect of NGF on the PC12 cells was carried out to ascertain whether ALCAR induction of NGFR resulted in an enhancement of NGF action. Treatment of PC12 cells for 6 days with ALCAR (10 mM) stimulated [125I]NGF PC12 cell uptake, consistent with increased NGFR levels. Also, neurite outgrowth elicited in PC12 cells by NGF (100 ng/ml) was greatly augmented by ALCAR pretreatment. When PC12 cells were treated with 10 mM ALCAR and then exposed to NGF (1 ng/ml), an NGF concentration that is insufficient to elicit neurite outgrowth under these conditions, there was an ALCAR effect on neurite outgrowth. The concentration of NGF necessary for survival of serum-deprived PC12 cells was 100-fold lower for ALCAR-treated cells as compared to controls. The minimal effective dose of ALCAR here was between 0.1 and 0.5 mM. This is similar to the reported minimal concentration of ALCAR that stimulates the synthesis of NGFR in these cells. The data here presented indicate that one mechanism by which ALCAR rescues aged neurons may be by increasing their responsiveness to neuronotrophic factors in the CNS.

Local cerebral glucose utilization in the brain of old, learning impaired rats

The local cerebral glucose utilization (LCGU) was measured in 63 different cortical areas and nuclei of the telencephalon, diencephalon and rhombencephalon of young adult (3 to 4-month-old) rats and of 27-month-old Wistar rats, in which learning impairments had been proven by a water maze test. The LCGU was determined by [14C]2-deoxyglucose autoradiography. In the old rats the mean LCGU of all brain regions was significantly reduced by about 10% compared with the young control group; the mean LCGU was 74.2 mumol glucose/(100 g x min) in the young and 66.7 in the old rats. Different degrees of LCGU decrease were found in the different regions. Most of the brain regions with significantly reduced LCGU values in the aged, learning impaired rats were associated with auditory and visual functions, the dopaminergic system, and structures known to be involved in learning and memory processes. Therefore, the regional pattern of LCGU reduction found in the aged, learning impaired rats did not resemble any known pattern found after lesions of a single transmitter system or systemic administration of transmitter agonists or antagonists.

Recombinant human nerve growth factor is biologically active and labels novel high-affinity binding sites in rat brain

Iodinated recombinant human nerve growth factor (125I-rhNGF) stimulated neurite formation in PC12 cell cultures with a half-maximal potency of 35-49 pg/ml, compared with 39-52 pg/ml for rhNGF. In quantitative ligand autoradiography, the in vitro equilibrium binding of 125I-rhNGF to brain sections showed a 10-fold regional variation in density and was saturable, reversible, and specifically displaced by up to 74% with rhNGF or murine NGF (muNGF). At equilibrium, 125I-rhNGF bound to these sites with high affinity (Kd 52-85 pM) and low capacity (Bmax less than or equal to 13.2 fmol/mg of protein). Calculation of 125I-rhNGF binding affinity by kinetic methods gave average Kd values of 24 and 31 pM. Computer-generated maps revealed binding in brain regions not identified previously with 125I-muNGF, including hippocampus; dentate gyrus; amygdala; paraventricular thalamus; frontal, parietal, occipital, and cingulate cortices; nucleus accumbens; olfactory tubercle; subiculum; pineal gland; and medial geniculate nucleus. NGF binding sites were distributed in a 2-fold increasing medial-lateral gradient in the caudate-putamen and a 2-fold lateral-medial gradient in the nucleus accumbens. 125I-rhNGF binding sites were also found in most areas labeled by 125I-muNGF, including the interpedunucular nucleus, cerebellum, forebrain cholinergic nuclei, caudoventral caudate-putamen, and trigeminal nerve nucleus. 125I-rhNGF binding sites were absent from areas replete with low-affinity NGF binding sites, including circumventricular organs, myelinated fiber bundles, and choroid plexus. The present analysis provides an anatomical differentiation of high-affinity 125I-rhNGF binding sites and greatly expands the number of brain structures that may respond to endogenous NGF or exogenously administered rhNGF.

Spatial distributions of cytoskeletal proteins and the nerve growth factor receptor in septal transplants in oculo: protection from abnormal immunoreactivity by hippocampal co-grafts

Intraocular grafts of embryonic rat septum and co-grafts of septum plus hippocampus were studied with immunohistochemical markers after one and six months (short term) and 12 months (long term) of survival. Neurons in all the septal tissues expressed the epitope for the rat beta-nerve growth factor receptor in sections reacted with the monoclonal antibody 192-IgG. Stained fibers traversed the interface of the short and long term co-grafts and 192-IgG-positive processes were most prominent in the septum when combined with the hippocampal formation. In contrast, labeled processes were sparse and the perikarya of positive neurons appeared shrunken in the long term single septal transplants. Axon and dendrite profiles in the grafts were examined with antibodies that recognize the phosphorylated heavy neurofilament unit (RT97) and the high molecular weight microtubule-associated protein termed MAP 2, respectively. In the short term single and double grafts, characteristic arrays of RT97-positive processes defined the tissues and axonal tracts connecting the septum with the hippocampus. Typical immunostaining of the neuronal somas and the dendrite arbors were were outlined with the MAP 2 antibody. After one year in oculo, extensive changes in the patterns of axonal and dendritic immunoreactivity were noted in the isolated septal grafts. Abnormalities identified with the RT97 antibody included hypertrophied axons, short fragments of kinked axons and neurofilaments in the neuronal perikarya. The formation of circular "abnormal fiber aggregates" composed of densely packed abnormal and normal axonal processes were also distinctive in only the long term single septal transplants. In addition, a reduction in the density of dendrites and the presence of truncated arbors stained with the MAP 2 antibody suggested that regression of the dendrites had occurred. These spatial modifications in axonal and dendritic staining were not present in the septal portion of the combined preparations. In astrocytes, an increase in the antigenicity to glial fibrillary acidic protein paralleled the age of the transplant and was most extensive in the septal grafts. The results illustrate that intraocular co-grafts of hippocampus protect septal neurons and glial cells from abnormal changes in immunoreactivity to antibodies directed against cytoskeletal proteins and exemplify the long term supportive effects of the hippocampus on the morphology of septal neurons, including neurons that express the receptor for nerve growth factor.

Nerve growth factor and the neostriatum

1. The present review summarizes evidence describing the expression, immunoreactivity, binding, transport, development, aging, and functions of NGF in the mammalian neostriatum. 2. Neostriatal NGF binding sites and intrinsic cholinergic neurons are co-localized, increase at a similar rate during ontogeny, and are lost to an equal extent following age- or injury-induced loss of neostriatal neurons. 3. Exogenously administered NGF augments ChAT activity in the intact caudate-putamen, nucleus accumbens, and following mechanical or excitotoxin-induced cholinergic injury. NGF antibodies lower ChAT in the intact caudate-putamen. 4. Neostriatal cholinergic interneurons are lost in the aged rat but also in Alzheimer's disease, Parkinson's disease, supranuclear palsy, and Huntington's chorea. Future studies need to address the extent to which these losses result from an abbreviation of NGF production, binding, or transport and whether rhNGF administration may retard or reverse these cholinergic losses.

Exogenous nerve growth factor stimulates choline acetyltransferase activity in aging Fischer 344 male rats

The effect of age and exogenous nerve growth factor (NGF) infusion on choline acetyltransferase (ChAT) specific activity is examined in microdissections of cerebral and hippocampal cortices, and the cholinergic nuclei of the medial septum and diagonal band of Broca (MS/DB), the nucleus basalis magnocellularis (NBM), and striatum of Fischer 344 male rats. Significant, 20% losses in ChAT activity are found in the MS/DB and striatum of 24-month-old rats (n = 21) compared to 4-month-old animals, but there is no apparent loss of enzyme activity in the NBM. Loss of ChAT activity in the MS/DB is only observed in animals older than 19 months of age, while a striatal deficit is found in animals older than 7 months. Treatment for 2 weeks with NGF at 1.2 micrograms/day results in significant 70% increases of ChAT activity in the MS/DB and striatum of 24-month-old rats compared to untreated and vehicle-treated 4-month-old rats, but does not stimulate activity in the NBM. Sensitivity of ChAT activity in the MS/DB and striatum to exogenous NGF increases with age. These experiments indicate that in the MS/DB, NBM, and striatum of Fischer 344 male rat there is an age-associated, differential regulation of ChAT enzyme activity and sensitivity to exogenous NGF.

Nerve growth factor levels and choline acetyltransferase activity in the brain of aged rats with spatial memory impairments

Nerve growth factor (NGF) and choline acetyltransferase (ChAT) activity levels were measured in 7 different brain regions in young (3-month-old) and aged (2-years-old) female Sprague-Dawley rats. Prior to analysis the spatial learning ability of the aged rats was assessed in the Morris' water maze test. In the aged rats a significant, 15-30%, increase in NGF levels was observed in 4 regions (septum, cortex, olfactory bulb and cerebellum), whereas the levels in hippocampus, striatum and the brainstem were similar to those of the young rats. The NGF changes did not correlate with the behavioral performance within the aged group. Minor 15-30%, changes in ChAT activity were observed in striatum, brainstem and cerebellum, but these changes did not correlate with the changes in NGF levels in any region. The results indicate that brain NGF levels are maintained at normal or supranormal levels in rats with severe learning and memory impairments. The results, therefore, do not support the view that the marked atrophy and cell loss in the forebrain cholinergic system that is known to occur in the behaviorally impaired aged rats is caused by a reduced availability of NGF in the cholinergic target areas. The results also indicate that the slightly increased levels of NGF are not sufficient to prevent the age-dependent atrophy of cholinergic neurons, although they might be important for the stimulation of compensatory functional changes in a situation where the system is undergoing progressive degeneration.

Localization of NGF receptors in normal and Alzheimer's basal forebrain with monoclonal antibodies against the truncated form of the receptor

Four new monoclonal antibodies to the extracellular domain of the nerve growth factor receptor (NGFR) have been evaluated for their specificity to NGFR and their utility in localizing NGFR in human brain. All four antibodies, as well as Me20.4, show similar cellular localization and patterns of immunoreactivity in basal forebrain neurons. NGFR monoclonal antibody XIF1 stains optimally over the widest range of concentrations, with staining being reduced only slightly at less than 10 pg/ml or more than 100 ng/ml, and produces the lowest background of those tested. Staining with all NGFR monoclonal antibodies is blocked by the addition of as little as 5-fold excess human recombinant truncated NGFR protein. The distribution of NGFR-containing neurons is similar to that previously described in normal human forebrain, as is the reduction in cell size in nucleus basalis (Ch4am) in brains from patients with Alzheimer's disease. In addition, we find evidence in the two Alzheimer's cases examined for a previously unreported loss of cells in the horizontal limb nucleus of the diagonal band (Ch3) in Alzheimer's disease. The loss of these neurons, which in normal brain have characteristic varicose dendritic processes extending to the pial surface adjacent to the cisternal space, may indicate a change in the relationship of NGF-sensitive neurons to the vasculature. Since these neurons project to olfactory bulb and cortex in rodent and primate brains, their loss may also reflect damage to the olfactory system in Alzheimer's disease.

Exogenous nerve growth factor increases the activity of high-affinity choline uptake and choline acetyltransferase in brain of Fisher 344 male rats

The objective of this study was to determine the effect of age and chronic intracerebral administration of nerve growth factor (NGF) on the activity of the presynaptic cholinergic neuronal markers hemicholinium-sensitive high-affinity choline uptake (HACU) and choline acetyltransferase (ChAT) in the brain of Fisher 344 male rats. In 24-month-old rats, a substantial decrease in ChAT activity (30%) was measured in striatum, and decreases in HACU were found in frontal cortex (28%) and hippocampus (23%) compared with 4-month-old controls. Cholinergic neurons in brain of both young adult and aged rats responded to administration of exogenous NGF by increased expression of both phenotypes. In 4-month-old animals, NGF treatment at 1.2 micron/day resulted in increased activities of both ChAT and HACU in striatum (175 and 170%, respectively), frontal cortex (133 and 125%), and hippocampus (137 and 125%) compared with untreated and vehicle-treated 4-month-old animals; vehicle treatment had no effect on the activity of either marker. In 24-month-old animals treated with NGF for 2 weeks, ChAT activity was increased in striatum (179%), frontal cortex (134%), and hippocampus (119%) compared with 24-month-old control animals. Synaptosomal HACU in 24-month-old rats was increased in striatum (151%) and frontal cortex (128%) after 2 weeks of NGF treatment, but hippocampal HACU was not significantly different from control values.(ABSTRACT TRUNCATED AT 250 WORDS)

Nerve growth factor receptor in neural lobe of rat pituitary gland: immunohistochemical localization, biochemical characterization and regulation

Nerve growth factor-receptor immunoreactivity was detected in the neural lobe of the pituitary gland in developing and adult rats of both sexes. The presence of nerve growth factor receptor in the neural lobe was further verified by a quantitative 125I-nerve growth factor/crosslink/immunoprecipitation assay and subsequent visualization by SDS-PAGE autoradiography. Nerve growth factor-receptor immunoreactivity was detected in the neural lobe of postnatal 5-day-old rats, had increased by 2 months and was much higher in 1-year-old rats. In 2-month-old rats, no immunoreactivity was observed in anterior or intermediate lobes. Pituitary stalk transection in young adult rats greatly increased the expression of nerve growth factor-receptor immunoreactivity in the neural lobe, although the staining pattern remained the same. This increase began 3 days after surgery, and reached peak levels at approximately 15 days. Other physiological or non-physiological changes did not alter the nerve growth factor-receptor immunoreactivity in the neural lobe; these changes included dehydration, pregnancy and lactation, castration of male rats, bilateral superior cervical ganglionectomy and intraventricular injection of colchicine. Intravenously injected 125I-nerve growth factor was specifically accumulated in both normal and denervated neural lobe. Nerve growth factor-receptor immunohistochemical electron microscopy showed that the receptor-positive cells are fusiform and found both inside and outside the basal lamina that delimits the neural lobe parenchyma. Based upon the anatomical localization, morphology and response to axotomy, we identify, at least the perivascular component, as microglia. These data suggest a role for nerve growth factor and/or nerve growth factor receptor in microglial function.

Nerve growth factor and neuronal cell death

The regulation of neuronal cell death by the neuronotrophic factor, nerve growth factor (NGF), has been described during neural development and following injury to the nervous system. Also, reduced NGF activity has been reported for the aged NGF-responsive neurons of the sympathetic nervous system and cholinergic regions of the central nervous system (CNS) in aged rodents and man. Although there is some knowledge of the molecular structure of the NGF and its receptor, less is known as to the mechanism of action of NGF. Here, a possible role for NGF in the regulation of oxidant--antioxidant balance is discussed as part of a molecular explanation for the known effects of NGF on neuronal survival during development, after injury, and in the aged CNS.