Nerve growth factor affects passive avoidance learning and retention in developing mice

Time-dependent role of prefrontal cortex and hippocampus on cognitive improvement by aripiprazole in olfactory bulbectomized mice

Dopamine (DA) modulates cognitive functions in the prefrontal cortex (PFC) and hippocampus. Olfactory bulbectomy (OBX) in mice induces cognitive dysfunctions. Recently, we reported that aripiprazole (ARI) normalizes the behavioral hyper-responsivity to DA agonists in OBX mice. However, it remains unclear whether ARI affects OBX-induced cognitive dysfunctions. To address this question we evaluated ARI-treated and untreated OBX mice in a passive avoidance test. Then, we investigated the effects of ARI on cell proliferation in the hippocampal dentate gyrus by immunohistochemistry, and on c-fos levels in the PFC and hippocampus, as well as nerve growth factor (NGF) levels in the hippocampus by western blotting. On the 14th day after surgery OBX mice showed an alteration in passive avoidance and decreases in both cell proliferation and levels of p-ERK, p-CREB and NGF in the hippocampus. The cognitive dysfunctions in OBX mice improved 30min to 24h after the administration of ARI (0.01mg/kg). C-fos levels in the PFC but not in the hippocampus was increased 30min after the administration (early response). This early response was inhibited by the selective D₁ receptor antagonist SCH23390. Cell proliferation and NGF levels in the hippocampus increased 24h after ARI administration (late response), and these effects were also inhibited by SCH23390. The MEK1/2 inhibitor U0126 prevented ARI from improving the behavioral impairment as well as enhancing NGF levels in OBX mice. These findings revealed the potential of ARI to improve cognitive dysfunctions via D₁ receptors with the PFC and hippocampus being affected sequentially.

Effects of Hericium erinaceus on amyloid β(25-35) peptide-induced learning and memory deficits in mice

The mushroom Hericium erinaceus has been used as a food and herbal medicine since ancient times in East Asia. It has been reported that H. erinaceus promotes nerve growth factor secretion in vitro and in vivo. Nerve growth factor is involved in maintaining and organizing cholinergic neurons in the central nervous system. These findings suggest that H. erinaceus may be appropriate for the prevention or treatment of dementia. In the present study, we examined the effects of H. erinaceus on amyloid β(25-35) peptide-induced learning and memory deficits in mice. Mice were administered 10 µg of amyloid β(25-35) peptide intracerebroventricularly on days 7 and 14, and fed a diet containing H. erinaceus over a 23-d experimental period. Memory and learning function was examined using behavioral pharmacological methods including the Y-maze test and the novel-object recognition test. The results revealed that H. erinaceus prevented impairments of spatial short-term and visual recognition memory induced by amyloid β(25-35) peptide. This finding indicates that H. erinaceus may be useful in the prevention of cognitive dysfunction.

Nerve growth factor-inducing activity of Hericium erinaceus in 1321N1 human astrocytoma cells

Neurotrophic factors are essential to maintain and organize neurons functionally; thereby neurotrophic factor-like substances or their inducers are expected to be applied to the treatment of neurodegenerative diseases such as Alzheimer's disease. In the present study, we firstly examined the effects of ethanol extracts of four edible mushrooms, Hericium erinaceus (Yamabushitake), Pleurotus eryngii (Eringi), Grifola frondosa (Maitake), and Agaricus blazei (Himematsutake), on nerve growth factor (NGF) gene expression in 1321N1 human astrocytoma cells. Among the four mushroom extracts, only H. erinaceus extract promoted NGF mRNA expression in a concentration-dependent manner. In addition, secretion of NGF protein from 1321N1 cells was enhanced by H. erinaceus extracts, and the conditioned medium of 1321N1 cells incubated with H. erinaceus extract enhanced the neurite outgrowth of PC12 cells. However, hericenones C, D and E, constituents of H. erinaceus, failed to promote NGF gene expression in 1321N1 cells. The enhancement of NGF gene expression by H. erinaceus extracts was inhibited by the c-jun N-terminal kinase (JNK) inhibitor SP600125. In addition, H. erinaceus extracts induced phosphorylation of JNK and its downstream substrate c-Jun, and increased c-fos expression, suggesting that H. erinaceus promotes NGF gene expression via JNK signaling. Furthermore we examined the efficacy of H. erinaceus in vivo. ddY mice given feed containing 5% H. erinaceus dry powder for 7 d showed an increase in the level of NGF mRNA expression in the hippocampus. In conclusion, H. erinaceus contains active compounds that stimulate NGF synthesis via activation of the JNK pathway; these compounds are not hericenones.

Postnatal Development of Conditioned Reflex Behavior: Comparison of the Times of Maturation of Plastic Processes in the Rat Hippocampus

The formation of conditioned reflex fear, escape responses, and conditioned avoidance responses during acquisition of a conditioned two-way avoidance reflex was studied in rats of different ages. Rats aged 16-17 days acquired the conditioned reflex but not the escape reaction or the conditioned avoidance response; acquisition efficiency was higher than in adult rats. Escape responses appeared from postnatal day 18. The ability to acquire this type of learning was complete by age 3-4 weeks. Maturation of the mechanisms of the "classical" (the fear phase) and operant (transfer to another sector in response to the unconditioned stimulus) components did not facilitate acquisition of the conditioned two-way avoidance reflex until the middle of postnatal week 4. Learning efficiency in four-week-old rats was lower than in adults. It is suggested that the maturation of different types of memory may be associated with the periods at which plastic processes develop in the hippocampus.

Short- and long-term memory are differentialy modulated by hippocampal nerve growth factor and fibroblast growth factor

Rats were implanted with cannulae in the CA1 area of the dorsal hippocampus and trained in one-trial step-down inhibitory avoidance. Two retention tests were carried out in each animal, one at 1.5 h to measure short-term memory (STM) and another at 24 h to measure long-term memory (LTM). The purpose of the present study was to evaluate the modulation on hippocampal nerve growth factor (NGF) and basic fibroblast growth factor (bFGF) on short- and long-term memory. Immediately after training, animals received 5 microl of NGF (0.05, 0.5 or 5.0 ng), bFGF (1.25, 12.5 or 125 ng) or saline per side. At the higher dose, NGF blocked STM. In contrast, NGF at dose of 0.5 and 5.0 ng improved LTM. The bFGF infusion at a dose of 125 ng enhanced LTM. However, bFGF did not alter STM. These findings indicate that hippocampal NGF and bFGF modulate STM and LTM in a different manner.

Differential role of entorhinal and hippocampal nerve growth factor in short- and long-term memory modulation

We studied the effects of infusion of nerve growth factor (NGF) into the hippocampus and entorhinal cortex of male Wistar rats (250-300 g, N = 11-13 per group) on inhibitory avoidance retention. In order to evaluate the modulation of entorhinal and hippocampal NGF in short- and long-term memory, animals were implanted with cannulae in the CA1 area of the dorsal hippocampus or entorhinal cortex and trained in one-trial step-down inhibitory avoidance (foot shock, 0.4 mA). Retention tests were carried out 1.5 h or 24 h after training to measure short- and long-term memory, respectively. Immediately after training, rats received 5 microl NGF (0.05, 0.5 or 5.0 ng) or saline per side into the CA1 area and entorhinal cortex. The correct position of the cannulae was confirmed by histological analysis. The highest dose of NGF (5.0 ng) into the hippocampus blocked short-term memory (P < 0.05), whereas the doses of 0.5 (P < 0.05) and 5.0 ng (P < 0.01) NGF enhanced long-term memory. NGF administration into the entorhinal cortex improved long-term memory at the dose of 5.0 ng (P < 0.05) and did not alter short-term memory. Taken as a whole, our results suggest a differential modulation by entorhinal and hippocampal NGF of short- and long-term memory.

Behavioral patterns under cholinergic control during development: lessons learned from the selective immunotoxin 192 IgG saporin

The immunotoxin 192 IgG saporin (192 IgG-sap) offers a valuable tool to investigate the role of the developing basal forebrain cholinergic system in modulating behavioral functions in developing, as well as adult rats. After neonatal 192 IgG-sap lesions, rats display reduced ultrasonic vocalizations as neonates, deficits in passive avoidance learning as juveniles, and altered reactions to spatial novelty as adults. These data suggest that neonatal cholinergic depletion affects cognitive performance in juvenile and adult rats. Additionally, neonatal cholinergic depletion alters ultrasonic vocalizations, which could then alter establishing normal mother-infant relationships, and thus compound the pup's cognitive deficits. These findings underscore the importance of assessing behavior during ontogeny, as well as in adulthood.

Brain NGF and EGF administration improves passive avoidance response and stimulates brain precursor cells in aged male mice

Nerve growth factor (NGF) has been shown to improve damage in spatial cognition following aging, whereas epidermal growth factor (EGF) is important in brain cell proliferation. It is also known that the adult mammalian central nervous system contains persistent progenitor cells with characteristics of stem cells. These studies suggest that under appropriate external stimuli progenitor cells may generate neuronal and glial cells promoting recovery of the injured nervous system. However, little is known about the presence and responsiveness of progenitor cells in the aged brain. In the present investigation, we studied the effect of brain intracerebroventricular injections of EGF and/or NGF on progenitor cells of the subventricular area (SVZ) in aged male mice to test learning performances in the passive avoidance apparatus. We found that neither NGF nor EGF improved learning responses. However, combined NGF and EGF administration in the brain improved learning responses of aged mice in the passive avoidance when compared with aged matched nontreated controls. These findings resulted to be associated with increased immunopositivity to progenitor cells in the SVZ. The possible functional implications of these data are discussed.

NGF induces appearance of adult-like response to spatial novelty in 18-day male mice

We investigated the effects of Nerve Growth Factor (NGF) administration on the maturation of reactivity to spatial and non-spatial novelty in developing mice. CD-1 mice of both sexes received intracerebral administration of NGF on postnatal day (pnd) 15, and their response to object displacement (spatial novelty) and object substitution (object novelty) were assessed in a spatial open-field with four objects on pnd 18 or 28. On pnd 18, NGF induced only in males precocious appearance of spatial novelty discrimination, while increasing choline acetyltransferase activity in neocortex and hippocampus of both sexes. The behavioral and neurochemical effects disappeared by pnd 28. NGF triggers adult-like responding to spatial novelty in developing mice and such effect is gender-specific.

Passive avoidance response in mice infected with Schistosoma mansoni

Schistosomiasis is a parasitic disease of humans and rodents affecting more than 200 million people worldwide. Following the onset of infection, the worms induce granulomas around schistosome eggs in the liver, intestine and central nervous system (both brain and spinal cord), which are likely to cause changes in cognitive functions. In the present study, CD-1 female mice were percutaneously infected with 60 cercariae of Schistosoma mansoni and the effect on the mice's cognitive abilities were assessed by using the passive avoidance learning paradigm both in an early and a late phase of infection (independent groups). The results of the study show that infected animals without brain granulomas (early phase) had impairments in their passive avoidance response, whereas mice with brain granulomas (late phase) behaved as uninfected ones. Moreover, a decreased propensity to start exploration was observed in mice with granulomas in the brain. The results suggest that the murine model of infection may be a useful tool for studying human neuroschistosomiasis.

Ontogeny of spatial discrimination in mice: a longitudinal analysis in the modified open-field with objects

The present longitudinal study investigated the emergence of spatial discrimination and reaction to novelty in CD-1 mice, using a modified open-field test with four objects, a test in which responses to both spatial rearrangement of familiar objects and object novelty are assessed. Male and female mice were tested on postnatal days (pnd) 18, 28, 46 and 90. Locomotor activity was highest on pnd 90, whereas time spent on objects before rearrangement was highest on pnd 46. Eighteen-day old mice were unable to detect both object rearrangement and object novelty, suggesting immaturity in processing spatial information. On days 28 and 46 mice showed a clear response to object novelty, actively exploring the unfamiliar object placed in the arena, while at these ages object displacement elicited a generalized increase of exploration, not directed towards the displaced objects. A clear and selective response to object displacement emerged only at adulthood (day 90).

Learning performances, brain NGF distribution and NPY levels in transgenic mice expressing TNF-alpha

Tumor necrosis factor-alpha (TNF-alpha) is a cytokine involved in a variety of neurobiological activities including changing behavior and regulation of both neurotrophin and neuropeptide levels. In this study we used two lines of transgenic mice overexpressing brain TNF-alpha characterized by neurological deficits (line Tg6074) or phenotypically normal (line TgK3). We analyzed whether or not impairments in learning and memory processes due to TNF-alpha overexpression were associated with changes in endogenous brain NGF, NPY and beta-amyloid. The results indicate that full TNF-alpha transgene expression disrupted the learning capabilities of transgenic mice (both Tg6074 and TgK3). NGF decreased in the hippocampus of both transgenic mice whereas hippocampal NPY slightly potentiated in Tg6074. The decrease in NGF is correlated with deficits in spatial learning and memory whereas inflammation in the brain of Tg6074 could be responsible of the hippocampal increase in NPY. As a whole, these results show that transgenic mice overexpressing TNF-alpha in the brain represent a useful model for studying neuronal degeneration and brain inflammatory processes.

Time-dependent enhancement of inhibitory avoidance retention and MAPK activation by post-training infusion of nerve growth factor into CA1 region of hippocampus of adult rats

Several studies have demonstrated that chronic intracerebroventricular nerve growth factor (NGF) infusion has a beneficial effect on cognitive performance of lesioned as well as old and developing animals. Here we investigate: (i) the effect of post-training infusion of NGF into the CA1 region of hippocampus on inhibitory avoidance (IA) retention in rats; (ii) the extension of the effect, in time and space, of NGF infusion into CA1 on the activity of mitogen-activated protein kinase (MAPK, syn: ERK1/2, p42/p44 MAPK). NGF was bilaterally injected into the CA1 regions of the dorsal hippocampus (0.05, 0.5 or 5.0 ng diluted in 0.5 microL of saline per side ) at 0, 120 or 360 min after IA training in rats. Retention testing was carried out 24 h after training. The injection of 5.0 and 0.5, but not 0.05, ng per side of NGF at 0 and 120 min after IA training enhanced IA retention. The highest dose used was ineffective when injected 360 min after training. The infusion of 0. 5 microL of NGF (5.0 ng) induced a significant enhancement of MAPK activity in hippocampal microslices; this enhancement was restricted to a volume with 0.8 mm radius at 30 min after injection. The MAPK activation was still seen 180 min after NGF infusion, although this value showed only a tendency. In conclusion, localized infusion of NGF into the CA1 region enhanced MAPK activity, restricted in time and space, and enhanced IA retention in a time- and dose-dependent manner.

Neurobehavioral alteration in rodents following developmental exposure to aluminum

Aluminum (Al) is one of the most abundant metals in the earth's crust, and humans can be exposed to it from several sources. It is present in food, water, pharmaceutical compounds, and in the environment, e.g., as a result of acid rain leaching it from the soil. Exposure to Al has recently been implicated in a number of human pathologies, but it has not yet been definitely proved that it plays a major causal role in any of them. In this paper we review the effects of developmental exposure of laboratory animals to Al salts as a model for human pathological conditions. The data presented show behavioral and neurochemical changes in the offspring of AL-exposed mouse dams during gestation, which include alterations in the pattern of ultrasonic vocalizations and a marked reduction in central nervous system (CNS) choline acetyltransferase activity. Prenatal Al also affects CNS cholinergic functions under Nerve Growth Factor (NGF) control, as shown by increased central NGF levels and impaired performances in a maze learning task in young-adult mice. The need for more detailed studies to evaluate the risks for humans associated with developmental exposure to Al, as well as the importance of using more than one strain of laboratory animal in the experimental design, is emphasized.

Neonatal cocaine alters behavioural responsiveness to scopolamine and cholinergic development in mice

CD-1 mice received daily subcutaneous injections of either cocaine (20 mg/kg or 40 mg/kg) or saline solution (0.9% NaCl) from postnatal days 2 to 15. Pups were tested on days 16-17 for learning and 24-h retention of a passive avoidance task, where entering a dark compartment was punished with a mild foot shock. Locomotor activity and general behaviour in an open field arena were assessed on day 21, following administration of either the muscarinic blocker scopolamine (0.8 mg/kg) or saline solution. In addition, immunostaining for the enzyme choline acetyltransferase (ChAT) was measured in different basal forebrain areas (medial septum, striatum, and nucleus basalis) on day 30. Cocaine treatment failed to affect either learning or retention capabilities. Nonetheless, neophobic behaviour during the learning session was enhanced in control nonpunished mice exposed to the 20-mg/kg dose. In the open field test, although baseline activity levels were unaffected by cocaine exposure, the 40-mg/kg cocaine-treated pups showed decreased sensitivity to the hyperkinetic effects of scopolamine. ChAT immunocytochemistry revealed a significant reduction of the number of ChAT-immunopositive neurons in the nucleus basalis but not in the other cholinergic basal forebrain regions.