Nefiracetam (DM-9384) preserves hippocampal neural cell adhesion molecule-mediated memory consolidation processes during scopolamine disruption of passive avoidance training in the rat

TGF-beta signalling in the adult neurogenic niche promotes stem cell quiescence as well as generation of new neurons

Members of the transforming growth factor (TGF)-β family govern a wide range of mechanisms in brain development and in the adult, in particular neuronal/glial differentiation and survival, but also cell cycle regulation and neural stem cell maintenance. This clearly created some discrepancies in the field with some studies favouring neuronal differentiation/survival of progenitors and others favouring cell cycle exit and neural stem cell quiescence/maintenance. Here, we provide a unifying hypothesis claiming that through its regulation of neural progenitor cell (NPC) proliferation, TGF-β signalling might be responsible for (i) maintaining stem cells in a quiescent stage, and (ii) promoting survival of newly generated neurons and their functional differentiation. Therefore, we performed a detailed histological analysis of TGF-β1 signalling in the hippocampal neural stem cell niche of a transgenic mouse that was previously generated to express TGF-β1 under a tetracycline regulatable Ca-Calmodulin kinase promoter. We also analysed NPC proliferation, quiescence, neuronal survival and differentiation in relation to elevated levels of TGF-β1 in vitro and in vivo conditions. Finally, we performed a gene expression profiling to identify the targets of TGF-β1 signalling in adult NPCs. The results demonstrate that TGF-β1 promotes stem cell quiescence on one side, but also neuronal survival on the other side. Thus, considering the elevated levels of TGF-β1 in ageing and neurodegenerative diseases, TGF-β1 signalling presents a molecular target for future interventions in such conditions.

Effects of nefiracetam on the levels of brain-derived neurotrophic factor and synapsin I mRNA and protein in the hippocampus of microsphere-embolized rats

Our recent study demonstrated that nefiracetam, N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl) acetamide, prevented impairment of the cyclic AMP (cAMP)/cAMP-responsive element binding (CREB) protein signaling pathway in sustained cerebral ischemia. The purpose of the present study was to determine whether nefiracetam has an effect on the expression of brain-derived neurotrophic factor (BDNF) and synapsin I mRNAs that are believed to be produced via CREB, and the alteration in their protein contents in the hippocampus after cerebral ischemia. Sustained cerebral ischemia was induced by injection of 700 microspheres into the right hemisphere of each rat. The rats were treated once daily with 10 mg/kg nefiracetam, p.o., from 15 h after the operation. Treatment with nefiracetam reduced the prolongation of the escape latency in the water maze test on days 7-9 after microsphere embolism-induced sustained cerebral ischemia, suggesting an improvement in the spatial learning function. Microsphere-embolized rats on day 5 showed decreases in BDNF and synapsin I mRNA levels and their protein contents in the ipsilateral hippocampus. Treatment with nefiracetam partially attenuated the decreases. These results suggest that enhancement of BDNF and synapsin I expression by nefiracetam treatment may be, at least in part, due to the improvement in the CREB binding activity, contributing to the prevention of learning and memory dysfunction after sustained cerebral ischemia.

Effects of nefiracetam on cerebral adenylyl cyclase activity in rats with microsphere embolism-induced memory dysfunction

The effects of nefiracetam on the cerebral adenylyl cyclase (AC) activity of animals with microsphere embolism-induced memory dysfunction were examined. Sustained cerebral ischemia in the right cerebral hemisphere was induced by an injection of microspheres into the right internal carotid artery of rats. To examine learning and memory function, the water maze test was performed from day 7 to day 10 after the operation. The escape latency of the microsphere-embolized (ME) rat in the water maze task was longer than that of the sham-operated (Sham) rat, suggesting that spatial memory dysfunction occurred in the ME rat. Gsalpha and Gi(1/2)alpha protein levels in the cerebral cortex, striatum and hippocampus of the ME rat, when determined on day 11, were similar to those of the Sham rats. The basal AC activity in the striatum, but not in the other two regions, of the ME rat decreased. The AC activity in the presence of 10 microM colforsin daropate (Col), a direct stimulator of AC, was increased by approximately 20-fold in sham animals and 7- to 10-fold in the ME rat. Treatment of the ME rat with 10 mg/kg/d nefiracetam p.o. from day 1 to day 10 after the operation shortened the escape latency, restored the basal AC activity in the striatum, and reversed the Col-induced increases in AC in these three regions without any changes in the cerebral Gsalpha and Gi(1/2)alpha protein levels. These results suggest that nefiracetam-mediated activation of AC activity may contribute to the improvement of memory and learning function in sustained cerebral ischemia.

A synthetic ceramide analog ameliorates spatial cognition deficit and stimulates biosynthesis of brain gangliosides in rats with cerebral ischemia

A synthetic ceramide analog, L-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (L-PDMP) upregulates ganglioside biosynthesis in several cell lines. In cultured cortical neurons, neurotrophic effects of L-PDMP on neurite outgrowth and synaptic activity were demonstrated. In addition, it was found that L-PDMP could ameliorate the spatial cognition deficit in rats with ischemia. To elucidate this effect, we evaluated the effect of L-PDMP on brain ganglioside biosynthesis and its therapeutic efficacy against spatial cognition deficit in rats made ischemic. Rats were trained for 2 weeks, using an 8-arm radial maze task, and then forebrain ischemia was induced. L-PDMP was injected i.p. at 40 mg/kg twice a day starting from day 1 or 3 after ischemia induction for 6 or 4 days, respectively. The first study showed significantly reduced spatial cognition deficit at 12 h after the final drug administration, and L-PDMP tended to attenuate apoptosis in hippocampal CA1. To examine the effect of L-PDMP on brain ganglioside biosynthesis, N-[3H]acetyl-D-mannosamine was infused into the lateral ventricle via an injection cannula at 12 h after the final drug administration. After 4 h, the brain gangliosides were purified and analyzed. Upregulation of ganglioside biosynthesis by L-PDMP was observed on days 3 and 5 after ischemia. These results are an indication that L-PDMP may ameliorate spatial cognition deficit by upregulating ganglioside biosynthesis in ischemic brain.

A possible mechanism for improvement by a cognition-enhancer nefiracetam of spatial memory function and cAMP-mediated signal transduction system in sustained cerebral ischaemia in rats

1. Accumulated evidence indicates that the adenylyl cyclase (AC)/cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA)/cAMP-responsive element binding protein (CREB) signal transduction system may be linked to learning and memory function. 2. The effects of nefiracetam, which has been developed as a cognition enhancer, on spatial memory function and the AC/cAMP/PKA/CREB signal transduction system in rats with sustained cerebral ischaemia were examined. 3. Microsphere embolism (ME)-induced sustained cerebral ischaemia was produced by injection of 700 microspheres (48 micro m in diameter) into the right hemisphere of rats. Daily oral administration of nefiracetam (10 mg kg(-1) day(-1)) was started from 15 h after the operation. 4. The delayed treatment with nefiracetam attenuated the ME-induced prolongation of the escape latency in the water maze task that was examined on day 7 to 9 after ME, but it did not reduce the infarct size. 5. ME decreased Ca(2+)/calmodulin (CaM)-stimulated AC (AC-I) activity, cAMP content, cytosolic PKA Cbeta level, nuclear PKA Calpha and Cbeta levels, and reduced the phosphorylation and DNA-binding activity of CREB in the nucleus in the right parietal cortex and hippocampus on day 3 after ME. The ME-induced changes in these variables did not occur by the delayed treatment with nefiracetam. 6. These results suggest that nefiracetam preserved cognitive function, or prevented cognitive dysfunction, after sustained cerebral ischaemia and that the effect is, in part, attributable to the prevention of the ischaemia-induced impairment of the AC/cAMP/PKA/CREB signal transduction pathway.

Persistent effects of delayed treatment with nefiracetam on the water maze task in rats with sustained cerebral ischemia

The present study was aimed at determining whether nefiracetam might have a persistent cognition-enhancing effect in animals with sustained cerebral ischemia. Sustained cerebral ischemia was induced by injecting 700 microspheres into the right internal carotid artery of rats [microsphere-embolized (ME) rats]. The ME and sham-operated rats were treated with 10 mg/kg/day nefiracetam p.o. from the first to the 9th day after the operation. The escape latency of the ME rat in the water maze test, when performed on days 7 to 9 after the operation, was lengthened. This effect was attenuated by the delayed treatment with nefiracetam. The nefiracetam-treated ME rat showed a shortened escape latency in the retention test on day 17 as well as in the contraposition test on day 18. These results indicate that a persistent improvement of the spatial memory function impaired by sustained cerebral ischemia was achieved even after cessation of treatment with nefiracetam. The functional damage to learning and memory was associated with decreases in the membranous adenylyl cyclase I and cytosolic protein kinase A (PKA) catalytic subunit and regulatory subunit proteins in the right hippocampus and cerebral cortex. The delayed treatment with nefiracetam appreciably prevented the decreases in these proteins. The present study suggests that nefiracetam may have an ability to cause persistent improvement of learning and memory function, possibly through protection against the ischemia-induced impairment to the adenylyl cyclase/cAMP/PKA signal transduction pathway.

Effects of nefiracetam on spatial memory function and acetylcholine and GABA metabolism in microsphere-embolized rats

The present study aimed to determine whether nefiracetam, N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl) acetamide, a cognition enhancer, has an effect on learning and memory function in sustained cerebral ischemia, and whether the effect, if any, may accompany modification of the cholinergic or gamma-aminobutyric acid (GABA)ergic system, which are conceived to be involved in the learning and memory function, in the ischemic brain. Sustained cerebral ischemia was induced by the injection of 700 microspheres into the right hemisphere of the rat. The animals were treated once daily with 10 mg/kg nefiracetam p.o. from 15 h after the operation to either 10 days for the water maze study, or 3 or 5 days after the operation for neurochemical examination. Microsphere-embolized rats showed stroke-like symptoms 15 h after the operation and lengthened the escape latency in the water maze task on days 7-10, suggesting a spatial learning dysfunction. The delayed treatment did not reduce the stroke-like symptoms, but effectively shortened the escape latency. The animals at days 3 and 5 after the operation showed decreases in acetylcholine content and choline acetyltransferase activity, which were not prevented by nefiracetam. The microsphere-embolized rats showed decreases in GABA content and glutamic acid decarboxylase activity. The delayed treatment appreciably restored GABA content in the hippocampus on day 5 and reversed glutamic acid decarboxylase activity in both brain regions on day 5. These results suggest that the GABAergic activity rather than the cholinergic activity may be, at least in part, involved in the pharmacological effects of nefiracetam in the ischemic brain.

Learning and memory in mice treated with choline oxidase, a hydrolytic enzyme for choline

Learning and maintenance of memory in mice intraperitoneally (IP) injected with choline oxidase (ChO, 6 units/g), a hydrolytic enzyme for choline (Ch), were assessed by means of a step-through passive-avoidance task. The ChO treatment induced a hydrolysis of free Ch in plasma, which in turn, induced a decrease in cerebral acetylcholine (ACh) release. In the learning test, the ChO-treated mice showed significant inhibition to learn the avoidance from electric shock. In the retention test, the impairment of the memory once established was not produced by posttreated ChO. We concluded that the decreased cerebral cholinergic neurotransmission induced by ChO retarded acquisition of passive-avoidance learning more readily than the maintenance of memory.

Kv1.1 channel antisense attenuates learning and modulation of dentate polysialylated NCAM

The distribution and modulation of neural cell adhesion molecule polysialylation state (NCAM PSA) and the consequence of antisense inactivation of the Kv1.1 potassium channel was investigated following avoidance learning in mice. PSA immunoreactivity was most notable on cells at the inner denate border and in cortical layer II. Task acquisition resulted in a significant 30% transient increase in the frequency of dentate polysialylated neurons at the 12 h post-training time. In contrast, animals pretreated with the Kv1.1 antisense oligonucleotide exhibited both attenuated recall avoidance latencies and polysialylated cell frequency. As Kv1.1 is enriched on the dendrites of these granule-like cells, the attenuated polysialylation response is considered secondary to NCAM-mediated events during their transient synapse production in the 6-8 h post-training period.

Piracetam facilitates long-term memory for a passive avoidance task in chicks through a mechanism that requires a brain corticosteroid action

We investigated the effects of piracetam, a nootropic, on learning and memory formation for a passive avoidance task in day-old chicks. To test for the possible cognitive-enhancing properties of piracetam, a weak learning version of this task--whereby chicks maintain a memory to avoid pecking at a bead coated in a diluted aversant for up to 10 h--was used. Post-training (5, 30 or 60 min), but not pretraining, injections of piracetam (10 or 50 mg/kg, i.p.) increased recall for the task when the chicks were tested 24 h later. Because previous studies showed that long-term memory for the passive avoidance task is dependent upon a brain corticosteroid action, and because the efficacy of piracetam-like compounds is also modulated by corticosteroids, we tested whether the facilitating effect of piracetam was dependent upon a corticosteroid action through specific brain receptors (mineralocorticoid receptor and glucocorticoid receptor). First, increased plasma levels of corticosterone were found 5 min after piracetam injection. In addition, intracerebral administration of antagonists for each receptor type (RU28318, for mineralocorticoid receptors, and RU38486 for glucocorticoid receptors; i.c.) given before the nootropic inhibited the facilitative effect of piracetam on memory consolidation. These results give further support to a modulatory action of piracetam on the mechanisms involved in long-term memory formation through a neural action that, in this learning model, requires the activation of the two types of intracellular corticosteroid receptors.

Normal and aberrant functions of integrins in the adult central nervous system

Integrins are heterodimeric proteins mediating cell-cell and cell-extracellular matrix adhesive connections (Springer T.A., 1990, Nature 346, 425-434) and signal transduction across the plasma membrane. The important roles of integrins in neural development and cancer, where they subserve process outgrowth and cell migration, are well documented, but information on integrins in the adult central nervous system has been slower to arrive. Now that strong evidence, both molecular biological and immunocytochemical, has been collected, it is useful to speculate on what these interesting proteins may be doing in the adult central nervous system. Suggestive data now points to roles in functions characterized in part by morphological rearrangements, such as learning and memory, and injury responses.

Memory disturbance and hippocampal degeneration induced by continuous intraventricular infusion of a protease inhibitor, leupeptin

Effects of a protease inhibitor, leupeptin, on the memory function and the morphological changes in the hippocampus were examined in rats. The leupeptin was infused by an implanted-osmotic minipump into the lateral ventricle of the rats for 14 days. The acquisition and the maintenance of memory were evaluated by a step-down passive avoidance task. The control rats, infused with an artificial cerebral spinal fluid, showed good retention for the passive avoidance training for 21 days after training. The leupeptin-treated rats showed good retention for 7 days following training; however, pronounced impaired retention was observed on day 10 and thereafter. These rats were accompanied by a degeneration of the dentate gyrus in the histological examinations on Days 14 and 21. The granule cells in the dentate gyrus of the hippocampus appeared much more eosinophilic pyknotic. Numerous eosinophilic spherical structures of the cell processes were seen in the neuropil beneath the granule cell layer. Electron microscopic examination disclosed a marked accumulation of lipofuscin-like granules in the perikaryon of the cells and in the dendrites and the axons. These findings suggest that the memory impairment is closely related to the degeneration of the dentate gyrus in the hippocampus in the leupeptin-treated rats.

Effects of nefiracetam on amnesia animal models with neuronal dysfunctions

The effects of N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl) acetamide (nefiracetam; DM-9384), on learning and memory in several amnesia animal models with neuronal dysfunctions were investigated. Nefiracetam improved scopolamine-, bicuculline-, picrotoxin-, ethanol-, chlordiazepoxide- and cycloheximide-induced amnesia. Anti-amnesic action of nefiracetam on scopolamine model was antagonized by nifedipine and flunarizine, but not by diltiazem. Repeated administration of nefiracetam to AF64A-treated animals improved impairment of learning and memory as well as the alterations in cholinergic and monoaminergic neurotransmitters in the hippocampus. Basal forebrain (BF) lesioned rats induced by excitotoxin or by thermal coagulation showed impairment of learning accompanied by a marked reduction in choline acetyltransferase (ChAT) and acetylcholine esterase activities. Nefiracetam improved the learning deficit of the BF-lesioned rats. Nefiracetam also improved the carbon monoxide-induced delayed and acute amnesia. Nefiracetam stimulated acetylcholine release in the frontal cortex. Repeated administration of nefiracetam increased ChAT activity, gamma-aminobutyric acid (GABA) turnover and glutamic acid decarboxylase activity, and facilitated the Na(+)-dependent high-affinity GABA uptake. Nefiracetam activated the high voltage-activated (N/L-type) Ca2+ channel. The dose-response curves of nefiracetam were bell-shaped in both behavioral and biochemical studies. Therefore, it is suggested that nefiracetam improves the dysfunction of cholinergic, GABAergic and/or monoaminergic neuronal function by acting at Ca2+ channel and enhancing the release of neurotransmitters, and modifies impairment of memory processes induced by drugs and hypoxia.

Influence of nefiracetam on NGF-induced neuritogenesis and neural cell adhesion molecule polysialic acid expression: in vivo and in vitro comparisons

Previously, the ability of co-administered nefiracetam to reverse scopolamine-induced learning deficits has been attributed to the preservation of a transient increase in neural cell adhesion molecule (NCAM) polysialylation state during a late phase of memory consolidation (Doyle et al., J. Neurosci. Res., 31 (1992) 513-523). Using the PC-12 pheochromocytoma cell model, we now demonstrate nefiracetam pre-exposure to significantly enhance nerve growth factor-induced neuritogenesis and NCAM polysialylation, but not prevalence, in a dose-dependent manner with maximal effects being observed at the lowest dose (0.1 microM) examined. As the memory-associated increase in NCAM polysialylation in vivo is associated with a defined group of neurons at the dentate hilar/granule cell layer border (Regan and Fox, Neurochem. Res., 20 (1995) 521-526), the effect of chronic nefiracetam exposure in vivo was evaluated. Once-daily, intraperitoneal administration of either 3 or 9 mg/kg nefiracetam to adult male Wistar rats for 40 days significantly increased the number of hippocampal dentate polysialylated neurons only at the highest dose evaluated, suggesting it to prevent their age-dependent decline. These results are consistent with nefiracetam facilitating early induction events of long-term memory consolidation processes involving NCAM polysialylation state.

Nefiracetam (DM-9384) reverses apomorphine-induced amnesia of a passive avoidance response: delayed emergence of the memory retention effects

Nefiracetam is a novel pyrrolidone derivative which attenuates scopolamine-induced learning and post-training consolidation deficits. Given that apomorphine inhibits passive avoidance retention when given during training or in a defined 10-12h post-training period, we evaluated the ability of nefiracetam to attenuate amnesia induced by dopaminergic agonism. A step-down passive avoidance paradigm was employed and nefiracetam (3 mg/kg) and apomorphine (0.5 mg/kg) were given alone or in combination during training and at the 10-12h post-training period of consolidation. Co-administration of nefiracetam and apomorphine during training or 10h thereafter produced no significant anti-amnesic effect. However, administration of nefiracetam during training completely reversed the amnesia induced by apomorphine at the 10h post-training time and the converse was also true. These effects were not mediated by a dopaminergic mechanism as nefiracetam, at millimolar concentrations, failed to displace either [3H]SCH 23390 or [3H]spiperone binding from D1 or D2 dopamine receptor subtypes, respectively. It is suggested that nefiracetam augments molecular processes in the early stages of events which ultimately lead to consolidation of memory.

Integrins: possible functions in the adult CNS

Integrins comprise a large family of heterodimeric proteins that mediate cell-cell and cell-extracellular-matrix adhesive connections. There is an extensive literature on their importance in neural development and cancer, but evidence for the existence of integrins in the adult CNS has emerged only recently. With growing immunohistochemical and molecular biological evidence for the presence of integrins in the adult CNS, a variety of functions from microglial migration to synaptic rearrangements can be considered for these adhesive proteins.

Polysialylated neural cell adhesion molecule expression by neurons and astroglial processes in the rat dentate gyrus declines dramatically with increasing age

The expression of polysialylated neurons in the dentate gyrus of the hippocampal formation of young (postnatal day 40), mature (postnatal day 80) and aged (postnatal day 540) male Wistar rats has been investigated by immunohistochemical techniques employing a monoclonal antibody specific for neural cell adhesion molecule-linked alpha 2,8 polysialic acid. A strong immunoreactivity was found on the cell bodies, dendrites and axons of granule-like neuronal cells at the border between the hilar region and the granule cell layer of the young rat. In the mature animal the number of immunoreactive neurons declined dramatically and were virtually absent in the aged group. Using an alternative fixation procedure, glial fibrillary acidic protein-positive and polysialylated astroglia processes were found in close proximity to the dendrites of the polysialylated granule-like cells. The number of astroglial processes traversing the granule cell layer showed a similar age-dependent decline to that observed with the polysialylated neurons. Glial fibrillary acidic protein-positive and polysialylated stellate astroglia were present throughout the hippocampal formation, but did not show the marked age-dependent decline observed with the astroglial processes in the granule cell layer. The neuronal dendrites and astroglial processes exhibited a strict numerical ratio in the young and mature animal and, in double immunofluorescence studies with anti-polysialic acid and anti-glial fibrillary acidic protein, the astroglial processes exhibited apparent points of cell and/or dendritic contact. These findings suggest that loss of polysialylated astroglial processes precedes the decline in polysialylated dentate neurons.

Neural cell adhesion molecule (NCAM) as a quantitative marker in synaptic remodeling

The neural cell adhesion molecule (NCAM) participates in adhesion and neuritic outgrowth during nervous system development. In the adult brain, NCAM is considered to be involved in neuronal sprouting and synaptic remodeling. The NCAM concentration of brain tissue has proved to be a useful marker of these processes, especially when viewed in comparison with the concentration of a marker of mature synapses, e.g. D3-protein (SNAP-25) or synaptophysin. The present review focusses on studies of adult brain in which NCAM concentration estimates and NCAM/D3 ratios have been used to evaluate the rate of synaptic remodeling in brain damage and degenerative diseases.

Polysialylation as a regulator of neural plasticity in rodent learning and aging

Although generally accepted to play an important role in development, the precise functional significance of NCAM remains to be elucidated. Correlative and interventive studies suggest a role for polysialylated NCAM in neurite elaboration. In the adult NCAM polysialylation continues to be expressed in regions of the central nervous system which retain neuroplastic potential. During memory formation modulation of polysialylation on the synapse-enriched isoform of NCAM occurs in the hippocampus. The polysialylated neurons of this structure have been located at the border of the granule cell layer and hilar region of the dentate and their number increases dramatically during memory consolidation. The converse is also true for a profound decline in the basal number of polysialylated neurons occurs with ageing when neural plasticity becomes attenuated. In conclusion, it is suggested that NCAM polysialylation regulates ultrastructural plasticity associated with synaptic elaboration.