Effects of tacrine (THA) on spatial reference memory and cholinergic enzymes in specific rat brain regions

Pro-cognitive effects of dual tacrine derivatives acting as cholinesterase inhibitors and NMDA receptor antagonists

Therapeutic options for Alzheimer's disease are limited. Dual compounds targeting two pathways concurrently may enable enhanced effect. The study focuses on tacrine derivatives inhibiting acetylcholinesterase (AChE) and simultaneously N-methyl-D-aspartate (NMDA) receptors. Compounds with balanced inhibitory potencies for the target proteins (K1578 and K1599) or increased potency for AChE (K1592 and K1594) were studied to identify the most promising pro-cognitive compound. Their effects were studied in cholinergic (scopolamine-induced) and glutamatergic (MK-801-induced) rat models of cognitive deficits in the Morris water maze. Moreover, the impacts on locomotion in the open field and AChE activity in relevant brain structures were investigated. The effect of the most promising compound on NMDA receptors was explored by in vitro electrophysiology. The cholinergic antagonist scopolamine induced a deficit in memory acquisition, however, it was unaffected by the compounds, and a deficit in reversal learning that was alleviated by K1578 and K1599. K1578 and K1599 significantly inhibited AChE in the striatum, potentially explaining the behavioral observations. The glutamatergic antagonist dizocilpine (MK-801) induced a deficit in memory acquisition, which was alleviated by K1599. K1599 also mitigated the MK-801-induced hyperlocomotion in the open field. In vitro patch-clamp corroborated the K1599-associated NMDA receptor inhibitory effect. K1599 emerged as the most promising compound, demonstrating pro-cognitive efficacy in both models, consistent with intended dual effect. We conclude that tacrine has the potential for development of derivatives with dual in vivo effects. Our findings contributed to the elucidation of the structural and functional properties of tacrine derivatives associated with optimal in vivo pro-cognitive efficacy.

Inhibitory effect of asiatic acid on acetylcholinesterase, excitatory post synaptic potential and locomotor activity

The asiatic acid, a triterpenoids isolated from Centella asiatica was used to delineate its inhibitory effect on acetylcholinesterase (AChE) properties, excitatory post synaptic potential (EPSP) and locomotor activity. This study is consistent with asiatic acid having an effect on AChE, a selective GABA(B) receptor agonist and no sedative effect on locomotor.

Anti-amnesic effect of Chong-Myung-Tang on scopolamine-induced memory impairments in mice

AIM OF THE STUDY

Chong-Myung-Tang (CMT) consisted of Acorus gramineus Soland, Polygala tenuifolia Willdenow, and Poria cocos Wolf is one of the traditional Korean herbal medicines used for the therapy of learning and memory improvement. The present study was investigated the effect of CMT on learning and memory functions in SCOP-induced memory deficits mice.

MATERIALS AND METHODS

The cognitive-enhancing effect of CMT on amnesic mice induced by SCOP was investigated by assessing the passive avoidance test and the Morris water maze test. In order to confirm the underlying mechanisms of memory enhancing effects of CMT, activities of AChE, choline acetyltransferase (ChAT), and antioxidant enzymes were measured.

RESULTS

Administration of CMT significantly restored memory impairments induced by SCOP in the passive avoidance test and also reduced escape latency during trial sessions in the Morris water maze test. The increased AChE activity produced by SCOP was significantly inhibited by CMT. CMT significantly enhanced ChAT activity. Moreover, treatment with CMT to the amnesic mice induced by SCOP considerably decreased malondialdehyde levels and restored activities of superoxide dismutase and catalase to the control values.

CONCLUSIONS

These results suggest that CMT may be useful for the cognitive improvement via regulation of cholinergic marker enzyme activities and the antioxidant defense system.

SSR181507, a dopamine D(2) receptor antagonist and 5-HT(1A) receptor agonist, alleviates disturbances of novelty discrimination in a social context in rats, a putative model of selective attention deficit

RATIONALE

Selective attention deficit, characterised by the inability to differentiate relevant from irrelevant information, is considered to underlie many cognitive deficits of schizophrenia, and appears to be only marginally responsive to treatment with current antipsychotics.

OBJECTIVES

We compared the activity of the putative atypical antipsychotic SSR181507 (a dopamine D(2) receptor antagonist and 5HT(1A) receptor agonist) with reference compounds, on disturbances of novelty discrimination in a social context in rats, a behavioural paradigm that putatively models selective attention deficit.

METHODS

A first (familiar) juvenile rat was presented to an adult rat for a period (P1) of 30 min. A second (novel) juvenile was then introduced at the end of P1 for a period (P2) of 5 min. The ability of the adult rat to discriminate between the two juveniles, presented at the same time, was evaluated by measuring the ratio of the time spent in interaction with the novel vs the familiar juvenile during P2.

RESULTS

Adult rats spent more time exploring the novel than the familiar juvenile. This novelty discrimination capacity was disrupted by: (1) parametric modification of the procedure (reduction of time spent in contact with the familiar juvenile during P1); (2) acute injection of psychotomimetics that are known to induce schizophrenia-like symptoms in humans, such as phencyclidine (PCP; 3 mg/kg, i.p.) and d-amphetamine (1 mg/kg, i.p.) and (3) neonatal treatment with PCP (three injections of 10 mg/kg, s.c.), a model based on the neurodevelopmental hypothesis of schizophrenia. The potential atypical antipsychotic SSR181507 (0.03-3 mg/kg, i.p.) and the atypical antipsychotics clozapine (0.1-1 mg/kg, i.p.) and amisulpride (1-3 mg/kg, i.p.) attenuated deficits in novelty discrimination produced by parametric manipulation and by acute or neonatal treatment with PCP. The typical antipsychotic haloperidol (up to 0.3 mg/kg, i.p.) attenuated only deficits in novelty discrimination produced by parametric modification.

CONCLUSION

Collectively, these results suggest that SSR181507 can alleviate disturbances of novelty discrimination in a social context in rats, and that this paradigm may represent a suitable animal model of selective attention deficits observed in schizophrenia.

Expression changes of the mRNA of Alzheimer's disease related factors in the permanent ischemic rat brain

The rat with permanent occlusion of the bilateral common carotid arteries (2VO) is useful model for the study of dementia. The expression changes of amyloid precursor protein (APP), secretase, alpha7 nicotinic acetylcholine receptor (alpha7NicR) and acetylcholine esterase (AChE), which are involved in Alzheimer's disease, were examined by quantitative RT/PCR in this model rat brain. The expression of APP, alpha7NicR and secretase were increased 4 d after 2VO. The alpha7NicR level at 2 d after operation already tended to increase. These result suggest that alpha7NicR expression was enhanced at early stage of brain ischemia. Using this model to find drugs which regulate the alpha7NicR expression will be useful to assay the materials with anti-dementive effect.

Asiatic acid derivatives enhance cognitive performance partly by improving acetylcholine synthesis

Thirty-six semi-synthesized derivatives of asiatic acid were examined to determine if they had cognitive-enhancing activity in a passive avoidance test. Among the compounds tested, AS-2, AS-2-9-006 and AS-9-006 significantly alleviated scopolamine-induced memory impairment at doses of 1 and 10 mg kg(-1). Furthermore, AS-2 and AS-2-9-006 (1 mg kg(-1) administered four times daily) enhanced cognitive performance as determined in a water maze test. These three asiatic acid derivatives did not show any significant effect on the learning process in active avoidance tests. AS-2, AS-2-9-006 and AS-9-006 enhanced cholineacetyltransferase activity in a cholinergic neuroblastoma cell line, S-20Y, in-vitro. Therefore, AS-2, AS-2-9-006 and AS-9-006 may have therapeutic value in alleviating certain memory impairment observed in dementia.

Improvement of scopolamine-induced memory impairment by Z-ajoene in the water maze in mice

Z-ajoene, a major compound containing sulfur in oil-macerated garlic products, exhibited inhibitory effects against scopolamine-induced memory impairment in mice using the Morris water maze test. The effects of Z-ajoene were observed dose-dependently (0.25-25 mg/kg). At the highest dosage, the memory performance of mice was improved compared to normal mice. The acetylcholinesterase (AChE) activity in the brain was reduced by administration of Z-ajoene dose-dependently. However, alliin and diallyl disulfide, organosulfur compounds from garlic, did not improve memory performance nor AChE inhibitory effect. These results suggest that Z-ajoene may act on the cholinergic system and on memory impairment caused by excess activity of AChE.

Cognitive deficit associated with cholinergic and nerve growth factor down-regulation in experimental allergic encephalomyelitis in rats

Clinical symptoms in multiple sclerosis include cognitive dysfunction. Difficulties in learning and remembering new information represent the most common cognitive deficit and are associated with a general and progressive brain pathology. Possible pathogenetic mechanisms for neuronal damage such as neuroprotective strategies are under active investigation also in experimental allergic encephalomyelitis, the most widely used experimental model for multiple sclerosis. In this paper we demonstrate that a selective deficit in learning and memory performance, as investigated by the Morris water maze test, is a consistent feature in rat encephalomyelitis, which correlates with a decline in choline acetyltransferase activity and nerve growth factor mRNA level in cerebral cortex, hippocampus, and basal forebrain. Treatment aimed to restore acetylcholine content through chronic administration of selective acetylcholinesterase inhibitors (rivastigmine and donepezil) restores cognitive performance, choline acetyltransferase activity, and nerve growth factor mRNA expression.

Effects of chronic administration of huperzine A on memory in guinea pigs

Effects of subchronic administration of huperzine A, a cholinesterase inhibitor, on spatial memory were studied in guinea pig. Spatial memory was appreciated by the Morris water maze test. At a dose of 0.25 microgram/h, inhibiting 36% of blood AChE and 14-20% of central AChE, no effect on spatial learning was found. At a dose of 1 microgram/h, inhibiting 20% of blood AChE and 14-20% of central AChE, no memory impairment was found, on the other hand, a memory enhancing effect, limited to the first day was shown. It thus appears that subchronic administration of huperzine A did not induce deleterious effects on spatial memory.

N-tert-butyl-alpha-phenylnitrone, a free radical scavenger with anticholinesterase activity does not improve the cognitive performance of scopolamine-challenged rats

Reversible inhibitors of acetylcholinesterase improve spatial learning and memory in animal models of cognitive impairment. Here we investigate if the beneficial effects of free radical scavenger N-tert-butyl-alpha-phenylnitrone (PBN) on cognitive performance could be explained by its recently discovered anticholinesterase activity. Morris water maze experiment was performed to examine the effect of PBN on the impairment of spatial learning and memory induced by the antagonist of cholinergic muscarinic transmission scopolamine. In situ hybridization histochemistry experiment was performed to study its effects on the induction of immediate early gene expression (c-fos, c-jun) by dopamine D1 receptor agonist SKF-82958 and on the augmentation of the SKF-82958-induced expression of these genes by scopolamine. In both experiments, the effects of PBN were compared to the effects of reversible anticholinesterase physostigmine. We found that physostigmine but not PBN significantly reversed the cognitive impairment in scopolamine-challenged rats, prevented the induction of c-fos and c-jun mRNAs by SKF-82958 and attenuated the augmentation of the SKF-82958-induced expression of these genes by scopolamine. The present experiments did not reveal a significant in vivo anticholinesterase activity of PBN.

Effects of zinc on spatial reference memory and brain dopamine (D1) receptor binding kinetics in rats

1. The present study was designed to evaluate the effects of zinc on spatial reference memory and brain dopamine (D1) receptor binding kinetics in rats. Male Sprague-Dawley rats (120-150 g), adapted 12 hour light: 12 hour dark illumination cycle were used. Treated animals were given zinc chloride (25 mg/kg, 50 mg/kg, or 100 mg/kg) by oral gavage for 15 days at 11:00 hr. Controlrats received an equivalent volume of saline. 2. Spatial reference memory was evaluated in treated and control rats on days 10 through 15 using the Morris Water Maze. The time to find the platform (latency) was significantly increased in the 50 mg/kg and 100-mg/kg zinc treated animals as compared to the controls. One hour after the last spatial reference memory testing, the animals were sacrificed by decapitation; their brains were removed and dissected into various regions. 3. D1 receptor binding kinetics were measured using the ligand [3H] SCH23390. Results obtained indicate that zinc chloride administration resulted in a statistically significant decline in the binding affinity (increased Kd) of the D1 receptors in the frontal cortex, hypothalamus, hippocampus, and midbrain. However, there was a significant increase in the D1 receptor binding capacity (Bmax) in these same brain regions following zinc chloride administration. 4. These findings clearly indicate that administration of high doses of zinc to rats resulted in spatial reference memory deficit, which may in part be explained by alterations in dopamine receptor binding kinetics.

Antisense oligonucleotide sequences targeting the muscarinic type 2 acetylcholine receptor enhance performance in the Morris water maze

Blocking autoinhibitory muscarinic type 2 (m2) acetylcholine receptors in the central nervous system may increase the release of acetylcholine and improve learning and memory. Antisense oligonucleotides (OGNs) complementary to m2 receptor mRNA were synthesized and evaluated for their efficacy at decreasing receptor number and reversing deficits in a cognitive task. Three antisense OGNs, which decreased m2 receptor binding in NG108-15 cells, were continuously infused into the lateral cerebral ventricle of rats for 6 days at a rate of 0.5 micro1/h and a daily dose of 72 microg. Performance in the Morris water maze was compared to groups receiving control OGNs or vehicle alone. Decrements induced by 0.2 mg/kg of scopolamine i.p. were significantly reversed by 2 of the 3 antisense OGNs. Use of antisense OGNs targeting the m2 receptor may be a new strategy to increase cholinergic neurotransmission and improve learning and memory.

Effects of ginsenosides on maze performance and brain choline acetyltransferase activity in scopolamine-treated young rats and aged rats

In young adult rats with scopolamine-induced cognitive impairment, choline acetyltransferase activity was increased in the medial septum, but not in the diagonal band, caudate and hippocampus, 30 min after the injection of ginsenosides Rg1 or Re. Rb1 and Rd had no effect on choline acetyltransferase activity. Aged rats showed a smaller number of initial correct responses in the radial-arm maze and a lower choline acetyltransferase activity in the medial septum, diagonal band, caudate and hippocampus than did young adult rats. Repeated i.p. injections of Rg1 increased the number of initial correct responses and the activity of choline acetyltransferase in the medial septum, but not in the diagonal band, caudate and hippocampus, in aged rats. These results suggest that Rg1 and Re may contribute the ameliorative effects through an increase of choline acetyltransferase activity in the medial septum.