Cariprazine alleviates core behavioral deficits in the prenatal valproic acid exposure model of autism spectrum disorder.

RATIONALE: Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by deficits in social communication and interaction and restricted, repetitive behaviors. The unmet medical need in ASD is considerable since there is no approved pharmacotherapy for the treatment of these deficits in social communication, interaction, and behavior. Cariprazine, a dopamine D3-preferring D3/D2 receptor partial agonist, is already approved for the treatment of schizophrenia and bipolar I disorder in adults; investigation in patients with ASD is warranted. OBJECTIVES: The aim of this study was to investigate the effects of cariprazine, compared with risperidone and aripiprazole, in the rat prenatal valporic acid (VPA) exposure model on behavioral endpoints representing the core and associated symptoms of ASD. METHODS: To induce the ASD model, time-mated Wistar rat dams were treated with VPA during pregnancy. Male offspring were assigned to groups and studied in a behavioral test battery at different ages, employing social play, open field, social approach-avoidance, and social recognition memory tests. Animals were dosed orally, once a day for 8 days, with test compounds (cariprazine, risperidone, aripiprazole) or vehicle before behavioral assessment. RESULTS: Cariprazine showed dose-dependent efficacy on all behavioral endpoints. In the social play paradigm, only cariprazine was effective. On the remaining behavioral endpoints, including the reversal of hyperactivity, risperidone and aripiprazole displayed similar efficacy to cariprazine. CONCLUSIONS: In the present study, cariprazine effectively reversed core behavioral deficits and hyperactivity present in juvenile and young adult autistic-like rats. These findings indicate that cariprazine may be useful in the treatment of ASD symptoms.

Effects of Lidocaine and Src Inhibition on Metastasis in a Murine Model of Breast Cancer Surgery.

Breast cancer recurs in 20% of patients following intended curative resection. In vitro data indicates that amide local anaesthetics, including lidocaine, inhibit cancer cell metastasis by inhibiting the tyrosine kinase enzyme Src. In a murine breast cancer surgery model, systemic lidocaine reduces postoperative pulmonary metastases. We investigated whether the additional administration of bosutinib (a known Src inhibitor) influences lidocaine's observed beneficial effect in this in vivo model. Female BALB/c mice (n = 95) were inoculated with 25,000 4T1 cells into the mammary fad pad and after 7 days the resulting tumours were excised under sevoflurane anaesthesia. Experimental animals were randomized to one of four treatments administered intravenously prior to excision: lidocaine, bosutinib, both lidocaine and bosutinib in combination, or saline. Animals were euthanized 14 days post-surgery and lung and liver metastatic colonies were evaluated. Post-mortem serum was analysed for MMP-2 and MMP-9, pro-metastatic enzymes whose expression is influenced by the Src pathway. Lidocaine reduced lung, but not liver metastatic colonies versus sevoflurane alone (p = 0.041), but bosutinib alone had no metastasis-inhibiting effect. When combined with lidocaine, bosutinib reversed the anti-metastatic effect observed with lidocaine on sevoflurane anaesthesia. Only lidocaine alone reduced MMP-2 versus sevoflurane (p = 0.044). Both bosutinib (p = 0.001) and bosutinib/lidocaine combined (p = 0.001) reduced MMP-9 versus sevoflurane, whereas lidocaine alone did not. In a murine surgical breast cancer model, the anti-metastatic effects of lidocaine under sevoflurane anaesthesia are abolished by the Src inhibitor bosutinib, and lidocaine reduces serum MMP-2. These results suggest that lidocaine may act, at least partly, via an inhibitory effect on MMP-2 expression to reduce pulmonary metastasis, but whether this is due to an effect on Src or via another pathway remains unclear.

Effect of Perioperative Lidocaine, Propofol and Steroids on Pulmonary Metastasis in a Murine Model of Breast Cancer Surgery.

Addressing the hypothesis that anaesthetic-analgesic technique during cancer surgery might influence recurrence or metastatic spread is a research priority. Propofol, which has anti-inflammatory properties in vitro, is clinically associated with reduced risk of cancer recurrence compared with sevoflurane anaesthesia in retrospective studies. Amide local anaesthetics, such as lidocaine, have cancer inhibiting effects in vitro. Steroids have anti-inflammatory and immunosuppressive effects and are associated with improved recovery after major non-cancer surgery. We compared the effects of propofol, lidocaine and methylprednisolone on postoperative metastasis in a murine model of breast cancer surgery under sevoflurane anaesthesia. 4T1 tumour cells were introduced into the mammary fat-pad of female BALB/c mice and the resulting tumour resected seven days later under general anaesthesia with sevoflurane. Mice (n = 72) were randomized to four treatment groups: Sevoflurane alone (control); Propofol group received 5 mg.kg-1; Lidocaine group received 1.5 mg.kg-1 followed by 2 mg.kg-1.h-1 infusion; Methylprednisolone group received 30 mg.kg-1 methylprednisolone. The primary outcome measure was pulmonary metastasis colony count, as assessed by in-vitro proliferation, two weeks post-operatively. This was achieved by treating the post-mortem lung tissue with collagenase IV, straining and culturing for 14 days prior to colony count. Compared with control, lidocaine and propofol each individually reduced pulmonary metastasis colonies; mean (SD) 846 (±581) vs. 88 (±52) vs. 34 (±44) respectively, (p = 0.0001 and p = 0.0001). Methylprednisolone increased lung metastasis, 2555 (±609) vs. 846 (±581), p = 0.0001. Post-operative hepatic metastatic disease and serum interleukin-6 and vascular endothelial growth factor levels were similar in all groups. In conclusion, in a murine model of breast cancer surgery during sevoflurane anaesthesia, propofol and lidocaine each decreased pulmonary metastasis, while methylprednisolone increased it.

Effect of Perioperative Lidocaine and Cisplatin on Metastasis in a Murine Model of Breast Cancer Surgery.

BACKGROUND/AIM: Mortality from breast cancer is usually attributable to metastasis. In vitro data suggest that amide local anaesthetics, e.g. lidocaine, inhibit metastasis by multiple mechanisms and recent in vivo data support this. Experimental data also suggest that opioids may inhibit cisplatin chemotherapy. Whether lidocaine would influence cisplatin chemotherapy has not been evaluated. MATERIALS AND METHODS: 4T1 cells were injected into the mammary gland of immunocompetent female BALB/c mice, with resection of the tumour under sevoflurane anaesthesia one week later. Mice (n=45) were randomized into one of three groups: The cisplatin group received 3 mg.kg-1 cisplatin; cisplatin and lidocaine group received 3 mg.kg-1 cisplatin and lidocaine bolus of 1.5 mg.kg-1 followed by an infusion of 2 mg.kg-1.h-1 The control group received sevoflurane only. All agents were given perioperatively. After 14 postoperative days, post-mortem lung, serum and liver samples were collected. Primary outcome measure was lung metastasis colony count. RESULTS: During sevoflurane anaesthesia, the addition of lidocaine to cisplatin significantly decreased metastatic lung colony count [(mean±SD) (157±87)] compared to control [846±581, (p=0.001)], and cisplatin alone [580±383, (p=0.018)]. However, liver metastasis colony count was not reduced with the combination of cisplatin and lidocaine (9.3±13.9) when compared to control (74.7±257.3), p=0.78 or to cisplatin alone (110±388.8), p=0.569. Serum VEGF and interleukin-6 concentrations were not significantly different. CONCLUSION: In a 4T1 murine model of breast cancer surgery, under sevoflurane anaesthesia, lidocaine enhanced the metastasis-inhibiting action of cisplatin. Clinical evaluation of the hypothesis that co-administration of systemic lidocaine during cisplatin chemotherapy seems warranted.

Neurotoxicity of Inhalation Anesthetics in the Neonatal Rat Brain: Effects on Behavior and Neurodegeneration in the Piriform Cortex.

There is concern that clinical use of anesthetic drugs may cause neurotoxicity in the developing brain and subsequent abnormal neurobehavior. We therefore evaluated neurotoxic effects of inhalation anesthetics in the neonatal rat brain, using in vivo histological and neurobehavioral outcomes. Wistar rats (n=79, postnatal day 15) were subjected to a clinically relevant single exposure of urethane, isoflurane, sevoflurane, or placebo, without surgery. At 48 h and 96 h, behavioral parameters were recorded and the animals were sacrificed. In cryosectioned brains, total cells and dying cells in layer II of the piriform cortex were counted using unbiased stereology. At 48 h, cell numbers in layer II of the piriform cortex of all drug-treated animals were reduced versus controls (p=0.01). The effect persisted at 96 h in isoflurane- and urethane-exposed animals. Piriform cortical layer II neurons undergoing degeneration, detected histologically by pyknotic nuclei and eosinophilic cytoplasm, were increased in the animals treated with isoflurane (1.9 ± 0.7 at 96 h) and urethane (2.4 ± 0.8 at 96 h) versus sevoflurane (0.8 ± 0.3 at 96 h) and controls (0.9 ± 0.2 at 96 h). Sevoflurane- and isoflurane-treated animals exhibited increased activity and decreased suckling compared with controls, and sevoflurane-exposed animals also displayed increased rearing behavior at both timepoints.

Pentyl-4-yn-VPA, a histone deacetylase inhibitor, ameliorates deficits in social behavior and cognition in a rodent model of autism spectrum disorders.

In utero exposure of rodents to valproic acid (VPA) has been proposed to induce an adult phenotype with behavioural characteristics reminiscent of those observed in autism spectrum disorder (ASD). Our previous studies have demonstrated the social cognition deficits observed in this model, a major core symptom of ASD, to be ameliorated following chronic administration of histone deacetylase (HDAC) inhibitors. Using this model, we now demonstrate pentyl-4-yn-VPA, an analogue of valproate and HDAC inhibitor, to significantly ameliorate deficits in social cognition as measured using the social approach avoidance paradigm as an indicator of social reciprocity and spatial learning to interrogate dorsal stream cognitive processing. The effects obtained with pentyl-4-yn-VPA were found to be similar to those obtained with SAHA, a pan-specific HDAC inhibitor. Histones isolated from the cerebellar cortex and immunoblotted with antibodies recognising lysine-specific modification revealed SAHA and pentyl-4-yn-VPA to enhance the acetylation status of H4K8. Additionally, the action of pentyl-4-yn-VPA, could be differentiated from that of SAHA by its ability to decrease H3K9 acetylation and enhance H3K14 acetylation. The histone modifications mediated by pentyl-4-yn-VPA are suggested to act cooperatively through differential acetylation of the promoter and transcription regions of active genes.

Class I histone deacetylase inhibition ameliorates social cognition and cell adhesion molecule plasticity deficits in a rodent model of autism spectrum disorder.

In utero exposure of rodents to valproic acid (VPA), a histone deacetylase (HDAC) inhibitor, has been proposed to induce an adult phenotype with behavioural characteristics reminiscent of those observed in autism spectrum disorder (ASD). We have evaluated the face validity of this model in terms of social cognition deficits which are a major core symptom of ASD. We employed the social approach avoidance paradigm as a measure of social reciprocity, detection of biological motion that is crucial to social interactions, and spatial learning as an indicator of dorsal stream processing of social cognition and found each parameter to be significantly impaired in Wistar rats with prior in utero exposure to VPA. We found no significant change in the expression of neural cell adhesion molecule polysialylation state (NCAM PSA), a measure of construct validity, but a complete inability to increase its glycosylation state which is necessary to mount the neuroplastic response associated with effective spatial learning. Finally, in all cases, we found chronic HDAC inhibition, with either pan-specific or HDAC1-3 isoform-specific inhibitors, to significantly ameliorate deficits in both social cognition and its associated neuroplastic response. We conclude that in utero exposure to VPA provides a robust animal model for the social cognitive deficits of ASD and a potential screen for the development of novel therapeutics for this condition.

H3 receptor antagonism enhances NCAM PSA-mediated plasticity and improves memory consolidation in odor discrimination and delayed match-to-position paradigms.

To further understand the procognitive actions of GSK189254, a histamine H(3) receptor antagonist, we determined its influence on the modulation of hippocampal neural cell adhesion molecule (NCAM) polysialylation (PSA) state, a necessary neuroplastic mechanism for learning and memory consolidation. A 4-day treatment with GSK189254 significantly increased basal expression of dentate polysialylated cells in rats with the maximal effect being observed at 0.03-0.3 mg/kg. At the optimal dose (0.3 mg/kg), GSK189254 enhanced water maze learning and the associated transient increase in NCAM-polysialylated cells. The increase in dentate polysialylated cell frequency induced by GSK189254 was not attributable to enhanced neurogenesis, although it did induce a small, but significant, increase in the survival of these newborn cells. GSK189254 (0.3 mg/kg) was without effect on polysialylated cell frequency in the entorhinal and perirhinal cortex, but significantly increased the diffuse PSA staining observed in the anterior, ventromedial, and dorsomedial aspects of the hypothalamus. Consistent with its ability to enhance the learning-associated, post-training increases in NCAM PSA state, GSK189254 (0.3 mg/kg) reversed the amnesia induced by scopolamine given in the 6-h post-training period after training in an odor discrimination paradigm. Moreover, GSK189254 significantly improved the performance accuracy of a delayed match-to-position paradigm, a task dependent on the prefrontal cortex and degree of cortical arousal, the latter may be related to enhanced NCAM PSA-associated plasticity in the hypothalamus. The procognitive actions of H3 antagonism combined with increased NCAM PSA expression may exert a disease-modifying action in conditions harboring fundamental deficits in NCAM-mediated neuroplasticity, such as schizophrenia and Alzheimer's disease.

Curcumin-induced degradation of PKC delta is associated with enhanced dentate NCAM PSA expression and spatial learning in adult and aged Wistar rats.

Polysialylation of the neural cell adhesion molecule (NCAM PSA) is necessary for the consolidation processes of hippocampus-based learning. Previously, we have found inhibition of protein kinase C delta (PKCdelta) to be associated with increased polysialyltransferase (PST) activity, suggesting inhibitors of this kinase might ameliorate cognitive deficits. Using a rottlerin template, a drug previously considered an inhibitor of PKCdelta, we searched the Compounds Available for Purchase (CAP) database with the Accelrys((R)) Catalyst programme for structurally similar molecules and, using the available crystal structure of the phorbol-binding domain of PKCdelta, found that diferuloylmethane (curcumin) docked effectively into the phorbol site. Curcumin increased NCAM PSA expression in cultured neuro-2A neuroblastoma cells and this was inversely related to PKCdelta protein expression. Curcumin did not directly inhibit PKCdelta activity but formed a tight complex with the enzyme. With increasing doses of curcumin, the Tyr(131) residue of PKCdelta, which is known to direct its degradation, became progressively phosphorylated and this was associated with numerous Tyr(131)-phospho-PKCdelta fragments. Chronic administration of curcumin in vivo also increased the frequency of polysialylated cells in the dentate infragranular zone and significantly improved the acquisition and consolidation of a water maze spatial learning paradigm in both adult and aged cohorts of Wistar rats. These results further confirm the role of PKCdelta in regulating PST and NCAM PSA expression and provide evidence that drug modulation of this system enhances the process of memory consolidation.

The selective 5-HT6 receptor antagonists SB-271046 and SB-399885 potentiate NCAM PSA immunolabeling of dentate granule cells, but not neurogenesis, in the hippocampal formation of mature Wistar rats.

While there is now substantial evidence that 5-HT(6) antagonism leads to significantly improved cognitive ability, the mechanism(s) and/or pathway(s) involved are poorly understood. We have evaluated the consequence of chronic administration of the 5-HT(6) receptor antagonists SB-271046 and SB-399885 on neural cell adhesion molecule polysialylation state (NCAM PSA), a neuroplastic mechanism necessary for memory consolidation. Quantitative analysis of NCAM PSA immunopositive neurons in the dentate gyrus of drug-treated animals revealed a dose-dependent increase in polysialylated cell frequency following treatment with both SB-271046 and SB-399885. These effects could not be attributed to increased neurogenesis, as no difference in the rate of bromodeoxyuridine incorporation was apparent between the control and drug-treated groups. A substantial increase in the frequency of polysialylated cells in layer II of the entorhinal and perirhinal cortices was also observed, brain regions not previously associated with neurogenesis. Chronic treatment with SB-271046 or SB-399885 also significantly increased the activation of dentate polysialylation that is specific to learning. This effect does not occur with other cognition-enhancing drugs, such as tacrine, and this action potentially differentiates 5-HT(6) receptor antagonism as an unique neuroplastic mechanism for cognitive processes which may slow or reverse age/neurodegenerative related memory deficits.

GSK189254, a novel H3 receptor antagonist that binds to histamine H3 receptors in Alzheimer's disease brain and improves cognitive performance in preclinical models.

6-[(3-Cyclobutyl-2,3,4,5-tetrahydro-1H-3-benzazepin-7-yl)oxy]-N-methyl-3-pyridinecarboxamide hydrochloride (GSK189254) is a novel histamine H(3) receptor antagonist with high affinity for human (pK(i) = 9.59 -9.90) and rat (pK(i) = 8.51-9.17) H(3) receptors. GSK189254 is >10,000-fold selective for human H(3) receptors versus other targets tested, and it exhibited potent functional antagonism (pA(2) = 9.06 versus agonist-induced changes in cAMP) and inverse agonism [pIC(50) = 8.20 versus basal guanosine 5'-O-(3-[(35)S]thio)triphosphate binding] at the human recombinant H(3) receptor. In vitro autoradiography demonstrated specific [(3)H]GSK189254 binding in rat and human brain areas, including cortex and hippocampus. In addition, dense H(3) binding was detected in medial temporal cortex samples from severe cases of Alzheimer's disease, suggesting for the first time that H(3) receptors are preserved in late-stage disease. After oral administration, GSK189254 inhibited cortical ex vivo R-(-)-alpha-methyl[imidazole-2,5(n)-(3)H]histamine dihydrochloride ([(3)H]R-alpha-methylhistamine) binding (ED(50) = 0.17 mg/kg) and increased c-Fos immunoreactivity in prefrontal and somatosensory cortex (3 mg/kg). Microdialysis studies demonstrated that GSK189254 (0.3-3 mg/kg p.o.) increased the release of acetylcholine, noradrenaline, and dopamine in the anterior cingulate cortex and acetylcholine in the dorsal hippocampus. Functional antagonism of central H(3) receptors was demonstrated by blockade of R-alpha-methylhistamine-induced dipsogenia in rats (ID(50) = 0.03 mg/kg p.o.). GSK189254 significantly improved performance of rats in diverse cognition paradigms, including passive avoidance (1 and 3 mg/kg p.o.), water maze (1 and 3 mg/kg p.o.), object recognition (0.3 and 1 mg/kg p.o.), and attentional set shift (1 mg/kg p.o.). These data suggest that GSK189254 may have therapeutic potential for the symptomatic treatment of dementia in Alzheimer's disease and other cognitive disorders.

Structurally novel histamine H3 receptor antagonists GSK207040 and GSK334429 improve scopolamine-induced memory impairment and capsaicin-induced secondary allodynia in rats.

GSK207040 (5-[(3-cyclobutyl-2,3,4,5-tetrahydro-1H-3-benzazepin-7-yl)oxy]-N-methyl-2-pyrazinecarboxamide) and GSK334429 (1-(1-methylethyl)-4-({1-[6-(trifluoromethyl)-3-pyridinyl]-4-piperidinyl}carbonyl)hexahydro-1H-1,4-diazepine) are novel and selective non-imidazole histamine H(3) receptor antagonists from distinct chemical series with high affinity for human (pK(i)=9.67+/-0.06 and 9.49+/-0.09, respectively) and rat (pK(i)=9.08+/-0.16 and 9.12+/-0.14, respectively) H(3) receptors expressed in cerebral cortex. At the human recombinant H(3) receptor, GSK207040 and GSK334429 were potent functional antagonists (pA(2)=9.26+/-0.04 and 8.84+/-0.04, respectively versus H(3) agonist-induced changes in cAMP) and exhibited inverse agonist properties (pIC(50)=9.20+/-0.36 and 8.59+/-0.04 versus basal GTPgammaS binding). Following oral administration, GSK207040 and GSK334429 potently inhibited cortical ex vivo [(3)H]-R-alpha-methylhistamine binding (ED(50)=0.03 and 0.35 mg/kg, respectively). Functional antagonism of central H(3) receptors was demonstrated by blockade of R-alpha-methylhistamine-induced dipsogenia in rats (ID(50)=0.02 and 0.11 mg/kg p.o. for GSK207040 and GSK334429, respectively). In more pathophysiologically relevant pharmacodynamic models, GSK207040 (0.1, 0.3, 1 and 3mg/kg p.o.) and GSK334429 (0.3, 1 and 3mg/kg p.o.) significantly reversed amnesia induced by the cholinergic antagonist scopolamine in a passive avoidance paradigm. In addition, GSK207040 (0.1, 0.3 and 1mg/kg p.o.) and GSK334429 (3 and 10mg/kg p.o.) significantly reversed capsaicin-induced reductions in paw withdrawal threshold, suggesting for the first time that blockade of H(3) receptors may be able to reduce tactile allodynia. Novel H(3) receptor antagonists such as GSK207040 and GSK334429 may therefore have therapeutic potential not only in dementia but also in neuropathic pain.

SB-399885 is a potent, selective 5-HT6 receptor antagonist with cognitive enhancing properties in aged rat water maze and novel object recognition models.

SB-399885 (N-[3,5-dichloro-2-(methoxy)phenyl]-4-(methoxy)-3-(1-piperazinyl)benzenesulfonamide) has high affinity for human recombinant and native 5-HT(6) receptors, with pK(i) values 9.11+/-0.03 and 9.02+/-0.05, respectively and is a potent competitive antagonist (pA(2) 7.85+/-0.04). It displays over 200-fold selectivity for the 5-HT(6) receptor over all other receptors, ion channels and enzymes tested to date. SB-399885 inhibited ex vivo [(125)I]SB-258585 (4-Iodo-N-[4-methoxy-3-(4-methyl-piperazin-1-yl)-phenyl]-benzenesulfonamide) binding with an ED(50) of 2.0+/-0.24 mg/kg p.o. in rats. It had a minimum effective dose of 1 mg/kg p.o. in a rat maximal electroshock seizure threshold test and a long duration of action, overall demonstrating an excellent pharmacokinetic-pharmacodynamic correlation. Repeated administration of this agent (10 mg/kg p.o., b.i.d. for 7 days) significantly reversed a scopolamine-induced deficit (0.5 mg/kg i.p.) in a rat novel object recognition paradigm. Moreover, in aged rats (22 months old) SB-399885 (10 mg/kg p.o., b.i.d. for 7 days) fully reversed the age-dependent deficit in water maze spatial learning compared to vehicle-treated age-matched controls and significantly improved recall of the task measured by increases in the searching of the target quadrant on post-training days 1, 3 and 7. In vivo microdialysis in the rat medial prefrontal cortex demonstrated that acute SB-399885 (10 mg/kg p.o.) significantly increased extracellular acetylcholine levels. These data demonstrate that SB-399885 is a potent, selective, brain penetrant, orally active 5-HT(6) receptor antagonist with cognitive enhancing properties that are likely to be mediated by enhancements of cholinergic function. These studies provide further support for the potential therapeutic utility of 5-HT(6) receptor antagonists in disorders characterised by cognitive deficits such as Alzheimer's disease and schizophrenia.

Chronic exposure of rats to cognition enhancing drugs produces a neuroplastic response identical to that obtained by complex environment rearing.

Recent data suggest that Alzheimer's patients who discontinue treatment with cholinesterase inhibitors have a significantly delayed cognitive decline as compared to patients receiving placebo. Such observations suggest cholinesterase inhibitors to provide a disease-modifying effect as well as symptomatic relief and, moreover, that this benefit remains after drug withdrawal. Consistent with this suggestion, we now demonstrate that chronic administration of tacrine, nefiracetam, and deprenyl, drugs that augment cholinergic function, increases the basal frequency of dentate polysialylated neurons in a manner similar to the enhanced neuroplasticity achieved through complex environment rearing. While both drug-treated and complex environment reared animals continue to exhibit memory-associated activation of hippocampal polysialylated neurons, the magnitude is significantly reduced suggesting that such interventions induce a more robust memory pathway that can acquire and consolidate new information more efficiently. This hypothesis is supported by our findings of improved learning behavior and enhanced resistance to cholinergic deficits seen following either intervention. Furthermore, the level of enhancement of basal neuroplastic status achieved by either drug or environmental intervention correlates directly with improved spatial learning ability. As a combination of both interventions failed to further increase basal polysialylated cell frequency, complex environment rearing and chronic drug regimens most likely enhanced cognitive performance by the same mechanism(s). These findings suggest that improved memory-associated synaptic plasticity may be the fundamental mechanism underlying the disease modifying action of drugs such as cholinesterase inhibitors. Moreover, the molecular and cellular events underpinning neuroplastic responses are identified as novel targets in the search for interventive drug strategies for the treatment of neurodegenerative and neuropsychiatric disorders.

Complex-environment rearing prevents prenatal hypoxia-induced deficits in hippocampal cellular mechanisms necessary for memory consolidation in the adult Wistar rat.

Hypoxic episodes in utero can result in enduring and debilitating neurological sequelae that include nonprogressive motor disorders and/or significant learning deficits. The extent of long-term disruption of synaptic function following prenatal hypoxia and its subsequent effect on learning ability, however, remain to be established. Polysialylation of the neural cell adhesion molecule, a cellular event integral to the consolidation of diverse learning paradigms, was used to correlate cellular end points with learning deficits as a consequence of prenatal hypoxia. Pregnant Wistar dams exposed to hypobaric hypoxia during gestational days 10-20 had significantly reduced litter sizes, but the lack of effect on subsequent pup weight gain suggested no gross developmental deficit. By contrast, adult animals with prior in utero hypoxia exhibited significant learning difficulties in both acquisition of a water maze spatial learning task and recall of a passive avoidance paradigm. Learning deficits correlated with a significant reduction in the frequency of polysialylated neurons in the dentate infragranular zone and a blunting of their transient activation 12 hr following task acquisition. Rearing animals with prior prenatal hypoxia in a complex environment, however, eliminated the task acquisition and recall deficits and restored dentate polysialylated cell frequency and their transient posttraining increase.

Pentyl-4-yn-valproic acid reverses age-associated memory impairment in the Wistar rat.

Pentyl-4-yn-valproic acid (VPA), a cognition-enhancing agent whose mode of action has been attributed to cell adhesion molecule-mediated neuritogenesis, has been shown to enhance hippocampus-dependent spatial learning. Here, we investigated its potential to reverse age-related memory impairment that relates mainly to declarative memory. Aged spatial learning deficits in the water maze paradigm were demonstrated by swim angle analysis, the angle between axes of start-to-platform and start-to-animal position, and latency to reach a submerged platform. Chronic pentyl-4-yn-VPA administration mediated a significant improvement in both search strategy and latency to find the submerged platform in aged animals. Pentyl-4-yn-VPA also facilitated task recall in aged animals as evidenced by increased time in the target quadrant during a probe trial 3 days following the final training session. The action of pentyl-4-yn-VPA on platform latency, search strategy and task recall suggests that this agent may have great benefit in the treatment of age-dependent cognitive decline.

Differential enantioselective effects of pentyl-4-yn-valproate on spatial learning in the rat, and neurite outgrowth and cyclin D3 expression in vitro.

Previously, we demonstrated the racemic form of the valproate (VPA) analogue, 2-n-pentyl-4-pentynoic acid ([+/-]pentyl-4-yn-VPA), to be neuritogenic in vitro and to enhance cognition in vivo. To determine the enantioselectivity of these effects, the racemate and purified enantiomers of [+/-]pentyl-4-yn-VPA (84 mg/kg, i.p.) were administered to rodents 20 min prior to multi-session water maze training. The racemate and R-enantiomer significantly reduced escape latencies during water maze learning and enhanced its recall in a probe trial 3 days later. In contrast, S-pentyl-4-yn-VPA did not influence these behavioural parameters. The enantiomer-specific effects of [+/-]pentyl-4-yn-VPA were further discriminated in vitro using neuro 2A neuroblastoma and C6 glioma cell lines. In neuro 2A, the S-enantiomer induced profound neurite outgrowth at concentrations up to 0.5 mm, with the R-enantiomer and racemate being less neuritogenic. Immunoblot analysis of cyclin D3 expression in C6 glioma indicated the racemate and S-pentyl-4-yn-VPA to induce dose-dependent up-regulation of this protein, similar to that associated with G1-phase cell cycle arrest mediated by VPA, whereas R-pentyl-4-yn-VPA was without effect. These results indicate that the cognition-enhancing effects of pentyl-4-yn-VPA are due to the actions of the R-enantiomer, and that cyclin D3 up-regulation and associated anti-proliferative and pro-differentiative actions are predominantly associated with the S-enantiomer.

The 5-HT(6) receptor antagonist SB-271046 reverses scopolamine-disrupted consolidation of a passive avoidance task and ameliorates spatial task deficits in aged rats.

The highly potent and selective 5-HT(6) receptor antagonist SB-271046 [5-chloro-N-(4-methoxy-3-piperazin-1-yl-phenyl)-3-methyl-2-benzothiophenesulfonamide] has previously been demonstrated to improve retention significantly in a spatial water maze paradigm in adult rats. However, SB-271046 did not have any effect on task acquisition. As these apparently contradictory findings may be reconciled by a prime influence of SB-271046 on memory consolidation, the ability of this compound to reverse the discrete temporal action of a cholinergic antagonist in the 6-h period following passive avoidance training was investigated. SB-271046, given orally, by gavage, 30 min prior to training Wistar rats in a step-through, light-dark passive avoidance task, was found to reverse significantly the amnesia produced by administering scopolamine (0.8 mg/kg, intraperitoneal) in the 6-h post-training period. The effect was dose-dependent over a range of 3-20 mg/kg. Further, we investigated the cognition-enhancing effects of chronic SB-271046 administration (10 or 20 mg/kg/day; 40 days) on the acquisition and consolidation of a water maze spatial learning task in a population of 20-month-old Wistar rats with age-related learning deficits. Drug treatment progressively and significantly decreased platform swim angle and escape latencies over the five sequential trials on four consecutive daily sessions compared to vehicle-treated controls. SB-271046 also improved task recall as measured by significant increases in the searching of the target quadrant on post-training days 1 and 3, when the animals would have been substantially drug-free. This significant improvement of task recall suggests SB-271046, in addition to inducing symptomatic cognition-enhancing actions, also attenuates age-related decline in neural function.

Distribution of polysialylated neural cell adhesion molecule in rat septal nuclei and septohippocampal pathway: transient increase of polysialylated interneurons in the subtriangular septal zone during memory consolidation.

During memory consolidation neuroplastic events in the mediotemporal corticohippocampal pathway are accompanied by transient increases in the frequency of neurons expressing polysialylated neural cell adhesion molecule (NCAM PSA), a posttranslational modification associated with morphofunctional change. As a bidirectional pathway between the hippocampus and the septal nuclei also influences memory processing, we have determined the distribution of NCAM PSA within this system before and after learning in the adult Wistar rat. The most intense NCAM PSA immunoreactivity was observed in the medial and triangular septal nuclei, regions that regulate hippocampal theta rhythm during memory consolidation. Within the fimbria, NCAM PSA was expressed only in a subpopulation of fibres, most likely cholinergic projections from the medial septum to the hippocampus. Grey level analysis or direct cell counting revealed no learning-specific change in NCAM PSA expression in these septal subregions after avoidance conditioning or spatial training. A population of discrete polysialylated neurons in the subtriangular septal zone, however, exhibited a transient twofold frequency increase at 12 hr after training in either task. Immunohistochemical analysis revealed these cells to be gamma-aminobutyric acid (GABAergic) interneurons co-expressing vasoactive intestinal peptide. The unique location of these interneurons is proposed to provide a natural plexus by which bidirectional communication between the septum and hippocampus may be modified during memory consolidation.

Consolidation of memory for odour-reward association requires transient polysialylation of the neural cell adhesion molecule in the rat hippocampal dentate gyrus.

Cell adhesion molecule function is involved in hippocampal synaptic plasticity and is associated with memory consolidation. At the infragranular zone of the dentate gyrus, neurons expressing the polysialylated form of the neural cell adhesion molecule (NCAM PSA) transiently increase their frequency at the 12-hr posttraining time in behaviours elicited by stressful stimuli, such as those associated with conditioned avoidance, water maze, and fear conditioning paradigms. To determine whether learning-induced modulation of NCAM polysialylation is limited to stressful paradigms, we employed a reward-based odour discrimination task. Animals show a rapid acquisition and recall of this task in terms of latency to identify the food-associated odour and the number of choice errors. Immunohistochemical procedures were employed to determine the change in NCAM PSA expression following task acquisition. NCAM PSA immunoreactivity in the hippocampal formation was most intense on the granule-like neurons in the infragranular zone of the dentate gyrus, and their frequency transiently increased in the 12-hr posttraining period. The nature of the transient increase in NCAM PSA-immunoreactive neurons was indistinguishable from that observed following avoidance conditioning or spatial learning, in that it occurred at the same time. The transient increase in NCAM PSA expression is suggested to facilitate dendritic elaboration in response to the acquisition of novel behavioural repertoires.