Regional dissociation of paradigm-specific synapse remodeling during memory consolidation in the adult rat dentate gyrus.

Arising from studies on the amnesia that follows site-specific physical or chemical lesions, the acquisition and consolidation of certain behavioral tasks has been demonstrated to be associated with different hippocampal subregions. Although not absolute, spatial learning is reliant on the dorsal region of the hippocampus, whereas avoidance- and fear-conditioning tasks appear to be dependent on its more ventral aspects. Thus, if learning-associated synapse remodeling is a true feature of memory consolidation it must also follow these regional dissociations. We therefore determined if the learning-associated increases in synapse density that occur in the mid-molecular layer of the dentate gyrus at the 6-h post-training time and the frequency of polysialylated cells at the infragranular zone that occur at the 12-h post-training time were dissociated to specific hippocampal subregions following training in either a massed water maze task or light-dark passive avoidance response. Synapse remodeling was found to occur only in the dorsal hippocampus following spatial learning. We could not, however, discern any regional dissociation of neural remodeling following avoidance conditioning. These results point to strong associations between learning and specific groups of novel synapses during consolidation of spatial learning and avoidance conditioning paradigms.

Developmental emergence of reelin deficits in the prefrontal cortex of Wistar rats reared in social isolation.

As the pathophysiological mechanism(s) of many neuropsychiatric disorders relate to GABAergic interneuron structure and function, we employed isolation rearing of Wistar rats as a model to correlate developmental emergence of cognitive deficits with the expression of reelin-producing interneurons in the medial prefrontal cortex (PFC). Prepulse inhibition deficits emerged at postnatal day 60 and persisted into adulthood. Paralleling the emergence of these neurobehavioural deficits was an increase in reelin production and reelin-immunopositive cells in layer I of the PFC and this later became significantly reduced at postnatal day 80. Cells expressing reelin immunoreactivity in a horizontal orientation were mainly located to the upper regions of layer I whereas those with a vertical orientation, whose arbors extend into cortical layers II and III, were more numerous in the lower regions of layer I and became significantly dysregulated during postnatal development. No behavioural deficits or altered reelin expression was observed at postnatal days 30 or 40. Developmental emergence of neurobehavioural and reelin deficits in isolation reared animals is proposed to reflect maladaptive wiring within the medial prefrontal cortex during a critical maturation period of this circuitry.

Intraventricular infusions of anti-NCAM PSA impair the process of consolidation of both avoidance conditioning and spatial learning paradigms in Wistar rats.

Processing of information for long-term storage requires specific patterns of activity that lead to modification of synapse structure and eventual change in neural connectivity pattern. Morphological change associated with memory consolidation is reliant on neural cell adhesion molecule (NCAM) function and that of its polysialylated variant (NCAM PSA). Across species and paradigms, a transient frequency increase of polysialylated neurons in the hippocampal dentate has been found necessary for memory consolidation, however, recent studies suggest that NCAM PSA may serve to suppress memory formation in certain paradigms. As intraventricular infusions of NCAM blocking antibodies have been used successfully to demonstrate its time-dependent role at the 6 h post-training period of memory consolidation, we employed the same procedure to demonstrate a functional requirement for NCAM PSA in the consolidation of two commonly used behavioral paradigms: avoidance conditioning and spatial learning in Wistar rats. Anti-PSA was found to significantly induce amnesia of the passive avoidance response when infused at the 10 h post-training time, a period coincident with the learning-associated increase in dentate polysialylated cell frequency. Moreover, the amnesia became apparent at the 48 h recall time and was not apparent at the 24 h post-training time, suggesting a possible role in memory reconsolidation. A similar anti-PSA action was observed following water maze training in aged animals but was not apparent in young animals, an effect suggested to be due to inadequate antibody saturation of the polysialylated cell population. These studies confirm the requirement for NCAM PSA in memory consolidation and separate it from that of NCAM.

Outbreak of Legionnaires' disease on a cruise ship: lessons for international surveillance and control.

A sporadic case of Legionnaires' disease was linked to travel on a cruise ship. Investigation identified two further cases of Legionnaires' Disease and one case of non-pneumonic Legionella infection. An Incident Team confirmed the source to be the ship's water system and control measures were instituted that included pasteurisation, super chlorination and chlorine dioxide dosing. The Public Health Laboratory Service (PHLS) Communicable Disease Surveillance Centre (CDSC), through the European Surveillance Scheme for Travel Associated Legionnaires' Disease, identified three previous cases associated with the same ship's water system including one fatality. Lessons for the international surveillance and control of Legionnaires' disease on cruise ships are discussed.

Secular trends in the occurrence of tuberculosis in an urban community in north west England, 1918-2001: implications for a local tuberculosis control programme.

In recent years enhanced surveillance of tuberculosis has been undertaken for England and Wales to monitor national epidemiological trends. The Chief Medical Officer's strategy for communicable diseases has identified the development of a national strategy for the control of tuberculosis as a priority. Regional and sub-regional variations in the occurrence of tuberculosis require further exploration to inform local implementation of the national strategy. Secular epidemiological trends in tuberculosis for the period 1918-2001 are described for a deprived urban area in the north west of England, and implications for local enhanced surveillance and control measures are discussed. A substantial decline in mortality and morbidity from tuberculosis is shown due to interruption of transmission following improvements to the housing stock and the introduction of chemotherapy and BCG vaccination. The proportion of incident cases of tuberculosis in non-white groups has markedly increased over the period observed. The local tuberculosis control programme now specifically targets recent non-white immigrants. Other urban areas may need to adopt similar measures to improve local control of tuberculosis.

Local surveillance of influenza in the United Kingdom: from sentinel general practices to sentinel cities?

Surveillance of influenza in England and Wales utilises a disparate geographical network of general practices to provide clinical data in the form of weekly consultation rates for influenza and 'influenza-like illness'. This network accurately detects and monitors seasonal influenza activity at national and supra-regional levels. Localised regional and sub-regional epidemics are less easily detected. We describe a localised epidemic of influenza affecting a deprived urban community in the North West of England that was detected by a close knit network of general practices participating in the surveillance of communicable diseases as part of a primary care health needs assessment initiative.

Surveillance of influenza in the North-West Region of England 2001-02.

A local sentinel network of general practitioners has been established in the north west of England for the surveillance of influenza. In the 2001-02 winter, consultation rates for influenza-like-illness (ILI) were low but the surveillance network was able to demonstrate sub-regional variations in the timing of peak influenza activity, and the infection of different age groups. This suggests the network can contribute to better planning to winter pressures on the North West health service.

Pentyl-4-yn-valproic acid enhances both spatial and avoidance learning, and attenuates age-related NCAM-mediated neuroplastic decline within the rat medial temporal lobe.

2-N-Pentyl-4-pentynoic acid [pentyl-4-yn-valproic acid (VPA)] is an analogue of valproic acid that induces neuritogenesis and increases neural cell adhesion molecule (NCAM) prevalence in cultured neural cells. As memory consolidation involves synapse growth, aided by cell adhesion molecule function, we determined whether or not pentyl-4-yn-VPA had cognition-enhancing properties. Pentyl-4-yn-VPA (16-85 mg/kg) significantly improved water maze learning and task retention when given prior to each training session. Acute administration of pentyl-4-yn-VPA also influenced memory consolidation processes as, when given at 3 h post-passive avoidance training, the amnesia induced by scopolamine given 6 h post-training was prevented in a dose-dependent manner. Chronic administration of pentyl-4-yn-VPA (16.8 or 50.4 mg/kg) also significantly reduced escape latencies in the water maze task, 24 h following the last drug administration. This improved spatial learning was accompanied by enhanced neuroplasticity as the expression of NCAM polysialylated neurons in the infragranular zone of the dentate gyrus and in layer II of the perirhinal and piriform cortex was increased significantly following chronic drug treatment. The cognition-enhancing qualities of pentyl-4-yn-VPA, combined with its ability to attenuate the age-related loss of the NCAM polysialylation state, suggest that it may effectively slow the onset of cognitive decline.

Anti-ischemic and cognition-enhancing properties of NNC-711, a gamma-aminobutyric acid reuptake inhibitor.

NNC-711 [1-(2-((diphenylmethylene)amino)oxy)ethyl)-1,2,4,6-tetrahydro-3-pyridinecarboxylic acid hydrochloride], a gamma-aminobutyric acid (GABA) reuptake inhibitor with anticonvulsant activity, was investigated with respect to its cognition-enhancing and neuroprotective potency. In the rat, administration of NNC-711 immediately prior to training prevented amnesia for a passive avoidance task induced by the acetylcholine receptor antagonist scopolamine. NNC-711 was also effective in protecting against ischemia-induced death of CA1 pyramidal neurons in a model of bilateral common carotid artery occlusion in the gerbil. In addition to a neuroprotective activity, NNC-711 exhibited significant cognition-enhancing actions. Daily administration of NNC-711, immediately prior to a spatial learning task, significantly reduced escape latencies in the water maze paradigm in both mature (postnatal day 80) and aged (28 months) rats. All of the above actions exhibited a bell-shaped response with an optimal dose of 0.5-1.0 mg/kg. These investigations with NNC-711 and previous clinical observations on the structurally related anticonvulsant tiagabine confirm the potential of GABA reuptake inhibitors as anti-amnesia and cognition-enhancing agents.

Protein kinase C delta regulates neural cell adhesion molecule polysialylation state in the rat brain.

Polysialylation of neural cell adhesion molecule (NCAM PSA) modulates cell-cell homophilic binding and signalling during brain development and the remodelling of discrete brain regions in the adult. Following learning, a transient increase in the frequency of polysialylated neurones occurs in the dentate gyrus of the hippocampal formation, and this has been correlated with the selective retention and/or elimination of synapses that are transiently overproduced during memory consolidation. We now demonstrate that protein kinase C delta (PKCdelta) negatively regulates polysialyltransferase activity in the rat brain during development and also in the hippocampus during memory consolidation, where its down-regulation in the Golgi membrane fraction coincides with the transient increase in NCAM PSA expression. Decreased expression of PKCdelta was also observed in the hippocampus of rats reared in a complex environment and this directly contrasted the significant increase in frequency of hippocampal polysialylated neurones observed in these animals. These effects were isoform-specific as no change in total PKC enzyme activity was detected during memory consolidation and complex environment rearing had no effect on the hippocampal expression of PKCalpha, beta, gamma or epsilon. By sequential immunoprecipitation and immunoblot analysis, phosphorylation of polysialyltransferase protein(s) was (were) demonstrated to occur on both serine and tyrosine residues and this was associated with decreased enzyme activity. Moreover, a similar experimental approach revealed the degree of PKCdelta co-precipitation with polysialyltransferase protein(s) to be inversely correlated with polysialyltransferase activity. These findings support in vitro evidence indicating PKCdelta to regulate polysialyltransferase activity and NCAM polysialylation state.

The modulations of NCAM polysialylation state that follow transient global ischemia are brief on neurons but enduring on glia.

To investigate the role of polysialylated neural cell adhesion molecule (NCAM PSA)-mediated plasticity after injury, we examined the temporal and spatial expression of NCAM PSA immunoreactivity in the medial temporal lobe following global ischemia. Male Mongolian gerbils were subjected to bilateral common carotid artery occlusion for 5 min and killed at increasing times post-occlusion. The well-characterized delayed CAl pyramidal cell death was observed 5-7 days post-occlusion. At post-occlusion days 1-2 there was a small but significant increase of NCAM PSA-positive hippocampal granule cells followed by an equally significant decrease at post-occlusion day 5. In contrast, a substantial increase in glial PSA expression was observed in all hippocampal regions at 1-7 days post-occlusion that was associated generally with stellate astroglia and specifically with the radial processes of glia traversing the granule cell layer of the dentate gyrus. Administration of the glutamate antagonist 2,3-dihydroxy-6-nitro-7-sulfamoyl-ben-zo(F)quinoxaline significantly blocked the ischemia-induced modulation of neuronal and glial NCAM PSA expression. Astroglial NCAM polysialylation became attenuated by 35 days post-occlusion except in the CAI area of cell death. The temporal and regional pattern of polysialylated NCAM expression in the ischemic gerbil hippocampus implicates this neuroplastic marker in mechanisms of neurotrophic-dependent repair/remodeling that ensue following transient interruption of blood flow.

Consolidation of passive avoidance learning is associated with transient increases of polysialylated neurons in layer II of the rat medial temporal cortex.

Within the rat medial temporal lobe, transient modulations of neural cell adhesion molecule (NCAM) polysialylation have been observed to follow spatial learning. These have been attributed to neuroplastic events associated with the processing of information destined for long term memory consolidation. To determine if similar events are associated with avoidance learning, we investigated change in polysialylated cell number in the entorhinal, perirhinal, and piriform cortex, following acquisition of a passive avoidance task in the rat. Direct quantification of polysialylated neurons in layer II of these cortical regions revealed a significant increase in polysialylated cell frequency at 12 h following passive avoidance training. Unlike spatial learning, the increased expression of polysialylated neurons persisted for up to 24-48 h following training. In the more dorsal aspect of the perirhinal/entorhinal cortex, this increase was found to be specific to learning, as it was not observed in animals rendered amnesic with scopolamine. By contrast, change in polysialylated cell frequency in the ventral aspect of the medial temporal lobe was only partially reduced by amnesic doses of scopolamine. The persisting activation of NCAM polysialylation in the more dorsal aspects of the perirhinal and entorhinal cortex is suggested to reflect the need for more extensive synaptic alterations, as compared to those required for the consolidation of spatial learning. Moreover, the neuroplastic modulations observed in the more ventral regions of the entorhinal and perirhinal cortex appear to be a unique aspect of avoidance conditioning that reflects the activation of alternative learning strategies associated with motivational and/or contextual parameters of the task.

Regulation of neural cell adhesion molecule polysialylation state by cell-cell contact and protein kinase C delta.

Post-translational modification of neural cell adhesion molecule (NCAM) with alpha2,8-linked polysialic acid, which regulates homophilic adhesion and/or signal transduction events, is crucial to synaptic plasticity in the developing and adult brain. Evidence from in vitro models has implicated polysialylation in the regulation of cell growth, migration, and differentiation. Here, using two in vitro models, we demonstrate that polysialylation is downregulated by cell-cell contact and correlated with a state of neuronal differentiation. Furthermore, we report a role for protein kinase C delta (PKCdelta) in the regulation of NCAM polysialylation. Pharmacological studies using the PKC activator, phorbol myristate acetate, and inhibitors, calphostin-C, and staurosporine, demonstrated PKC activity to be inversely related to NCAM polysialylation in the mouse neuro-2A cell line. Isoform-specific immunoblot studies indicated this effect to be mediated by the calcium-independent PKCdelta isozyme, as its expression was inversely related to NCAM polysialylation state in both neuro-2A and rat PC-12 cell lines. Isoform specificity was further confirmed using the PKCdelta-selective inhibitor rottlerin, which produced a marked increase in PSA expression (36.9+/-5.25 a.u. vs. 24.7+/-0.80 arbitrary units control) coupled with a neuritogenic response. Likewise, decreased expression of PKCdelta was seen in nerve growth factor (NGF)-differentiated PC-12 cells. These findings suggest that the neuronal differentiation process may involve inhibition of PKCdelta, resulting in enhanced morphological plasticity, as evidenced by activation of NCAM polysialylation.

Transient spine density increases in the mid-molecular layer of hippocampal dentate gyrus accompany consolidation of a spatial learning task in the rodent.

In previous studies, we observed a transient increase in dendritic spine frequency in the molecular layer of the dentate gyrus at 6h following passive avoidance training [O'Malley A., O'Connell C. and Regan C. M. (1998) Neuroscience 87, 607-613]. To determine if a similar change is associated with spatial forms of learning, we have estimated time-dependent modulations of spine number in the dentate gyrus of the adult rat following water maze training. All animals exhibited significant reductions in the latency to locate the platform over the five training sessions of the single trial (median and interquartile ranges of 60, 8 versus 8, 3 s for trials 1 and 5, respectively) and this improved performance was retained just prior to killing at the 6h post-training time. The unbiased dissector stereological procedure was used to estimate spine number in serial pairs of ultrathin coronal sections obtained at a point 3.3 mm caudal of Bregma. This analysis revealed a significant learning-associated increase in spine number at the 6h post-training time (1.32+/-0.18 spines/microm(3)) as it was not observed in paired controls exposed to the water maze for a similar swim-time (0.66+/-0.11 spines/microm(3)). The increase was transient as spine number returned to control levels at the 72 h post-training time. These spine frequency changes are proposed to reflect increased synapse turnover rate and concomitant change in connectivity pattern in the processing of information for long-term storage.

A synthetic peptide ligand of neural cell adhesion molecule (NCAM) IgI domain prevents NCAM internalization and disrupts passive avoidance learning.

The neural cell adhesion molecule (NCAM) mediates cell adhesion and signal transduction through trans-homophilic- and/or cis-heterophilic-binding mechanisms. Intraventricular infusions of anti-NCAM have revealed a functional requirement of NCAM for the consolidation of memory in rats and chicks in a specific interval 6-8 h after training. We have now extended these studies to a synthetic peptide ligand of NCAM (C3) with an affinity for the IgI domain and the capability of inhibiting NCAM-mediated neurite outgrowth in vitro. Intraventricular administration of a single 5 microg bolus of C3 strongly inhibited recall of a passive avoidance response in adult rats, when given during training or in the 6-8-h posttraining period. The effect of C3 on memory consolidation was similar to that obtained with anti-NCAM as the amnesia was not observed until the 48-h recall time. The unique amnesic action of C3 during training could be related to disrupted NCAM internalization following training. In the 3-4-h posttraining period NCAM 180, the synapse-associated isoform, was down-regulated in the hippocampal dentate gyrus. This effect was mediated by ubiquitination and was prevented by C3 administration during training. These findings indicate NCAM to be involved in both the acquisition and consolidation of a passive avoidance response in the rat. Moreover, the study provides the first in vivo evidence for NCAM internalization in learning and identifies a synthetic NCAM ligand capable of modulating memory processes in vivo.

Antiproliferative actions of inhalational anesthetics: comparisons to the valproate teratogen.

The antiproliferative potential of the volatile anesthetics isoflurane, enflurane and sevoflurane was determined and compared to the valproate teratogen. The in vitro system employed, a G1 phase proliferative arrest endpoint in C6 glioma, has served previously to discriminate agents with known teratogenic potential in vivo. Based on estimated IC(50) values that were within twice the estimated minimum aveolar concentration value, the rank antiproliferative potency of the inhalational anesthetics employed was isoflurane=enflurane>>sevoflurane. Flow cytometric analysis of growth-arrested cell populations failed to reveal specific accumulation in any cell cycle phase and the lack of a G1 phase-specific effect was confirmed by the absence of a transient, time-dependent sialylation event in synchronized cells. The antiproliferative mechanism of volatile anesthetics, and valproate, was mediated at hydrophobic binding sites, as increasing the hydration sphere of the drug-micelle complex, using the hygroscopic qualities of the dimethylsulfoxide vehicle, completely reversed this effect. Our findings suggest inhalational anesthetics lack the specific in vitro characteristics of the valproate teratogen.

CREB phosphorylation coincides with transient synapse formation in the rat hippocampal dentate gyrus following avoidance learning.

Spine density change in the hippocampal dentate gyrus accompanies memory consolidation and coincides with the increased expression of ribosome-rich, hyperchromatic granule cells. Although this suggests increased protein synthesis to be required for synaptic growth in the 5 to 7 h post-training period, little temporal mapping of the associated molecular mechanisms has been done. Here, we demonstrate a similar frequency of hyperchromatic cells in naïve animals and in those sacrificed 6 h post-training, suggesting a transient repression of protein synthesis in the early post-training period. Immunoblot analysis of CREB phosphorylation in the dentate gyrus supported this view, with downregulation from basal levels observed at 2 to 3 h and at 12 h post-training. Protein synthesis reactivation appears to be specific for de novo spine production as no change in spine frequency accompanies the immediate post-training period of depressed protein synthesis. These findings support the view that CREB-mediated gene transcription is a requirement for long-term memory consolidation and may be directly implicated in the process of synaptic growth.

Effects of alcohol cues on cognitive processing in heavy and light drinkers.

The effects of alcohol-related visual cues on cognitive processing in heavy and light social drinkers were assessed. Participants were exposed to either alcohol or control cues while they completed a cognitively demanding emotional Stroop task that used alcohol-related and control words as potential distracters. Heavy drinkers exposed to alcohol cues had significantly slower reaction times on the Stroop task than: (a) heavy drinkers exposed to control cues; and (b) light drinkers exposed to either alcohol or control cues. Results indicate that the effects of alcohol cues on automatic cognitive processes previously found in dependent drinkers' also occur in social drinkers. The magnitude of these effects varies directly with social drinkers' level of habitual alcohol use.