Dissociating the effects of distraction and proactive interference on object memory through tests of novelty preference.

Encoding information into memory is sensitive to distraction while retrieving that memory may be compromised by proactive interference from pre-existing memories. These two debilitating effects are common in neuropsychiatric conditions, but modelling them preclinically to date is slow as it requires prolonged operant training. A step change would be the validation of functionally equivalent but fast, simple, high-throughput tasks based on spontaneous behaviour. Here, we show that spontaneous object preference testing meets these requirements in the subchronic phencyclidine rat model for cognitive impairments associated with schizophrenia. Subchronic phencyclidine rats show clear memory sensitivity to distraction in the standard novel object recognition task. However, due to this, standard novel object recognition task cannot assess proactive interference. Therefore, we compared subchronic phencyclidine performance in standard novel object recognition task to that using the continuous novel object recognition task, which offers minimal distraction, allowing disease-relevant memory deficits to be assessed directly. We first determined that subchronic phencyclidine treatment did not affect whisker movements during object exploration. Subchronic phencyclidine rats exhibited the expected distraction standard novel object recognition task effect but had intact performance on the first continuous novel object recognition task trial, effectively dissociating distraction using two novel object recognition task variants. In remaining continuous novel object recognition task trials, the cumulative discrimination index for subchronic phencyclidine rats was above chance throughout, but, importantly, their detection of object novelty was increasingly impaired relative to controls. We attribute this effect to the accumulation of proactive interference. This is the first demonstration that increased sensitivity to distraction and proactive interference, both key cognitive impairments in schizophrenia, can be dissociated in the subchronic phencyclidine rat using two variants of the same fast, simple, spontaneous object memory paradigm.

Water and T-maze protocols are equally efficient methods to assess spatial memory in 3xTg Alzheimer's disease mice.

Rodent spatial memory is commonly tested using the water-maze; however, there is a potential confound of stress on learning in this behavioural paradigm. This is particularly relevant when testing spatial memory in models of neurodegeneration, such as the 3xTg mouse model for Alzheimer's disease. Here, we first confirmed that 3xTgAD mice express fear conditioning and then compared the performance of young and middle-aged mice on short-duration versions of the radial arm water-maze (RAWM) and the minimally stressful T-maze spontaneous alternation task. Our main questions were: (1) does the reliance on stressors in water-maze training mask the true cognitive ability of 3xTgAD mice; and (2) are 3xTgAD mice similarly impaired in water-maze and T-maze protocols. Firstly, male and female 3xTgAD mice displayed intact freezing responses in both contextual and Pavlovian fear conditions. As male 3xTgAD mice displayed relatively enhanced fear responses the remaining tests were performed using only female 3xTgAD and control mice in order to equate for response to stressors. We found that alternation rates after both short and long delays were impaired at both ages in female 3xTgAD mice, indicative of robust spatial working memory deficits. For RAWM, again performance deficits were found in young 3xTgAD mice. As both tasks had similar efficacy at revealing early spatial memory deficits, we suggest that spontaneous behavioural protocols be prioritised over water maze testing in models such the 3xTgAD mouse as the former provide a far less stressful but equally effective alternative.

The subiculum: a review of form, physiology and function.

We review the neuroanatomical, neurophysiological and functional properties of the mammalian subiculum in this paper. The subiculum is a pivotal structure positioned between the hippocampus proper and entorhinal and other cortices, as well as a range of subcortical structures. It is an under-investigated region that plays a key role in the mediation of hippocampal-cortical interaction. We argue that on neuroanatomical, physiological and functional grounds, the subiculum is properly part of the hippocampal formation, given its pivotal role in the hippocampal circuit. We suggest that the term "subicular complex" embraces a heterogenous range of distinct structures and this phrase does not connote a functionally or anatomically meaningful grouping of structures. The subiculum has a range of electrophysiological and functional properties which are quite distinct from its input areas; given the widespread set of cortical and subcortical areas with which it interacts, it is able to influence activity in quite disparate brain regions. The rules which govern the plasticity of synaptic transmission are not well-specified; it shares some properties in common with the hippocampus proper, but behaves quite differently in other respects. Equally, its functional properties are not well-understood, it plays an important but ill-defined role both in spatial navigation and in mnemonic processing. The important challenges for the future revolve around the theoretical specification of its unique contribution to hippocampal formation processing on the one hand, and the experimental investigation of the many open questions (anatomical, physiological, pharmacological, functional) regarding its properties, on the other.

Metabotropic glutamate receptor activation and blockade: their role in long-term potentiation, learning and neurotoxicity.

Metabotropic glutamate receptors represent a fairly recent addition to the family of glutamate receptors. These receptors have the distinguishing feature of being coupled to G-proteins rather than ion channels and they appear to have a variety of functional characteristics. These receptors play a vital role, for example, in the induction and maintenance of long-term potentiation, the most popular current model of the biological correlates of learning and memory. Blockade of metabotropic glutamate receptors prevents long-term potentiation induction and learning in a variety of tasks in different species. Chronic metabotropic glutamate receptor activation is also associated with neurodegeneration and selective neuronal loss when agonists of these receptors are injected in high concentrations directly into the brain. Metabotropic glutamate receptors also play a role in the normal development of the nervous system and these sites within the central nervous system offer possible routes for drug therapies; selective receptor antagonists, for example, may prove to have the very desirable feature of endowing neuroprotection during ischaemic episodes whilst allowing normal excitatory neurotransmission to occur.

Training-induced increases in neuronal activity recorded from the forebrain of the day-old chick are time dependent.

Spontaneous neuronal bursting occurs in many areas of chick forebrain. Day-old chicks trained using a one-trial task to avoid a methylanthranilate-coated bead (methyl-chicks) show a significant increase in bursting when compared to chicks trained to peck a water-coated bead (water-chicks). This increase occurs in two forebrain areas: the intermediate medial hyperstriatum ventrale and the lobus parolfactorius. Bursting was recorded from the intermediate medial hyperstriatum ventrale of anaesthetized methyl- and water-chicks at eight time-points over the period 1-9 h post-test. Data merged over this period showed that methyl-chicks displayed an overall increase in bursting in both left and right hemispheres when compared to water-chicks. When burst activity was compared against time, bursting in methyl-chicks was significantly elevated only during the period 3-7 h post-test. Maximal bursting in methyl-chicks was seen 6-7 h post-test. These results suggest that the training-induced increase in bursting seen in the intermediate medial hyperstriatum ventrale of methyl-chicks is not a simple, generalized increase with time but rather has a significant temporal aspect. These results may have particular relevance to previously proposed models of memory formation in the chick.

Interaction between paired-pulse facilitation and long-term potentiation in the projection from hippocampal area CA1 to the subiculum.

Studies of the interaction between long-term potentiation (LTP) and paired-pulse facilitation (PPF) may throw light on the role of presynaptic factors in LTP. We examine here, for the first time, the nature of PPF in the CA1-subiculum projection. PPF peaks at a 50 ms interstimulus interval (ISI) and is evident at ISIs from 10 to 500 ms. There is no PPF effect at a 1000 ms ISI. PPF decreases in magnitude post-LTP induction across the middle range of ISI values tested (30, 50 and 100 ms). There is a positive correlation between initial PPF values and LTP; this correlation increases as the ISI increases. Initial values and the change in PPF post-LTP are also negatively correlated.

The projection from hippocampal area CA1 to the subiculum sustains long-term potentiation.

Long-term potentiation (LTP) is a popular model of the synaptic plasticity which may be engaged by the biological processes underlying learning and memory. Most available studies of LTP have concentrated on the analysis of LTP occurring in 'early' components of the hippocampal circuit (for example, dentate gyrus and area CA1). We examine here, for the first time, LTP as it occurs in the massive, unidirectional projection from CA1 to the subiculum in vivo. We show that this projection sustains high-frequency stimulus-induced LTP (10 trains of 20 stimuli at 200 Hz; intertrain interval 2 s; LTP 181 +/- 9% at 30 min post-LTP induction). In addition, input-output (I/O) curves show a leftward shift for all stimulation values.

Disorientation combined with bilateral parietal cortex lesions causes path integration deficits in the water maze.

The navigational abilities of rats were examined using the water maze after disorientation induced by rotation and/or swimming in darkness. Control and light-disoriented groups performed similarly, whereas the dark group and the dark-disoriented groups were initially much slower but improved to control levels. After receiving bilateral parietal lesions, multiple start position tests showed that both rotation groups were severely impaired in finding the hidden platform. The effects of disorientation induced by darkness and by rotation are therefore separable.

Neurophysiology and neuropharmacology of projections from entorhinal cortex to striatum in the rat.

We studied projections from the entorhinal cortex (Ent) to the striatum in anesthetized rats using extra- and intracellular recording and multibarrel iontophoresis. The majority of recording were from the caudate-putamen (CPu) and core of the nucleus accumbens (AcbC). Electrical stimulation of the Ent evoked synaptic responses in 77% of tests with AcbC neurons and 48% of tests with CPu neurons. In the case of AcbC neurons, 61% of these tests proved to be excitatory and were often followed by inhibitory phases. In contrast to this, only 18% of tests from CPu neurons were excitatory. Intracellular HRP labeling showed that responsive cells were medium spiny neurons. During iontophoretic experiments, application of the glutamatergic AMPA antagonist DNQX could selectively decrease or block excitatory responses. The GABAA antagonist bicuculline methiodide increased cellular firing rates and could reveal excitatory responses, suggesting block of a short-latency, short-duration inhibitory component. Ejection of the GABAB antagonist CGP-35348 could attenuate a later, longer-duration component of inhibition. The results indicate that the Ent excites striatal neurons at least in part by glutamatergic receptors and suggest that this excitation is followed by secondary prolonged GABAergic inhibition.

Responses of rat subicular neurons to convergent stimulation of lateral entorhinal cortex and CA1 in vivo.

There has been little electrophysiological examination of the afferent projection from lateral entorhinal cortex to dorsal subiculum. Here we provide evidence that synaptic inputs from lateral entorhinal cortex and CA1 converge onto single dorsal subicular neurons in vivo. Subicular responses to CA1 stimulation consisted of excitation and/or long-duration inhibition. Neurons excited by CA1 activation usually showed inhibition to entorhinal stimulation. The latter inhibition was usually of short duration, however, long duration inhibition was seen in a significant proportion of responses. Entorhinal stimulation produced excitatory responses in four bursting cells and it was these cells that also tended to show the longest inhibition. Only bursting cells could be driven antidromically by entorhinal stimulation. Biocytin-filled multipolar and pyramidal cells displayed excitation-inhibition sequences to CA1 and inhibition to entorhinal stimulation. These data strongly suggest that subicular inhibitory neurons receive excitatory input from CA1 and display mutual inhibition. The source of entorhinal-evoked inhibition is less clear. The relative sparseness of observed entorhinal-evoked responses suggests that the input to dorsal subiculum from any one part of lateral entorhinal cortex is spatially restricted. These data show that excitation-inhibition sequences can be seen in subicular pyramidal and multipolar cells and that single subicular neurons receive convergent inputs from CA1 and entorhinal cortex. We show for the first time that bursting cells can be driven both orthodromically and antidromically by direct entorhinal stimulation. These data support the existence of a reciprocal excitatory connection between lateral entorhinal cortex and dorsal subiculum and suggest further that this connection may involve only bursting subicular neurons.

The effects of single and multiple episodes of theta patterned or high frequency stimulation on synaptic transmission from hippocampal area CA1 to the subiculum in rats.

Long-term potentiation (LTP) is a popular model for the synaptic changes that may occur during learning and memory; it involves a strengthening of synaptic response and is readily induced in the hippocampus, an area of the brain implicated in learning and memory. Previous research on LTP has focused on 'early' components of the hippocampal circuitry, that is, the dentate gyrus and areas CA1 and CA3. This paper examines the plasticity of the CA1-subiculum pathway; we extend our previous work in this area demonstrating that the projection from area CA1 to subiculum sustains theta-patterned stimulus-induced LTP in vivo. We show that this pathway remains potentiated over a long period (3 h). Furthermore, once this projection is potentiated, it seems resistant to further episodes of high-frequency stimulation. We discuss the implications of these findings for theories of hippocampal-cortical interaction during the biological consolidation of memory.

The allyl group for protection in carbohydrate chemistry. 17. Synthesis of propyl O-(3,6-di-O-methyl-beta-D-glucopyranosyl)-(1----4)-O-(2,3- di-O-methyl-alpha-L-rhamnopyranosyl)-(1----2)-3-O-methyl-alpha- L-rhamnopyranoside: the oligosaccharide portion of the major serologically active glycolipid from Mycobacterium leprae.

Allyl 4-O-benzyl-alpha-L-rhamnopyranoside was converted into allyl 4-O-benzyl-3-O-methyl-alpha-L-rhamnopyranoside and this was condensed with 2,3,4-tri-O-acetyl-alpha-L-rhamnopyranosyl chloride to give a disaccharide derivative which was converted into allyl 4-O-benzyl-2-O-(2,3-O-isopropylidene-alpha-L-rhamnopyranosyl)-3-O-methyl -alpha- L-rhamnopyranoside. This disaccharide derivative was condensed with 2,4-di-O-acetyl-3,6-di-O-methyl-alpha-D-glucopyranosyl chloride to give a trisaccharide derivative which was converted into the title compound. This compound represents the oligosaccharide portion of the major serologically active glycolipid from Mycobacterium leprae which is required to prepare a synthetic diagnostic agent for leprosy infection at an early stage and to investigate the specificities of monoclonal antibodies directed towards the glycolipid.

Synthesis of methyl 2-O-allyl-(and 3-O-allyl)-5-O-benzyl-beta-D- ribofuranoside.

D-Ribose was converted into methyl 5-O-benzyl-beta-D-ribofuranoside and this, on tin-mediated allylation, gave a mixture of the 2-O-allyl and 3-O-allyl derivatives which were separated by chromatography. The more polar isomer was characterised as the 3-O-allyl derivative after conversion via 3-O-allyl-5-O-benzyl-1,2-O-isopropylidene-alpha-D-ribofuranose (which was also synthesised from 3-O-allyl-1,2:5,6-di-O-isopropylidene-alpha-D-allofuranose) into the known 5-O-benzyl-1,2-O-isopropylidene-alpha-D-ribofuranose. Methyl 3-O-allyl-5-O-benzyl-beta-D-ribofuranoside was converted into methyl 2-O-allyl-5-O-benzyl-beta-D-ribofuranoside via methyl 2-O-allyl-5-O-benzyl-3-O-(prop-1-enyl)-beta-D-ribofuranoside.

The preparation and phosphorylation of 2,5- and 1D-2,6-di-O-benzyl-myo-inositol.

1,3,4,6-Tetra-O-allyl-myo-inositol was converted into the 2,5-di-O-benzyl- and 2,5-di-O-p-methoxybenzyl ethers, and the products were deallylated to give the 2,5-di-O-benzyl (and p-methoxybenzyl) ethers of myo-inositol, which were converted into the mono-O-isopropylidene derivatives. Both the 2,5-di-O-benzyl ether and its mono-O-isopropylidene derivative were converted into the crystalline octa(2-cyanoethyl) ester of 2,5-di-O-benzyl-myo-inositol 1,3,4,6-tetrakisphosphate. (+-)-1,3,4,5-Tetra-O-allyl-myo-inositol was converted into (+-)-2,4-di-O-benzyl-myo-inositol which gave a separable mixture of the 1,6- and 5,6-O-isopropylidene derivatives. The 1,6-O-isopropylidene derivative was resolved via (-)- and (+)-omega-camphanates and was also converted into (+-)-2,6-di-O-benzyl-1,5-di-O-p-methoxybenzyl-myo-inositol, which was resolved via the (-)-omega-camphanates. The 5,6-O-isopropylidene derivative and 1,3-di-O-allyl-myo-inositol were converted into (+-)-1,3-di-O-allyl-2,6-di-O-benzyl-myo-inositol, which was resolved as the (-)-omega-camphanates. 1D-1,3,4,5-Tetra-O-allyl-myo-inositol and the above described, relevant diaste reoisomers were converted into 1D-2,6-di-O-benzyl-myo-inositol which gave the syrupy octabenzyl ester of 1D-2,6-di-O-benzyl-myo-inositol 1,3,4,5-tetrakisphosphate.

The preparation of intermediates for the synthesis of 1D-myo-inositol 1,4,5-trisphosphate, a second messenger for signal transduction in cells.

Racemic 1,2,4-tri-O-benzyl-5,6-O-isopropylidene-myo-inositol was prepared by a new route involving crotyl (but-2-enyl) ethers and converted into the (-)-omega-camphanates to give the pure crystalline 1L-diastereoisomer and the chirally impure, syrupy 1D-diastereoisomer. The latter was converted via the 1-O-allyl or 1-O-p-methoxybenzyl ethers into chirally pure 1D-2,3,6-tri-O-benzyl-myo-inositol [required as an intermediate for the synthesis of 1D-myo-inositol 1,4,5-trisphosphate (1,4,5-IP3)], which was also prepared by de-p-methoxybenzylation of 1D-2,3,6-tri-O-benzyl-1,5-di-O-p-methoxybenzyl-myo-inositol. Racemic 2,4-di-O-benzyl-5,6-O-isopropylidene-1-O-p-methoxybenzyl-myo-inositol was prepared in a similar way to the analogous tribenzyl ether (using crotyl ethers) and the omega-camphanate esters behaved similarly, allowing efficient resolution by crystallisation of the (-)- and (+)-omega-camphanates. Racemic 1,2,4-tri-O-allyl-3-O-(but-2-enyl)-myo-inositol was resolved via the (-)-omega-camphanates and was also converted into 1,2,4-tri-O-(cis-prop-1-enyl)-myo-inositol, an alternative intermediate for the synthesis of 1,4,5-IP3.

The preparation of intermediates for the synthesis of 1D-myo-inositol 1,4,5- and 2,4,5-trisphosphates, 1,4-bisphosphate 5-phosphorothioate, and 4,5-bisphosphate 1-phosphorothioate from 1D-3,6-di-O-benzyl-1,2-O-isopropylidene-myo-inositol.

The preparation of 1D-1,6-di-O-benzyl-2,5-di-O-p-methoxybenzyl-myo-inositol is described. This compound and 1D-3,6-di-O-benzyl-1,2-O-isopropylidene-myo-inositol were converted into 1D-1,3,6-tri-O-benzyl-myo-inositol which was phosphorylated to give an intermediate for the synthesis of 1D-myo-inositol 2,4,5-trisphosphate. 1D-3,6-Di-O-benzyl-1,2-O-isopropylidene-myo-inositol was converted into 1D-2,3,6-tri-O-benzyl-myo-inositol (an intermediate for the synthesis of 1D-myo-inositol 1,4,5-trisphosphate) and 1D-2,3,6-tri-O-benzyl-1-O-p-methoxybenzyl-myo-inositol (an intermediate for the synthesis of the 1-phosphorothioate analogue of 1D-myo-inositol 1,4,5-trisphosphate). 1D-3,6-Di-O-benzyl-1,2-O-isopropylidene-myo-inositol was also converted into 1D-2,3,6-tri-O-benzyl-5-O-p-methoxybenzyl[and -5-O(cis-prop-1-enyl)]-myo- inositol both of which are intermediates for the synthesis of the 5-phosphorothioate analogue of 1D-myo-inositol 1,4,5-trisphosphate. The synthesis of 1D-2,3,6-tri-O-benzyl-myo-inositol 1,4-bis(dibenzyl phosphate) 5-(dibenzyl phosphorothioate) from 1D-2,3,6-tri-O-benzyl-myo-inositol 1,4-bis(dibenzyl phosphate) is described.

The synthesis and resolution of (+/-)-1,5,6-tri-O-benzyl-myo-inositol.

Racemic 1,5,6-tri-O-benzyl-myo-inositol was prepared by five routes and converted into 1,5,6-tri-O-benzyl-2,3-O-isopropylidene-myo-inositol, the camphanates of which were readily separated by chromatography. The absolute configurations of the chiral derivatives were established by their conversion into the known chiral 1,4,5,6-tetra-O-benzyl-myo-inositols. 1D-1,5,6-Tri-O-benzyl-2,3-O-isopropylidene-myo-inositol was converted into 1D-1,3,5,6-tetra-O-benzyl-myo-inositol and thence into 1D-2,4-di-O-methyl-myo-inositol. 1D-1,5,6-Tri-O-benzyl-myo-inositol was converted into 1D-1,2,5,6-tetra-O-benzyl-myo-inositol, the diacetate of which is a chiral analogue of "thermosalient crystals". The potential of the above compounds for the synthesis of natural products is surveyed.

Increases in neuronal bursting recorded from the chick lobus parolfactorius after training are both time-dependent and memory-specific.

Day-old-chicks can be trained in one trial to avoid a methylanthranilate-coated bead (methyl-chicks). The lobus parolfactorius of the chick forebrain is an important structure for memory of this avoidance response. To examine training-induced electrophysiological changes in this structure, spontaneous neuronal bursting activity was measured from the lobus parolfactorius of anaesthetized, day-old methyl- and water-chicks (the latter chicks trained to peck at a water-coated bead) over the period 1-10 h post-test. Bursting was significantly higher in methyl-chicks over this period. This post-test increase was time-dependent: bursting in methyl-chicks was significantly higher only during the period 4-7 h post-test. In a second experiment, methyl-chicks were subjected to brief, subconvulsive electroshock 5 min post-training. When tested 1 h later about half of these chicks showed recall (avoided the bead) and half were amnesic (pecked the bead). These chicks were anaesthetized and bursting was recorded from the lobus parolfactorius. Chicks that showed recall exhibited a significantly higher level of bursting over the period 1-10 h post-test when compared to chicks that were amnesic. The time course of bursting was similar to that seen in non-electroshocked methyl-chicks. These results suggest that passive avoidance training induces a memory-specific, time-dependent increase in neuronal activity within the lobus parolfactorius of day-old chicks. This increase may be directly associated with long-term consolidation of memory for the task.

Glutamatergic hippocampal formation projections to prefrontal cortex in the rat are regulated by GABAergic inhibition and show convergence with glutamatergic projections from the limbic thalamus.

Anatomic and physiologic studies in the rat have shown projections from the hippocampal formation (HF) and mediodorsal (MD) thalamic nucleus to the medial prefrontal cortex (mPFC). The authors used multi-barrel iontophoresis to: confirm the neurotransmitter used in the projection from HF to mPFC; investigate the role of GABAergic inhibition in the regulation of this projection; and examine the functional convergence of projections from HF and MD onto single mPFC neurons. During HF stimulation, nine cells (6%) showed excitation followed by prolonged inhibition, 39 cells (26%) showed prolonged inhibition alone and 100 cells (68%) showed no clear response. In a further 12 cells that showed no predrug excitation to HF stimulation (representing 16% of the cells in this category), iontophoresis of the GABAA antagonist bicuculline methiodide (BMI) revealed excitatory responses. A total of six mPFC cells (38% of the cells showing excitatory responses to HF stimulation) showed convergent excitation to HF and MD thalamic (or adjacent paratenial nucleus) stimulation. Five out of eight (63%) of the predrug or BMI-revealed excitatory responses of mPFC neurons to HF stimulation were selectively decreased after AMPA antagonist iontophoresis (either CNQX or DNQX). These data confirm that the HF projection to prefrontal cortex is, at least in part, glutamatergic; suggest that the responses of mPFC neurons to activity in this HF pathway are regulated by GABAergic inhibition; and indicate that projections from HF and MD converge onto single mPFC neurons.

Glutamatergic excitatory responses of anterior cingulate neurons to stimulation of the mediodorsal thalamus and their regulation by GABA: an in vivo iontophoretic study.

Anatomical and physiological studies in the rat have shown projections from the medial dorsal thalamus to the anterior cingulate cortex. We used multibarrel iontophoresis to identify the neurotransmitter used in this thalamic projection. Extracellular responses were recorded from 165 cingulate neurons in anesthetized rats after electrical stimulation of the medial dorsal thalamus and vicinity. Forty-four of these cells (27%) showed an excitatory response to thalamic stimulation. In a further 40 cells that showed no baseline excitation, iontophoresis of the GABAA antagonist bicuculline methiodide revealed excitatory responses. The GABAB antagonist CGP-35348 attenuated longer-latency inhibition in 5 of 10 cells. In 23 of 49 (47%) of the above cells, AMPA antagonist iontophoresis (either CNQX or DNQX) selectively decreased the excitatory response to thalamic stimulation. The NMDA antagonist 3[(R)-2-carboxypiperazin-4-yl]-propyl-1-phosphonic acid had no such effect. These data suggest that the thalamic projection to anterior cingulate cortex is glutamatergic, acting principally via AMPA receptors, and that the response of cingulate neurons to thalamic stimulation is regulated by GABA acting at both GABAA and GABAB receptors.