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At least 1,747 records · Page 97Linked to original sources
PubMed1991

The competitive NMDA antagonist AP5, but not the non-competitive antagonist MK801, induces a delay-related impairment in spatial working memory in rats.

Rats were trained to alternate responses on a discrete trial working memory task on a T-maze. In Experiment 1, the rats were then matched for choice accuracy and allocated to three treatment groups. These were: implantation of osmotic minipumps for intraventricular infusion of either (a) 15 mM D-2-amino-5-phosphonopentanoic acid (AP5) or (b) artificial cerebrospinal fluid (VEH); and an unoperated control group (UNOP). In Phase 1 we assessed alternation performance with a minimal delay between responses: the UNOP and VEH rats continued to choose accurately; the AP5 rats showed an impairment of choice accuracy, but recovered over days. In Phase 2 a 20-s delay between responses was enforced, and choice accuracy was assessed following injections either of saline or of Milacemide HCl (10 mg/kg). There was now a severe and enduring impairment of choice accuracy in the AP5 group, but Milacemide injections did not affect performance in any of the treatment groups. In Experiment 2 rats were trained in a similar way, and then given intraperitoneal injections of MK801 or of physiological saline in a within-subjects design and tested for T-maze performance with a minimal or a 20-s delay between responses. In the first Phase, MK801 was given 10-min before behavioural testing commenced; in the second Phase, it was given 28-40 min before behavioural testing commenced. The outcome depended critically on the time between drug injection and testing. There was a significant drug-induced impairment of choice accuracy in both Phases; but in Phase 1 there was no impairment in testing with a minimal retention interval and an impairment with a 20-s retention both retention intervals. We conclude that AP5, but not MK801, interferes with temporary memory storage in a delay-dependent manner.

2-Amino-5-phosphonovalerate↗
PubMed1998

The effects of cytotoxic entorhinal lesions and electrolytic medial septal lesions on the acquisition and retention of a spatial working memory task.

Rats with lesions either of medial septal nucleus (MSN) or the entorhinal cortex (ECx) were compared postoperatively with unoperated controls in a discrete-trial, delayed matching-to-position (DMTP) task, conducted on an elevated T-maze. A DMTP trial consisted of two consecutive visits to the maze: an information run and a choice run. The animals were first forced to visit a randomly selected choice arm in the information run. In the choice run, the correct response was to match the choice arm that had been visited on the information run, regardless of whether the information run itself had been rewarded or not. MSN animals failed to succeed in this task, performing at close to chance level throughout training. On the other hand, ECx rats consistently perform at a level comparable with that of unoperated controls; both groups attained more than 90% correct after 192 trials. Long-term retention testing was carried out after an intermission of 4 weeks, when the same task was re-administered to the ECx and unoperated control animals. ECx animals showed significantly less saving than controls in the retention test. In contrast, when the retention interval within a DMTP trial was increased by the imposition of a 20-s delay between the information and choice runs, the ECx group was not selectively affected by this manipulation.

Acetylcholinesterase↗
PubMed1991

Excitotoxic lesions of the rat entorhinal cortex. Effects of selective neuronal damage on acquisition and retention of a non-spatial reference memory task.

The neurotoxin N-methyl-D-aspartate was used to induce selective bilateral neuronal loss in the entorhinal cortex, in order to model one aspect of the neurodegeneration observed in Alzheimer's disease, Down's syndrome and aging. Lesioned, sham-lesioned and intact control rats learned a reference memory task involving a brightness discrimination for water reward. Rats were trained over 1 week until reaching criteria and tested for retention after a 10-day interval. Lesioned rats showed impaired retention compared to shams and controls, but were able to reacquire the task. Anatomical analysis confirmed excitotoxic lesions of the entorhinal cortex, and showed collateral sprouting of acetylcholinesterase-stained fibers into the outer molecular layer of the dentate gyrus, indicating denervation plasticity in the hippocampus. This functional anatomical study of the entorhinal cortex demonstrates the importance of the entorhinal cortex in memory retention, and raises the possibility that functional deficits in certain neurodegenerative diseases may be modeled by partial neuronal loss in the entorhinal cortex.

Animals↗
PubMed1982

A multiple choice apparatus for electrophysiological investigations of spatial working memory in rats.

A multiple choice apparatus, minimizing the rat's movements and thus simplifying brain stimulation and/or recording in working memory experiments, consists of a dodecagonal enclosure (30 cm diameter, 100 cm high) with a horizontal platform assuming either an upper or a lower position, 43 or 65 cm below the top of the wall, respectively. The platform is moved between these two levels by a pneumatic system controlled by solid-state programming circuits. Each wall segment contains a choice window, 7 cm above the upper floor level, providing access to a recessed feeder. When the platform with a food-deprived rat moves into the upper position, the animal opens the hinged shutter of one window and gets the pellet. Five seconds later, a self-locking relay marks the visited window and the floor descends to the low position where it remains for a predetermined interval (e.g. 20 s), until it is raised again. The above cycle repeats as a long as different windows are chosen. When a choice is directed to an already visited window (error), the floor returns to the low position at once. During one trial, the animal is allowed 12 choices and the number of errors (i.e. choices directed to already entered windows) is recorded. In spite of the great reduction of kinaesthetic and vestibular signals and the almost complete elimination of visual extramaze cues, the working memory performance is similar to that in analogous radial maze.

Animals↗
PubMed1994

The effects of perirhinal cortical lesions on spatial reference memory in the rat.

Rats with bilateral, electrolytic lesions of the perirhinal cortex and sham operated control rats were tested in the Morris water maze, a procedure which has repeatedly been shown to be sensitive to hippocampal and limbic system dysfunction. The results of the present study demonstrate that perirhinal lesioned rats were mildly impaired on this task. The lesioned animals took significantly longer than controls to locate the hidden platform during place navigation acquisition, and had significantly larger heading errors across the entire experimental procedure. In addition, these lesioned animals made fewer platform crossings than control rats during the probe trials. These results suggest that the perirhinal cortex, like the anatomically related entorhinal cortex and hippocampus, may be involved in mnemonic processing.

Animals↗
PubMedDate not supplied

Vasopressin analogues and spatial working memory in the 24-arm radial maze.

The effect of vasopressin analogues dAVP, dDAVP, and desgly NH2 dDAVP on working memory was tested in the 24-arm radial maze in twelve 6-month-old and twelve 19-month-old rats. No age dependent effects were found. All three peptides tested (3 micrograms/kg) tended to improve the performance but only the desgly NH2 dDAVP significantly decreased the number of errors. A second application of desgly NH2 dDAVP was ineffective. The specificity of activation of memory mechanisms by desgly NH2 dDAVP can be questioned.

Animals↗
PubMed1991

Differential effects of chronic ethanol consumptions or thiamine deficiency on spatial working memory in Balb/c mice: a behavioral and neuroanatomical study.

This study was aimed to compare the effects of either a thiamine deficiency or a chronic ethanol consumption on memory and on neuronal density within the median mammillary nucleus. Results showed that alcohol-treated (48 weeks) mice exhibited a behavioral impairment in a sequential alternation task characterized by a progressive decay of alternation rates as a function of the number of trials; such a deficit was not observed in controls and thiamine-deficient subjects. A quantitative analysis using histological sections showed an important reduction of neuronal density within the mammillary bodies following the alcohol treatment but not following thiamine deficiency.

Alcoholism↗
PubMed1995

A pen-and-paper human analogue of a monkey prefrontal cortex activation task: spatial working memory in patients with schizophrenia.

In order to pursue the hypothesis that the dorsolateral prefrontal cortex is a source of cognitive deficit in schizophrenia, we developed an easily administered pen-and-paper human analogue of a visuospatial working memory task that in non-human primates activates the neurons of Walker area 46 (Goldman-Rakic, 1987). Compared to normal controls, schizophrenic patients made significantly greater errors in identifying where a visuospatial stimulus had been presented to them 30 and 60 seconds earlier, and these differences were significantly greater than in an immediate recall condition. These data suggest that schizophrenic patients have visuospatial working memory deficits that are sensitive to pen-and-paper versions of the tasks that activate the Walker area 46 in non-human primates. The availability of an easily administered test that may be associated with the functioning of the prefrontal cortex may enable more specific assessment of this brain region in humans.

Adolescent↗
PubMed2007

Impaired spatial working memory and altered choline acetyltransferase (CHAT) immunoreactivity and nicotinic receptor binding in rats exposed to intermittent hypoxia during sleep.

Exposure to intermittent hypoxia (IH), such as occurs in sleep-disordered breathing (SDB), is associated with cognitive impairment, neurodegeneration, oxidative stress, and inflammatory responses within rodent brain regions such as the basal forebrain. In this region, damage to cholinergic neurons correlates with working memory deficits in a number of neurodegenerative disorders, suggesting that degeneration of cholinergic systems may also contribute to the working memory impairments observed after IH exposures. We therefore examined basal forebrain choline acetyltransferase (CHAT) immunohistochemistry, nicotinic receptor binding in the prefrontal cortex (PFC), and working memory, in male rats tested on a delayed matching to place (DMP) task in the water maze following exposure to either room air (RA) or intermittent hypoxia (IH; alternating 90s epochs of 21% and 10% O(2) during sleep). IH-treated animals displayed impaired working memory with respect to controls, along with significant reductions in CHAT-stained neurons in the medial septal nucleus, in both the vertical and horizontal limbs of the diagonal band, and the substantia inominata after 14 days of IH exposure. In addition, increases in nicotinic binding and receptor affinity in the PFC were observed after 14 days of IH exposure. Thus, a loss of cholinergic neuronal phenotype in the basal forebrain may contribute to the cognitive impairments associated with CIH exposure. However, compensatory mechanisms may also be activated in other brain regions, and may provide potential therapeutic targets for the cognitive impairments associated with SDB.

Animals↗
PubMed2003

Systemic sulpiride modulates striatal blood flow: relationships to spatial working memory and planning.

The dopamine D2 receptor antagonist sulpiride can produce a range of cognitive deficits in normal volunteers, consistent with those seen in Parkinson's disease (PD). This, together with studies in experimental animals, implies sulpiride might be acting in the striatum. However, subtle changes in prefrontal cortex (PFC) activity are seen following L-Dopa withdrawal in PD during working memory tasks, suggesting that this may be a further site of action for dopamine D2 receptor antagonists. We have investigated the effects of sulpiride within the PFC and striatum in normal male volunteers. In two separate experiments, using identical PET regional cerebral blood flow (rCBF) methods, a combined drug and psychological challenge was performed, utilising working memory and planning tasks, and oral sulpiride 400 mg and placebo. Data were analysed using SPM99. Sulpiride increased striatal rCBF bilaterally and the working memory and planning tasks activated discrete frontoparietal networks in keeping with previous studies. However, for the working memory tasks, no changes in performance or task-induced rCBF were observed after sulpiride. For the planning task, improved performance was seen on sulpiride. Also, sulpiride attenuated striatal activity during planning (as assessed using a small volume correction, P<0.05 corrected), and this attenuation was related to performance changes. These findings suggest that (1) sulpiride produces clear increases in striatal rCBF, (2) in contrast to previous studies no effects of sulpiride on performance of the working memory tasks or the associated neural networks were observed, and (3) sulpiride may modulate performance of more complex cognitive tasks via alterations in striatal neural activity.

Adult↗
PubMed2005

Coherence between fMRI time-series distinguishes two spatial working memory networks.

Widespread and distributed brain regions are thought to form networks that together support working memory. We recently demonstrated that different cortical areas maintain relatively different codes across a memory delay (Curtis et. al., J Neurosci, 2004; 24:3944-3952). The frontal eye fields (FEF), for example, were more active during the delay when the direction of the memory-guided saccade was known compared to when it was not known throughout the delay. Other areas showed the opposite pattern. Despite these task-dependent differences in regional activity, we could only assume but not address the functional interactions between the identified nodes of the putative network. Here, we use a bivariate technique, coherence, to formally characterize functional interactions between a seed region and other brain areas. We find that the type of representational codes that are being maintained in working memory biases frontal-parietal interactions. For example, coherence between FEF and other oculomotor areas was greater when a motor representation was an efficient strategy to bridge the delay period. However, coherence between the FEF and higher-order heteromodal areas, e.g., dorsolateral prefrontal cortex, was greater when a sensory representation must be maintained in working memory.

Adolescent↗
PubMed2005

Symmetry and binding in visuo-spatial working memory.

Three experiments study the impact of symmetry on a sequential block tapping immediate memory task in human subjects. Experiment 1 shows an advantage from vertical symmetry over non-symmetrical sequences, while finding no effect of horizontal or diagonal symmetry. Experiment 2 tests the possible role of verbal labeling by means of a secondary task that prevents this by articulatory suppression. No evidence of verbalization was observed. A third study examines the effects of a concurrent executive load, finding an overall impairment, that did not differ between symmetrical and asymmetric patterns, suggesting that the effect of symmetry reflects automatic rather than executive processes. Implications for the episodic buffer component of working memory are discussed.

Adult↗
PubMed2007

alpha7 Nicotinic receptor gene delivery into mouse hippocampal neurons leads to functional receptor expression, improved spatial memory-related performance, and tau hyperphosphorylation.

Brain alpha7 nicotinic receptors have become therapeutic targets for Alzheimer's disease (AD) based on their memory-enhancing and neuroprotective actions. This study investigated the feasibility of increasing neuronal alpha7 receptor functions using a gene delivery approach based on neuron-selective recombinant adeno-associated virus (rAAV)-derived vectors. In order to determine whether alpha7 receptor-mediated cytotoxicity was dependent on receptor density, rat alpha7 nicotinic receptors were expressed at high concentrations in GH4C1 cells as measured with nicotine-displaceable [3H]methyllycaconitine (MLA) binding. The potency of GTS-21 (an alpha7 receptor agonist) to induce cell loss was similar in these cells to that seen in pheochromocytoma (PC12) cells expressing nine-times-lower receptor levels, suggesting that cytotoxicity was more dependent on agonist concentration than receptor density. Hippocampal transduction with rat alpha7 nicotinic receptors increased [3H]MLA binding in this region in wild type and alpha7 receptor-knockout (KO) mice without apparent cytotoxicity. No difference was observed in Kd values for MLA binding between endogenous and transgenic receptors. Single cell recordings demonstrated that dentate granule cells that normally have no alpha7 receptor response did so following alpha7 receptor gene delivery in wild type mice. Recovery of alpha7 function was also observed in stratum oriens and stratum radiatum neurons of KO mice following gene delivery. Wild type mice exhibited improved acquisition performance in the Morris water task 1 month after bilateral hippocampal transductions with the rat alpha7 receptor gene compared with green fluorescent protein-transduced controls. However, both groups reached similar training levels and there was no difference in subsequent probe performance. Finally, this gene delivery approach was used to test whether alpha7 receptors affect tau-phosphorylation. Chronic (i.e. 2 month but not 2 week) expression of high levels of alpha7 receptors in hippocampus increased AT8 staining characteristic of hyperphosphorylated tau in that region, indicating that endogenous agonist-mediated receptor activation may be able to modulate this process.

Aconitine↗
PubMed1999

Prenatal exposure to low concentrations of carbon monoxide alters habituation and non-spatial working memory in rat offspring.

Inhalation of low concentrations (75 and 150 ppm) of carbon monoxide (CO) by pregnant rats from days 0 to 20 of gestation leads to alterations in habituation and working memory in young adult male offspring subjected to the novel exploration object test. In particular, lack of habituation upon the second presentation of the objects and failure in the ability to discriminate between the novel and the familiar object were found in CO (75 and 150 ppm)-exposed offspring. These alterations were not accompanied by changes in spontaneous motor activity (open field test). The subtle behavioral deficits observed in the present study have been produced by prenatal exposure to CO levels resulting in maternal blood carboxyhaemoglobin (HbCO) concentrations equivalent to those observed in human cigarette smokers.

Animals↗
PubMed1997

Scopolamine impairs spatial working memory in the radial maze: an analysis by error type and arm choice.

The effects of scopolamine hydrobromide on performance in uninterrupted and delayed radial maze trials were studied in the rat. In addition to defining errors as incorrect arm entries, errors were defined by incorrect nose pokes in a food trough and were summed across the number of correct choices remaining. The average time elapsed from arm entry to nose poke was also calculated as a new measure of motivation and mobility. Working memory errors increased significantly following scopolamine injection in the uninterrupted trials and occurred significantly more often before the last correct choice. Errors in nonbaited arms during the last portion of a 3-h delay task increased significantly following scopolamine injection both before and after the first portion of the task and occurred more often before the last correct choice. However, nonbaited errors occurred more readily and at lower doses when scopolamine was injected 20 min before the onset of the task than when scopolamine was injected immediately after the completion of the first portion of the task. These data indicate that scopolamine affects current working memory and specifically affects acquisition more than consolidation of working memory.

Animals↗