Pretraining or previous non-spatial experience improves spatial learning in the Morris water maze of nucleus basalis lesioned rats

Impact of Chronic Oral Administration of Gold Nanoparticles on Cognitive Abilities of Mice

The influence of gold nanoparticles after their prolonged oral administration to mice (during pregnancy and lactation) on spatial memory and anxiety levels in offspring was investigated. Offspring were tested in the Morris water maze and in the elevated Plus-maze. The average specific mass content of gold which crossed the blood-brain barrier was measured using neutron activation analysis and constituted 3.8 ng/g for females and 1.1 ng/g for offspring. Experimental offspring showed no differences in spatial orientation and memory compared to the control, while their anxiety levels increased. Gold nanoparticles influenced the emotional state of mice exposed to nanoparticles during prenatal and early postnatal development, but not their cognitive abilities.

Comparative study of the neuroprotective and nootropic activities of the carboxylate and amide forms of the HLDF-6 peptide in animal models of Alzheimer's disease

A comparative study of the neuroprotective and nootropic activities of two pharmaceutical substances, the HLDF-6 peptide (HLDF-6-OH) and its amide form (HLDF-6-NH2), was conducted. The study was performed in male rats using two models of a neurodegenerative disorder. Cognitive deficit in rats was induced by injection of the beta-amyloid fragment 25-35 (βA 25-35) into the giant-cell nucleus basalis of Meynert or by coinjection of βA 25-35 and ibotenic acid into the hippocampus. To evaluate cognitive functions in animals, three tests were used: the novel object recognition test, the conditioned passive avoidance task and the Morris maze. Comparative analysis of the data demonstrated that the neuroprotective activity of HLDF-6-NH2, evaluated by improvement of cognitive functions in animals, surpassed that of the native HLDF-6-OH peptide. The greater cognitive/ behavioral effects can be attributed to improved kinetic properties of the amide form of the peptide, such as the character of biodegradation and the half-life time. The effects of HLDF-6-NH2 are comparable to, or exceed, those of the reference compounds. Importantly, HLDF-6-NH2 exerts its effects at much lower doses than the reference compounds.

Spatial memory alterations by activation of septal 5HT 1A receptors: no implication of cholinergic septohippocampal neurons

INTRODUCTION

In rats, activation of medial septum (MS) 5-HT(1A) receptors with the 5-HT(1A)/5-HT(7) receptor agonist 8-OH-DPAT disrupts encoding and consolidation, but not retrieval of a spatial memory in the water maze task. These findings might be explained by an action of 8-OH-DPAT on 5-HT(1A) receptors located on cholinergic neurons which the drug could transiently hyperpolarise. If so, selective damage of these neurons should mimic the effects of 8-OH-DPAT, or, at least, synergistically interfere with them.

METHODS

To test this hypothesis, rats were subjected to intraseptal infusions of 8-OH-DPAT (or phosphate-buffered saline) during acquisition of a water maze task before and/or after 192 IgG-saporin-induced MS cholinergic lesion (vs. sham-operated).

RESULTS

We confirmed that only pre-acquisition intraseptal 8-OH-DPAT infusions prevented learning and subsequent drug-free retrieval of the platform location in intact rats and found that (1) the cholinergic lesion did not prevent recall of the platform location, and (2) the impairing effects of 8-OH-DPAT were similar in sham-operated and lesioned rats, whether naïve or not, to the task before lesion surgery.

CONCLUSIONS

An action of 8-OH-DPAT on only MS cholinergic neurons is not sufficient to account for the drug-induced memory impairments. A concomitant 8-OH-DPAT-induced hyperpolarisation of cholinergic and/or GABAergic and/or glutamatergic neurons (intact rats), or of only GABAergic and/or glutamatergic ones after cholinergic lesion, might be necessary to obliterate task acquisition, confirming that, in the MS, (1) the three neuronal populations could cooperate to process hippocampal-dependent information, and (2) non-cholinergic septohippocampal neurons might be more important than cholinergic ones in serotonin-induced modulation of hippocampus-dependent memory processing.

Engagement of the PFC in consolidation and recall of recent spatial memory

The standard model of system consolidation proposes that memories are initially hippocampus dependent and become hippocampus independent over time. Previous studies have demonstrated the involvement of the medial prefrontal cortex (mPFC) in the retrieval of remote memories. The transformations required to make a memory undergo system's consolidation are thought to require synaptic plasticity. In this study, we investigated the participation of the mitogen-activated protein kinase (MAPK)/ERK pathway in acquisition, memory consolidation, and recent memory recall of the Morris water maze (MWM) task using a 1-d training protocol. To this end, bilateral injections of the MEK inhibitor U0126 into the rat mPFC were performed. The injection of the MEK inhibitor in the mPFC did not affect the acquisition of the MWM. However, MEK inhibitor resulted in impairments on recent memory retrieval either when applied at the end of the learning phase (memory consolidation) or prior to the retention test. The results strongly support the concept that recently acquired and consolidated spatial memories require the mPFC, and that local activation of the MAPK/ERK pathway in the mPFC is necessary for the consolidation and recall of recent memories.

Validation of a 2-day water maze protocol in mice

We present a 2-day water maze protocol that addresses some of potential confounds present in the water maze when using the aged subjects typical of studies of neurodegenerative disorders, such as Alzheimer's disease. This protocol is based on an initial series of training trials with a visible platform, followed by a memory test with a hidden platform 24h later. We validated this procedure using aged (15-18m) mice expressing three Alzheimer's disease-related transgenes, PS1(M146 V), APP(Swe), and tau(P301L). We also tested these triple transgenic mice (3xTG) and age and sex-matched wild-type (WT) in a behavioral battery consisting of tests of motor coordination (balance beam), spatial memory (object displacement task) visual acuity (novel object recognition task) and locomotor activity (open field). 3xTG mice had significantly longer escape latencies in the memory trial of the 2-day water maze test than WT and than their own baseline performance in the last visible platform trial. In addition, this protocol had improved sensitivity compared to a typical probe trial, since no significant differences between genotypes were evident in a probe trial conducted 24h after the final training trial. The 2-day procedure also resulted in good reliability between cohorts, and controlled for non-cognitive factors that can confound water maze assessments of memory, such as the significantly lower locomotor activity evident in the 3xTG mice. A further benefit of this method is that large numbers of animals can be tested in a short time.

Lesions to the nucleus basalis magnocellularis lower performance but do not block the retention of a previously acquired learning set

Rats were first trained to acquire an olfactory discrimination learning set (ODLS) on 40 olfactory-unique discrimination problems. Following acquisition of ODLS, animals were lesioned bilaterally in the nucleus basalis magnocellularis (nBM) using either quisqualic acid (QUIS) or 192 IgG-saporin (SAP). QUIS animals performed significantly worse than control animals following surgery and SAP animals performed transiently worse than control animals. Despite lowered performances, both QUIS and SAP animals performed significantly better than expected by chance on trial 2 indicating retention of the ODLS previously acquired. Implications for the role of the nBM in aspects of cognitive flexibility and its role in acquisition versus retention are discussed.

Neuroprotective effects of behavioural training and nicotine on age-related deficits in spatial learning

Studies in humans and animals show a clear decline in spatial memory with age and several approaches have been adopted to alleviate this impairment. The purpose of our review is to assess the studies that have suggested the possible neuroprotective actions of behavioural training and nicotine-applied both independently and in conjunction-on age-related deficits in spatial learning. Both spatial pretraining and nonspatial experiences influence an animal's performance in spatial tasks. In aged rats, the experience of training in the water maze task increases the number of newly generated neurons in the hippocampus. The neuroprotective effects of nicotine have been demonstrated in both in-vitro and in-vivo models, although the molecular mechanisms underlying these actions are not yet fully understood. It had been concluded in different studies that nicotine can improve, impair or have no effect on performance in the water maze. Neurobiological data also suggest an interaction between nicotine and prior experience in complex tasks, although few studies have raised the question of whether nicotine treatment and training in spatial tasks may contribute in an interactive manner to alleviate spatial cognition impairment associated with the ageing process. Different findings suggest that past experience could be a confounding variable in longitudinal studies that aim to evaluate the neuroprotective effects of nicotine on age-related deficits in spatial learning.