Septal lesions impair the acquisition of a cued place navigation task: attentional or memory deficit?

Memory Recovery Effect of a New Bioactive Innovative Combination in Rats with Experimental Dementia

Alzheimer's disease manifests as a complex pathological condition, with neuroinflammation, oxidative stress and cholinergic dysfunction being a few of the many pathological changes. Due to the complexity of the disease, current therapeutic strategies aim at a multitargeted approach, often relying on a combination of substances with versatile and complementary effects. In the present study, a unique combination of α-lipoic acid, citicoline, extracts of leaves from olive tree and green tea, vitamin D3, selenium and an immune-supporting complex was tested in scopolamine-induced dementia in rats. Using behavioral and biochemical methods, we assessed the effects of the combination on learning and memory, and elucidated the mechanisms of these effects. Our results showed that, compared to its components, the experimental combination was most efficient in improving short- and long-term memory as assessed by the step-through method as well as spatial memory as assessed by T-maze and Barnes maze underlined by decreases in AChE activity (p < 0.05) and LPO (p < 0.001), increases in SOD activity in the cortex (p < 0.05) and increases in catalase (p < 0.05) and GPx (p < 0.01) activities and BDNF (p < 0.001) and pCREB (p < 0.05) levels in the hippocampus. No significant histopathological changes or blood parameter changes were detected, making the experimental combination an effective and safe candidate in a multitargeted treatment of AD.

Neuronal diversity and reciprocal connectivity between the vertebrate hippocampus and septum

A hallmark of the nervous system is the precision with which myriad cell types are integrated into functional networks that control complex behaviors. The limbic system governs evolutionarily conserved processes essential for survival. The septum and the hippocampus are central to the limbic system, and control not only emotion-related behaviors but also learning and memory. Here, we provide a developmental and evolutionary perspective of the hippocampus and septum and highlight the neuronal diversity and circuitry that connects these two central components of the limbic system. This article is categorized under: Nervous System Development > Vertebrates: Regional Development Nervous System Development > Vertebrates: General Principles Comparative Development and Evolution > Regulation of Organ Diversity.

Quantitative measurement of regional cerebral blood flow and oxygen metabolism in a rat model of cerebral hypoperfusion

This study was aimed at evaluating the regional changes in the cerebral metabolic rate of oxygen (CMRO₂) in relation to the cerebral blood flow (CBF) in the bilateral common carotid artery occlusion (BCAO) rat model. Ligation of the bilateral common carotid arteries (or a sham operation in control animals) was performed in 10-week-old male Wistar rats. O-15 PET images were acquired in the subacute phase (1 week after the surgery) and chronic phase (6 weeks after the surgery) with the animals under anesthesia, using a small-animal PET system and the O-15 gas steady-state inhalation method with arterial blood sampling developed in our previous study. Histopathological staining by Klüver-Barrera method and immunocytochemistry staining by glial fibrillary acidic protein were performed. Cognitive function was tested by using the apparatus of Y-maze. Significantly lower CBF and higher oxygen extraction fraction were observed in broad areas of the cerebrum in the subacute phase in the BCAO rats, with recovery in the chronic phase. A stable decrease of the CMRO₂ in the subacute phase of arterial occlusion and later was observed in the BCAO rat model, mainly in the anterior cerebral artery territory. Atrophy and rarefaction of corpus callosum were found in the BCAO in the chronic phase. Activity of astrocytes in the BCAO was prominent in the both phases. Working memory was impaired in the BCAO in the chronic phase. Regional changes in cerebral perfusion and oxygen metabolism in the subacute and chronic phases of arterial occlusion were clarified in a rat model of BCAO by quantitative O-15 PET based on the steady-state method.

NKX2-1 Is Required in the Embryonic Septum for Cholinergic System Development, Learning, and Memory

The transcription factor NKX2-1 is best known for its role in the specification of subsets of cortical, striatal, and pallidal neurons. We demonstrate through genetic fate mapping and intersectional focal septal deletion that NKX2-1 is selectively required in the embryonic septal neuroepithelium for the development of cholinergic septohippocampal projection neurons and large subsets of basal forebrain cholinergic neurons. In the absence of NKX2-1, these neurons fail to develop, causing alterations in hippocampal theta rhythms and severe deficiencies in learning and memory. Our results demonstrate that learning and memory are dependent on NKX2-1 function in the embryonic septum and suggest that cognitive deficiencies that are sometimes associated with pathogenic mutations in NKX2-1 in humans may be a direct consequence of loss of NKX2-1 function.

Acute oral administration of low doses of methylphenidate targets calretinin neurons in the rat septal area

Methylphenidate (MPD) is a commonly administered drug to treat children suffering from attention deficit hyperactivity disorder (ADHD). Alterations in septal driven hippocampal theta rhythm may underlie attention deficits observed in these patients. Amongst others, the septo-hippocampal connections have long been acknowledged to be important in preserving hippocampal function. Thus, we wanted to ascertain if MPD administration, which improves attention in patients, could affect septal areas connecting with hippocampus. We used low and orally administered MPD doses (1.3, 2.7 and 5 mg/Kg) to rats what mimics the dosage range in humans. In our model, we observed no effect when using 1.3 mg/Kg MPD; whereas 2.7 and 5 mg/Kg induced a significant increase in c-fos expression specifically in the medial septum (MS), an area intimately connected to the hippocampus. We analyzed dopaminergic areas such as nucleus accumbens and striatum, and found that only 5 mg/Kg induced c-fos levels increase. In these areas tyrosine hydroxylase correlated well with c-fos staining, whereas in the MS the sparse tyrosine hydroxylase fibers did not overlap with c-fos positive neurons. Double immunofluorescence of c-fos with neuronal markers in the septal area revealed that co-localization with choline acethyl transferase, parvalbumin, and calbindin with c-fos did not change with MPD treatment; whereas, calretinin and c-fos double labeled neurons increased after MPD administration. Altogether, these results suggest that low and acute doses of methylphenidate primary target specific populations of caltretinin medial septal neurons.

Impairment of the septal cholinergic neurons in MPTP-treated A30P α-synuclein mice

Dementia in Parkinson's disease (PDD) and dementia with Lewy bodies (DLB) are characterized by loss of acetylcholine (ACh) from cortical areas. Clinical studies report positive effects of acetylcholine esterase (AChE) inhibitors in PDD and dementia with Lewy bodies. We here report that the number of neurons expressing a cholinergic marker in the medial septum-diagonal band of Broca complex decreases in A30P α-synuclein-expressing mice during aging, paralleled by a lower AChE fiber density in the dentate gyrus and in the hippocampal CA1 field. After inducing dopamine depletion by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP), no acute but a delayed loss of cholinergic neurons and AChE-positive fibers was observed, which was attenuated by L-3,4-dihydroxyphenylalanine (DOPA) treatment. Expression of nerve growth factor (NGF) and tyrosine receptor kinase A (TrkA) genes was upregulated in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride-treated wild type mice, but not in A30P α-synuclein expressing animals. In contrast, upregulation of sortilin and p75(NTR) genes was found in the A30P α-synuclein-expressing mice. These results suggest that dopamine deficiency may contribute to the impairment of the septohippocampal system in patients with PDD and that L-3,4-dihydroxyphenylalanine may not only result in symptomatic treatment of the akinetic-rigid syndrome but may also alleviate the degeneration of basal forebrain cholinergic system and the cognitive decline.

Bidirectional interactions between circadian entrainment and cognitive performance

Circadian rhythms influence a variety of physiological and behavioral processes; however, little is known about how circadian rhythms interact with the organisms' ability to acquire and retain information about their environment. These experiments tested whether rats trained outside their endogenous active period demonstrate the same rate of acquisition, daily performance, and remote memory ability as their nocturnally trained counterparts in tasks of sustained attention and spatial memory. Furthermore, we explored how daily task training influenced circadian patterns of activity. We found that rats demonstrate better acquisition and performance on an operant task requiring attentional effort when trained during the dark-phase. Time of day did not affect acquisition or performance on the Morris water maze; however, when animals were retested 2 wk after their last day of training, they showed better remote memory if training originally occurred during the dark-phase. Finally, attentional, but not spatial, task performance during the light-phase promotes a shift toward diurnality and the synchronization of activity to the time of daily training; this shift was most robust when the demands on the cognitive control of attention were highest. Our findings support a theory of bidirectional interactions between cognitive performance and circadian processes and are consistent with the view that the circadian abnormalities associated with shift-work, aging, and neuropsychiatric illnesses may contribute to the deleterious effects on cognition often present in these populations. Furthermore, these findings suggest that time of day should be an important consideration for a variety of cognitive tasks principally used in psychological and neuroscience research.

Direct gene transfer to the CNS prevents emergence of neurologic disease in a murine model of mucopolysaccharidosis type I

The mucopolysaccharidoses (MPSs) are a group of 11 storage diseases caused by disruptions in glycosaminoglycan (GAG) catabolism, leading to their accumulation in lysosomes. Resultant multisystemic disease is manifested by growth delay, hepatosplenomegaly, skeletal dysplasias, cardiopulmonary obstruction, and, in severe MPS I, II, III, and VII, progressive neurocognitive decline. Some MPSs are treated by allogeneic hematopoietic stem cell transplantation (HSCT) and/or recombinant enzyme replacement therapy (ERT), but effectiveness is limited by central nervous system (CNS) access across the blood-brain barrier. To provide a high level of gene product to the CNS, we tested neonatal intracerebroventricular (ICV) infusion of an adeno-associated virus (AAV) serotype 8 vector transducing the human α-L-iduronidase gene in MPS I mice. Supranormal levels of iduronidase activity in the brain (including 40× normal levels in the hippocampus) were associated with transduction of neurons in motor and limbic areas identifiable by immunofluorescence staining. The treatment prevented accumulation of GAG and GM3 ganglioside storage materials and emergence of neurocognitive dysfunction in a modified Morris water maze test. The results suggest the potential of improved outcome for MPSs and other neurological diseases when a high level of gene expression can be achieved by direct, early administration of vector to the CNS.

Consciousness and epilepsy: why are complex-partial seizures complex?

Why do complex-partial seizures in temporal lobe epilepsy (TLE) cause a loss of consciousness? Abnormal function of the medial temporal lobe is expected to cause memory loss, but it is unclear why profoundly impaired consciousness is so common in temporal lobe seizures. Recent exciting advances in behavioral, electrophysiological, and neuroimaging techniques spanning both human patients and animal models may allow new insights into this old question. While behavioral automatisms are often associated with diminished consciousness during temporal lobe seizures, impaired consciousness without ictal motor activity has also been described. Some have argued that electrographic lateralization of seizure activity to the left temporal lobe is most likely to cause impaired consciousness, but the evidence remains equivocal. Other data correlates ictal consciousness in TLE with bilateral temporal lobe involvement of seizure spiking. Nevertheless, it remains unclear why bilateral temporal seizures should impair responsiveness. Recent evidence has shown that impaired consciousness during temporal lobe seizures is correlated with large-amplitude slow EEG activity and neuroimaging signal decreases in the frontal and parietal association cortices. This abnormal decreased function in the neocortex contrasts with fast polyspike activity and elevated cerebral blood flow in limbic and other subcortical structures ictally. Our laboratory has thus proposed the "network inhibition hypothesis," in which seizure activity propagates to subcortical regions necessary for cortical activation, allowing the cortex to descend into an inhibited state of unconsciousness during complex-partial temporal lobe seizures. Supporting this hypothesis, recent rat studies during partial limbic seizures have shown that behavioral arrest is associated with frontal cortical slow waves, decreased neuronal firing, and hypometabolism. Animal studies further demonstrate that cortical deactivation and behavioral changes depend on seizure spread to subcortical structures including the lateral septum. Understanding the contributions of network inhibition to impaired consciousness in TLE is an important goal, as recurrent limbic seizures often result in cortical dysfunction during and between epileptic events that adversely affects patients' quality of life.

Remodeling of hippocampal mossy fibers is selectively induced seven days after the acquisition of a spatial but not a cued reference memory task

Relating storage of specific information to a particular neuromorphological change is difficult because behavioral performance factors are not readily disambiguated from underlying cognitive processes. This issue is addressed here by demonstrating robust reorganization of the hippocampal mossy fiber terminal field (MFTF) when adult rats learn the location of a hidden platform but not when rats learn to locate a visible platform. Because the latter task requires essentially the same behavioral performance as the former, the observed MFTF growth is seen as the consequence of specific input-dependent hippocampal activity patterns selectively generated by processing of extramaze but not intramaze cues. Successful performance on the hidden platform task requires formation of spatial memory. Increased MFTFs in hidden platform-trained rats are observed 7 d but not 2 d after training nor in swim controls. These results suggest that structural plasticity of the mossy fiber:CA3 circuit may contribute to the maintenance of long-lasting memory but not to the initial storage of the spatial context.

Methanesulfonyl fluoride, an acetylcholinesterase inhibitor, attenuates simple learning and memory deficits in ischemic rats

Methanesulfonyl fluoride (MSF), a highly selective CNS inhibitor of acetylcholinesterase, has been recently demonstrated to promote improvement in cognitive performance in patients with senile dementia of Alzheimer type. Because a similar cognitive impairment may accompany stroke, we investigated in the present study whether treatment with MSF could produce beneficial effects in adult rats subjected to an experimental stroke model. Sprague-Dawley rats received transient 60 min intraluminal occlusion of the right middle cerebral artery (MCAo) and were given i.p. injections of either MSF (1 mg/kg at 24 and 48 h post-MCAo and 0.3 mg/kg thereafter every other day) or the vehicle, peanut oil, for 4 weeks. Behavioral tests and biochemical assays were performed at 28 days post-surgery. MSF treatment produced about 90% inhibition of acetylcholinesterase in the brain. Ischemic animals that received the vehicle displayed significant elevated body swing biased activity (84.8 +/- 10%) and significantly prolonged acquisition (398 +/- 62 s) and shortened retention (79 +/- 26 s) of the passive avoidance task. Interestingly, while the ischemic animals that received the MSF exhibited elevated body swing biased activity (87.7 +/- 8%), they performed significantly better in the passive avoidance task (255 +/- 36 s and 145 +/- 18 s in acquisition and retention) than the vehicle-treated animals. Moreover, whereas brains from both groups of animals revealed similar extent and degree of cerebral infarction, the MSF-treated ischemic animals showed more intense immunoreactivity, as well as a significantly higher number (10-15% increase) of septal choline acetyltransferase-positive cells than the vehicle-treated ischemic animals. These results show that MSF, possibly by preserving a functional cholinergic system, attenuated stroke-induced deficits in a simple learning and memory task.

Role of glutamate receptors in nucleus accumbens core and shell in spatial behaviour of rats

The nucleus accumbens (NAC) is considered to be an important neural interface between corticolimbic and motor systems of the brain. Several studies have shown that the NAC is not only involved in motivation and reward-related processes but also in spatial behavior. We here investigated the involvement of different glutamate receptor subclasses within NAC core and shell subregions on behavior in a radial-maze. Rats were first trained in a four-arm-baited eight-arm radial maze task for baseline performance. Thereafter, the effects of microinjection of the nonselective glutamate receptor antagonist kynurenic acid (4.5 microg), the NMDA receptor antagonist 2-amino-5-phosphonopentanoic acid (1 microg) and the non-NMDA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (0.75 microg) in NAC core and shell were tested on reference memory errors (RME) and working memory errors (WME). Moreover, the choice pattern of entries and duration of arm-entries were evaluated. Microinjection of all drugs increased RME. Additionally, non-NMDA receptor blockade in NAC shell but not core increased WME. After microinjection of all drugs into NAC core and shell rats preferentially choose the arms next to the previously visited arm. This work shows that glutamate receptors in both NAC subregions are important for spatial behavior. The deficits seen after glutamate receptor blockade may not be working- or reference memory-related but caused by a switch from a memory-dependent allocentric strategy to an egocentric response strategy.

Differential pattern of cAMP response element-binding protein activation in the rat brain after conditioned aversion as a function of the associative process engaged: taste versus context association

Ample data indicate that cAMP-response element-binding protein (CREB) is essential for the formation of long-term memory in various species and learning systems. This implies that activated CREB could delineate neuronal circuits that subserve items in memory, while leaving open the possibility that the specifics of CREB activation itself contribute to the specificity of the internal representation encoded by the relevant circuit. We describe here the differential activation of CREB in the rat brain as a function of two related yet distinct forms of aversive conditioning: conditioned taste aversion (CTA) and conditioned context aversion (CCA). We found that CTA induces strong CREB activation in the insular cortex (IC) and the lateral septum (LS), but not in the parietal cortex (PC) and the medial septum (MS). In contrast, CCA results in strong activation in the PC and MS, but not in the IC and LS. These findings are congruent with a model that links differential pattern of activity within the LS and the MS with the acquisition of elemental versus contextual conditioning and, more generally, with the notion that CREB activation delineates learning-dependent circuits as a function of the type of cognitive process engaged.

Hippocampal serotonergic damage induced by MDMA (ecstasy): effects on spatial learning

3,4-Methylenedioxymethamphetamine (MDMA) use has been associated with a decline in various aspects of mnemonic function in humans. We therefore postulated that MDMA-induced damage of serotonergic nerve terminals would alter hippocampal processing. Seven days following treatment with MDMA (2 x 20 mg/kg sc, given 12 h apart), rat spatial learning and memory were tested utilizing the Morris water maze (MWM). No statistical differences were found in MWM platform acquisition latency or pathlength between controls and MDMA-treated animals. Probe trials revealed significantly higher proximity score averages and significantly reduced preference for the target quadrant in the MDMA-treated animals. MDMA treatment resulted in significant reduction (34%) in hippocampal serotonin (5-HT) levels 14 days after initial treatment. The findings of this study demonstrate that hippocampal serotonergic lesions induced by MDMA may be ostensibly linked to a reference memory deficit in rats tested with the MWM.

Differential involvement of NMDA and AMPA receptors within the nucleus accumbens in consolidation of information necessary for place navigation and guidance strategy of mice

Recent evidence now points to a role of glutamate transmission within the nucleus accumbens (Nacc) in spatial learning and memory. Unfortunately, the role of the distinct classes of glutamate receptors within this structure in mediating the different steps of the memorization process is not clear. The aim of this study therefore was to further investigate this issue, trying to assess the involvement of the two classes of glutamate receptors within the Nacc in consolidation of spatial information using an associative spatial task, the water maze. For this purpose, focal injections of the NMDA antagonist, AP-5, and of the AMPA antagonist, DNQX, have been performed immediately after the training phase, and mice have been tested for retention 24 h later. Two different versions of the water-maze task have been used: In the place version, animals could learn the position of the platform using visual distal cues, and in the cue version, the location of the platform was indicated by a single proximal cue. The results demonstrated that posttraining NMDA receptor blockade affects mice response in the place but not in the cue water-maze task. On the contrary, AMPA receptor blockade induced no effect in either version of the task. These data confirm a functional dissociation between glutamate receptors located in the Nacc in modulating spatial memory consolidation and indicate that they are specifically involved in consolidation of information necessary to acquire a place but not to a guidance strategy.

Olfactory and/or visual cues for spatial navigation through ontogeny: olfactory cues enable the use of visual cues

This study analyzed the spatial memory capacities of rats in darkness with visual and/or olfactory cues through ontogeny. Tests were conducted with the homing board, where rats had to find the correct escape hole. Four age groups (24 days, 48 days, 3-6 months, and 12 months) were trained in 3 conditions: (a) 3 identical light cues; (b) 5 different olfactory cues; and (c) both types of cues, followed by removal of the olfactory cues. Results indicate that immature rats first take into account olfactory information but are unable to orient with only the help of discrete visual cues. Olfaction enables the use of visual information by 48-day-old rats. Visual information predominantly supports spatial cognition in adult and 12-month-old rats. Results point out cooperation between vision and olfaction for place navigation during ontogeny in rats.

Unpacking the cognitive map: the parallel map theory of hippocampal function

In the parallel map theory, the hippocampus encodes space with 2 mapping systems. The bearing map is constructed primarily in the dentate gyrus from directional cues such as stimulus gradients. The sketch map is constructed within the hippocampus proper from positional cues. The integrated map emerges when data from the bearing and sketch maps are combined. Because the component maps work in parallel, the impairment of one can reveal residual learning by the other. Such parallel function may explain paradoxes of spatial learning, such as learning after partial hippocampal lesions, taxonomic and sex differences in spatial learning, and the function of hippocampal neurogenesis. By integrating evidence from physiology to phylogeny, the parallel map theory offers a unified explanation for hippocampal function.

Behavioral characterization of the Tg2576 transgenic model of Alzheimer's disease through 19 months

Behavioral characterization of Alzheimer's disease (AD) transgenic models over multiple time points during aging has been largely inadequate, usually being limited to one or two cognitive-based tasks. In this context, the present study utilized a comprehensive 6-week behavioral battery to characterize sensorimotor and cognitive performance of Tg2576 AD transgenic (Tg+) mice and nontransgenic (Tg-) controls aged 3, 9, 14, and 19 months. Compared collectively to Tg- mice over all four time points, Tg+ mice were impaired in Y-maze spontaneous alternation, visible platform recognition, and several sensorimotor tasks; Tg+ mice also showed an overall increase in activity measures. The deficits in visible platform became evident by 9 months of age, while those in sensorimotor tasks became clearly manifest by 14 months. Although the behavioral impairments exhibited by Tg+ mice were usually progressive through 19 months, Tg- animals also showed similar progressive decline in the same behavioral measures; thus, no task revealed a progressive behavioral decline exclusive to Tg+ mice. Moreover, although the 6-week behavioral battery included six cognitively based tasks (i.e., Y-maze, visible platform, Morris water maze, circular platform, passive avoidance, and active avoidance), behavioral analysis through 19 months revealed Tg+ mice to be impaired in only the Y-maze and visible platform tasks. Consequently, Tg2576 mice do not exhibit widespread, profound cognitive impairment, even into old age. This may reflect their predominant C57BL/6 background and an apparent inability of the mutant transgene to profoundly alter performance therein.

Perinatal choline treatment modifies the effects of a visuo-spatial attractive cue upon spatial memory in naive adult rats

The improvement in memory functions by choline supplementation is hypothesized to be due to increased synthesis and release of acetylcholine in the brain. We have found previously that combined pre- and postnatal choline supplementation results in long-lasting facilitation of spatial memory in juvenile rats when training was conducted in presence of a local salient cue. The present work aims to analyze the effects of peri- and postnatal choline supplementation on spatial abilities of naive adult rats. Treated rats were trained in various cued procedures of the Morris navigation task of 5 months of age. The treatment had a specific effect of reducing the escape latency of the rats when the platform was at a fixed location in space and indicated by a suspended cue. This effect was associated with an improved spatial memory when the cue and the platform were removed. In this condition, the control rats showed impaired spatial discrimination following the removal of the target cue, most likely due to an overshadowing of the distant environmental cues. This impairment was not observed in the treated rats. Further training with the suspended cue at unpredictable places in the pool revealed longer escape latencies in the control than in the treated rats suggesting that this procedure induced a selective perturbation of the normal but not of the treated rats. A special probe trial with the cue at an irrelevant location and no escape platform revealed a significant bias of the control rats towards the cue, but in treated rats towards the uncued spatial escape position. This behavioral dissociation suggests that a salient cue associated with the target induces an alternative "non spatial" guidance strategy in normal rats, with the risk of overshadowing attention towards more distant spatial cues. As a consequence, the improved escape in the presence of the cue in the treated rats is associated with a stronger memory of the spatial position following disappearance of the cue. This and previous observations suggest that a specific spatial attentional process relies on the buffering of highly salient visual cues to facilitate integration of their relative position in the environment.

Differential effects of PACAP-38 on synaptic responses in rat hippocampal CA1 region

Pituitary adenylate cyclase-activating polypeptide (PACAP-38) is a member of the vasointestinal polypeptide (VIP)/secretin/glucagon family of neuropeptides for which neuroregulatory functions have been postulated. PACAP-38 receptors are expressed in different brain regions, including hippocampus. In this study, we examined the dose-dependent effects of PACAP-38 on the excitatory postsynaptic field potential (fEPSP) evoked at the Schaffer collateral-CA1 synapse in rat hippocampal slices. Bath application of low dose (0.05 nM) of PACAP-38 induced long-lasting facilitation of the fEPSP. This enhancement was blocked by the cholinergic receptor antagonist atropine and partially by the NMDA receptor antagonist 2-amino-5-phosphonovalerate (APV) and therefore, shares a common mechanism with LTP. In contrast, a high dose (1 microM) of PACAP-38 induced a persistent depression of the fEPSP that was not blocked by antagonists of cholinergic receptors (i.e., atropine and mecamylamine), adenosine receptors (i.e., DCPCX), or glutamatergic NMDA receptors (APV). Intermediate doses (0.1-0.5 microM) of PACAP-38 produced an initial decrease of the fEPSP followed by an enhancement. This decrease was not blocked by atropine whereas the facilitation was. These results show that PACAP-38 modulates CA1 synaptic transmission in a dose-dependent manner and that the peptide interacts with cholinergic and glutamatergic systems.

Applications of the Morris water maze in the study of learning and memory

The Morris water maze (MWM) was described 20 years ago as a device to investigate spatial learning and memory in laboratory rats. In the meanwhile, it has become one of the most frequently used laboratory tools in behavioral neuroscience. Many methodological variations of the MWM task have been and are being used by research groups in many different applications. However, researchers have become increasingly aware that MWM performance is influenced by factors such as apparatus or training procedure as well as by the characteristics of the experimental animals (sex, species/strain, age, nutritional state, exposure to stress or infection). Lesions in distinct brain regions like hippocampus, striatum, basal forebrain, cerebellum and cerebral cortex were shown to impair MWM performance, but disconnecting rather than destroying brain regions relevant for spatial learning may impair MWM performance as well. Spatial learning in general and MWM performance in particular appear to depend upon the coordinated action of different brain regions and neurotransmitter systems constituting a functionally integrated neural network. Finally, the MWM task has often been used in the validation of rodent models for neurocognitive disorders and the evaluation of possible neurocognitive treatments. Through its many applications, MWM testing gained a position at the very core of contemporary neuroscience research.

Auditory cues support place navigation in rats when associated with a visual cue

Rats, like other crepuscular animals, have excellent auditory capacities and they discriminate well between different sounds [Heffner HE, Heffner RS, Hearing in two cricetid rodents: wood rats (Neotoma floridana) and grasshopper mouse (Onychomys leucogaster). J Comp Psychol 1985;99(3):275-88]. However, most experimental literature concerning spatial orientation almost exclusively emphasizes the use of visual landmarks [Cressant A, Muller RU, Poucet B. Failure of centrally placed objects to control the firing fields of hippocampal place cells. J Neurosci 1997;17(7):2531-42; and Goodridge JP, Taube JS. Preferential use of the landmark navigational system by head direction cells in rats. Behav Neurosci 1995;109(1):49-61]. To address the important issue of whether rats are able to achieve a place navigation task relative to auditory beacons, we designed a place learning task in the water maze. We controlled cue availability by conducting the experiment in total darkness. Three auditory cues did not allow place navigation whereas three visual cues in the same positions did support place navigation. One auditory beacon directly associated with the goal location did not support taxon navigation (a beacon strategy allowing the animal to find the goal just by swimming toward the cue). Replacing the auditory beacons by one single visual beacon did support taxon navigation. A multimodal configuration of two auditory cues and one visual cue allowed correct place navigation. The deletion of the two auditory or of the one visual cue did disrupt the spatial performance. Thus rats can combine information from different sensory modalities to achieve a place navigation task. In particular, auditory cues support place navigation when associated with a visual one.

PACAP-38 enhances excitatory synaptic transmission in the rat hippocampal CA1 region

Specific receptors for pituitary adenylate cyclase-activating polypeptide (PACAP), a novel peptide with neuroregulatory and neurotrophic functions, have been identified recently in different brain regions, including the hippocampus. In this study, we examined the effects of PACAP-38 on the excitatory postsynaptic field potentials (fEPSPs) evoked at the Schaffer collateral-CA1 synapses. Brief bath application of PACAP-38 (0.05 nM) induced a long-lasting facilitation of the basal transmission. Enhancement of this response was occluded in part by previous high-frequency-induced long-term potentiation (LTP). PACAP-38 did not significantly alter the paired-pulse facilitation (PPF). PACAP-38 has been shown to have a presynaptic effect on the septohippocampal cholinergic terminals, which results in an increase in basal acetylcholine (ACh) release. To assess whether the PACAP-38 enhancement of CA1 synapses was related to the activation of the cholinergic system we examined the effect of this peptide in the presence of atropine, a muscarinic receptor antagonist. The enhancement of the fEPSPs by PACAP-38 was blocked by bath application of atropine. These results show that PACAP-38 induces facilitation of hippocampal synaptic transmission through activation of the cholinergic system via the muscarinic receptors.

Postnatal intracerebroventricular administrations of NGF alter spatial memory in adulthood

The present work assessed the effects of intracerebroventricular injections (2x5 mg/2.5 ml) of recombined human nerve growth factor (rhNGF) at postnatal days 2 and 3 upon the development of spatial learning capacities in rats. The treated rats were trained at the age of 22 days to escape onto an invisible platform at a fixed position in space in a Morris navigation task. For half of the subjects, the training position was also cued, a procedure aimed at facilitating escape and reducing attention to the distant spatial cues. At the age of 2 months all the rats were retrained in the same task. Treatment effects were found in both immature and adult rats. The injection of NGF induced a slight alteration of the immature rats' performance. In contrast, a marked impairment of spatial abilities was shown in the 2-month-old rats. The most consistent effects were a significant increase in the escape latency and a decrease bias towards the training platform area during probe trials. The reduction of spatial memory was particularly marked if the subjects had been trained in a cued condition. Taken together, these experiments reveal that an acute pharmacological treatment that leads to transient modifications during early development might induce a behavioural change long after treatment. Thus, the development and the maintenance of an accurate spatial representation are tightly related to the development of brain structures that could be altered by precocious NGF administrations.

Enhanced visuospatial memory following intracerebroventricular administration of nerve growth factor

The present work assessed the effects of intracerebroventricular injections of rh recombined human nerve growth factor (rh NGF) (5 micrograms/2.5 microl) at postnatal days 12 and 13 upon the development of spatial learning capacities. The treated rats were trained at the age of 22 days to escape onto an invisible platform at a fixed position in space in a Morris navigation task. For half of the subjects, the training position was also cued, a procedure aimed at facilitating escape and at reducing attention to the distant spatial cues. Later, at the age of 6 months, all the rats were trained in a radial-arm maze task. Treatment effects were found in both immature and adult rats. The injection of NGF improved the performance in the Morris navigation task in both training conditions. There was a significant reduction in the escape latency and an increased bias toward the training platform quadrant during probe trials. The most consistent effect was the precocious development of an adult-like spatial memory. In the radial-arm maze, the NGF-treated rats made significantly fewer reentries than vehicle rats and this effect was particularly marked in the treated female rats. Taken together, these experiments reveal that the development and the maintenance of an accurate spatial representation are tightly related to the development of brain structures facilitated by the action of NGF. Moreover, these experiments demonstrate that an acute pharmacological treatment that leads to a transient modification in the choline acetyltransferase activity can induce a behavioral change long after the treatment.

Excitotoxic septal lesions result in spatial memory deficits and altered flexibility of hippocampal single-unit representations

The septal nuclei are reciprocally connected with the hippocampal formation and contribute importantly to spatial and memory processing. Using excitotoxic lesions of the septal area, we investigated whether neurodegeneration in subcortical projections to hippocampus can compromise flexible information processing by hippocampal single units. In agreement with the mild effects of excitotoxic septal lesions on hippocampal physiology compared with fimbria-fornix lesions and septal inactivation, we observed limited lesion effects on single-unit activity. The location specificity of hippocampal complex spike cells remained unchanged, but a less reliable location-dependent discharge was observed in experimental animals with a pronounced postoperative working memory deficit. Testing in the absence of ambient illumination and in a new environment revealed that the spatial correlates of complex spike cells in lesioned animals may rely on a more limited set of sensory cues. Altered sensory cues resulted in a significantly different response pattern between the control and lesion group in the new environment, a situation that normally results in place field reorganization. Such a group difference was not observed during dark testing, a condition in which place field reorganization is less prominent. A contribution of hippocampal interneurons to the observed alterations in the spatial properties of the principal cells was suggested by decreased theta modulation in the lesioned group. Because excitotoxic lesions result in memory deficits that resemble age-related memory problems in the absence of age-related degenerative processes, we suggest that septal neurodegeneration could directly contribute to those behavioral changes with advanced age that correlate with functional alterations in the hippocampal formation.