Neonatal γ-Ray Irradiation Impairs Learning and Memory of an Olfactory Associative Task in Adult Rats

Adult neonatally γ-irradiated rats were compared with control animals in a non-spatial olfactory associative task using two different procedures. Irradiation induced a clear reduction in the total mean area of the olfactory bulbs and hippocampus but not of the orbital prefrontal cortex, diagonal band and cell layers of the entorhinal and piriform cortex. The γ-irradiation affected the granule cells of the olfactory bulbs and differentially altered the cell layers of the subfields of the ammonic fields and the dorsal and ventral blades of the dentate gyrus. In the CA1 ammonic field, dorsal and ventral blades of the dentate gyrus, the cellular loss was significant in comparison with control adult rats. The behavioural data indicated that irradiated rats were deeply disturbed in learning the odour-reward association, and substantially impaired in a reversal experiment, but not in the discrimination of the odours per se. The cellular loss in the olfactory bulbs, in the CA1 and in the ventral blade of the gyrus dentatus was positively correlated with the deficit in behavioural performance. The data support the findings that the hippocampal system participates in the odour-reward associations and facilitates the long-term storage of associations after learning is achieved in this olfactory associative task.     

Neuron-Specific Expression of Tomosyn1 in the Mouse Hippocampal Dentate Gyrus Impairs Spatial Learning and Memory

Tomosyn, a syntaxin-binding protein, is known to inhibit vesicle priming and synaptic transmission via interference with the formation of SNARE complexes. Using a lentiviral vector, we specifically overexpressed tomosyn1 in hippocampal dentate gyrus neurons in adult mice. Mice were then subjected to spatial learning and memory tasks and electrophysiological measurements from hippocampal slices. Tomosyn1-overexpression significantly impaired hippocampus-dependent spatial memory while tested in the Morris water maze. Further, tomosyn1-overexpressing mice utilize swimming strategies of lesser cognitive ability in the Morris water maze compared with control mice. Electrophysiological measurements at mossy fiber-CA3 synapses revealed impaired paired-pulse facilitation in the mossy fiber of tomosyn1-overexpressing mice. This study provides evidence for novel roles for tomosyn1 in hippocampus-dependent spatial learning and memory, potentially via decreased synaptic transmission in mossy fiber-CA3 synapses. Moreover, it provides new insight regarding the role of the hippocampal dentate gyrus and mossy fiber-CA3 synapses in swimming strategy preference, and in learning and memory.     

Altered Heterosynaptic Plasticity Impairs Visual Discrimination Learning in Adenosine A1 Receptor Knock-Out Mice

Theoretical and modeling studies demonstrate that heterosynaptic plasticity—changes at synapses inactive during induction—facilitates fine-grained discriminative learning in Hebbian-type systems, and helps to achieve a robust ability for repetitive learning. A dearth of tools for selective manipulation has hindered experimental analysis of the proposed role of heterosynaptic plasticity in behavior. Here we circumvent this obstacle by testing specific predictions about the behavioral consequences of the impairment of heterosynaptic plasticity by experimental manipulations to adenosine A1 receptors (A1Rs). Our prior work demonstrated that the blockade of adenosine A1 receptors impairs heterosynaptic plasticity in brain slices and, when implemented in computer models, selectively impairs repetitive learning on sequential tasks. Based on this work, we predict that A1R knock-out (KO) mice will express (1) impairment of heterosynaptic plasticity and (2) behavioral deficits in learning on sequential tasks. Using electrophysiological experiments in slices and behavioral testing of animals of both sexes, we show that, compared with wild-type controls, A1R KO mice have impaired synaptic plasticity in visual cortex neurons, coupled with significant deficits in visual discrimination learning. Deficits in A1R knockouts were seen specifically during relearning, becoming progressively more apparent with learning on sequential visual discrimination tasks of increasing complexity. These behavioral results confirm our model predictions and provide the first experimental evidence for a proposed role of heterosynaptic plasticity in organism-level learning. Moreover, these results identify heterosynaptic plasticity as a new potential target for interventions that may help to enhance new learning on a background of existing memories.SIGNIFICANCE STATEMENT Understanding how interacting forms of synaptic plasticity mediate learning is fundamental for neuroscience. Theory and modeling revealed that, in addition to Hebbian-type associative plasticity, heterosynaptic changes at synapses that were not active during induction are necessary for stable system operation and fine-grained discrimination learning. However, lacking tools for selective manipulation prevented behavioral analysis of heterosynaptic plasticity. Here we circumvent this barrier: from our prior experimental and computational work we predict differential behavioral consequences of the impairment of Hebbian-type versus heterosynaptic plasticity. We show that, in adenosine A1 receptor knock-out mice, impaired synaptic plasticity in visual cortex neurons is coupled with specific deficits in learning sequential, increasingly complex visual discrimination tasks. This provides the first evidence linking heterosynaptic plasticity to organism-level learning.     

RVG-Mediated Calpain2 Gene Silencing in the Brain Impairs Learning and Memory

In the central nervous system, two calpain isoforms are highly expressed: calpain1 and calpain2. Here, we show for the first time that activation of the calpain isoform, calpain2, is a necessary event in hippocampal synaptic plasticity and in learning and memory. We developed a fluorescence resonance energy transfer–based animal model to monitor in vivo calpain activation in single cells and in real time. Additionally, utilizing a novel rabies virus glycoprotein-chimeric peptide, which enabled the transvascular delivery of small interfering RNA to the brain against calpain2, we down-regulated the calpain2 isoform in vivo. Calpain2 gene silencing eliminated long-term potentiation and impaired learning and memory. Our results not only identify the calpain2 isoform as a critical mediator in learning and memory but also highlight an innovative, highly efficient calpain2-targeting peptide capable of isoform-specific gene silencing in the brain. We anticipate these innovative technologies and our better understanding of the calpain machinery, particularly of the calpain2 isoform, will have substantial influence on future translational studies, attracting considerable interest in the use of calpain models and calpain-specific inhibitors in the development of therapeutics.     

Formaldehyde Impairs Learning and Memory Involving the Disturbance of Hydrogen Sulfide Generation in the Hippocampus of Rats

Formaldehyde (FA), a well-known indoor and outdoor pollutant, has been implicated as the responsible agent in the development of neurocognitive disorders. Hydrogen sulfide (H₂S), the third gasotransimitter, is an endogenous neuromodulator, which facilitates the induction of hippocampal long-term potentiation, involving the functions of learning and memory. In the present study, we analyzed the effects of intracerebroventricular injection of FA on the formation of learning and memory and the generation of endogenous H₂S in the hippocampus of rats. We found that the intracerebroventricular injection of FA in rats impairs the function of learning and memory in the Morris water maze and novel object recognition test and increases the formation of apoptosis and lipid peroxidation in the hippocampus. We also showed that FA exposure inhibits the expression of cystathionine β-synthase, the major enzyme responsible for endogenous H₂S generation in hippocampus and decreases the production of endogenous H₂S in hippocampus in rats. These results suggested that FA-disturbed generation of endogenous H₂S in hippocampus leads to the oxidative stress-mediated neuron damage, ultimately impairing the function of learning and memory. Our findings imply that the disturbance of endogenous H₂S generation in hippocampus is a potential contributing mechanism underling FA-caused learning and memory impairment.     

Somatostatin Neurons of the Bed Nucleus of Stria Terminalis Enhance Associative Fear Memory Consolidation in Mice

Excessive fear learning and generalized, extinction-resistant fear memories are core symptoms of anxiety and trauma-related disorders. Despite significant evidence from clinical studies reporting hyperactivity of the bed nucleus of stria terminalis (BNST) under these conditions, the role of BNST in fear learning and expression is still not clarified. Here, we tested how BNST modulates fear learning in male mice using a chemogenetic approach. Activation of GABAergic neurons of BNST during fear conditioning or memory consolidation resulted in enhanced cue-related fear recall. Importantly, BNST activation had no acute impact on fear expression during conditioning or recalls, but it enhanced cue-related fear recall subsequently, potentially via altered activity of downstream regions. Enhanced fear memory consolidation could be replicated by selectively activating somatostatin (SOM), but not corticotropin-releasing factor (CRF), neurons of the BNST, which was accompanied by increased fear generalization. Our findings suggest the significant modulation of fear memory strength by specific circuits of the BNST.SIGNIFICANCE STATEMENT The bed nucleus of stria terminalis (BNST) mediates different defensive behaviors, and its connections implicate its integrative modulatory role in fear memory formation; however, the involvement of BNST in fear learning has yet to be elucidated in detail. Our data highlight that BNST stimulation enhances fear memory formation without direct effects on fear expression. Our study identified somatostatin (SOM) cells within the extended amygdala as specific neurons promoting fear memory formation. These data underline the importance of anxiety circuits in maladaptive fear memory formation, indicating elevated BNST activity as a potential vulnerability factor to anxiety and trauma-related disorders.     

The L2/HNK-1 Carbohydrate is Carried by the Myelin Associated Glycoprotein and Sulphated Glucuronyl Glycolipids in Muscle but not Cutaneous Nerves of Adult Mice

We have previously shown that myelinating Schwann cells associated with motor, but not sensory, axons in peripheral nerves of adult mice express the L2/HNK-1 carbohydrate epitope. This carbohydrate structure carried by glycolipids and neural cell adhesion molecules has been suggested to specifically foster regrowth of motor as opposed to sensory axons after infliction of a lesion. To determine which molecular components may be the carriers of the L2 carbohydrate in motor axon-associated myelinating Schwann cells, we have isolated the purely sensory, cutaneous branch and the mixed sensory and motor muscle branch of the femoral nerve of adult mice, isolated the myelin fraction thereof and analysed the molecules expressing the L2 carbohydrate by several immunochemical methods. L2 immunoreactivity in myelin of the muscle branch was four to five times higher than that of the cutaneous branch. The 110 kDa L2-immunoreactive glycoprotein in myelin of the muscle branch, which is not L2-immunoreactive in the cutaneous branch, was identified as the myelin-associated glycoprotein by a combination of immunoprecipitation and Western blot analysis. Myelin extraction with organic solvents additionally revealed the two L2-carrying glycolipids, which amounted to-40 ng glycolipid/mg dry weight in myelin of the muscle branch, whereas no significant amounts of the L2 glycolipids were found in myelin of the cutaneous branch. These observations suggest an astonishing degree of differential regulation of carbohydrate-synthesizing activities in myelinating Schwann cells.     

Single Exposure to Cocaine Impairs Reinforcement Learning by Potentiating the Activity of Neurons in the Direct Striatal Pathway in Mice

Plasticity in the glutamatergic synapses on striatal medium spiny neurons (MSNs) is not only essential for behavioral adaptation but also extremely vulnerable to drugs of abuse. Modulation on these synapses by even a single exposure to an addictive drug may interfere with the plasticity required by behavioral learning and thus produce impairment. In the present work, we found that the negative reinforcement learning, escaping mild foot-shocks by correct nose-poking, was impaired by a single in vivo exposure to 20 mg/kg cocaine 24 h before the learning in mice. Either a single exposure to cocaine or reinforcement learning potentiates the glutamatergic synapses on MSNs expressing the striatal dopamine 1 (D1) receptor (D1-MSNs). However, 24 h after the cocaine exposure, the potentiation required for reinforcement learning was disrupted. Specific manipulation of the activity of striatal D1-MSNs in D1-cre mice demonstrated that activation of these MSNs impaired reinforcement learning in normal D1-cre mice, but inhibition of these neurons reversed the reinforcement learning impairment induced by cocaine. The results suggest that cocaine potentiates the activity of direct pathway neurons in the dorsomedial striatum and this potentiation might disrupt the potentiation produced during and required for reinforcement learning.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12264-021-00687-8.     

Mice deficient for the HNK-1 sulfotransferase show alterations in synaptic efficacy and spatial learning and memory

The HNK-1 carbohydrate structure, a sulfated glucuronyl-lactosaminyl residue carried by many neural recognition molecules, is involved in cell interactions during ontogenetic development and in synaptic plasticity in the adult. To characterize the functional role of the HNK-1 carbohydrate in vivo, we have generated mice deficient for the HNK-1 sulfotransferase (ST). The ST-/- allele is inherited with Mendelian frequencies, and the ST-/- mice are viable and fertile. The anatomy of all major brain areas appeared histologically normal. However, basal synaptic transmission in pyramidal cells in the CA1 region of the hippocampus was increased and long-term potentiation evoked by theta-burst stimulation was reduced in ST mutants. In the water maze, ST-/- mice showed an impaired long-term memory and a poorer spatial learning when a short inter-trial interval was used. These observations indicate an essential role for the sulfate group of the HNK-1 carbohydrate in synaptic plasticity of the hippocampus.     

阿尔茨海默病APPswe/PS1dE9双转基因型与野生型小鼠学习记忆能力的比较

目的：比较不同年龄段阿尔茨海默病（AD）APPswe/PS1dE9双转基因型与野生型小鼠的学习记忆能力。方法：C57BL/6J雌鼠与C3H/HeJ雄鼠交配产下F1代,再将F1代与3月龄的APPswe/PS1dE9双转基因型小鼠交配产下F2代。提取F2代小鼠鼠尾DNA,PCR扩增目的基因并鉴定。依据是否含APP和PS1基因分为转基因型组和野生型对照组,小鼠分别于6、8月龄行Morris水迷宫实验,11月龄行Y迷宫实验检测学习记忆能力。结果：繁育F2代小鼠33只,其中转基因型组18只,野生型对照组15只。6月龄转基因型与野生型小鼠定位航行实验潜伏期的差异无统计学意义,空间探索实验目标象限时间和路程百分比的差异无统计学意义（P〉0.05）。与8月龄野生型小鼠比较,转基因型小鼠定位航行实验第1天潜伏期延长（P〈0.05）。与11月龄野生型小鼠比较,转基因型小鼠达到学会标准的训练次数增加（P〈0.05）。结论：ADAPPswe/PS1dE9双转基因型与野生型小鼠比较,于11月龄时出现学习记忆能力障碍。     

Performance of PAC1-R Heterozygous Mice in Memory Tasks-II

An involvement of pituitary adenylate cyclase activating polypeptide-specific receptor type 1 (PAC1-R) in behavioral performance of retrieval of memory upon the stimulation of perception of sensory modality was investigated in mice. Eighteen heterozygous (-/+) transgenic mutant PAC1-R-deficient mice ((-/+) mice) and 18 wild-type (+/+) mice of littermates ((+/+) mice) as a control were used. No homozygous (-/-) transgenic mutant PAC1-R-deficit mouse was bred in our colony. It was observed that; (1) changing a single alley in the multiple mazes interfered with retrieval of memory in both (-/+) mice and (+/+) mice, and they made considerable errors; (2) a rotation of the multiple mazes for 180 degrees in relation to the geomagnetic field made also considerable errors, but in only (+/+) mice and not in (-/+) mice; and (3) an exposure for perception of fear signals made also considerable errors, but in only (+/+) mice and not in (-/+) mice. It is inferred that PAC1-R may play a gating role in passage permitting through perception of geomagnetic orientation and fear signals, but not perception of visual orientation, and it regulates behavioral performance in retrieval of memory in mice.     

Reduced Firing of Nucleus Accumbens Parvalbumin Interneurons Impairs Risk Avoidance in DISC1 Transgenic Mice

A strong animal survival instinct is to approach objects and situations that are of benefit and to avoid risk. In humans, a large proportion of mental disorders are accompanied by impairments in risk avoidance. One of the most important genes involved in mental disorders is disrupted-in-schizophrenia-1 (DISC1), and animal models in which this gene has some level of dysfunction show emotion-related impairments. However, it is not known whether DISC1 mouse models have an impairment in avoiding potential risks. In the present study, we used DISC1-N terminal truncation (DISC1-N^TM) mice to investigate risk avoidance and found that these mice were impaired in risk avoidance on the elevated plus maze (EPM) and showed reduced social preference in a three-chamber social interaction test. Following EPM tests, c-Fos expression levels indicated that the nucleus accumbens (NAc) was associated with risk-avoidance behavior in DISC1-N^TM mice. In addition, in vivo electrophysiological recordings following tamoxifen administration showed that the firing rates of fast-spiking neurons (FS) in the NAc were significantly lower in DISC1-N^TM mice than in wild-type (WT) mice. In addition, in vitro patch clamp recording revealed that the frequency of action potentials stimulated by current injection was lower in parvalbumin (PV) neurons in the NAc of DISC1-N^TM mice than in WT controls. The impairment of risk avoidance in DISC1-N^TM mice was rescued using optogenetic tools that activated NAc^PV neurons. Finally, inhibition of the activity of NAc^PV neurons in PV-Cre mice mimicked the risk-avoidance impairment found in DISC1-N^TM mice during tests on the elevated zero maze. Taken together, our findings confirm an impairment in risk avoidance in DISC1-N^TM mice and suggest that reduced excitability of NAc^PV neurons is responsible.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12264-021-00731-7.     

The L2/HNK-1 Carbohydrate Epitope is Involved in the Preferential Outgrowth of Motor Neurons on Ventral Roots and Motor Nerves

Based on the observation that in adult mice the carbohydrate epitope L2/HNK-1 is detectable on Schwann cells in ventral spinal roots, but only scarcely in dorsal roots (Martini et al., Dev. Biol., 129, 330 - 338, 1988), the possibility was investigated that the carbohydrate is involved in the outgrowth of regenerating motor neuron axons on peripheral nerve substrates expressing the epitope. To monitor whether the L2 carbohydrate remains present during the time periods in which regenerating axons penetrate the denervated distal nerve stumps, the expression of L2 in motor and sensory branches of the femoral nerve was investigated in normal animals and after a crush lesion. During the first two postoperative weeks, L2 immunoreactivity remained high in the myelinating Schwann cells of the motor branch, whereas L2 immunoreactivity was virtually absent in the sensory branch. In a first experimental approach, cryosections of ventral and dorsal spinal roots and of motor and sensory nerves of adult rats and mice were used as substrates for neurite outgrowth. Neurites of motor neurons from chicken embryos were approximately 35% longer after 30 h of maintenance on ventral roots than on dorsal roots. Neurites from sensory neurons had the same length on dorsal as on ventral motors and were as long as neurites from motor neurons grown on dorsal roots. L2 antibodies reduced neurite outgrowth of motor neurons on ventral roots but not on dorsal roots. Neurite outgrowth of sensory neurons on both roots was not altered by the antibodies. Neurite outgrowth of motor neurons on a mixture of the extracellular matrix glycoprotein laminin and the L2 carbohydrate-carrying glycolipid was significantly higher than on the laminin substrate mixture with GD1b ganglioside or sulphatide. L2 antibodies reduced neurite outgrowth of motor neurons by 50% on the L2 glycolipid, but not on GD1b or sulphatide. These observations indicate that the L2 carbohydrate promotes neurite outgrowth of motor neurons in vitro and may thus contribute to the preferential reinnervation of motor nerves by regenerating motor axons in vivo.     

A Single High Dose of Methamphetamine Reduces Monoamines and Impairs Egocentric and Allocentric Learning and Memory in Adult Male Rats

Methamphetamine (MA) alters dopamine markers and cognitive function in heavy users. In rodents, there are MA dosing regimens that induce concordant effects using repeated administration at spaced intervals. These regimens are effective but complicate experiments designed to disentangle the effects of the drug on different brain regions in relation to their cognitive effects because of treatment spacing. In an effort to simplify the model, we tested whether a single dose of MA could induce the same monoamine and cognitive effects as multiple, spaced dosing without affecting survival. Adult male Sprague-Dawley rats were treated with 40 mg/kg MA subcutaneously once and tested starting 2 weeks later. MA-treated rats showed deficits in egocentric navigation in Cincinnati water maze, in spatial navigation in the Morris water maze, and in choosing a consistent problem-solving strategy in the Star water maze when given the option to show a preference. MA-treated rats had persistent dopamine and serotonin reductions in the neostriatum and nucleus accumbens, and serotonin reductions in the hippocampus of the same magnitude as in repetitive treatment models. The data demonstrate that a single dose recapitulates the neurocognitive and monoamine effects of multiple-dose regimens, thereby simplifying the model of MA-induced neurotoxicity.     

Chronic Administration of Quinolinic Acid in the Rat Striatum Causes Spatial Learning Deficits in a Radial Arm Water Maze Task

Chronic intrastriatal administration of quinolinic acid (QA) in the rat produces a pattern of neurodegeneration similar to that seen in Huntington's disease (HD). Although these changes have been related to transient motor abnormalities, the effects of chronic QA administration on cognitive abilities have not been assessed. The present study investigated whether the striatal deterioration observed during chronic QA administration produces cognitive impairments in this animal model of HD by testing the effects of chronic administration of QA on spatial learning ability of rats in a radial arm water maze (RAWM) task. Rats were given bilateral implantation of a chronic dialysis probe apparatus which delivered either vehicle or QA (20 mM) into the striatum. Beginning 1 day after implantation, the rats were tested daily for 3 weeks in the RAWM. Nocturnal activity levels were also assessed at 1-, 3-, 5-, 7-, 14-, and 21-days following probe implantation. Results of behavioral testing indicated that chronic exposure to QA causes spatial learning deficits in the RAWM task with only a transient increase in activity levels. Collectively, these results suggest that chronic striatal exposure to QA mimics some aspects of the cognitive deficits observed in HD.     

Organic Anion Transporter 1 Deficiency Accelerates Learning and Memory Impairment in tg2576 Mice by Damaging Dendritic Spine Morphology and Activity

Journal of Molecular Neuroscience - To investigate whether and how organic anion transporter 1 (OAT1) is involved in the process of Alzheimer’s disease (AD), we crossbred OAT1 knockout mice...     

The Influence of the Stroop Interference Effect on an Event-based Prospective Memory Task in Alzheimer's Disease Patients

Background : Prospective memory is known as the memory of a plan to carry out an intended action in the future. Although it is associated with many activities in everyday life, to date there have been no well controlled laboratory studies of prospective memory in patients with Alzheimer's dementia (AD). In this study, we investigated the ability of prospective memory in AD subjects using an event-based prospective memory task in which prospective remembering is triggered by a specific external cue.
Methods : Using a personal computer, we conducted event-based prospective memory tasks embedded in the Stroop task. The concurrent cognitive task such as the Stroop task was called the ongoing task. In the event-based prospective memory task, subjects were required to react by pressing a mouse key whenever a stimulus during the Stroop task (identification of the name of a color printed in black, of the correct color of a colored circle, or the name of a color printed in an incorrect color) appeared in a larger-than-normal size. This target stimulus was designed to appear eight times in each condition, i.e., word condition, color condition, and incorrect-color condition, during the Stroop task.
Results : Normal elderly people showed good event-based prospective memory performance across all three conditions in the Stroop task. In contrast, AD subjects performed poorly in the event-based prospective memory task under the incorrect-color condition in the Stroop task.
Conclusion : This study indicated that an ongoing concurrent task with a high attention demand affects the performance of event-based prospective memory in AD subjects. The performance of event-based prospective memory in AD subjects was more sensitive to the Stroop interference effect observed in the ongoing task than in normal elderly people. The breakdown of this event-based prospective memory may reflect the limited attention capacity of AD subjects.     

Subchronic Administration of Haloperidol Influences the Functional Deficits of Postnatal Iron Administration in Mice

C57/BL6 mice were administered either 7.5 mg Fe (II)/ kg or vehicle (saline) postnatally on Days 10-12 after birth. From 64 days of age onwards for 24 days, groups of mice were administered either haloperidol (0.25 or 1 or 2 mg/kg, s.c.) or vehicle (Tween-80). Twenty-four hours after the final injection of either neuroleptic compound or vehicle, spontaneous motor activity was measured over a 60-min interval. Postnatal Fe (II)-treatment (7.5 mg/kg, postnatally) reduced motor activity parameters during the initial 20-min periods (0-20 and 20-40 min) and then induced hyperactivity during the final 20-min period over all three parameters of activity, confirming previous observations. Subchronic administration of haloperidol, at the 1 and 2 mg/kg doses, and to a lesser extent the 0.25 mg/kg dose, increased the levels of activity in all three motor activity parameters in postnatal iron-treated mice: locomotion (1st and 2nd 20 min periods), rearing (1st and 2nd 20 min periods) and total activity (1st 20 min period). All three doses of haloperidol abolished the later hyperactivity in iron-treated mice, with the exception of the 0.25 mg/kg dose with regard to rearing behaviour. Apomorphine (1 mg/kg, s.c.) -induced activity was elevated by postnatal iron administration and by subchronic administration of apomorphine at the higher dose levels. In the context of these and other observations, it is suggested that subchronic administration of haloperidol interacting with postnatal iron induces different expressions of dopamine neuron comorbidity underlying movement disorder.