The puzzle of spontaneous alternation and inhibition of return: How they might fit together

Two isolated spatial phenomena share a similar "been there; done that" effect on spatial behavior. Originally discovered in rodent learning experiments, spontaneous alternation is a tendency for the organism to visit a different arm in a T-maze on subsequent trials. Originally discovered in human studies of attention, inhibition of return is a tendency for the organism to orient away from a previously attended location. Whereas spontaneous alternation was identified by O'Keefe & Nadel as dependent on an intact hippocampus, inhibition of return is dependent on neural structures that participate in oculomotor control (the superior colliculus, parietal and frontal cortex). Despite the isolated literatures, each phenomenon has been assumed to reflect a basic novelty-seeking process, avoiding places previously visited or locations attended. In this commentary, we explore and compare the behavioral manifestations and neural underpinnings of these two phenomena, and suggest what is still needed to determine whether they operate in parallel or serial.

Utilizing the Modified T-Maze to Assess Functional Memory Outcomes After Cardiac Arrest

BACKGROUND

Evaluating mild to moderate cognitive impairment in a global cerebral ischemia (i.e. cardiac arrest) model can be difficult due to poor locomotion after surgery. For example, rats who undergo surgical procedures and are subjected to the Morris water maze may not be able to swim, thus voiding the experiment. New Method: We established a modified behavioral spontaneous alternation T-maze test. The major advantage of the modified T-maze protocol is its relatively simple design that is powerful enough to assess functional learning/memory after ischemia. Additionally, the data analysis is simple and straightforward. We used the T-maze to determine the rats' learning/memory deficits both in the presence or absence of mild to moderate (6 min) asphyxial cardiac arrest (ACA). Rats have a natural tendency for exploration and will explore the alternate arms in the T-maze, whereas hippocampal-lesioned rats tend to adopt a side-preference resulting in decreased spontaneous alternation ratios, revealing the hippocampal-related functional learning/memory in the presence or absence of ACA.

RESULTS

ACA groups have higher side-preference ratios and lower alternations as compared to control. Comparison with Existing Method(s): The Morris water and Barnes maze are more prominent for assessing learning/memory function. However, the Morris water maze is more stressful than other mazes. The Barnes maze is widely used to measure reference (long-term) memory, while ACA-induced neurocognitive deficits are more closely related to working (short-term) memory.

CONCLUSIONS

We have developed a simple, yet effective strategy to delineate working (short-term) memory via the T-maze in our global cerebral ischemia model (ACA).

Antioxidant Treatment with N-acetyl Cysteine Prevents the Development of Cognitive and Social Behavioral Deficits that Result from Perinatal Ketamine Treatment

Alterations of the normal redox state can be found in all stages of schizophrenia, suggesting a key role for oxidative stress in the etiology and maintenance of the disease. Pharmacological blockade of N-methyl-D-aspartic acid (NMDA) receptors can disrupt natural antioxidant defense systems and induce schizophrenia-like behaviors in animals and healthy human subjects. Perinatal administration of the NMDA receptor (NMDAR) antagonist ketamine produces persistent behavioral deficits in adult mice which mimic a range of positive, negative, and cognitive symptoms that characterize schizophrenia. Here we tested whether antioxidant treatment with the glutathione (GSH) precursor N-acetyl-cysteine (NAC) can prevent the development of these behavioral deficits. On postnatal days (PND) 7, 9 and 11, we treated mice with subanesthetic doses (30 mg/kg) of ketamine or saline. Two groups (either ketamine or saline treated) also received NAC throughout development. In adult animals (PND 70-120) we then assessed behavioral alterations in a battery of cognitive and psychomotor tasks. Ketamine-treated animals showed deficits in a task of cognitive flexibility, abnormal patterns of spontaneous alternation, deficits in novel-object recognition, as well as social interaction. Developmental ketamine treatment also induced behavioral stereotypy in response to an acute amphetamine challenge, and it impaired sensorimotor gating, measured as reduced prepulse inhibition (PPI) of the startle response. All of these behavioral abnormalities were either prevented or strongly ameliorated by NAC co-treatment. These results suggest that oxidative stress is a major factor for the development of the ketamine-induced behavioral dysfunctions, and that restoring oxidative balance during the prodromal stage of schizophrenia might be able to ameliorate the development of several major symptoms of the disease.

Reentrainment Impairs Spatial Working Memory until Both Activity Onset and Offset Reentrain

Compression of the active phase (α) during reentrainment to phase-shifted light-dark (LD) cycles is a common feature of circadian systems, but its functional consequences have not been investigated. This study tested whether α compression in Siberian hamsters (Phodopus sungorus) impaired their spatial working memory as assessed by spontaneous alternation (SA) behavior in a T-maze. Animals were exposed to a 1- or 3-h phase delay of the LD cycle (16 h light/8 h dark). SA behavior was tested at 4 multiday intervals after the phase shift, and α was quantified for those days. All animals failed at the SA task while α was decompressing but recovered spatial memory ability once α returned to baseline levels. A second experiment exposed hamsters to a 2-h light pulse either early or late at night to compress α without phase-shifting the LD cycle. SA behavior was impaired until α decompressed to baseline levels. In a third experiment, α was compressed by changing photoperiod (LD 16:8, 18:6, 20:4) to see if absolute differences in α were related to spatial memory ability. Animals performed the SA task successfully in all 3 photoperiods. These data show that the dynamic process of α compression and decompression impairs spatial working memory and suggests that α modulation is a potential biomarker for assessing the impact of transmeridian flight or shift work on memory.

Involvement of Glutamate NMDA Receptors in the Acute, Long-Term, and Conditioned Effects of Amphetamine on Rat 50 kHz Ultrasonic Vocalizations

BACKGROUND

Rats emit 50 kHz ultrasonic vocalizations (USVs) in response to either natural or pharmacological pleasurable stimuli, and these USVs have emerged as a new behavioral measure for investigating the motivational properties of drugs. Earlier studies have indicated that activation of the dopaminergic system is critically involved in 50 kHz USV emissions. However, evidence also exists that non-dopaminergic neurotransmitters participate in this behavioral response.

METHODS

To ascertain whether glutamate transmission plays a role in 50 kHz USV emissions stimulated by amphetamine, rats received five amphetamine (1-2mg/kg, i.p.) administrations on alternate days in a test cage, either alone or combined with the glutamate N-methyl-D-aspartate receptor antagonist MK-801 (0.1-0.5mg/kg, i.p.). Seven days after treatment discontinuation, rats were re-exposed to the test cage to assess drug conditioning, and afterwards received a drug challenge. USVs and locomotor activity were evaluated, along with immunofluorescence for Zif-268 in various brain regions and spontaneous alternation in a Y maze.

RESULTS

Amphetamine-treated rats displayed higher 50 kHz USV emissions and locomotor activity than vehicle-treated rats, and emitted conditioned vocalizations on test cage re-exposure. Rats co-administered amphetamine and MK-801 displayed lower and dose-dependent 50 kHz USV emissions, but not lower locomotor activity, during repeated treatment and challenge, and scarce conditioned vocalization compared with amphetamine-treated rats. These effects were associated with lower levels of Zif-268 after amphetamine challenge and spontaneous alternation deficits.

CONCLUSIONS

These results indicate that glutamate transmission participates in the acute, long-term, and conditioned effects of amphetamine on 50 kHz USVs, possibly by influencing amphetamine-induced long-term neuronal changes and/or amphetamine-associated memories.

APP transgenic mice for modelling behavioural and psychological symptoms of dementia (BPSD)

The discovery of gene mutations responsible for autosomal dominant Alzheimer's disease has enabled researchers to reproduce in transgenic mice several hallmarks of this disorder, notably Aβ accumulation, though in most cases without neurofibrillary tangles. Mice expressing mutated and wild-type APP as well as C-terminal fragments of APP exhibit variations in exploratory activity reminiscent of behavioural and psychological symptoms of Alzheimer dementia (BPSD). In particular, open-field, spontaneous alternation, and elevated plus-maze tasks as well as aggression are modified in several APP transgenic mice relative to non-transgenic controls. However, depending on the precise murine models, changes in open-field and elevated plus-maze exploration occur in either direction, either increased or decreased relative to controls. It remains to be determined which neurotransmitter changes are responsible for this variability, in particular with respect to GABA, 5HT, and dopamine.

Zero net flux estimates of septal extracellular glucose levels and the effects of glucose on septal extracellular GABA levels

Although hippocampal infusions of glucose enhance memory, we have found repeatedly that septal glucose infusions impair memory when gamma-aminobutyric acid (GABA) receptors are activated. For instance, hippocampal glucose infusions reverse the memory-impairing effects of co-infusions of the GABA agonist muscimol, whereas septal glucose infusions exacerbate memory deficits produced by muscimol. One potential explanation for these deleterious effects of glucose in the septum is that there are higher levels of endogenous extracellular fluid glucose concentrations in the septum than in the hippocampus. Another hypothesis is that septal glucose infusions impair memory by increasing septal GABA synthesis or release, which is possible because elevating glucose increases GABA levels in other brain regions. To test these hypotheses, Experiment 1 quantified extracellular fluid glucose levels in the septum and hippocampus using zero net flux in vivo microdialysis procedures in conscious, freely moving rats. Experiment 2 determined whether septal infusions of glucose would increase GABA concentrations in dialysates obtained from the septum. The results of Experiment 1 indicated that extracellular fluid glucose levels in the hippocampus and septum are comparable. The results of Experiment 2 showed that co-infusions of glucose with muscimol, at doses that did not affect memory on their own, decreased percent alternation memory scores. However, none of the infusions significantly affected GABA levels. Collectively, these findings suggest that the memory-impairing effects of septal infusions of glucose are not likely due to regional differences in basal extracellular fluid glucose concentrations and are not mediated via an increase in septal GABA release.

Blocking GABA-A receptors in the medial septum enhances hippocampal acetylcholine release and behavior in a rat model of diencephalic amnesia

Wernicke-Korsakoff syndrome (WKS), a form of diencephalic amnesia caused by thiamine deficiency, results in severe anterograde memory loss. Pyrithiamine-induced thiamine deficiency (PTD), an animal model of WKS, produces cholinergic abnormalities including decreased functional hippocampal acetylcholine (ACh) release and poor spatial memory. Increasing hippocampal ACh levels has increased performance in PTD animals. Intraseptal bicuculline (GABA(A) antagonist) augments hippocampal ACh release in normal animals and we found it (0.50 microg/microl and 0.75 microg/microl) also increased in-vivo hippocampal ACh release in PTD animals. However, the 0.75 microg/microl dose produced a greater change in hippocampal ACh release in control animals. The 0.50 microg/microl dose of bicuculline was then selected to determine if it could enhance spontaneous alternation performance in PTD animals. This dose of bicuculline significantly increased hippocampal ACh levels above baseline in both PTD and control rats and resulted in complete behavioral recovery in PTD animals, without altering performance in control rats. This suggests that balancing ACh-GABA interactions in the septohippocampal circuit may be an effective therapeutic approach in certain amnestic syndromes.

Increasing hippocampal acetylcholine levels enhance behavioral performance in an animal model of diencephalic amnesia

Pyrithiamine-induced thiamine deficiency (PTD) was used to produce a rodent model of Wernicke-Korsakoff syndrome that results in acute neurological disturbances, thalamic lesions, and learning and memory impairments. There is also cholinergic septohippocampal dysfunction in the PTD model. Systemic (Experiment 1) and intrahippocampal (Experiment 2) injections of the acetylcholinesterase inhibitor physostigmine were administered to determine if increasing acetylcholine levels would eliminate the behavioral impairment produced by PTD. Prior to spontaneous alternation testing, rats received injections of either physostigmine (systemic=0.075 mg/kg; intrahippocampal=20, 40 ng/muL) or saline. In Experiment 2, intrahippocampal injections of physostigmine significantly enhanced alternation rates in the PTD-treated rats. In addition, although intrahippocampal infusions of 40 ng of physostigmine increased the available amount of ACh in both pair-fed (PF) and PTD rats, it did so to a greater extent in PF rats. The increase in ACh levels induced by the direct hippocampal application of physostigmine in the PTD model likely increased activation of the extended limbic system, which was dysfunctional, and therefore led to recovery of function on the spontaneous alternation task. In contrast, the lack of behavioral improvement by intrahippocampal physostigmine infusion in the PF rats, despite a greater rise in hippocampal ACh levels, supports the theory that there is an optimal range of cholinergic tone for optimal behavioral and hippocampal function.

Involvement of the sigma1 (sigma1) receptor in the anti-amnesic, but not antidepressant-like, effects of the aminotetrahydrofuran derivative ANAVEX1-41

BACKGROUND AND PURPOSE

Tetrahydro-N, N-dimethyl-5, 5-diphenyl-3-furanmethanamine hydrochloride (ANAVEX1-41) is a potent muscarinic and sigma(1) (sigma (1)) receptor ligand. The sigma (1) receptor modulates glutamatergic and cholinergic responses in the forebrain and selective agonists are potent anti-amnesic and antidepressant DRUGS. WE HAVE HERE ANALYSED THE SIGMA (1) COMPONENT IN THE BEHAVIOURAL EFFECTS OF ANAVEX1-41.

EXPERIMENTAL APPROACH

Binding of ANAVEX1-41 to muscarinic and sigma (1) receptors were measured using cell membranes. Behavioural effects of ANAVEX1-41 were tested in mice using memory (spontaneous alternation, passive avoidance, water-maze) and antidepressant-like activity (forced swimming) procedures.

KEY RESULTS

In vitro, ANAVEX1-41 was a potent muscarinic (M(1)>M(3), M(4)>M(2) with K(i) ranging from 18 to 114 nM) and selective sigma (1) ligand (sigma (1), K(i)=44 nM; sigma (2), K(i)=4 microM). In mice, ANAVEX1-41 failed to affect learning when injected alone (0.03-1 mg kg(-1)), but attenuated scopolamine-induced amnesia with a bell-shaped dose response (maximum at 0.1 mg kg(-1)). The sigma (1) antagonist BD1047 blocked the anti-amnesic effect of ANAVEX1-41 on both short- and long-term memories. Pretreatment with a sigma (1) receptor-directed antisense oligodeoxynucleotide prevented effects of ANAVEX1-41 only in the passive avoidance procedure, measuring long-term memory. ANAVEX1-41 reduced behavioural despair at 30 and 60 mg kg(-1), without involving the sigma (1) receptor, as it was not blocked by BD1047 or the antisense oligodeoxynucleotide.

CONCLUSIONS AND IMPLICATIONS

ANAVEX1-41 is a potent anti-amnesic drug, acting through muscarinic and sigma (1) receptors. The latter component may be involved in the enhancing effects of the drug on long-term memory processes.

Septal co-infusions of glucose with a GABAB agonist impair memory

Septal infusions of glucose exacerbate memory deficits produced by co-infusions of drugs that increase gamma-aminobutyric acid (GABA)(A) receptor activity. To further understand the interaction between glucose and GABA, this experiment tested whether glucose would also potentiate spatial working memory deficits produced by septal infusions of the GABA(B) receptor agonist baclofen. Fifteen minutes prior to assessing spontaneous alternation (SA), male Sprague-Dawley derived rats were given septal infusions of vehicle, glucose (33 nmol), baclofen (0.1 nmol), or glucose combined with baclofen in one solution. Septal co-infusions of glucose with baclofen, at doses that individually had no effect, significantly impaired SA. Thus, the memory-impairing effects of glucose are observed with either GABA(A) or GABA(B) receptor ligands. This raises the possibility that glucose may impair memory by increasing synaptic levels of GABA and subsequent activation of these different receptor subtypes. These effects of glucose could contribute to the memory-impairing effects of hyperglycemia.

Impaired recognition memory in rats after damage to the hippocampus

Rats with radio-frequency or ibotenic acid lesions of the hippocampus and rats with radio-frequency lesions of the fornix were tested on the visual paired comparison task (VPC), a test of recognition memory. Memory was assessed at five different delay intervals ranging from 10 sec to 24 hr. All operated groups performed normally at the shorter delays (10 sec and 1 min). Across longer delays, the two groups with hippocampal damage were impaired. Rats with fornix lesions performed well on the VPC task but were impaired on a spatial task (spontaneous alternation). The results show that the hippocampus is essential for normal recognition memory. Moreover, fornix lesions need not mimic the effects of direct damage to hippocampal tissue. The findings are discussed in the context of the contribution of the hippocampus to recognition memory.

Nociceptin/orphanin FQ and nocistatin on learning and memory impairment induced by scopolamine in mice

1. Nociceptin, also known as orphanin FQ, is an endogenous ligand for the orphan opioid receptor-like receptor 1 (ORL1) and involves in various functions in the central nervous system (CNS). On the other hand, nocistatin is recently isolated from the same precursor as nociceptin and blocks nociceptin-induced allodynia and hyperalgesia. 2. Although ORL1 receptors which display a high degree of sequence homology with classical opioid receptors are abundant in the hippocampus, little is known regarding their role in learning and memory. 3. The present study was designed to investigate whether nociceptin/orphanin FQ and nocistatin could modulate impairment of learning and memory induced by scopolamine, a muscarinic cholinergic receptor antagonist, using spontaneous alternation of Y-maze and step-down type passive avoidance tasks in mice. 4. While nocistatin (0.5-5.0 nmol mouse-1, i.c.v.) administered 30 min before spontaneous alternation performance or the training session of the passive avoidance task, had no effect on spontaneous alternation or passive avoidance behaviours, a lower per cent alternation and shorter median step-down latency in the retention test were obtained in nociceptin (1.5 and/or 5.0 nmol mouse-1, i.c.v.)-treated normal mice. 5. Administration of nocistatin (1.5 and/or 5.0 nmol mouse-1, i.c.v.) 30 min before spontaneous alternation performance or the training session of the passive avoidance task, attenuated the scopolamine-induced impairment of spontaneous alternation and passive avoidance behaviours. 6. These results indicated that nocistatin, a new biologically active peptide, ameliorates impairments of spontaneous alternation and passive avoidance induced by scopolamine, and suggested that these peptides play opposite roles in learning and memory.

Memory modulation across neural systems: intra-amygdala glucose reverses deficits caused by intraseptal morphine on a spatial task but not on an aversive task

Based largely on dissociations of the effects of different lesions on learning and memory, memories for different attributes appear to be organized in independent neural systems. Results obtained with direct injections of drugs into one brain region at a time support a similar conclusion. The present experiments investigated the effects of simultaneous pharmacological manipulation of two neural systems, the amygdala and the septohippocampal system, to examine possible interactions of memory modulation across systems. Morphine injected into the medial septum impaired memory both for avoidance training and during spontaneous alternation. When glucose was concomitantly administered to the amygdala, glucose reversed the morphine-induced deficits in memory during alternation but not for avoidance training. These results suggest that the amygdala is involved in modulation of spatial memory processes and that direct injections of memory-modulating drugs into the amygdala do not always modulate memory for aversive events. These findings are contrary to predictions from the findings of lesion studies and of studies using direct injections of drugs into single brain areas. Thus, the independence of neural systems responsible for processing different classes of memory is less clear than implied by studies using lesions or injections of drugs into single brain areas.

Insensitivity of the hippocampus to environmental stimulation during postnatal development

Development of cortical sensory systems is influenced by environmental experience during "sensitive periods," before onset of behavioral function. During these periods, synaptic plasticity is observed, and neuronal function shows increased responsiveness to environmental stimulation. Because the hippocampus is late to develop, and because it demonstrates synaptic plasticity before the onset of behavioral function, this experiment was designed to determine whether, like the sensory cortices, the hippocampus undergoes a period of enhanced responsiveness to the environment. Rats at three ages [postnatal day 16 (P16), P23, and P30] were tested on a hippocampally dependent task, spontaneous alternation, and exposed to a novel environment. They were then killed and processed for immunocytochemistry to Fos or for in vitro electrophysiology in hippocampal area CA1. Age-matched control subjects were killed immediately after removal from the home cage. Spontaneous alternation was only observed in the oldest (P30) animals. In these same animals, the environmental manipulation resulted in an increase in Fos-like immunoreactivity (FL-IR), relative to controls, and a decrease in the ability to induce long-term potentiation (LTP). In P16 and P23 animals, the environmental manipulation resulted in no differences in hippocampal FL-IR or LTP. These results suggest that, rather than showing increased responsiveness to the environment at these ages, the hippocampus is environmentally insensitive and that it is isolated from the effects of environmental stimuli. The hippocampus, a neural region important for higher cognitive function, may develop via a mechanism different from those observed in the primary sensory cortices.