Collaboration with Dr. Holahan’s lab

Effects of juvenile pretraining on performance on two spatial tasks and structural markers in hippocampus and associated regions

This project is a follow-up to one described by Keeley, Wartman, Hausler, and Holahan (2010). One goal of the current study is to determine whether enhanced performance on a spatial task during adolescence is due to exposure to task-specific characteristics or general contextual information during the juvenile period. A second goal is to observe whether there are structural differences in the hippocampus and associated regions between rats that received pretraining and those that did not. Two spatial tasks were used in this study; the fixed platform place navigation task (i.e. watermaze) and the novel object in-place preference (NOiP) task. Both tasks were conducted in the same room and in the same apparatus (i.e. Morris watermaze). Forty-eight rats were randomly assigned to one of 6 groups; no pretraining/ watermaze adolescent training, no pretraining/NOiP adolescent training, watermaze pretraining/watermaze adolescent training, watermaze pretraining/NOiP adolescent training, NOiP pretraining/NOiP adolescent training, and NOiP pretraining/watermaze adolescent training. A total of four graduate and three undergraduate students in both the Mumby and Holahan labs have been involved in data collection. Behavioural data thus far suggest that pretraining on either task leads to enhanced performance that generalizes to both tasks. Currently, data concerning structural markers of synaptogenesis and neural activity are being analyzed.

Collaboration with Dr. Séguéla's lab

 

Persistent firing of neurons, which occurs in the absence of stimulation, has been demonstrated in regions such as the medial prefrontal cortex (mPFC) and medial entorhinal cortex (mEC). This persistent firing is associated with the delay phase of working memory tasks. It has been proposed that this persistent firing of neurons in such regions promotes transient storage of task-relevant information necessary for performance. Persistent firing has been shown to be modulated by muscarinic receptor activation and blocking such activation has been shown to prevent persistent firing and impair performance on working memory tasks. Although it is unknown how muscarinic receptor activation promotes persistent firing, one potential mechanism might be via increased intracellular nonselective cation conductance. Zhang, Reboreda, Alonso, Barker, and Seguela (2010) reported that transient receptor potential (TRP) channels, which are calcium permeable nonselective cation channels, influence muscarinic receptor activation and persistent firing in layer V neurons of the mEC.  Similar results have been reported for the anterior cingulate cortex (Zhang & Seguela, 2010). Thus, it has been proposed that TRP channel activation may be important for performance on working memory tasks. The purpose of the collaborative project between the Mumby and Séguéla labs are to observe whether blocking TRP channels in either the anterior cingulate cortex, or mEC leads to performance deficits on a working memory task and whether the performance deficits resemble those seen by blocking muscarinic receptor activity.

Modulatory effects of 17-β estradiol on two object recognition memory tasks

Nicole Gervais

17-β estradiol (E2) affects object recognition memory.  Using the Novel Object Preference (NOP) test, systemic or local injection of E2 into the hippocampus either before or immediately after familiarization resulted in a preference for the novel object, whereas vehicle injection produced no preference (Fernandez et al., 2008; Luine et al., 2003). This would indicate that higher levels of this hormone during consolidation leads to enhanced object recognition memory. However, Mumby (2001), suggested that lack of preference may not reflect impaired object recognition memory, as many confounds can prevent increased exploration of the novel object.  As such, the goal of the present study was to observe whether E2 enhances performance on two object recognition memory tasks; the commonly used NOP test and a delayed nonmatching-to-sample (DNMS) task. Ovariectomized female rats all received a chronic low doseof E2 (leading to ~25 pg/ml serum) via silastic tubing implanted in the nape of the neck. 4 hr prior to familiarization on the NOP task, rats received either 10μg/kg doseof E2 (~90 pg/ml serum; high dose) or vehicle (low dose E2). Following a 72 hr retention interval, a 4 min test was given. The DNMS involved a similar hormonal regimen, but required a briefer delay between sample and test phase. Relative to low E2 dose, the high dose produced enhanced performance on the NOP task. Convergent results were also obtained on the DNMS task. Thus, data from both tasks provides further support that E2 enhances object recognition memory. Future research investigating E2’s modulatory role in object recognition memory via effects in extrahippocampal structures are being explored.

Temporally-graded retrograde amnesia for unreinforced, non-navigational, spatial information in rats with continuous inactivation of the hippocampus

Stephane Gaskin Ph.D.

We investigated whether systems consolidation of spatial memory could be detected in a non-navigational, spatial-learning test that takes advantage of rats' natural propensity to preferentially investigate an object that was displaced relative to spatial cues more than an object that remained stationary. Previous studies using navigational spatial-learning tests have generally failed to reveal temporally-graded retrograde amnesia, possibly because the hippocampus needs to be intact for the retrieval and/or processing of navigational information during the test. In the present study, the hippocampus of rats was kept inactivated, at two sites along its septo-temporal axis (dorsal and intermediate), for four consecutive days, beginning either 3h or 5 days after familiarization to two identical objects in an open field. Rats that had their hippocampus inactivated beginning 5 days but not 3h after familiarization showed evidence that they remembered the previous location of the displaced object. The results suggest that systems consolidation of spatial memories can be detected using a non-navigational test of spatial memory.

Effects of dorsolateral entorhinal cortex damage on performance on three spatial memory tasks

Nicole Gervais

The discovery of grid cells in the medial band of the EC (Hafting et al., 2005) confirms the role of this structure in processing spatial information. Although this region has also been implicated in working memory and memory consolidation (Hasselmo, 1999), behavioral data available to date are inconsistent. Whereas some studies report deficits following lesions to the EC, others do not. This discrepancy may be due to the location of damage within the medial EC, and the choice of task used to assess spatial memory.The goal of the present study was to examine the effect of lesions to the dorsolateral band of the medial EC (DLEC), which receives the majority of visuospatial input to the EC, on three separate spatial tasks. DLEC lesions were expected to result in impaired performance on tasks of non-navigational incidental spatial memory, and navigational allocentric spatial reference and working memory. A performance deficit was observed for the DLEC lesion group on the non-navigational incidental spatial memory task, and the allocentric spatial working memory task when the retention delay was long (120s) but not short (15s). No impairment was observed on the allocentric spatial reference memory task. Histological data confirms damage was restricted mainly to the DLEC.Overall, results suggest that the DLEC is involved in certain spatial memory abilities when longer retention delays are involved. Click here to view poster.

Lateral internal medullary lamina lesions disrupt retrograde and anterograde object-recognition memory in rats

Anastasia Arvanitidis

Despite evidence that the diencephalic structures may underlie memory impairments in animal models of Wernicke-Korsakoff syndrome, little is known about the types of memory impairments. First, the precise contribution of specific thalamic nuclei and fiber tracts to various memory processes remains unclear. In addition, there is little existing evidence for a retrograde memory impairment following diencephalic damage in animals, despite the chronic retrograde memory impairment seen in Korsakoff patients. Finally, the majority of learning and memory tasks used to assess both anterograde and retrograde memory impairments in PTD rats are spatial in nature (e.g., t-maze, water maze task). The present study examined the effects of bilateral electrolytic lesions to the lateral internal medullary lamina (IML) of the thalamus on retrograde and anterograde object-recognition memory in rats, using a test that takes advantage of rats’ natural propensity to explore novelty. For the retrograde test, rats were familiarized to two identical copies of an object (sample) in an open field, for five minutes on five consecutive days. Twenty-four hours later, rats received either bilateral electrolytic lesions of the IML or sham surgeries. Following a 10 day recovery period, rats were placed back into the open field, which now contained a copy of the sample object and a novel object. Rats that received IML lesions did not spend significantly more time investigating the novel object, indicating that they did not remember the sample object. For the anterograde test, the same rats were then familiarized to a different pair of identical objects for 5 minutes and tested 24 hours later, on two different occasions. As in the retrograde test, rats with IML lesions did not spend significantly more time investigating the novel object, suggesting that they did not remember the sample object. Taken together, these results suggest that the IML may be important for acquisition and consolidation of memories for objects. Click here to view poster.

Long-term synaptic potentiation in layer II of the lateral entorhinal cortex in the presence of dopamine in vitro

Shawnna Barrett

The entorhinal cortex is a major structure linking neocortical areas with the hippocampal formation, and is thought to contribute to the integration and encoding of sensory information. The superficial layers of the entorhinal cortex receive a large projection from the piriform (primary olfactory) cortex, and synaptic plasticity within this input pathway may affect olfactory information processing. In addition, the mesocortical dopamine system provides a substantial input to layer II of the lateral entorhinal cortex and dopamine may therefore play an important role in modulating sensory processing in the entorhinal cortex. Recently, we have shown that systemic administration of the dopamine reuptake inhibitor GBR12909, which elevates extracellular dopamine levels in the lateral entorhinal cortex, also inhibits the induction of both long-term potentiation (LTP) and long-term depression (LTD) in the entorhinal cortex of the awake rat. In the present study, we have used field potential recordings from slices of entorhinal cortex maintained in vitro to assess the effects of dopamine on the induction of LTP in synaptic inputs to layer II. Acute brain slices (400 μm thick) were obtained using a vibratome and were maintained in a gas-fluid interface recording chamber at a temperature of 32 ºC. Stimulation pulses (0.1 ms duration) were delivered to layer I using a concentric bipolar electrode, and field excitatory postsynaptic potentials were obtained in layer I close to the cells of layer II using glass pipettes filled with ACSF (in mM, 124 NaCl, 5 KCl, 1.25 NaH2PO4, 2 MgSO4, 2 CaCl2, 26 NaHCO3, 10 dextrose, ascorbic acid; 2-4 MΩ). Following a 10 min baseline period, dopamine (10 μM) was bath-applied for a period of 15 min prior to induction of LTP using three 1-sec duration trains of pulses delivered at 100 Hz. Control cells received tetanisation in the absence of dopamine, or dopamine alone. As demonstrated previously, results of initial experiments show that application of 10 μM dopamine causes a reversible enhancement of the amplitude of fEPSPs. However, dopamine did not cause a significant change in the amount of LTP observed, and both control slices exposed to normal ACSF, and slices that underwent 15 min pre-exposure to dopamine, showed similar levels of LTP 60 min post-tetanization. The present findings therefore suggest that 10 uM dopamine does not result in a marked modulation of the induction of LTP as tested here using strong tetanizing stimuli in vitro.

Object familiarization and novel object preference in both normal rats and rats with lesions of the hippocampus

Emily Cole

The effect of hippocampus (HPC) lesions on object-recognition memory remains controversial. A common method used to test rats’ object recognition memory is the novel object preference (NOP) test. This test takes advantage of rats’ natural tendency to explore novelty. On a conventional NOP test, a rat is familiarized with two identical sample objects. Following a retention interval, the rat is presented with a copy of the sample object along with a novel object. Object recognition is inferred if rats spend more time investigating the novel object over the sample object. The typical dependent measure is an investigation ratio which is derived from the amount of time spent investigating the novel object relative to the total time spent investigating the familiar and novel object. In some studies object-recognition impairment (i.e. in a group of rats that received brain lesions) is inferred when the average investigation ratio for a treatment group is significantly below that of the control group. In other studies, object recognition memory impairment is inferred if a treatment groups’ average investigation ratio is not greater than what would be expected by chance (50%), regardless of whether this investigation ratio differs from that of the control group. The former method may not be an ideal way to interpret behavioural data because in order to do so, one assumes that a larger investigation ratio signifies better memory. We hypothesized that if a larger investigation ratio signifies better memory, then the amount of time spent investigating (encoding) objects during familiarization should be correlated with the magnitude of investigation ratios. We examined whether a relationship exists between these two variables while testing both normal rats and rats with HPC lesions. We present the results of two experiments which suggest that 1) there is no relationship between the amount of time spent investigating objects during familiarization and subsequent investigation ratios for both normal rats and in rats with HPC lesions, suggesting a comparison of average investigation ratios to chance is favourable rather than a direct, between group comparison and 2) rats with hippocampal lesions showed an unreliable pattern of object recognition when given multiple test trials at two different retention intervals. Click here to view poster.

Olfactory discrimination following selective damage to the entorhinal cortex

Nicole Gervais

Anatomical, electrophysiological, and behavioural evidence suggests that the lateral entorhinal cortex (LEC) is involved in processing and mnemonic functions related to olfactory stimuli (Kerr et al., 2007; Petrulis et al., 2005; Staubli et al., 1986). However, the precise role of this structure in the acquisition, consolidation, and retrieval of olfactory-based information remains unclear. Although studies aimed at clarifying these issues have been conducted, procedural differences have resulted in continued uncertainty. Olfactory discrimination, which involves differentiating one odor from another based upon previous associations with food reward, is a simple memory task that can clarify such questions. The present study was designed to assess whether bilateral neurotoxic lesions to the dorsolateral EC would result in impairments on a version of this task involving concurrent training on 4 problems. Given the evidence presented above, it was predicted that lesions to this structure result in impaired performance during training and test phases. The results of the present study disconfirm our predictions. The EC group required fewer trials to reach criterion and performed better during the test phase than the control group. Histological findings confirm lesions were restricted to the EC, which is in contrast to damage reported in previous studies reporting impairments on olfactory discrimination tasks (i.e. Staubli et al., 1986). Future research is needed to clarify the continued inconsistencies in the literature regarding the precise role of the EC.

Effect of hippocampal ablation shortly following ischemia on object-recognition memory

Sophie Duranceau

Does blocking transient receptor potential ion channels in the medial entorhinal cortex affect performance on an allocentric spatial working memory task?

Jessica Starck

Intact unreinforced and reinforced spatial learning in rats with large lesions of the ventral hippocampus

Stephane Gaskin Ph.D.

Rats with large ventral and dorsal hippocampal lesions were tested on an unreinforced test of spatial memory that takes advantage of their natural propensity to explore novelty. Rats were presented with two copies of an identical object in a large circular open field arena. Subsequently, the rats were placed back into the open field with one of the objects displaced to an adjacent quadrant of the arena. Sham-operated rats and rats with ventral hippocampal lesions spent more time in the quadrant that contained the displaced object than in the quadrant that contained the non-displaced object, and more time investigating the displaced object than the non-displaced object. Rats with dorsal hippocampal lesions were impaired on both measures. Both sham and ventral hippocampal lesioned rats subsequently learned to retrieve a food pellet in the ends of each arm of a radial maze. Rats with lesions to the dorsal hippocampus showed no significant improvement in the number of errors made across training sessions and made significantly more errors, overall, than rats with ventral hippocampal or sham lesions. These results support previous findings that an intact dorsal but not ventral hippocampus is necessary for spatial learning in rats. In addition, the present findings extend these findings to a test of spatial memory that does not make use of reinforcers. Click here to view poster.

Patterns of retrograde amnesia for incidental spatial learning in rats

Stephane Gaskin Ph.D.

Memory consolidation refers to a hypothesized process by which memories, initially stored in a labile state, are gradually stabilized in a more permanent form in the brain. Newly acquired memories are initially dependent on the hippocampus (HPC) for retrieval but as they are stored in the neocortex over time, these memories are no longer dependent on the HPC. Therefore, damage to the HPC often gives rise to a temporally graded retrograde amnesia (TGRA), with a loss of recent memories but preserved remote memories. One issue concerns the lack of TGRA in studies involving the Morris water-maze. One explanation for this is that a functional HPC is required for navigation, or other on-line processes, during the test. In the present study we tested rats in a non-navigational place-learning test, which takes advantage of rats’ ability to detect spatial changes in their environment. Rats were familiarized with a pair of identical objects in a large open field for 7 minutes a day for 7 consecutive days. Following the training phase, rats received NMDA lesions of the HPC either 1-3 days (recent condition) or 3 weeks (remote condition) after the last day of training. Following recovery, rats were placed back in the open field for the test phase. This time, one object remained in its respective location while the other object was displaced. Rats that received HPC lesions 3 weeks after training, but not during the week of training, showed evidence of preserved remote spatial memory, suggesting that memory for the spatial location of objects may become independent of the hippocampus over time. Click here to view poster.

Relationship between hippocampal damage and behavioural outcome in rats following global cerebral ischemia

Pavel Piterkin

Memory impairments following global cerebral ischemia have traditionally been associated with damage to the hippocampal formation, but some ensuing impairments, such as object-recognition deficits, suggest the presence of extra-hippocampal neuropathology. The goal of the present study was to determine whether hippocampal damage induced by global cerebral ischemia is related to rats’ performance on spatial memory and object recognition tasks. Transient global cerebral ischemia was induced and following a recovery period, rats’ were then tested on their spatial memory and object recognition memory. The delayed matching-to place (DMTP) task conducted in the water-maze was used to assess spatial memory. During the sample phase of each trial, rats were given an opportunity to search for and find the hidden platform. After a delay (15 or 60 seconds), rats were returned to the maze and were allowed to find the platform again in the same location. Object-recognition memory was tested using the novel object preference (NOP) test of object recognition. Rats were placed in an open field arena and allowed to explore two identical sample objects. After a delay (15 minutes or 24 hours) rats were returned to the arena with a novel object and a copy of the sample for the recognition test. The results suggest that ischemic rats are impaired relative to controls on both, spatial memory and object recognition tasks. Similarly to previous studies, we found a significant relationship between performance on a spatial memory task and the degree of hippocampal damage induced by global cerebral ischemia. Click here to view poster.

Effects of hippocampal inactivation during ischemia on allocentric spatial memory

Cynthia Di Giandomenico

Effects of intrahippocampal muscimol infusion on the occurrence and frequency of hippocampal epileptiform activity following transient global ischemia

Paul Mereau

Following global cerebral ischemia, it is believed that seizure activity originating in the hippocampus (HPC) spreads to extra-hippocampal regions. These postischemic seizures may play a critical role in subsequent neuropathology and memory impairments. Thus, the goal of the present experiment is to investigate whether temporary inactivation of the HPC following ischemia will lead to an attenuation of seizure activity. Muscimol, a GABA agonist, will be used to temporarily inactivate the HPC for 24 hours following ischemia. A total of 16 rats will be used, eight of which will receive ischemia and the remaining eight will receive sham ischemia. Within each group, half will receive an intrahippocampal infusion of muscimol and the other half will receive saline. EEG activity will be recorded for 72 hours following ischemia for each animal. It is expected that there will be significantly less epileptiform spiking in the hippocampal EEG of rats injected with muscimol compared to rats injected with saline following ischemia.

The effects of hippocampal infusion of muscimol on the induction of long-term synaptic potentiation in the prefrontal cortex in rats that have undergone transient global cerebral ischemia

Xu Dan

LTP is commonly accepted as the cellular model for memory consolidation. Following transient cerebral ischemia, there is a reduction in the capacity for LTP induction from the hippocampus to the prefrontal cortex. It is believed that this impairment is caused by the postischemic seizure activity originating in the HPC. The present experiment will investigate whether a reduction in seizure activity in the hippocampus following ischemia can prevent this reduced capacity for LTP in the prefrontal cortex. In order to reduce seizure activity in the HPC, we will temporarily inactivate the HPC for 24 hours following ischemia. Rats will either receive an injection of muscimol, a GABA receptor agonist, or saline (vehicle) directly into the HPC following ischemia. We will then assess the capacity for LTP from the HPC to the prefrontal cortex by conducting input/output tests. We hypothesize that rats receiving saline injections will have a significantly reduced capacity for LTP induction compared to rats injected with muscimol.  

The effects of context shifts on object recognition in rats with hippocampal lesions

Emily Cole

Object recognition memory improves when both learning and testing occur in the same context. The hippocampus (HPC) plays an important role in this process. Rats with HPC lesions and control rats were tested on their object recognition memory in either the same context that the object was initially observed in or a different one. Using the novel object preference (NOP) test, 19 adult male Long-Evans rats were familiarized with four object pairs in four contextually distinct compartments of a circular track. On the test phase, one of the objects in each of the object pairs was replaced with a novel object. Also, two of the familiar objects remained in their respective compartments and the other two switched compartments. The results showed that both control rats and rats with HPC lesions performed normally on the NOP test when the objects remained in their respective compartment for the test phase. However, when the objects were displaced to a new compartment, both control rats and rats with HPC lesions were impaired on the NOP test. The results thus far, suggest that rats with HPC lesions recognize objects when they remain in the same context for both the learning and test phase. Although the rats with HPC lesions were impaired when testing occurred in a different context, our control group was also impaired. Further experimentation is required to better understand this type of context shift on rats with HPC lesions and control rats.   

Activation of object representations in rats by exposure to associated contexts

Anafa Gamliel

Rats perform better on recognition tasks if learning and testing occur in the same context. One interpretation of this phenomenon is that exposure to a particular familiar context activates the representations of individual objects that were previously encountered in that context. The assumption underlying this interpretation was tested by familiarizing rats to two different objects in two different contexts. After a retention interval, rats were exposed to either one of the contexts or a control context. Lastly, rats encountered the two objects seen in the familiarization phase in a different context for the test phase. Rats tend to show exploratory preference for novel objects rather than familiar ones. It was found that subjects spent an equal amount of time investigating both objects during the test phase. This could suggest that exposure to a particular familiar context does not activate the representations of individual objects that were previously encountered in that context.

Locomotor activity rhythms are resistant to disruption by global cerebral ischemia

Sara-Claude Michon

Environmental enrichment leads to species-typical behavior in rats

Leanna Segal-Lopatka

Context-specific memory and memory for context in rats with hippocampal lesions

Pavel Piterkin

Examining retrograde memory for shock-probe fear conditioning following perirhinal cortex lesions

StephanieYamin

Short-term and long-term synaptic plasticity following transient global cerebral ischemia

Pavel Piterkin

Memory impairments following global cerebral ischemia have traditionally been associated with damage to the hippocampal formation, but ablation of the hippocampus one hour after ischemia can prevent such deficits. It has been suggested that the post-ischemic hippocampus may mediate functional damage in other structures involved in memory processing. In the present study, acute field potential recordings were used to assess short-term and long-term changes in synaptic plasticity in the perirhinal and prefrontal cortices of urethane-anesthetized rats three weeks after sham or global ischemia. Although high-frequency stimulation of the CA1/subicular region of the hippocampus induced long-term potentiation in the prefrontal cortex of both sham and ischemic rats, there was no significant difference in the amount of LTP induced in each group. Furthermore, no significant group differences were observed in short-term inhibitory and facilitatory mechanisms in the prefrontal and perirhinal cortices following paired-pulse stimulation of the CA1/subiculum. The results are discussed and implications for future research are considered.

Group setting socially transmitted food preferences in rats

Nicoletta Petsoulakis

Examining behavioral variability in rats after exposure to an enriched or impoverished environment

Carolina Cook

Small cages are used to house rodents when doing research in order to control for variability. Animals housed in this fashion are prevented from reaching a normal development because they are confined to small spaces; furthermore, their species typical natural behaviors are restricted. Since the early 90’s considerable amounts of research has been conducted to assess the effects of enriched environment on brain structures and cognitive abilities. These studies in fact suggest that exposure to an enriched environment during the critical period of development does have important effects and also results in changes in brain structures and improvements in learning and memory. The fact that results are consistent as a consequence of environment restriction does not mean that research has been based on a proper animal model. Ultimately, no study has yet been conducted to evaluate the effects of enrichment on species typical behavior. The proposed study intends to evaluate if there are any fundamental differences in species typical natural behavior between two groups: rats exposed to an enriched environment and rats in an impoverished environment. A more natural developmental pattern should result from enrichment therefore, it is hypothesized that behavioral responses of rats in the enriched group will be more similar. On the other hand, lack of experience should result in great variability in behavioral responses in the impoverished group.

The effects of chronic mild stress on behavioural and physiological measures in female rats

Lisa Barbagallo

Hippocampal damage and anterograde object-recognition in rats after long retention intervals

Kenny Stein

Density of sleep spindles during learning of a skilled-reaching task

Sara-Claude Michon / Christine Werk

Behavioral variability in rats exposed to enriched environments

Nadia Vracotas

Post-ischemic object-recognition impairments: Evaluation at short and long term after surgery

Leanna  Segal-Lopatka

Synaptic plasticity in the prefrontal cortex and perirhinal cortex following global cerebral ischemia

Pavel Piterkin