Biomedical subjects

Sean Commins

Publications and source records attributed to Sean Commins.

12 recordsLinked to original sources

PubMed2006

The subiculum to entorhinal cortex projection is capable of sustaining both short- and long-term plastic changes.

The hippocampus communicates with the neocortex via the entorhinal cortex. These areas are thought to be critically involved in the consolidation of memories. The hippocampus is considered to be the site of association of sensory information, which is then laid down for long-term storage in the neocortex. We examined the projection from the subiculum to the entorhinal cortex to determine whether it could function to transfer this hippocampally-processed information to the neocortex. Following stimulation in the subiculum we demonstrate a negative-going deflection followed by a positive-going deflection in the entorhinal cortex. This projection is capable of short-term plastic changes in the form of PPF. FIn addition, we demonstrate that long-term synaptic changes in the form of LTP and LTD could be sustained for at least 30min on this pathway. Finally we show that PPF changes after LTP and LTD, suggesting that a presynaptic mechanism may be involved in both of these pathways.

Analysis of Variance↗

PubMed2006

Interleukin-10 (IL-10) but not Lipopolysaccharide (LPS) produces increased motor activity and abnormal exploratory patterns while impairing spatial learning in Balb/c mice.

Lipopolysaccharide (LPS) is a potent endotoxin, which produces "sickness behaviours" including loss of weight, loss of interest in food and decreased exploration. LPS has also been shown in some studies to cause deficits in various learning and memory abilities, while in others these LPS-induced learning impairments have been attributed to performance-related deficits rather than learning deficits per se. Here, we use the novelty-preference paradigm, a task that minimises performance-related factors such as motivation, in an attempt to extract and examine the effects of LPS on spatial learning. In addition, some studies have indicated that the anti-inflammatory cytokine Interleukin-10 (IL-10) can alleviate some of the symptoms induced by LPS. Here, we also examine the effect of IL-10 on feeding, motor and learning behaviours. We demonstrate that a single injection of LPS does produce a lack of interest in food and weight loss; LPS, however, does not impair habituation in the novelty-preference paradigm. Furthermore, co-injection of IL-10 with LPS does not attenuate the LPS-induced effects of weight loss and lack of food intake. Interestingly, a single injection of IL-10 produces abnormal patterns of exploration, a general increase in activity and abnormal patterns of habituation.

Analysis of Variance↗

PubMed2005

Cyclooxygenase inhibition attenuates endotoxin-induced spatial learning deficits, but not an endotoxin-induced blockade of long-term potentiation.

Peripheral administration of lipopolysaccharide (LPS), a potent bacterial endotoxin, can cause a variety of central effects, including production of cytokines and cyclooxygenases in the brain, as well as peripheral increases in corticosterone. These, in turn, may contribute to neuroimmune-induced neurocognitive deficits. We show here LPS causes deficits in hippocampal-dependent spatial learning in the water maze but that treatment with ibuprofen, a broad-spectrum cyclooxygenase inhibitor, reverses the deficits induced in spatial learning by LPS. We also show that LPS causes an impairment in the induction of long-term potentiation in the dentate gyrus in vivo, a major contemporary model of learning and memory. No differences were found in corticosterone levels in trunk blood but we find a decrease in brain-derived neurotrophic factor (BDNF) expression in LPS group compared to saline controls. Paradoxically compared to the behavioral findings treatment with ibuprofen does not attenuate the LPS-induced impairment in LTP or BDNF concentration in tetanized tissue.

Brain-Derived Neurotrophic Factor↗

PubMed2005

Vestibular influence on water maze retention: transient whole body rotations improve the accuracy of the cue-based retention strategy.

Spatial learning in the water maze is thought to rely both on distal cues and vestibular information [Aggleton JP, Vann SD, Oswald CJP, Good M. Identifying cortical inputs to the rat hippocampus that subserves allocentric spatial processes: a simple problem with a complex answer. Hippocampus 2000;10:466-74; Pearce JM. Animal learning and cognition: an introduction. UK: Psychology Press; 1997]. Experiment 1 demonstrates that while water maze retention relies primarily on cue-platform based associations, this strategy is not precise, as animals tend to focus at the side of the pool. In experiment 2, we demonstrate that vestibular rotation eliminates this inaccuracy. These experiments highlight the importance of both cue and vestibular information for accurate retention of the water maze.

Analysis of Variance↗

PubMed2005

Long-term retention and overshadowing of proximal and distal cues following habituation in an object exploration task.

The object displacement task is a popular tool used to investigate spatial learning and memory. However, little attention has previously been given to long-term retention of spatial information following habituation to this task. Furthermore, the role of both proximal and distal cues in this type of passive retention of spatial information is controversial. In Study 1, we examined habituation in the object displacement task across 4 days and examined reactivity to spatial change 7 days post-acquisition. We found that rats habituated rapidly to the environment and retained this environment for the 7 days. Furthermore, this experiment shows that both proximal and distal spatial cues are important in the encoding of the environment during object displacement learning task. In Study 2, we examined the effect of overshadowing and demonstrate that proximal visual spatial cues can overshadow distal spatial cues if a conflict arises between both set.

Animals↗

PubMed2005

Interaction between paired-pulse facilitation and long-term potentiation in the projection from hippocampal area CA1 to the entorhinal cortex.

The hippocampus communicates with the neocortex via the entorhinal cortex and is thought to be critically involved in the consolidation of memories. This paper contains in vivo evidence of a projection from the hippocampal area CA1 to the entorhinal cortex. Current theories of memory formation suggest that the backprojections from the hippocampus to the neocortex should undergo some form of plastic change in order that memories become consolidated. Paired-pulse facilitation (PPF) and long-term potentiation (LTP) are forms of short- and long-term plasticity, respectively. We show that the CA1 to entorhinal cortex projection is capable of sustaining PPF over a wide range of stimulus intervals. In addition we demonstrate that following high frequency stimulation of this pathway the evoked response in the entorhinal cortex remains potentiated for at least 30 min. Finally, we demonstrate that PPF changes following LTP depending on the initial ratio of PPF, suggesting that LTP expression on this pathway may contain a presynaptic component. These findings should provide insight into the hippocampal function in memory formation.

Animals↗

PubMed2005

Derived stimulus relations, semantic priming, and event-related potentials: testing a behavioral theory of semantic networks.

Derived equivalence relations, it has been argued, provide a behavioral model of semantic or symbolic meaning in natural language, and thus equivalence relations should possess properties that are typically associated with semantic relations. The present study sought to test this basic postulate using semantic priming. Across three experiments, participants were trained and tested in two 4-member equivalence relations using word-like nonsense words. Participants also were exposed to a single- or two-word lexical decision task, and both direct (Experiment 1) and mediated (Experiments 2 and 3) priming effects for reaction times and event-related potentials were observed within but not across equivalence relations. The findings support the argument that derived equivalence relations provides a useful preliminary model of semantic relations.

Adolescent↗

PubMed2005

Relating derived relations as a model of analogical reasoning: reaction times and event-related potentials.

The current study aimed to test a Relational Frame Theory (RFT) model of analogical reasoning based on the relating of derived same and derived difference relations. Experiment 1 recorded reaction time measures of similar-similar (e.g., "apple is to orange as dog is to cat") versus different-different (e.g., "he is to his brother as chalk is to cheese") derived relational responding, in both speed-contingent and speed-noncontingent conditions. Experiment 2 examined the event-related potentials (ERPs) associated with these two response patterns. Both experiments showed similar-similar responding to be significantly faster than different-different responding. Experiment 2 revealed significant differences between the waveforms of the two response patterns in the left-hemispheric prefrontal regions; different-different waveforms were significantly more negative than similar-similar waveforms. The behavioral and neurophysiological data support the RFT prediction that, all things being equal, similar-similar responding is relationally "simpler" than, and functionally distinct from, different-different analogical responding. The ERP data were fully consistent with findings in the neurocognitive literature on analogy. These findings strengthen the validity of the RFT model of analogical reasoning and supplement the behavior-analytic approach to analogy based on the relating of derived relations.

Adolescent↗

PubMed2004

Retention of cue-based associations in the water maze is time-dependent and sensitive to disruption by rotating the starting position.

Research has focused mainly on the acquisition phase of spatial tasks, while retention has been relatively ignored. In three experiments, we determine the type of information that is retained in spatial memory using the water maze task. In experiment 1, we demonstrate that by rotating the distal cues 180 degrees post-acquisition Wistar rats search in the opposite area to where the platform should be. This search continues for a maximum of 30 s. We then demonstrate (experiment 2) that by rotating the starting position (180 degrees post-acquisition) animals remain at the starting-point for 10 s. They then commence searching in the platform area. In experiment 3, we demonstrate that rotations of distal cues and starting position post-acquisition impair retention of the platform's location. We suggest that the association between the configuration of distal cues and platform location is retained in memory but the association is fragile and sensitive to disruption.

Analysis of Variance↗

PubMed2003

Massed but not spaced training impairs spatial memory.

The Morris water maze and the object displacement task are two popular tools used to investigate spatial learning and memory. Research has focused mainly on the acquisition of spatial tasks while little attention has been given to the retention phase. We examined the effects of different training procedures on retention of the water maze and also reactivity to spatial change in the object displacement task 7 days post-acquisition. We found that massed-trained animals were impaired on retention of the water maze compared to those animals that had received spaced-training. We also found that the massed-trained animals habituated readily to their environment in the object displacement task while the spaced-trained group did not. Furthermore the massed-trained group did not react to spatial change 7 days post-habituation compared to the increased reactivity displayed by the spaced-trained group. Results are discussed in terms of poor encoding of the environment leading to poor retention.

Analysis of Variance↗

PubMed2003

Deficits in spatial learning and synaptic plasticity induced by the rapid and competitive broad-spectrum cyclooxygenase inhibitor ibuprofen are reversed by increasing endogenous brain-derived neurotrophic factor.

Cyclooxygenase (COX), which is present in two isoforms (COX1 and 2), synthesizes prostaglandins from arachidonic acid; it plays a crucial role in inflammation in both central and peripheral tissues. Here, we describe its role in synaptic plasticity and spatial learning in vivo via an effect on brain-derived neurotrophic factor (BDNF) and prostaglandin E2 (PGE2; both measured by Elisa). We found that broad-spectrum COX inhibition (BSCI) inhibits the induction of long-term potentiation (LTP; the major contemporary model of synaptic plasticity), and causes substantial and sustained deficits in spatial learning in the watermaze. Increases in BDNF and PGE2 following spatial learning and LTP were also blocked. Importantly, 4 days of prior exercise in a running wheel increased endogenous BDNF levels sufficiently to reverse the BSCI of LTP and spatial learning, and restored a parallel increase in LTP and learning-related BDNF and PGE2. In control experiments, we found that BSCI had no effect on baseline synaptic transmission or on the nonhippocampal visible-platform task; there was no evidence of gastric ulceration from BSCI. COX2 is inhibited by glucorticoids; there was no difference in blood corticosterone levels as measured by radioimmunoassay in any condition. Thus, COX plays a previously undescribed, permissive role in synaptic plasticity and spatial learning via a BDNF-associated mechanism.

Animals↗

PubMed2002

Physiological evidence for a possible projection from dorsal subiculum to hippocampal area CA1.

The substantial forward projection from hippocampal area CA1 to the subiculum has been comprehensively described, both anatomically and neurophysiologically. There are few data, however, regarding the existence of a backward projection from the subiculum to area CA1. We present here new electrophysiological evidence for the existence of this projection. We demonstrate a positive-going deflection in the evoked synaptic response in area CA1 following stimulation in dorsal subiculum. We also found a small, but significant, paired-pulse facilitatory effect at a 100-ms interstimulus interval. We were unable to induce long-term potentiation following high-frequency stimulation, but were able to induce short-term potentiation.

Animals↗