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NESC 3043 (1)
Lecture

NESC 3043.docx

16 Pages
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Department
Neuroscience
Course Code
NESC 3043
Professor
Leslie Phillmore

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October 10th, 2012 October-10-12 11:36 AM Hippocampus HM o Had medial temporal lobe removed to solve epilepsy problems o He was able to learn new motor tasks, but was never able to remember doing them. Had procedural (implilcit) memory, but not explicit memory Active during spatial tasks o Lesions show that it's important for tasks requiring spatial memory, like remembering how to get to school (london taxi driver example) Has specific "place cells", that encode specific locations o Each individual space cell fires the most when the animal is closest to that space Anatomy of Hippocampus Two interlocking folded pieces of cortex Receives connections from sensory regions of the cortex, and each sense has a different specialized connection area in the hippocampus (vision connects here, smell here, ect.) Located in different anatomical places in different animals Don't identify hippocampus in animals by how it looks, because they all look different, identify it by how it responds 3 main structures o Dentate gyrus o Ca1 o Ca3 LTP and hippocampus Not same in each pathway In collateral and perforant pathways o Is cooperative, glutamate must bind, and mg2+ plug must be released o Need firing in pre and postsynaptic cells Mossy-fibre pathway o Nonassociative Binds to nmda and non-nmda receptors, but are not influential Blocking NMDA receptors does not block LTP So is non-nmda dependent LTP Depends on calcium influx into presynaptic cell Testing associative and nonassociative Can test both in one region Can measure from Ca3 in one organism, and receive LTP from two separate pathways o Associative from CA3 on contralateral side o Non-associative from mossy fibre on ipsilateral side BAPTA blocked the associative LTP because it blocked all second messenger pathways in post- synaptic cell Non-associative wasn't affected because it relies on pre-synaptic signals for LTP Tagging One synapse on a neuron can facilitate the strengthening of every synapse on that neuron, even if it's not the same one thats stimulated after tagging Spatial memory without a hippocampus? Slime mold o 1 celled organism o Remembers where it's been by leaving a slime trail o Avoids the slime trails o A form of external memory o Masking the slime trail interferes with it's memory October 12th, 2012 October-12-12 11:42 AM Place field The actual place that corresponds to a particular place cell, and that cell will fire when you're in that place field O'Keefe Placed rat in chamber, and observed which neurons fired when the rat was in a specific spot There were some cells that fired no matter where the rat was, o They decided these might be interneurons, but there may be a different reason Place fields Pyramidal cells fire in relation to where the animal is in space NON-topigraphic representation of spatial environment How do they contribute to goal-directed nagivation? Annular water maze Goal was to find platform, but had to swim a full lap before it was available 1 group, the platform stayed in the same location 1 group, the placement was random Rats were implanted with electrodes in hippocampus for recording o Allowed for recording of individual neurons o Cells being recorded are NOT direction specific o Firing of the neuron ceased as soon as the rat made it onto the platform Potentially for conservation of energy, because the neurons are to help you navigate to that spot, once you have made it to the spot, and achieved what's wanted, why waste energy by still firing the neuron Rats were put through several trials, and then probe trial o Trial where platform was not presented, then they measured how much time the rats spent in the area where the platform was Rats with consistent placement, spent much of their time where platform was, learned location quite quickly (5 trials) In (A), there was no platform (probe), trial (B) had a platform Stability of place fields New place fields form in a matter of minutes Can be stable for months Early vs. Late NMDA receptor blockers interfere with long term stability of place fields, but not formation and short term maintenance Setup of experiment Animals have a familiar (trained) environment, and a novel environment Recorded place fields for animals in familiar or novel environment Injected with anisomycin (protein inhibitor) Measured place fields at 1, 6, and 24 hours Place fields already formed in familiar environment, need to be formed in novel environment Place fields look the same in familiar environment with saline injection at 1, 6, and 24 hours In novel environment, with saline, place fields are pretty much the same Place fields in familiar environment with anisomycin are still same In novel environment though, place field same from 0-1hour, but from 1-6, there is a significant change because of blocked protein synthesis But the same from 6-24 hours, because drug is not inhibiting anymore at that point Previous research 2 hippocampal regions lesioned o Either ventral or dorsal Spatial memory in morris water maze o Ventral lesion, they were still able to learn where the platform was, but not quite as much as control o Dorsal lesion, they spent equal time in all zones, were not able to learn where platform was Told researchers that dorsal and ventral regions of hippocampus were doing different jobs o Does it have to do with the scale of the task? Larger apparatus was created for larger scale spatial task Small apparatus also created Electrodes were implanted in dorsal or ventral CA3 regions Place fields were small and specific in dorsal hippocampus As they progressed into ventral regions, place fields became much larger ZIP injection disrupts stable, already established place cells October 17th, 2012 October-17-12 11:33 AM Location of HP Can be in very different spots in different organisms o There can be structural differences o And some connecting structures can be different Anatomical similarities Avian and mammalian hippocampi emerge from same portion of developing telencephalon Many input and output connections similar Task type #1 Hippocampus lesioned in these animals DNMS o Hippocampus does not appear to play a role in this task in monkeys and pigeons o But any animal with damage outside the hippocampus (in big lesion including hippocampus) showed deficits, especially if amygdala lesioned Concurrent discrimination o No difference in HP only lesion o Again, with damage outside hippocampus there were deficits shown Concurrent discrimination with retention within and between task measurements o No loss in performance with any lesion Task type #2 Usually multimodal input (auditory and visual) Navigation task o Such as morris water maze, or homing in pigeons o Lesions to HP affect both of these tasks Navigation in pigeons Have a navigation map o For pointing in the right direction initially Landmark map o Switch to this when close, use visual landmarks to pinpoint home Lesion in adults o Can take homeward bearing, but take longer to find loft, and take less direct path o Moving home base (loft) after lesion = pigeon unable to find the loft Hippocampal neurogenesis Maybe they're recruiting more cells to the HP when they are recalling the memory (retrieval of food) as opposed to when the memory was formed (hiding the food)
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