1 8 1 Invertebrate Learning and Memory BIO 361T Fall 2014 1 The graph below illustrates voltage measurements from two cells in the sea slug Aplysia a Is the graph showing habituation or sensitization Habituation b What cell is being recorded from to get the presynaptic impulses Sensory afferent from the siphon c What cell is being recorded from to get the postsynaptic potentials Motor efferent to the gill d Why are the postsynaptic spikes getting progressively smaller in response to identical presynaptic input Give molecular details Inactivation of voltage gated Ca2 channels which leads to less neurotransmitter release and less downstream motor efferent gill muscle contraction activity Exact molecular mechanism is unclear but decreased activity is seen at multiple synapses effects of habituation are widespread e Why do you think this is called antifacilitation Can you contrast it with another process Because it decreases intracellular Ca2 and neurotransmitter release and motor response Opposite of facilitation which is seen in sensitization f Why is habituation an adaptive learning process It allows animals to learn not to pay attention to irrelevant stimuli and use energy for necessary responses 2 2 The figure below shows an experimental set up and recordings from the process of sensitization in Aplysia When the tail sensory afferent fires it excites the facilitating interneuron which releases serotonin onto the axon terminal of the siphon sensory afferent a This binds a n metabotropic ionotropic metabotropic receptor which activates adenylate cyclase via a G protein This converts ATP into cAMP which activates protein kinase A PKA which phosphorylates K channels in the membrane causing them to close When K efflux is inhibited the membrane will stay depolarized longer which opens more voltage gated Ca2 channels causing more vesicles of glutamate to be released onto the gill motor efferent b This binds another metabotropic ionotropic metabotropic receptor that activates phospholipase C PLC via a different G protein This splits PIP2 into two molecules one of which is diacylglycerol DAG which goes on to activate protein kinase C PKC which activates L type Ca2 channels causing more vesicles of glutamate to be released onto the gill motor efferent 3 Why is this process referred to as pre synaptic facilitation Explain the pre synaptic part and the facilitation part Pre synaptic directly affects the siphon sensory afferent not the gill motor efferent Facilitation increases intracellular Ca2 and vesicle release 3 4 What will happen if a serotonin receptor antagonist is injected then the process of sensitization is repeated As part of your explanation draw a pair of graphs similar to the control and sensitization pairs of graphs that illustrate what will happen Sensitization will fail to occur and with repeated siphon stimulation gill withdrawal may actually decrease habituation With no serotonin binding at the axon terminal of the siphon sensory afferent there will be no increase in glutamate release to the gill motor efferent Graph showing single peaks similar to the ones given should look same as control 5 Long term learning requires protein synthesis but short term does not Explain this statement using CREB in Aplysia as an example CREB is a transcription factor that binds CRE enhancer sequences which are found in promoters for genes that control protein synthesis specifically for increasing PKA activity and new neuron growth This is involved in making Aplysia sensitive to its environment over a longer time course because PKA stays over active and more synapses are created In short term learning only proteins that are already present get activated or inhibited There is no change in gene expression and no pruning as in long term habitation or growth as in long term sensitization of neurons Short term learning is the result of several trials given in a short period of time such as ten times in a few minutes whose effects may last a day or so Spontaneous recovery depends on length of rest between each stimulus if the animal is constantly bombarded with the stimulus it will take longer to recover Long term learning is the result of several trials spaced out over a longer period such as once a day for a week whose effects can last for a month or longer Habituation can be short or long term but sensitization is usually only short term a week or so stronger for stronger stimuli as it would be maladaptive to remain extremely sensitive to stimuli when the threat has long since passed However it does occur as it does via CREB in Aplysia 6 Imagine an animal is exposed to a strong stimulus and a weak stimulus It habituates to one and becomes sensitized to another Which do you think will cause which process Which effect do you expect to last longer Explain your answers Habituation occurs more rapidly to weaker stimuli as they are less relevant Sensitization occurs more often to stronger stimuli as it is likely to be maladaptive for an animal to get used to intense changes in their environment Habituation will probably last longer as it would be maladaptive to remain extremely sensitive to your environment for a long time if there is not a continued threat Note that sensitization in the gill withdrawal reflex in Aplysia requires pre synaptic facilitation via an additional stimulus the tail shock but this is not always necessary Example if you hear a loud noise in the middle of the night you will become more aware of the sounds around you for a little while You have become sensitized to your auditory environment by a strong stimulus Sensitization is usually only adaptive over short time spans It would be maladaptive to be in a heightened state of awareness for months or years without any kind of reinforcement 7 Why are habituation and sensitization referred to as non associative learning Contrast these processes with associative learning There is no association between multiple stimuli just a decrease or increase in response to a natural stimulus respectively Associative learning involves pairing stimuli In classical conditioning a natural stimulus is learned to be associated with an unnatural stimulus such that the unnatural stimulus alone then elicits the reflexive response to the natural stimulus In operant conditioning an unnatural stimulus is positively or negatively reinforced to increase or decrease its likelihood of inducing a response respectively Good example is Skinner boxes which can
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