Chapter 10, 3/30/17

classic Morris experiment

(A) A cannula was implanted into the ventricles of the rat's brain and attached to a time-release pellet that contained the NMDA receptor antagonist APV. (B) Rats were trained on the place-learning version of the water-escape task. (C) Rats infused with APV could not sustain LTP in the dentate gyrus. (D) Rats infused with APV were impaired in learning the location of the hidden platform. (E) Control rats selectively searched the quadrant that contained the platform during training, but rats infused with APV did not. T = training quadrant; A = adjacent quadrant; O = opposite quadrant.

Memory formation

(A) The formation of a memory trace begins when a behavioral experience activates a set of weakly connected neurons. (B) The cellular-molecular processes activated in these neurons strengthen their synaptic connections, thereby creating a neural representation of the behavioral experience, called a memory trace.

Morris

1. used a pharmological approach to understanding memory formation involving NMDARs. 2. He infused APV into the cerebral ventricle using implanted cannula 3. concluded that NMDARs are involved in spatial learning, and LTP is involved in learning.

In the radial methodology maze tasks, rats without any manipulation A. Rarely make reference or working memory errors B. Make reference memory errors but not working memory errors C. Making working memory errors but not reference memory errors D. Make both types of errors equally E. Both a and d

A(they rarely make these errors)

NMDA and AMPA receptors involvement in acquisition and Retrival

A) This graphic is a schematic of the arena Morris and his colleagues used to study the role of glutamate receptors in the acquisition and retrieval of a memory for the location of flavored food pellets. On the retrieval test, the two sand wells that contained the flavored pellets on the acquisition trial were uncovered. The rat was fed one of the pellets in the release point. Its task was to remember which sand well contained that pellet during acquisition. (B) When given before acquisition, both APV and CNQX interfered with establishing the food-location memory. However, only CNQX, the AMPA receptor antagonist, interfered with the retrieval of the memory. Con = control group. (After Day et al., 2003.) Timing of the appliation matters to correct the percent of time digging in correct sand well.

Why did Malinow use mice with different gluR1 function?

Because it allows us to functionally evaluate the contribution from the AMPARs

What happens with Ca1KO mice?

Doesnt show an LTP detected at CA1 but still shows at CA3

What happens with Ca3KO mice?

Doesnt show an LTP detected at CA3 but still shows at CA1

Glun2B

Doogie mouse is genetically engineered to overexpress ____ subunits

Discoveries from Doogie mouse research

Drugs and genetic manipulations can modify behavior without affecting learning and memory. These agents can have multiple effects. Memory formation may take place without the contribution of NMDA receptors. Other mechanisms that can produce memories when NMDA receptors are not functional. A component of the brain is removed and this has no effect on memory formation, one cannot say the component is not involved in memory formation when it is normally present.

True or False: GluN1 subunits are not required to form functional NMDARs

False

Working memory cannot be studied in animals because they cannot communicate what problems they are trying to solve

False

AMPARs are needed only for memory acquisition, but NMDARs are required for both acquisition and retrieval.

False (AMPA neeeded for acquisition and retrival, NMDA needed for just acquisition.)

True or False: Morris used genetically engineered mice in the first study that investigated the role of NMDARs in memory formation.

False( he was first to apply pharmacological methodology.)

CaMKII and fear memories

Fear conditioning produces increased phosphorylated CaMKII in dendritic spines in the amygdala. (A) A micrograph showing particles of phosphorylated CaMKII in a spine. (B) Rats that received paired presentations of a tone and shock have more particles of phosphorylated CaMKII in spines than control animals that received either no shock or unpaired presentations of the tone and shock. (C) The drug KN-62, which inhibits the phosphorylation of CaMKII, impairs both contextual and tone-fear conditioning. In micrograph (A), the black particles in greater numbers means more CaMKII gets phosphorylated

testing Dummy AMPARs

Figure 10.8 (A) Modified nonfunctional GluA1 receptors are injected into the lateral amygdala. These modified receptors compete with endogenous functional GluA1 receptors for trafficking into spines. (B) Rats injected with this receptor display impaired fear conditioning to a tone paired with shock. SO DO NEED THIS REGION. (C) Slices from animals injected with the modified receptor cannot sustain LTP induced in the lateral amygdala

GluN1

Functional NMDARs require a ___________ subunit. So you can target this subunit to change the receptor function

Malinow's experiment

Genetically engineered GluR1 AMPAs that had electrical conductance properties that were different from endogenous GluR1s function. This allows us to functionally evaluate the contribution from this AMPARs. Labeled the receptors with a fluorescent protein Used a viral vector system to deliver these receptors into neurons located in the amygdala Exposed the mice to a fear conditioning experience Took out their brains and tested slices to look for evidence of trafficking of the engineered receptors

How is glutamate receptor composition (Glua1) critical to working memory?

GluA1 knockout mice can display an enduring LTP but not the rapidly formed early phase. These mice can learn and remember the reference memory component of the task. However, they are impaired on the working memory component. This result suggests that GluA1 receptors are critical for working memory. It mediates the working memory. Figure 10.15 (A) GluA1 knockout (KO) mice do not express early-phase, short-lasting LTP but do express late-phase, enduring LTP. (After Romberg et al., 2009.) (B) The GluA1 KO mice do not differ from control mice in learning the reference memory component of the radial maze task but display severely impaired working memory. (After Sanderson and Bannerman, 2012.)

NMDA _______ subunits are required for working memory but not for reference memory

GluN2A (this was proved using GluN1 KO mice which did not show deficit.)

Working and Reference memory depend on _________ receptors

Glutamate

Silva expteriment

He worked with CaMKII-deficient mice (CaMKII KO). It can learn to swim to the visible platform but cannot learn the location of the hidden platform. Note that control mice selectively search the target quadrant on a probe trial while the defective CaMKII KO mice do not. T = training quadrant; A = adjacent quadrant; O = opposite quadrant. This means CaMKII is involved in spatial learning. autophosphorylates

Joe Tsien

His experiment determined the overexpression of gluN2B subunits in the forebrain using the Doogie Mouse. They found that overexpression may improve learning and memory. During development there is a shift in the ratio of GluN1-GluN2 to GluN1-GluN2B. GluN1-GluN2B receptors channels can stay open longer with higher Ca2+ permeability than GluN1-GluN2A channels. Also performed other tests to find that this mouse is smart!!

Tonegawa experiment

His experiment involved deleting the GluN1 subunit in CA1 pyramidal neurons. Note that LTP could be induced in the dentate gyrus but could not be induced in the CA1 region.

What does water-maze fixed platform experiment say about Ca1 and Ca3 KO mice?

It can confirm in vivo memory/learning impairments. It would show escape latency significantly prolonged with CA1KO, allowing us to claim that the NMDARs in the CA1 region is mediating the spatial learning. Also, both regions show they have different types of space learning involvement

Malinows fear conditioning expt

LTP studies have shown that GluA1 AMPA receptors are inserted into the plasma membrane of dendritic spines in response to synaptic activity. Malinow and his colleagues used a special technique to insert modified glutamate receptors, GluA1s, into the lateral amygdala. (A) These receptors were labeled with a fluorescent molecule and could be visualized. (B) Rats with these fluorescent AMPA receptors were tested for fear of a tone paired with shock or tested for fear of a tone unpaired with shock. Rats in the paired condition displayed fear to the tone. The rats were then sacrificed and slices were taken from their brains. An analysis of these slices revealed fear conditioning had driven the GluA1 AMPA receptors into the spines. (C) Schematic representation of the distribution of the GluA1 receptors prior to training. (D) After the training, rats in the paired condition had more GluA1 receptors trafficked into the plasma membrane than rats in the unpaired condition. These results indicate that a behavioral experience that produces fear conditioning also drives AMPA receptors into the synapse. (After Rumpel et al., 2005.)

Heterotramer

NMDA receptor subunits make up this shape.

NMDAR subtypes

NMDA receptors are composed of four subunits. All functional NMDA receptors contain GluN1 subunits. There are a variety of GluN2 subunits. This figure illustrates NMDA receptor complexes composed of GluN1-GluN2A and GluN1-GluN2B subunits. GluN2C, GluN2D

The Doogie Mouse

Shows enhanced memory. Why? In this specific mouse, the GluN1-GluN2B NMDA complex is overexpressed in several regions of the brain, including the cortex, hippocampus, and amygdala (photo courtesy of J. Z. Tsien). (A) Slices from the Doogie mouse show enhanced LTP. (B) The Doogie mouse shows a stable and enhanced memory for a contextual fear-conditioning experience. These adult mice displayed enhanced LTP and enhanced learning and memory in several tasks.

Dummy AMPARs

These compete with endogenous receptors for delivery to synapses and impair fear conditioning and LTP

Ampakines

These modulate receptor channel function and enhance learning. Are known to induce cognitive enhancement When glutamate binds to AMPA receptors the conductance channel is briefly opened and this allows positive ions to enter. (B) When ampakines and glutamate both bind to the AMPA receptor, the channel stays open longer and therefore more ions enter and the synaptic response is enhanced. (C) Ampakines enhance the rate of auditory fear conditioning. Picture slide 26 explains why Ampakines can facilitate AMPAR function, which is proved b the behavioral result.

AMPAR trafficking

These receptors are trafficked to be inserted/replaced into the membrane. We can hypothesize the receptors are involved in early stage of memory formation. Malinow's experiment supports this

Preventing Autophosphorylation of CaMKII

This impairs learning! Autophosphorylation is critical for rapid formation of a fear memory but not essential for memories produced with multiple training trials. In this experiment, mice genetically engineered to impair autophosphorylation of CaMKII (T286A mice) and control mice received 1, 3, or 5 pairings of a tone and shock. Control mice acquired fear to the context and to the tone after only one pairing; however, the defective mice required several pairings to acquire the fear memory. (compensate with trial #).

e

To influence NMDA function, morris: A. used a pharmacological approach, B. infused aPV into the brain, C. implanted annula into the cerebral verticle, D. tested rats int the space learning swim task E. All of the above

NMDA receptor role

To open the NMDA receptor, glutamate must bind to the receptor and the neuron must depolarize. Depolarization is produced when glutamate binds to AMPA receptors allowing Na+ to enter. When this happens the Mg2+ plug is forced out of the receptor and Ca2+ enters the channel.

True or False: Behavioral experience that produces a memory is likely to result in more phosphorulated cofilin and more autophosphoylated CaMKII

True

b

Which is true about NMDARs A. Are activated by calcium B. Channels allow calcium to enter cell C. Composed of NR1/NR2A subunits remained open longer than those composed of NR1/NR2B subunits D. Early in development, the ratio of NR1/NR2B to NR1/NR2A containing NMDA receptors facvors the NR1/NR2A complex E. None of the above

e ( both A and B: GluN1 subunits are absent in CA1 region and LTP cannot be induced in CA1 slices)

Which of the following is true about the CA1KO mouse? A. GLuN1 subunits are absent in the Ca1 region B. LTP cannot be induced in CA1 in slices C. LTP cannot be induced in the dentate gyrus D. GluN1 subunits are absent in the dentate gyrus E. Both A and B

In the radial maze, a rat can make either a ____________ error or a __________ error.

Working memory or reference memory error

Are AMPARs needed for acqusition, retrival, or both for memory?

both

The radial maze

can be used to study both working memory and reference memory. It has 8 arms: 4 arms bated while 4 arms are not bated. The rats, during the training session, has to learn which 4 arms are never bated (reference memory component) and to remember which arms have previously been visited (working memory component.) A trial begins when the rodent is placed in the center of the maze. It ends when the animal has retrieved the food reward from all baited arms. Only four of the eight arms are baited but the same four arms are baited on each trial. The rat has to learn which four arms are never baited (the reference memory component) and to remember which arms it previously visited (the working memory component). The rat can now make two types of errors on a trial: (1) a working memory error—it enters a previously sampled arm, and (2) a reference memory error—it enters an arm that was never baited. G = goal.

True or False: CA1KO mouse was ale to display LTP in CA1 regions but not in Dentate gyrus

false

True or False: Remembering the plot of ta book you read a few months ago is an example of working memory.

false

Hippocampus structure

it is trisynaptic, remember: please don't make 3 sandwiches in 1 day

Are NMDARs needed for acqusition, retrival, or both for memory?

just acquisition

Malinow

performed fear conditioning experiment to induce AMPAR trafficking using genetically engineered GluR1 AMPAs that had electrical conductance properties that were different from endogenous GluR1s function. He discovered fear conditioning drives AMPARs into the synapse.