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Psy 110 Experiments

Terms in this set (17)

Neher and Sakmann
wanted to be able to record, not just from a single neuron, but from a single ion channel. A recording pipette filled with an electricity-conducting solution is placed in contact with a neuron's membrane. Slight suction clamps a patch of the membrane to the pipette tip. Retracting the pipette removes the membrane patch, often with one or more ion channels in it; the opening and closing of ion channels can be recorded electrically through the pipette
Alan Hodgkin and Andrew Huxley
• studied the squid giant axon (0.5 mm in diameter, ~100x bigger than mammalian neurons)
• motor neuron responsible for escape response • dissected neuron can survive in sea water for up to 2 days
• wires are too thick to place in the neuron so developed the glass microelectrode
• <1000th mm in diameter
• glass doesn't conduct electricity so
filled with potassium chloride solution
MacKinnon Nobel Prize
...
Loewi Nobel Prize
At the beginning of the 20th century there was debate over whether neural communication occurred electrically or chemically. So let me explain what this Lowei fella did. He's a true trooper. He took two hearts, and put them in two separate cups, and these cups were connected with a tube. Then he stimulated the first heart with electricity, so action potentials were fired. Oh but wait!! The second heart was also fired, even though the electricity shouldn't have reached it. So he was like arite, it's gonna be chemically. So he termed the nonknown chemical "Vagusstoff". But then we was like nahh breh, we gonna change it to acetylcholine. Poor Loewi. Cry evertim.
Rita Levi-Montalcini
discovered a substance called Nerve Growth Factor (NGF) that caused a neuron to increase in size and grow many more processes. Thus, neuronal death might arise due to a competition for NGF. Since the discovery of NGF many different growth factors have been identified.
Charles Gross and Elizabeth Gould
Used BrdU (5-bromo-3'-deoxyuridine) which is taken up by dividing cells during mitosis, and is thus a marker of proliferating cells and their progeny.
But if a cell is seen to be stained with BrdU it might simply be a glial cell (which are known to die and be replaced throughout our lives).
Thus a second stain is required to detect neurons. There are now several of these stains available, e.g. NeuN (Neuronal Nuclei).
Gross and Gould observed double-labeled cells in prefrontal cortex (a), the hippocampus (b, c) and the parietal cortex (d).

When accused by Pasko, they countered by Gould and Gross showed their own stains in which the double-labeling appears to cover the full extent of the cell.
Pasko Rakic
Uses the street fighter move, "CROSS COUNTER!" on Charles Gross and Elizabeth Gould. He said that

One problem is that the microscope gives a 2D image. If images were taken at several sections it became clear that at least some of the double-labeled cells could be a glial cell and a neuron in close proximity.

When countered by Gross and Gould, Pasko "CROSS-COUNTERED!" again by saying that Rakic has countered with an attack on the specificity of the stains used to identify neurons. What does this mean? I have NO idea. Ask Ian.
Apparently this dude was right.
The ferret experiment
We train the ferret to tell us whether it is hearing a sound or seeing a light (if it hears a sound it moves its head in one direction, if it sees a light it moves its head in the opposite direction).
Then we rewire the ferret by removing the inputs from the ear to the MGN.

The ferret is now deaf, because sound cannot get from the ear into the brain.

We also remove V1, so that the animal should now be blind.

We now ask the ferret what he experiences when we show him a light.

He 'tells' us (by moving his head in the appropriate direction) that he is seeing a light.

We know (because we've got rid of V1) that to see this light he must be relying on A1.

In other words, A1 is processing its 'new' signals as visual signals.
Hubel and Wiesel
They covered Cat's eyes and stuff. Refer to image 12
Kandel
Studied the sea slug by poking it and stuff. Yum
Hebb
Neurons that fire together wire together. Why is this important for learning? For the Hebbian synapse to work, some mechanism at the synapse must be able to detect that both the pre-synaptic and post-synaptic neuron are active. This leads to Long-Term Potentiation (LTP)
timothy bliss and terje lomo
The discovery of LTP.

A stimulating electrode is placed in neurons in the perforant path and a recording electrode is placed in the dentate gyrus.

A single pulse of electrical stimulation is applied to the perforant path and the resulting EPSP is recorded in the dentate gyrus.

The axons in the perforant path are then stimulated with a burst of about 100 pulses in the space of a few seconds.

This results in the pre-synaptic and post-synaptic neurons being active at the same time.

Subsequent single pulses to the perforant path now produce larger EPSPs in the dentate.
Rats experiment using optogenetics
...
Golgi stain
Camilo Golgi (1873) invented a staining method using potassium dichromate and silver nitrate, that randomly stained individual neurons, enabling them to "pop-out" against the background of other neurons.

A Golgi stain reveals how neurons are organized in the hippocampus, which cannot be seen in the Nissl stained section (inset) which stains neuronal cell bodies.
Cajal
Some anatomists argued that neurons formed a nearly endless series of interconnected tubes.


Cajal used the Golgi stain to postulate the 'neuron doctrine'. From his detailed drawings he insisted that although neurons came very close to one another there were tiny gaps that kept them separate and that they were individual cells.
Jeff Lichtman
"Brainbow"

Mice are engineered with a genes express three different fluorescent proteins (R, G and B)

Different neurons express different amounts of each protein
Karl Diesseroth
CLARITY. By removing the lipid around cells (essentially by washing the brain in detergent), while using a hydrogel to maintain support for the cell components, Diesseroth was able to make the brain transparent.

This technique can be combined with the brainbow techniques to allow us to visualize individual neurons throughout the brain.

However, they are invasive (require post-mortem tissue)

hard to get big picture for a wiring diagram (computational complexity)

So Anatomists have traditionally replied on tract tracing
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