Download BME 502 - Engineering Class s

BME 502
Exam #3 (2001)
CLOSED BOOK
Name: _______________________
TOTAL TIME: 3.0 hrs
Question #1
Distinguish between AMPA, NMDA, and metabotrobic glutamatergic receptor subtypes with
respect to the following:
(a) the conditions required to induce a change in the postsynaptic neuron; identify each of the
major molecular steps involved and their sequence, e.g.,
AMPA:
glutamate binding to the receptor
channel opening to allow influx of Na+ and efflux of K+
BME 502
Exam #3 (2001)
Name: _______________________
Question #1 (cont.)
(b) the respective time courses of their postsynaptic effects; give numbers for the time-to-peak
and duration for AMPA and NMDA; explain why one is longer than the other; you don't know
the time course for the metabotrobic receptor subtype, so just tell me whether it should be
expected to be longer or shorter than AMPA or NMDA and why
(c) identify 2 different procedures for blocking the effects of NMDA receptor-channels using
extracellular manipulations
BME 502
Exam #3 (2001)
Name: _______________________
Question #1 (cont.)
(d) identify a procedure for blocking the effects of NMDA receptor-channels using an intracellular,
pharmacological/ionic manipulation
(e) identify a procedure for blocking the effects of NMDA receptor-channels using an intracellular,
electrophysiological manipulation
BME 502
Exam #3 (2001)
Name: _______________________
Question #2
You are experimentally investigating neurotransmitter release from a nerve terminal of an animal
that changes the subtype of voltage-dependent calcium channels throughout its development.
Your job is to figure out which subtype of calcium channel predominates at different
developmental stages. You are able to electrically stimulate a population of afferent fibers to a
population of postsynaptic neurons, to record intracellularly from a single presynaptic
axon/terminal, to record intracellularly from a single postsynaptic neuron, and to add drugs to the
extracellular medium.
(a) When the beast is "young", you can stimulate the afferents so as to produce a single
presynaptic action potential and you record a clear, robust postsynaptic response (EPSP).
But when you stimulate the afferents so as to produce subthreshold activity presynaptically
(only an EPSP, and not an action potential), you also record an EPSP postsynaptically, though
it is smaller in amplitude. What is most likely subtype of voltage-dependent calcium channel
to predominate at the "young" stage? Explain your answer. How would you test your
hypothesis pharmacologically?
BME 502
Exam #3 (2001)
Name: _______________________
Question #2 (cont.)
(b) When the beast is an "adult", subthreshold stimulation of presynaptic afferents produces no
release because you do not record an EPSP in response to subthreshold stimulation. When
you stimulate the afferents so as to produce a single presynaptic action potential, you record a
clear, robust postsynaptic response (EPSP). When you stimulate with a train of action
potentials, each additional action potential is associated with an approximately equivalent
amplitude EPSP. What is most likely subtype of voltage-dependent calcium channel to
predominate at the "adult" stage? Explain your answer. How would you test your hypothesis
pharmacologically?
(c) When the beast is "aged", subthreshold stimulation of presynaptic afferents produces no
release because you do not record an EPSP in response to subthreshold stimulation. When
you stimulate the afferents so as to produce a single presynaptic action potential, you record a
clear, robust postsynaptic response (EPSP). When you stimulate with a train of action
potentials, each additional action potential is associated with an increasingly larger amplitude
EPSP. What is most likely subtype of voltage-dependent calcium channel to predominate at
the "aged" stage?
Explain your answer.
How would you test your hypothesis
pharmacologically?
BME 502
Exam #3 (2001)
Name: _______________________
Question #3
You are experimentally investigating the effects of GABA on neocortical pyramidal neurons by
applying small amounts of the neurotransmitter from a pipette while recording intracellularly from
the cell body (so you have one moveable pipette to apply GABA anywhere on the cell, and a
second, fixed electrode to record intracellularly from the soma). When you apply GABA to the cell
body region, you record a hyperpolarization. Because you know that neocortical neurons have
GABA-A receptors on their cell bodies, you expect this result. What you really want to investigate
is the effects of GABA on dendritic regions of neocortical pyramidal cells. You move your GABAcontaining pipette to the dendritic region, and you find that when you apply the same amount of
GABA to the dendrite you record a depolarization (you're still recording from the same cell). This
is puzzling.
(a) What pharmacological manipulation would you use to test the hypothesis that GABA is acting
through GABA-A receptors to cause the depolarization (procedurally, you apply the drug to the
bath and then apply GABA to the dendrites as before)?
(b) Your test for GABA-A receptors is positive, i.e., when you apply the drug you identified above,
the GABA-induced depolarization is completely blocked. For the sake of completion,
however, you also test to see if GABA is acting through GABA-B receptors. What drug would
you apply to block GABA-B receptors?
(c) Much to your surprise, when you apply GABA in the presence of the drug you identified in (b),
the depolarization is enhanced. Although you're still confused about the GABA-A finding, how
are the effects of blocking GABA-B receptors consistent with the known actions of GABA-B
receptors?
BME 502
Exam #3 (2001)
Name: _______________________
Question #3 (cont.)
(d) What simple electrophysiological postsynaptic manipulation could you use to test your
hypothesis about the effects of blocking GABA-B receptors on the depolarization? Explain
your answer.
(e) Having satisfied yourself that the GABA-induced depolarization depends primarily on
activation of GABA-A receptors, the next most logical step is to see if the GABA-A receptors
responsible for the depolarization are like most other GABA-A receptors, i.e., linked to a
chloride channel. What drug would you use to test this hypothesis?
(f) Your test of action through a chloride channel is positive -- so chloride acting through the
same receptor-channel complex (GABA-A receptor linked to a chloride channel) is causing a
depolarization in the dendrites and a hyperpolarization in the soma!! Some days it just doesn't
pay to come into work. Explain how this is possible. Hint: Only fundamental concepts are
necessary; nothing bizarre is needed to understand this.
BME 502
Exam #3 (2001)
Name: _______________________
Question #4
Explain the mechanisms responsible for the link between theta rhythm and LTP induction in CA1
(use of a schematic for the neuronal circuitry is recommended).