Need help with transmitters and receptors

Richard Norman rsnorman at mw.mediaone.net
Sat Feb 14 10:03:29 EST 1998


In article <34E5140D.3F0122B1 at enigmatic.org>, larry at enigmatic.org says...
>
>    I am a senior in college taking a Neurobiology class and am having
>difficulty with a question.  We are learning specifics about action
>potentials and about different transmitters and receptors.
>    The question is:
>
>    "You are using the patch clamp recording method on a new kind of
>neuron from a hippocampal slice.  When you stimulate a specific group of
>input neurons, the frequency of inward current deflections increase.
>The reversal potential of the events is around +50mV and is not blocked
>by TTX.  Conventional transmembrane microelectrode recording reveals
>that synaptic activation resulting in an EPSP is mimiced by application
>of glutamate rather than ACh, norepinephrine or other transmitters.
>Addition of GABA to the bath (surrounding the slice) decreases the EPSP
>amplitude.  Addition of Peptide X, a putative neurotransmitter found in
>the slice, slightly increases and extends the duration of glutamate's
>effect.
>    a.   Given the above observations what are the most likely molecular
>events occurring after stimulation of the input neurons?
>    b.   Why might GABA decrease the EPSP amplitude?  Explain if and how
>GABA addition would affect the patch clamp (single channel recording)
>data mentioned above.  Why?
>    c.   List two possible molecular mechanisms that might be
>responsible for peptide X's effect.
>    d.   Describe an experiamnt that would distinguish between your two
>theories."
>
>Any help would be greatly appreciated.  I am having real difficulty with
>this and no one can seem to help me.  Thank you very much for your time
>and help.
>

One of main purposes of a question like this is to challenge you to
take the details of what you have learned in one context and to apply
it to a new context.  It requires specific knowledge plus some imagination.
In my opinion, it is inappropriate to answer the question for you.

However, it is helpful to get you to understand individual pieces.

To start with:  do NOT try to do research on hippocampal slices to answer
the question.  Instead, build on the premises of the question.

You know from the statement of the problem:
    1) patch clamp data about the epsp, including the reversal potential
    2) some neurochemistry about the epsp, glutamate
    3) the effect of two other pharmacological agents, GABA and peptide X.

You know from your knowledge of neurobiology:
    1) something about the mechanism of action of post-synaptic receptors
       and ion channels.
    2) something about the mechanism of action of inhibition
    3) something about the mechanism of action of neuromodulation

Now, can you make some reasonable and intelligent connections between
these two sets of information.

The really good part is question d).  Question c) requires you to make
two different hypotheses about what peptide X might do.  Can you frame
those hypotheses is a form that would allow you to differentiate between
them experimentally?  Think about what you know of channel activity or 
neuromodulation.  Think about the experimental data you have been taught
about these factors.  Now form your hypotheses in terms so that you can
use these known experiments.

Good luck.  It looks like you are in a good course!

Richard Norman
Department of Natural Sciences
University Michigan - Dearborn
rnorman at umich.edu

 




More information about the Neur-sci mailing list