[Neuroscience] Re: young rat's pain aversive behavior, and patch clamp analysis

Bill via neur-sci%40net.bio.net (by connelly.bill from gmail.com)
Tue Sep 7 03:33:19 EST 2010


> Q1:
> Does anyone know that when the young rats begin to show the right pain av=
ersive behavior?
> Or can the young rats have similar aversive behavior to painful stimuli a=
s the adult ones?

Sorry, I don't know.

> Q2:
> We know for pyramidal neurons in cortex, they show a tendency of spike fr=
equency adaption,
> How can I quantitatively compare frequency accommodation of spikes evoked=
 by depolarizing currents among different experimental groups?

I would be tempted to plot the interspike interval (or instantaneous
frequency, 1/ISI) versus spike number over a variety of depolarizing
current intensities. Theoretically, you could then do a three way
anova on this data, but I think just looking at the data should tell
you the answer.

See Figure 6BC in
 J Neurosci. 2003 Feb 1;23(3):859-66.
Functional autaptic neurotransmission in fast-spiking interneurons: a
novel form of feedback inhibition in the neocortex.
Bacci A, Huguenard JR, Prince DA.

> Q3, in our experiment, we observed increases in amplitude, frequency, and=
 half-width of sEPSCs, so we think the changes are both presynaptic and pos=
tsynaptic mechanisms.

Hard to comment on any sEPSC data. Voltage clamp in slices is so poor,
even changes in half-width are hard to comment on.

>On the other hand, we also =A0observed that the frequency of mEPSCs was in=
crease without affecting their amplitude and half-width. This observation o=
n mEPSCs >indicates the presynaptic but not postsynaptic mechanism . What a=
re the reasons for this discrepancy are?

It is hard to comment without knowing the age ranges. Changes in mEPSC
frequency should mean either a) increase in calcium sensitivity of
vesicular release or b)an increase in releasable vesicles (increase in
RRP, increase in the number of terminals etc).

If I had to hazard a guess (and we rule out technical issues like poor
space clamp, poor voltage clamp etc) is sEPSCs are increasing, but
minis aren't, I'd guess at something like multivesicular release
during sEPSCs accessing some extrasynaptic receptors, which are
normally not activated during mono-vesicular release during minis. You
could test this by dropping the Calcium concentration to mean that
during action-potential dependent release you only get monovesicular
release, or you could add dextran to reduce neurotransmitter
diffusion.

But honestly, I think poor space-clamp and voltage clamp are a far
more likely answer.


> In my opinion, this is because sEPSCs is action potential dependent, when=
 got stimulated, a lot of glutamate will be released. Considering there are=
 always enough receptors postsynaptically, therefore, for sEPSCs, there are=
 increase of amplitude and half width.
> However, for mEPSC, which reflects the quanta release, therefore, only th=
e probability for presynaptic transmitter release was increased.
> Therefore, combined the results from sEPSC and mEPSC, still only presynap=
tic changes took place.

Well the problem is that classically, action potential dependent
release is just a sum of lots of quantal release. That is, no synaptic
terminal should be any more saturated during quantal events than
during action potential dependent release. That is why I brought up
multivesicular release. Here, a single terminal should get exposed to
more glutamate.

If this is a viable option, you need to look to see if a quantal event
saturates the postsynaptic receptors (and hence multivesicular release
can't do any more). Checking to see if quantal events saturate
postsynaptic receptors is a tricky business with AMPA receptors (easy
with GABA, you just add benzodiazepine). But if I were you, I would
look at this paper:
Developmental increase in vesicular glutamate content does not cause
saturation of AMPA receptors at the calyx of held synapse.
Yamashita T, Ishikawa T, Takahashi T.
J Neurosci. 2003 May 1;23(9):3633-8



You should read something like:
Biophys J. 2003 November; 85(5): 3375=963387.
Distinct Quantal Features of AMPA and NMDA Synaptic Currents in
Hippocampal Neurons: Implication of Glutamate Spillover and Receptor
Saturation
Yuri V. Pankratov and Oleg A. Krishtal


Hope this helps.


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