Neal Prakash wrote:
>Does anyone have experience, opinions, or references as to the
>advantages/disadvantages of using these methods to inject small amounts of
>compounds into the brain while simultaneously recording from extracellular
>single units?
I have a reference, experience with one, but some opinions on all three.
The reference is
Federov NB and Reymann KG (1993) J Neurosci Methods 50:83-90
in which they compare the effects of picospritzing (pneumatic pressure
ejection) and iontophoresis.
The opinion is that it is different horses for different courses.
Syringe pressure ejection is good for bigger volumes, but mainly a fairly
slow process. Whether the time course of ejection is important depends on
what you aim to do.
Picospritzing can allow very short pulse times. This is the main point of the
reference above. I would add a caveat that although the authors used a 25ms
pulse, the actual rise-time of drug action is 400ms - an order of magnitude
longer. In a recent paper of mine using iontophoresis: Vickery R.M. & Bindman
L.J. (1997) Long-lasting decreases of AMPA responses following postsynaptic
activity in single hippocampal neurons. Synapse 25: 103-106, I used longer
pulses (500ms) but the response rise-time and duration were very similar to
the very short picospritzing pulse effects. Where volumetric changes are
important (stretch-activated channels etc) then iontophoresis is probably
preferable.
Iontophoresis is slower than spritzing, but is better if you are using potent
channel antagonist because you can retain the ion whereas the other systems
have difficulty preventing diffusion (though most can prevent actual flow).
Iontophoresis requires charged species whereas the other two methods don't, so
the precise nature of what you want to deliver is critical. Iontophoresis
should generally be done with a second barrel providing a balance current to
minimize direct electrical effects on the cell under study.
Hope this helps,
(we've just ordered a 4 channel spritzer mainly 'cos we want to use it for
retrograde tracer dye ejection as well as for drug work)
Richard Vickery Our quest is for Meaning, \ /
Physiology & Pharmacology but the meaning is The Quest. (oVo)
UNSW, Australia ) (
http://acsusun.acsu.unsw.edu.au/~s8970107/ Life's a Hoot! ^ ^
