Hello, I'm recording neurons in vivo in the ventral tegmental area of rat brains using stereotaxic equipment. What is an effective way of determining whether my equipment is accurately horizontal and/or perpendicular with relation to the animal other than just "eye-balling" it? The VTA is 7-8 mm deep and I'm attempting to target an area that is roughly 0.4mm wide and 0.8 mm long so even small deviations from being being perfectly perpendicular will have an effect.
A related question: how can I ensure that the head of the animal is properly secured in a position that is perfectly horizontal?
Any help is greatly appreciated. Thank you.
Wie use a so called alignment indicator (http://www.kopfinstruments.com/Stereotaxic/1905-15.html ) to adjust the Head/skull and Identify bregma (or lambda) as reference points.
I would say the most important thing is that the skull is positioned properly on the horizontal plane parallel to the base of the apparatus. For this you have to be sure that the earbars are aligned, positioned in the ear canals at the same level (when the position is correct you can feel the skull perfectly immobile). Then, once the skin is opened, you can move the skull (rotating on the ear axis) assuring that lamba and bregma are positioned at the same z-level. Sorry, maybe this was not your point. Just hope it helped anyway.
Place a needle in a needle holder and bring it down to about 15 mm. Keep a scale horizontally on the stereotaxic frame in such a way that needle touches the scale (parellel to the oerator), if the needle/ vertical axis is perpendicular there will not be any change in the scale reading.
Alignment indicator is a nice thing, but costs several thousand $$. We usually spent a lot of time leveling the skull horizontally until we developed a simple bubble (spirit) level probe ( http://www.invilog.com/products-services/auxiliary-equipment/making-sure-the-skull-is-in-a-level-position-takes-a-mere-2-minutes-with-the-invilog-bubble-level-probe/ ) which is working either in rats or in mice.
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