Assessment of Neurovascular Coupling - Animal Models of Acute Neurological Injuries: Injury and Mechanistic Assessments - page 342

Fig. 2. Schematic drawing of the rat skull with several recording devices. This open window is suitable for the use of
microelectrodes. It only has an infl ow to the window for the infusion of aCSF while a closed window would have an outfl ow
on the other side in addition. Intracortical microelectrodes can be used to measure the DC-ECoG of which the upper fre-
quency limit is determined by the sampling rate and the low-pass fi lter of the amplifi er. Moreover, extracellular ion concen-
tration changes can be recorded when microelectrodes are equipped with an ion-selective barrel. Ag/AgCl wire electrodes
allow measurement of surface DC-ECoG, either sub- or epidurally. Laser-Doppler fl ow probes can be used for one-spot
measurements of rCBF in a sample volume of about 1 mm 3 . The fl ow probes are placed above the cortex. The inset on the
left ( red arrow ) shows a pial arteriole in the cranial window.
possibility for topical pharmacological interventions, and combination
of rCBF measurements with microelectrode recordings ( 5, 28 )
(Fig. 2 ).
To implant a cranial window, the animal is fi xed in a stereotaxic
frame and a midline scalp incision is performed after local anesthe-
sia with lidocaine. The soft tissue is removed and bleedings are
stopped with bone wax. A high-speed micro drill is used to thin a
circular or rectangular area of desired size at the region of interest
(depending on paradigm, often up to 4×6 mm, record the dis-
tance from bregma). Drilling is performed under a dissection
microscope and under cooling with saline or aCSF. The drilling
should continue until the dural blood vessels become clearly visible
and the bone fl ap becomes instable. An appropriate thinning is
essential for safe removal of the bone fl ap later on. Importantly, it
should be avoided to apply any pressure on the bone while drilling.
When the bone fl ap is clearly moving during the drilling, it is ready
to be removed but do not remove it now. Now, two canals are
drilled for the placement of the in- and outfl ow tubes. A third canal
can be drilled between them if you want to use a subdural electrode
as described above (also compare Fig. 2 ). The canals are fi lled with
bone wax after drying. Then, the in- and outfl ow tubes and the
subdural electrode are pressed into the wax and fi xed with the wax.
Thereafter, a wax wall of ~1-mm height is built around the drilled