Assessment of Neurovascular Coupling - Animal Models of Acute Neurological Injuries: Injury and Mechanistic Assessments - page 341

For tracheotomy, the animal is placed in a supine position and
a ~1.5-cm skin incision is made from the superior thorax aperture
up to the level of the lower jaw after local anesthesia of the skin with
lidocaine. The salivary glands are exposed and gently divided in the
midline by the use of small forceps. Forceps are also used to spread
the muscles covering the trachea. Thereafter, two fi laments are
placed for fi xation of the tracheal tube around the trachea with
approximately 1-cm distance between them. Care should be taken
to avoid touching the jugular vein or the carotid arteries during this
step since the vagus nerve accompanies these vessels and its irrita-
tion may cause increased bronchial mucus secretion and respiratory
problems later on. The respirator is then switched on. Thereafter, a
small incision is made below the larynx between two tracheal carti-
lages. The tracheal tube is now quickly inserted (Portex, polythene
tubing, Smiths Medical, ID 1.67, OD 2.42) and fi xated by liga-
tures. The tube is then connected to the respirator. The region is
again treated with lidocaine solution and closed with a suture.

3.3. Vessel
Cannulation

In order to monitor mean arterial blood pressure (MAP) and for
intravenous application of anesthetics or specifi c drugs, the femoral
artery and vein are cannulated. For this purpose, the leg is fi rst
gently pulled and fi xed with adhesive tape before the femoral arter-
ies and veins are exposed with an incision below and parallel to the
inguinal ligament after local anesthesia with lidcoaine. The soft tis-
sue around the vessels is carefully removed and two fi laments are
placed around each vessel for later fi xation. The distal fi lament is
closed with a knot and the other is gently pulled until the vessel
lumen is occluded. Now, the vessel is opened by a small cut and the
tip of the polyethylene tube is inserted while it is already connected
to the infusion pump and fi lled with normal saline solution. An
angular shape of the tip facilitates insertion (importantly, use a very
sharp knife to cut the tip). After the catheter is secured in place by
ligatures, the wounds are closed and infusion is started (0.5-1 ml/h)
to keep the vessels open. In a similar fashion, the tail artery can be
cannulated. Cannulation of the tail artery has the advantage that
there are suffi cient collaterals in the tail to compensate fully for loss
of the tail artery. This allows to let the animal wake up after the
procedure if this is necessary for the scientifi c question (e.g., for
histology after ischemic stroke). The tail veins are less suitable for
insertion of a catheter. To sacrifi ce the animal after the experiment,
20 ml of air are injected into the femoral vein.

3.4. Cranial Window
Preparation

Cranial windows are an important tool for studies of neurovascular
coupling ( 2, 26, 27 ). They are frequently used in combination
with a variety of experimental blood fl ow measurement techniques.
In principle, rCBF measurements can also be performed through a
thinned skull preparation in which the bone is thinned to translucency.
The advantages of exposing the brain are the superior optical prop-
erties, ability for direct observation of the surface vasculature,