Biomedical Engineering Reference
In-Depth Information
A pair of thin needle copper electrodes was inserted under the
skin of the chosen forepaw(s). Square wave current pulses of 0.3
ms duration and variable amplitude (0.2-5 mA) were generated
by use of an isolator unit (WPI, Sarasota, FL) connected to the
electrodes. To control stimulus timing and frequency (typically
1-9 Hz), digital output signals were generated by the CED unit
using Spike2 software.
2.1.4. ForepawStimulator
2.2. Animal
Preparation
All procedures were performed in accordance with protocols
approved by the Yale Animal Care and Research Committee.
Experiments were conducted on male rats (Charles River,
Wilmington, MA; fed
ad libitum
) weighing between 180 and
350 g. In all rats, a femoral artery was cannulated with a
polyethylene catheter (PE-50) to withdraw blood samples for
blood gas analysis and to monitor arterial blood pressure, an
intraperitoneal catheter (PE-10) was inserted for administration
of soluble anesthetics, and a femoral vein was cannulated with a
polyethylene catheter (PE-10) to administer other drugs. Blood
pressure was continuously monitored. Ventilation parameters
were adjusted to maintain arterial blood gas tensions (pCO
2
,
pO
2
, pH) within normal range. A rectal temperature probe was
inserted to monitor and maintain the core body temperature at
∼
37
◦
C with a temperature-controlled recirculated warm water
pad. All monitoring equipment, consisting of magnetic materials,
were placed outside the scanner room and sampled by the CED
unit for online recording. A standard block stimulation protocol
was used in all experiments. We monitored analgesia depth by
pain response to an automated electrical (5 mA, 0.3 ms, 1 Hz, 1
s) tail-pinch every 1/4 hour.
The rats (Sprague-Dawley) were initially anesthetized with 1.5-
2% halothane in a mixture of 70% N
2
O and 30% O
2
. Tracheotomy
was performed and the animal was artificially ventilated with
0.75-1% halothane in a mixture of 70% N
2
O and 30% O
2
dur-
ing all other surgical procedures.
D
-tubocurarine chloride (initial
0.5 mg/kg; supplemental 0.25 mg/kg/h; intravenous) was used
to immobilize the rat. After all surgical procedures were com-
pleted, halothane was discontinued and anesthesia was maintained
with
2.2.1. Forepaw and
Whisker Studies
-chloralose (initial 80 mg/kg; supplemental 40 mg/kg/h;
intraperitoneal).
α
The commonly used albino strains of experimental rats, such as
Sprague-Dawley, possess significantly poorer visual acuity than
their wild counterparts
(40)
. The primary causes may be the lack
of pigment in the retinal epithelium, leading to light scattering
in the eye and abnormal development of retinothalamic
(41, 42)
and interhemispheric cortical connections
(42, 43)
. Therefore, we
2.2.2. Visual Studies
