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Arterial pressure was measured with a pressure transducer
(P23Gb; Statham
Instruments, Hato Hey, Puerto Rico, USA).
Recording of baroreceptor activity from the aortic depressor nerve.
The procedures for recording the whole nerve activity from the
aortic depressor
nerve have been described elsewhere [Salgado et al, 2006].
Using a dissecting
microscope (MC- M2222, D.F. Vasconcelos, São Paulo, SP, Brazil), a 4-6
mm length of
the left aortic depressor nerve was carefully isolated from surrounding connective
tissue, below its junction with the superior laryngeal nerve and placed on a bipolar
stainless steel
electrode with an inter electrode distance of 2 mm. The correct
identification of the nerve was confirmed by its typical pattern
of discharge synchronous
with arterial pulse pressure. Nerve activity
was amplified using a differential high
impedance amplifier (Princeton Applied Research, Oak Ridge, TN, USA) and digitally
sampled (10 kHz), simultaneously, with the carotid pressure, in an IBM/PC equipped
with an analog-to-digital
interface (DI-220, Dataq Inc, Akron, OH, USA).
Stimulation of aortic depressor nerve.
The same electrode that contains the aortic depressor nerve isolated for
recording was connected to a stimulator (AVS-100, AVS Projetos, São Paulo, SP,
Brazil) by means of a key that allowed to switch the electrode from recording to
stimulus. Before the stimulus, the nerve was sectioned at a point rostral to the
electrode. Thus,
the nerve was stimulated with rectangular (5 V, 2 ms, 20 Hz) pulses
delivered during 10s. After the antidromic electrical stimulation the key was
immediately returned to the recording position and the aortic depressor nerve activity
was continuously recorded during 5 min.
Protocol
Afferent aortic depressor nerve activity and arterial pressure were recorded
during 2 min prior to
antidromic electrical stimulation of the aortic depressor nerve. The
effect of the stimulation was evaluated during 5 min. After this first set of stimulus, the
COX inhibitor indomethacin (5 mg/kg, iv, N=7, Sigma, St. Louis, MO, USA), membrane
permeable H
2
O
2
scavenger PEG-Catalase (10
4
U/kg, IV, N=7, Sigma, St. Louis, MO,
USA) or vehicle (saline, 0.1 mL/100g, iv, N=6) was administrated and then proceeded
with new set of stimulus. The differences between the pre-stimulation
baseline levels of
mean arterial pressure and aortic depressor nerve activity measured
over 5 minutes
were quantified before and after drugs administration.
Data Analysis
Data are presented as means ± SE. Aortic depressor nerve activity was