AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 5 1230-R1235, Copyright © 1995 by American Physiological Society
Sympathoexcitatory influence of a fast conducting raphe-spinal pathway in the rat
S. Y. Zhou and M. P. Gilbey
Department of Physiology, Royal Free Hospital School of Medicine, London, United Kingdom.
Experiments were carried out on 20 pentobarbitone sodium (alpha-chloralose
supplemented)-anesthetized, artificially ventilated, and paralyzed rats.
The possibility was explored that raphe-spinal neurons with myelinated
axons arising in the rostral part of raphe obscurus provide excitatory
drive to sympathetic neurons. Electrical stimulation within obscurus was
observed to evoke an "early" sympathoexcitatory response compatible with
its conduction over such a pathway. The effect of the microinjection of
excitatory and inhibitory amino acids [DL-homocysteic acid (DLH) and
gamma-aminobutyric acid (GABA), respectively] on the evoked response was
studied at the sites of electrical stimulation. The size of the early
response was increased by 91.7 +/- 24.4% (n = 7) and depressed by -48 +/-
4.8% (n = 7) by DLH and GABA, respectively. Saline was without effect
(-14.5 +/- 12.2%, n = 6). The evoked responses were decreased when blood
pressure was raised by administration of phenylephrine (2-6 micrograms/kg
iv) and totally suppressed by an increase in blood pressure of 19.3 +/- 4.3
mmHg (baseline 89.1 +/- 2.5 mmHg, n = 7). It is concluded that some cell
bodies located in rostral raphe obscurus that project to the spinal cord
relay excitatory drive to sympathetic neurons.
