Nucleus tractus solitarius neurons with carotid chemoreceptor
inputs arborize in the rostral ventrolateral medulla.
Koshiya, Naohiro, and Patrice G. Guyenet.
University of Virginia, Department of Pharmacology,
Charlottesville, VA 22908, USA
APStracts 3:0007R, 1996.
Neurons that were excited by hypoxic stimulation of carotid
chemoreceptors were recorded in the caudal portion of the nucleus of
the solitary tract (cNTS) of urethane-anesthetized, vagotomized,
aortic deafferented, artificially ventilated rats (n=23). The focus
of the study is on 26 chemosensitive neurons (classified as early and
late response cells) that were tonically activated by chemoreceptor
stimulation and never fired in bursts synchronized with the phrenic
discharge cycle (PND). The discharge of early response cells (n=14)
started up to 2.5 s before the onset of PND activation while the
discharge of late response cells (n=14) started 1.5-5 s after onset
of PND response. Four early response cells were antidromically
activated from the rostral ventrolateral medulla (RVLM; latencies: 7
- 13 ms) and two had axonal collaterals in the region of the nucleus
ambiguus. Four late response neurons were antidromically activated
from RVLM (latencies: 6 - 12 ms) but no collateral was found in this
area. The basal discharge of early and late response cells ranged
from 0 to 10, and 0 to 30 spikes/s, respectively, but most of them
had a very low spontaneous firing rate (median: 0.2 and 0.6 spikes/s,
respectively). Neither type was excited by baroreceptor stimulation.
cNTS also contained neurons that were firing in bursts synchronized
with the phrenic discharge cycle. These cells were activated by
chemoreceptor stimulation and were not antidromically activated from
the RVLM. Chemosensitive neurons made up 33% of cNTS neurons
antidromically activated from RVLM (8/24). In conclusion, a
population of cNTS chemosensitive neurons devoid of respiratory
modulation projects through the RVLM and arborizes in this region.
Received 7 June 1995; accepted in final form 1 December 1995.
APS Manuscript Number R341-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96