Medullary pathways mediating depressor responses from na+ -
sensitive sites in nucleus tractus solitarius.
Hochstenbach, Susan L., and John Ciriello.
Department of Physiology, Health Science Centre, University of
Western Ontario, London, Canada, N6A 5C1
APStracts 3:0284R, 1996.
Two series of experiments were done in male Wistar rats to investigate
the medullary pathways that mediate the depressor responses from
sodium-sensitive sites in the nucleus of the solitary tract (NTS). In
the first series, the anterograde tract-tracer Phaseolus vulgaris
leucoagglutinin (PHA-L) was iontophoresed unilaterally at sites in
NTS at which microinjections (20 nl) of a 154-175 mM NaCl solution
elicited depressor responses. PHA-L injection sites were found to be
localized within the medial subnucleus of NTS (Sm). In the medulla,
PHA-L labelled fibers and presumptive terminal boutons were observed
bilaterally, but with an ipsilateral predominance, throughout the
rostrocaudal extent of NTS, the dorsal motor nucleus of the vagus,
area postrema, the ventrolateral medulla (VLM), and nucleus ambiguus.
The pontine region containing the A5 catecholaminergic cell group and
the parabrachial nucleus also received projections from Sm. In the
second series of experiments, the effect of blocking synaptic
transmission in VLM with cobalt chloride (CoCl2; 5 mM, 100 nl) on the
cardiovascular response elicited by microinjection (20 nl) of
hypertonic saline (154-175 mM) into the ipsilateral Sm was
investigated in the alpha-chloralose anesthetized, paralyzed and
artificially ventilated rat. Microinjection of CoCl2 into VLM, at
sites shown in the previous study to receive efferent projections
from Sm, significantly attenuated the depressor (60 %) and
bradycardic (80 %) responses to stimulation of Sm. These data
indicate that the sodium-sensitive region of the caudal Sm innervates
VLM neurons and suggest that these VLM neurons are involved in
mediating the depressor and bradycardic responses elicited by changes
in the extracellular concentration of sodium.
Received 23 February 1996; accepted in final form 3 July 1996.
APS Manuscript Number R111-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 4 August 1996