Journal of Neuroscience, Vol 4, 1208-1216, Copyright © 1984 by Society for Neuroscience
Lateral hypothalamic modulation of the gustatory-salivary reflex in rats
R Matsuo and K Kusano
It is well recognized that the basic mechanism for the gustatory- salivary
reflex is located in the lower brainstem and that suprabulbar structures
possibly influence this mechanism. This study is designed to evaluate the
neurophysiological mechanism underlying the effect of the lateral
hypothalamic area (LHA) on the bulbar gustatory-salivary reflex.
Submandibular salivary secretion and the electrical activity of the
preganglionic parasympathetic fibers innervating the submandibular and
sublingual glands were recorded in anesthetized rats. Stimulation of the
tongue with high concentrations of chemical solutions (1 M and 2 M NaCl and
0.01 M and 0.05 M HCl) and/or pinching the tongue with a small clamp
induced a profuse salivary secretion (3 to 28.5 microliter/5 min) recorded
from a unilateral submandibular gland. The preganglionic fibers consisted
of three types: taste-related fibers, which increased their firing rate by
taste stimuli; pinch-related fibers, which increased their firing rate by
pinching; and unidentified fibers, which did not respond to taste or
pinching stimulations of the tongue. Electrical stimulation of the
ipsilateral LHA caused the secretion of a small amount of saliva (1.5
microliter/5 min), and it appeared that taste-related fibers more often
received polysynaptic connections from the LHA than other types of fibers.
Conditioning stimulation of the LHA increased the magnitude of impulse
discharges by the test stimulation of the tongue in the taste-related
fibers. Therefore, the results of this study demonstrate that the LHA
enhances the activity of the gustatory-salivary reflex in the lower
brainstem.