Cb. Halsell et Sp. Travers, ANTERIOR AND POSTERIOR ORAL CAVITY RESPONSIVE NEURONS ARE DIFFERENTIALLY DISTRIBUTED AMONG PARABRACHIAL SUBNUCLEI IN RAT, Journal of neurophysiology, 78(2), 1997, pp. 920-938
The responses of single parabrachial nucleus (PEN) neurons were record
ed extracellularly to characterize their sensitivity to stimulation of
individual gustatory receptor subpopulations (G neurons, n = 75) or m
echanical stimulation of defined oral regions (M neurons, n = 54) then
localized to morphologically defined PEN subdivisions. Convergence fr
om separate oral regions onto single neurons occurred frequently for b
oth G and M neurons, but converging influences were more potent when t
hey arose from nearby locations confined to the anterior (AO) or poste
rior oral cavity (PO). A greater number of G neurons responded optimal
ly to stimulation of AO than to PO receptor subpopulations, and these
AO-best G neurons had higher spontaneous and evoked response rates but
were less likely to receive convergent input than PO-best G neurons.
In contrast, proportions, response rates, and convergence patterns of
AO-and PO-best M neurons were more comparable. The differential sensit
ivity of taste receptor subpopulations was reflected in PEN responses.
AO stimulation with NaCl elicited larger responses than PO stimulatio
n; the converse was true for QHCl stimulation. Within the AO, NaCl eli
cited a larger response when applied to the anterior tongue than to th
e nasoincisor duct. Hierarchical cluster analysis of chemosensitive re
sponse profiles suggested two groups of PEN G neurons. One group was c
omposed of neurons optimally responsive to NaCl (N cluster); the other
to HCl (H cluster). Most N- and H-cluster neurons were AO-best. Altho
ugh they were more heterogenous, all but one of the remaining G neuron
s were unique in responding best or second-best to quinine and so were
designated as quinine sensitive (Of). Twice as many Of neurons were P
O-compared with AO-best. M neurons were scattered across PEN subdivisi
ons, but G neurons were concentrated in two pairs of subdivisions. The
central medial and ventral lateral subdivisions contained both G and
M neurons but were dominated by AO-best N-cluster G neurons. The distr
ibution of G neurons in these subdivisions appeared similar to distrib
utions in most previous studies of PEN gustatory neurons. In contrast
to earlier studies, however, the external medial and external lateral-
inner subdivisions also contained G neurons, intermingled with a compa
rable population of M neurons. Unlike cells in the central medial and
ventral lateral subnuclei, nearly every neuron in the external subnucl
ei was PO best, and only one was an N-cluster cell. In conclusion, the
present study supports a functional distinction between sensory input
from the AO and PO at the pontine level, which may represent an organ
izing principle throughout the gustatory neuraxis. Furthermore, two mo
rphologically distinct pontine regions containing orosensory neurons a
re described.