M. Armstrongjames et al., THE CONTRIBUTION OF NMDA AND NON-NMDA RECEPTORS TO FAST AND SLOW TRANSMISSION OF SENSORY INFORMATION IN THE RAT SL BARREL CORTEX, The Journal of neuroscience, 13(5), 1993, pp. 2149-2160
The main objective of this study was to establish the contribution of
NMDA receptors to natural processing of somatosensory information with
in rat SI barrel cortex. Responses of 52 cells in layers I-IV of the r
at barrel cortex were analyzed by PSTH (peristimulus histogram) analys
is of evoked spikes in reply to brief deflections of the principal whi
sker in animals anesthetized with urethane. Short and longer peak late
ncy responses within PSTHs were compared in the presence and absence o
f the specific NMDA and non-NMDA antagoniStS D(-)-2-amino-5-phosphonov
aleric acid and 6,7-dinitroquinoxaline-2,3-dione, which were administe
red locally to neurons by iontophoresis and additionally tested agains
t their putative specific agonists, NMDA and quisqualate, respectively
. The results suggest the following. (1) The generation of most spikes
from cells in layers I-IV is dependent upon activation of NMDA recept
ors. However, NMDA receptors do not contribute to responses at very sh
ort latencies commensurate with monosynaptic thalamocortical relay for
layer IV cells. These appear to be entirely mediated through non-NMDA
receptors. (2) In the absence of transmission through NMDA receptors,
non-NMDA receptors do not generate significant spike activity in late
r (10-100 msec latency) discharges. (3) NMDA receptor participation in
first spike generation is directly dependent upon the latency of resp
onse of the cell to principal whisker deflection. (4) Latency of respo
nse, non-NMDA receptor-mediated spike generation and laminar location
were powerfully covariant. (5) In addition, it was found that cells ex
hibiting short-duration spikes (<0.7 msec; ''fast-spike units'') in la
yer IV responded powerfully at short latencies, first spikes being ent
irely dependent upon non-NMDA but not NMDA receptor action, later spik
es (10-100 msec poststimulus) being >80% dependent upon NMDA receptor
action. It is concluded that most sensorially driven spike activity in
layers I-IV is dependent upon NMDA receptor action. This appears to b
e enabled by contingent subthreshold depolarization largely through no
n-NMDA receptor action, whereas the earliest thalamocortical discharge
s are evoked solely through non-NMDA receptors.