Js. Isaacson et B. Walmsley, RECEPTORS UNDERLYING EXCITATORY SYNAPTIC TRANSMISSION IN SLICES OF THE RAT ANTEROVENTRAL COCHLEAR NUCLEUS, Journal of neurophysiology, 73(3), 1995, pp. 964-973
1. The anteroventral cochlear nucleus (AVCN) contains two principal ce
ll types that receive input from the auditory nerve. Stellate cells re
ceive conventional synapses on their dendrites, and bushy cells of the
AVCN receive axosomatic input via large, calyceal terminals (the end
bulbs of Held). We have used whole cell patch-clamp recording techniqu
es to study excitatory postsynaptic currents (EPSCs) in these two prin
cipal cells of the rat AVCN. 2. EPSCs evoked in stellate cells by stim
ulation of the auditory nerve were graded with stimulus strength, indi
cating a high degree;ee of convergence of input to these cells. At dep
olarized membrane potentials, EPSCs evoked in stellate neurons had a d
ual-component time course. The slow component was blocked by the N-met
hyl-D-aspartate(NMDA) receptor antagonist DL-2-amino-5-phosphonovaleri
c acid (APV), and the fast component was abolished by the non-NMDA rec
eptor antagonist 6-cyano-7-nitroquinoxaiine-2,3-dione (CNQX). 3. EPSCs
evoked in bushy cells by auditory nerve stimulation were large (50 nS
average conductance) and all-or-none at the threshold stimulus level.
At -70 mV, the time course of the EPSC was very brief (average time c
onstant of decay 700 mu s at room temperature). Membrane depolarizatio
n revealed a slow component to the EPSC. The fast and slow components
were mediated by non-NMDA and NMDA receptors, respectively. The switch
-off of end bulb NMDA EPSCs by voltage jumps to the EPSC reversal pote
ntial was very rapid, suggesting that the NMDA component arises from s
ites on or close to the soma. 4. Miniature EPSCs, recorded in the pres
ence of tetrodotoxin (?TX) at depolarized potentials, also had a dual-
component time course. The fast and slow components of the miniature E
PSCs were blocked by CNQX and APV, respectively. This result indicates
that NMDA and non-NMDA receptors can be co-localized at the same, pre
sumably end bulb, release sites. 5. The relative contribution of the s
low, NMDA component to the end bulb EPSC declined significantly with a
ge (postnatal days 11-22). 6. These results indicate that both NMDA an
d non-NMDA receptors underlie excitatory synaptic transmission in the
AVCN of young rats. The end bulb synapse onto bushy cells generates a
non-NMDA receptor-mediated EPSC with very fast kinetics, NMDA receptor
s can also mediate synaptic transmission at the end bulb synapse, but
their contribution becomes less as the auditory system matures. This f
inding suggests that NMDA receptors may play an important role in the
development of this synapse.