Journal of Neuroscience, Vol 15, 7528-7538, Copyright © 1995 by Society for Neuroscience
Long-term potentiation of glutamatergic pathways in the lamprey brainstem
S Alford, I Zompa and R Dubuc
Departement de Kinanthropologie, Universite du Quebec a Montreal, Canada.
Plasticity of synaptic transmission has been investigated in the lamprey
brainstem. In this preparation, neurons of the vestibular nuclei make
monosynaptic connections to reticulospinal neurons of the posterior (PRRN)
and middle (MRRN) rhombencephalic reticular nuclei. This glutamatergic
projection shows a long-lasting enhancement in efficacy following a brief
high frequency (50 Hz) train of stimuli (tetanus). Enhancement was found on
the inputs from the octavomotorius intermediate (nOMI) and octavomotorius
posterior (nOMP) nuclei to the reticulospinal neurons of the PRRN and MRRN,
and persisted for the entire duration of the recordings. The enhancement
was limited to the pathway that received tetanic stimulation for the inputs
to any given reticulospinal neuron. It depended upon the activation of
postsynaptic processes at least in part; dialysis of the reticulospinal
neuron by recording with a whole-cell patch pipette prevented its
induction. This dialysis-dependent abolition of enhancement was shown to be
dependent on a change in Ca2+ concentration in the postsynaptic neuron. The
enhancement was not affected by blockade of NMDA receptors with D,L-2-
amino-5-phosphonopentanoate (AP5) but was prevented by the metabotropic
glutamate receptor (mGluR) antagonist (R,S)-alpha-methyl-4-
carboxyphenylglycine (MCPG). In conclusion, this study demonstrates that
vestibular inputs to reticulospinal neurons are capable of undergoing
long-term potentiation (LTP) and that this LTP shows synapse specificity.
Furthermore, this LTP is activated by synaptic stimulation of a subtype of
the m-GluR family and its induction is mediated by changing Ca2+
concentrations in the postsynaptic neuron.
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