LONG-TERM POTENTIATION OF GLUTAMATERGIC PATHWAYS IN THE LAMPREY BRAIN-STEM

Plasticity of synaptic transmission has been investigated in the lampr ey brainstem, In this preparation, neurons of the vestibular nuclei ma ke monosynaptic connections to reticulospinal neurons of the posterior (PRRN) and middle (MRRN) rhombencephalic reticular nuclei, This gluta matergic projection shows a long-lasting enhancement in efficacy follo wing a brief high frequency (50 Hz) train of stimuli (tetanus), Enhanc ement was found on the inputs from the octavomotorius intermediate (nO MI) and octavomotorius posterior (nOMP) nuclei to the reticulospinal n eurons of the PRRN and MRRN, and persisted for the entire duration of the recordings, The enhancement was limited to the pathway that receiv ed tetanic stimulation for the inputs to any given reticulospinal neur on, It depended upon the activation of postsynaptic processes at least in part; dialysis of the reticulospinal neuron by recording with a wh ole-cell patch pipette prevented its induction, This dialysis-dependen t abolition of enhancement was shown to be dependent on a change in Ca 2+ concentration in the postsynaptic neuron, The enhancement was not a ffected by blockade of NMDA receptors with D,L-2-amino-5-phosphonopent anoate (AP5) but was prevented by the metabotropic glutamate receptor (mGluR) antagonist (R,S)-alpha-methyl-4-carboxyphenylglycine (MCPG), I n conclusion, this study demonstrates that vestibular inputs to reticu lospinal neurons are capable of undergoing long-term potentiation (LTP ) and that this LTP shows synapse specificity, Furthermore, this LTP i s activated by synaptic stimulation of a subtype of the mGluR family a nd its induction is mediated by changing Ca2+ concentrations in the po stsynaptic neuron.