[Effect of penicillin on the synaptic activity of isolated spinal cord motor neurons in the lamprey].

Penicillin (PCN) has been studied for its effect on the membrane potential (MP) and synaptic activity of lamprey spinal cord motoneurons using intracellular recording in the in vitro spinal cord-notochord preparation. In one group of motoneurons with relative low MP (58.7 +/- 5.2 mV, n = 28) PCN induced depolarization, enhancement and prolongation (up to 80-220%) of the initial amplitude of excitatory postsynaptic potentials (EPSPs) evoked by the stimulation of dorsal roots spinal tracts. If the MPs (in the other group of motoneurons) were high (70.0 +/- 5.7 mV, n = 20) depolarization was not observed and the potentiation of EPSPs did not exceed 25-70% of the initial value. These effects of PCN can be eliminated by a preliminary addition of excitatory or inhibitory amino acid antagonists in the superfusion solution. The obtained results allow suggesting the presence of two different acceptor sites for PCN in membranes of lamprey spinal cord motoneurons.