The C-terminal glycopeptide of propressophysin potentiates excitatory transmission in the rat lateral septum

Effects of peptides synthesized from the same precursor as vasopressin, i.e. the C-terminal 39-amino acid long glycopeptide and neurophysin II, were investigated for biological activities in electrophysiological experiments in brain slices of the rat lateral septum. These slices contained the glycopeptide as the predominant form and a fragment of it, amino acid sequence 22–39, as a minor form (8% of the glycopeptide 1–39), as shown by high performance liquid chromatography of extracts and by radioimmunoassay. None of the peptides, neurophysin II, the glycopeptide 1–39 and the fragment 22–39, tested in a concentration of 10−12M, had measurable effects on the resting membrane potential of the neurons. The glycopeptide and the fragment 22–39, however, increased, in some cells, for tens of minutes the excitatory postsynaptic potentials evoked in these neurons by stimulation of the fimbria fibers. The increase in input resistance, seen in many septal neurons treated with either of the peptides was not correlated with the excitatory postsynaptic potential increase. Neurophysin II affected neither the excitatory postsynaptic potentials nor the input resistance of the neurons.