[The monosynaptic connection: the modulating effect of opioid peptides on the plasticity of presynaptic neurons and identified synapses].

Study of opioid peptides (leucine-enkephalin and methionine-enkephalin) action on plastic properties of the system of monosynaptically connected neurones LPa7--LPa3, PPa3 and LPa8--LPa3, PPa3 was conducted in the snail brain. It has been shown that all three links in the system studied (presynaptic neurone, postsynaptic neurone and synapse) manifest one and the same type of plasticity--habituation to rhythmic stimulation. Enkephalins have a modulating action on plastic properties of the presynaptic neurone and synapse: they retard the habituation of the presynaptic neurone to intracellular stimulation and retard the development of habituation at synaptic level. However, changes in the character of postsynaptic response in the presence of enkephalins are not a direct consequence of their influence on plastic properties of the presynaptic neurone. Besides, enkephalines reduce the effectiveness of synaptic transmission in the given system: they reduce EPSP duration in the postsynaptic neurone.