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The results of electrophysiological studies of the quantal release features of glutamate in hippocampal neurons' synapses in long-term depression of synaptic transmission are presented. To research the topic, weused the primary culture of the rat hippocampus. Using the patch-clamp technique, the frequencies and amplitudes of excitatory spontaneous postsynaptic currents (EPSCs) were determined, theirdistributions were analyzed and the basicquantal parameters were calculated. Long-term depression of synaptic transmission was achieved by tetanic stimulation of the axon of the presynaptic cell for 5 minutes with a stimulation frequency of 5 Hz. Spontaneous current in depression was recorded 20-30 min after tetanic stimulation. It has been shown that the amplitude of the EPSCs registered in hippocampal neurons decreased in the long-term depression of synaptic transmission. It has been found that two neurotransmitter vesicles are usually released in the control at the same time and one during the long-term depression of synaptic transmission.It means that the probability of release decreased. In addition, the average quantalamplitude and quantum content decreased. It indicates the effect of presynaptic mechanisms in the expression of long-term depression of synaptic neurotransmission between hippocampal neurons in culture.In the conditions of long-term depression, no significant changes were found in the frequency of EPSCs. The analysis of quantum parameters in long-term depression of glutamatergic synaptic transmission between neurons is important for the formation of more complete ideas about the mechanisms that play a fundamental role in the normal functioning of the CNS and the development of neural networks. [ABSTRACT FROM AUTHOR]