[The simultaneous activation of excitatory and inhibitory inputs as a condition for the induction of homo-, hetero- and associative long-term excitation depression].

Hypothetical mechanism of homo-, hetero-, and associative LTD in the efficacy of excitatory synaptic transmission is suggested. According to this hypothesis, the same mechanisms underlie these effects. It is proposed that the following conditions are necessary and sufficient to produce different types of LTD. Conditioning and test stimuli must activate the common inhibitory neuron which is presynaptic to the target cell. The postsynaptic Ca2+ concentration which is regulated by metabotropic mGlu and GABAb receptor activation and opening of voltage-dependent Ca2+ channels must exceed a certain moderate level. This leads to an increase in protein phosphatase and decrease in protein kinases concentrations and cause dephosphorylation of ionotropic AMPA, NMDA, and GABAa receptors. Dephosphorylation results in a decrease of the sensitivity of excitatory and increase in the sensitivity of inhibitory receptors and causes simultaneous LTD excitatory and LTP of inhibitory synaptic transmission.