Heterosynaptic inhibition modifies the presynaptic plasticities of the transmission process at the synapse in Aplysia californica.
The monosynaptic and unitary excitatory postsynpatic potential (EPSP) observed in cell R15 of the abdominal ganglion of Aplysia californica upon minimal stimulation of the right visceropleural connective exhibits several presynaptic plasticities (synaptic depression, frequency facilitation, post-tetanic potentiation). We studiied effects of branchial nerve stimulation (heterosynaptic stimulation) on these plasticities of the homosynaptic (right connective) path. A burst of heterosynaptic stimulation (20 pulses at 4/sec) decreased the amplitude of an isolated homosynaptic EPSP. The rate of recovery from heterosynaptic inhibition (HSI) was a function of the rate of stimulation of the homosynaptic path so that at a stimulus frequency of 1 pulse/sec to the right connective (RC) the HSI lasted less than 20 sec while at a RC stimulus frequency of 1/10 sec the HSI persisted for more than 60 sec. While the frequency facilitated EPSP (during homosynaptic stimulation at 1/sec) was only transiently affected by heterosynaptic stimulation the effect on the subsequent post-tetanic potentiation was much more pronounced and longer lasting (more than 30 min). This suggests a specific effect of HSI on the rate constant of decay of elevated fractional release, as observed upon bath applications of biogenic amines. Heterosynaptic stimulation also reduces synaptic depression but the reduction in the depression is more than would be caused by comparable reduction of the first EPSP of a pair of high Mg2+, low Ca2+ or the addition of carbachol to the perfusion medium. The duration of the effect on synaptic depression was the same as the effect on EPSP1.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D005724:Ganglia / Q000502:physiology*; D008094:Lithium / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D008974:Mollusca / Q000502:physiology; D009433:Neural Inhibition; D013570:Synaptic Membranes / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects
D002217:Carbachol; D008094:Lithium; D008274:Magnesium; D002118:Calcium