The concept that neurotransmitter released from a neurone may feed back and influence the excitability of the same neurone has been suggested by a variety of evidence. Anatomical studies have shown that axon collaterals can arborize among the dendrites of the parent neurone1-7, suggesting a direct feedback via axon collaterals. In addition, the dendritic release of dopamine from substantia nigra neurones has suggested that dopamine may exert a direct feedback inhibition of these neurones8,9. Little electrophysiological evidence is available, however, to indicate that such a mechanism does exist. Based on intracellular recordings, Park et al.10 have proposed a direct inhibitory feedback in the neostriatum, but a presynaptic mechanism was not entirely excluded. We have now found that blockade of synaptic inhibition of relay neurones in the olfactory bulb unmasks long-lasting depolarizing potentials which can trigger repetitive discharges. These depolarizing potentials result from direct feedback of dendritically released excitatory transmitter onto the same and neighbouring relay neurones. Such a process might contribute to epileptogenic neuronal discharge.
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