Neurochemical and electrophysiological studies on the functional significance of burst firing in serotonergic neurons

S. E. Gartside, É Hajós-Korcsok, E. Bagdy, L. G. Hársing, T. Sharp, M. Hajós

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We have previously described a population of 5-hydroxytryptamine neurons which repetitively fires bursts of usually two (but occasionally three or four) action potentials, with a short (< 20 ms) interspike interval within a regular low-frequency firing pattern. Here we used a paradigm of electrical stimulation comprising twin pulses (with 7- or 10-ms inter-pulse intervals) to mimic this burst firing pattern, and compared the effects of single- and twin-pulse electrical stimulations in models of pre- and postsynaptic 5- hydroxytryptamine function. Firstly, we measured the effect of direct electrical stimulation (2 Hz for 2 min) of rat brain slices on efflux of preloaded [3H]5-hydroxytryptamine. In this in vitro model, twin-pulse stimulation increased the efflux of tritium by about twice as much as did single-pulse stimulation. This effect was evident in the medial prefrontal cortex (area under the curve: 2.59±0.34 vs 1.28±0.22% relative fractional release), as well as in the caudate-putamen (3.93±0.65 vs 2.17±0.51%) and midbrain raphe nuclei (5.42±1.05 vs 2.51±0.75%). Secondly, we used in vivo microdialysis to monitor changes in endogenous extracellular 5- hydroxytryptamine in rat medial prefrontal cortex in response to electrical stimulation (3 Hz for 10 min) of the dorsal raphe nucleus. In this model, twin-pulse stimulation of the dorsal raphe nucleus increased 5- hydroxytryptamine by approximately twice as much as did single-pulse stimulation at the same frequency (area under the curve: 50.4±9.0 vs 24.2±4.4 fmol). Finally, we used in vivo extracellular recording to follow the response of postsynaptic neurons in the rat medial prefrontal cortex to 5-hydroxytryptamine released by dorsal raphe stimulation. Electrical stimulation of the dorsal raphe nucleus (1 Hz) induced a clear-cut poststimulus inhibition in the majority of cortical neurons tested. In these experiments, the duration of poststimulus inhibition following twin-pulse stimulation was markedly longer than that induced by single-pulse stimulation (200±21 vs 77±18.5 ms). Taken together, the present in vitro and in vivo data suggest that in 5-hydroxytryptamine neurons, short bursts of action potentials will propagate along the axon to the nerve terminal and will enhance both the release of 5-hydroxytryptamine and its postsynaptic effect. (C) 2000 IBRO.

Original languageEnglish
Pages (from-to)295-300
Number of pages6
Issue number2
Publication statusPublished - Jun 1 2000



  • 5-hydroxytryptamine
  • Burst firing
  • Dorsal raphe nucleus
  • Electrophysiology
  • Medial prefrontal cortex
  • Microdialysis

ASJC Scopus subject areas

  • Neuroscience(all)

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