Neurochemical and electrophysiological studies on the functional significance of burst firing in serotonergic neurons
Section snippets
Animals
Male Sprague–Dawley rats [250–300 g; Harlan–Olac, Bicester, U.K. (microdialysis and electrophysiological experiments) or Charles River, Budapest, Hungary (brain slice experiments)] were housed in groups of up to six under conditions of controlled temperature and lighting, with food pellets and water freely available. All in vivo procedures were carried out in accordance with the U.K. Animals (Scientific Procedures) Act, 1986, and its associated guidelines.
Measurement of [3H]5-hydroxytryptamine efflux in vitro
Electrically evoked efflux of [3H]5-HT
Effect of single- and twin-pulse stimulation on efflux of [3H]5-hydroxytryptamine in vitro
Electrical stimulation (2 min, 2 Hz) of the superfused brain slices increased the efflux of tritium, and this effect lasted for three or four fractions. In the same slice, stimulations comprising twin pulses evoked a greater efflux of tritium than did stimulations comprising single pulses (Fig. 1). Thus, following twin-pulse stimulation the peak of tritium efflux was increased, with no consistent effect on the duration of the response. This effect was independent of the order in which the twin-
Discussion
Recent electrophysiological studies have established the existence of neurons in the rat DRN and MRN which discharge action potentials in short, high-frequency bursts within an otherwise slow and regular firing pattern.16., 18. Much evidence suggests that these neurons are a subpopulation of 5-HT neurons (see Introduction). In the present study, we used a stimulation pattern of twin pulses (7–10-ms interspike interval) within a regular 1–3 Hz firing pattern to mimic the burst firing pattern of
Acknowledgements
This work was supported by an MRC programme grant (G9102310) and the Hungarian Research Fund OTKA (T025060).
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Present address: Psychiatry Research Laboratory, The Medical School, Newcastle, U.K.
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Present address: Pharmacia Corp., Kalamazoo, MI-49007, U.S.A.