Neurochemical and anatomical identification of fast- and slow-firing neurones in the rat dorsal raphe nucleus using juxtacellular labelling methods in vivo
Section snippets
Animals
Adult Sprague–Dawley rats (270–330 g) were housed in a temperature-controlled environment on a 12-h light/dark cycle (lights on 07:00 a.m.), and had free access to food and water. All experiments were carried out in accordance with the UK Animals (Scientific Procedures) Act (1986) and Home Office guidelines. All experiments were designed to minimize animal suffering and the number of animals used.
Electrophysiology
Animals were anaesthetized with 1.25 g/kg i.p. urethane (plus 4% lignocaine injected at the cranial
Juxtacellular labelling of slow- and fast-firing DRN neurones
A total of 34 slow- or fast-firing DRN neurones (one neurone/rat) were successfully labelled with neurobiotin and included in the analysis. We excluded from the analysis a small number of cases that demonstrated dense labelling in one cell but light ‘halo’ labelling in surrounding cells. This occasional spreading of neurobiotin over short distances was often due to the use of low resistance electrodes (5–10 Mohm) or the ejection of current to ‘clear’ the electrode of debris.
Electrophysiology and neurochemistry
Twenty-four neurones
Discussion
DRN GABA neurones are thought to play a role in the regulation of the ascending 5-HT system, but advances in the understanding of these neurones are hampered by the lack of knowledge of their physiological and anatomical properties. The present study applied in vivo juxtacellular labelling (Pinault, 1996) to characterise a population of fast-firing DRN neurones of unknown chemical identity. Slow-firing 5-HT neurones were analysed for comparison. It was found that DRN neurones with narrow spikes
Acknowledgements
This work was supported by a Medical Research Council (U.K.) programme grant (G9102310, T.S.). The authors would like to thank Dr. Peter J. Magill for assistance with the juxtacellular procedure.
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