Neurochemical and anatomical identification of fast- and slow-firing neurones in the rat dorsal raphe nucleus using juxtacellular labelling methods in vivo

Neuroscience. 2003;122(1):193-204. doi: 10.1016/s0306-4522(03)00518-9.


GABA neurones in the dorsal raphe nucleus (DRN) influence ascending 5-hydroxytryptamine (5-HT) neurones but are not physiologically or anatomically characterised. Here, in vivo juxtacellular labelling methods in urethane-anaesthetised rats were used to establish the neurochemical and morphological identity of a fast-firing population of DRN neurones, which recent data suggest may be GABAergic. Slow-firing, putative 5-HT DRN neurones were also identified for the first time using this approach. Fast-firing, DRN neurones were successfully labelled with neurobiotin (n=10) and the majority (n=8/10) were immunoreactive for the GABA synthetic enzyme glutamic acid decarboxylase. These neurones were located in the DRN (mainly lateral regions), and consistently fired spikes with short width (1.1+/-0.1 ms) and high frequency (12.1+/-2.0 Hz). In most cases spike trains were regular but displayed low frequency oscillations (1-2 Hz). These neurones were morphologically heterogeneous but commonly had branching axons with varicosities and dendrites that extended across DRN subregions and the midline. Slow-firing DRN neurones were also successfully labelled with neurobiotin (n=24). These neurones comprised a population of neurones immunopositive for 5-HT and/or tryptophan hydroxylase (n=12) that fired broad spikes (2.2+/-0.2 ms) with high regularity and low frequency (1.7+/-0.2 Hz). However, a slow-firing, less regular population of neurones immunonegative for 5-HT/tryptophan hydroxylase (n=12) was also apparent. In summary, this study chemically identifies fast- and slow-firing neurones in the DRN and establishes for the first time that fast-firing DRN neurones are GABAergic. The electrophysiological and morphological properties of these neurones suggest a novel function involving co-ordination between GABA and 5-HT neurones dispersed across DRN subregions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials*
  • Animals
  • Biotin / analogs & derivatives*
  • Electrophysiology
  • Glutamate Decarboxylase / analysis
  • Immunohistochemistry
  • Neurons / chemistry*
  • Neurons / physiology*
  • Raphe Nuclei / chemistry*
  • Raphe Nuclei / cytology
  • Raphe Nuclei / physiology*
  • Rats
  • Rats, Sprague-Dawley
  • Serotonin / analysis*
  • Tryptophan Hydroxylase / analysis
  • Tyrosine 3-Monooxygenase / analysis
  • gamma-Aminobutyric Acid*


  • neurobiotin
  • Serotonin
  • gamma-Aminobutyric Acid
  • Biotin
  • Tyrosine 3-Monooxygenase
  • Tryptophan Hydroxylase
  • Glutamate Decarboxylase