Excitatory responses of neurones in rat bulbar reticular formation to bulbar raphe stimulation and to iontophoretically applied 5‐hydroxytryptamine, and their blockade by LSD 25.

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Abstract
The micro-iontophoretic technique was used to study the responses of single neurons in the bulbar reticular formation to 5-hydroxytryptamine [5-HT] and to noradrenaline [norepinephrine] ACh [acetylcholine] or glutamate, and to compare these with the responses to electrical stimulation in or near the bulbar raphe nuclei. In the bulbar reticular formation, most neurons were excited by 5-HT; 43 of 51 neurons excited by 5-HT were also excited by stimulation in nucleus raphe magnus, nucleus raphe pallidus or nucleus raphe obscurus. Most of these stimulation-induced excitations were of long latency: LSD reduced 6 of 7 of these excitations tested, while 5-HT excitations were blocked on all 7. Stimulation of areas adjacent to the raphe nuclei excited only 15 of 46 neurons excited by 5-HT. Most of these stimulation effects were of short latency, and none of the 3 tested were reduced by LSD, although 5-HT excitations were blocked. The relationship of the long-latency excitatory effects of stimulation with the position of the stimulating electrode in the raphe nuclei indicates that these effects are probably mediated via the raphe neurons; this is supported by the correlation of the effects of raphe stimulation with the effects of 5-HT applied iontophoretically and by the ability of LSD to block both effects. A physiological basis was provided for the excitatory effects of iontophoretically applied 5-HT in the bulbar reticular formation.