Histochemical Fluorescence of Raphe Neurons: Selective Enhancement by Tryptophan

Abstract

The histochemical fluorescence of those neurons in brainstem raphe nuclei which are presumed to contain serotonin is selectively and stereospecifically enhanced by L-tryptophan at doses that also produce an elevation in the concentration of serotonin. However, contrary to our assumptions, the increase in raphe fluorescence is not prevented by p-chlorophenylalanine, an inhibitor of serotonin synthesis. These results suggest that under some conditions derivatives of tryptophan other than, or in addition to, serotonin may be of significance in raphe neurons.

Is 5-Methoxytryptamine the B-Type Fluorophore in Rat Brain?

“…Even following a tryptophan loading sched ule, as described by Aghajanian and Asher (1971), which greatly enhances the concentra tion of fluorescence in the raphe system of the brain stem, we could not detect 5-MT with our methods. This does not support the hypothesis that 5-MT is the identity of the B-type fluo rophore as suggested by Green et al (1973) and Koslow (1974).…”

“…These authors have defined this amine as a 'B-type' fluorophore and have differ entiated it by microspectrofluorimetry from other fluorophores produced by the catechol amines and serotonin (Bjorklund et al, 1971b). Aghajanian and Asher (1971) have shown that after a tryptophan preload there is an increase in fluorescence in the raphe nuclei of the mes encephalon both in terms of numbers of cells and brilliance of reaction. This increase in fluo rescence is resistant to p-chlorophenylalanine (PCPA) treatment (which lowers brain 5-HT).…”

Evidence for a serotonin‐mediated slow excitatory potential in the guinea‐pig coeliac ganglia.

“…The intensity as well as the number of fibres that exhibited serotonin-like immunoreactivity was less conspicuous in the ganglion without pre-treatment with tryptophan; the reason for this is not clear. In this context, the serotonin histofluorescence of the central (Aghajanian & Asher, 1971) and enteric (Dreyfus, Bornstein & Gershon, 1977) neurones was also shown to be markedly enhanced by pre-loading the animals with the precursor. As the serotonin-like immunoreactivity could be traced along the nerve fibres that enter the ganglion, the origin of these fibres is of interest.…”

Uptake of 5‐hydroxytryptamine in the Catecholamine Containing Areas of the Hypothalamus of the Rat After Treatment With Phenelzine and Tryptophan

“…(1965) and Collard & Roberts ( 1974) measured the accumulation of 5-HT in the brain by chemical estimation. The increase of 5-HT in such experiments in the 5-HT containing neurone system was described by Aghajanian & Asher (1971), Aghajanian, Kuhar & Roth (1973) and also after treatment with 5-hydroxytryptophan (the precursor of 5-HT) an increase of fluorescence in various structures in rat brain was shown by Fuxe (1965). Due to non-specific uptake, 5-HT can also be found in areas normally containing only catecholamines (Bertler etal., 1964;Fuxe etal., 1971;Butcher et al, 1972;Dow & Laszlo, 1976).…”