Serotonin release from the superior cervical ganglion of the cat.

Serotonin of the superior cervical ganglion is contained in a distinct and separate population of small intensely fluorescent (SIF) cells. We provide evidence, in in vitro experiments, that newly synthesized serotonin can be released in the cat superior cervical ganglion from the serotonin-containing SIF cells. Resting steady state in the release of [(3)H]serotonin was observed 30 min after the beginning of the superfusion with l-[(3)H]tryptophan. A marked increase was seen in the serotonin release either in the presence of fluoxetine, a potent reuptake blocker of serotonin, or during depolarization with potassium chloride or veratridine. Calcium-free medium led to a decrease of spontaneous and potassium-evoked release. The veratridine-stimulating response was abolished by tetrodotoxin. Paradoxically, a slight increase in the spontaneous release of serotonin was observed in the presence of tetrodotoxin. Serotonin released from serotonin-containing SIF cells could be involved in the modulation of ganglionic transmission.

The stimulation of GABA(B) receptors increases serotonin release in the rat suprachiasmatic area.

The action of ?-aminobutyric acid (GABA) and related compounds on the spontaneous release of newly synthesized [(3)H]5-hydroxytryptamine ([(3)H]5-HT) was studied in the suprachiasmatic area (SCA) using a superfusion system. GABA (10 ?M) increased [(3)H]5-HT release from SCA by up to 190%. Bicuculline or picrotoxin (10 ?M) failed to inhibit the stimulatory effect of GABA. Muscimol (10 ?M), a GABA(A) agonist, was ineffective, however ?-p-chlorophenyl GABA, R(?)baclofen, enhanced over 200% the release of the indoleamine; this latter effect was stereospecific. RS baclofen was twice less potent than the R(?)isomer in increasing the [(3)H]5-HT release. S(+)baclofen failed to affect the release of the indoleamine, whereas it attenuated the effect of its enantiomer. The effect of R(?)baclofen was Ca(2+) dependent and was abolished by tetrodotoxin (TTX). Taken together these results suggest that in the SCA, [(3)H]5-HT release is facilitated by the stimulation of GABA(B) receptors. The possible localization of these receptors is discussed in the light of morphological data recently reported by Bosler et al. (1985) and results obtained after TTX application.

Effect of vasoactive intestinal peptide on serotonin metabolism in the suprachiasmatic area of the rat: mechanism of action.

Vasoactive intestinal peptide (VIP) inhibits serotonin (5-HT) uptake in the suprachiasmatic area (SCA) of the rat. The present study investigates the possibility of a functional relationship between 5-HT uptake mechanisms and 5-HT autoreceptor activity in this effect of VIP in the SCA. The hypothesis of a linkage between these two mechanisms of 5-HT regulation has been recently proposed. We investigated the possibility of the presence of 5-HT autoreceptors in the SCA. Using superfusion system, exogenous 5-HT (500 and 50 nM) increased the release of newly synthesized 3H-5-HT. In contrast, 5 nM of exogenous 5-HT inhibited this release. This latter effect was antagonized by methiothepin (10(-7) M). In contrast, the concentration of methiothepin required to inhibit the VIP effect was 10(-6) or 10(-5) M, the same molarity found to decrease the 5-HT uptake. On the other hand, the increase of the 3H-5-HT in the synaptic cleft, induced by VIP, did not modify the inhibition of 3H-5-HT release induced by 5 nM of exogenous 5-HT. We conclude that the effect of VIP on 5-HT metabolism in the SCA is linked to the 5-HT uptake mechanism but not to the activity of 5-HT presynaptic autoreceptors. In our experimental conditions, the activity of 5-HT autoreceptors is independent of the 5-HT uptake processes.

Serotonin-like immunoreactivity in paraffin-sections of the nodose ganglia of the cat.

The presence of serotonin (5-HT)-like immunoreactivity has been detected in ganglionar cell bodies of the nodose ganglia of the cat, using the peroxidase-antiperoxidase immunohistochemical method, applied to sections of ganglia previously embedded in paraffin. The antibodies were raised in rabbits following injection of 5-HT conjugated to bovine serum albumin, with formaldehyde as the condensation reagent. Immunoreactive cell bodies are morphologically and topographically described. The ubiquitous distribution and non-uniform labelling suggest that these 5-HT-containing vagal neurones may give rise to several functionally different 5-HT types in vagal afferent fibres.

Endogenous levels of tryptophan, serotonin and 5-hydroxyindole acetic acid in the developing brain of the cat.

Using spectrofluorimetric methods, endogenous levels of tryptophan (TRP), serotonin (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) were determined in various structures of the growing brain of cats. After one month, 5-HT metabolism is comparable to that observed in adult cats. The third week after birth is marked by increasing levels of TRP and 5-HIAA and seems to be a critical period for the maturation of serotoninergic neurons.

Endogenous serotonin (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) levels in large regions and in discrete brain areas of C57BL and BALBc mice at three times of the day.

The serotoninergic system has been analysed in the brainstem and the forebrain of adult C57BL and BALBc mice. Endogenous 5-HT and 5-HIAA levels have also been measured in the different raphe nuclei and in the caudate nucleus and the hippocampus of these strains, using the micropunch technique and the radioenzymatic method (for 5-HT) and a new radioimmunoassay (for 5-HIAA). This investigation was performed at three times of the day: 9:00 hr; 14:00 hr; 20:00 hr to underline the differences between the strains. Most of the time, higher 5-HT and 5-HIAA levels are found in the brainstem and the raphe nuclei of the BALBc strain compared to C57BL. In the forebrain the differences are reversed, except in the caudate nucleus and the hippocampus where the levels of 5-HT are identical in the two strains. Moreover the 5-HIAA/5-HT ratio shows a higher turn-over of the amine in the C57BL strain.

Developmental variations of brain serotonin, tryptophan, 5-hydroxyindole acetic acid, and noradrenaline and dopamine content in two inbred strains of mice.

Endogenous levels of tryptophan (TRP), serotonin (5-HT), 5-hydroxyindol acetic acid (5-HIAA), noradrenaline (NA) and dopamine (DA), were measured in the brain-stem and anterior regions of C57BL and BALBc mice whose ages ranged from 1 day postnatal to 12 weeks. In C57BL mice levels of NA were found to be higher in the brainstem from week 1 onwards (except at week 3), and in the anterior region from week 6 onwards than in BALBc mice. 5-HT levels were found to be higher in C57BL mice from day 1 to week 2 in the brain-stem, and in the anterior region at week 1 and from week 5 onwards, compared to BALBc. The evolution of DA levels in the anterior region shows opposite differences before and after week 3-4. Before week 3 lower levels of DA were found in C57BL mice and the reverse is observed from week 5 onwards. Moreover during the postnatal development, the variation of the different components of the serotoninergic metabolism (TRP, 5-HT, 5-HIAA) is similar to that observed in other species.

Comparison of brain serotoninergic systems in C57BL and BALBc mice during development.

Adult C57BL and BALBc mice will exhibit differences in behaviour and in their sleep patterns which may be correlated with monoamine content. In this study, we measured the endogenous levels of serotonin (5-HT), tryptophan (TRP), 5-hydroxyindole acetic acid (5-HIAA), noradrenaline (NA) and dopamine (DA) in the forebrain and hindbrain regions of these strains of mice from day 1 to 12 weeks of age. Using the micropunch technique and a radioenzymatic method, we also determined the endogenous 5-HT levels in the nuclei raphe dorsalis, centralis, magnus-pallidus and obscurus. During development, NA levels in the brain stem are higher in the C57BL than in the BALBc mice. From 5 weeks of age onwards, the levels of 5-HT, DA and NA in the forebrain are also higher in the C57BL mice. However, no differences in 5-Ht and DA content was found for the brain stems of these two strains. When the 5-HT levels in the different raphe nuclei were analyzed, the nucleus raphe dorsalis of the BALBc showed a higher 5-HT content.

Distribution of choline acetyltransferase in the brain stem of the cat.

Activities of choline acetyltransferase were detected in various structures of the brain stem of the cat by radiochemical methods on square punches of fresh tissue. High activities were measured in all cranial motor nuclei and in reticular nuclei such as the gigantocellular tegmental nucleus. Low activities were found in sensory nuclei and in the pyramidal tract, trapezoïd body and inferior and superior olive complex. Raphe nuclei, that also contain serotonergic neurons, exhibit relatively high activities of choline acetyltransferase. In spite of some exceptions, the results are in good accordance with those previously obtained by histochemical methods for acetylcholinesterase.

5-HT metabolism in the intestinal wall of the rabbit.

The levels of TRP, 5-HTP, 5-HT and 5-HIAA were measured in the proximal colon of the rabbit using ion exchange chromatography and spectrofluorimetry. Assays were performed on fragments of the intact colonic wall, on the muscle layers containing nerve plexuses, and on the mucosa-containing enterochromaffin cells. In spite of identical TRP concentration, 5-HT levels were higher in the mucosa than in the muscle containing nerve plexus. In the muscle, the ratio 5-HIAA/5-HT was about 1, i.e., comparable to that of the brain, whereas the ratio was very low in the mucosa, suggesting a weak 5-HT catabolism in the enterochromaffin cells. When the mucosa was severed from the muscle, 5-HT synthesis was increased. In this case, 5-HT and 5-HIAA concentrations in the reconstituted wall (muscles + mucosa) were higher than in the intact wall. In in vitro studies, levels of newly synthesized (3H)5-HT from (3H)TRP were 3 times higher in the reconstituted wall than in the intact one, and the conversion index of TRP to 5-HT was higher in the mucosa and in the reconstituted wall respectively. These results suggest that enterochromaffin cells do synthesize 5-HT from TRP when the mucosa is divided from the muscle. (3H)5-HT was taken up by both nerve plexuses and mucosa, with a high affinity mechanism. Results from tryptophan loading experiments indicated that 5-HTP decarboxylase in the gut might be involved in the regulation of 5-HT synthesis. The mucosa severed from the muscles might represent a good model for the study of carcinoid tumour development.

[Kinetic study of serotonin metabolism in the suprachiasmatic nucleus of the rat: neuroendocrine incidence (author's transl)]. / Etude cinétique du métabolisme de la 5 HT dans le noyau suprachiasmatique de rat. Incidence neuroendocrinienne.

The suprachiasmatic nucleus (SCN), which is implicated in the regulation of several cyclic neuroendocrine rhythms, displays a conspicuous and apparently specific serotoninergic innervation. Our study was intended to establish more precise correlations between the incidence of serotonin (5 HT) metabolism in the activity of the SCN, and neuroendocrine rhythms. For this purpose, castrated female rats, having subcutaneous implants of estradiol, were studied. These animals display very marked circadian fluctuations in plasma levels of the pituitary hormones ACTH, LH and PRL; a relatively well-synchronized increment in all these hormones occurs between 11.00 and 15.00. Punches were obtained to determine the endogenous content of 5 HT, measured by a radioenzymatic technique, simultaneously in SCN and median eminence (ME). An index of SCN activity was determined from in vivo SCN 2-deoxy (1-14C) glucose (DG) uptake; the retention was estimated on radioautographs. Endogenous level of 5 HT displayed a marked circadian rhythm with a peak between 12.00 and 15.00 in the SCN; 5 HT levels were constant throughout the day in the ME. 14C-DG uptake was greater at 15.00 than at 9.00. However, after PCPA treatment or raphe lesions, the uptake of 14C-DG was the same at 9.00 and 15.00. Taken together, these results strongly suggest that in our model: (1) SCN displays a rhythm of activity in the light period; (2) SCN displays specific rhythms in the content of 5 HT; (3) the SCN rhythm of activity must be under an inhibitory control of 5 HT, since the lowest metabolic level is increased at 9.00 by inactivation of 5 HT system; (4) the close relationships between the initial release phase of several pituitary hormones, the increase of metabolic activity in the SCN and the higher level of the 5 HT in the nucleus suggest that 5 HT terminals in the SCN play an important part in the control of cyclic hormonal secretion.

Release of endogenous serotonin from "encéphale isolé" cats. I - Technical aspects.

Ventricular perfusion, push-pull cannulae at the caudate level and cortical superfusion were used in "encéphale isolé" cats in order to estimate endogenous 5-HT release. The amine was measured using the radioenzymatic assay. These different methods are described and compared. Technical aspects and advantages of cortical superfusion under physiological conditions are discussed.