Comparison of diurnal and nocturnal rates of 5-hydroxytryptamine turnover in the rat mediobasal hypothalamus

Summary Rates of 5-hydroxytryptamine (5-HT) turnover in the mediobasal hypothalamus of male rats were estimated using pharmacological methods during the daytime and at night. Concentrations of 5-HT in this hypothalamic area were higher nocturnally than diurnally; this was apparently due to increased 5-HT synthesis and decreased 5-HT catabolism at night.Supported by NIH grant RR07187 (TSK) and NIH grant HD10202 (Neuroendocrine Core).     

The enteric neural receptor for 5-hydroxytryptamine

An enteric neural receptor for serotonin (5-HT) has been characterized. This receptor was assayed, using 3H-5-HT as a radioligand, by rapid filtration of isolated enteric membranes and by radioautography. In addition, intracellular recordings were made from ganglion cells of the myenteric plexus. High affinity, saturable, reversible, and specific binding of 3H-5-HT was demonstrated both to membranes of the dissected longitudinal muscle with adherent myenteric plexus and the mucosa-submucosa. Radioautographs showed these 3H-5-HT binding sites to be in myenteric ganglia and in a broad unresolved band at the mucosal-submucosal interface. Antagonists active at receptors for other neurotransmitters than 5-HT, at either of the two known types of CNS 5-HT receptor, and at 5-HT uptake sites on serotonergic neurons failed to inhibit binding of 3H-5-HT. The structural requirements of analogues for binding to the enteric 5-HT receptor matched the known pharmacology of M or neural 5-HT receptors. A novel 5-HT antagonist was found. This compound, N-acetyl-5-hydroxytryptophyl-5-hydroxytryptophan amide (5-HTP-DP), antagonized the action of 5-HT on type II/AH cells of the myenteric plexus but did not affect the release or actions of acetylcholine (nicotinic or muscarinic) or substance P. 5-HTP-DP was also an equally potent displacer of 3H-5-HT from its binding sites on enteric membranes. It is concluded that the sites responsible for specific binding of 3H-5-HT are enteric M or neural 5-HT receptors. These receptors differ from those now known to be present in the CNS.     

The enteric neural receptor for 5-hydroxytryptamine

Summary An enteric neural receptor for serotonin (5-HT) has been characterized. This receptor was assayed, using³H-5-HT as a radiologand, by rapid filtration of isolated enteric membranes and by radioautography. In addition, intracellular recordings were made from ganglion cells of the myenteric plexus. High affinity, saturable, reversible, and specific binding of³H-5-HT was demonstrated both to membranes of the dissected longitudinal muscle with adherent myenteric plexus and the mucosa-submucosa. Radioautographs showed these³H-5-HT binding sites to be in myenteric ganglia and in a broad unresolved band at the mucosal-submucosal interface. Antagonists active at receptors for other neurotransmitters than 5-HT, at either of the two known types of CNS 5-HT receptor, and at 5-HT uptake sites on serotonergic neurons failed to inhibit binding of³H-5-HT. The structural requirements of analogues for binding to the enteric 5-HT receptor matched the known pharmacology of M or neural 5-HT receptors. A novel 5-HT antagonist was found. This compound, N-acetyl-5-hydroxytryptophyl-5-hydroxytryptophan amide (5-HTP-DP), antagonized the action of 5-HT on type II/AH cells of the myenteric plexus but did not affect the release or actions of acetylcholine (nicotinic or muscarinic) or substance P. 5-HTP-DP was also an equally potent displacer of³H-5-HT from its binding sites on enteric membranes. It is concluded that the sites responsible for specific binding of³H-5-HT are enteric M or neural 5-HT receptors. These receptors differ from those now known to be present in the CNS.     

Circadian rhythms of serotonin and the electrical activity of the frontal ganglion of the cockroach,Periplaneta americana

Summary Rhythmic circadian variations in the spontaneous electrical activity of the frontal ganglion (FG) of the cockroach,Periplaneta americana, have been shown, and the neurotransmitter (NT) involved in this activity has been identified as serotonin (5-hydroxytryptamine, 5-HT). During the 24-h day, the diurnal variations in the electrical activity and the levels of 5-HT and its immediate metabolite 5-hydroxyindole acetic acid (5-HIAA) were maximal at 24.00 h and minimal at 12.00 h.     

Daily variation in the eye's 5-HT stores

Summary Eyes from mice have been assayed for 5-HT content at various times during the day. 5-HT levels are highest midway in the light period and lowest during the dark period. In general this daily variation conforms with other published reports for variation of 5-HT stores in brain and pineal.     

In vitro development ofXenopus skin glands producing 5-hydroxytryptamine and caerulein

The granular glands of amphibian skin synthesize and store a large amount of bioactive amines and peptides which are structurally similar to mammalian brain-gut peptides. To investigate the development of peptide- and amine-producing cells in the granular glands, pieces of dorsal skin taken at various stages fromXenopus laevis tadpoles were cultured, and the contents of caerulein and 5-hydroxytryptamine (5-HT) were measured. When pieces of skin from tadpoles at stages 57 to 60 (Nieuwkoop and Faber stages) were cultured in a medium containing 10% fetal calf serum (FCS medium) or one containing FCS treated with charcoal (chFCS medium), the caerulein and 5-HT levels were increased for the six days of the incubation period. The caerulein content was lower in the chFCS medium than in the FCS medium. Addition of thyroxine to the chFCS medium had no significant effect on the caerulein content. These results show that the caerulein-and 5-HT-producing cells of the granular glands can develop in a culture system with FCS- or chFCS-containing media, and suggest that FCS contains substances which are absorbed by charcoal and stimulate development of the amine- and peptideproducing cells of the glands. In a preliminary search for correlation between caerulein and 5-HT synthesis, addition of 5-hydroxytryptophan (5-HTP), a precursor to 5-HT, to the FCS medium increased 5-HT content and, conversely, caused significant decrease in caerulein content, suggesting that accumulation of caerulein in the granular glands is influenced by the amount of 5-HT synthesis. These studies indicate that this culture system is a useful model for investigating the development of peptide- and amine-producing cells.     

A circannual rhythm in bovine pineal serotonin

Summary Bovine pineal serotonin (5-HT) was analyzed at the time of the solstices and equinoxes from December, 1975 until June, 1978. The highest values of 5-HT were detected at the winter solstices and lowest values at the summer solstices of each year examined. The peaks in bovine pineal 5-HT correspond with a lessened fertility in cattle reported during the winter months.Supported by NSF grant PCM 77-05734.The authors wish to thank Roeglein's Provision Company, Beef Processing Division and especially H. Schmidt, Foreman.     

Selective effects of gonadal steroids on the response of peripheral serotonin receptors

Summary The maximal contraction provoked by serotonin (5-HT) in isolated stomach strips of adult rats, a functional index for peripheral 5-HT receptors, was sexually differentiated, androgen-sensitive, and estrogen refractory. This is at variance with the reported sensitivity of central 5-HT receptors to estrogen.     

Selective effects of gonadal steroids on the response of peripheral serotonin receptors

The maximal contraction provoked by serotonin (5-HT) in isolated stomach strips of adult rats, a functional index for peripheral 5-HT receptors, was sexually differentiated, androgen-sensitive, and estrogen refractory. This is at variance with the reported sensitivity of central 5-HT receptors to estrogen.     

Human platelet 5-hydroxytryptamine receptors: binding of [3H]-lysergic acid diethylamide (LSD). Effects of chronic neuroleptic and antidepressant drug administration

Chronic treatment with phenothiazines and thioxanthenes has been found to enhance 5-HT-induced aggregation of human platelets. A method has been developed to study 5-HT2 receptor binding sites on platelets utilising [3H]-LSD and more recently 125I/LSD. Results are presented which suggest that the LSD binding site is indeed the 5-HT2 binding site and that the LSD binding characterises the specific receptor responsible for 5-HT-induced shape change and aggregation. In a group of patients receiving phenothiazines or thioxanthenes, the Bmax of LSD binding was increased. The mean binding affinity was decreased possibly due to a persistence of neuroleptic in the platelet membrane preparation. Analysis showed that this was not the reason why the mean binding capacity was increased. The results show that chronic phenothiazine and thioxanthene delta treatment 'up-regulates' platelet 5-HT2 binding sites and that this may be accompanied by increased sensitivity to platelet aggregation by 5-HT. In normal subjects desipramine treatment increased the Bmax of platelet LSD binding and this was accompanied by an increased prolactin response to tryptophan which is thought to be mediated by central 5-HT function.     

Serotoninergic modulation of mesolimbic and frontal cortical dopamine neurons

Summary Potentiation of the effect of haloperidol on dopamine metabolism by the 5-HT uptake inhibitor CGP 6085 A, and antagonism of this effect by the 5-HT antagonist mianserin were observed in the mesolimbic area and the frontal cortex of the rat brain. A similar effect was reported earlier in the corpus striatum. This suggests that serotoninergic modulation of dopamine neurons is a generally-occurring phenomenon in the brain.     

Serotoninergic modulation of mesolimbic and frontal cortical dopamine neurons

Potentiation of the effect of haloperidol on dopamine metabolism by the 5-HT uptake inhibitor CGP 6085 A, and antagonism of this effect by the 5-HT antagonist mianserin were observed in the mesolimbic area and the frontal cortex of the rat brain. A similar effect was reported earlier in the corpus striatum. This suggests that serotoninergic modulation of dopamine neurons is a generally-occurring phenomenon in the brain.     

Extraneuronal serotonin accumulation in peripheral arteries of the rat

Accumulations of serotonin (5-HT) and norepinephrine (NE) were compared in control and 6-hydroxydopamine (6-OHDA) pretreated rat aorta, mesenteric and tail arteries. The distribution of these amines was corrected by subtracting tissue uptake of tritiated sorbitol in the extracellular space. 5-HT greatly accumulated both in control and 6-OHDA pretreated arteries. In contrast, NE accumulation in mesenteric and tail arteries was substantially decreased after 6-OHDA treatment. In the aorta 6-OHDA pretreatment did not affect the accumulation of both amines. These findings suggest that 5-HT accumulation in these arteries is mainly extraneuronal, and NE mainly neuronal. Since the accumulation of 5-HT in the aorta was not influenced by pretreatment with 10 microM NE, the extraneuronal uptake mechanisms for 5-HT and NE appear to be different.     

The involvement of serotonin in induced ovulation in the immature rat.

In pregnant mare's serum gonadotropin (PMS) treated immature rats the cortex, cerebellum, caudate nucleus and hypothalamus were isolated and analyzed for their serotonin (5-HT) content at 6-h intervals for 72 h. Results showed a general trend of significant variation occurring in days 1 and 3 after PMS injection with no major variations observed on the second day. The results obtained suggest a possible involvement of 5-HT in the control of ovulation.     

The involvement of serotonin in induced ovulation in the immature rat

Summary In pregnant mare's serum gonadotropin (PMS) treated immature rats the cortex, cerebellum, caudate nucleus and hypothalamus were isolated and analyzed for their serotonin (5-HT) content at 6-h intervals for 72 h. Results showed a general trend of significant variation occurring in days 1 and 3 after PMS injection with no major variations observed on the second day. The results obtained suggest a possible involvement of 5-HT in the control of ovulation.     

Effect of des-Tyr1-gamma-endorphin on serotonin metabolism in rat brain regions

Intracerebroventricular (i.c.v.) administration of des-Tyr1-gamma-endorphin (0.1 and 1.0 microgram) caused a decrease of the serotonin (5-HT) concentration of the hippocampus. The concentration of 5-HIAA and the pargyline-induced alterations in 5-HT and 5-HIAA were not affected. No effects were noticed in other brain regions.     

The plasma level of some amino acids and physical and mental fatigue

Tryptophan is converted to 5-hydroxytryptamine (5-HT) in the brain and evidence is presented that an increase in the concentration of 5-HT can result in physical and mental fatigue during prolonged exercise. The entry of tryptophan in the brain is influenced by the plasma level of free tryptophan (that not bound to albumin) and, from competition for entry into brain, by the plasma level of branched chain amino acids. Hence, oral administration of branched chain amino acids could, theoretically, prevent the increase in 5-HT level during exercise and therefore delay physical and mental fatigue. Evidence in support of this hypothesis is presented.     

5-HT hyperpolarization of bullforg sympathetic ganglion cell membrane

Zusammenfassung Die Membran der sympathischen Ganglienzelle des Ochsenfrosches (Rana catesbiana) wird durch 5-HT depolarisiert; 5-HT erzeugt jedoch in Gegenwart von Nicotin eine Hyperpolarisation. Es scheint, dass sowohl die Depolarisation als auch die Hyperpolarisation von 5-HT durch direkte Wirkung auf die Zell-Membran zustande kommt. Die durch 5-HT erzeugte Hyperpolarisation zeigte ähnliche Eigenschaften wie des «slow IPSP» welches jedoch während der Entwicklung der 5-HT Hyperpolarisation stark zunimmt. Es wird vermutet, dass 5-HT wahrscheinlich nicht als Überträgerstoff für das «slow IPSP» in Frage kommt.     

Serotonin metabolism in the CNS in cerebellar ataxic mice

The metabolism of 5-hydroxytryptamine (5-HT) in the CNS was investigated in four kinds of morphologically different ataxic mice; reeler, staggerer, weaver and Purkinje cell degeneration mutants, and in hypocerebellar mice experimentally produced by injection of cytosine arabinoside. 5-HT and 5-hydroxyidoleacetic acid concentrations and tryptophan hydroxylase (TrpOH) activity were measured in the cerebrum, cerebellum and brain stem, respectively. TrpOH activity was significantly reduced only in the reeler mouse. The enhancements of the cerebellar 5-HT metabolism observed in the ataxic mice other than the reeler were supposed to be pseudo-enhancements subsequent to the cerebellar hypoplasia.     

Butanol extracts from myelin fragments. IV. Some interactions between 5-hydroxytryptamine and other neurotransmitters binding

Summary To examine the interaction between 5-HT and other neurotransmitters binding to the butanol extracts from myelin, double labelling experiments were done. The binding peaks of C¹⁴. ACh and NA were clearly different from that of H³. 5-HT. At 5×10^–7 M, binding of 5-HT, ACh, NA, GABA and DA was 62.7, 2.3, 7.0, 5.8 and 1.9 nmoles/mg protein, respectively. These results suggest that the 5-HT binding components of myelin butanol extracts may have high selectivity and specificity.