Tryptamine transport in rat brain slices: A comparison with 5-hydroxytryptamine

The uptake of [¹⁴C]tryptamine (¹⁴C-T) and [³H]serotonin (³H-5HT) into slices of rat hypothalamus (HT), fronto-parietal cortex (CX), and caudate nucleus (Cau) has been investigated. In all three brain areas, the uptake of³H-5HT at 37°C was much greater than that in an ice-bath at 1.0–1.5°C. In contrast, the uptake of¹⁴C-T at 37°C was not much greater than uptake at 1.0–1.5°C. While markedly different amounts of³H-5HT were accumulated by each of the brain areas studied, the regional uptake of¹⁴C-T was quantitatively similar. In general the uptake of¹⁴C-T was inhibited less than³H-5HT by cocaine, DNP, ouabain, and decreased Na⁺ concentrations. Similarly,¹⁴C-T was less susceptible to serotonin uptake inhibitors except in the caudate. It was concluded that though a common indoleamine uptake system accumulates both T and 5HT, a non-specific low affinity or diffusional process also transports both amines and is predominantly responsible for T, but not 5HT, uptake. The spontaneous release, or wash-out, of¹⁴C-T from the caudate was much faster than that of³H-5HT. In addition, while depolarizing stimuli caused little or no release of¹⁴C-T, large releases of³H-5HT were observed. T, therefore, does not behave like a conventional neurotransmitter.     

Neuroprotective actions of deferiprone in cultured cortical neurones and SHSY-5Y cells

Alzheimer's disease (AD) is a common neurodegenerative disorder, but the initiating molecular processes contributing to neuronal death are not well understood. AD is associated with elevated soluble and aggregated forms of amyloid beta (Abeta) and with oxidative stress. Furthermore, there is increasing evidence for a detrimental role of iron in the pathogenic process. In this context, iron chelation by compounds such as 3-hydroxypyridin-4-one, deferiprone (Ferriprox) may have potential neuroprotective effects. We have evaluated the possible neuroprotective actions of deferiprone against a range of AD-relevant insults including ferric iron, H(2)O(2) and Abeta in primary mouse cortical neurones. We have investigated the possible neuroprotective actions of deferiprone (1, 3, 10, 30 or 100 microM) in primary neuronal cultures following exposure to ferric iron [ferric nitrilotriacetate (FeNTA); 3 and 10 microM], H(2)O(2) (100 microM) or Abeta1-40 (3, 10 and 20 microM). Cultures were treated with deferiprone or vehicle either immediately or up to 6 h after the insult in a 24-well plate format. In order to elucidate a possible neuroprotective action of deferiprone against Parkinson's disease relevant insults another group of experiments were performed in the human neuroblastoma catecholaminergic SHSY-5Y cell line. SHSY-5Y cells were treated with MPP(+) iodide, the active metabolite of the dopaminergic neurotoxin MPTP and the neuroprotective actions of deferiprone evaluated. Cytotoxicity was assessed at 24 h by lactate dehydrogenase release, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium-bromide turnover (FeNTA and hydrogen peroxide) and morphometric analysis of cell viability by Hoechst 33324/propidium iodide (FeNTA, Abeta and MPP(+)) or 6-carboxyfluorescein diacetate and annexin V-Cy3 (Abeta). The present study demonstrates that deferiprone protects against FeNTA, hydrogen peroxide, MPP(+) and Abeta1-40-induced neuronal cell death in vitro, which is consistent with previous in vitro and in vivo studies that have demonstrated similar protection with other iron chelators.     

Evidence for 5-hydroxytryptamine in neurones in the gut of the toad,Bufo marinus

Summary The stomach, small intestine and large intestine of the toad, Bufo marinus, were processed for formaldehyde-induced fluorescence histochemistry. After extrinsic denervation or pretreatment with 6-hydroxydopamine to remove catecholamine fluorescence, yellow fluorescence typical of 5-hydroxytryptamine was observed in neurones in the small intestine only. The cell bodies and their processes were confined to the myenteric plexus. Additional pretreatment with 5-hydroxytryptamine enhanced the fluorescence of neurones in the small intestine and revealed yellowfluorescent nerve fibres, but not cell bodies, in the longitudinal and circular muscle layers and myenteric plexus of the large intestine. No fluorescent neurones were observed in the stomach. Following reserpine treatment, which removed native yellow fluorescence in the small intestine, exposure to 5-hydroxytryptophan produced yellow fluorescence in axons in both small and large intestine; exposure to tryptophan never restored fluorescence. The neurotoxin, 5,7-dihydroxytryptamine had no effect on the distribution of yellow-fluorescent neurones in the small and large intestine. No 5-HT-containing mast cells were present in either the small or large intestine. Thin layer chromatography with three different mobile phases showed a 5-hydroxytryptamine-like compound in extracts of mucosa-free small and large intestine but not of stomach.     

Dopamine and 5-hydroxytryptamine actions on the cardiac ganglion of the lobster Homarus americanus

The cardioexcitor monoamines dopamine (DA) and 5-hydroxytryptamine (5HT) accelerate bursting by isolated cardiac ganglia of the lobster Homarusamericanus most effectively when they act on a region of the ganglionic trunk anterior to the small cells which have been considered the pacemakers of the system. 5HT may exert its acceleratory action by depolarizing cell processes. Neither the somata nor the spike-initiating zones of the small cells have to be directly exposed to 5HT or DA in order for acceleration to occur. When 5HT is applied selectively to the small cells bursts are prolonged, probably as a result of increases in the duration of the endogenous burst-organizing potentials (driver potentials) generated by these neurons. This action on the small cells can lead to prolonged and intensified bursts of the full ganglion during the onset of 5HT action when the whole ganglion is exposed to the monoamine. Neither DA nor 5HT has a direct effect on the characteristics of large cell (motorneuron) driver potentials. Accepted: 3 September 1997     

Methionine sulfoximine shows excitotoxic actions in rat cortical slices

Methionine sulfoximine (MSO) is a rare amino acid. It occurs in nature or as a by-product of some forms of food processing. A notable example of the latter was a former method for bleaching wheat flour, using nitrogen trichloride, the "agene process," in use for most of the first 50 years of this century. "Agenized" flour was found to be responsible for various neurological disorders in animals, and MSO was identified as the toxic factor. The agene process was subsequently discontinued in the United States and the United Kingdom circa 1950. MSO inhibits the synthesis of both glutathione and glutamine, and it is possible that its actions on the nervous system arise from alterations in the amount or distribution of these molecules. Structurally, MSO resembles glutamate, an observation that has also raised the possibility that it might have more direct glutamate-like actions on neurons. In the present investigation, we report excitatory and toxic actions of MSO in an in vitro preparation of adult rat cortex. Field potential recordings in this preparation show that MSO application evokes a sustained depolarization, which can be blocked by the N-methyl-D-aspartate (NMDA) antagonist L-(+)-2-amino-5-phosphonovalerate (AP5). However, competition assays using MSO on [3H]CGP-39653 (DL-(E)-2-amino-4-propyl-1-phosphono-3-pentenoate) binding in rat cortical homogenates show only 20% displacement of total binding, suggesting that MSO is acting indirectly, perhaps by releasing glutamate. To investigate this possibility, we measured glutamate release during MSO application. Time course and dose-response experiments with MSO showed significant [3H]glutamate release, which was partially attenuated by AP5. To assess cellular toxicity, we measured lactate dehydrogenase (LDH) release from cortical sections exposed to MSO. MSO treatment led to a rapid increase in LDH activity, which could be blocked by AP5. These data suggest that MSO acts by increasing glutamate release, which then activates NMDA receptors, leading to excitotoxic cell death. These data suggest the possibility that MSO in processed flour had excitotoxic actions that may have been contributing factors to some human neuronal disorders.     

Role of brain 5-hydroxytryptamine in audiogenic seizure in the rat

The effects of various treatments on brain 5-hydroxytryptamine (5-HT) levels were compared to their effects on audiogenic seizure (AGS) intensity. Although some of these procedures also altered norepinephrine (NE) and dopamine (DA) concentrations, it was possible to observe differences in the depletion of these 2 catecholamines and 5-HT. The data indicated that depletion of brain 5-HT itself enhances AGS, whereas an increase in the concentration of this amine above physiologic levels diminishes the intensity of seizure. It appears that 5-HT exerts an inhibitory effect in the brain which limits spread of the seizure discharge. Thus, depletion of this amine disrupts inhibitory activity, allows more efficient spread of seizure activity in the brain and increases severity of AGS.     

Effect of prolonged 5-hydroxytryptamine uptake inhibition by paroxetine on cortical beta 1 and beta 2-adrenoceptors in rat brain

The effects of prolonged (21 day) oral administration of the antidepressants paroxetine (0.9 to 8.9 mg/kg/day) and amitriptyline (2.7 to 27 mg/kg/day), on rat brain cortical beta 1- and beta 2-adrenoceptor numbers and affinities were investigated using [3H]-CGP 12177. Although amitriptyline, 27 mg/kg, caused a significant (p less than 0.05) 20% reduction in the number of beta 1-adrenoceptors, paroxetine, at doses up to 8.9 mg/kg p.o., did not influence binding of [3H]-CGP 12177 to cortical beta 1- or beta 2-adrenoceptors. This study with paroxetine provides further evidence that the down-regulation of central beta 1-adrenoceptors in rat brain after repeated administration is not a property of all antidepressant drugs.     

Removal of 5-hydroxytryptamine by rat lungs.

Isolated rat lungs perfused with Krebs solution removed free radioactive 5-Hydroxytryptamine (5 HT or serotonin) from the fluid perfusing them. However, when platelets labelled with 111In-oxine to tag them individually, and with 14C-labelled 5 HT were also perfused via the lungs, there was no significant removal of the labelled 5 HT from the platelets. Paper chromatography showed that 46.7% of the platelet bound 5 HT was metabolished to an unidentified material. Rat lungs remove free 5 HT from plasma but not when it is platelet bound.     

Feedback control of rat brain 5-hydroxytryptamine synthesis

Abstract— The effect of increased levels of 5-hydroxytryptamine (5-HT) on the synthesis of [³H]5-HT from intracisternally injected tracer doses of [³H]tryptophan was studied in the rat brain stem. The [³H]5-HT which accumulated in the first 15 min after [³H]tryptophan injection was measured at various times after the acute intraperitoneal administration of the monoamine oxidase inhibitors Catron or Pargyline. The 5-HT levels reached two and three times control values respectively at 20 min and 180 min after monoamine oxidase inhibitor administration but [³H]5-HT accumulation was decreased (40 per cent) at 180 min when compared with 20 min. These data as well as those obtained after chronic treatment with monoamine oxidase inhibitors revealed that there is an inverse relationship between [³H]5-HT accumulation and the endogenous 5-HT level. Monoamine oxidase activity was undetectable during all the intervals in which [³H]5-HT accumulation was measured. No inhibition of [³H]5-HT accumulation was detected when [³H]5-hydroxytryptophan was injected instead of [³H]tryptophan. The results are consistent with a negative feedback of 5-HT synthesis at the rate-limiting tryptophan hydroxylation step.