Inhibition of Serotonin Synthesis Induces Negative Hepatic Lipid Balance

BACKGROUND: Hepatic steatosis is caused by metabolic stress associated with a positive lipid balance, such as insulin resistance and obesity. Previously we have shown the anti-obesity effects of inhibiting serotonin synthesis, which eventually improved insulin sensitivity and hepatic steatosis. However, it is not clear whether serotonin has direct effect on hepatic lipid accumulation. Here, we showed the possibility of direct action of serotonin on hepatic steatosis. METHODS: Mice were treated with para-chlorophenylalanine (PCPA) or LP-533401 to inhibit serotonin synthesis and fed with high fat diet (HFD) or high carbohydrate diet (HCD) to induce hepatic steatosis. Hepatic triglyceride content and gene expression profiles were analyzed. RESULTS: Pharmacological and genetic inhibition of serotonin synthesis reduced HFD-induced hepatic lipid accumulation. Furthermore, short-term PCPA treatment prevented HCD-induced hepatic steatosis without affecting glucose tolerance and browning of subcutaneous adipose tissue. Gene expression analysis revealed that the expressions of genes involved in de novo lipogenesis and triacylglycerol synthesis were downregulated by short-term PCPA treatment as well as long-term PCPA treatment. CONCLUSION: Short-term inhibition of serotonin synthesis prevented hepatic lipid accumulation without affecting systemic insulin sensitivity and energy expenditure, suggesting the direct steatogenic effect of serotonin in liver.

5-HT1A/1B receptors, alpha2-adrenoceptors and the post-receptor adenylate cyclase activation in the mice brain are involved in the antidepressant-like action of agmatine / 药学学报

This study is to explore the possible mechanisms of the antidepressant-like effect of agmatine. By using two traditional "behavior despair" model, tail suspension test and forced swimming test, we examined the effects of some monoamine receptor antagonists (including beta-adrenergic receptor antagonist propranolol, beta-adrenergic receptor antagonist/5-HT1A/1B receptor antagonist pindolol, alpha2-adrenergic receptor antagonists yohimbine and idazoxan and 5-HT3 receptor antagonist tropisetron) on the antidepressant-like action of agmatine in mice. Activity of adenylate cyclase (AC) in the synapse membrane from rat frontal cortex was determined by radioimmunoassay. Single dose of agmatine (5-40 mg x kg(-1), ig) dose-dependently decrease the immobility time in tail suspension test in mice, indicating an antidepressant-like effect. The effect of agmatine (40 mg x kg(-1), ig) was antagonized by co-administration of beta-adrenergic receptor antagonist/5-HT1A/1B receptor antagonist pindolol (20 mg x kg(-1), ip), alpha2-adrenergic receptor antagonists yohimbine (5-10 mg x kg(-1), ip) or idazoxan (4 mg x kg(-1), ip), but not beta-adrenergic receptor antagonist propranolol (5-20 mg x kg(-1), ip) and 5-HT3 receptor antagonist tropisetron (5-40 mg x kg(-1), ip). Agmatine (5-40 mg x kg(-1), ig) also dose-dependently decrease the immobility time in forced swimming test in mice. The effect of agmatine (40 mg x kg(-1), ig) was also antagonized by pindolol (20 mg x kg(-1), ip), yohimbine (5-10 mg x kg(-1), ip), or idazoxan (4 mg x kg(-1), ip). Incubation of agmatine (0.1-6.4 micromol x L(-1)) with the synaptic membrane extracted from rat frontal cortex activated the AC in a dose-dependent manner in vitro. While the effect of agmatine (6.4 micromol x L(-1)) was dose-dependently antagonized by pindolol (1 micromol x L(-1)) or yohimbine (0.25-1 micromol x L(-1)). Chronic treatment with agmatine (10 mg x kg(-1), ig, bid, 2 w) or fluoxetine (10 mg x kg(-1), ig, bid, 2 w) increased the basic activity, as well as the Gpp (NH)p (1-100 micromol x L(-1)) stimulated AC activity in rat prefrontal cortex. These results indicate that regulation on 5-HT1A/1B and alpha2 receptors, and activation AC in the frontal cortex is one of the important mechanisms involving in agmatine's antidepressant-like action.

A reassessment of the role of serotonergic system in the control of feeding behavior

O papel do sistema serotonérgico no comportamento alimentar foi avaliado através de lesões eletrolíticas do núcleo dorsal da rafe (L-NDR) e da administração de para-clorofenilalanina (PCPA, 3 mg/5 µl, icv). Avaliações crônicas foram realizadas durante 120 e 360 dias em ratos injetados com PCPA e L-NDR, respectivamente. Avaliações agudas foram realizadas em ratos em jejum e injetados com PCPA e l-triptofano (LHTP, 30 mg/kg, ip). Ratos lesionados apresentaram um aumento de 22-80% na ingestão de alimento até o sexto mês enquanto a obesidade foi evidenciada e mantida por todo o período. Ratos injetados com PCPA apresentaram um aumento da ingestão alimentar seguido de uma hipofagia do 25º ao 30º dia e um aumento transitório do peso corporal do 5º ao 60º. Agudamente, o LHTP reverteu parcialmente o aumento da ingestão de alimento em ratos tratados com PCPA e jejuados, sugerindo a preservação da capacidade de descarboxilação do precursor pelos neurônios serotonérgicos. A lenta recuperação dos níveis de ingestão alimentar em ratos lesionados revela um mecanismo de neuroplasticidade dos sistemas de regulação do comportamento alimentar. Estabelecimento de platô na curva de peso corporal dos ratos lesionados representaria o estabelecimento de um novo e mais elevado ponto de calibração do balanço energético.

Effects of autacoid inhibitors and of an antagonist on malaria infection in mice

The effects of p-chlorophenylalanine, an inhibitor of serotonin synthesis, indomethacin, an inhibitor of prostaglandin synthesis, cyproheptadine, a serotonin, bradykinin and histamine antagonist, were assessed separately and in combination with chloroquine (CQ) in Vom strains of Swiss albino mice (18-22 g) of either sex infected intraperitoneally with 1 x 10(7) Plasmodium yoelii nigeriensis-induced malaria. As prophylactic, these agents reduced from 31.9 ± 4.5 to 16.1 ± 8.1 percent the level of parasitemia relative to control but had no appreciable activity as curative agents when administered subcutaneously once daily for 4 days after 72 h of parasites innoculum in vivo. However, CQ alone and the combination of these agents with CQ in curative and prophylactic treatments significantly reduced (from 50.3 ± 5.8 to 4.9 ± 0.75 percent) the level of parasitemia (P < 0.05), which was taken only once 72 h after the parasites innoculum. The prophylactic result was shown to produce better results than the curative treatment. The data indicate that inhibitors and an antagonist can reduce the parasitemia load (the extent of damage and the severity of infection) as well as enhance the effects of CQ when combined with it for malaria therapy. The study reveals that the production of autacoids in established infection renders autacoid inhibitors and an antagonist ineffective for radical cure in malarial mice; however, selective inhibition of local hormones implicated in the pathological manifestations of malaria infection by autacoid inhibitors and an antagonist may be a possible pathway to reduce the severity of infection and the associated tissue damage and to enhance the efficacy of available anti-malarials.

Effect of p-CPA pretreatment on EEG power spectra in experimental open brain injury in rats

Continuous four hours EEG [electroencephalogram] recordings and its power spectrum analysis using fast fourier transform [FFT] in urethane anesthetized male Charles Foster rats were performed in two groups: open brain injury and p-CPA [para-Chlorophenylalanine] pretreated before brain injury, respectively, and compared with the EEG power spectrum of control rats. The EEG power spectrum analysis showed that there was a faster recovery in p-CPA pretreated group than the injury group of rats. The results showed that the p-CPA [a 5-HT inhibitor] prevents pathological changes following brain injury. Simultaneously, the inference can also be drawn that EEG power spectrum analysis is a useful technique for monitoring the brain injury and its recovery following pharmacological treatments

Serotonergic mechanism in imipramine induced antinociception in rat tail flick test.

Substantial evidence has accumulated that spinally projecting serotonergic neurons modulate nociception. However, the exact receptor subtypes that mediate the antinociceptive response of serotonin within the spinal cord continue to be a subject of debate. Therefore, we explored the effect of serotonergic system on imipramine induced antinociception by using 5-Hydroxytryptamine-3 (5HT3) receptor antagonist ondansetron and 5-Hydroxytryptamine-2 (5HT2) receptor antagonist mianserine, and depletion of brain 5-Hydroxytryptamine (5HT) with p-chlorophenyl alanine (PCPA). Male wistar strain rats were pretreated with either ondansetron (0.5 mg/kg, i.p.) or mianserine (1 mg/kg, i.p.). After 15 minutes, rats received injection of imipramine (10 mg/kg). Nociception was assessed by tail-flick method. Imipramine (2 mg, 5 mg, 10 mg, and 20 mg/kg) produce antinociceptive response in the dose dependent manner. Prior treatment with 5HT3 antagonist, Ondansetron and 5HT2 antagonist, mianserine reduce the antinociceptive response of imipramine. In PCPA treated rats imipramine (10 mg/kg) failed to produce antinociception. These results indicate that the 5HT plays an important role in imipramine induced antinociception.

Effects of pretreatment of serotonin synthesis inhibitor p-chlorophenylalanine on lipopolysaccharide-induced anorexia in rats

In the present study, we investigated the effect of pretreatment of p-chlorophenylalanine (PCPA), inhibitor of serotonin synthesis, on lipopolysaccharide (LPS)-induced anorexia in rats. First of all, effects of PCPA injection on food intake and body weight in rats were investigated. During 4 days of PCPA injection (300 mg/kg BW once a day), food intake was decreased by 33% and daily gain in body weight was inhibited compared with controls. Twenty-four hours after last PCPA injection, food intake and gain in body weight returned toward almost normal. Pair-feeding to PCPA (PCPAP) injection revealed that body weight of rats in PCPA group was not different from rats in PCPAP groups. To quantify the effects of LPS on food intake and body weight, we administered varying doses (10, 100, 500 microgram/kg BW) of LPS to rats. LPS induced a reduction of food intake and weight loss in a dose dependent manner compared with controls. To evaluate the effects of PCPA pretreatment on LPS injection, rats were treated with PCPA for 4 days (300 mg/kg BW once a day), which was followed by LPS injection for 2 days (500 microgram/kg BW once a day) (PCPA+LPS group), while rats in LPS group had injections with normal saline instead of PCPA for 4 days, which was followed by LPS administration. Rats in control group received 0.9% NaCl for 6 days. LPS decreased food intake by 80% and inhibited gain in body weight, while PCPA pretreated rats showed normalized food intake and gain in weight during the days of LPS injections compared with controls. In conclusion, pretreatment of PCPA prevented LPS-induced anorexia.

Effects of p-chlorophenylalanine on the synthesis of pancreatic amylase in rats

Previously, we have reported that p-chlorophenylalanine (PCPA), a serotonin depletor, profoundly increased pancreatic fluid and bicarbonate secretion but remarkably inhibited pancreatic amylase secretion in anesthetized rats. The present study was performed to verify the detailed effects of PCPA on pancreatic amylase synthesis that is directly related to amylase exocrine secretion. PCPA significantly decreased pancreatic RNA and protein contents as well as the amylase activity. However, pancreatic DNA content, trypsin and chymotrypsin activities were not influenced by the treatment of PCPA. The rate of pancreatic amylase synthesis, which was assessed by the amount of incorporated (35S)-methionine into amylase for 1 h, was also significantly decreased by 44% in PCPA-treated rats. In order to determine whether the PCPA-induced decrease of amylase synthesis resulted from change in the level of amylase mRNA, Northern blot analysis was performed. The mRNA expression level of amylase was also decreased by 48% in the PCPA-treated rats, indicating that the inhibitory effect of PCPA on the synthesis of pancreatic amylase was mainly regulated at a step prior to translation. It was also revealed in SDS-polyacrylamide gel electrophoresis that the qualitative change of amylase was induced by PCPA. The 54 KDa amylase band seems to be degraded into small molecular weight protein bands in PCPA-treated rats, suggesting that the PCPA-induced decrease of amylase may be partly attributed to the degradation of synthesized amylase.

Effects of p-chlorophenylalanine-induced depletion of brain serotonin on retrieval of appetitive and aversive memories.

This study examined whether depletion of central serotonin produces an improved retrieval of aversive memories in the same way as pre-exposure to inescapable footshocks, in rats. Animals conditioned in a T-maze with appetitive (10% sucrose) and aversive (2.0 mA footshock) events were given i.c.v. 24 hr later a single dose of p-chlorophenylalanine (p-CPA). (100, 200, 400 micrograms/rat) or drug vehicle. The retention performance and activity were assessed 48 hr after treatment with this depletor. While lower doses of p-CPA selectively reduced serotonin levels in striatum and anterior cortex, higher doses reduced both serotonin and norepinephrine levels in hippocampus in a dose-dependent fashion. The depletor however, failed to produce a differential improvement of aversive memory retrieval. On the contrary, p-CPA reduced the latency to enter both, previously shocked and appetitively reinforced, goalboxes. The enhanced traversing behaviour in T-maze, together with an increased central entry in the open field that observed in depleted groups, might suggest an anxiolytic activity of p-CPA.

Effects of P-chlorophenylalanine and naloxone on forced swimming induced analgesia in mice / 신경정신의학

No abstract available.

Serotonergic modulation of footshock induced aggression in paired rats.

Footshock induced aggression (FIA) was induced in paired rats and three paradigms of aggressive behaviour were recorded, namely, latency to fight (LF), total period of physical contact (TPP) and cumulative aggression scores (CAS). The effects of increasing or decreasing central serotonergic activity, by using a number of pharmacological agents with well defined effects on rat brain serotonin, were investigated on FIA and on FIA augmented by apomorphine, a dopamine receptor agonist. The results show that centrally administered serotonin, the serotonin precursor, 5-hydroxytryptophan administered with clorgyline, a selective MAO A inhibitor, quipazine, a serotonin receptor agonist, and fluoxetine, a selective inhibitor of neuronal re-uptake of serotonin, attenuated all paradigms of FIA and apomorphine induced potentiation of FIA. On the contrary, the other re-uptake inhibitor used, citalopram, appeared to have a dual effect and decreased LF and CAS, while increasing TPP. The serotonin synthesis inhibitor, p-chlorophenylalanine and the selective serotonin receptor (5-HT2) antagonist, ketanserin, augmented all paradigms of FIA per se and apomorphine induced augmentation of FIA. However, the other serotonin receptor antagonist used, metergoline, which blocks both 5-HT1 and 5-HT2 receptor subtypes, attenuated FIA per se but decreased only CAS in apomorphine induced increase in FIA. The data confirm the inhibitory effect of the central serotonergic system on aggressive behaviour and the inverse relationship existing between it and the central dopaminergic system in the modulation of FIA, as has also been confirmed in earlier biochemical investigations from this laboratory. The data has been discussed in the light of existing knowledge on serotonin receptor subtypes and the presence of modulatory serotonergic heteroreceptors on central dopaminergic neurones.

A functional interaction between GABA and 5-HT in inhibiting picrotoxin-induced myoclonus in rats.

Pretreatment with 5-hydroxytryptophan (5-HTP), a precursor of 5-HT, antagonised while pretreatment with p-chlorophenylalanine (PCPA), a 5-HT depletor, potentiated the myoclonus induced by picrotoxin, a GABA antagonist. Pretreatment with aminooxyacetic acid (AOAA), a GABA transaminase inhibitor, antagonised picrotoxin-induced myoclonus. The combined effect of the least protective doses of AOAA and 5-HTP was greater than the sum of their individual inhibitory effects on picrotoxin-induced myoclonus. Further, AOAA failed to inhibit picrotoxin-induced myoclonus in PCPA pretreated rats. These findings suggest that the central 5-HT-ergic system exerts a facilitatory influence on the GABA-ergic system and thus it is involved in the antimyoclonic action of GABA.

Acute neurobehavioural toxicity of phosphamindon and its drug-induced alteration.

Phosphamidon, a systemic organophosphate insecticide, (1.4 mg/kg - dose 1/4th of LD50 given ip), produced several autonomic, neurological and behavioral effects in mice with peak effects being at 15 min. Similar dose in rats also abolished conditioned avoidance response. Pre-treatment with atropine, iproniazid, alpha-methyl-p-tyrosine, p-chlorophenylalanine or thiosemicarbazide reduce many of these effects. This suggests that phosphamidon toxicity involves the central cholinergic, adrenergic, serotonergic and GABAergic systems in addition to peripheral cholinergic effects.

Influence of 6-hydroxydopamine on ethanol narcosis in mice

Se estudian los efectos de la administración de 6-hidroxidopamina (6-OHDA0, 100 Y 200 microng i.c.v., en la duración de la narcosis por etanol en ratones sin o con tratamiento de alfa-metil-p-tirosina (AMPT), p-cloro-fenilalanina (PCPA) o 5-hidroxitriptófano (5-HTP). La narcosis por etanol fue significativamente más prolongada en los ratones que recibieron 200 microng de 6-OHDA i.c.v. que en los testigos. La duración de la narcosis en los ratones tratados con ambas dosis de 6-OHDA fue significativamente más larga cuando éstos recibieron previamente AMPT (inhibidor de la biosíntesis de seotonina). En 5-HTP (precursor de la biosíntesis de serotonina). En cambio, en los pretratados con PCPA (inhibidor de la triptófano hidroxilasa), la 6-OHDA no modificó la duración de la narcosis por etanol. Las alcoholemias al momento de despertar no cambiaron significativamente por la 6-OHDA. Estos resultados son consistentes con la hipótesis de que la disminución de noradrenalina así como el aumento de serotonina cerebrales prolongan la narcosis por etanol y, en cambio, el aumento de noradrenalina o la disminución de serotonina en el cerebro reducen la narcosis por etanol

Participaçäo da serotonina na hipertermia desencadeada por lesäo eletrolítica mesencefálica em ratos / Participation of serotonin in the hyperthermia induced by mesencephalic electrolytic in rats

O presente estudo tentou determinar o papel da serotonina na etiologia de uma elevaçäo anormal da temperatura corporal observada em ratos após a lesäo eletrolítica feita nas áreas dorsais do mesencéfalo. A hipertermia observada mostrou ser bloqueada pela administraçäo prévia de para-clorofenilalanina, um inibidor da síntese de serotonina. Estes resultados reforçam a sugestäo de que a lesäo eletrolítica desencadeia uma atividade irritativa das vias serotoninérgicas, que ascendem próximas ao local da lesäo, ativando os mecanismos termogênicos

Effect of para-chlorophenylalanine on male rats: histopathological and biochemical changes in the testes.

Spermatogenically active testes of rat challenged by 100 mg/kg body weight of p- Chlorophenylalanine for 45 days displayed marked and drastic changes in the seminiferous epithelium. Degenerative changes followed by immense necrosis of germ cells lead to complete breakdown of seminiferous tubules. Leydig cells, however, remained unaffected histologically in the treated animals. Among the accessory sex organs, epididymis alone showed a marked decrease in its weight. A biochemical study in the drug treated rats revealed a significant accumulation of glycogen in the testes accompanied by increase in the activities of enzymes like the succinic dehydrogenase, glucose-6-phosphatase, ATP-ase and acid phosphatases. However, a marked decrease was noticed in the activities of enzymes like alkaline phosphatase, phosphohexose isomerase and lactate dehydrogenase. No significant change was found in the protein, DNA and RNA concentrations in the drug treated testes. The histological and biochemical changes induced in the testes by p-CPA suggest the deleterious effect of the drug on the seminiferous tubules of the testes.