Effects Of Parachlorophenylalanine Research Articles

Visceral hypersensitivity induced by activation of transient receptor potential vanilloid type 1 is mediated through the serotonin pathway in rat colon

This study aimed to clarify the relationship between TRPV1 activation-induced visceral pain and the serotonin pathway in the colon of rats. The effects of para-chlorophenylalanine ( pCPA) on visceral pain threshold pressure were assessed in capsaicin -induced visceral pain of rats. The expression of TRPV1 in the colon was examined by immunohistochemistry and Western blot analysis, and TRPV1 excitability in dorsal root ganglion (DRG) neurons was examined by whole-cell patch-clamp recording in pCPA-treated rats. Calcineurin and Ca 2+-calmodulin-dependent kinase II (CaMKII), the important proteins in maintaining TRPV1 function in the colon, were also tested by Western blot analysis and immunofluorescence staining. Results showed that pCPA significantly increased the capsaicin-induced visceral pain threshold by 2.3-fold, and the enhanced visceral pain threshold corresponded with decreased 5-HT content (58% depleted) and enterochromaffin cell number (80% reduced). The reduced excitability of TRPV1 in DRG neurons, instead of changed TRPV1 expression, is responsible for the enhanced visceral pain threshold in 5-HT-depleted rats, and the mechanism may be related to the decreased expression of pCaMKII. These results indicate that visceral hypersensitivity induced by TRPV1 activation is modulated through 5-HT pathways and the attenuated function of TRPV1 and decreased protein expression of pCaMKII may play an important role in capsaicin-induced TRPV1 desensitization under 5-HT-depleted condition. The important role of TRPV1 and 5-HT in generating and maintaining visceral hypersensitivity may provide insights for the treatment of visceral hypersensitivity.

Influence of PCPA and MDMA (ecstasy) on physiology, development and behavior in Drosophila melanogaster

The effects of para-chlorophenylalanine (PCPA) and 3,4 methylenedioxy-methamphetamine (MDMA, 'ecstasy') were investigated in relation to development, behavior and physiology in larval Drosophila. PCPA blocks the synthesis of serotonin (5-HT) and MDMA is known to deplete 5-HT in mammalian neurons; thus these studies were conducted primarily to target the serotonergic system. Treatment with PCPA and MDMA delayed time to pupation and eclosion. The developmental rate was investigated with a survival analysis statistical approach that is unique for Drosophila studies. Locomotion and eating were reduced in animals exposed to MDMA or PCPA. Sensitivity to exogenously applied 5-HT on an evoked sensory-central nervous system (CNS)-motor circuit showed that the CNS is sensitive to 5-HT but that when depleted of 5-HT by PCPA a decreased sensitivity occurred. A diet with MDMA produced an enhanced response to exogenous 5-HT on the central circuit. Larvae eating MDMA from the first to third instar did not show a reduction in 5-HT within the CNS; however, eating PCPA reduced 5-HT as well as dopamine content as measured by high performance liquid chromatography from larval brains. As the heart serves as a good bioindex of 5-HT exposure, it was used in larvae fed PCPA and MDMA but no significant effects occurred with exogenous 5-HT. In summary, the action of these pharmacological compounds altered larval behaviors and development. PCPA treatment changed the sensitivity in the CNS to 5-HT, suggesting that 5-HT receptor regulation is modulated by neural activity of the serotonergic neurons. The actions of acute MDMA exposure suggest a 5-HT agonist action or possible dumping of 5-HT from neurons.

Behavioral effects of para-chlorophenylalanine in gonadectomized male rats.

Para-chlorophenylalanine restores impaired conditioning and retention of active avoidance reaction in castrated animals and improved their behavior in the open field test.

Effect of Serotonin Inhibition on Glucocorticoid and Mineralocorticoid Expression in Various Brain Structures

Many studies have shown the existence of functional interactions between central neurotransmitter systems and the hypothalamo-pituitary adrenal axis. Mineralocorticoid receptors (MR) and glucocorticoid receptors (GR) are regulated by multiple factors including glucocorticoids themselves. Neurotransmitters such as serotonin (5-hydroxytryptamine: 5-HT) can regulate brain corticosteroid receptors in a complex way. The present study examined the short-term (48 h) effects of parachlorophenylalanine (PCPA), a drug which specifically inhibits 5-HT synthesis, on corticosteroid receptor levels and on the expression of their respective messenger ribonucleic acids (mRNA) in the rat hippocampus, hypothalamus and brain stem. The study was performed in bilaterally adrenalectomized animals, in order to avoid potential drug-induced changes in plasma corticosterone levels, which could secondarily regulate MR and GR. Short-term inhibition of 5-HT synthesis by PCPA significantly increased the number of hippocampal MR-binding sites. PCPA treatment did not alter the number of GR-binding sites in the hippocampus, hypothalamus and brain stem. We observed no change in the affinities of GR and MR sites in all the structures studied. In PCPA-treated rats, restoration of control 5-HT levels by injection of its immediate precursor, 5-hydroxytryptophan (5-HTP) brings the number of hippocampal MR-binding sites back to control levels. It can therefore be concluded that the increase in number of MR-binding sites induced by acute PCPA treatment is dependent on the decrease in 5-HT levels. The increase in hippocampal MR binding sites was correlated with an induction of their messengers, suggesting that 5-HT modulates the synthesis of MR protein. Although PCPA did not modify the number of hippocampal GR-binding sites, a decrease in hippocampal GR mRNA expression was observed. This study shows that 5-HT inhibits hippocampal mineralocorticoid receptor synthesis and that this effect is not mediated by changes in corticosterone hormone secretion, and illustrates the existence of complex mechanisms for corticosteroid receptor regulation in the hippocampus.

Effects of para-chlorophenylalanine (pCPA) on the bush baby auditory brainstem response

Click-evoked auditory brainstem responses were recorded in a prosimian primate, the bush baby ( Otolemur garnettii), before and after depletion of serotonin (by systemic injection of para-chlorophenylalanine; pCPA) and up to 20 days after discontinuing pCPA injections (during the recovery of serotonin). Biphasic 100 μs clicks were presented at five repetition rates (13.2, 33.2, 53.2, 73.2, and 93.2 clicks/s; RATE) and sound pressure levels (SPL) were varied in 10 dB steps from 120–60 dB SPL peak equivalent. Absolute latencies of vertex-positive peaks I, III, IV, and V were measured from click onset. The latencies from each wave were statistically analyzed with a two-way analysis of variance using either RATE or SPL (but not both) and TIME AFTER pCPA as independent variables. Prior to pCPA, brainstem response latencies increased as a function of both decreasing SPL and increasing RATE. After pCPA, these normal increases in wave latency increased even more, particularly in response to high click rates. After pCPA was discontinued, measurements taken at weekly intervals indicated that latencies decreased after 1 week, increased to the highest values recorded after 2 weeks, and returned to normal after 3 weeks. These dynamic changes were interpreted to be the result of post-synaptic receptor up-regulation during the 10 days of continuous pCPA administration. These results suggest that serotonin plays an important role in sensory processing at the cellular level and, tonically, facilitates the auditory brainstem response to sound.

Effects of parachlorophenylalanine, quipazine and cyproheptadine on growth hormone and adrenocorticotropin secretion in steers

Adrenergic and perhaps dopaminergic neurons provide inhibitory regulation of growth hormone (GH) secretion in ruminants. This suggests that either serotonergic or other neurons regulate the stimulatory release of GH. The nature of neurotransmitter control of adrenocorticotropin (ACTH) secretion in ruminants has not been determined. Parachlorophenylalanine (PCPA; serotonin synthesis inhibitor), quipazine (serotonin receptor agonist) and cyproheptadine (serotonin receptor antagonist) were utilized in Holstein steers to determine whether serotonin receptors mediate stimulatory actions on GH and ACTH secretion. PCPA (100 mg/kg BW) administered each day at 1900 hr for three successive days did not alter mean GH concentrations, amplitude of GH peaks, nor the number of GH peaks. Likewise, PCPA altered none of these parameters for ACTH. Quipazine injected iv at .1 or .5 mg/kg BW increased plasma GH (P<.05) and ACTH (P<.001) concentrations. There was a dose effect of quipazine on both GH (P<.05) and ACTH (P<.001) secretion. Pretreatment of steers with cyproheptadine (.06 and .6 mg/kg BW) reduced the stimulation of GH by quipazine (P<.0001) and decreased basal GH concentrations (P<.0004). Cyproheptadine at .06 mg/kg BW did not alter quipazine effects on ACTH, however, the higher dose decreased the peak ACTH response (P<.02) to quipazine. Studies with quipazine and cyproheptadine indicated that serotonergic mechanisms are likely involved in the regulation of GH and ACTH secretion in steers.

Stress analgesia: Effects of PCPA, yohimbine, and naloxone

Evidence suggests that morphine analgesia depends on the integrity of monoaminergic transmitter systems. Some forms of stress analgesia seem to be related to morphine analgesia, while others are not. To assess whether opioid and non-opioid stress analgesia differ in their reliance on monoamine systems, the effects of parachlorophenylalanine (PCPA) and yohimbine on analgesia produced by prolonged intermittent and brief continuous footshock were examined on the hotplate test. The interaction of adrenergic and endorphinergic activity with serotonergic mechanisms following these stressors was also investigated by testing the effects of yohimbine and naloxone on rats with prior PCPA treatment. Yohimbine alone significantly reduced baseline hotplate latencies, while PCPA and naloxone did not. The two stressors differed in the effects produced by both naloxone and PCPA. Naloxone significantly reversed stress analgesia in the prolonged stress condition, but not the brief stress condition. PCPA significantly enhanced the antinociceptive effect of brief continuous shock, while leaving the response to prolonged intermittent shock unaffected. In contrast, yohimbine blocked the analgesic effects of prolonged stress. For the brief stress condition, naloxone reversed the elevated thresholds elicited in PCPA treated rats. Naloxone also reversed stress analgesia for PCPA treated rats exposed to prolonged intermittent stress. Yohimbine lowered the responses of PCPA treated rats subjected to brief continuous shock. These results support an interactive model of stress analgesia dependent upon serotonergic, adrenergic, and endorphinergic transmitter systems.

The effects of Parachlorophenylalanine and stimulus intensity on open-field test measures in rats

An inhibitor of 5-hydroxytryptamine synthesis, p-chlorophenylalanine (PCPA), or an inert saline solution was administered intraperitoneally to rats. At maximum depletion of serotonin (72 hr after injection), the rats were tested in the standard, four-day open-field test. A further four days of testing in the open field in which the sound level was raised from the standard 78 to 93 dB showed that, while PCPA increased defaecation in both sexes and under both sound levels, the controls increased defaecation at the higher level stimulus intensity, whereas PCPA-injected rats defaecated less. Parachlorophenylalanine increased ambulation in males on the first day of open-field testing but not in females. On the remaining seven days of testing PCPA markedly reduced ambulation in females but did not affect ambulation in males. Across-trial habituation of neither the defaecation nor the ambulation measure was influenced by PCPA.

Effects of para-chlorophenylalanine, a brain serotonin depletor, on pituitary cyclic AMP levels in the rainbow trout, Salmo gairdneri

The tryptophan hydroxylase inhibitor para-chlorophenylalanine (pCPA) was employed in an investigation of the role of brain serotonin in the regulation of pituitary cyclic AMP levels in Salmo gairdneri. Hypothalamic serotonin content was measured with a fluorometric assay, while pituitary cAMP was determined by means of a double-antibody radioimmunoassay. A time-course study revealed that 250 mg pCPA/kg significantly reduced hypothalamic serotonin content within 1 hr after injection. Lower doses were effective in reducing serotonin content after 48 hr. Pituitary cAMP levels declined significantly 1 hr after injection of 250 mg pCPA/kg. Administration of pCPA at 50 and 250 mg/kg doses reduced cAMP levels within 24 hr. These data indicate that a serotonergic mechanism is involved with the regulation of pituitary cyclic AMP levels in the rainbow trout.

Role played by serotonin in the control of estrous receptivity. Ovarian activity and ovulation in the cyclic female rat.

The effects of parachlorophenylalanine (pCPA) on ovulation and on estrous sexual receptivity have been investigated in gonadally intact four-day cyclic female rats. (1) When injected at 1800 hr on diestrus II, pCPA was shown to inhibit both ovulation and estrous sexual receptivity, an effect which was prevented by 5-hydroxytryptophan (5HTP). (2) The inhibitory effects of pCPA were overcome by 10 μg estradiol benzoate (EB) when injected on the morning of diestrus II at 1000 hr. No changes in the timing of either LH release or ovulation resulted from EB injection. (3) Blood estradiol 17β (E 2 ) concentration did not appear to be modified at 2400 hr during the night from diestrus II to proestrus following pCPA injection. (4) A significant decrease in E 2 was noted on proestrus at 0800 hr in pCPA-treated females but this effect was not prevented by 5HTP. (5) While no changes in blood progesterone (P) concentration occurred from 0900 hr until 1300 hr on proestrus, a specific decrease in blood P concentration was observed on proestrus at 1530 hr after pCPA treatment on diestrus II at 1800 hr.

Effects of parachlorophenylalanine and 5, 6-dihydroxytryptamine on the free-running rhythms of locomotor activity and plasma corticosterone in the rat exposed to continuous light

Parachlorophenylalanine (PCPA) and 5,6-dihydroxytryptamine (5,6-DHT), depletors of brain serotonin, were administered to the rat and circadian rhythms of locomotor activity and plasma corticosterone were determined simultaneously in individual rats in light-dark cycles (LD) and in 200 lux continuous light (LL). Free-running periods and acrophases on the 12th day in LL (LL12) were calculated by a least squares spectrum method. In PCPA-treated rats which showed 70% depletion of brain serotonin, circadian rhythns of locomotor activity in LL and of plasma corticosterone and ACTH in LD disappeared for several days after the drug injection. Circadian rhythms of locomotor activity reappeared after the LL7 day and free-ran with a phase shift. Free-running periods of these rats did not differ significantly from that of control rats. However, the acrophase of PCPA-treated group on the LL11 day was 5 h advanced as compared to that of control. Circadian rhythm of plasma corticosterone in the PCPA-treated rats was detected on the LL12 day but their peak times were distributed around 24:00 h instead of 08:00 h observed in control rats. The 5,6-DHT-treated rats which showed only 40% depletion of brain serotonin exhibited normal free-running rhythms in both locomotor activity and plasma corticosterone in LL and no difference in the acrophases of these functions on the LL12 day as compared to controls. These results suggest that PCPA affects the circadian clock (or clocks) itself in such a way that it blocks the clock to free-run or at least it effectively shortens the free-running periods of locomotor activity and plasma corticosterone in the rat.

Effects of parachlorophenylalanine and 5,6-dihydroxytryptamine on aggressive behaviour evoked by cholinomimetics and anticholinesterases injected into the cerebral ventricles of conscious cats

Carbachol, muscarine, eserine and neostigmine injected into the cerebral ventricles of conscious cats, evoked emotional behaviour with aggression and autonomic and motor phenomena with clonic-tonic convulsions. The main and the most impressive feature of the gross behavioural effects of intraventricular cholinomimetics and anticholinesterases was an affective type of aggression. After 5,6-dihydroxytryptamine and parachlorophenylalanine, intraventricular carbachol, muscarine, eserine and neostigmine elicited aggression and autonomic and motor phenomena with clonic-tonic convulsions. The affective type of aggressive behaviour was modified with biting attack predominant, while hissing and snarling (i.e. vocalization) were depressed or absent. The manifestations of affective aggressive behaviour caused by muscarine were most resistent to 5,6-dihydroxytryptamine and parachlorophenylalanine. When 5-hydroxytryptophan was given to parachlorophenylalanine treated-cats, intraventricular carbachol, muscarine and eserine evoked emotional behaviour with aggression and autonomie and motor phenomena with clonic-tonic convulsions. Hissing and snarling reappeared, but they were less intense and shorter in duration than in control animals. Based on these experiments, it is concluded that an intact central 5-hydroxytryptamine network is required for the expression of emotional behavioural phenomena, especially vocalization in the appearance of the affective type of aggression. On the other hand, intact central 5-hydroxytryptamine pathways are not essential for the performance of the motor act for the attack and biting.

Effects of para-chlorophenylalanine on amphetamine and haloperidol-induced changes in striatal dopamine turnover

Para-chlorophenylalanine (PCPA) was administered to rats, and the animals were sacrificed 48 h later. Animals received various doses of S(+)-amphetamine (AMPH) 31 min before sacrifice or of haloperidol (HAL) 46 min before sacrifcie and an intracerebral injection of [ 3H]tyrosine 15 min prior to sacrifice. PCPA pretreatment potentiated the increased accumulation of striatal [ 3H]dopamine (DA) induced by doses of AMPH to 1.5 mg/kg, and inhibited the decrease in striatal [ 3H]DA accumulation observed at higher doses (> 2.5 mg/kg) of AMPH. Furtherm the AMPH-induced increase in endogeneous levels of striatal DA was inhibited by PCPA pretreatment. Similarily, PCPA pretreatment potentiated the HAL-induced increase in striatal [ 3H]DA accumulation. The data are discussed with respect to an inhibitory serotonergic influence on nigrostriatal DA function, and the relationship of nigrostriatal biochemical events to AMPH-induced behavioral changes.

Effects of para-chlorophenylalanine and 5-hydroxytryptophan on mouse killing behavior in killer rats

The effects of para-chlorophenylalanine (PCPA) on mouse killing behavior were examined in natural killer rats. Forty-eight hr after injection, this serotonin synthesis inhibitor, at relatively low doses of 75 and 150 mg/kg, facilitated mouse killing, as indicated by a decrease in latency to attack the mouse. This effect was revealed in a test of satiation, in which five successive mice were presented to the rat, and also in a novel cage situation. Other than the shorter latencies to attack and kill mice, the killing response was similar in topography to the natural kill. The increase in killing after PCPA injection was associated with a reliable reduction in brain serotonin and in 5-hydroxyindoleacetic acid, and the time courses of the behavioral and biochemical changes were generally similar. In contrast to PCPA, injection of the serotonin precursor 5-hydroxytryptophan (5-HTP, 100 mg/kg) reliably lengthened attack and kill latencies in killer rats. In rats pretreated with PCPA, 5-HTP not only reversed this drug's facilatation of killing, but completely blocked killing in 67% of the rats tested. These results strengthen the hypothesis that brain serotonergic neurons are involved in the inhibition of mouse killing.

An analysis of dorsal and median raphe self-stimulation: Effects of para-chlorophenylalanine

The role of serotonergic systems in intracranial self-stimulation (ICSS) of the dorsal and median raphe nuclei of rats was investigated. Intragastric administration of 400 mg/kg of parachlorophenylalanine (PCPA) depressed ICSS rates in the group with dorsal raphe electrode placements over a similar time course to the depletion of brain serotonin which results from treatment with PCPA. An intrasessional analysis of these behavioral changes on the fourth day after PCPA revealed that dorsal raphe ICSS was depressed over both halves of the 2 hr test session, whereas a significant depression in median raphe ICSS occurred only in the last hr of the session. The data from these studies suggest that brain serotonin systems contribute to the phenomenon of brain-stimulation reward in the dorsal and median raphe nuclei. The involvement of multiple neurochemical substrates of brain stimulation reward is discussed.

Effects of parachlorophenylalanine and amphetamine on habituation of exploration

Parachlorophenylalanine (PCPA, 400 mg/kg) retarded the habituation of exploration in the rat recorded over 3 successive days. A more detailed analysis showed that this was not due to any retention deficit, but was secondary to an impairment of habituation within each session. PCPA also disrupted the response of rats to a change of stimuli. (+)amphetamine (4 mg/kg) prevented exploration in the rat and a 2 mg/kg dose reduced exploration and impaired within-session habituation. (+)amphetamine (1 mg/kg) in mice impaired within-session habituation, without significantly reducing exploration. The nature of the deficits produced by these 2 drugs is discussed.

Effects of parachlorophenylalanine on indoleamines in maturing mouse brain

1. 1. The effects of parachlorophenylalanine (PCPA), the tryptophan-5-hydroxylase (T5-H) inhibitor, on the maturation of 5-hydroxytryptamine (5-HT) and 5-hydroxy-indole acetic acid (5-HIAA) have been studied in regions of the maturing mouse brain. 2. 2. PCPA does not affect 5-HT levels in 1-day old mice treated on the day of birth, but does decrease it at all subsequent stages studied after 24 hr exposure. 3. 3. 5-HIAA level was unchanged in 1-day old and adult mice treated 24 hr earlier but was lower in almost all brain regions at other stages studied. 4. 4. The results lend support to the hypothesis that the newborn brain is able to synthesize more indoleamine than previously suspected but is unable to store it during the stages of neuronal outgrowth and terminalization.

Effects of parachlorophenylalanine on ethanol self-selection in the rat

The efficacy of p-chlorophenylalanine (PCPA) in producing conditioned taste aversions and unconditioned avoidance of ethanol was investigated in two experiments. It was found that administering PCPA to rats having free access to a saccharine solution and water produced robust aversions to saccharin that extinguished within 6 days after termination of the PCPA treatments, thereby indicating that PCPA can produce conditioned aversions to substances consumed during its administration. In a second experiment, intraperitoneal injections of PCPA and/or ethanol given to rats not having access to ethanol were found to produce no change in their subsequent ethanol preferences. The results support the contention of earlier investigators that the reported effects of PCPA on the rat's preference for ethanol may have been due largely to the animals acquiring conditioned aversions to ethanol during PCPA treatments.

Effects of parachlorophenylalanine and amphetamine on habituation of orienting

Parachlorophenylalanine significantly reduced the orienting response to the first presentation of a tone but did not alter the size of responses to subsequent tone presentations nor the rate of habituation. In contrast amphetamine did not alter the orienting response but significantly impaired habituation. It was concluded that there was little evidence for a serotonergic involvement in behavioral habituation, although a role for the catecholamine system could not be excluded.

Effects of para-chlorophenylalanine on pregnancy in the rat.

To test the hypothesis that 5-hydroxytryptamine (5HT) may play a role in the onset of parturition, rats were given p-chlorophenylalanine (PCPA), an inhibitor of 5HT synthesis, via gavage. PCPA administration greatly affected pregnant rats. High dosages of PCPA (316 mg/kg/day on alternate days) induced total resorption between Days 12 and 15 and reduced maternal weight gain. Lower dosages of PCPA (158 mg/kg/day on Days 2, 4, 6, 8, 10, and 12 and 316 mg/kg/day on Days 14, 16, 18, 20, and 21) resulted in partial resorption, reduced maternal and fetal weight gain, immediate neonatal death, and cannibalism. 5HT was significantly reduced in maternal brain (97%), placentas (82%), whole fetuses (96%), and uteri (69%). Maternal adrenal hypertrophy occurred only when conceptuses were present. Because gestational length was not altered, we concluded that 5HT did not play a significant role in the onset of parturition.