Inhalation of Cedrus atlantica essential oil alleviates pain behavior through activation of descending pain modulation pathways in a mouse model of postoperative pain

ETHNOPHARMACOLOGICAL RELEVANCE

Cedrus atlantica essential oil (CaEO) presents analgesic and anti-inflammatory sedative properties. However, it remains unknown whether CaEO alleviates acute postoperative pain.

MATERIALS AND METHODS

Here, we investigated the effect of CaEO on postoperative pain and its mechanisms related to the descending pain control in Swiss males mice induced by a plantar incision surgery (PIS) in the hindpaw.

RESULTS

Inhalation of CaEO (5', 30' or 60') markedly reduced mechanical hypersensitivity. This effect was prevented by pre-treatment with naloxone or p-chlorophenylalanine methyl ester (PCPA, 100mg/kg, i.p.)-induced depletion of serotonin. In addition, p-alpha-methyl-para-tyrosin (AMPT, 100mg/kg, i.p.)-induced depletion of norepinephrine, intraperitoneal injection of the α2-adrenergic receptor antagonist yohimbine (0.15 mg/kg, i.p.) or haloperidol (1mg/kg, i.p.) an antagonist of dopaminergic (D1 and D2) receptors prevented the effect of CaEO on hypersensitivity.

CONCLUSIONS

These findings suggest that CaEO alleviates postoperative pain by activating the descending pain modulation pathways on the opioidergic, serotonergic, noradrenergic (α2-adrenergic) and dopaminergic (dopamine D1 and D2 receptors) systems.

Involvement of opioidergic and serotonergic systems in the analgesic activity of Cissus quadrangularis L. stem extract in mice

BACKGROUND

Cissus quadrangularis L. (Vitaceae) is used as a bonesetter and as an analgesic. However, the bioactive fractions and the pharmacological mechanism of analgesic activity are not clearly known. Hence, this study aimed to characterize the analgesic activity profile of successively extracted fractions of C. quadrangularis and the pharmacological mechanism of analgesic activity in mice.

METHODS

Dried C. quadrangularis stem was extracted successively with chloroform and methanol. The dried extracts were separately administered to mice intraperitoneally at the doses of 75, 150 and 300 mg/kg. The mice were tested separately in hot plate and tail flick tests. The mechanism of analgesic activity of chloroform extract was explored in the hot plate test at the dose of 300 mg/kg after pretreatment with naloxone, p-chlorophenylalanine methyl ester (pCPA) and phentolamine. The data were analyzed by one-way analysis of variance followed by Dunnett's test.

RESULTS

Chloroform extract showed significant (p<0.05) analgesic effect at the doses of 75, 150 and 300 mg/kg in hot plate and tail flick tests. Methanol extract showed significant (p<0.05) analgesic effect at the dose of 300 mg/kg in hot plate and tail flick tests. Analgesic activity was not blocked (p<0.05) in the group pretreated with phentolamine but blocked in the groups pretreated with naloxone and pCPA.

CONCLUSIONS

The chloroform extract was found to be more potent than methanol extract in inducing analgesic effect in mice, and the analgesic activity may be mediated through opioidergic and serotonergic pathways.

Involvement of monoaminergic system in the antidepressant-like effect of aqueous extract of Channa striatus in mice

BACKGROUND

In our previous study, the aqueous extract of Channa striatus (family: Channidae) fillet (AECSF) showed an antidepressant-like effect in mice. However, the mechanism of the antidepressant-like effect is unknown.

AIM

The objective of this study was to explore the involvement of monoamines in the antidepressant-like effect of AECSF in mice.

MATERIALS AND METHODS

AECSF was prepared by steaming the fillets of C. striatus. The male ICR mice were pretreated with various monoaminergic antagonists viz., p-chlorophenylalanine (100 mg/kg, i.p.), prazosin (1 mg/kg, i.p.) and yohimbine (1 mg/kg, i.p.), SCH23390 (0.05 mg/kg, s.c.) and sulpiride (50 mg/kg, i.p.) followed by treatment with AECSF and tested in tail suspension test (TST). Two-way ANOVA with Tukey test were used at p < 0.05 for significance.

RESULTS

The pretreatments with p-chlorophenylalanine, prazosin and yohimbine, but not with SCH23390 and sulpiride, were able to reverse the antidepressant-like effect of AECSF in TST.

CONCLUSIONS

The antidepressant-like effect of AECSF may be mediated through the serotonergic and noradrenergic systems and not through the dopaminergic system.

Desipramine potentiation of the acute depressant effects of ethanol: modulation by alpha2-adrenoreceptors and stress

Ethanol exerts effects on the brain noradrenergic system, and these are thought to contribute to the sedative/hypnotic (depressant) effects of ethanol. Recent studies suggest that the norepinephrine transporter (NET) plays an important role in modulating ethanol's depressant effects. The aim of the present study was to further characterize this role. Transporter blockers with varying affinity for NET versus the serotonin transporter (desipramine>fluoxetine>citalopram) were tested for their ability to alter ethanol's depressant effects, and for comparison, hypothermic effects. Effects of desipramine on another depressant, pentobarbital, were examined. Desipramine potentiation of ethanol's depressant effects was assessed following depletion of brain norepinephrine via N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP-4) treatment, or depletion of brain 5-HT via para-chlorophenylalanine methyl ester hydrochloride (PCPA) treatment. The effects of co-administration of either the selective alpha2-adrenoreceptor agonist (dexmedetomidine) or the selective alpha2-adrenoreceptor antagonist (atipamezole) on desipramine's effect on ethanol's depressant effects were examined. Given the close link between stress, ethanol and norepinephrine, desipramine potentiation of ethanol's depressant effects was tested following repeated forced swim stress. Results showed that desipramine, but not SERT-selective doses of citalopram or fluoxetine, strongly potentiated the depressant (not hypothermic) effects of ethanol. These effects were mimicked by dexmedetomidine and blocked by atipamezole, but not by depletion of either norepinephrine or 5-HT. Desipramine potentiation of ethanol's depressant effects was abolished following repeated stress. Present findings further support a major role for NET and the alpha2-adrenoreceptor in modulating the depressant effects of ethanol, with possible implications for understanding the role of noradrenergic dysfunction in stress-related alcoholism.

cAMP response element-binding protein deficiency allows for increased neurogenesis and a rapid onset of antidepressant response

cAMP response element-binding protein (CREB) has been implicated in the molecular and cellular mechanisms of chronic antidepressant (AD) treatment, although its role in the behavioral response is unclear. CREB-deficient (CREB(alpha delta) mutant) mice demonstrate an antidepressant phenotype in the tail suspension test (TST) and forced-swim test. Here, we show that, at baseline, CREB(alpha delta) mutant mice exhibited increased hippocampal cell proliferation and neurogenesis compared with wild-type (WT) controls, effects similar to those observed in WT mice after chronic desipramine (DMI) administration. Neurogenesis was not further augmented by chronic DMI treatment in CREB(alpha delta) mutant mice. Serotonin depletion decreased neurogenesis in CREB(alpha delta) mutant mice to WT levels, which correlated with a reversal of the antidepressant phenotype in the TST. This effect was specific for the reversal of the antidepressant phenotype in these mice, because serotonin depletion did not alter a baseline anxiety-like behavior in CREB(alpha delta) mutant mice. The response to chronic AD treatment in the novelty-induced hypophagia (NIH) test may rely on neurogenesis. Therefore, we used this paradigm to evaluate chronic AD treatment in CREB(alpha delta) mutant mice to determine whether the increased neurogenesis in these mice alters their response in the NIH paradigm. Whereas both WT and CREB(alpha delta) mutant mice responded to chronic AD treatment in the NIH paradigm, only CREB(alpha delta) mutant mice responded to acute AD treatment. However, in the elevated zero maze, DMI did not reverse anxiety behavior in mutant mice. Together, these data show that increased hippocampal neurogenesis allows for an antidepressant phenotype as well as a rapid onset of behavioral responses to AD treatment.

Monoaminergic agents modulate antidepressant-like effect caused by diphenyl diselenide in rats

In this study, the antidepressant-like effect caused by diphenyl diselenide on rat forced swimming test (FST) was investigated. The involvement of the monoaminergic system in the antidepressant-like effect was also evaluated. Diphenyl diselenide (0.1-30 mg/kg), given by oral route (p.o.), 30 min earlier, reduced the immobility time in the FST, without accompanying changes in ambulation when assessed in an open field. The anti-immobility effect of diphenyl diselenide (1 mg/kg, p.o.) on the FST was prevented by pretreatment of rats with p-chlorophenylalanine methyl ester (PCPA; 100 mg/kg, i.p., an inhibitor of serotonin synthesis, given once a day, for 3 consecutive days), WAY100635 (0.1 mg/kg, s.c., a selective 5-HT(1A) receptor antagonist), ketanserin (1 mg/kg, i.p., a 5-HT(2A)/(2C) receptor antagonist), ondasentron (1 mg/kg, i.p., a 5-HT(3) receptor antagonist), haloperidol (1 mg/kg, i.p., a D(1), D(2) and D(3) receptor antagonist), SCH233390 (0.05 mg/kg, s.c., a D(1) receptor antagonist), sulpiride (50 mg/kg, i.p., a D(2) receptor antagonist), prazosin (1 mg/kg, i.p., an alpha(1)-adrenoceptor antagonist), yohimbine (1 mg/kg, i.p., an alpha(2)-adrenoceptor antagonist). However, the anti-immobility effect caused by diphenyl diselenide (1 mg/kg, p.o.) on the FST was not affected by pretreatment with propanolol (2 mg/kg, i.p., a beta-adrenoceptor antagonist). Furthermore, monoamine oxidase (MAO) activity was inhibited (39%) in the animals treated with diphenyl diselenide (30 mg/kg, p.o.) when compared to the control group. Taken together these data demonstrated that the antidepressant-like effect caused by diphenyl diselenide seems to be mediated by involvement of the central monoaminergic system.

Specificity and efficacy of noradrenaline, serotonin depletion in discrete brain areas of Swiss mice by neurotoxins

The aim of this work is to define neurotoxins doses to have efficient and specific depletion of noradrenaline (NA), serotonin (5-HT) neurotransmission in cortex, striatum, hippocampus and hypothalamus of Swiss mice after intraperitoneal administration of, respectively, N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP-4) and para-chlorophenylalanine methyl ester hydrochloride (PCPA). The neurotransmitters concentrations were determined by high performance liquid chromatography with amperometric detection. The minimal single dose necessary to produce a highly significant decrease of NA levels (p<0.01 in comparison with control group) in hypothalamus (-44%), hippocampus (-91%), striatum (-40%) and cortex (-68%) was 50mg/kg but DA and 5-HT levels were modified, respectively, in hypothalamus and striatum. Three doses of PCPA 300 mg/kg over 3 consecutive days involve a profound depletion of 5-HT transmission in all discrete brain areas but NA and DA levels were also significantly reduced. In conclusion, DSP-4 has a different efficacy in discrete brain areas with a noradrenergic specificity which is not absolute, PCPA has a similar efficacy in all brain areas but is unspecific of 5-HT transmission.

Differential involvement of serotonin and dopamine systems in cost-benefit decisions about delay or effort

RATIONALE

Although tasks assessing the role of dopamine in effort-reward decisions are similar to those concerned with the role of serotonin in impulsive choice in that both require analysis of the costs and benefits of possible actions, they have never been directly compared.

OBJECTIVES

This study investigated the involvement of serotonin and dopamine in two cost-benefit paradigms, one in which the cost was delay and the other in which it was physical effort.

METHODS

Sixteen rats were trained on a T-maze task in which they chose between high and low reward arms. In one version, the high reward arm was obstructed by a barrier, in the other, delivery of the high reward was delayed by 15 s. Serotonin and dopamine function were manipulated using systemic pCPA and haloperidol injections, respectively.

RESULTS

Haloperidol-treated rats were less inclined either to exert more effort or to countenance a delay for a higher reward. pCPA had no effect on the performance of the rats on the effortful task, but significantly increased the rats' preference for an immediate but smaller reward. All animals (drug treated and controls) chose the high reward arm on the majority of trials when the delay or effort costs were matched in both high and low reward arms.

CONCLUSION

A dissociation was found between the neurotransmitter systems involved in different types of cost-benefit decision making. While dopaminergic systems were required for decisions about both effort and delay, serotonergic systems were only needed for the latter.

Evidence for serotonin receptor subtypes involvement in agmatine antidepressant like-effect in the mouse forced swimming test

This study investigated the involvement of 5-HT(1) and 5-HT(2) receptors in the antidepressant-like effect of agmatine in the mouse forced swimming test (FST). Pretreatment with p-chlorophenylalanine methyl ester (PCPA; 100 mg/kg, intraperitoneally (i.p.), an inhibitor of serotonin synthesis, for 4 consecutive days), methysergide (5 mg/kg, i.p., a serotonin (5-HT) antagonist), pindolol (32 mg/kg, i.p., a 5-HT(1A/1B) receptor/beta-adrenoceptor antagonist), N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridynyl)cyclohexanecarboxamide (WAY 100635; 0.3 mg/kg, subcutaneously (s.c.), a selective 5-HT(1A) receptor antagonist), 1-(2-methoxyphenyl)-4[-(2-phthalimido)butyl]piperazine) (NAN-190; 0.5 mg/kg, i.p., a 5-HT(1A) receptor antagonist), 1-(2-(1-pyrrolyl)-phenoxy)-3-isopropylamino-2-propanol (isamoltane; 2.5 mg/kg, i.p., a 5-HT(1B) receptor antagonist), cyproheptadine (3 mg/kg, i.p., a 5-HT(2) antagonist) or ketanserin (5 mg/kg, i.p., a 5-HT(2A/2C) receptor antagonist), but not with propranolol (2 mg/kg, i.p., a beta-adrenoceptor antagonist), prevented the effect of agmatine (10 mg/kg, i.p.) in the FST. A subeffective dose of agmatine (0.001 mg/kg, i.p.) produced a synergistic antidepressant-like effect with pindolol (32 mg/kg), NAN-190 (0.5 mg/kg, i.p.), WAY 100635 (0.03 mg/kg, s.c.), (+)-8-hydroxy-2-(di-n-propylamino)tetralin HBr (8-OH-DPAT; 0.01 mg/kg, i.p., a 5-HT(1A) receptor agonist), R(-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl (DOI; 1 mg/kg, i.p., a preferential 5-HT(2A) receptor agonist), or fluoxetine (10 mg/kg, i.p., a selective serotonin reuptake inhibitor, SSRI) but not with isamoltane (2.5 mg/kg, i.p.), ritanserin (4 mg/kg, i.p., a 5-HT(2A/2C) receptor antagonist) or ketanserin (5 mg/kg, i.p.). Taken together, the results firstly demonstrate that agmatine antidepressant-like effects in the FST seem to be mediated, at least in part, by an interaction with 5-HT(1A/1B) and 5-HT(2) receptors.

Elimination of serotonergic cells induces a marked increase in generation of dopaminergic neurons from mesencephalic precursors

Production of dopaminergic (DA) neurons from stem/precursor cells for transplantation in Parkinson's disease has become a major focus of research. However, the inductive signals mediating the production of DA neurons remain poorly understood, and the influence of other cell populations simultaneously generated within the cell aggregates has not been studied. We investigated whether DA phenotype (i.e. tyrosine hydroxylase-immunoreactive, TH-ir), serotonergic, floor plate (FP4-ir), and fibroblast growth factor 8 (FGF-8)-ir cells differentiate from proliferating cell aggregates obtained from rat mesencephalic precursors, and we also investigated the effects of serotonergic cells on differentiation of DA cells. We observed FP4-ir, FGF-8-ir, TH-ir and serotonergic cells within the aggregates. The TH-ir cells appeared within or in close proximity to a central FP4-ir core, and then concentrated peripherally forming a cap that surrounded the central FP4-ir area. The serotonergic cells and fibers formed a cap surrounding that of TH-ir neurons. Cell aggregates treated with an antibody against FGF-4 or with the serotonergic toxin 5,7-dyhydroxytryptamine or the serotonin synthesis inhibitor dl-p-chlorophenylalanine showed a marked decrease in the number of 5-HT-ir cells (10-20% of controls) and a marked increase in that of TH-ir neurons (700-900% of controls). The present results show that manipulation of other cell populations in the cell aggregates, particularly the serotonergic population, may be an effective method of increasing the production of DA neurons from stem/precursor cells.

5-HT1 and 5-HT2 receptor activation reduces N-methyl-D-aspartate (NMDA)-stimulated LH secretion in prepubertal male and female rats

OBJECTIVE

Excitatory amino acids and serotonin are involved in the control of gonadotropin secretion. The actions of these neurotransmitters are interconnected and recently we have reported that 5-HT(1) and 5-HT(2) receptor agonists blunted (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-stimulated GH secretion in prepubertal rats. The present experiments were carried out to analyze the effects of activation of different 5-hydroxytryptamine (5-HT) receptor subtypes on gonadotropin secretion and their role in the N-methyl-d-aspartate (NMDA)-stimulated LH release.

DESIGN AND METHODS

We analyzed the gonadotropin secretion after manipulation of serotoninergic and aminoacidergic systems and their interactions in 5-, 16- and 23-day-old male and female rats. To this end, serum LH and FSH concentrations were measured in rats treated with 5-hydroxytryptophan methyl ester (5-HTP) (a precursor of 5-HT synthesis) plus Fluoxetine (Fx, a blocker of 5-HT reuptake), d,l-p-chlorophenyl-alanine methyl ester (PCPA, a blocker of 5-HT synthesis), R-(+)-8-hydroxydipropylaminotetralin hydrobromide (8-OH-DPAT, an agonist of 5-HT(1A) receptors), (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI) and alpha-methyl-5-hydroxytryptamine (alpha-Me-5-HT, agonists of 5-HT(2) receptors), and 1-Phenylbiguanide (1-PHE an agonist of 5-HT(3) receptors). In addition, the effects of 8-OH-DPAT and DOI on NMDA-stimulated LH secretion were analyzed.

RESULTS

Neither the activation nor blockade of the serotoninergic system modified LH secretion. Basal gonadotropin secretion remained unchanged in 23-day-old male and female rats after activation of 5-HT(1A), 5-HT(2) and 5-HT(3) receptors. The stimulatory effect of NMDA on LH secretion was blocked in both sexes after activation of the serotoninergic system, through specific 5-HT(1) and 5-HT(2) receptor agonists.

CONCLUSIONS

Activation of serotoninergic receptors decreased the stimulatory effect of NMDA on LH secretion in prepubertal male and female rats.

The antidepressant activity of inositol in the forced swim test involves 5-HT(2) receptors

The effect of inositol as an antidepressant was previously demonstrated in both animal models of depression-like behavior and in clinical trials. Unlike most antidepressant drugs, inositol does not have a clear target in the synapse and was not demonstrated to alter monoamine levels in the brain. The present study attempted to draw a psychopharmacological profile of inositol's behavioral effects by exploring the interactions between the drug and specific receptor agonists and antagonists in the forced swim test. Rats received inositol treatment (or control) in combination with the serotonergic metabolism inhibitor PCPA or with the noradrenergic neurotoxin DSP-4. Results indicated that PCPA but not DSP-4 abolished the ability of inositol to cause a reduction in immobility time in the forced swim test. In mice, the specific 5-HT(2A)/5-HT(2C) antagonist ritanserin, but not the 5-HT(1A)/5-HT(1B)/beta adrenergic antagonist pindolol, abolished inositol's effect in the forced swim test. The 5-HT(2A)/5-HT(2C) agonist DOI and the 5-HT(1A) agonist 8-OH-DPAT did not have any significant effects on inositol's activity. The present data indicates that the antidepressant effect of inositol may involve 5-HT(2) receptors. It is thus possible that the effects of reuptake antidepressant drugs and the effects of inositol may have a common final pathway.

Acceleration of gastrointestinal transit by momordin Ic in mice: possible involvement of 5-hydroxytryptamine, 5-HT(2) receptors and prostaglandins

Possible involvement of 5-hydroxytryptamine (5-HT), 5-HT receptors and prostaglandins in the acceleration of gastrointestinal transit by momordin Ic was investigated in mice. Accelerative effect of momordin Ic (25 mg/kg, p.o.) on gastrointestinal transit was attenuated by pretreatment with a bolus of DL-p-chlorophenylalanine methyl ester (an inhibitor of 5-HT synthesizing enzyme), but not repeated pretreatment with DL-p-chlorophenylalanine methyl ester. Furthermore, cyproheptadine (a nonselective 5-HT(2) receptor antagonist), ritanserin (a 5-HT(2A/2B/2C) receptor antagonist) and clozapine (a 5-HT(2A/2C) receptor antagonist) also attenuated the effect of momordin Ic, but methiothepin (a 5-HT(1) receptor antagonist), MDL 72222 (3-tropanyl-3,5-dichlorobenzoate) and metoclopramide (5-HT(3) receptor antagonists), tropisetron (a 5-HT(3/4) receptor antagonist), ketanserin and haloperidol (5-HT(2A) receptor antagonists) did not. These results suggested a possible involvement of endogenous 5-HT and 5-HT(2B/2C) over 5-HT(2A) receptors. Attenuation by pretreatment with indomethacin (an inhibitor of prostaglandins synthesis) suggested involvement of prostaglandins. It is postulated that momordin Ic accelerates gastrointestinal transit partially by stimulating synthesis of 5-HT to act through 5-HT(2), possibly 5-HT(2C) and/or 5-HT(2B) receptors, which, in turn, increases synthesis of prostaglandins.

Influence of fluoxetine and litoxetine on 5-HT4 receptor-mediated relaxation in the rat isolated oesophagus

The influence of two selective serotonin reuptake inhibitors (SSRIs), litoxetine and fluoxetine, has been studied on 5-HT4 receptor-mediated relaxation in the rat isolated oesophageal muscularis mucosae. In carbachol-precontracted oesophageal tissues, 5-hydroxytryptamine (5-HT) (0.1 nM-1 microM) induced concentration-dependent relaxations. Concentration-response curves were monophasic and reproducible. Litoxetine at concentrations without antimuscarinic properties (10 nM-1 microM) caused concentration-dependent relaxations, which reduced carbachol tone up to 37%. Higher litoxetine concentrations (3 microM-300 microM) were associated with marked relaxation up to the abolition of carbachol tone. The overall curve profile of litoxetine was biphasic in nature with a high (10 nM-1 microM) and a low (3 microM-300 microM) potency phase. Unlike 5-HT, the second curve of litoxetine was not reproducible, with a reduction involving mainly the low potency phase. Compared to litoxetine, fluoxetine caused minimal relaxation (less than 10% at 1 microM). Treatment of rats with parachlorophenylalanine (pCPA: 375 mg kg-1 per day, for two days), to deplete endogenous 5-HT stores, did not modify the relaxant effect of 5-HT, while it significantly reduced the high potency phase of litoxetine. In tissues from untreated rats, this phase was reduced by the 5-HT4 receptor antagonist GR 125487 (10 nM) to an extent similar (P = 0.20: ANOVA for continuous-by-class effects) to that induced by pCPA treatment. However, in tissues from pCPA treated animals GR 125487 (10 nM) exerted a slight but significant antagonism of litoxetine response (P = 0.037: ANOVA for continuous-by-class effects) mainly involving the high potency phase. In tissues from untreated rats, litoxetine (1 microM) increased the relaxant effects of 5-HT, while in tissues from pCPA treated animals it exerted a small but significant depression of the maximal response to 5-HT, without changing its potency value. Fluoxetine (1 microM) slightly, but significantly, antagonized the relaxant effect of 5-HT in an unsurmountable manner. In conclusion, litoxetine up to 1 microM relaxed the rat isolated oesophageal muscularis mucosae through a mechanism involving release of endogenous 5-HT, which in turn activates 5-HT4 receptors. However, based on results with GR 125487 in tissues from pCPA treated rats, a small component of litoxetine-induced relaxation may involve a direct activation of 5-HT4 receptors. It is unlikely that blockade of 5-HT reuptake can participate in the action of litoxetine, since fluoxetine, a 5-HT reuptake inhibitor equipotent to litoxetine, was ineffective in the same range of concentrations. The antimuscarinic activity of litoxetine, previously demonstrated in the isolated guinea-pig intestine, played a role at concentrations greater than 1 microM. The 5-HT-releasing action of litoxetine could account for the potentation by litoxetine of 5-HT-induced relaxation in tissues from untreated rats, which was reversed by pCPA treatment. Under these conditions, litoxetine depressed relaxations to high 5-HT concentrations only. In tissues from untreated rats, fluoxetine slightly but unsurmountably antagonized 5-HT-induced relaxations, thus confirming previous observations in the guinea-pig small intestine.

Serotonin and acetylcholine are crucial to maintain hippocampal synapses and memory acquisition in rats

Treatment with serotonin and acetylcholine depletors reduced the number of synapses in the rat hippocampus. Animals that received the drug treatment lost a substantial number of synapses and showed an apparent impairment in memory acquisition. Although the animals were behaviorally impaired following the treatment, spatial memory was nonetheless eventually attained despite the disappearance of long-term potentiation. These data suggest that synapses in the hippocampus that are normally maintained by serotonin and acetylcholine are crucial for normal acquisition of spatial memory. The number of synapses maintained by biogenic amines may be a basic mechanism for neurobehavioral plasticity.

Presence of pancreatitis-associated protein in pancreatic acinar cells of rats treated with chlorophenylalanine methyl ester

The biological significance and function of pancreatitis-associated protein (PAP), identified in 1984 as a new secretory protein appearing during pancreatitis, remain to be elucidated. The purpose of this study was to evaluate the presence of PAP in pancreatic tissue upon its exposure to chlorophenylalanine methyl ester (CPME), a drug known to disrupt the regulated secretory pathway of acinar cells, an experimental condition that differs from acute pancreatitis. Pancreatic tissues were processed either for immunocytochemistry or for Northern blot analysis at 17-72 h after a single intraperitoneal injection of CPME in rats. Pancreatic acinar cells displayed endoplasmic reticulum intracisternal crystals consisting of an abnormal aggregation of secretory proteins as well as a sub-population of small and aberrant secretory granules. PAP mRNA was strongly increased at 17-24 h after CPME treatment, and PAP immunoreactivity was detected along the regulated secretory pathway, particularly in the small and aberrant secretory granules at these same time points. Levels of PAP and PAP mRNA decreased gradually, to become undetectable after 72 h. Autoradiographic experiments demonstrated that these small aberrant granules stored preferentially newly synthesized proteins. Our results indicate that the induction of PAP is not exclusive to acute pancreatitis since it appears in pancreatic cells as a response to certain insults and is secreted preferentially through a particular population of small aberrant granules.

Inhibition of hypothalamic nitric oxide synthase gene expression in the rat paraventricular nucleus by food deprivation is independent of serotonin depletion

We have investigated the effects of food deprivation on nitric oxide synthase (NOS) transcript levels in the rat paraventricular (PVN) and supraoptic nuclei (SON), using in situ hybridization histochemistry. Food deprivation for 48 h significantly and consistently reduced NOS transcript prevalence by approximately 50% in both sites. Since there is considerable evidence for an important role of 5-HT in feeding behaviour, we then examined the effect of food deprivation on NOS gene expression in the PVN following para-chlorophenylalanine (PCPA)-induced hypothalamic 5-HT depletion. As starvation causes central down-regulation of the thyroid axis, changes in thyrotropin-releasing hormone (TRH) and pituitary thyrotrophin (TSH) transcript prevalence were used as internal controls. PCPA pretreatment (200 mg/kg body weight as a single daily dose ip for 2 days) had no significant effect on basal levels of NOS, TRH or TSH transcripts, or on the effect of a subsequent 48 h fast, which significantly reduced all three. These results show for the first time, that food deprivation for 48 h significantly reduces NOS gene expression in the rat PVN and SON. Secondly, that basal levels and the fasting-induced reductions in the prevalence of NOS, TRH and TSH transcripts were not affected by PCPA-induced hypothalamic 5-HT depletion. Therefore, at least under the experimental conditions used here, 5-HT does not appear to be involved in setting baseline levels- or in the starvation-induced inhibition of NOS or thyroid axis gene expression in the PVN.

Serotonin depletion decreases serotonin transporter mRNA levels in rat brain

In order to study the impact of serotonin depletion on gene expression of the serotonin transporter (5-HTt) we measured 5-HTt mRNA levels by Northern blot in rats treated with p-chlorophenylalanine methyl ester (PCPA) for 10 days. Six rats received PCPA i.p. only, and another 6 rats receiving 0.9% NaCl served as controls. An additional group of 6 rats received both PCPA i.p. and imipramine, 5 mg/kg/day by osmotic minipumps. 5-HTt mRNA levels decreased to 81.1% (P = 0.05) and 76.0% (P = 0.05) of the control level for PCPA treated animals without and with concomitant imipramine treatment, respectively. The average level of the PCPA treated groups was 78.6% (P = 0.03). The isolated effect of 21 days of imipramine treatment was a 5-HTt mRNA level of 89.4%, which was not significantly different from the control level. In conclusion, 5-HTt gene expression is suppressed in the serotonin depleted state. A decreased synaptic reuptake of 5-HT may be interpreted as a compensatory mechanism aiming at preserving adequate synaptic 5-HT levels in a generally deficient state.

Tiapride attenuates pain transmission through an indirect activation of central serotonergic mechanism

Tiapride dose-dependently attenuated the biphasic nociceptive responses induced by s.c. injection of formalin to the hindpaw of mice, and its activity on the first (ED50 = 110 mg/kg p.o.) and the second (ED50 = 32.0 mg/kg p.o.) phases paralleled that on the nociceptive response to intrathecal injection of substance P (ED50 = 190 mg/kg p.o.) and somatostatin (ED50 = 56.0 mg/kg p.o.), respectively. Moreover, a similar antinociceptive activity was observed in streptozotocin-induced diabetic or genetically diabetic (db/db) mice. The effects of tiapride (100 mg/kg p.o.) on both phases of the formalin test in normal mice were abolished by pretreatment with p-chlorophenylalanine (800 x 2 mg/kg p.o.), a 5-hydroxytryptamine (5-HT) depletor, or pindolol (1 mg/kg i.p.), a 5-HT1 antagonist, but were scarcely affected by 3-tropanyl-indole-3-carboxylate, a 5-HT3 antagonist. Ketanserin (1 mg/kg i.p.), a 5-HT2 antagonist, attenuated the effect of tiapride on the second phase but not on the first phase. This study on the antinociceptive mechanism of action of tiapride (that blocks painful neuropathy in diabetic patients) has led us to hypothesize that the drug attenuates pain transmission through an indirect activation of central 5-HT1 and 5-HT2 receptors.

Involvement of raphe-hippocampal serotonergic and septo-hippocampal cholinergic mechanisms in the penile erection induced by FR121196, a putative cognitive enhancer

FR121196 (N-[4-acetyl-1-piperazinyl]-4-fluorobenzenesulfonamide), a putative cognitive enhancer, induced penile erection in naive rats; the dose-response curve was bell-shaped with the maximum response obtained at the dose of 3.2 mg/kg. The response to FR121196 was abolished in rats treated with intra-raphe injections of 5,7-dihydroxytryptamine or systemic injections of p-chlorphenylalanine (150 mg/kg, i.p. for three consecutive days) as well as in rats with electrolytic medial-septum lesion or surgical fimbria-fornix lesion. In addition, the penile erection induced by FR121196 (3.2 mg/kg) was dose-dependently attenuated by pindolol (0.1-3.2 mg/kg), a serotonin (5-HT)1 antagonist with beta-antagonistic activity, but not by metoprolol, a selective beta=antagonist. The inhibitory activity was shared by ICS205-930, a 5-HT3 antagonist, but not by ketanserin, a 5-HT2 antagonist, or sulpiride, a dopamine D2 antagonist. Scopolamine (0.032-1 mg/kg), but not methyl-scopolamine (0.032-1 mg/kg), also attenuated the penile erection induced by FR121196. Neurochemical analysis revealed that intraperitoneal injection of FR121196 significantly elevated the levels of 5-HT and its major metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the hippocampus and that raphe-lesion significantly reduced both 5-HT and 5-HIAA levels without affecting choline-acetyltransferase activity in all cortical and subcortical regions examined. It is thus postulated that FR121196 facilitates the raphe-hippocampal serotonergic pathway resulting in an activation of the septo-hippocampal cholinergic pathway and finally induces the penile erectile response.

Isolation-induced aggression in mice: effects of 5-hydroxytryptamine uptake inhibitors and involvement of postsynaptic 5-HT1A receptors

The inhibitory potencies of selective serotonin (5-hydroxytryptamine, 5-HT) uptake inhibitors on isolation-induced aggressive behaviour in male mice were studied. Furthermore, the role of postsynaptic 5-HT1A receptors in the mediation of aggressive behaviour was studied. The selective 5-HT uptake inhibitors, sertraline, floxetine, femoxetine and fluvoxamine, showed weak antiaggressive effects, and citalopram and paroxetine were ineffective. This rank of potencies corresponded with neither uptake inhibitory potencies in vitro nor potentiation of 1-5-hydroxytryptophan (1,5-HTP)-induced motor effects in vivo, as citalopram and paroxetine were among the most potent compounds in these tests. A subeffective dose of 1,5-HTP (110 mumol/kg = 25 mg/kg, s.c.) potentiated the antiaggressive effect of citalopram and paroxetine more than 110 and 1600 times, respectively. The effects of sertraline, fluvoxamine, fluoxetine and femoxetine were only potentiated 3, 36, 4 and 16 times, respectively. The 5-HT releasing compound fenfluramine inhibited the aggressive behaviour dose dependently, and depletion of 5-HT by treatment with p-chloro-phenylalanine methyl ester attenuated this effect significantly. p-Chloro-phenylalanine methyl ester was ineffective itself, but potentiated the antiaggressive effect of the 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamin)tetralin (8-OH-DPAT). The beta-adrenoceptor/5-HT1A receptor antagonist, (-)-penbutolol, reversed the antiaggressive effects of 8-OHDPAT. In conclusion, selective 5-HT uptake inhibitors act in different ways on isolation-induced aggressive behaviour, and postsynaptic 5-HT1A receptors are involved in mediating the aggressive behaviour.

Involvement of molecular chaperones in the aberrant aggregation of secretory proteins in pancreatic acinar cells

Molecular chaperones have recently been shown to be accurately located along distinct cellular compartments of the secretory pathway of pancreatic acinar cells. Since the aberrant aggregation of secretory proteins leading to the formation of RER intracisternal crystals induced by DL-p-chlorophenylalanine methyl ester (CPME) comprises major changes in the sorting, selective transport, and/or posttranslational modifications of secretory proteins, we decided to investigate the possible involvement of chaperones in this phenomenon by applying the protein A-gold immunocytochemical approach. In addition to their presence in the cellular compartments of the secretory pathway, the chaperonins cpn10 and cpn60 were found to also be concentrated in the RER intracisternal crystals. In contrast, the hsp70 protein remained confined to the trans-Golgi network and was absent from the crystals. In both control and experimental conditions the three chaperones were present in mitochondria. Quantitative evaluations confirmed these observations and revealed an overall decrease in the labeling, particularly for hsp70 after CPME treatment. These labeling patterns suggest a participation of the chaperonins cpn10 and cpn60 but not of the hsp70 in the aberrant aggregation of secretory proteins leading to RER crystal formation. The role played by chaperones in this process, however, remains to be elucidated.

Role of the serotonergic system in the control of gonadotropin secretion in prepubertal male rats

To analyze the role of brain serotonin in the control of gonadotropin secretion in prepubertal males, serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH) concentrations were studied at different ages after administration of 5-hydroxytryptophan (5-HTP), a precursor of serotonin synthesis, alone or in combination with fluoxetine, a specific inhibitor of serotonin uptake; 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), a serotonin 1A agonist; or D,L-p-chlorophenylalanine methyl ester hydrochloride (PCPA), an inhibitor of serotonin synthesis. Also, serum gonadotropin concentrations were measured in castrated males implanted with silastic capsules containing testosterone or 5 alpha-androstane-3 alpha, 17 beta-diol (alpha-diol). We found that: (i) the blockade of the serotoninergic system after PCPA administration did not modify basal gonadotropin secretion but did strongly reduce the response to orchidectomy; (ii) a stimulatory effect of 5-HTP on FSH secretion was only observed in intact males at the age of 8 days; (iii) the serotonin 1A agonist 8-OH-DPAT did not change serum gonadotropin concentrations; (iv) 5-HTP increased serum FSH and LH concentrations in 16-day-old castrated males; (v) FSH and LH serum concentrations decreased after 5-HTP in castrated animals implanted with testosterone, whereas castrated animals implanted with alpha-diol showed, like the intact males, a lack of response to 5-HTP.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Interaction between norepinephrine and serotonin in the neuroendocrine control of growth hormone release in the rat

Both alpha 2-adrenergic (alpha 2) and serotonergic (5HT) neurons are associated with stimulation of GH secretion via GRH release. The object of this study was to determine whether the 5HT system is involved in the stimulation of GH secretion by alpha 2-receptor agonists. There are two parts of this study. In the first, the relationship between alpha 2-5HT systems were analyzed by determining if alpha 2-stimulated GH release is mediated by 5HT. In this model, systemically administered alpha 2-agonists [clonidine (CLON) or UK14,304] were tested against 5HT antagonists (meterogoline or cyproheptadine) or 5HT synthesis inhibitors (p-chlorophenylalanine methylester hydrochloride). In the second, sites of 5HT-GRH interaction were determined by testing the response to CLON after 5HT neurotoxin [5,7-dihydroxytryptamine (5,7-DHT)] microinjection at specific hypothalamic nuclei. In both experiments sequential blood samples were withdrawn from silastic jugular cannulas in unanesthetized, freely moving animals. Metergoline (0.045 and 0.135 mg/kg, iv) and cyproheptadine (0.969 micrograms/kg, iv) suppressed, in a dose-dependent manner, the CLON (33 or 66 micrograms/kg, iv)-induced GH surge that was detected 15-30 min after injection in control animals. Both cyproheptadine (0.969 micrograms/kg, iv) and p-chlorophenylalanine (300 mg/kg, ip) effectively suppressed the UK14,304 (220 micrograms/kg, iv)-induced GH surge that occurred 15-30 min after injection in control animals. These data suggest that an intact 5HT system is required for alpha 2-stimulated GH release. 5,7-DHT neurotoxin microinjected into the midline arcuate nucleus (6 micrograms/mg,iv) or bilaterally into the ventromedial nucleus or perifornical area (4 micrograms/0.2 microliter) 5 days previously suppressed the CLON (30 micrograms/kg)-induced GH surge only in animals with arcurate nucleus lesions. To determine if the suppression was mediated by inhibition of GH-releasing hormone (GRH) or stimulation of somatostatin (SRIF), an additional experiment was conducted including 5,7-DHT arcuate nucleus-lesioned animals injected with anti-SRIF. Inasmuch as anti-SRIF failed to reverse the 5,7-DHT suppression of GH secretion, the results of this experiment suggest that GRH mediates NE-5HT-induced GH secretion. In conclusion, these data suggest that alpha 2 activation of GH secretion requires intact serotonergic terminals in the arcuate nucleus and most likely involves GRH rather than SRIF, release.

Tryptophan hydroxylase activity in hypothalamus and brainstem of neonatal and adult rats treated with hydrocortisone or parachlorophenylalanine

The present study has been undertaken to determine whether glucocorticoid, and parachlorophenylalanine (PCPA, a tryptophan hydroxylase inhibitor) affects tryptophan hydroxylase (TPH) levels in brainstem and hypothalamus of neonatal and adult rats. Our results show that: (1) administration of hydrocortisone causes small but significant increases in TPH activity of neonatal brainstem: (2) treatment with PCPA plus glucocorticoid results in a marked decrease of TPH activity in brainstem and hypothalamus of both neonatal and adult rats.

Reevaluation of the regulation of beta-adrenergic receptor binding by desipramine treatment

Treatment of rats with desipramine (DMI) has been shown to down-regulate beta-adrenergic receptor-stimulated adenylate cyclase and reduce the Bmax of beta-adrenergic receptors in some brain areas. Recent reports have indicated that the down-regulation in the number of beta-adrenergic receptors following DMI treatment does not occur if the serotonin system has been impaired following parachlorophenylalanine (PCPA) or 5,7-dihydroxytryptamine injection. We have previously shown that [3H]dihydroalprenolol ([3H]DHA), the most commonly used radioligand to measure central nervous system beta-adrenergic receptors, labels another site under normal experimental procedures, in addition to the beta-adrenergic receptors. This second site has some pharmacological characteristics of the 5-hydroxytryptamine1A receptor. The depletion of serotonin following PCPA injection was indeed able to prevent the down-regulation of [3H]DHA binding sites after DMI injection. However, PCPA alone increased the density of [3H]DHA binding sites. If the nonlinear, least squares, curve-fitting program LIGAND was allowed to define [3H]DHA nonspecific binding or if the more selective beta-adrenergic receptor radioligand [3H]CGP-1277 was used, the Bmax of beta-adrenergic receptors was not changed after PCPA injection. Importantly, PCPA did not prevent beta-adrenergic receptor down-regulation following DMI treatment. The blockade of 5-hydroxytryptamine2 receptors, via ketanserin administration, during DMI treatment did not change the response of beta-adrenergic receptors. Furthermore, if LIGAND was used to define the nonspecific binding of [3H]DHA, the down-regulation of beta-adrenergic receptors was significant 24 hr after a single DMI injection. The same rapid down-regulation was demonstrated with [3H]CGP-12177. However, if [3H]DHA was used to label beta-adrenergic receptors in the "typical" manner (nonspecific binding defined by 10 microM alprenolol), a decrease in the number of beta-adrenergic receptors was significant only after seven daily DMI injections. These data demonstrate that the use of [3H]DHA to measure beta-adrenergic receptors can be misleading, because changes in its second binding site can conceal the changes occurring in beta-adrenergic receptors. Moreover, these results suggest that a similarity in the time course of action of DMI cannot be used to support the hypothesis that its therapeutic antidepressant action is related to beta-adrenergic receptor down-regulation.

Modified coeruleo-cortical noradrenergic neurotransmission after serotonin depletion by PCPA: electrophysiological studies in the rat

To detect eventual modifications in the efficacy of the noradrenergic (NA) coeruleo-cortical system after serotonin (5-HT) depletion by parachlorophenylalanine (PCPA), three electrophysiological parameters were investigated in urethane-anesthetized rats which were treated for 2 days with daily injections of this inhibitor of 5-HT synthesis. 1) The spontaneous activity of locus coeruleus (LC) noradrenergic neurons showed a significant increase in PCPA-treated compared to control rats (4.3 vs. 2.6 Hz). 2) The sensitivity of NA autoreceptors was measured in the LC by the effect of intravenous administrations of clonidine or microiontophoretic applications of NA on spontaneous neuronal firing. In treated rats, clonidine and NA induced a lesser reduction of LC neuron firing than in the controls (27 vs. 75% decreases and 1,367 vs. 280 nC, respectively). 3) The responsiveness of cortical neurons to electrical stimulation of the LC was assessed by peristimulus time histograms in the dorsal fronto-parietal cortex. Following stimulation at 2 or 4 Hz, a majority of spontaneously firing cortical units was inhibited by electrical stimulation of the LC, but the percentage of such units was reduced and showed a decreased responsiveness after PCPA treatment. These findings suggest that following 5-HT depletion by PCPA, cortical NA neurotransmission is markedly reduced in its efficacy in spite of some increase in the spontaneous activity of coeruleo-cortical NA neurons.

Evidence for the combined involvement of serotonergic and alpha 2 adrenergic mechanisms in the analgesic activity of tazadolene succinate

The analgesic activity of tazadolene succinate was assessed in mice and rats subsequent to pretreatment with various depletors and antagonists of monoamine neurotransmitters. In the mouse warm plate assay, reserpine was confirmed to cause a profound antagonism of tazadolene analgesia. However, yohimbine, Sch 23390 and haloperidol, antagonists of alpha 2 adrenergic, D1 dopaminergic and D2 dopaminergic receptors respectively, did not block tazadolene, nor did the serotonin depletor, p-chlorophenylalanine. But mice treated with both the depletor and yohimbine were significantly resistant to the analgesic effects of tazadolene. Combined treatments of haloperidol or prazosin (an alpha1 adrenergic antagonist) and p-chlorophenylalanine were not similarly effective. In the rat, reserpine blocked tazadolene analgesia in both the hot plate and air induced writhing assays. Likewise, combined treatment with yohimbine and p-chlorophenylalanine also antagonized the analgesia. These results confirm the monoamine dependence of tazadolene analgesia and indicate that both serotonergic and alpha 2 adrenergic mechanisms are involved. The results further suggest that these systems may be in parallel and integrated such that either one is capable of the primary expression of the analgesic effect of tazadolene. Thus, the unique analgesia properties of tazadolene are apparently due to the ability of this compound to activate both serotonergic and alpha 2 adrenergic antinociceptive systems.

Stress-induced prolactin release in female, male and androgenized rats: influence of progesterone treatment

Ether stress applied at 10.00 h induced a 100% increase in serum prolactin in intact and ovariectomized androgenized rats. Ovariectomy significantly diminished the basal serum prolactin values observed in intact androgenized rats. Two doses of progesterone (5 mg) given to intact and ovariectomized androgenized rats 14 and 2 h before exposure to ether stress increased prolactin values in the control groups but completely prevented the effect of stress. Exposure to ether stress induced a 100% increase in serum prolactin values in androgenized rats with increased serum progesterone levels 4 days after the induction of ovulation and the luteal phase with human chorionic gonadotropin (hCG). A group of androgenized rats with induced maternal behaviour and which had been suckled for 6 days was given 100 i.u. hCG and suckled for another 6 days after the hCG-induced luteal phase had been established. The serum prolactin and progesterone values of these rats were significantly higher than those treated with hCG only and ether stress did not increase prolactin release. A greatly increased serum concentration of prolactin was obtained in pro-oestrous and oestrous virgin rats after exposure to ether stress. Serum prolactin was also increased by stress in male rats. Progesterone administration to these female and male rats prevented stress-induced prolactin release. To ascertain the part played by dopamine and serotonin in the effect of stress on prolactin release, groups of androgenized and oestrous female rats were treated with bromocriptine or p-chlorophenylalanine methylester hydrochloride (pCPA).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of long-term immobilization stress on regional blood-brain barrier permeability, cerebral blood flow and 5-HT level in conscious normotensive young rats

Eight hours immobilization stress in young rats has increased the blood-brain barrier (BBB) permeability in 12 out of 14 brain regions studied. In the same regions cerebral blood flow (CBF) diminished by 2-37%, but the magnitude of flow reduction was not correlated with the degree of increased BBB permeability. On the other hand, a correlation was observed with increased plasma and brain 5-HT levels. The increased BBB permeability and increased 5-HT levels were prevented by pretreatment with p-CPA, indomethacin and diazepam. Cyproheptadine and vinblastine pretreatment prevented the occurrence of increased BBB permeability alone. The probable mechanism(s) underlying the breakdown of BBB permeability is discussed.

Suppression of lordotic responsiveness in the female rat during mesencephalic electrical stimulation

The effects of biphasic electrical stimulation of the mesencephalic median (MRN) and dorsal raphe (DRN) nuclei, as well as the adjacent periaqueductal gray (PAG), on lordotic behavior were investigated in ovariectomized rats primed with three daily injections of estradiol benzoate (2 micrograms). Animals were tested between 4-8 hours after a progesterone (0.5 mg) injection on day four which normally facilitates high levels of receptivity during this period. Although stimulation of the MRN had no significant effect on lordosis, DRN activation at 100 Hz (0.5 msec pulse duration) or 10 Hz (2 msec pulse duration) caused a marked and immediate suppression (53% and 56%, respectively) in receptivity. This suppression does not appear to be due to activation of serotoninergic neurons originating in the DRN since pretreatment with an inhibitor of serotonin synthesis (parachlorophenylalamine, 320 mg/kg) essentially did not modify the suppression, thus providing no evidence in support of an inhibitory role for serotonin in lordotic behavior. Activation within the PAG adjacent to the DRN at 10 Hz (0.5 or 2 msec pulse duration) produced an immediate, dramatic decrease (81% and 80%, respectively) in receptivity. The suppressions induced by DRN and PAG stimulation appear most likely to be due to activation of a descending pathway inhibitory to the lordosis reflex at medullary or spinal cord levels.

Parachlorophenylalanine does not affect pontine-geniculate-occipital waves in rats despite significant effects on other sleep-waking parameters

The effects of 376 mg/kg parachlorophenylalanine (PCPA) methyl ester on spontaneous and elicited pontine-geniculate-occipital (PGO) waves, locomotor activity, and sleep-staging were studied in albino rats. It was found that PCPA had no effect on the frequency per minute of spontaneously occurring PGO waves or on the relationship between elicited PGO waves and the sleep-waking cycle, which has been reported in normal rats. In contrast, significant decreases in sleep, increases in spontaneous locomotor activity, and alterations in other spontaneously emitted behaviors were observed. It was concluded that PCPA does not affect PGO waves in rats in contrast to the dramatic effects of this drug on PGO waves in cats.

Effect of brain monoamines on the secretion of adrenocorticotrophic hormone

The role of brain monoamines (5-HT, NA and DA) in the secretion of adrenocorticotrophic hormone (ACTH) was studied in view of contradictory reports. Plasma corticosterone levels and the rate of synthesis of corticosterone in vitro by the adrenal gland were estimated in albino rats and have been taken as the index of ACTH activity. These estimations were done in unstressed and stressed, and in untreated and treated rats. Drugs were administered intracerebroventricularly to the rats to cause selective degeneration of tryptaminergic, noradrenergic or dopaminergic neurons. The results show that plasma corticosterone levels and the rate of synthesis of corticosterone were significantly decreased after selective degeneration of tryptaminergic neurons in unstressed rats. After selective degeneration of either tryptaminergic or noradrenergic neurons, the acute increase in the plasma corticosterone levels and rate of synthesis of corticosterone in vitro by adrenal glands in stressed rats were significantly inhibited. These results have been interpreted to suggest that the central tonic control on adrenal glands may be 5-HT mediated and that during stress ACTH secretion may be both 5-HT and NA mediated. DA does not seem to have significant role in the regulation of ACTH secretion.

Plasma luteinizing hormone in ovariectomized rats following pharmacologic manipulation of endogenous brain serotonin

Ovariectomized rats were treated with pharmacologic agents to manipulate endogenous brain serotonin (5-HT). Neither the magnitude nor the timing of luteinizing hormone (LH) pulses in plasma were affected by drug-induced decreases in 5-HT. Acute increases in extraneuronal 5-HT resulting from fluoxetine administration to inhibit 5-HT uptake into neurons, decreased the magnitude of LH pulses, but did not affect the interval between successive LH pulses.

Monoaminergic mechanism of electroacupuncture analgesia

We studied the effects of systemic injections of monoamine depletors, enhancers or receptor blockers on electroacupuncture analgesia (EAA) in mice. The following results emerged. (i) EAA is reduced by depletors of monoamines (tetrabenazine, TBZ depletes all monoamines; para-chlorophenylalanine, PCPA depletes serotonin; alpha-methyl-para-tyrosine, AMPT depletes catecholamines). However, depletion of noradrenaline and increase of serotonin by disulfiram enhances EAA. (ii) Replacement of depleted monoamines after TBZ treatment by their precursors (5-HTP or L-DOPA) restores EAA. (iii) EAA is enhanced by potentiating serotonin and dopamine by probenecid. EAA is also enhanced by the administration of monoamine precursors (L-DOPA for dopamine, 5-HTP for serotonin). The dopamine receptor stimulator, apomorphine, reduces EAA. (iv) EAA is also reduced by receptor blockade of catecholamines (by haloperidol), or blockade of noradrenaline (by yohimbine) or serotonin (by cinanserin). However, blockade of dopamine by pimozide has no significant effect on EAA. There are two main conclusions: (i) EAA results are similar to those previously reported for SPA for all drugs except apomorphine and pimozide; and (ii) EAA shows consistent results only with manipulations of serotonin: the data indicating that EAA (at 200 Hz) is mediated by serotonin. Since previous studies show that raphe or DLF (dorsolateral fasciculus) lesions abolish EAA, we postulate that descending axons from raphe release serotonin to inhibit trigeminal or spinal cord nociception during EAA.

Modifications of brain steroidogenesis and plasma steroids after p-chlorophenylalanine-methyl-ester treatment in male rats and rabbits

The effect of p-chlorophenylalanine (p-CPA) on testosterone (T) hypothalamic metabolism and on plasma levels of T, estradiol (E2) and corticosterone (B) was studied in male rats and rabbits: both were sacrificed 48 hours after the last injection. In both rats and rabbits a significant increase in T leads to E2 transformation (aromatization) was evident after p-CPA treatment. This increase could be responsible for the stimulatory effect on sexual behavior which has been described in literature following p-CPA administration. Moreover p-CPA caused a decrease of circulating T and E2 in both species.

A serotonergic mechanism of the prolactin-stimulating action of metoclopramide

The PRL-stimulating effect of metoclopramide (2-methoxy-5-chloroprocainamide) was examined in normal and adrenalectomized male rats pretreated with DL-p-chlorophenylalanine methyl ester (PCPA), an inhibitor of serotonin biosynthesis. PCPA significantly reduced the hypothalamic content of serotonin, increased basal PRL in adrenalectomized rats but not in controls, and potentiated PRL elevation in response to metoclopramide. In the PCPA-pretreated groups, the maximal PRL response to metoclopramide was 60% and 85% higher than that in the saline controls of normal and adrenalectomized rats, respectively. PCPA did not enhance the PRL-stimulating effect of haloperidol, a well established dopamine antagonist, L-alpha-Methyl-p-tyrosine pretreatment in rats depleted hypothalamic dopamine without any change in serotonin and elevated basal PRL, but failed to show an additive effect with metoclopramide's action on serum PRL. Rats pretreated with mianserin, a specific brain serotonin receptor blocker, attenuated PRL elevation in response to low doses of metoclopramide but produced the same response to high doses of metoclopramide as the control rats. These data indicated that metoclopramide stimulated rats pituitary PRL secretion by a serotonergic mechanism in addition to its dopamine antagonist properties.

Alteration of lidocaine- or procaine-induced convulsions by manipulation of brain amines

Lidocaine and procaine seizure thresholds were studied. The i.p. median convulsant dose (CD50) of lidocaine and procaine with saline pre-treatment was 95 and 240 mg/kg, respectively. Dopamine depletion by pre-treatment with d1-alpha-methyl-p-tyrosine plus dihydroxyphenylserine resulted in a significant drop of CD50 to 69 and 175 mg/kg for lidocaine and procaine, respectively. Serotonin depletion by pre-treatment with p-chlorophenylalanine resulted in a significant drop of CD50 to 68 mg/kg for lidocaine, but no significant change for procaine.

Immobilization stress in rats: effect on rectal temperature and possible role of brain monoamines in hypothermia

Immobilization of albino rats for 2 h showed ambient temperature-dependent changes in rectal temperature, hypothermia at temperatures below 30 degrees C, and hyperthermia at 35 degrees C and above. Adrenalectomized (Adre) rats showed more hypothermia compared to sham operated controls at 25 +/- 2 degrees C. The increased hypothermia in adrenalectomized rats was reversed by 10 mg/kg IP or 100 microgram/rat ICV of hydrocortisone. Groups of rats pretreated with desmethylimipramine (DMI, 25 mg/kg IP) and 6-hydroxydopamine (6-HD, 100 microgram/rat ICV) or methyl ester of parachlorophenylalanine (ME-PCPA, 100 microgram/rat ICV for 3 days) or 5,6-dihydroxytryptamine (DHT, 75 microgram/rat ICV) showed significantly less hypothermia at the end of 2 h of immobilization. Applying analysis of variance test, the hypothermia in Adre, ME-PCPA and DHT groups, was found to be not significantly different from their respective control groups between 0 and 45 min of immobilization but was significantly different between 45 to 120 min of immobilization. DMI-6-HD group however, showed significant difference between 0--45 min only and not between 45--120 min of immobilization. The results suggest that the early phase of immobilization induced hypothermia between 0--45 min is dopamine and the late phase of hypothermia between 45--120 min is 5-hydroxytryptamine mediated.

On the neurochemical basis of self-stimulation with midbrain raphe electrode placements

Bar-pressing for electrical stimulation of the median raphe nucleus in rats was not attenuated by 5HT receptor blockade with metergoline or cyproheptadine, by 5HT depletion induced with parachloroamphetamine or by prior destruction of ascending 5HT pathways with intracerebral microinjections of 5,7-dihydroxytryptamine. Furthermore, in a shuttle box paradigm in which rats could both initiate and terminate stimulation, parachlorophenylalanine did not antagonize initiation of stimulation. It is concluded that the rewarding effects of raphe stimulation are not mediated by serotonergic mechanisms. In contrast to these results, alpha-methyl-paratyrosine induced catecholamine depletion exerted an inhibitory effect on initiation behaviour without impairing termination of stimulation. It is concluded that the rewarding component of raphe stimulation is mediated by catecholamines. Termination of (escape from) stimulation was not materially affected by catecholamine or 5HT depletion suggesting the aversive component of raphe stimulation may not be mediated by these monoamines.

Morphine and ethanol as discriminative stimuli: absence of antagonism by p-chlorophenylalanine methyl ester, cinanserin, or BC-105

It is well established that the effects of morphine and ethanol can function as discriminative stimuli in the rat. The present investigation sought to determine whether discriminated responding mediated by morphine and ethanol is affected by (a) p-chlorophenylalanine methyl ester (p-CPA) an inhibitor of the synthesis of 5-hydroxytryptamine (5-HT) and (b) antagonists of 5-HT. The blocking agents employed were cinanserin, in ethanol-trained subjects, and BC-105, in morphine-trained subjects. No evidence of antagonism was obtained with either BC-105 or cinanserin. Results with p-CPA were somewhat variable but no consistent or statistically significant reduction in the efficacy of morphine or ethanol as discriminative stimuli was observed. The present results with p-CPA are at variance with earlier work by Schechter (1973) and by Rosecrans et al. (1973) who observed antagonism of the stimulus effects of ethanol and morphine, respectively, following depletion of 5-HT with p-chlorophenylalanine.

Clonidine antinociceptive activity: effects of drugs influencing central monoaminergic and cholinergic mechanisms in the rat

Clonidine is able to increase the threshold for vocalisation during stimulation and the threshold for vocalisation after withdrawal of stimulus (vocalisation afterdischarge). These effects of clonidine were investigated after treatment of rats with drugs influencing central monoaminergic and cholinergic mechanisms. Chlorpromazine, atropine and p-chlorophenylalanine increased the activity of clonidine at both thresholds while phenoxybenzamine and reserpine pretreatment increased the activity at the thresholds for vocalisation only. Yohimbine decreased clonidine activity at both thresholds while 5-HTP and alpha-methyl-p-tyrosine decreased the effects at the threshold for vocalisation afterdischarge. Naloxone did not change the activity of clonidine at either pain response studied. It is concluded from the present findings that influence from several neuronal systems modulate the antinociceptive action of clonidine. The inhibition of the medullary nociceptive response after clonidine might be connected to a decreased activity of noradrenergic neurons. Endogenous noradrenaline seems to be of minor importance in mediating this effect. It is moreover shown that decreased cholinergic receptor activity enhances clonidine antinociceptive action on both medullary and diencephalic-rhinencephalic pain responses. The possible involvement of serotonin these functional responses after clonidine is also discussed.