Pergolide, terguride and N,N'-spacer-linked oligomers of both interact with 5-HT2A receptors of rat tail artery

Pergolide, terguride and N,N'-spacer-linked oligomers of both have been tested for their ability to interact with 5 hydroxytryptamine(HT)2A receptors of rat tail artery. Pergolide was a potent partial agonist (pEC50 7.5, Emax 55 %) and antagonized 5-HT-induced contractions (pKp 7.2). Pergolide dimer 3 with a p-xylene spacer between the indole nitrogens (N-1) displayed somewhat lower agonist potency than pergolide (pEC50 7.0, Emax 55 %, pKp 6.6). The contractile responses to pergolide and dimer 3 were antagonized by the 5-HT2A receptor antagonist ketanserin (pA2 9.4, 9.1). In contrast to pergolide dimer 3, pergolide dimers 5 and 9 with an alkyl and an aralkyl spacer between the piperidine nitrogens (N-6) lacked agonism and displayed low affinity at 5-HT2A receptors (pA2 < 5.5). Terguride behaved as an insurmountable antagonist of 5-HT (pA2 8.4). Oligomers of terguride showed 5 to 50-fold lower affinity. It is concluded that pergolide and terguride show a high affinity for 5-HT2A receptors, but dimerization (oligomerization) of both drugs fails to increase affinity.     

Role of the serotoninergic system in the acceleration of sexual maturation in wild Norway rats selected for reduced aggressiveness toward humans

The role of the serotoninergic system in acceleration of the sexual development of domesticated rats (Rattus norvegicus) was assessed. The onset of age-related changes in hypothalamic serotonin during prepubertal period occurred earlier in domesticated than in aggressive male rats. Blockade of the serotoninergic system after p-chlorophenylalanine (PCPA) administration on days 40 and 44 delayed the development of the reproductive system in both aggressive and domesticated males. In 60-day-old rats treated with PCPA, levels of testosterone in plasma and the number of mature spermatozoa in epididymis were decreased compared to controls. At the same time, the administration of PCPA on days 30 and 34 did not modify basal testosterone secretion and other parameters in 60-day-old aggressive rats and produced a decrease similar to PCPA injections on days 40 and 44, although less pronounced, in the weights of testes in domesticated animals. Administration of 5-hydroxytryptophan (5-HTP), a precursor of serotonin synthesis, on days 30, 32, 34, 36 and 38 increased plasma testosterone levels and weights of the sex organs in 60-day-old domesticated males, but did not significantly affect the development of reproductive system in aggressive animals. These data indicate that serotonin stimulates sexual development of males during prepubertal period and this activating effect of serotonin occurs earlier in domesticated than in aggressive males. They also suggest that the acceleration in sexual maturation of domesticated rats could result from changes in the ontogenetic dynamic of hypothalamic serotonin induced by a selection for low aggressiveness towards man.     

mCPP but not TFMPP is an antagonist at cardiac 5HT3 receptors.

The prototypic arylpiperazines, meta-chlorophenylpiperazine (mCPP), meta-trifluoromethylphenylpiperazine (TFMPP) and quipazine are widely studied serotonergic ligands with nonselective effects at 5HT1 and 5HT2 receptor subtypes. The present study was designed to compare the affinities of these arylipiperazines at 5HT3 receptors, and to determine agonist or antagonist activity at 5HT3 receptors. Quipazine showed high affinity at brain 5HT3 receptors (IC50 = 4.4 nM) and was a potent agonist of the von Bezold-Jarisch reflex in anesthetized rats, a response mediated by cardiac 5HT3 receptors. In concentrations that activated 5HT3 receptors, quipazine also antagonized serotonin-induced bradycardia in anesthetized rats. Taken together, these data suggest that quipazine is an agonist/antagonist with high affinity at 5HT3 receptors in both brain and cardiac tissue. Although mCPP also showed relatively high affinity at brain 5HT3 receptors (IC50 = 61.4 nM), it did not activate the von Bezold-Jarisch reflex; instead, mCPP potently antagonized serotonin-induced bradycardia. Thus, mCPP acts as an antagonist at 5HT3 receptors in the periphery. Although both quipazine and mCPP possessed relatively high affinity at brain 5HT3 receptors, TFMPP did not bind appreciably to 5HT3 receptors in brain (IC50 = 2373 nM) and neither activated nor inhibited cardiac 5HT3 receptors. That TFMPP did not interact with 5HT3 receptors, whereas quipazine and mCPP did, is in marked contrast to the similar effects of all three arylpiperazines at other serotonin receptors. The selectivity of TFMPP for 5HT1 and 5HT2 receptors (i.e., its minimal affinity for 5HT3 receptors) suggests that this arylpiperazine may be a preferred ligand relative to mCPP when studying 5HT1 or 5HT2 receptor mediated responses.     

Terguride attenuates prolactin levels and ameliorates insulin sensitivity and insulin binding in obese spontaneously hypertensive rats

Glucose tolerance, serum insulin, insulin receptors in epididymal fat tissue, circulating total cholesterol and triglyceride concentrations as well as serum prolactin were studied in obese and lean spontaneously hypertensive rats (SHR) of both sexes. Obese animals displayed insulin resistance and elevated insulin and triglyceride concentrations. Moreover, in obese rats the increased mass of epididymal fat tissue was accompanied with decreased capacity of high affinity binding sites of insulin receptors in the tissue plasma membranes. Terguride treatment lowered prolactin serum levels which was accompanied by ameliorated insulin sensitivity in obese animals of both sexes. In addition, terguride treatment decreased serum insulin and triglyceride concentrations in obese females and at the same time enhanced the affinity of high affinity insulin binding sites. Our results show that obesity in SHR is associated with a decreased capacity of insulin receptors and that prolactin may play a role in obesity-induced insulin resistance, particularly in female rats.     

Cerebral serotonin and the hypothalamo-hypophyseal-adrenal system of the rat during aging]

The role of brain serotonin (5HT) on the hypothalamus-pituitary-adrenal system (HPAs) under basal condition and after injections of p-chlorophenylalanine (pCPA) and L-5-hydroxytryptophan (L-5HTP) has been studied in 6, 12 and 28 month old male Wistar rats. Four experimental groups were made for each age: control, saline, injected with pCPA (250 mg/kg i.p.) and L-5HTP (200 mg/kg i.p.), the effects being valued 2 hours after L-5HTP administration and 24 hours after pCPA injection. In all groups the plasmatic ACTH, the corticosterone levels as well as the simultaneous changes of the 5TH content tryptophan hydroxylase activity in whole brain were estimated two hours after the L-5HTP injection and 24 hours after that of pCPA. Significant changes are not found in the plasmatic ACTH and corticosterone values with respect to age under basal condition. Nevertheless, the response of HPAs differs with the age after pCPA or L-5HTP injection. The ACTH and corticosterone levels augment by L-5HTP and decrease by pCPA in all age groups, but this corresponding increase or decrease was less marked in the older rats. The 5HT content as tryptophan hydroxylase activity in brain decreased in old animals. pCPA and L-5HTP determine, respectively, high falls and rise of 5TH values, these changes being more intense for pCPA in old rats and for L-5HTP in young and mature animals. The tryptophan hydroxylase activity is decreased by pCPA as L-5HTP injections.(ABSTRACT TRUNCATED AT 250 WORDS)     

Further evidence that the serotonin receptor in the rat stomach fundus is not 5HT1A or 5HT1B

The nature of the receptor mediating serotonin contraction in the rat stomach fundus has not been clearly associated with either 5HT1 or 5HT2 receptors. We have explored the possibility that such receptors in the rat fundus may better correlate with 5HT1A or 5HT1B receptor subtypes as defined by radiolabeled ligand binding studies with brain cortical membranes. Meta chlorophenylpiperazine (CPP) and meta trifluoromethylphenylpiperazine (TFMPP), selective ligands for the 5HT1B receptor and LY165163, a selective ligand for the 5HT1A receptor, have been evaluated for their agonist and antagonist activity at serotonin receptors in the rat stomach fundus. CPP and TFMPP were partial agonists in the rat stomach fundus whereas LY165163 showed no agonist activity in this smooth muscle in concentrations up to 10(-4)M. All three phenylpiperazines antagonized serotonin-induced contractions in the rat stomach fundus. The affinity for serotonin receptors in the rat fundus was similar for all three phenylpiperazines in spite of the reported selectivity of MCPP and TFMPP for 5HT1B and of LY165163 for 5HT1A receptors. Furthermore, the affinity of these agents for serotonin receptors in the rat stomach fundus did not agree with their reported affinity for either 5HT1A or 5HT1B binding sites in rat cortical membranes. Thus, the similarity in affinities of these phenylpiperazine derivatives for serotonin receptors mediating contraction in the rat fundus along with their different affinities for 5HT1A and 5HT1B binding sites argues against the possibility that the serotonin receptor in the rat fundus is of the 5HT1A or 5HT1B subtype of serotonin receptor.     

Effects of triple therapy with octreotide, galanin and serotonin on a human colon cancer cell line implanted in mice: comparison between different routes of administration

A human colon cancer cell line was implanted subcutaneously in nude mice. After 7 days, the animals were divided into four groups. The first group received an intraperitoneal (i.p.) continuous infusion by an osmotic pump, the second was given i.p. bolus injections, the third received continuous subcutaneous (s.c.) infusion by an osmotic pump and the fourth group was given bolus s.c. injections. Each group was divided into 2 subgroups. The first subgroup received triple treatment with octreotide, galanin, and serotonin, 40 microg/kg body weight/day of each. The second subgroup was given sterile saline solution. Treatment lasted for 14 days. The volume and wet weight of the tumours in all treated groups tended to decrease, but was statistically significant only in the group with continuous i.p. infusion. The number of viable cells tended to decrease in all the treated groups, but was not statistically significant. Proliferation index was significantly reduced in mice given triple therapy i.p. as bolus injection and as continuous infusion, as compared with their respective controls. The apoptotic index increased significantly in mice receiving triple therapy as continuous i.p. infusion as revealed by both the TUNEL method and by poly (ADP-ribose) polymerase (PARP) expression. The number of tumour blood vessels was significantly reduced in the mice given triple therapy as continuous i.p. infusion, as compared with controls. There was no statistical difference between animals treated by different routes, regarding proliferation or apoptosis of the cancer cells, or the number or mean luminal area of tumour blood vessels. The present investigation showed that regardless of the route of administration, triple therapy with octreotide, galanin and serotonin generally reduced the volumes, weights, viable cells, vascularization and proliferation of the tumours, as well as inducing apoptosis. Continuous i.p. infusion appears, however, to be the most effective route of administration.     

Effects of the partial dopamine receptor agonist, terguride, on the field-stimulated vas deferens in the mouse

Transdihydrolisuride (terguride), a 9,10-dihydrogenated analogue of the ergot dopamine agonist lisuride, is characterized as partial dopamine receptor agonist at CNS level. This compound was investigated for its effects on peripheral neurotransmission in the attempt to delineate its pharmacological profile. The contractile responses of field-stimulated mouse vas deferens were slightly inhibited by terguride at very high concentrations (10(-5)-10(-2) M); the selective antagonists for alpha 2-adrenergic and dopamine receptors failed to counteract this effect. Terguride was very effective in blocking the inhibitory effects of LY 171555 (selective DA2 agonist), SK&F 38393 (selective DA1 agonist) and clonidine (selective alpha 2 agonist). In no case the antagonism was competitive: the control dose-response curves were not shifted in a parallel and dose-dependent manner. Therefore terguride displays a mixed DA1, DA2 and alpha 2 antagonistic activity.     

Lateral hypothalamic serotonergic responsiveness to food intake in rat obesity as measured by microdialysis.

The hypothalamic serotonergic system is involved in the regulation of food ingestion and energy metabolism. Since disturbances of both energy intake and expenditure can contribute to obesity, the objective of the present study was to evaluate the serotonergic response stimulated by food ingestion in two different models of obesity: the hyperphagic Zucker and the hypophagic and hypometabolic, monosodium glutamate (MSG) obese Wistar rat. For this we used microdialysis to examine the release of 5-hydroxytryptamine (serotonin, 5HT) and 5-hydroxyindoleacetic acid (5HIAA) in the lateral hypothalamus. Daily intake of MSG-obese rats was 40% lower while that of Zucker obese rats was 60% higher than that of the respective lean controls. In overnight-fasted animals, 20-min microdialysate samples were collected before (basal release) and during a 2-h period of access to a balanced palatable food mash. The animals began to eat during the first 20 min of food access, and food consumption was similar among the four groups in all six individual 20-min periods recorded. Ingestion of food increased 5HT release in all groups. In MSG-obese and lean Wistar rats, 5HT levels were similarly elevated during the whole experimental period. In the Zucker strain, 5HT increments of basal release tended to be higher in obese than in lean rats at 20 and 40 min, and a significantly higher increment was observed at 60 min after food access (40 and 135% for lean and obese, respectively). The area under the curve relating serotonin levels to the 120 min of food availability was significantly higher in Zucker obese (246.7 +/- 23.3) than MSG-obese (152.7 +/- 13.4), lean Wistar (151.9 +/- 11.1), and lean Zucker (173.5 +/- 24.0) rats. The present observation, of a food-induced serotonin release in the lateral hypothalamus of lean Wistar and Zucker rats, evidences that 5HT in the lateral hypothalamus is important in the normal response to feeding. In obese animals, the serotonin response was similar to (in the hypophagic-hypometabolic MSG model) or even higher than (in the hyperphagic Zucker model) that seen in the respective lean controls. This result indicates that the energy homeostasis disturbances of both these obesity models may not be ascribed to an impairment of the acute lateral hypothalamic serotonin response to a dietary stimulus.     

Cotyledon and binucleate cell nitric oxide synthase expression in an ovine model of fetal growth restriction.

Heat exposure early in ovine pregnancy results in placental insufficiency and intrauterine growth restriction (PI-IUGR). We hypothesized that heat exposure in this model disrupts placental structure and reduces placental endothelial nitric oxide synthase (eNOS) protein expression. We measured eNOS protein content and performed immunohistochemistry for eNOS in placentas from thermoneutral (TN) and hyperthermic (HT) animals killed at midgestation (90 days). Placental histomorphometry was compared between groups. Compared with the TN controls, the HT group showed reduced delivery weights (457 +/- 49 vs. 631 +/- 21 g; P < 0.05) and a trend for reduced placentome weights (288 +/- 61 vs. 554 +/- 122 g; P = 0.09). Cotyledon eNOS protein content was reduced by 50% in the HT group (P < 0.03). eNOS localized similarly to the vascular endothelium and binucleated cells (BNCs) within the trophoblast of both experimental groups. HT cotyledons showed a reduction in the ratio of fetal to maternal stromal tissue (1.36 +/- 0.36 vs. 3.59 +/- 1.2; P< or = 0.03). We conclude that eNOS protein expression is reduced in this model of PI-IUGR and that eNOS localizes to both vascular endothelium and the BNC. We speculate that disruption of normal vascular development and BNC eNOS production and function leads to abnormal placental vascular tone and blood flow in this model of PI-IUGR.     

5HT2 and 5HT3 receptors' contribution to modeling of post-serotonin respiratory pattern in cats

Cardio-respiratory reflex effects of an exogenous serotonin challenge are suggested to be modulated by activation of the peripheral 5HT2 and 5HT3 receptors. In the present experiments the blocking effects of serotoninergic active drugs: ketanserin and tropanserin (MDL 72222) were studied in six pentobarbitone-chloralose anaesthetized cats. Bolus injection of serotonin (0.05 mg.kg(-1)) into the right femoral vein evoked prompt apnea, hypotension followed by tachypnoeic breathing. Pre-treatment with ketanserin (0.1 mg.kg(-1)), 5HT2 receptor antagonist, shortened the duration of post-serotonin apnea (P < 0.05), but had no effect on the pattern of post-apnoeic breathing. 5HT3 receptor blockade with the selective antagonist MDL 72222 (0.2 mg.kg(-1)) totally eliminated respiratory response to serotonin. In breaths that followed post-serotonin apnea, peak amplitude of the integrated phrenic signal was reduced (P < 0.001), unbiased by ketanserin blockade, and remained at the baseline level in MDL treated rats. Serotonin-induced hypotension was unaffected by the blockade of 5HT2 receptors. Inactivation of 5HT3 receptors with MDL attenuated the fall in blood pressure (P < 0.05). This data suggests that the squeal of serotonin-induced pulmonary chemoreflex, i.e. respiratory arrest, post-apnoeic pattern of breathing, bradycardia, and partially hypotension are mediated by 5HT3 receptors.     

Variations of brain histamine levels in germ-free and nephrectomized rats

The influence of nephrectomy on brain and peripheral tissue histamine and on brain norepinephrine, dopamine, serotonin, and 5-hydroxyindoleacetic acid was studied in germ-free and conventionally housed rats. The conventional controls had higher levels of histamine in the hypothalamus than the germ-free control animals, but no differences existed for histamine in whole brain minus the hypothalamus or in peripheral tissues. Nephrectomy increased brain histamine and 5-hydroxyindoleacetic acid levels in both germ-free and conventional rats, but had no effect on norepinephrine, dopamine or serotonin. In contrast, the histamine level in the heart of the nephrectomized germ-free animals was lower than that for germ-free controls. There were no changes in the heart or liver histamine levels of the conventional nephrectomized rats.     

Developmental changes in ovine myocardial glucose transporters and insulin signaling following hyperthermia-induced intrauterine fetal growth restriction

Developmental changes in ovine myocardial glucose transporters and insulin signaling following hyperthermia-induced intrauterine fetal growth restriction (IUGR) were the focus of our study. Our objective was to test the hypothesis that the fetal ovine myocardium adapts during an IUGR gestation by increasing glucose transporter protein expression, plasma membrane-bound glucose transporter protein concentrations, and insulin signal transduction protein concentrations. Growth measurements and whole heart tissue were obtained at 55 days gestational age (dGA), 90 dGA, and 135 dGA (term = 145 dGA) in fetuses from control (C) and hyperthermic (HT) pregnant sheep. Additionally, in 135 dGA animals, arterial blood was obtained and Doppler ultrasound was used to determine umbilical artery systolic (S) and diastolic (D) flow velocity waveform profiles to calculate pulsatility (S - D/mean) and resistance (S - D/S) indices. Myocardial Glut-1, Glut-4, insulin signal transduction proteins involved in Glut-4 translocation, and glycogen content were measured. Compared to age-matched controls, HT 90-dGA fetal body weights and HT 135-dGA fetal weights and gross heart weights were lower. Heart weights as a percent of body weights were similar between C and HT sheep at 135 dGA. HT 135-dGA animals had (i) lower fetal arterial plasma glucose and insulin concentrations, (ii) lower arterial blood oxygen content and higher plasma lactate concentrations, (iii) higher myocardial Glut-4 plasma membrane (PM) protein and insulin receptor beta protein (IRbeta ) concentrations, (iv) higher myocardial glycogen content, and (v) higher umbilical artery Doppler pulsatility and resistance indices. The HT ovine fetal myocardium adapts to reduced circulating glucose and insulin concentrations by increasing plasma membrane Glut-4 and IRbeta protein concentrations. The increased myocardial Glut-4 PM and IRbeta protein concentrations likely contribute to or increase the intracellular delivery of glucose and, together with the increased lactate concentrations, enhance glycogen synthesis, which allows for maintained myocardial growth commensurate with fetal body growth.     

Clustered ergot alkaloids modulate cell-mediated cytotoxicity.

Dimers of agroclavine (1) and terguride (2), as well as a series of terguride oligomers, for example trimers (5, 6), tetramer (7), hexamer (8) and functionalized tergurides for further complex clustering were synthesized. Terguride oligomers were screened for their direct cellular toxicity on lymphoma cell lines in vitro and for their immunomodulating activities, represented by the natural killer (NK) cell-mediated cytotoxicity, as the most sensitive screening marker during immune responses. Dimers linked via aromatic spacer showed a high toxicity (1 microM) to lymphoma cells, which was not detected in other derivatives. In vitro and ex vivo experiments performed on mouse spleen lymphocytes in the presence of terguride oligomers demonstrated an immunosuppressive effect of dimers with aromatic spacer (4c-d) and NK cell stimulatory effect of terguride hexamer (8) and trimer with aliphatic spacer (5c). There is a considerable evidence that indolic part of molecule contributes to immunosuppressive action of terguride, which is potentiated in dimers carrying aromatic linker. This effect can be reversed by higher oligomerization of the respective alkaloids.     

Dual influence of spontaneous hypertension on membrane properties and ATP production in heart and kidney mitochondria in rat: effect of captopril and nifedipine, adaptation and dysadaptation

This study deals with changes, induced by hypertension and its treatment, in the function and properties of mitochondria in the heart and kidneys. Male, 16-week-old hypertensive rats were allocated to 3 groups: (i) animals treated daily for 4?weeks with captopril (CAP, 80?mg·(kg body mass)(-1), n = 45), (ii) animals treated with CAP?+?nifedipine (NIF, 10?mg·kg(-1), n = 45), or (iii) untreated hypertensive controls (n = 96). Wistar rats (n = 96) were used as normotensive controls. Systolic blood pressure (SBP), heart rate (HR), and heart mass / body mass (HW/BW) ratio were measured at the beginning and end of the experiments; measurements for mitochondrial Mg(2+)-ATPase activity, O(2)-consumption (QO(2)), respiratory control index (RCI), ADP/O, oxidative phosphorylation rate (OPR), conjugated diene content (CD), and membrane fluidity (MF) were also taken at different time intervals. In the heart, elevated SBP, HR, and HW/BW accompanied increased QO(2), OPR, and Mg(2+)-ATPase activity, indicating an adaptive response to hypertension-induced increase in the energy demands of the myocardium. Treatments with CAP or with CAP?+?NIF were very similar in their prevention of increase in SBP, HR, HW/BW, and the rise in OPR (all p?< 0.05-0.01). In the kidneys, hypertension induced a drop in OPR; however, antihypertensive therapy aggravated the resulting energy deficiency, whereby treatment with CAP?+?NIF was more detrimental than treatment with CAP alone. Heart and kidney mitochondria exhibited negligible changes in CD and moderately increased MF, which was more potentiated by treatment with CAP alone than with CAP?+?NIF.     

Neurochemical changes following the administration of depleters of biogenic monoamines.

A variety of drugs which were thought to selectively effect the synthesis, release or reuptake of the biogenic monoamines, and thereby deplete their stores in brain, were administered to rats. The animals were given intraperitoneal injections of reserpine, α-methyl-meta-tyrosine, α-methyl-para-tyrosine, para-cholorophenylalanine and tetrabenazine, and were killed at intervals known to cause maximum depletion of serotonin, dopamine and norepinephrine. When compared to saline controls, the drugs depleted the respective monoamines, as expected, but changes in the levels of acetylcholine, alanine, glycine, γ-aminobutyric acid, and aspartate and glutamate were also observed.     

High-performance liquid chromatographic determination of terguride in solid dosage forms and plasma

A simple and rapid HPLC method was developed to determine terguride in terguride hydrogenmaleate, coated tablets and plasma. The assay was carried out on a glass column of SGX CN (150 × 3.3 mm I.D.) using methanol and phosphate buffer solution (pH 7.0) as the mobile phase, with detection at 227 nm. Terguride was quantified using promethazine as an internal standards. The tablet matrix was extracted into methanol. Plasma samples were deproteinated with acetonitrile and the supernatant was injected into the HPLC system. The method is linear, quantitative and reproducible.     

Serotonin involvement in analgesia induced by transcranial electrostimulation

The experiments described here were intended to investigate whether serotonin (5HT) may be involved in analgesia induced by low current transcranial electrostimulation (TE). The TE stimulus is a 10 mu-ampere, 10 Hz, pulsed current transmitted via electrodes in the pinnae. Combinations of the following were given as intraperitoneal injections: 300 mg/kg p-chlorophenylalanine (pCPA) 48 hours before testing, 100 mg/kg 5-hydroxytryptophan (5HTP) 30 min before testing and the saline vehicle for these drugs. Rats were tested prior to and 30 minutes after TE or sham TE. Testing for analgesia consisted of putting progressively increasing pressure on the rat tail 1/4 inch from the tip with a pneumatically driven, right angle wedge. The amount of pressure at which the rat moved its tail was measured both before and after TE, or sham TE, and recorded as the difference in tolerated peak pressure (DTPP). TE produced analgesia as manifested by a 613 percent increase in DTPP compared with sham TE treatment values. Among TE treated rats, pretreatment with pCPA decreased DTPP 91.5 percent compared with saline control values, indicating 5HT involvement. 5HTP restored TE induced analgesia in pCPA treated rats to the level of saline treated control animals, confirming 5HT involvement.     

Serotonin and Dopamine Sensitization in the Nucleus Accumbens, Ventral Tegmental Area, and Dorsal Raphe Nucleus Following Repeated Cocaine Administration

Abstract— The present study was designed to examine the effects of chronic cocaine administration on the extracellular response of serotonin (5-HT) and dopamine (DA) to a peripheral cocaine injection using in vivo brain microdialysis in awake rats. Two different dual probe preparations were used: One group of animals had guide cannulae aimed at the ventral tegmental area (VTA) and nucleus accumbens (N ACC) and a second group of animals had guide cannulae aimed at the dorsal raphe nucleus (DRN) and N ACC. Rats from both groups were given daily injections of either cocaine (20 mg/kg i.p.) or saline (0.9%; 0.05 ml/kg i.p.) for 10 consecutive days. On day 11, baseline dialysate levels of DA, 5-HT, dihydroxyphenylacetic acid, and 5-hydroxyindoleacetic acid were obtained from either the N ACC and VTA or the N ACC and DRN, followed by a 10 mg/kg i.p. cocaine injection and an additional 150 min of dialysate sampling. The percent baseline increases of both 5-HT and DA were significantly higher in the N ACC, VTA, and DRN of animals that received daily injections of cocaine compared with saline controls ( p < 0.05, in each region). Maximum dialysate 5-HT concentrations after cocaine challenge were significantly higher in the N ACC and VTA ( p < 0.05) and DRN ( p < 0.01) of chronically treated animals compared with saline controls. Maximum dialysate DA concentrations were significantly higher in the N ACC and DRN ( p < 0.05) of chronically treated animals compared with saline controls. There was no significant difference between acute and chronic animals in the maximum dialysate DA concentration from the VTA after cocaine challenge. 5-HT was significantly more sensitized in the 5-HT cell body region (DRN) than the N ACC terminal field ( p < 0.05), whereas DA was significantly more sensitized in the N ACC terminal field than the DA cell bodies of the VTA ( p < 0.05).     

Desensitization to PAF-induced rat paw oedema by repeated intraplantar injections

The intraplantar injection of PAF-acether (PAF), induced acute oedema in the rat paw, and desensitized it to subsequent challenges with the same agonist, but not to serotonin. The desensitization was maximal (up to 80% of initial response) after seven consecutive daily injections. In this condition, PAF-induced oedema of the contralateral paw was maintained. The analogue 2-methyl carbamate-PAF (2MC-PAF) was more effective than PAF as a desensitizing agent. Furthermore, the PAF-desensitized paw was refractory to challenges with 2-MC and vice-versa. PAF-acether, but not serotonin-induced rat paw oedema was inhibited by previous intravenous injection of PAF. Intravenous injections of serotonin were also effective in inhibiting selectively serotonin-induced paw oedema, but it was not possible to induce desensitization by repeated intraplantar injections of serotonin. Desensitization to PAF or the pre-treatment with the PAF antagonist BN 52021 did not block the edematogenic response induced by carrageenan.