We have used X-ray microangiography to investigate the hypothesis that the potent endogenous vasodilator endothelium-derived relaxing factor (EDRF) contributes to the maintenance of "optimality" in vascular branching by modulating the diameters of the parent (D0) and daughter (D1 and D2) arteries at bifurcations. Five anatomically different types of bifurcation were studied in buffer-perfused rabbit ear preparations both under resting conditions and after pharmacological constriction by 5-hydroxytryptamine (<em>5HT</em>). A range of flow rates (1-5 ml min-1) was employed as release of EDRF from endothelial cells is stimulated by shear stress. Experimental data obtained in the presence and absence of EDRF activity were compared with theoretical predictions in three ways. (1) Junction exponents (x) were determined at each bifurcation from the equation Dx1 + Dx2 = Dx0, and their frequency distributions constructed. Murray (1926a, Proc. natn. Acad. Sci., U.S.A. 12, 207-214; 1926b, J. gen. Physiol. 9, 835-841.) proposed that x will be exactly 3 if power losses and intravascular volume are minimized simultaneously. In unconstricted preparations, either in the presence or absence of EDRF activity, and in preparations constricted by 0.1 microM <em>5HT</em> in the presence of EDRF activity, the modes and medians of the frequency distributions of x were found to be close to 3 at all flow rates. In contrast, in 0.1 microM <em>5HT</em>-constricted preparations in the absence of EDRF activity, no single mode common to all flow rates was apparent and medians were significantly larger at all flow rates. (2) Theoretically "optimal" branching angles were derived from experimental diameter measurements using four mathematical models which minimize respectively the total surface area, total volume, total drag (shear stress) and total power losses at bifurcations (Murray, 1926b). These calculated branching angles were then compared with actual branching angles. EDRF activity was found to be necessary for accurate prediction of branching angles by the minimum volume and power loss models in <em>5HT</em>-constricted but not in resting preparations. (3) For each model or "minimization principle", there is an optimal mathematical relationship between the junction exponent, x, and the angle between daughter arteries, psi 12, at a bifurcation (Roy & Woldenberg, 1982, Bull. math. Biol. 44, 349-360.) Experimentally determined values of x and psi 12 agreed closely with those predicted both by the minimum volume and the minimum power loss principles, except again in <em>5HT</em>-constricted preparations in the absence of EDRF activity.(ABSTRACT TRUNCATED AT 250 WORDS)

BACKGROUND

Red chili has been reported to modulate visceral hypersensitivity, probably by the action of its active ingredient, capsaicin. The role of <em>5HT</em>-3 receptors on capsaicin-sensitive visceral nociceptive pathways is unknown.

OBJECTIVE

To test the hypothesis that capsaicin-containing red chili induces rectal hypersensitivity in healthy humans and <em>5HT</em>-3 receptors participate in this effect.

METHODS

Eighteen healthy volunteers, each underwent three rectal barostat studies under three conditions: (i) oral placebo; (ii) oral chili (5 g daily x 3 days); and (iii) oral chili with 1-mg intravenous (i.v.) granisetron, in randomized, double-blinded, cross-over fashions. Rectal sensation was evaluated by using a 5-point Likert scale.

RESULTS

Chili ingestion significantly decreased rectal threshold for first, moderate and severe urgency (18 +/- 0.9, 24 +/- 1.2, and 38 +/- 1.5 mmHg, respectively) compared with placebo (22 +/- 0.9, 31 +/- 1.3, and 45 +/- 1.4 mmHg, respectively, P < 0.01). The threshold for first, moderate and severe urgency after chili with i.v. granisetron was 20 +/- 0.9, 28 +/- 1.2 and 44 +/- 1.3 mmHg, respectively. This is a significant increase compared with chili ingestion without granisetron (P < 0.05). After placebo ingestion, i.v. granisetron produced no effect on rectal sensation compared with i.v. placebo in 10 healthy volunteers (P>> 0.05).

CONCLUSIONS

Low-dose granisetron, a <em>5HT</em>-3 receptor antagonist, partially reversed chili-induced rectal hypersensitivity but had no effect on rectal perception induced only by mechanical balloon distention. This study suggests that <em>5HT</em>-3 receptors may be involved in chili-induced rectal hypersensitivity and potentially participate in the capsaicin-sensitive nociceptive pathways of the human gut.

Initially identified as an RNA modification in the anticodon loop of tRNAs from animal, plant and eubacterial origin, the deamination of adenosine-to-inosine by RNA editing has become increasingly recognized as an important RNA processing event to generate diversity in both the transcriptome and proteome and is essential for modulating the activity of numerous proteins critical for nervous system function. Here, we focus on the editing of transcripts encoding the 2C-subtype of serotonin receptor (<em>5HT</em>(2C)) to generate multiple receptor isoforms that differ in G-protein coupling efficacy and constitutive activity. <em>5HT</em>(2C) receptors have been implicated in the regulation of anxiety, components of the stress response, and are thought to play a role in compulsive behavioral disorders, depression and drug addiction. A number of studies have been conducted to assess whether <em>5HT</em>(2C) editing is altered in individuals suffering from psychiatric disorders, yet the results from these studies have been inconsistent, and thus inconclusive. This review provides a discussion of the challenges involved with characterizing <em>5HT</em>(2C) editing patterns in human postmortem tissue samples and how differences in quantitative methodology have contributed to the observed inconsistencies between multiple laboratories. Additionally, we discuss new high-throughput sequencing tools, which provide an opportunity to overcome previous methodological challenges, and permit reliable systematic analyses of RNA editing in control and pathologic disease states.

Persistent neurochemical changes consistent with parkinsonism have been reported in brains of mice treated with repeated high doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). We now report that ethanol or acetaldehyde potentiate MPTP-induced damage to mouse striatum. One hour after the combined treatments (ethanol and MPTP or acetaldehyde and MPTP), the animals exhibited a marked and long-lasting catatonic posture and then returned gradually to apparently normal locomotion. Seven days after MPTP administration, depletion of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in mouse striatum were further potentiated in the group of animals treated with ethanol. This effect was more evident when the treatment was repeated twice and was dose-dependent. Acetaldehyde was more potent than ethanol in enhancing MPTP neurotoxicity. A single exposure to acetaldehyde before and during MPTP treatment produced a very consistent fall of DA, DOPAC and HVA but not serotonin (<em>5HT</em>) or 5-hydroxyindoleacetic acid (5HIAA) in the striatum. This suggests that ethanol effects on MPTP neurotoxicity might be related to acetaldehyde formation.

Repeated amphetamine treatment results in sensitisation both of its behavioural effects, and of its dopamine (DA)-releasing effects on which the former largely depend. Understanding the nature of the sensitised response may help to explain behaviours which emerge only with repeated treatment, such as particular stereotypies and effects on social behaviour in animals, and links between these effects and the emergence of dependence and psychotic symptoms in humans. We show here that a single pretreatment with amphetamine (1mg/kg) is sufficient to sensitise the locomotor response to amphetamine challenge (1mg/kg) 24h later. We have used in vivo microdialysis in the nucleus accumbens in unrestrained rats to demonstrate a corresponding potentiation in the DA response; the marked increase in accumbens dialysate DA following amphetamine (to 427% of basal) was significantly potentiated (to 675% of basal) by the pretreatment, without any alteration in the basal DA. There was also no change in the expected reduction in DA metabolites. Replacement of perfusate calcium by magnesium left the response to acute amphetamine challenge substantially unaffected, as expected from previous reports; however, the potentiation of the DA response by amphetamine pretreatment was prevented. Similarly the potentiated response was attenuated by administration of ondansetron, a <em>5HT</em>-3 antagonist, (0.01mg/kg) before each amphetamine treatment. The ability of amphetamine to disrupt latent inhibition (L1), which is also disrupted in acute schizophrenia, has been suggested to provide a model of schizophrenia linking underlying cognitive deficits with the DA theory of the disorder. Since LI is disrupted by two systemic administrations of amphetamine 24h apart, but not by one, the present results are consistent with the concept that it is the calcium, and hence impulse, dependence of increased accumbal DA release, rather than its magnitude, which is critical for the disruption of LI.

Newborn male rats were treated with a single dose of 3 mg vitamin A (retinol) or 0.05 mg vita-min D (cholecalciferol), and three months later five brain regions (frontopolar cortex, hypothalamus, hippocampus, striatum, and brainstem) were studied for tissue levels of dopamine (DA), serotonin (<em>5HT</em>), and metabolites such as homovanillic acid (HVA), as well as 5-hydroxyindole-3-acetic acid (5HIAA). Vitamin A treatment as hormonal imprinting significantly decreased 5HIAA levels in each brain region. Vitamin D imprinting significantly elevated DA only in the brainstem and HVA levels in striatum and hypothalamus. Present and earlier brain-imprinting results (with brain-produced substances), show that the profound and life-long effect of neonatal hormonal imprinting on neurotransmitter production of the adult brain seems to be well established. As prophylactic treatment with these vitamins is frequent in the perinatal period, the imprinting effect of vitamin A and vitamin D must be taken into consideration.

The goal of these experiments was to test the role of serotonin (<em>5HT</em>) in classical conditioning of the touch-elicited shortening reflex in the leech (Hirudo medicinalis). The toxin 5,7-dihydroxytryptamine (5,7-DHT) was used to deplete serotonin. The results indicated that <em>5HT</em> depletion significantly impairs the expression of conditioned responding; however, depleted leeches experiencing conditioned stimulus-unconditioned stimulus (CS-US) pairings still performed significantly better than depleted leeches experiencing unpaired CS-US presentations, suggesting that a <em>5HT</em>-dependent mechanism does not account fully for learning in this preparation. Moreover, the residual pairing dependent effect is observed, although the depletions eliminate sensitization, suggesting that the amplification of sensitization may not be sufficient to account for classical conditioning of this reflex. Histological analyses of the ganglia revealed an absence of staining in 100% of the Retzius cells in the toxin group.

Binding of [3H]-serotonin ([3H]5-hydroxytryptamine, [3H]<em>5HT</em>) to high and low affinity sites in brain membranes from frontal cortex was compared in rats fed control chow or fluoxetine (0.01%) containing chow. A reduction in the number of high affinity binding sites and in the affinity of the low affinity binding sites was observed after 2, 4 or 6 weeks. Reduction in the number of [3H]<em>5HT</em> binding sites was also observed in cerebral cortex of rats given fluoxetine by daily intraperitoneal injection for 4 or 6 weeks. Thus, long-term treatment with a selective inhibitor of serotonin uptake, fluoxetine, caused subsensitivity of <em>5HT</em> receptors in frontal cortex and cerebral cortex of rat brain.

Nonlinear excitation of the neurotransmitter serotonin (<em>5HT</em>) in aqueous solution is shown to generate a blue-green-emitting photoproduct in addition to UV fluorescence characteristic of native <em>5HT</em>. The visible emission rate in diffusional steady-state measurements scales as the sixth power of excitation intensity, demonstrating that absorption of six near-IR photons is required to generate emission of one visible photon. Transient measurements reveal that this process is composed of two sequential nonlinear steps, the first excited by four photons and the second by two photons. These results, in combination with measurements of multiphoton-excited serotonin UV fluorescence, support a model in which <em>5HT</em> is photochemically transformed as a consequence of four-photon absorption (Etot approximately 6 eV) to a photoproduct that then emits in the visible region via two-photon excitation. A minimum bound of approximately 10(-51) cm4 s photon-1 is observed for the two-photon emission action cross section at 830 nm. Photoionization, rather than reaction with a dissolved oxygen species, appears to be the primary mechanism for generation of the blue-green-emitting photoproduct. The peak intensities required to generate significant blue-green emission (approximately 5 x 10(11) W cm-2 from 80 MHz 150 fs titanium: sapphire laser pulses) are approximately five-fold higher than are typically used in two-photon laser scanning microscopy but are still substantially lower than the estimated intensity needed to induce dielectric breakdown of water.

Radioligand binding, Northern blot analysis, and changes in [Ca2+]i were used to study serotonin [5-hydroxytryptamine (<em>5HT</em>)] receptor subtypes in primary cultures of astrocytes from neonatal rat cerebral cortex. Radioligand binding studies revealed the presence of <em>5HT</em>2, but not the <em>5HT</em>1 or <em>5HT</em>3 receptor subtypes. Radioligand binding was also used to show the presence of serotonin uptake sites, which had previously been shown to be present by [3H]-<em>5HT</em> uptake, and also alpha 1-adrenergic receptors as has previously been reported by binding studies. Northern blot analysis of cortical astrocyte mRNA demonstrated the presence of transcripts for <em>5HT</em>2 receptors, but failed to identify mRNA for <em>5HT</em>1a or <em>5HT</em>1c receptors. Thus, results from Northern blot analysis correlated with the radioligand binding data which showed only <em>5HT</em>2 receptors. Equilibrium saturation studies, using 125[I]-LSD to label <em>5HT</em>2 receptors, yielded a KD of 9 nM and a Bmax of 177 fmol/mg protein. Radioligand binding studies or primary astrocyte cultures prepared from other brain regions also showed the presence of alpha 1-adrenergic, <em>5HT</em>2 receptor, and <em>5HT</em>-uptake sites, but no detectable <em>5HT</em>1a receptors, which were the only <em>5HT</em>1 receptors studied. Studies demonstrating <em>5HT</em>-induced, spiperone- and ketanserin-sensitive increases in free [Ca2+]i as measured by FURA-2, showed that the <em>5HT</em>2 receptors were functional in these cells. These data provide clear evidence for the existence of both <em>5HT</em>2 receptors and <em>5HT</em>-uptake sites in the same primary astrocyte cultures from neonatal rat cerebral cortex, with no detectable evidence of <em>5HT</em>1a or <em>5HT</em>1c subtypes.

Modulation of serotonin signaling by RNA editing of the serotonin 2C receptor (<em>5HT</em>(2C) R) may be relevant to affective disorder as serotonin functions regulate mood and behavior. Previously, we observed enhanced endogenous behavioral despair in ADAR2 transgenic mice. As the transcript of the <em>5HT</em>(2C) R is a substrate of ADAR2, we hypothesized that perturbed ADAR2 equilibrium in the prefrontal cortex of ADAR2 transgenic mice alters the normal distribution of edited amino acid isoforms of the <em>5HT</em>(2C) R and modifies the receptor function in downstream basal extracellular signal-regulated kinase (ERK) signaling. We examined groups of naive control and ADAR2 transgenic mice and found significantly increased ADAR2 expression, increased RNA editing at A, C, D and E sites and significantly altered normal distribution of edited amino acid isoforms of the <em>5HT</em>(2C) R with increased proportions of valine asparagine valine, valine serine valine, valine asparagine isoleucine, isoleucine asparagine valine and decreased isoleucine asparagine isoleucine amino acid isoforms of the <em>5HT</em>(2C) R in ADAR2 transgenic mice. Localized serotonin levels (5-HT) were unchanged and perturbed ADAR2 equilibrium coincides with dysregulated edited amino acid isoforms of the <em>5HT</em>(2C) R and reduced basal ERK signaling. These results altogether suggest that altered <em>5HT</em>(2C) R function could be contributing to enhanced depression-like behavior of ADAR2 transgenic mice and further implicate ADAR2 as a contributing factor in cases of affective disorder.

Bizarreness is a cognitive feature common to REM sleep dreams, which can be easily measured. Because bizarreness is highly specific to dreaming, we propose that it is most likely brought about by changes in neuronal activity that are specific to REM sleep. At the level of the dream plot, bizarreness can be defined as either discontinuity or incongruity. In addition, the dreamer's thoughts about the plot may be logically deficient. We propose that dream bizarreness is the cognitive concomitant of two kinds of changes in neuronal dynamics during REM sleep. One is the disinhibition of forebrain networks caused by the withdrawal of the modulatory influences of norepinephrine (NE) and serotonin (<em>5HT</em>) in REM sleep, secondary to cessation of firing of locus coeruleus and dorsal raphe neurons. This aminergic demodulation can be mathematically modeled as a shift toward increased error at the outputs from neural networks, and these errors might be represented cognitively as incongruities and/or discontinuities. We also consider the possibility that discontinuities are the cognitive concomitant of sudden bifurcations or "jumps" in the responses of forebrain neuronal networks. These bifurcations are caused by phasic discharge of pontogeniculooccipital (PGO) neurons during REM sleep, providing a source of cholinergic modulation to the forebrain which could evoke unpredictable network responses. When phasic PGO activity stops, the resultant activity in the brain may be wholly unrelated to patterns of activity dominant before such phasic stimulation began. Mathematically such sudden shifts from one pattern of activity to a second, unrelated one is called a bifurcation. We propose that the neuronal bifurcations brought about by PGO activity might be represented cognitively as bizarre discontinuities of dream plot. We regard these proposals as preliminary attempts to model the relationship between dream cognition and REM sleep neurophysiology. This neurophysiological model of dream bizarreness may also prove useful in understanding the contributions of REM sleep to the developmental and experiential plasticity of the cerebral cortex.

5-Methoxy-N,N-dimethyltryptamine (5-MeODMT) is an indolealkylamine which has agonist activity at <em>5HT</em> receptors. In the present investigation, 5-MeODMT had two types of effects on medullary respiratory neurons of the cat. Iontophoretic administration or i.v. doses (43 +/- 8.9 micrograms/kg) of 5-MeODMT hyperpolarized respiratory neurons and severely reduced action potential discharges. Cinanserin, a <em>5HT</em>-2/1 c receptor antagonist, when injected i.v. reduced the inhibition produced by i.v. injection of 5-MeODMT. Iontophoresis of cinanserin did not antagonize inhibition produced by iontophoresis of 5-MeODMT or 5-HT. The depression of respiratory discharge by i.v. injection of 5-MeODMT is attributed to presynaptic effects (network depression) and post-synaptic activation of <em>5HT</em>-1A receptors on respiratory neurons. 5-MeODMT (27 +/- 2.78 micrograms/kg i.v.) also increased discharge frequency of inspiratory and expiratory neurons. Inspiratory neuron discharges were briefer and expiratory neuron discharges occurred earlier in relation to phrenic nerve activity. It is suggested that the effects of the smaller doses are due to binding of 5-MeODMT to <em>5HT</em>-1A receptors on early inspiratory neurons of the medulla.

Drosophila melanogaster has been successfully used as a simple model to study the cellular and molecular mechanisms underlying behaviors, including the generation of motor programs. Thus, it has been shown that, as in vertebrates, CNS biogenic amines (BA) including serotonin (<em>5HT</em>) participate in motor control in Drosophila. Several evidence show that BA systems innervate an important association area in the insect brain previously associated to the planning and/or execution of motor programs, the Mushroom Bodies (MB). The main objective of this work is to evaluate the contribution of <em>5HT</em> and its receptors expressed in MB to motor behavior in fly larva. Locomotion was evaluated using an automated tracking system, in Drosophila larvae (3(rd)-instar) exposed to drugs that affect the serotonergic neuronal transmission: alpha-methyl-L-dopa, MDMA and fluoxetine. In addition, animals expressing mutations in the <em>5HT</em> biosynthetic enzymes or in any of the previously identified receptors for this amine (<em>5HT</em>1AR, <em>5HT</em>1BR, <em>5HT</em>2R and <em>5HT</em>7R) were evaluated in their locomotion. Finally, RNAi directed to the Drosophila <em>5HT</em> receptor transcripts were expressed in MB and the effect of this manipulation on motor behavior was assessed. Data obtained in the mutants and in animals exposed to the serotonergic drugs, suggest that <em>5HT</em> systems are important regulators of motor programs in fly larvae. Studies carried out in animals pan-neuronally expressing the RNAi for each of the serotonergic receptors, support this idea and further suggest that CNS <em>5HT</em> pathways play a role in motor control. Moreover, animals expressing an RNAi for <em>5HT</em>1BR, <em>5HT</em>2R and <em>5HT</em>7R in MB show increased motor behavior, while no effect is observed when the RNAi for <em>5HT</em>1AR is expressed in this region. Thus, our data suggest that CNS <em>5HT</em> systems are involved in motor control, and that <em>5HT</em> receptors expressed in MB differentially modulate motor programs in fly larvae.

Halogenated analogs of the potent norepinephrine (NE) uptake inhibitor, tomoxetine, were synthesized and their affinities for the serotonin (<em>5HT</em>) and NE uptake sites evaluated. One of the most potent was the 2-iodo substituted analog (289306) that inhibited [3H]tomoxetine binding to rat cerebral cortex with a Ki of 0.37 nM. The compound also inhibited the uptake of [3H]NE into rat hypothalamic synaptosomes with a Ki of 3.5 nM. This analog was significantly less potent at the <em>5HT</em> uptake site, as exhibited by a Ki of 25 nM in the inhibition of [3H]paroxetine binding and a Ki of 121 nM in [3H]<em>5HT</em> uptake. The resolved (R) enantiomer (303926) was 10 times more potent as a [3H]NE uptake inhibitor and 29 times more potent as an inhibitor of [3H]tomoxetine binding than the (S) enantiomer (303884). Administration of 289306 to rats prior to an i.c.v. injection of 6-hydroxydopamine prevented the depletion of hypothalamic NE and Epi with ED50 values of 0.28 and 0.47 mg/kg, respectively. Thus, 289306 was a potent inhibitor of NE uptake in vitro and in vivo. In addition, these compounds provide structures for potential ligands for the study of NE uptake sites by autoradiography, PET or SPECT imaging.

The field of serotonin (<em>5HT</em>) receptor pharmacology has been at least as dramatically altered by the advent of molecular neurobiology and recombinant DNA techniques as has any other neurotransmitter receptor field. The principal reason for this is the unforeseen multitude of genes expressing different types of <em>5HT</em> receptors. Classic pharmacological studies as well as radioligand binding studies convinced workers in the field that there were multiple <em>5HT</em> receptors. The extent of that multiplicity was not generally foreseen. At the time of this writing, no less than 13 <em>5HT</em> receptor genes have been cloned and functionally expressed. In addition, a fourteenth receptor has been well studied and will undoubtedly be cloned in the near future. These novel <em>5HT</em> receptor clones are appearing at an astonishing rate. All 13 receptors have been cloned between the years 1987 to 1993, with more than half of the clones appearing in the literature in the last 18 months. Furthermore, there is no indication that all of the <em>5HT</em> receptors present in the mammalian genome have been cloned. In fact, there are classic pharmacological data as well as radioligand binding data that implicate the existence of additional <em>5HT</em> receptor subtypes not yet fully defined or cloned. Bringing order to this rapid outpouring of information at this time is a very difficult task. Not only is there a great multiplicity of receptor subtypes, each with a unique pharmacology and distribution, but there are species variants of <em>5HT</em> receptors. In order to provide a concise and timely review, this article focuses on the strategies used to clone and express multiple <em>5HT</em> receptors. Unique properties of the various receptors are emphasized.

Induction of long-term synaptic changes at one synapse can facilitate the induction of long-term plasticity at another synapse. Here we show that if Aplysia sensory neuron (SN) somata and their remote motor neuron (MN) synapses are simultaneously exposed to serotonin (<em>5HT</em>) pulses, which at either site alone are insufficient to induce long-term facilitation (LTF), processes activated at these sites interact to induce LTF. Coincident induction of LTF requires: (1) that the synaptic pulse occurs within a brief temporal window of the somatic pulse and (2) that local protein synthesis occurs immediately at the synapse, followed by delayed protein synthesis at the soma. LTF at the SN-MN synapses can also be induced with cell-wide application of repeated pulses of <em>5HT</em>. However, these two forms of LTF differ mechanistically: (1) coincident LTF requires protein synthesis in the postsynaptic motor neuron, whereas repeated <em>5HT</em> LTF does not, and (2) repeated <em>5HT</em> LTF is accompanied by intermediate-term (3 h) facilitation, whereas coincident LTF is not. Thus LTF expressed in the same temporal domain can result from different underlying mechanisms.

In a neuroendocrine challenge paradigm, the present study investigated responses of schizophrenic patients to m-chlorophenylpiperazine (MCPP), a serotonin (5-hydroxytryptamine, <em>5HT</em>) agonist. In an oral dose of 0.25 mg/kg, MCPP was administered in a placebo-controlled double-blind design to male schizophrenic patients (n = 7) and normal male controls (n = 8). Behavioral (Positive and Negative Syndrome Scale; PANSS) and hormonal (cortisol, prolactin) variables were measured over the subsequent 210 min. The schizophrenic patients experienced an overall exacerbation of psychopathology on MCPP as compared with placebo (p less than 0.05), with specific worsening of PANSS-positive symptoms (p less than 0.025) and PANSS activation (p less than 0.001). In addition, the schizophrenic patients showed significantly lower cortisol (p less than 0.05) and prolactin (p less than 0.05) responses than the normal subjects. The schizophrenic patients had lower peak MCPP blood levels than the normal subjects, although this difference was not statistically significant. The findings are discussed in terms of <em>5HT</em> receptor(s) sensitivity and the pharmacokinetics of MCPP in schizophrenia.

OBJECTIVE

The effect of serotonin (5-hydroxytryptamine; <em>5HT</em>) on the in vitro proliferation of mitogen-stimulated lymphocytes was studied in primary cultures of rat spleen cells.

METHODS

<em>5HT</em> was added to the cultures 1 h prior to the mitogen, at final concentrations from 10(-13) up to 10(-2) M. T and B cell mitogens (concanavalin A, pokeweed mitogen and lipopolysaccharide) were used at suboptimal and optimal concentrations. The cell proliferation was measured 24-72 h after the addition of mitogen. The effect of each <em>5HT</em> concentration was studied on a group of 6-12 animals and was expressed as a percentage of the control values obtained with mitogen alone.

RESULTS

No significant effect of <em>5HT</em> at concentrations from 10(-13) to 10(-5) M was found. At concentrations of>> or =10(-4) M, a regular dose-dependent inhibition of the lymphocyte proliferation appeared, the concentration producing the half-maximal effect being 6 x 10(-4) M. The observed suppression was not due to <em>5HT</em> cytotoxicity toward spleen cells.

CONCLUSIONS

With the experimental system used, we failed to confirm an immunostimulatory effect of <em>5HT</em> in the range of concentrations of its receptor sensitivities or lower, but found a clear-cut immunoinhibitory effect at higher concentrations.

The density of substance P (SP) and serotonin (<em>5HT</em>) immunoreactivity in laminae I and II of rat spinal cord changes following dorsal rhizotomy in a manner consistent with sprouting by intrinsic SP and descending <em>5HT</em> systems (Wang et al. J. Comp. Neurol. 304: 555, 1991). In this study we used quantitative EM-immunocytochemistry to examine whether the increase in substance P and serotonin immunoreactivity seen at the light microscopic level was related to increased numbers of SP- and <em>5HT</em>-containing terminals in lamina II. Dorsal roots were sectioned and their ganglia removed from L1 to S2 unilaterally in 18 rats. After 3 (acute), 10 (subacute), or 60 (chronic) days, rats were perfused, and the L5 segments of the spinal cord were removed and prepared for electron microscopy. Lumbosacral deafferentation completely and permanently eliminated complex terminals in lamina II at L5 but the number of simple terminals increased by 46% compared to the control side. This result was similar to that shown previously in cat (Murray and Goldberger, J. Neurosci. 6: 3205, 1986) and suggested that intact intrinsic systems sprouted to form new terminals to compensate for the terminals lost by deafferentation. Quantitative electron microscopic immunocytochemistry demonstrated that the number of terminals containing SP in deafferented lamina II decreased by 58% at 3 days post-operatively and then increased by 10 days and recovered to normal levels by 60 days. The loss of SP terminals in the acute group is due to the loss of SP-containing dorsal root afferents, while the recovery in the chronic group suggests replacement of lost terminals by intrinsic SP systems. These results therefore indicate that SP-containing terminals show homotypic sprouting in response to complete dorsal root deafferentation. The number of <em>5HT</em>-containing terminals in lamina II of spinal cord increased by 56% on the deafferented side in the chronic group. The increase in <em>5HT</em>-containing terminals indicates that descending <em>5HT</em> systems undergo heterotypic sprouting in response to dorsal rhizotomy.

Angiotensin II in sub-contractor concentrations enhanced the contractions of rabbit isolated aortic strips to noradrenaline, potassium chloride, histamine, acetylcholine, isoprenaline and <em>5HT</em>. The potentiation of noradrenaline responses by angiotensin II was independent of any effect of angiotensin II on neuronal uptake of noradrenaline. The sensitization of this tissue to spasmogens induced by angiotensin II occurred in reserpine-treated preparations and in normal tissues suspended in calcium-free bathing medium. Procedures which abolished the transfer of sodium ions across membranes such as substitution of fructose for glucose in the bathing medium, absence of potassium ions or treatment with ouabain each abolished the non-specific sensitization. The evidence suggests that angiotensin II may cause a non-specific sensitization of this tissue by inhibiting sodium transfer across the cell membrane.

Previous studies demonstrated that the formamidine pesticide chlordimeform (CDM) reversibly inhibited prostaglandin biosynthesis and prevented the late (PG-mediated) phase of carrageenin-induced hind paw edema. This study emphasizes antagonism by CDM of the early (<em>5HT</em> and histamine-mediated) phase of carrageenin edema. CDM and cyproheptadine both antagonized paw edema induced by albumin (<em>5HT</em> and histamine-mediated) and by the direct injection of <em>5HT</em> and histamine, whereas aspirin and the PG antagonist, SC-19220, were ineffective. As expected, cyproheptadine selectively reduced the early phase, whereas aspirin and SC-19220 selectively reduced the late phase of carrageenin-induced edema. These results are thus consistent with earlier studies demonstrating PG mediation of the late phase of carrageenin edema, and <em>5HT</em> and histamine mediation of albumin edema and the early phase of carrageenin edema. In addition, they indicate that CDM possesses multiple acute anti-inflammatory actions not exhibited by aspirin, by SC-19220 or by cyproheptadine alone.

Serotonin (<em>5HT</em>) receptor signaling and <em>5HT</em>-related agents, such as the anorexogen fenfluramine (Fen), have been associated with heart valve disease. We investigated the hypothesis that Fen may disrupt mitral valve interstitial cell (MVIC) homeostasis through its effects on mitogenesis and extracellular matrix biosynthesis. Normal and myxomatous mitral valves, both human and canine, were harvested, and primary MVIC cultures were established. <em>5HT</em> caused increased phosphorylation of extracellular signal-related kinase in MVIC; Fen alone did not. However, Fen combined with <em>5HT</em> increased the level of MVIC extracellular signal-related kinase, when compared with <em>5HT</em> alone. In addition, MVIC mitogenesis per (3)H-thymidine ((3)HTdR) demonstrated a <em>5HT</em> dose-dependent increase, with no effect of Fen alone. In contrast, Fen combined with <em>5HT</em> inhibited the MVIC (3)HTdR response when compared with <em>5HT</em> alone. Furthermore, fluoxetine, a <em>5HT</em> transporter inhibitor, while having no effect alone, suppressed Fen-<em>5HT</em> (3)HTdR inhibition when administered with Fen plus <em>5HT</em>. Finally, MVIC incorporations of (3)H-proline and (3)H-glucosamine, measures of extracellular matrix collagen and glycosaminoglycan respectively, were increased with <em>5HT</em> alone; however, Fen did not affect MVIC glycosaminoglycan or collagen either alone or in combination with <em>5HT</em>. Taken together, the ratios of (3)H-proline or (3)H-glycosaminoglycan to (3)HTdR in MVIC, normalized to <em>5HT</em> alone, demonstrated a significant imbalance of extracellular matrix production versus proliferation in MVIC cultures with Fen plus <em>5HT</em> exposure. This imbalance may explain in part the pathophysiology of Fen-related mitral valve disease.