Effect of 5HT2 receptor blockade on the startle reflex and its prepulse inhibition in mice and rats of various strains]

Effects of 5-HT2 receptor blockade on the amplitude of startle reflex, induced by an unexpected sound, and on its prepulse inhibition (PPI) were studied on mice of CBA strain and rats of Wistar and the genetically predisposed to catalepsy (GC) strains. The effect was dependent on type and dose of 5-HT2 antagonist used: 5-HT2A antagonist ketanserin increased startle amplitude at the dose of 0.5 mg/kg and decreased it at the dose of 2 mg/kg. Mixed 5-HT2A/2C antagonist ritanserin (0.1 and 0.2 mg/kg) markedly increased startle in mice. Ketanserin and cyproheptadine produced opposite effects on startle reflex in rats with inherited neuropathology and in rats with normal genotype: marked decrease in GC rats and increase in Wistar rats was shown. Ketanserin and cyproheptadine produced a pronounced potentiation of PPI in mice and rats of both strains, ritanserin was ineffective. Results suggest 5-HT2 receptors implication in both startle and PPI regulation with 5-HT2C receptors in startle response and 5-HT2A in PPI predominant involvement.     

Down-Regulation of [3H]5-Hydroxytryptamine Binding Sites in Chick Embryo Brain by Monoamine Oxidase Inhibitors or Fenfluramine and Potentiation by d,l-5-Hydroxytryptophan

Three monoamine oxidase (MAO) inhibitors--pargyline, clorgyline and deprenyl--as well as the serotonin (5-HT, 5-hydroxytryptamine) releasing agent fenfluramine were administered to developing chick embryos and the effects on [3H]5-HT binding parameters and endogenous 5-HT levels were assessed. Multiple, but not acute, pretreatments with any of the three MAO inhibitors significantly increased 5-HT levels (p less than 0.01) and decreased receptor number (Bmax) to a maximum of 20% (p less than 0.01) without affecting the affinity (KD). When d,l-5-hydroxytryptophan (d,l-5-HTP) was similarly administered there were large increases in 5-HT levels (p less than 0.01), but no significant effects on either Bmax or KD. However, if d,l-5-HTP was co-administered with any of the MAO inhibitors there was a significant (p less than 0.01) enhancement of the MAO inhibitor-induced down-regulation to a maximum of about 40%. Multiple pretreatments with fenfluramine resulted in dose-related decreases in 5-HT levels (p less than 0.01) and Bmax (p less than 0.01) without affecting KD. The largest decrease in [3H]5-HT binding sites inducible by fenfluramine treatment alone was also about 40%. When given in combination with d,l-5-HTP, there was a potentiation of the down-regulation capabilities of fenfluramine at several different dosage levels; however, maximal down-regulation was also limited to 40%. Evidence was presented suggesting that these effects were not due to endogenous 5-HT or drugs remaining in the tissue preparation. The overall evidence implies that merely increasing endogenous 5-HT levels, as by precursor administration, does not necessarily induce down-regulation unless the 5-HT is also made available as functional 5-HT.     

Sensitization to the influenza virus in a combined experimental infection

Two groups of guinea-pigs were infected with live attenuated A2 virus in nasal drops and with simultaneous and subsequent administration of virus vaccine and live Haemophilus influenzae. In combined infection the late skin reactions to virus antigens proved to be significantly higher. H. influenzae infection stimulated the production of antiviral homocytotropic antibodies in guinea-pigs probably due to the adjuvant effect of the capsulated bacteria.     

Some evidence for the maturity of peripheral adrenergic nerves in new-born guinea-pigs.

The fluorescence histochemical technique of Falck and Hillarp revealed a similar distribution and density of peripheral adrenergic nerves in new-born and adult guinea-pigs. The accumulation of tritiated noradrenaline by tracheae from new-born guinea-pigs, assumed to be uptake into adrenergic nerves, was not less than the accumulation by tracheae from adult animals. There was equal potentiation by cocaine (1 x 10(-5)M) of responses to noradrenaline on tracheal chain preparations taken from new-born and adult guinea-pigs. The evidence supports the hypothesis that the guinea-pig has a functional, well differentiated peripheral adrenergic nervous system at birth. This would account for the apparent inability to produce a long-lasting sympathectomy by administration of 6-hydroxydopamine to new-born guinea-pigs.     

Alterations of central hypercapnic respiratory response induced by acute central administration of serotonin re-uptake inhibitor, fluoxetine

Long-term neurochemical changes are responsible for therapeutic actions of fluoxetine. The role of increased central concentration of serotonin by inhibiting its re-uptake via fluoxetine on the central hypercapnic ventilatory response is complex and little is known. We aimed to research the effect of acute intracerebroventricular (ICV) injection of fluoxetine on hypercapnic ventilatory response in the absence of peripheral chemoreceptor impulses and the role of 5-HT2 receptors on responses. Eighteen anesthetized albino rabbits were divided as Fluoxetine and Ketanserin groups. For ICV administration of fluoxetine and ketanserin, a cannula was placed in the left lateral ventricle by the stereotaxic method. Respiratory frequency (fR), tidal volume (V(T)) and ventilation minute volume (V(E)) were recorded in both groups. ICV fluoxetine (10.12 mmol/kg) injection during normoxia caused significant increases in V(T) and V(E) (both P < 0.01) in the fluoxetine group. When the animals were switched to hypercapnia f/min, V(T) and V(E) increased significantly. The increases in percentage values in V(T) and V(E) in Fluoxetine + Hypercapnia phase were higher than those during hypercapnia alone (P < 0.01 and P < 0.05, respectively). On blocking of 5-HT2 receptors by ketanserin (0.25 mmol/kg), the ventilatory response to Fluoxetine was abolished and the degree of increases in V(T) and V(E) in the Ketanserin + Hypercapnia phase were lower than those during hypercapnia alone (P < 0.01 and P < 0.001, respectively). We concluded that acute central fluoxetine increases normoxic ventilation and also augments the stimulatory effect of hypercapnia on respiratory neuronal network by 5-HT2 receptors in the absence of peripheral chemoreceptor impulses.     

N-Methyl-d-Aspartic Acid/Glycine Interactions on the Control of 5-Hydroxytryptamine Release in Raphe Primary Cultures

Abstract: Glutamic acid and glycine were quantified in cells and medium of cultured rostral rhombencephalic neurons derived from fetal rats. In the presence of 1 mM Mg²⁺, NMDA (50 μM) significantly stimulated (by 69%) release of newly synthesized 5-[³H]hydroxytryptamine ([³H]5-HT). d -2-Amino-5-phosphonopentanoate (AP-5; 50 μM) blocked the stimulatory effect of NMDA. AP-5 by itself inhibited [³H]5-HT release (by 25%), suggesting a tonic control of 5-HT by glutamate. In the absence of Mg²⁺, basal [³H]5-HT release was 60% higher as compared with release with Mg²⁺. AP-5 blocked the increased [³H]5-HT release observed without Mg²⁺, suggesting that this effect was due to the stimulation of NMDA receptors by endogenous glutamate. Glycine (100 μM) inhibited [³H]5-HT release in the absence of Mg²⁺. Strychnine (50 μM) blocked the inhibitory effect of glycine, indicating an action through strychnine-sensitive inhibitory glycine receptors. The [³H]5-HT release stimulated by NMDA was unaffected by glycine. In contrast, when tested in the presence of strychnine, glycine increased NMDA-evoked [³H]5-HT release (by 22%), and this effect was prevented by a selective antagonist of the NMDA-associated glycine receptor, 7-chlorokynurenate (100 μM). 7-Chlorokynuren-ate by itself induced a drastic decrease in [³H]5-HT release, indicating that under basal conditions these sites were stimulated by endogenous glycine. These results indicate that NMDA stimulated [³H]5-HT release in both the presence or absence of Mg²⁺. Use of selective antagonists allowed differentiation of a strychnine-sensitive glycine response (inhibition of [³H]5-HT release) from a 7-chlorokynurenate-sensitive response (potentiation of NMDA-evoked [³H]5-HT release).     

Serotonergic agonists stimulate inositol lipid metabolism in rabbit platelets

The metabolism of inositol phospholipids in response to serotonergic agonists was investigated in rabbit platelets. In platelets prelabelled with [3H]-inositol, in a medium containing 10 mM LiCl which blocks the enzyme inositol-1-phosphatase, 5-hydroxytryptamine (5-HT) caused a dose-dependent accumulation of inositol phosphates (IP). This suggests a phospholipase-C-mediated breakdown of phosphoinositides. Ketanserin, a selective 5-HT2 antagonist, was a potent inhibitor of the 5-HT response, with a Ki of 28 nM, indicating that 5-HT is activating receptors of the 5-HT2 type in the platelet. Lysergic acid diethylamide (LSD) and quipazine also caused dose-related increases in inositol phosphate levels, though these were considerably less than those produced by 5-HT. These results show that relatively small changes in phosphoinositide metabolism induced by serotonergic agonists can be investigated in the rabbit platelet, and this cell may therefore be a useful model for the study of some 5-HT receptors.     

Serotonin, dopamine, noradrenaline and their metabolites: levels in the brain of the house cricket (Acheta domesticus L.) during a 24-hour period and after administration of quipazine--a 5-HT2 receptor agonist.

1. The levels of 5-HT, DA, NA and DA metabolites (NADA, DOPAC) measured by HPLC (with electrochemical detection) in the brain of the house cricket did not change over a 24-hr period. The level of 5-HIAA, a 5-HT metabolite, was below the limit of detection. 2. The 5-HT and DOPAC levels decreased and NADA increased after quipazine injection but DA and NA levels did not change after it. 3. [3H]Ketanserin was used to identify serotonin receptors bound to sites in the house cricket brain with a KD of 5 nM and a concentration of Bmax 180 fmol/mg protein.     

Inhibitory effects of cis- and trans-resveratrol on noradrenaline and 5-hydroxytryptamine uptake and on monoamine oxidase activity

This study investigated for the first time the potential effects of cis- and trans-resveratrol (c-RESV and t-RESV) on noradrenaline (NA) and 5-hydroxytryptamine (5-HT) uptake by synaptosomes from rat brain, on 5-HT uptake by human platelets, and on monoamine oxidase (MAO) isoform activity. Both c-RESV and t-RESV (5-200 microM) concentration-dependently inhibited the uptake of [3H]NA and [3H]5-HT by synaptosomes from rat brain and the uptake of [3H]5-HT by human platelets. In both experimental models, t-RESV was slightly more efficient than c-RESV. Furthermore, in synaptosomes from rat brain, the RESV isomers were less selective against [3H]5-HT uptake than the reference drug fluoxetine (0.1-30 microM). On the other hand, both c-RESV and t-RESV (5-200 microM) concentration-dependently inhibited the enzymatic activity of commercial (human recombinant) MAO isoform (MAO-A and MAO-B) activity, c-RESV being slightly less effective than t-RESV. In addition, both RESV isomers were slight but significantly more selective against MAO-A than against MAO-B. Since the principal groups of drugs used in the treatment of depressive disorders are NA/5-HT uptake or MAO inhibitors, under the assumption that the RESV isomers exhibit a similar behaviour in humans in vivo, our results suggest that these natural polyphenols may be of value as structural templates for the design and development of new antidepressant drugs with two important biochemical activities combined in the same chemical structure: NA/5-HT uptake and MAO inhibitory activity.     

Serotonin,dopamine, noradrenaline and their metabolites: Levels in the brain of the house cricket (Acheta domesticus L.) during a 24-hour period and after administration of quipazine—a 5-HT2 receptor agonist

1. The levels of 5-HT, DA, NA and DA metabolites (NADA, DOPAC) measured by HPLC (with electrochemical detection) in the brain of the house cricket did not change over a 24-hr period. The level of 5-HIAA, a 5-HT metabolite, was below the limit of detection.2. The 5-HT and DOPAC levels decreased and NADA increased after quipazine injection but DA and NA levels did not change after it.3. [³H]Ketanserin was used to identify serotonin receptors bound to sites in the house cricket brain with a K_d of 5 nM and a concentration of B_max 180 fmol/mg protein.     

The pharmacology of the isolated foregut of the locust Schistocerca gregaria—II. characterization of a 5-HT2-like receptor

1. 5-HT (10⁻⁸−5 × 10⁻⁶ M) relaxed isolated locust foreguts.2. The effects of 5-HT were mimicked by 5,6-DHT, 5-MeOT, tryptamine, 5-MeT, MK212 and methysergide while 5-hydroxyindole, 5-hydroxyindole acetic acid, 5-hydroxytryptophol, NN-DMT, 8-OH DPAT and RU 24969 were without effect.3. Ketanserin (pA₂ = 5.65) was a competitive antagonist of the effects of 5-HT, MK212 and methysergide.4. Mianserin (pA₂ = 6.3) was also a competititve antagonist of 5-HT but ICS 205-930 had no antagonistic effect on 5-HT-induced relaxation.5. It is concluded that 5-HT relaxes the locust foregut by interacting with 5-HT₂-like receptors.     

Morphological correlates of serotonin-neuropeptide Y interactions in the rat suprachiasmatic nucleus: Combined radioautographic and immunocytochemical data

Summary The morphological substrate of putative serotonin (5-HT)/neuropeptide Y (NPY) interactions in thé suprachiasmatic nucleus (SCN) was investigated by combined radioautography and immunocytochemistry after intraventricular administration of (³H)5-HT in the rat. In the ventral portion of the SCN, the distribution of (³H)5-HT uptake sites overlapped closely the NPY-immunoreactive terminals. Previous investigations have shown that the dense 5-HT and NPY innervations of the SCN originate in different structures, i.e., the midbrain raphe nuclei and the ventral lateral geniculate nucleus, respectively. Accordingly, in the present study, destruction of 5-HT afferents by 5,7-dihydroxytryptamine was not found to induce any modification in NPY staining and, in ultrastructural immuno-radioautographic preparations, two distinct pools of axonal varicosities could be identified. Both 5-HT and NPY terminals established morphologically defined synaptic junctions, sometimes on the same neuronal target. Some cases of direct axo-axonic appositions between the two types of terminals were also encountered. These data constitute additional criteria for characterizing the cytological basis of the multiple transmitter interactions presumably involved in the function of the SCN as a central regulator of circadian biological rhythms.     

Direct effects of serotonin, and 5-HT2, alpha 1 and H1 receptor-antagonists on embryonic chick skin in vitro: a morphological and functional study

Ketanserin (K), a 5-HT2, alpha 1 and H1 receptor antagonist, at a concentration of 5 micrograms/ml inhibits keratinisation, but increases DNA-, collagen and glycosaminoglycan (GAG) synthesis in embryonic chick skin in vitro. On the other hand, serotonin (S) at a concentration of 10 micrograms/ml stimulates keratinisation and does not enhance DNA, collagen and GAG synthesis. 5 nM doses of ketanserin and serotonin give analogous results. The effects of other 5-HT2-receptor antagonists (e.g. BW 501 and cinanserin) are comparable to those of K, whereas prazosin (an alpha 1 receptor antagonist) and pyrilamin (an H1 receptor antagonist) do not show any effect on embryonic chick skin in vitro.     

Feedback control of rat brain 5-hydroxytryptamine synthesis

Abstract— The effect of increased levels of 5-hydroxytryptamine (5-HT) on the synthesis of [³H]5-HT from intracisternally injected tracer doses of [³H]tryptophan was studied in the rat brain stem. The [³H]5-HT which accumulated in the first 15 min after [³H]tryptophan injection was measured at various times after the acute intraperitoneal administration of the monoamine oxidase inhibitors Catron or Pargyline. The 5-HT levels reached two and three times control values respectively at 20 min and 180 min after monoamine oxidase inhibitor administration but [³H]5-HT accumulation was decreased (40 per cent) at 180 min when compared with 20 min. These data as well as those obtained after chronic treatment with monoamine oxidase inhibitors revealed that there is an inverse relationship between [³H]5-HT accumulation and the endogenous 5-HT level. Monoamine oxidase activity was undetectable during all the intervals in which [³H]5-HT accumulation was measured. No inhibition of [³H]5-HT accumulation was detected when [³H]5-hydroxytryptophan was injected instead of [³H]tryptophan. The results are consistent with a negative feedback of 5-HT synthesis at the rate-limiting tryptophan hydroxylation step.     

褪黑素对谷氨酸钠致痫大鼠海马5-色胺水平的影响

目的观察褪黑素（Melatonin,MT）对谷氨酸钠（Glutamate,Glu）致痫大鼠海马5-羟色胺（5-hydroxytryptamine,5-HT）水平的影响,研究其抑制癫痫的作用机制。方法40只健康雄性SD大鼠随机分为4组（每组10只）,分别为生理盐水对照组（NS组）;谷氨酸钠致痫组（Glu组）;褪黑素＋谷氨酸钠组（MT＋Glu组）;Luzidole＋褪黑素＋谷氨酸钠组（Luz＋MT＋Glu组）。观察并记录大鼠行为学及脑电图改变,用免疫组织化学方法检测大鼠海马内5-HT含量变化。结果行为学观察和EEG显示,NS组无痫样发作和痫样放电,Glu组和Luz＋MT＋Glu组痫样发作重（Ⅲ—Ⅴ级）,脑电图显示频发高幅的痫样波,TM＋Glu组无或仅有轻微发作（0-Ⅱ级）,脑电图上无或偶见散在单个微小痫样波;免疫组织化学分析结果显示,Glu组和Luz＋MT＋Glu组大鼠海马内5-HT含量与对照组比较均减少,差异性明显（P〈0．05）,MT＋Glu组较Glu组和Luz＋MT＋Glu组5-HT含量升高,差异性明显（P〈0．05）。结论MT对谷氨酸钠致痫大鼠痫样发作程度、痫样放电有抑制作用,其机制之一是经由其特异性的膜受体,通过某种机制增强5-HT作用,进而发挥抑痫效应。     

Antihypertensive properties of ketanserin (R 41 468)

The serotonergic receptor antagonist 3-(2-[4-(4-fluorobenzoyl)-1-piperidinyl]ethyl)-2,4-[1H, 3H] quinazolinedione (ketanserin) causes dose-dependent inhibition of the effects of 5-hydroxytryptamine (5-HT) on 5-HT2-serotonergic receptors. These receptors mediate facilitation of platelet aggregation, direct vasoconstriction in several arteries and veins, and direct amplification of vasoconstrictor responses to other neurohumoral mediators. Ketanserin does not inhibit vasodilator effects of 5-HT. At higher concentrations, ketanserin has alpha 1-adrenergic blocking properties. The compound causes dose-related reductions in arterial blood pressure in hypertensive animals and humans that are larger and occur at lower doses than in normotensive controls. In humans, the antihypertensive properties of ketanserin do not appear to involve alpha 1-adrenergic inhibition, because the compounds given i.v. (10 mg) do not affect the pressor dose-response curve to phenylephrine.     

5-HT(7)-like receptors mediate serotonergic modulation of photo-responsiveness of the medulla bilateral neurons in the cricket,Gryllus bimaculatus

Serotonin (5-HT) suppresses the photo-responsiveness of medulla bilateral neurons (MBNs) that are involved in the coupling mechanism of the bilaterally paired optic lobe circadian pacemakers in the cricket, Gryllus bimaculatus. We found that forskolin, a highly specific activator of adenylate cyclase, mimicked the effects of serotonin on the MBNs. This fact suggests the involvement of cyclic 3', 5'-adenosine monophosphate (cAMP) in mediating the action of serotonin. We therefore tested the effects of various 5-HT receptor agonists and antagonists that are coupled to adenylate cyclase to specify the receptor involved. Application of 8-OH-DPAT that has affinity for both 5-HT(1A) and 5-HT(7) receptors suppressed the photo-responsiveness, like forskolin. The inhibitory effect of 8-OH-DPAT was effectively blocked by clozapine, a high affinity 5-HT(7) receptor antagonists with a very low affinity for 5-HT(2). Ketanserin, a selective 5-HT(2) antagonist, and NAN-190, a 5-HT(1A) antagonist, did not block it. These results suggest that serotonergic suppression of the photo-responsiveness of the MBNs is mediated by 5-HT(7)-like receptor subtypes.     

Effects of FMRFamide-related peptides and morphine on the isolated foregut of the locust schistocerca gregaria

1. Morphine and YAGFMamide were the most effective potentiators of 5-hydroxytryptamine (5-HT)-induced relaxation of the isolated foregut.2. Morphine had no effect on proctolin-induced tissue contraction which was inhibited by YGGF-Mamide and YFMRFamide.3. The differing potency of FaRPs and morphine to potentiate 5-HT effects and reduce proctolin responses suggests that there are two separate FaRP receptor sub types.4. This proposal is supported by the observation that, while naloxone (10⁻⁵ M) is a relatively potent antagonist of FaRP induced inhibition of proctolin contraction, it has less effect on FaRP-induced potentiation of 5-HT-induced relaxation.     

Effect of methiothepin on imipramine- or mianserin-induced subsensitivity of serotonergic receptors

Effect of methiothepin on imipramine- or mianserin-induced subsensitivity of serotonergic receptors was examined in rat brain. Treatment with either imipramine plus methiothepin or mianserin plus methiothepin for 4 days resulted in a significant decrease in [³H] 5-hydroxytryptamine ([³H] 5-HT) binding in synaptic membranes. The binding was not significantly decreased after treatment for this period of time with either methiothepin, imipramine or mianserin alone. It is suggested that the elevated intrasynaptic 5-HT levels could contribute to potentiation effect of methiothepin on imipramine- or mianserin-induced down regulation of serotonergic receptors.     

Effect of long-term administration of the antidepressant drug milnacipran on serotonergic and noradrenergic neurotransmission in the rat hippocampus

The effect of a long-term administration of the antidepressant milnacipran on the function of the serotonergic (5-HT) and noradrenergic (NE) systems was studied using single cell recording of CA3 hippocampal pyramidal cells in chloral hydrate-anesthetized male Sprague-Dawley rats, and in vitro [3H]5-HT release measurement from hippocampal slices. The sensitivity of neither the extrasynaptic nor that of the postsynaptic 5-HT1A receptors of the pyramidal neurons was altered, as indicated by their unchanged responsiveness to the microiontophoretic application of 5-HT, and by the unchanged effect of the electrical stimulation at low frequency of the ascending 5-HT bundle, respectively. Increasing the frequency of stimulation (from 1 to 5 Hz) decreased its efficacy in control rats; the milnacipran treatment abolished this phenomenon. This cannot be attributed to a desensitisation of the terminal 5-HT1B autoreceptor, since the suppressive effect of 5-HT agonist 5-carboxyamidotryptamine on [3H]5-HT release was enhanced in milnacipran-treated rats. As for the NE system, the unchanged suppressing effect of microiontophoretic applications of NE and that of the 5 Hz stimulation in the locus coeruleus (LC) on the firing activity of pyramidal neurons indicates that the milnacipran treatment not altered the sensitivity of extrasynaptic alpha2- and postsynaptic alpha1-adrenergic receptors on pyramidal cells, as well as that of the presynaptic alpha2-autoreceptor on NE terminals. The decreased inhibitory effect of NE on the [3H]5-HT release in milnacipran-treated rats revealed that this treatment results in a desensitisation of the presynaptic alpha2-heteroreceptor located on serotonergic terminals. Taken together with the decreased suppressive effect of a low frequency of stimulation of the NE tract, the present results suggest that long-term milnacipran treatment enhances the efficacy of the 5-HT and reduces that of the NE neurotransmission.