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Results for “Serotonin Receptor Agonists”

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At least 19 recordsLinked to original sources
PubMed2003

5-HT(1B/1D) serotonin receptor agonist attenuates nitroglycerin-evoked nitric oxide synthase expression in trigeminal pathway.

This study was conducted to investigate the effect of 5-HT(1B/1D) receptor activation on nitroglycerin (NTG)-induced cerebral hyperaemia and neuronal nitric oxide synthase (nNOS) expression in trigeminovascular neurones. NTG (10 mg/kg) was infused intravenously to adult male Wistar rats with or without pretreatment with 5-HT(1B/1D) receptor agonist, sumatriptan (0.4 mg/kg, intravenously). Cortical blood flow and expression of nNOS enzyme in trigeminal ganglia, trigeminal nucleus caudalis and perivascular nerve fibre surrounding superior sagittal sinus were measured. The results showed that pretreatment with sumatriptan could significantly shorten the period of NTG-induced cerebral hyperaemia without compromising the magnitude of hyperaemic peak. Sumatriptan pretreatment also attenuated the NTG-evoked expression of nNOS in all studied areas. Based on these findings, we suggest that 5-HT(1B/1D) receptor has an important role in stabilizing the trigeminovascular system by attenuating the expression of nNOS enzyme, hence reducing nitric oxide production.

Animals↗
PubMed2006

Different serotonin receptor agonists have distinct effects on sound-evoked responses in inferior colliculus.

The neuromodulator serotonin has a complex set of effects on the auditory responses of neurons within the inferior colliculus (IC), a midbrain auditory nucleus that integrates a wide range of inputs from auditory and nonauditory sources. To determine whether activation of different types of serotonin receptors is a source of the variability in serotonergic effects, four selective agonists of serotonin receptors in the serotonin (5-HT) 1 and 5-HT2 families were iontophoretically applied to IC neurons, which were monitored for changes in their responses to auditory stimuli. Different agonists had different effects on neural responses. The 5-HT1A agonist had mixed facilitatory and depressive effects, whereas 5-HT1B and 5-HT2C agonists were both largely facilitatory. Different agonists changed threshold and frequency tuning in ways that reflected their effects on spike count. When pairs of agonists were applied sequentially to the same neurons, selective agonists sometimes affected neurons in ways that were similar to serotonin, but not to other selective agonists tested. Different agonists also differentially affected groups of neurons classified by the shapes of their frequency-tuning curves, with serotonin and the 5-HT1 receptors affecting proportionally more non-V-type neurons relative to the other agonists tested. In all, evidence suggests that the diversity of serotonin receptor subtypes in the IC is likely to account for at least some of the variability of the effects of serotonin and that receptor subtypes fulfill specialized roles in auditory processing.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed2006

Headache, Raynaud's syndrome and serotonin receptor agonists in systemic lupus erythematosus.

There are potential concerns regarding serotonin receptor agonists in SLE patients with migraine, particularly patients with concomitant Raynaud's syndrome. We estimated the prevalence of lupus-related headache and Raynaud's syndrome in the Montreal General Hospital SLE clinic cohort and evaluated the relationship between these two variables in multivariable logistic regression models, controlling for age, sex, race, SLE duration and the presence of lupus anticoagulant and antibodies to cardiolipin and beta2 glycoprotein I. We also assessed, through chart review in those individuals with both Raynaud's syndrome and migraine, a history of serotonin receptor agonist use, and any associated worsening vasospasm. Based on Systemic Lupus Activity Measure (SLAM) scores, the cumulative incidence of lupus-related headache in our sample (n = 391) was 46.1%; the prevalence of Raynaud's syndrome was 49.4%. The adjusted odds ratio (OR) for lupus-related headache and Raynaud's syndrome was 1.7 (95% CI 1.1, 2.5). In addition, there was a strong independent relationship between headache and anti-beta2 glycoprotein I antibodies (adjusted OR 5.6 [95% CI 1.8, 17.0]). The data from our chart review suggest that careful use of serotonin receptor agonists in patients with both Raynaud's syndrome and migraines may be undertaken, although caution would necessitate that these agents not be used in individuals with very severe Raynaud's (eg, digital ulcerations, and so on).

Adult↗
PubMed2004

Beta-oxygenated analogues of the 5-HT2A serotonin receptor agonist 1-(4-bromo-2,5-dimethoxyphenyl)-2-aminopropane.

Activation of 5-HT(2A) serotonin receptors represents a novel approach to lowering intraocular pressure. Because 5-HT(2A) serotonin receptor agonists might also produce undesirable central effects should sufficient quantities enter the brain, attempts were made to identify 5-HT(2) serotonin receptor agonists with reduced propensity to penetrate the blood-brain barrier. 1-(4-Bromo-2,5-dimethoxyphenyl)-2-aminopropan-1-ol (6), an analogue of the 5-HT(2) serotonin receptor agonist 1-(4-bromo-2,5-dimethoxyphenyl)-2-aminopropane (DOB; 1a) bearing a benzylic hydroxyl group, was identified as a candidate structure. Of the four optical isomers of 6, the 1R,2R-isomer (6d; K(i) = 0.5 nM) was found to bind at 5-HT(2A) receptors with an affinity similar to that of R(-)DOB (K(i) = 0.2 nM). Like R(-)DOB, 6d behaved as a partial agonist (efficacy ca. 50%) in a 5-HT(2)-mediated calcium mobilization assay. However, in an in vivo test of central action (i.e., stimulus generalization with rats as subjects), 6d was >15 times less potent than R(-)DOB. O-Methylation of 6d (i.e., 7d; 5-HT(2A) K(i) = 0.3 nM) resulted in an agent that behaved as a full (93% efficacy) agonist. Intraocular administration of 300 microg of 6d and 7d to ocular hypertensive monkeys was shown to reduce intraocular pressure by 20-27%. Given the route of administration (i.e., topical), and concentrations necessary to reduce intraocular pressure, compounds such as 6d should demonstrate minimal central effects at potentially useful therapeutic doses and offer useful leads for further development.

DOM 2,5-Dimethoxy-4-Methylamphetamine↗
PubMed2003

Modification of spontaneous contractility of smooth muscle preparations from the bovine abomasal antrum by serotonin receptor agonists.

The effects of serotonin (5-hydroxytryptamine, 5-HT), a 5-HT2-receptor agonist, alpha-methyl-5-hydroxytryptamine (alpha-M-5-HT) and RS-67506, a 5-HT4 receptor partial agonist, on spontaneous contractility of bovine abomasal smooth muscle preparations were investigated in vitro. Preparations from the abomasal antrum of freshly slaughtered healthy dairy cows were cut parallel to the longitudinal fibres, suspended in isolated organ baths, and concentration-response curves were performed by cumulative application of the 5-HT receptor agonists. Blockade of 5-HT2-induced response was tested with atropine and hexamethonium. Serotonin evoked a significant increase in the area under curve (AUC), whilst the 5-HT2 receptor agonist alpha-M-5-HT significantly increased the AUC and resting tone (RT). RS-67506 induced a significant increase in AUC and RT and a significant decrease in the maximum force. The effect of alpha-M-5-HT was mediated by a muscarinic cholinergic pathway, as the effect of alpha-M-5-HT was inhibited in the presence of atropine but not hexamethonium. It is concluded that 5-HT2 and 5-HT4 receptors are present in the bovine abomasal antrum. Muscarinic receptors are involved in the increase in RT seen after 5-HT2 receptor stimulation.

Abomasum↗
PubMed1978

The effect of quipazine, a serotonin receptor agonist, on serum corticosterone concentration in rats.

Quipazine, a serotonin receptor agonist, increased serum corticosterone within 30 min after its i.p. injection (at 10 mg/kg) into rats; the effect persisted at 1 and 2 hrs, but not at 4 hrs. Elevation of serum corticosterone did not occur with a 1.25 mg/kg dose of quipazine but was dose-related over a 2.5-20 mg/kg dose range. The effect of quipazine was completely prevented by methergoline, a serotonin receptor antagonist. The effect of quipazine was present in rats pretreated with 5,7-dihydroxytryptamine to destroy serotonin nerves and was not enhanced (as was the effect of L-5-hydroxytryptophan) by fluoxetine pretreatment. These data are compatible with the idea that quipazine increases serum corticosterone as a consequence of direct stimulation of serotonin receptors in brain.

5,7-Dihydroxytryptamine↗
PubMed2006

In vitro characterization of SLV308 (7-[4-methyl-1-piperazinyl]-2(3H)-benzoxazolone, monohydrochloride): a novel partial dopamine D2 and D3 receptor agonist and serotonin 5-HT1A receptor agonist.

Present Parkinson's disease treatment strategies are far from ideal for a variety of reasons; it has therefore been suggested that partial dopamine receptor agonism might be a potential therapeutic approach with potentially fewer side effects. In the present study, we describe the in vitro characterization of the nonergot ligand SLV308 (7-[4-methyl-1-piperazinyl]-2(3H)-benzoxazolonemonohydrochloride). SLV308 binds to dopamine D(2), D(3), and D(4) receptors and 5-HT(1) (A) receptors and is a partial agonist at dopamine D(2) and D(3) receptors and a full agonist at serotonin 5-HT(1) (A) receptors. At cloned human dopamine D(2,L) receptors, SLV308 acted as a potent but partial D(2) receptor agonist (pEC(50) = 8.0 and pA(2) = 8.4) with an efficacy of 50% on forskolin stimulated cAMP accumulation. At human recombinant dopamine D(3) receptors, SLV308 acted as a partial agonist in the induction of [(35)S]GTPgammaS binding (intrinsic activity of 67%; pEC(50) = 9.2) and antagonized the dopamine induction of [(35)S]GTPgammaS binding (pA(2) = 9.0). SLV308 acted as a full 5-HT(1) (A) receptor agonist on forskolin induced cAMP accumulation at cloned human 5-HT(1) (A) receptors but with low potency (pEC(50) = 6.3). In rat striatal slices SLV308 concentration-dependently attenuated forskolin stimulated accumulation of cAMP, as expected for a dopamine D(2) and D(3) receptor agonist. SLV308 antagonized the inhibitory effect of quinpirole on K(+)-stimulated [(3)H]-dopamine release from rat striatal slices (pA(2) = 8.5). In the same paradigm, SLV308 had antagonist properties in the presence of quinpirole (pA(2) = 8.5), but the partial D(2) agonist terguride had much stronger antagonistic properties. In conclusion, SLV308 combines high potency partial agonism at dopamine D(2) and D(3) receptors with full efficacy low potency serotonin 5-HT(1) (A) receptor agonism and is worthy of profiling in in vivo models of Parkinson's disease.

Animals↗
PubMed2001

Migraine headache treatment with eletriptan, a second-generation serotonin receptor agonist.

Eletriptan is a member of the triptan family of selective serotonin receptor agonists. These act against migraine by inducing vasoconstriction of the meningeal arteries. In pharmacological tests, eletriptan has shown high affinity for the 5-HT(1B/1D) receptors, which have been implicated in the etiology of migraine headache attacks. Pharmacokinetic evaluations have concluded that eletriptan offers greater bioavailability than sumatriptan, the effective predecessor to eletriptan. A rapid onset of action has also been characteristic of eletriptan in clinical trials, which have likewise demonstrated eletriptan's superiority to sumatriptan in granting relief of headache pain and other symptoms associated with migraine to a greater number of migraine patients. The drug has generally been well tolerated with only mild to moderate adverse events reported. These characteristics make eletriptan an attractive alternative to sumatriptan in the treatment of migraine. (c) 2001 Prous Science. All rights reserved.

Journal Article↗
PubMed2001

Behavioral effect of 1A-serotonin receptor agonist ipsapirone in mice previously defeated in male-male encounters.

The effect of 1A-serotonin receptor agonist ipsapirone (3 mg/kg) on mouse behavior was studied in the "wall" and Porsolt tests. The effects of the test drug were compared in intact animals and mice previously defeated in 20 intermale encounters (victims). Ipsapirone was ineffective in victims and effective in intact mice in the wall test. In the Porsolt test the drug prolonged stupor in victims.

Animals↗
PubMed2001

Effects of type 1A serotonin receptor agonist 8-OH-DPAT on immune response.

The selective agonist of type 1 A serotonin receptors 8-hydroxy-2-(di-n-propyl-amino)tetra-lin (8-OH-DPAT) suppressed the immune response. Intraperitoneal administration of 1 mg/kg 8-OH-DPAT to Wistar rats over 2 days after immunization decreased the count of plaque- and rosette-forming cells on day 5. Our results indicate that type 1A serotonin receptors are involved in the realization of the immunosuppressive effects of the serotoninergic system.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed2003

5HT1A serotonin receptor agonists inhibit Plasmodium falciparum by blocking a membrane channel.

To identify new leads for the treatment of Plasmodium falciparum malaria, we screened a panel of serotonin (5-hydroxytryptamine [5HT]) receptor agonists and antagonists and determined their effects on parasite growth. The 5HT1A receptor agonists 8-hydroxy-N-(di-n-propyl)-aminotetralin (8-OH-DPAT), 2,5-dimethoxy-4-iodoamphetamine, and 2,5-dimethoxy-4-bromophenylethylamine inhibited the growth of P. falciparum in vitro (50% inhibitory concentrations, 0.4, 0.7, and 1.5 microM, respectively). In further characterizing the antiparasitic effects of 8-OH-DPAT, we found that this serotonin receptor agonist did not affect the growth of Leishmania infantum, Trypanosoma cruzi, Trypanosoma brucei brucei, or Trichostrongylus colubriformis in vitro and did not demonstrate cytotoxicity against the human lung fibroblast cell line MRC-5. 8-OH-DPAT had similar levels of growth inhibition against several different P. falciparum isolates having distinct chemotherapeutic resistance phenotypes, and its antimalarial effect was additive when it was used in combination with chloroquine against a chloroquine-resistant isolate. In a patch clamp assay, 8-OH-DPAT blocked a P. falciparum surface membrane channel, suggesting that serotonin receptor agonists are a novel class of antimalarials that target a nutrient transport pathway. Since there may be neurological involvement with the use of 8-OH-DPAT and other serotonin receptor agonists in the treatment of falciparum malaria, new lead compounds derived from 8-OH-DPAT will need to be modified to prevent potential neurological side effects. Nevertheless, these results suggest that 8-OH-DPAT is a new lead compound with which to derive novel antimalarial agents and is a useful tool with which to characterize P. falciparum membrane channels.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1999

Cardiovascular responses produced by microinjection of serotonin-receptor agonists into the paraventricular nucleus in conscious rats.

Activation of serotonin (5-hydroxytryptamine, 5-HT) receptors in the brain produces cardiovascular responses by altering autonomic outflow. The paraventricular nucleus (PVN) contains a modest density of 5-HT receptors and has connections to autonomic centers. Experiments were designed to determine whether cardiovascular responses were produced by the administration of 5-HT2- and 5-HT1A-receptor agonists into the PVN of conscious rats. The microinjection of the 5-HT2-receptor agonist DOI [(+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl] into the PVN produced dose-dependent (1-10 nmol) increases in heart rate and blood pressure; the peak responses were +39 +/- 10 beats/min and +6 +/- 2 mm Hg, respectively. Both responses were blocked by the concomitant administration of the selective 5-HT2-receptor antagonist LY53857 into the PVN. By contrast, the microinjection of the selective 5-HT1A-receptor agonist R(+)-8-OH-DPAT [R(+)8-hydroxy-2-(di-n-propylamino) tetralin HBr; 1-10 nmol] into the PVN did not affect blood pressure or heart rate. These data suggest that 5-HT neurons projecting from the raphe nuclei to or near the PVN can participate in the central control of the cardiovascular system by way of 5-HT2 receptors. Apparently 5-HT neurons terminating in the PVN can increase blood pressure and heart rate and produce sympathoadrenal activation, metabolic and hormonal responses consistent with those observed in several different stress paradigms.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1997

Effects of chronic ethanol on the mobilization of arachidonate and docosahexaenoate stimulated by the type 2A serotonin receptor agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride in C6 glioma cells.

We studied the effects of chronic ethanol exposure on the mobilization of polyunsaturated fatty acids stimulated by activation of the type 2A serotonin receptor in C6 glioma cells. In our in vitro model, we prelabeled cells with [3H]arachidonate and [14C]docosahexaenonate and subsequently stimulated with the type 2A serotonin receptor agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride. In as early as 10 days of exposure to 20 or 50 mM ethanol, the (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride-simulated mobilization of [3H]arachidonic acid [[3H]AA) and [14C]docosahexaenoic acid ([14C]DHA) was significantly inhibited, and this inhibition was accompanied by decreased mobilization of intracellular [Ca2+]i. Exposure to ethanol did not alter significantly the release of [3H]AA and [14C]DHA stimulated by the calcium ionophore A23187 nor the incorporation of [3H]AA and [14C]DHA into cellular lipids. Decreased mobilization of polyunsaturated fatty acids and calcium in astroglia may contribute to neurotoxicity caused by chronic ethanol exposure.

Amphetamines↗
PubMed2004

Inhibition of bladder activity by 5-hydroxytryptamine1 serotonin receptor agonists in cats with chronic spinal cord injury.

The serotonin (5-hydroxytryptamine1A) 5-HT1A receptor agonist 8-OH-DPAT [(R)- (+)-8-hydroxy-2-(di-n-propylamino)tetralin] inhibits bladder activity under nociceptive but not innocuous conditions in cats with an intact spinal cord, suggestive of an effect on primary afferent C fibers or their targets. Because C fibers play a key role in reflex micturition in chronic spinal cord injury (SCI), we investigated the effect of 8-OH-DPAT on micturition in SCI cats. We also investigated GR-46611 (3-[3-(2-dimethylaminoethyl)-1H-indol-5-yl]-N-(4-methoxybenzyl)acrylamide), which has agonist activity predominantly at 5-HT1B and 5-HT1D receptors but also at the 5-HT1A receptor. Chloralose-anesthetized cats were catheterized through the bladder dome for saline-filling cystometry. Dose-response curves for i.v. 8-OH-DPAT (0.3-30 microg/kg) and GR-46611 (0.03-300 microg/kg) were followed in three cases each by 5-HT1A antagonist WAY-100635 [N-tert-butyl-3-(4-(2-methoxyphenyl)-piperazin-1-yl)-2-phenylpropanamide] at 300 microg/kg. Threshold volume, capacity, residual volume, micturition volume, and arterial pressure were measured. Intact cats showed few significant changes in cystometric variables. SCI cats responded to both 8-OH-DPAT and GR-46611 with dose-dependent increases in threshold volume, capacity, and residual volume, significant at > or =10 microg/kg for 8-OH-DPAT and at > or =3 microg/kg for GR-46611. Effects of 8-OH-DPAT but not GR-46611 were largely reversed by WAY-100635. Both 5-HT1A and 5-HT1B/1D agonists may offer a promising means of reducing bladder hyperactivity and increasing bladder capacity in patients with chronic SCI.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1993

Effect of selective serotonin receptor agonists on prolactin secretion in male rats.

The effect of different serotonin (5-HT) receptor agonists on the release of prolactin (PRL) was investigated in conscious male rats. The 5-HT1 receptor agonists 5-carboxamidotryptamine and RU 24969 stimulated the PRL secretion dose dependently. RU 24969 possessed almost the same potency and efficacy (maximal effect) as 5-HT, while 5-carboxamidotryptamine was more potent and had a higher efficacy. The 5-HT1 + 2 receptor agonist MK 212 stimulated the PRL secretion only at high doses. The 5-HT2 receptor agonist S(alpha)methyl-5-HT and the 5-HT3 receptor agonist 2-methyl-5-HT had minor or no effect on the PRL secretion. The PRL-releasing effect of submaximal doses of 5-carboxamidotryptamine and RU 24969 was blocked by the 5-HT1 + 2 receptor antagonist methysergide and enhanced by other 5-HT agonists, but was unaffected by the 5-HT2 and 5-HT3 receptor antagonists. MK 212, S(alpha)methyl-5-HT, and--in particular--2-methyl-5-HT potentiated the effect of 5-carboxamidotryptamine. Likewise, 2-methyl-5-HT potentiated the effect of RU 24969, while MK 212 or S(alpha)methyl-5-HT had an additive to slightly potentiating effect. The findings show that 5-HT stimulates PRL secretion via 5-HT1 as well as 5-HT2 receptors and that activation of 5-HT2 and 5-HT3 receptors significantly augment the PRL-stimulating effect of 5-HT1 receptor activation. This indicates that the 5-HT receptor subtypes may interact functionally in the mediation of the PRL-releasing effect of the serotonergic system.

Animals↗
PubMed2002

Frovatriptan: a selective type 1B/1D serotonin receptor agonist for the treatment of migraine headache.

Frovatriptan belongs to an innovative family of compounds aimed at breaking through the long-standing barrier of migraine headache understanding and treatment. While a typology of headaches has been recognized for some time, and a number of therapies have been introduced for reduction of headache pain and duration, the causes of migraine remain a subject of debate. Those prone to attacks continue to endure them and suffer the related symptoms such as nausea and disorientation. Frovatriptan, like all the triptans, acts by inducing vasoconstriction of the meningeal arteries. It has been shown in pharmacological tests to act selectively as a potent agonist of serotonin 5-HT1B/1D receptors. Frovatriptan has been well tolerated in humans and efficacious in reducing headache pain and duration in clinical trials, which have also indicated that dose adjustments for age or gender are not necessary for the drug. Patients have found the use of frovatriptan acceptable over the long-term, and overall a low-incidence of adverse effects has been reported. Though not a prophylactic, frovatriptan has demonstrated the potential to significantly improve the therapeutic approaches to the treatment of migraine.

Adult↗
PubMed1994

Serotonin and human myoclonus. Rationale for the use of serotonin receptor agonists and antagonists.

This is a critical review of the serotonin hypothesis of myoclonus for the purpose of identifying new pharmacologic therapies. The literature on myoclonus and serotonin neuropharmacology reveals evidence for serotonergic abnormalities in some human myoclonic disorders, new serotonin receptor subtypes and data on their molecular structure and function, more selective drugs, and experimental evidence linking certain serotonin receptor subtypes with myoclonus. This article provides an overview of clinical experience with serotonergic drugs, new investigational drugs, and strategies for gathering data critical to linking particular receptor abnormalities and drugs with specific human myoclonic disorders. Such information will allow the use of receptor subtype-selective agonists and antagonists for the treatment of myoclonus.

5-Hydroxytryptophan↗
PubMed1992

Food intake and rumen motility in dwarf goats. Effects of some serotonin receptor agonists and antagonists.

The serotonergic regulation of feeding behaviour has not so far been studied in ruminants. Therefore, the effects of some serotonin (5-HT) receptor agonists and antagonists on food intake and forestomach motility were studied in dwarf goats. Goats ate less food when treated intravenously (IV) with the 5-HT precursor 5-HTP (25 micrograms, 50 micrograms or 100 micrograms kg-1 min-1 over 15 min) than when they were treated with 5-HT (which does not pass the blood-brain barrier) or with saline. Accordingly, IV dexfenfluramine infusions (50 micrograms or 100 micrograms kg-1 min-1 over 15 min), which induces release of brain 5-HT, also led to dose-related reductions in food intake. In contrast, no anorectic effects were observed after IV infusions with the selective 5-HT reuptake inhibitor fluoxetine (100 micrograms kg-1 min-1 over 15 min), the selective 5-HT1A agonist 8-OH-DPAT (0.5 micrograms kg-1 min-1 over 15 min), or eltoprazine (4 or 8 micrograms kg-1 min-1 over 15 min), a mixed 5-HT1A/5HT1B receptor agonist. None of the 5-HT antagonists tested gave any increase in food consumption in this model. Interestingly, the non-selective 5-HT receptor antagonist methysergide (360 micrograms/kg IV) reduced food intake. This effect was most noticeable at 3 h after injection. The 5-HT3 receptor antagonist ondansetron (IV 10 micrograms kg-1 min-1 over 15 min) and the peripheral 5-HT2 receptor antagonist xylamidine (IV 100 micrograms kg-1 min-1 over 10 min) failed to modify food intake. These results provide evidence for central serotonergic involvement in the control of feeding. However, this control system differs markedly in goats and rodents. Dexfenfluramine, 5-HTP and eltoprazine administered at similar dose rates to those used in the food intake experiments induced some clinical signs including inhibition of forestomach contractions. These results, together with our earlier in vivo and in vitro observations, suggest that the inhibitory effects of serotonin receptor agonists on forestomach contractions are due to interactions with both peripheral and central serotonergic receptors. The change in smooth muscle tension, which leads to a change in the signals transmitted via vagal afferents to the central nervous system, appears not to modify feeding behaviour in dwarf goats.

Animals↗