Modulation of cholinergic neurotransmitter release from myenteric plexus by somatostatin

Efflux of radiolabeled acetylcholine (Ach) was studied in vitro using myenteric plexus-longitudinal muscle strips from guinea pig small intestine. The data showed that somatostatin (6.0 x 10(-7) M) depressed resting output of Ach from enteric neurons and this inhibition was unaltered in the presence of naloxone (1.0 x 10(-6) M). The inhibition by somatostatin on field-stimulated Ach release was dose-dependent but this inhibition was never complete; there was a 40% fraction of total release remained resistant to somatostatin. Both caerulein (2.85 x 10(-9) M) and guanidine (3.0 x 10(-3) M) stimulated release of [H3]-Ach from plexus neurons. The release of Ach induced by guanidine or caerulein was also susceptible to inhibition by somatostatin (6.0 x 10(-7) M). This study provides functional evidence to further substantiate an inhibitory action on plexus cholinergic neurons by somatostatin.     

Hymenolepis diminuta: ultrastructural observations on complement-mediated tegumental lysis and destrobilation of 4-day-old worms in vitro

Changes in the ultrastructure of the tegument and subtegumental cells of 4-day-old Hymenolepis diminuta were studied in vitro in 50% fresh normal rat serum over a 5-h period and compared with heat-inactivated serum and saline controls. First, membrane-bound vesicles accumulate above the microthrix-border. After 30–40 min large vacuoles, which may contain membranous elements, appear in the tegument at a time when the surface of the young strobila is virtually denuded of the microthrix-border. With prolonged incubations there are subtegumental secretory inclusions with dark, enveloping cytoplasm in the tegument and finally the apical plasma membrane, together with the majority of the matrix, is lost. The disrupted portion of the worm is abruptly demarcated from the comparatively intact scolex/anterior neck region by a constriction. Even after 5 h incubation there is no evidence of loss of tegumental matrix components from regions anterior to the constriction but the neck region shows a significant denudation of the microthrix layer and the tegument contains numerous inclusions. The scolex tegument only showed little evidence of loss of membrane from the surface. Possible mechanisms for the avoidance of complement-mediated lysis in the anterior region are discussed.     

Effect of serotonin (5-HT) and other monoamines on murine macrophages: modulation of interferon-gamma induced phagocytosis

We have previously shown that serotonin (5-HT) suppresses interferon-gamma (IFN-gamma)-induced Ia expression. In the present report, we show that 5-HT as well as other monoamines, histamine and dopamine, modulate IFN-gamma-induced phagocytosis in murine bone marrow macrophages. The effect of 5-HT on IFN-gamma-induced phagocytosis varied according to the concentration of IFN-gamma to which the macrophages were exposed. At low concentrations of IFN-gamma, 5-HT augmented phagocytosis, whereas at high concentrations of IFN-gamma, 5-HT suppressed phagocytosis. At both low and high IFN-gamma concentrations the response to 5-HT was dose-related and occurred at physiologic concentrations; the half-maximal effect was 6 X 10(-7) M and 3 X 10(-7) M for low and high IFN-gamma concentrations, respectively. Both histamine and dopamine also augmented IFN-gamma (1 U/ml) induced phagocytosis, at half-maximal augmenting concentrations of 7 X 10(-8) M and 4 X 10(-7) M, respectively. The 5-HT effects were blocked by the 5-HT antagonists spiperone, ketanserin, LY53857, mCPP, and PAPP, but not by the histamine antagonists pyrilamine, chlorpheniramine, or cimetidine. Histamine augmentation of IFN-gamma-induced phagocytosis was blocked by the H1 antagonists pyrilamine and chlorpheniramine, but not by the H2 antagonist cimetidine. The dopamine effect was blocked by spiperone and pyrilamine, both of which have been shown to block dopaminergic effects in other systems. This data provides functional evidence that at least part of the modulation of IFN-gamma-induced phagocytosis by 5-HT occurs through a 5-HT receptor-mediated mechanism, and 5-HT, dopamine, and histamine modulate IFN-gamma-induced phagocytosis independently through their respective receptors.     

Serotonin 5-HT(2) receptor stimulation of dopamine release in the posterior but not anterior nucleus accumbens of the rat

The objective of the present study was to examine the involvement of serotonin 5-HT(2) receptors within the rat nucleus accumbens (Acc) in the regulation of dopamine (DA) release using in vivo microdialysis. Perfusion with the 5-HT(2) agonist (+)-1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), at concentrations of 25-250 microM, through microdialysis probes located in the posterior Acc increased extracellular DA levels to a maximum of 200% of baseline. DOI-induced increases in the extracellular levels of DA were Ca(2+) dependent and were inhibited by co-perfusion with the 5-HT(2) antagonist LY-53,857. DOI enhancement of the extracellular concentrations of DA was observed when probes were implanted in the Acc core and shell regions posterior to anteroposterior +1.2 mm from bregma, whereas a small reduction in the extracellular levels of DA was observed in the anterior Acc. There were no differences between core and shell subdivisions within either the anterior or the posterior Acc. These results suggest that activation of 5-HT(2) receptors within the posterior, but not anterior, Acc stimulates DA release, indicating rostral-caudal differences in the interactions of 5-HT with DA systems in the Acc.     

Glycogen synthase in the rat tapeworm, Hymenolepis diminuta--I. Enzyme activity during development and with crowding.

1. Activity of glycogen synthase (E.C. 2.4.1.11) in Hymenolepis diminuta (Cestoda: Cyclophyllidea) was investigated as a function of development and with crowding. 2. Synthase activity was low in the anterior and posterior ends of the worms and highest in the pregravid proglottids in the mid-portion of the strobila. 3. The enzyme activity increased during development of the cestode at least up to 15 days postinfection, but the increase in activity apparently was not due to conversion of the inactive to the active form. 4. Mature oncospheres also contained glycogen synthase, but the activity was lower than in strobilar tissues. 5. Synthase I activities and the proportion of total activity in the I form were generally higher in worms from high density (100 worm) infections than in those from low density (10 worm) infections.     

Regional Effects of Sodium Valproate on Extracellular Concentrations of 5-Hydroxytryptamine, Dopamine, and Their Metabolites in the Rat Brain: An In Vivo Microdialysis Study

The effects of sodium valproate (VPA; 100, 200, and 400 mg/kg, i.p.) on ventral hippocampal and anterior caudate putamen extracellular levels of dopamine (DA) and 5-hydroxytryptamine (5-HT) were examined using in vivo microdialysis. VPA induced dose-related increases in dialysate DA, 3,4-dihydroxyphenylacetic acid, and 5-HT in the ventral hippocampus. Anterior caudate putamen dialysate 5-HT was also dose dependently elevated by the drug, whereas DA levels tended to decrease with increasing VPA dose. In contrast, VPA (200, 400, and 800 mg/kg, i.p.) produced no significant elevation of DA in posterior caudate putamen dialysates, although 5-HT levels were significantly elevated at the 400- and 800-mg/kg doses. In all three regions studied, dialysate concentrations of 5-hydroxyindoleacetic acid and homovanillic acid remained at basal levels following VPA treatments. The results are discussed with regard to the possible anticonvulsant mode of action of VPA.     

Endothelial cell junctional integrity modulation by serotonin: an ultrastructural analysis

We have reported previously that exogenous serotonin (5-hydroxytryptamine, 5-HT) alters cultured bovine aortic endothelial cell (BAEC) structural integrity by modulating the assembly of stress fibers. In the present study a 5-HT stimulus-coupled change in BAEC junctional integrity was quantitated by determining the width and percentage of intercellular openings in a monolayer. BAEC treated with 5-HT at concentrations of 10(-9) M to 10(-3) M caused a significant dose-dependent decrease in interendothelial cell junctional openings compared to controls, with the greatest reduction induced at 10(-6) M (92% from control). Treatment of BAEC with histamine (10(-4) M) increased the junctional openings by 82% when compared to controls. This change could be prevented by either pretreatment of the monolayers with 5-HT or by adding 5-HT in conjunction with the histamine. To assess a direct interaction of 5-HT with actin filaments, cultured BAEC monolayers were extracted, treated with 5-HT, and processed for immunocytochemical localization of 5-HT using the Avidin-Biotin method. Electron microscopy revealed 5-HT antibody bound to actin filaments and dense in areas of filament intersection, which implies a role for internalized 5-HT in stimulating the assembly of an actin filament network. Collectively, these results suggest that 5-HT helps to regulate the endothelial junctional barrier by promoting actin filament formation and stability, which may in turn increase the junctional apposition between endothelial cells.     

Nomimoscolex semenasae n sp (proteocephalidea: Monticelliidae), a cestode parasite of Diplomystes viedmensis (Pisces: Siluriformes) from the Patagonian region of Argentina

Nomimoscolex semenasae n. sp. is described from the primitive fish Diplomystes viedmensis (Siluriformes) from the Patagonian region of Argentina. The new species is placed in Nomimoscolex because of the cortical position of the vitelline follicles, medullary position of the testes, ovary and uterus, and having a scolex with four uniloculate suckers. N. semenasae differs from all other species in the genus by the following combination of characters: (1) apical organ absent; (2) strobila acraspedote; (3) vagina anterior or posterior to cirrus-sac and lacking a sphincter; (4) testes in one irregular layer and in two fields connected anteriorly; (5) uterine stem cortical in immature proglottides, growing from cortical stem into medullary region in mature proglottides; (6) long uteroduct; and (7) presence of spiniform microtriches on all regions of the scolex, proliferation zone and immature proglottis. This is the first record of a proteocephalidean tapeworm in D. viedmensis and in the family Diplomystidae.     

The in vitro effects of histamine and metiamide on neutrophil motility and their relationship to intracellular cyclic nucleotide levels.

Histamine at concentrations of 1 x 10(-5) M to 5 x 10(-5) M consistently increased neutrophil movement as measured in Boyden chambers. This effect was entirely caused by stimulation of chemokinesis (stimulated random migration) and true chemotaxis was inhibited by these concentrations. This inhibition of chemotaxis could be abolished by pretreatment with metiamide, an H-2 receptor antagonist, and levamisole, but not by diphenylhydramine, an H-1 receptor antagonist. Metiamide at similar concentrations produced a mild stimulation of chemokinesis but has no effect on true chemotaxis. The histamine effects on neutrophil motility were associated with increased levels of intracellular cAMP wehreas cAMP levels were unaffected. Agents known to elevate intracellular cAMP levels produced effects on neutrophil motility similar to those of histamine. It is suggested that histamine exerts a 2-fold effect on neutrophil motility mediated via an H-2 receptor site and associated with elevated levels of cAMP.     

Serotoninergic control of somatostatin and gastrin release from the isolated rat stomach

The influence of exogenous serotonin on the secretion of gastric somatostatin and gastrin was investigated under in vitro conditions using an isolated, vascularly perfused rat stomach preparation. Serotonin stimulated gastrin release, maximal effects were observed at 10(-6) M which increased gastrin levels by 78%; on the contrary, somatostatin secretion was inhibited (maximal inhibition of 56% at 10(-6) M). Changes in hormone secretion in response to serotonin were reversed by combined blockade of 5-HT1 and 5-HT2 receptors by methysergide and blockade of 5-HT2 receptors by ketanserin (10(-5) and 10(-6) M, respectively), and of cholinoreceptors by atropine (10(-5) M). It is concluded that in rats in vitro serotonin inhibits release of gastric somatostatin and stimulates gastrin secretion via specific serotonin receptors but muscarinic cholinergic receptors are also involved.     

Effects of monoamine neuromediators on the growth-related variables of <Emphasis Type="Italic">Escherichia coli</Emphasis> K-12

The monoamine neuromediators serotonin (5-HT), histamine, dopamine (DA), and norepinephrine (NE), added to an Escherichia coli K-12 strain MC 4100 culture upon inoculation, stimulate cell proliferation (determined from CFU formation) and biomass accumulation (monitored nephelometrically) during the late lag phase and the early exponential growth phase. These effects are less significant in the late exponential and stationary phase cultures. According to the concentration dependence of the stimulatory effects, the neuromediators can be classified into two groups: (i) the catecholamines DA and NE, whose effects increase almost linearly with increasing concentrations within the range of 0.1–100 μM, and (ii) histamine and 5-HT, which are characterized by bell-shaped concentration dependence curves with maxima at 0.1 (histamine) and 1 μM (5-HT). On an agar-containing medium, the growing E. coli population includes solitary cells and compact cell groups (microcolonies). In this system, both tested catecholamines exert a relatively weak stimulatory influence that manifests itself as an increase in the number of both solitary cells and cell groups, and occurs at concentrations of 10 μM and higher. In analogy to the culture grown on the liquid medium, 5-HT and histamine are distinguished by nonlinear concentration dependence curves: their effects peak at 0.1 μM (histamine) or 1 μM (5-HT); an increase in the neuromediator concentrations results in a decrease in effects that are enhanced by further increasing the concentrations to the submillimolar range. DA increases the percentage of solitary cells, whereas the other tested amines promote cell group formation. The results are interpreted in terms of specific (probably receptor-dependent) mechanisms of action in the neuromediators involved.     

Effect of the ionic environment and of various neurotransmitters on spontaneous motility in snail intestine (author's transl)]

A spontaneous rhythmic motility of the isolated intestine in snail, Chryptomphalus hortensis, has been registered at 30 degrees C with the aid of an electronic transductor and an appropriate amplification. These slow regular movements are affected by ionic composition changes in the suspension medium. Na+, K+ and Ca++ ions prove to be important in this motility, and the addition of Ba++ markedly stimulates it. ACh produces hypermotility from 1.8 X 10(-11) g/ml. Its effect decreases in the presence of atropine and increases in that of pyridostigmine. The intestine is sensitive to 5-HT from 10(-10) g/ml, which stimulates its activity. The effect of histamine is weak. Low concentrations of adrenaline tend to increase the amplitude, whereas concentrations from 10(-5) g/ml onward produce a cease of motility in relaxation.     

Octopamine action on the contractile system of crustacean skeletal muscle

1. In the opener muscle of walking legs of crayfish (Astacus leptodactylus) octopamine (OA) greatly enhances the contractions resulting from brief applications of L-glutamate or of elevated K-concentrations. Synephrine is as effective as OA. 2. In the case of potentiation of responses to high-K applications a presynaptic component of the OA action was excluded by first desensitising the muscle fibres to the action of the natural transmitter, using a high concentration (1 mM) of glutamate. 3. The Ca-antagonists Co, Ni and Mn (1 mM) reduced the effects of glutamate and of elevated K to about one-half. In preparations treated with OA, the same Ca-antagonists also depressed the potentiated contractural responses to glutamate and to elevated K, again to about one-half. 4. OA also enhanced contractions resulting from the application of caffeine. 5. With 5-hydroxytryptamine (5-HT) application, the same postsynaptic effects were obtained as described for OA, except that the 5-HT actions were much weaker. 6. With OA, maximal effects were obtained with concentrations of 5 x 10(-6)-10(-5) M; maximally effective concentrations of 5-HT were around 10(-5) M. 7. The lowest effective concentrations of OA were around 10(-8) M; those of 5-HT were around 10(-7) M. 8. In the same preparation, 5-HT is far more effective in enhancing transmitter release (presynaptic action) than OA, the lowest effective concentration being around 10(-11) M while no presynaptic effects of OA were seen at concentrations below 10(-8) M, in some cases even below 10(-5) M.     

Hymenolepis diminuta: effects of decerebration on thermal response behavior.

Hymenolepis diminuta propels itself with unidirectional peristaltic-like waveforms. When intact adult H. diminuta are placed in a thermal gradient, with the anterior proglottids hot relative to the posterior proglottids, the worms migrate up the gradient toward the hot side. When the anterior is cold, relative to the posterior, the worms moved slightly or little. These behaviors in a thermal gradient represent true thermokinetic responses for an organism with undirectional locomotion. Removal of the scolex, containing the worm's cerebral ganglia, did not significantly alter these thermal responses. These data suggest that the peripheral nervous system is capable of integrating sensory input over the length of the strobila and coordinating locomotory behavior, in the absence of the central nervous system.     

Effect of serotonin on murine macrophages: suppression of Ia expression by serotonin and its reversal by 5-HT2 serotonergic receptor antagonists

Serotonin (5-HT), a mediator released from platelets at sites of inflammation, suppressed IFN-gamma-induced Ia expression in mouse bone marrow macrophages maintained in vitro. (Mean percent suppression = 63.9% +/- 9.2, n = 40.) This suppression was not toxic or endotoxin-related, was concentration-dependent, and occurred at the physiologic concentrations of 5-HT present at inflammatory sites. The concentration of 5-HT producing the half-maximal effect was 2.5 to 5.5 X 10(-8) M. Related compounds, dopamine, histamine, and tryptamine, were much less potent in suppressing IFN-gamma-induced Ia, with maximally suppressing concentrations more than 100-fold higher than the maximally suppressing 5-HT concentration. L-5-hydroxytryptophan (5-HTP), the most potent analog tested, was 10-fold less potent than 5-HT in suppressing Ia expression. The concentration of 5-HTP producing the half-maximal effect = 4 X 10(-7) M. 5-HT suppression of IFN-gamma-induced Ia expression was antagonized by the 5-HT2 type receptor antagonists spiperone, ketanserin, and LY53857. Concentrations of these agents resulting in 50% inhibition of the serotonin effect were 1.5 X 10(-8) M, 7.5 X 10(-8) M, and 4.5 X 10(-12) M, respectively. 5-HT was most effective in suppressing IFN-gamma-induced Ia when added early in culture simultaneously with IFN-gamma. These data provide functional evidence that 5-HT suppression of IFN-gamma-induced Ia expression is mediated through a 5-HT receptor with some characteristics of the 5-HT2 type. 5-HT may play a physiologic role at sites of inflammation as a modulator of the effects of IFN-gamma on macrophage function.     

Contractile responses of canine isolated pulmonary lobar arteries and veins to norepinephrine, serotonin, and tyramine.

Isolated helical strips of canine intrapulmonary lobar arteries and veins (about 4 mm in diameter) undergo dose-related tension development when exposed to increasing concentrations (10(-8) - 10(-3) M) of norepinephrine (NE), serotonin or 5-hydroxytryptamine (5-HT) and tyramine (Tyr). Venous segments were generally more sensitive while the maximum tension development was greater in the arterial strips, probably owing to their greater thickness. Both strips were more sensitive to 5-HT than NE and only responded to Tyr at high concentrations. Norepinephrine and 5-HT were nearly equally efficacious, whereas Tyr was less so. Responses to the latter were slow to develop, exhibited tachyphylaxis, and were greatly inhibited by phentolamine (10(-8) M), an alpha-adrenergic blocker. Exposure to cocaine (10(-5) M) enhanced submaximal NE responses, inhibited Tyr contractions and had no consistent effect on 5-HT responses. Phentolamine (10(-8) M) was also found to inhibit NE responses without altering 5-HT probably acts on other receptors. Tyramine may, in part, act directly on alpha-adrenergic receptors but may also release NE from surviving adrenergic nerve terminals in the preparation. Cocaine inhibits this effect and potentiates responses to lower levels of NE, presumably by blocking NE uptake into nerve terminals although a post-junctional action cannot be excluded.     

Presynaptic Control of the Synthesis and Release of Dopamine from Striatal Synaptosomes: A Comparison Between the Effects of 5-Hydroxytryptamine, Acetylcholine, and Glutamate

The effects of 5-HT and glutamate on dopamine synthesis and release by striatal synaptosomes were investigated and compared with the action of acetylcholine, which acts presynaptically on this system. 5-HT inhibited (28%) synthesis of [¹⁴C]dopamine from L-[U-¹⁴C]tyrosine, at 10-⁵M and above. This contrasts with the action of acetylcholine, which stimulated [¹⁴C]-dopamine synthesis by 24% at 10-⁴ M. Tissue levels of GABA were unaffected by either 5-HT or acetylcholine up to concentrations of 10-⁴ M. The inhibitory action of 5-HT (5 × 10^?5 M and 2 × 10^?4 M) on [¹⁹C]dopamine synthesis was completely abolished by methysergide (2 × 10^?6 M). Higher concentrations of methysergide (10^?4 M) or cyproheptadine (10^?5 M) inhibited [¹⁴C]dopamine synthesis by 28% and 25%, respectively, when added alone to synaptosomes. However, only methysergide prevented the further inhibition of synthesis caused by 5-HT. At concentrations of 2 × 10^?5 M and above, 5-HT stimulated [¹⁴C]dopamine release. This releasing action differed from that of acetylcholine, which occurred at lower concentrations (e.g., 10^?6 M). Methysergide (up to 10^?4 M) or cyproheptadine (2 × 10^?4 M) did not reduce the 5-HT (5 × 10^?5 M)-induced release of [¹⁴C]dopamine, but methysergide (10^?4 M) showed a potentiation (49%) of this increased release. The stimulatory effects of 5-HT (2 × 10^?5 M) and K⁺ (56 mM) on [¹⁴C]dopamine release were additive, indicating that two separate mechanisms were involved. However, when both agents were present the stimulatory effect of K⁺ (56 mM) on [¹⁴C]dopamine synthesis was not seen above the inhibitory effect of 5-HT. Glutamate (0.1-5 mM) did not affect [⁴C]dopamine release or its synthesis from L-[U-¹⁴C]tyrosine. It is concluded that 5-HT modulates the synthesis of dopamine in striatal nerve terminals through a presynaptic receptor mechanism, an action antagonised by methysergide. The releasing action of 5-HT apparently occurs through a separate mechanism which is also distinct from that involved in the response to K⁺ depolarisation.     

α-Tocopherol Improves Microcirculatory Dysfunction on Fructose Fed Hamsters

Fructose, an everyday component of western diet associated to chronic hyperglycemia and enhanced free radical production, impairs endothelial function and supplementation with antioxidants might improve it. In this study we investigated if vitamin E could reverse the microvascular damage elicited by fructose. Male Syrian golden hamsters drank either 10% fructose solution (F) or filtered water (C), combined with three concentrations of vitamin E in their chows [zero, normal (VE) or 5X (5XVE)] during 60 days. Microvascular reactivity in response to topical application of acetylcholine (Ach; endothelium-dependent vasodilator) or sodium nitroprusside (SNP; endothelium-independent vasodilator) and macromolecular permeability increase induced by either 30 min ischemia followed by reperfusion (I/R) or topical application of histamine (5 μM) were assessed using the cheek pouch preparation. Compared to controls (drinking filtered water), fructose-drinking animals showed decreased vasodilatation to acetylcholine in all concentrations tested (-56.2% for 10^-9M, -53.9% for 10^-7M and -43.7% for 10^-5M). On the other hand, vitamin E supplementation resulted in increased responses for both water and fructose drinking groups (177.4% for F vs. F/5XVE and 241.6% for C vs. C/5XVE for 10^-5M Ach). Endothelial-independent vasodilatation explored by topical application of SNP was restored and even enhanced with the supplementation of 5X vitamin E in both groups (80.1% for F vs. F/5XVE; 144.2% for C vs. C/5XVE; 3.4% of difference for C/5XVE vs. F/5XVE on 10^-5M SNP). The number of leaky sites after I/R and histamine stimuli in vitamin E supplemented animals decreased (-25.1% and -15.3% for F vs. F/5XVE; and -21.7% and -16% of leaky sites comparing C vs. C/5XVE, respectively for I/R and histamine stimuli) pointing to tightening of the endothelial barrier for macromolecular permeability. Our results strongly suggest that vitamin E could improve the endothelial function and permeability barrier and also reverse impairments elicited by sugar overload.     

A new triaenophorid tapeworm from blackfish Centrolophus niger

Milanella familiaris n. gen. and n. sp. (Bothriocephalidea: Triaenophoridae) is proposed to accommodate a new cestode from blackfish Centrolophus niger (Gmelin) (Perciformes: Centrolophidae). Milanella is characterized as follows: trapeziform, i.e., markedly craspedote proglottids with a velum-like posterior margin and horn like lateral projections; pyriform uterine sac in the first gravid proglottids; arrow-shaped scolex with well-developed apical disc and prominent posterior margins; strobila with intensively stained corpuscles, most numerous in the anterior part; deeply lobated ovary; absence of a neck; a large, pyriform, thin-walled cirrus-sac with the proximal part bent anteromedially; vagina posterior to the cirrus-sac; and cortical vitelline follicles. Milanella most closely resembles Bathycestus Kuchta and Scholz, 2004, Pistana Campbell and Gartner, 1982, and Probothriocephalus Campbell, 1979, differing mainly in the shape of proglottids and uterine sac.     

Serotonergic influences on pituitary gland and hypothalamic induction of prolactin and luteinizing hormone release in the young turkey (Meleagris gallopavo)

Primary anterior pituitary cell cultures were utilized to study the influence of serotonin (5-HT) directly on the pituitary. Cells incubated with 10(-5) and 10(-4) M 5-HT exhibited a significant prolactin (Prl) release, whereas cells incubated with 10(-10) to 10(-6) M 5-HT did not. Cells incubated with 10(-10) to 10(-4) M quipazine (5-HT agonist) or methysergide (MES; 5-HT antagonist) did not release Prl in amounts greater/less (P greater than 0.01) than spontaneous release. Luteinizing hormone (LH) release from cells incubated in the presence of 5-HT, quipazine, or MES was similar to spontaneous release. The hypothalamic extract-induced Prl and LH release from cells was not influenced by quipazine, but Prl release was diminished in a dose-related fashion by MES. The influence of 5-HT on hypothalamic induction of Prl and LH release was investigated utilizing in vitro culture of hypothalamic fragments (HF). Media samples from HF incubated with 10(-6) and 10(-4) M 5-HT induced a release of Prl. Media samples from HF incubated with 10(-4) M MES induced less Prl release than media samples from control fragments. When HF were incubated with both 10(-4) M 5-HT and 10(-4) M MES, the expected 5-HT-mediated Prl release was not evident. These culturing situations had no influence on LH release. In vitro Prl release from pituitary cells of the young turkey was stimulated through 5-HT activity at the hypothalamus, but not by direct 5-HT action on the pituitary cells.